| 1. |
- Aguilar-Mamani, Wilson, et al.
(author)
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Solution-mediated growth of NBA-ZSM-5 crystals retarded by gel entrapment
- 2018
-
In: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 487, s. 57-64
-
Journal article (peer-reviewed)abstract
- The synthesis of flat tablet-shaped ZSM-5 crystals from a gel using metakaolin as aluminosilicate source and n-butyl amine as structure directing agent was investigated. The evolution inside the solid phase was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry and mass spectrometry. A kinetic study indicated that the nucleation of the majority crystals occurred concurrently with the formation of the gel upon heating the starting liquid suspension. Microstructural evidences undeniably showed that the gel precipitated on ZSM-5 crystals and mineral impurities originating from kaolin. As a result, crystal growth was retarded by gel entrapment, as indicated by the configuration and morphology of the embedded crystals. The results presented herein are harmonized with a solution-mediated nucleation and growth mechanism. Our observations differ from the autocatalytic model that suggests that the nuclei rest inside the gel until released when the gel is consumed. Our results show instead that it is crystals that formed in an early stage before entrapment inside the gel that rest inside the gel until exposed at the gel surface. These results illustrate the limitation of the classical method used in the field to determine nucleation profiles when the crystals become trapped inside the gel.
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| 2. |
- Akhtar, Farid, et al.
(author)
-
A new kind of age hardenable martensitic stainless steel with high strength and toughness
- 2007
-
In: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 34:4, s. 285-289
-
Journal article (peer-reviewed)abstract
- Following analysis of typical age hardenable martensitic stainless steels, a new kind of maragingstainless was developed. The new maraging stainless steel showed high strength, ultimate tensilestrength (UTS) 5 1670 MPa, high toughness, K IC 5 83·9 MPa m1/2 and hardness as high as 478 HVin the age hardened condition. Microstructural study with an optical and transmission electron microscope revealed the typical microstructure of age hardenable stainless steel containing lathmartensite and precipitates. TixNi precipitates were identified by transmission electron microscopy, which were responsible for the increase in mechanical properties after age hardening. The results of natural salt spray test showed that the corrosion resistance of new maraging stainless steel approached to the corrosion resistance of 304L stainless steel.
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| 3. |
- Akhtar, Farid
(author)
-
A new method to process high strength TiCN stainless steel matrix composites
- 2007
-
In: Powder Metallurgy. - 0032-5899 .- 1743-2901. ; 50:3, s. 250-254
-
Journal article (peer-reviewed)abstract
- Layered composites of Ti(C, N) reinforcements and stainless steel have been prepared successfully by powder technology. The layer composite consisted of two layers. The upper layer consisted of TiCN reinforcements and stainless steel as binder material. The lower layer was entirely of binder material (stainless steel). The micro structural study revealed that the upper layer (TiCN/465 stainless steel) showed core–rim microstructure of conventional cermets and the lower layer showed the structure of sintered steel. An intermediate layer was formed due to diffusion reaction of upper and lower layers. This intermediate layer showed a gradient microstructure. The bending strength of the layered material measured was remarkably higher. Ninety per cent increase in the bending strength in the case of 50 wt-% reinforcement in the upper layer was found. The fracture morphologies of upper, lower and intermediate layers are also reported
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| 4. |
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| 5. |
- Akhtar, Farid, et al.
(author)
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A study of the sintering of diatomaceous earth to produce porous ceramic monolithswith bimodal porosity and high strength
- 2010
-
In: Powder Technology. - Amsterdam, Netherlands : Elsevier B.V.. - 0032-5910 .- 1873-328X. ; 201, s. 253-257
-
Journal article (peer-reviewed)abstract
- Diatomite powder, a naturally occurring porous raw material, was used to fabricate ceramic materials withbimodal porosity and high strength. The effect of the sintering temperature on the density and porosity ofdry pressed diatomite green bodies was evaluated using mercury porosimetry and water immersionmeasurements. It was found that the intrinsic porosity of the diatomite particles with a pore size around0.2 μm was lost at sintering temperatures above 1200 °C. Maintaining the sintering temperature at around1000 °C resulted in highly porous materials that also displayed a high compressive strength. Microstructuralstudies by scanning electron microscopy and energy-dispersive X-ray analysis suggested that the porecollapse was facilitated by the presence of low melting impurities like Na2O and K2O.
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| 6. |
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| 7. |
- Akhtar, Farid, et al.
(author)
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Aluminophosphate monoliths with high CO2-over-N2 selectivity and CO2 capture capacity
- 2014
-
In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:99, s. 55877-55883
-
Journal article (peer-reviewed)abstract
- Monoliths of microporous aluminophosphates (AlPO4-17 and AlPO4-53) were structured by binder-free pulsed current processing. Such monoliths could be important for carbon capture from flue gas. The AlPO4-17 and AlPO4-53 monoliths exhibited a tensile strength of 1.0 MPa and a CO2 adsorption capacity of 2.5 mmol g-1 and 1.6 mmol g-1, respectively at 101 kPa and 0°C. Analyses of single component CO2 and N2 adsorption data indicated that the AlPO4-53 monoliths had an extraordinarily high CO2-over-N2 selectivity from a binary gas mixture of 15 mol% CO2 and 85 mol% N2. The estimated CO2 capture capacity of AlPO4-17 and AlPO4-53 monoliths in a typical pressure swing adsorption (PSA) process at 20°C was higher than that of the commonly used zeolite 13X granules. Under cyclic sorption conditions, AlPO4-17 and AlPO4-53 monoliths were regenerated by lowering the pressure of CO2. Regeneration was done without application of heat, which would regenerate them to their full capacity for CO2 adsorption.
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| 8. |
- Akhtar, Farid
(author)
-
An investigation on the solid state sintering of mechanically alloyed nano-structured 90W--Ni--Fe tungsten heavy alloy
- 2008
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 26:3, s. 145-151
-
Journal article (peer-reviewed)abstract
- In this study, 90W–7Ni–3Fe heavy alloy was investigated for its microstructure development, mechanical properties and fracture behavior after solid state sintering. The nano-sized powders were synthesized by mechanical alloying (MA). The microstructure of solid state sintered heavy alloys consisted of tungsten matrix. The average tungsten grain size in the range of 1.7–3.0 μm was obtained. It was found that the grain size largely affected the mechanical properties. Tensile strength more than 1200 MPa was achieved at a sintering temperature of 1350 °C. Fracture mechanisms based on microscopical observations on the fracture surfaces were studied. Matrix failure, tungsten-intergranular cleavage and tungsten–matrix interfacial separation were found to be the possible failure mechanisms.
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| 9. |
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| 10. |
- Akhtar, Farid
(author)
-
Ceramic reinforced high modulus steel composites : processing, microstructure and properties
- 2014
-
In: Canadian metallurgical quarterly. - 0008-4433 .- 1879-1395. ; 53:3, s. 253-263
-
Journal article (peer-reviewed)abstract
- Ceramic reinforced steel matrix composites are materials for automotive, aerospace, wear and cutting applications. Such metal matrix composites (MMCs) combine attractive physical, mechanical and wear properties with ease of fabrication and low cost. The review focuses on the current state of the art of producing these metal matrix composites, ceramics reinforcements, composition of steel matrix, microstructure evolution and parameters influencing the mechanical and wear properties. Processing methods to fabricate ceramic reinforced steel matrix composites are discussed to produce these composites with low number of defects, homogeneous microstructure and high mechanical and wear performance. The influence of chemical nature of ceramic reinforcements and composition of steel matrix on the microstructure, mechanical and wear properties is presented. The strengthening mechanisms and parameters controlling wear performance of steel MMCs are described as a function of the content of ceramic reinforcements, microstructural design and structure of the steel matrix. Keeping in view the stability of ceramics in steels, suitable ceramic reinforcements and steel matrix materials are discussed. Moreover, the importance of microstructure and interface between ceramic reinforcement and steel matrix in controlling the mechanical properties of steel MMCs is highlighted. The review identifies area of research for development to fully appreciate and tailor the properties of these industrially important composites.
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| 11. |
- Akhtar, Farid, et al.
(author)
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Colloidal processing and CO2 capture performance of sacrificially templated zeolite monoliths
- 2012
-
In: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 97, s. 289-296
-
Journal article (other academic/artistic)abstract
- Sacrificial templating of suspension cast and subsequently thermally treated zeolite monoliths with glassy carbon spheres and fibers yielded zeolite 13X and silicalite-1 monoliths with macroporosities up to 50 vol%. Homogeneous distribution of the macroporosity in hierarchically porous monoliths was obtained by tailoring the surface chemistry of the carbon particles by polyelectrolyte-assisted adsorption of zeolite particles. The effect of amount of kaolin binder and temperature for the thermal treatment on the monoliths strength, surface area and CO2 uptake was studied by diametral compression tests, electron microscopy, X-ray diffraction and gas adsorption. Cyclic adsorption and regeneration measurements showed that zeolite 13X monoliths display a high CO2 uptake while the silicalite-1 monoliths could be regenerated with a relatively low energy penalty.
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| 12. |
- Akhtar, Farid, et al.
(author)
-
Colloidal Processing and Thermal Treatment of Binderless Hierarchically Porous Zeolite 13X Monoliths for CO2 Capture
- 2011
-
In: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 94:1, s. 199-205
-
Journal article (peer-reviewed)abstract
- Adsorbents with high surface area are potential candidates forefficient postcombustion CO2 capture. Binderless zeolite 13Xmonoliths with a hierarchical porosity and high CO2 uptakehave been produced by slip casting followed by pressurelessthermal treatment. The zeolite powder displayed an isoelectricpoint at pH 4.7 and electrostatically stabilized suspensions couldbe prepared at alkaline pH. The volume fraction-dependentsteady shear viscosity could be fitted to a modified Krieger–Dougherty model with a maximum volume fraction of 0.66. Thenarrow temperature range where monoliths could be producedwithout significant loss of the microporous surface area wasidentified and related to the phase behavior of the 13X material.Slip casting of concentrated suspensions followed by thermaltreatment of the powder bodies at a temperature of 8001Cwithout holding time resulted into strong hierarchically porouszeolite 13X monolith that displayed a CO2 uptake larger than29 wt%.
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| 13. |
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| 14. |
- Akhtar, Farid, et al.
(author)
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Development of Si3N4/ Al composite by pressureless melt infiltration
- 2006
-
In: European PM 2005 conference proceedings. - Shrewsbury : European powder metallurgy association. - 9781899072187 ; 16:3, s. 629-632
-
Conference paper (peer-reviewed)abstract
- Pressureless infiltration process to synthesize Si3N4/ Al composite was investigated. Al- 2%Mg alloy was infiltrated into the Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al- 2%Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with Aluminium to form Si and AlN. The growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. First, preform without Al2O3 content gave rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Second, perform with 10% Al2O3 content gave rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.
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| 15. |
- Akhtar, Farid, et al.
(author)
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Effect of adding a type of binder phase on the microstructure, properties and heat treatment of steel bonded TiC cermets
- 2007
-
In: Progress in powder metallurgy. - Uetikon-Zürich : Trans Tech Publications Inc.. ; , s. 1161-1164
-
Conference paper (peer-reviewed)abstract
- Particulate TiC reinforced 465 maraging stainless steel matrix Cermets were processed by conventional P/M. The binder phase was added in the form of elemental powders and master alloy powders. The microstructures, binder phase variation with TiC content and mechanical properties were evaluated. The addition of a type of binder phase largely effects the microstructure and mechanical properties. When a master alloy binder phase was used the microstructure showed interphase debondings, microcracks and large growths of TiC particles. Where as, elemental powders in the composition of binder phases showed defect free microstructure of steel bonded cermets. The binder phase variation from starting composition was observed with increase in wt% TiC content and this variation was higher when the master alloy powders were used as a binder. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The response to heat treatment was decreased with an increase in TiC content due to the shift of binder phase from the starting composition.
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| 16. |
- Akhtar, Farid
(author)
-
Effect of additive Cu-10Sn alloy on sintering Behavior of elemental powders in composition of 465 stainless steel
- 2007
-
In: Journal of Iron and Steel Research International. - 1006-706X .- 2210-3988. ; 14:4, s. 61-74
-
Journal article (peer-reviewed)abstract
- The addition of Cu-10Sn alloy for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated include the sintering temperature, the sintering time, and the mass percent of Cu-10Sn. For vacuum sintering, effective sintering occurs at temperature between 1250°C and 1300°C. The maximum sintered density was achieved at 1300°C for 60 min with 3% (in mass percent) Cu-10Sn alloy. More than 3% (in mass percent) Cu-10Sn content and temperature above 1300°C caused slumping of the samples. A maximum density of 7.4 g/cm3 was achieved with 3% (in mass percent) Cu-10Sn content at a sintering temperature of 1300°C for 60 min. A maximum ultimate tensile strength (UTS) of 517 MPa was achieved with 3% (in mass percent) Cu-10Sn content. With content higher than 2% (in mass percent) Cu-10Sn, a maximum increase in the density was observed. The fracture morphologies of the sintered samples are also reported.
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| 17. |
- Akhtar, Farid, et al.
(author)
-
Effect of Cu3P addition on sintering behaviour of elemental powders in the composition of 465 stainless steel
- 2006
-
In: Powder Metallurgy. - 0032-5899 .- 1743-2901. ; 49:1, s. 28-33
-
Journal article (peer-reviewed)abstract
- The addition of Cu3P for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated were sintering temperature, sintering time and wt-%Cu3P. In vacuum sintering, effective sintering took place between 1300 and 1350°C. The maximum sintered density of 7·44 g cm−3 was achieved at 1350°C for 60 min with 4–6 wt-%Cu3P. More than 6 wt-%Cu3P content and temperature >1350°C caused slumping of the specimens. The sintered specimens were heat treated and a maximum ultimate tensile strength (UTS) of 767 MPa was achieved with 4 wt-%Cu3P content. The maximum hardness of 45·5 HRC was achieved in heat treated condition with 4 wt-%Cu3P content. Above 4 wt-%Cu3P content increase in density was observed whereas the response to heat treatment decreased. Fracture morphologies of the sintered specimens were also reported. A comparison of sintering behaviour and mechanical properties of elemental powders with prealloyed powders was also given in the present study
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| 18. |
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| 19. |
- Akhtar, Farid, et al.
(author)
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Effect of microstructure on the properties of pulse current sintered bimodal hardmetals
- 2008
-
In: Proceedings of the 7th International Conference on Tungsten, Refractory and Hardmaterials. - 9780979348884 ; , s. 41-48
-
Conference paper (peer-reviewed)abstract
- This study deals with the pulse current processing, microstructure and mechanical properties of WC-20wt%(W,Ti,Ta)C-6wt%Co cemented carbides. The conventional WC particles of 4μm size and ultrafine particles of 200nm were introduced in the system with varying ratio to synthesize bimodal hardmetals. Pulse current processing effectively controlled the grain size of WC particles in the presence of (W,Ti,Ta)C phase to synthesize fine microstructure. The microstructure of pulse current consolidated hardmetals was sensitive to the ratio of conventional WC particles to ultrafine WC particles. The ratio of conventional WC particles to ultrafine WC particles was very effective to enhance the mechanical properties of bimodal hardmetals. Hardness of bimodal hardmetals increased with decrease in the ratio of conventional WC particles to ultrafine WC carbide particles. The bending strength showed the similar trend of the hardness. The fracture behavior showed transgranular fracture mode as a dominant fracture mechanism in bimodal hardmetals with varying ratio of conventional WC particles to ultrafine WC particles.
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| 20. |
- Akhtar, Farid, et al.
(author)
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Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC--(W, Ti, Ta) C--6wt% Co cemented carbides
- 2007
-
In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 25:5-6, s. 405-410
-
Journal article (peer-reviewed)abstract
- This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.
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| 21. |
- Akhtar, Farid, et al.
(author)
-
Enhanced sintering, microstructure evolution and mechanical properties of 316L stainless steel with MoSi(2) addition
- 2011
-
In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 509:35, s. 8794-8797
-
Journal article (peer-reviewed)abstract
- Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi(2) ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi(2) as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi(2) content. The distribution of MoSi(2) was characterized by XMAPs. It was found that MoSi(2) dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 degrees C for 60 min with 5 wt.% MoSi(2) content. The stainless steel sintered with 5 wt.% MoSi(2) exhibited very attractive mechanical properties.
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| 22. |
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| 23. |
- Akhtar, Farid, et al.
(author)
-
Hierarchically porous binder-free silicalite-1 discs : a novel support for all-zeolite membranes
- 2011
-
In: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 21:24, s. 8822-8828
-
Journal article (peer-reviewed)abstract
- Thermal expansion mismatch between the zeolite film and the support is an important cause for the formation of defects and cracks during the fabrication and use of zeolite membranes. We have studied how silicalite-1 discs with a permeability comparable to commercially available alumina supports can be produced by pulsed current processing (PCP) as a novel substrate for all-zeolite membranes. Hierarchically porous and mechanically strong membrane supports where the surface area and crystallography of the silicalite-1 particles were maintained could be obtained by carefully controlling the thermal treatment during PCP consolidation. In situ X-ray diffraction and dilatometry showed that the coefficient of thermal expansion (CTE) of the silicalite-1 substrate was negative in the temperature range 200-800 degrees C while the commonly used alumina substrate displayed a positive CTE. The critical temperature variation, Delta T, and thicknesses for crack-free supported zeolite films with a negative CTE were estimated using a fracture energy model. Zeolite films with a thickness of 1 mu m can only sustain a relatively modest Delta T of 100 degrees when supported onto alumina substrates while the all-zeolite membranes can support temperature variations above 500 degrees
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| 24. |
- Akhtar, Farid, et al.
(author)
-
Hierarchically porous binder-free silicalite-1 discs : a novel support for all-zeolite membranes
- 2011
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 21:24, s. 8822-8828
-
Journal article (peer-reviewed)abstract
- Thermal expansion mismatch between the zeolite film and the support is an important cause for the formation of defects and cracks during the fabrication and use of zeolite membranes. We have studied how silicalite-1 discs with a permeability comparable to commercially available alumina supports can be produced by pulsed current processing (PCP) as a novel substrate for all-zeolite membranes. Hierarchically porous and mechanically strong membrane supports where the surface area and crystallography of the silicalite-1 particles were maintained could be obtained by carefully controlling the thermal treatment during PCP consolidation. In situ X-ray diffraction and dilatometry showed that the coefficient of thermal expansion (CTE) of the silicalite-1 substrate was negative in the temperature range 200-800 degrees C while the commonly used alumina substrate displayed a positive CTE. The critical temperature variation, Delta T, and thicknesses for crack-free supported zeolite films with a negative CTE were estimated using a fracture energy model. Zeolite films with a thickness of 1 mu m can only sustain a relatively modest Delta T of 100 degrees when supported onto alumina substrates while the all-zeolite membranes can support temperature variations above 500 degrees.
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| 25. |
- Akhtar, Farid, et al.
(author)
-
Hierarchically Porous Ceramics from Diatomite Powders by Pulsed Current Processing
- 2009
-
In: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 92:2, s. 338-343
-
Journal article (peer-reviewed)abstract
- Hierarchically porous ceramic monoliths have been fabricated by pulsed current processing (PCP) of diatomite powders. The partial sintering behavior of the porous diatomite powders during PCP or spark plasma sintering was evaluated at temperatures between 600 degrees and 850 degrees C. Scanning electron microscopy and mercury porosimetry measurements showed that the PCP method was able to bond the diatomite powder together into relatively strong monoliths without significantly destroying the internal pores of the diatomite powder at a temperature range of 700 degrees-750 degrees C. Little fusion at the particle contact points occurred at temperatures below 650 degrees C while the powder showed partial melting and collapse of both the interparticle pores and the internal structure at temperatures above 800 degrees C.
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| 26. |
- Akhtar, Farid
(author)
-
High volume fraction carbide reinforced copper matrix composites for sliding contact applications
- 2007
-
In: PRICM 6. - Stafa-Zurich : Trans Tech Publications Inc.. ; , s. 627-630
-
Conference paper (peer-reviewed)abstract
- This study deals with the processing, microstructure and properties of the carbide reinforced copper matrix composites. Powder technology was used to successfully fabricate the composites. NbC particulates were used as reinforcements for copper matrix. The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the NbC particles were distributed uniformly in the matrix phase. No interface debonding and micro- cracks were observed in the composite. NbC particles were found in round shape in copper matrix composite. The composite hardness of 78 HRA was found with 60vol% NbC content. Electrical conductivity as high as 7%IACS was achieved. The wear performance and conductivity value predicts that NbC reinforced copper matrix composites can be used as sliding contact applications.
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| 27. |
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| 28. |
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| 29. |
- Akhtar, Farid, et al.
(author)
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Microstructure and property evolution during the sintering of stainless steel alloy with Si 3 N 4
- 2008
-
In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 472:1-2, s. 324-331
-
Journal article (peer-reviewed)abstract
- This paper describes the sintering of a martensitic stainless steel alloy with addition of Si3N4. Sintering behavior was studied at different sintering temperatures ranging from 1250 to 1400 °C with different holding times (20–80 min) and with varying Si3N4. Results showed that the samples were densified rapidly via liquid phase sintering mechanism. Nearly full density was obtained at 1300 °C after 60 min of holding time with 5 wt% Si3N4. Temperature above 1350 °C and Si3N4 content 10 wt% caused slumping of the samples. Two weight percent Si3N4 was found chemically stable in steel alloy. Above 2 wt% Si3N4 dissolved in the steel matrix. The distribution of dissolved Si and N was characterized by XMAP. When N content reached much above its solubility limit in steel alloy it diffused out leaving pores in steel alloy with considerable decrease in the sintered density. The mechanical properties of the sintered product with varying Si3N4 were measured. A maximum ultimate tensile strength of 1011 MPa was achieved with 2 wt% Si3N4 sintered at 1300 °C after 60 min of holding time. Fracture morphologies of tensile samples are also reported.
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| 30. |
- Akhtar, Farid
(author)
-
Microstructure evolution and wear properties of in situ synthesized TiB 2 and TiC reinforced steel matrix composites
- 2008
-
In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 459:1-2, s. 491-497
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Journal article (peer-reviewed)abstract
- Steel matrix composite reinforced with TiB2 and TiC reinforcements (30 to 70wt%) have been produced through the synthesis reaction from Ti, C and FeB. The sintered composites were characterized by X-ray diffraction and scanning electron microscopy. TiB2, TiC and steel were detected by X-ray diffraction analysis. The scanning electron micrographs revealed the morphology and distribution of the reinforcements. TiB2 and TiC were thermally stable in the steel matrix. The results showed that different mechanisms of evolution of reinforcements in steel matrix were operative. TiB2 grew in hexagonal prismatic or rectangular shape and TiC in spherical shape. The reciprocating sliding wear test was conducted on the composite. The results of sliding wear showed that the wear loss decreased with increase in the reinforcement content. The wear mechanisms were polishing wear and microploughing for the composites containing high volume fraction of the reinforcements, whereas microploughing and grooving were the dominant wear mechanisms for the composites containing low volume fraction of the reinforcements.
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| 31. |
- Akhtar, Farid, et al.
(author)
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Microstructure, mechanical and fretting wear properties of TiC-stainless steel composites
- 2008
-
In: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 59:1, s. 84-90
-
Journal article (peer-reviewed)abstract
- This study deals with the processing, microstructure, and wear behavior of TiC-reinforced stainless steel matrix composites, containing 50 to 70 wt.% TiC. Powder technology was used to successfully fabricate the composites. The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the TiC particles were distributed uniformly in the steel matrix phase. Interface debonding and microcracks were not observed in the composite. The composite hardness increased with TiC content. The fretting wear resistance of the composites was studied against high speed steel. The wear mechanisms are discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microplowing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microplowing and rapid removal of material from the wear surface was observed at high wear load. The variation of wear loss with volume fraction and mean free path of the binder phase is also reported
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| 32. |
- Akhtar, Farid, et al.
(author)
-
Microstructure, mechanical properties, electrical conductivity and wear behavior of high volume TiC reinforced Cu-matrix composites
- 2009
-
In: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 60:4, s. 327-336
-
Journal article (peer-reviewed)abstract
- This study deals with the processing, microstructure, mechanical properties, electrical conductivity and wear behavior of high volume titanium carbide reinforced copper matrix composites. The microstructural study revealed that the titanium carbide particles were distributed uniformly in the matrix phase. No interface debonding and micro-cracks were observed in the composite. The addition of alloying elements in the copper considerably increased the sintered density and properties. The composite hardness and strength increased with titanium carbide content and alloying elements in the matrix phase. The electrical conductivities of the composites were predicted using three point upper bound and two phase self consistent predictive models. The wear resistance of the composites was studied against high speed steel. Wear mechanisms were discussed by means of microscope observations on the worn surfaces. The ratio of titanium carbide average grain size to the mean free path of the binder was introduced as a parameter to determine wear performance.
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| 33. |
- Akhtar, Farid
(author)
-
On the microstructure and properties of tungsten heavy alloys
- 2007
-
In: Advanced materials and processing. - Stafa-Zurich : Trans Tech Publications Inc.. ; , s. 1055-1058
-
Conference paper (peer-reviewed)abstract
- In this research, the effect of microstructure on the mechanical properties of tungsten heavy alloys is discussed. The tensile properties of tungsten heavy alloys are found to be dependent on volume fraction of W, contiguity and grain size of W particle. The ductility is found to be influenced by contiguity and connectivity. The volume fraction of matrix increases sharply with the increase in rare metal oxide impurity, which adversely affects the mechanical properties of tungsten heavy alloys.
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| 34. |
- Akhtar, Farid, et al.
(author)
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On the processing, microstructure, mechanical and wear properties of cermet/stainless steel layer composites
- 2007
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In: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 55:4, s. 1467-1477
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Journal article (peer-reviewed)abstract
- This study deals with layer composites of carbide reinforcements and stainless steel prepared successfully by powder technology. The layer material consisted of two layers. The top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as the binder material for the carbides. The bottom layer was entirely of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the top layer (TiC–NbC/465 stainless steel) showed the typical core–rim microstructure of conventional steel bonded cermets and the bottom layer showed the structure of sintered steel. An intermediate layer was found with a gradient microstructure, having a higher carbide content towards the cermet layer and lower carbide content towards the stainless steel layer. The bending strength of the layered material measured in the direction perpendicular to the layer alignment was remarkably high. The variation of strength as a function of the thickness of the bottom layer revealed that the character of the material changed from the cermet, to a layer composite and then towards metallic materials. The wear resistance of the top layer was studied against high speed steel. The wear mechanisms were discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microploughing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microploughing and rapid removal of material from the wear surface was observed at high wear load. The fracture morphologies of the top, bottom and intermediate layers are reported
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| 35. |
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| 36. |
- Akhtar, Farid, et al.
(author)
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Preparation of graded silicalite-1 substrates for all-zeolite membranes with excellent CO2/H-2 separation performance
- 2015
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In: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 493, s. 206-211
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Journal article (peer-reviewed)abstract
- Graded silicalite-1 substrates with a high gas permeability and low surface roughness have been produced by pulsed current processing of a thin coating of a submicron silicalite-1 powder onto a powder body of coarser silicalite-1 crystals. Thin zeolite films have been hydrothermally grown onto the graded silicalite-1 support and the all-zeolite membranes display an excellent CO2/H-2 separation factor of 12 at 0 degrees C and a CO2 permeance of 21.3 x 10(-7) mol m(-2) s(-1) Pa-1 for an equimolar CO2/H-2 feed at 505 kPa and 101 kPa helium sweep gas. Thermal cracking estimates based on calculated surface energies and measured thermal expansion coefficients suggest that all-zeolite membranes with a minimal thermal expansion mismatch between the graded substrate and the zeolite film should remain crack-free during thermal cycling and the critical calcination step.
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| 37. |
- Akhtar, Farid, et al.
(author)
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Pressureless infiltration of Si3N4 preforms with an Al-2wt% Mg alloy
- 2005
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In: International Journal of Minerals, Metallurgy and Materials. - 1674-4799 .- 1869-103X. ; 12:4, s. 351-356
-
Journal article (peer-reviewed)abstract
- The pressureless infiltration process to synthesize a silicon nitride composite was investigated. An Al-2wt%Mg alloy was infiltrated into silicon nitride preforms in the atmosphere of nitrogen. It is possible to infiltrate the Al-2wt%Mg alloy in silicon nitride preforms. The growth of the composite with useful thickness wasfacilitated by the presence of magnesium powder at the interface and by flowing nitrogen. The microstructure of the Si3N4-Al composite has been characterized using scanning electron microscope.During the infiltration of Si3N4 preforms, Si3N4 reacted with aluminium to form silicon and AlN. Thesilicon produced during the growth consumed in the formation of MgSiAlO, MgSiAlN and Al3.27Si0.47 type phases. The growth of the composite was found to proceed in two ways, depending on the oxide content in the initial preforms. First, less oxide content preforms gave rise to MgAlSiO and MgAlSiN type phases after infiltration. Second, more oxide content preforms gave rise to AlN-Al2O3 solid solution phase(AlON). The AlON phase was only present in the composite, containing 10% aluminium in the silicon nitride preforms before infiltration.
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| 38. |
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| 39. |
- Akhtar, Farid, et al.
(author)
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Processing, microstructure and mechanical properties of TiC-465 stainless steel/465 stainless steel layer composites
- 2007
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 439:1-2, s. 287-293
-
Journal article (peer-reviewed)abstract
- Layered composites of carbide reinforcements and stainless steel have been prepared successfully by powder technology. The layer material consisted of two layers. Top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as binder material for carbides. The substrate material was of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that top layer (TiC-NbC/465 stainless steel) showed the typical core-rim microstructure of conventional steel bonded cermets and the substrate material showed the structure of sintered steel. An intermediate layer was formed due to diffusion reaction of top layer and substrate material. This intermediate layer showed a gradient microstructure. The bending strength of layered material measured in the direction perpendicular to the layer alignment was remarkably higher. Nineteen percent increase in bending strength in case of 53 wt% reinforcement in top layer and 35% increase in case of 73 wt% reinforcement in top layer was found. The variation of strength as a function of thickness of substrate material revealed that the character of material changed from cermet to a layer composite and then towards metallic materials. The fracture morphologies of top layer, substrate material and intermediate layer are also reported
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| 40. |
- Akhtar, Farid
(author)
-
Processing, microstructure, properties and wear behavior of in situ synthesized TiB 2 and TiC thick films on steel substrates
- 2007
-
In: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 201:24, s. 9603-9609
-
Journal article (peer-reviewed)abstract
- TiB2 and TiC reinforced Fe matrix thick films (2 mm thickness) were produced through the synthesis reaction from Ti, C and FeB powders with varying porosity on the steel substrates. Powder technology was used as a processing method. The films and the substrates were sintered in a single step. TiB2, TiC and Fe were detected in the films by X-ray diffraction analysis. The fact that no other reaction product was detected revealed the thermal stability of TiB2 and TiC. The formation of secondary reaction products was inhibited during the reactive sintering. The films showed maximum strength of 163–466 MPa when sintered separately at 1350 °C. The strength of the films varied with their porosity. The films showed considerable bonding strength with the steel substrates. The delamination of the films from the steel substrates was observed at stress values from 454–781 MPa. The microstructure, fracture and delaminated surface morphologies were studied. The wear resistance against hardened high speed steel was studied in reciprocating sliding tests. The wear mechanisms were discussed by means of microscopical observation on the worn surfaces
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| 41. |
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| 42. |
- Akhtar, Farid, et al.
(author)
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Reactive sintering and properties of TiB 2 and TiC porous cermets
- 2008
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In: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 62:8-9, s. 1242-1245
-
Journal article (peer-reviewed)abstract
- TiB2, TiC reinforced Fe matrix porous cermets were produced through the synthesis reaction of Ti, C and FeB powders with 30% sintered porosity. The X-ray diffraction analysis confirmed the completion of reaction. The TiB2, TiC and Fe were detected by X-ray diffraction analysis. The formation of secondary reaction products was inhibited during the reactive sintering. Porous cermets showed large and small pores in their structure. Maximum bending strength of 163 MPa was obtained with 30% sintered porosity. Furthermore, the fabricated samples were found to possess reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells.
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| 43. |
- Akhtar, Farid, et al.
(author)
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Sintering behavior, microstructure and properties of TiC-FeCr hard alloy
- 2007
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In: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material. ; 14:1, s. 89-93
-
Journal article (peer-reviewed)abstract
- TiC based cermets were produced with FeCr, as a binder, by conventional P/M (powder metallurgy) to near >97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of >1360°C caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360°C for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettability of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals
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| 44. |
- Akhtar, Farid
(author)
-
Sintering behavior of elemental powders with FeB addition in the composition of martensitic stainless steel
- 2007
-
In: Journal of materials engineering and performance (Print). - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 16:6, s. 726-729
-
Journal article (peer-reviewed)abstract
- The effect of sintering additive for the development of high-strength martensitic stainless steel from elemental powders was studied. The sintering parameters investigated were: sintering temperature, sintering time, and wt.% of FeB. In vacuum sintering, effective sintering took place between 1300 and 1350 °C with 1-1.5 wt.% FeB addition. The maximum sintered density and ultimate tensile strength (UTS) were achieved after sintering at 1350°C for 60 min with 1 wt.% FeB. Secondary pores were observed in samples containing more than 1.5 wt.% FeB sintered at 1350 °C for 60 min. More than 1.5 wt.% FeB content and temperature above 1350°C caused slumping of the specimens. Maximum UTS of 505 MPa was achieved with 1 wt.% FeB content. Above 0.5 wt.% FeB content, maximum increase in density was observed. Fracture morphologies of the sintered samples are reported.
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| 45. |
- Akhtar, Farid, et al.
(author)
-
Stainless steel binder for the development of novel TiC-reinforced steel cermets
- 2006
-
In: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material. ; 13:6, s. 546-550
-
Journal article (peer-reviewed)abstract
- Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC-reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy (P/M). TiC-reinforced maraging stainless steel composites with >97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.
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| 46. |
- Akhtar, Farid
(author)
-
Stainless Steel Polymer Composites
- 2012
-
In: Wiley Encyclopedia of Composites. - Hoboken, NJ, USA : John Wiley & Sons. - 9780470275689
-
Book chapter (peer-reviewed)abstract
- In electronic, automotive, medical, and aerospace industries, electrostatic discharge (ESD) control and electromagnetic interference (EMI) shielding are important design considerations. Conductive polymer composites are well researched and commercially available materials for ESD control and EMI shielding. Several kinds of conductive fillers are incorporated in the form of particulates and fibers in polymer matrix. A comparison between various conductive fillers in polymer matrix is presented. Stainless steel fibers as conductive filler for polymer matrix offer several advantages. Polymer composites show resistivities in the range of 103−106 Ω/sq at a volume fraction as low as 0.75 vol% of stainless steel fibers. The effect of filler size, shape of the filler, critical volume fraction, and effect of polymer matrix on the ESD control/EMI shielding properties of the stainless steel-reinforced conductive polymer composite is discussed. Important parameters are described to obtain effective ESD control and EMI shielding using stainless fiber polymer matrix composites. Several reported stainless steel-reinforced polymer composites are summarized and their effectiveness for ESD control and EMI shielding is compared
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| 47. |
- Akhtar, Farid, et al.
(author)
-
Strong and binder free structured zeolite sorbents with very high CO2-over-N-2 selectivities and high capacities to adsorb CO2 rapidly
- 2012
-
In: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 5:6, s. 7664-7673
-
Journal article (peer-reviewed)abstract
- Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N-2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N-2 were determined and used to predict the co-adsorption of CO2 and N-2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N-2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 degrees C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N-2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g(-1)) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N-2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.
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| 48. |
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| 49. |
- Akhtar, Farid
(author)
-
Structured adsorbents with High CO2 over N2 selectivity and CO2 uptake capacity
- 2012
-
In: 2012 AIChE annual meeting. - New York : American Institute of Chemical Engineers. - 9780816910731
-
Conference paper (peer-reviewed)abstract
- Structured adsorbents with high CO2 adsorption capacity, CO2 over N2 selectivity and rapid adsorption and desorption kinetics are ideal for CO2 capture from power-plant flue gas at a low cost. We report here binder-free zeolite monoliths with high CO2 over N2 selectivity (> 500) and uptake capacity (4mmolg-1) at 298 K and 101 kPa. Binder-free zeolite monoliths were consolidated by a rapid and facile processing approach called pulse current processing (PCP) from partially K exchanged NaA powders. The pore widow size of NaA was optimized by partially exchanging Na with K cations to achieve a high CO2 over N2 selectivity while maintaining a high CO2 uptake capacity. The CO2 uptake from binary mixtures of 0.10CO2-0.90N2 was obtained from the single component CO2 and N2 adsorption isotherms by applying Ideal adsorption solution (IAS) and Fast IAS theories. The binder-free adsorbents with an optimum degree of ion exchange display extraordinarily high CO2 over N2 selectivity and high CO2 uptake, together with a rapid CO2 adsorption and desorption kinetics and high mechanical stability. The performance of the new adsorbent has been compared with other potential candidates for efficient swing adsorption processes by a figure of merit. Key words: CO2 Capture; Zeolite monoliths; Pulse current processing; Selectivity; Adsorption; Ideal adsorbed solution (IAS) theory
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| 50. |
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