| 1. |
- Balachandramurthi, Arun Ramanathan, et al.
(författare)
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On the microstructure of laser beam powder bed fusion alloy 718 and its influence on the low cycle fatigue behaviour
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:22, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing of Alloy 718 has become a popular subject of research in recent years. Understanding the process-microstructure-property relationship of additively manufactured Alloy 718 is crucial for maturing the technology to manufacture critical components. Fatigue behaviour is a key mechanical property that is required in applications such as gas turbines. Therefore, in the present work, low cycle fatigue behaviour of Alloy 718 manufactured by laser beam powder bed fusion process has been investigated. The material was tested in as-built condition as well as after two different thermal post-treatments. Three orientations with respect to the building direction were tested to evaluate the anisotropy. Testing was performed at room temperature under controlled amplitudes of strain. It was found that defects, inclusions, strengthening precipitates, and Young’s modulus influence the fatigue behaviour under strain-controlled conditions. The strengthening precipitates affected the deformation mechanism as well as the cycle-dependent hardening/softening behaviour. The defects and the inclusions had a detrimental effect on fatigue life. The presence of Laves phase in LB-PBF Alloy 718 did not have a detrimental effect on fatigue life. Young’s modulus was anisotropic and it contributed to the anisotropy in strain-life relationship. Pseudo-elastic stress vs. fatigue life approach could be used to handle the modulus-induced anisotropy in the strain-life relationship.
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| 2. |
- Gupta, R. K., et al.
(författare)
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Hot Deformation Studies on beta(0) Stabilized TiAl Alloy Made Through Ingot Metallurgy Route
- 2021
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Ingår i: Transactions of the Indian Institute of Metals. - : Springer Science and Business Media LLC. - 0972-2815 .- 0975-1645. ; 74:12, s. 2977-2989
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Tidskriftsartikel (refereegranskat)abstract
- Hot deformation studies of a newly designed gamma + alpha(2) based TiAl alloy of composition Ti-42Al-6Nb-3Cr-0.1B at.% (nominal) realized through ingot metallurgy route using double vacuum arc remelting were carried out. Hot isothermal compression testing was performed in Gleeble (TM) 3500 at different temperatures ranging from 1123 to 1373 K at 50 K intervals and strain rates of 0.001-1 s(-1). Processing maps were developed using an approach of dynamic material modeling of the flow curves to establish the safe hot working regime. Strain rate sensitivity and Zener-Holloman parameters were calculated and constitutive equation was derived. Microstructural investigation revealed dynamic recrystallization and activation of multiple twin systems as the main softening mechanisms operating at optimum hot working conditions. Safe hot working temperature and strain rate regime for the alloy was found to be in the temperature range of 1323-1373 K and strain rate range of 0.001-0.01 s(-1).
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| 3. |
- Jaladurgam, Nitesh Raj, 1993
(författare)
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Deformation mechanisms and load distribution in multi-phase engineering materials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- While the transition to carbon neutral technologies is still in progress, it is vital to reduce the environmental impact of existing processes. The efficiency of combustion processes for e.g. power generation and aviation can be greatly improved by increasing the operating temperature. This, however, requires development of new and improved materials with increased temperature capability. Similarly, materials which enable e.g. storage of hydrogen or liquid natural gas at cryogenic temperatures can contribute to the above transition. Such high performance engineering materials are usually very complex, with many alloying elements and multiple phases. During deformation the behaviour of the phases, and the grains with different orientations within each phase, is a result of elastic and plastic interactions. Quantifying how the stresses and strains are redistributed within and among the phases is essential for the development of quantitative models capable of accurately predicting the macroscopic mechanical response from the single crystal properties. This thesis explores the use of in-situ neutron diffraction for investigating load partitioning and deformation mechanisms in two different advanced multi-phase materials, a Ni-based superalloy and a eutectic high entropy alloy, across a wide temperature range (from 20 to 1000 K). For the superalloy, the main findings are: (i) the effect of particle size on the deformation mechanisms and load partitioning was consistent across all temperatures; (ii) plastic deformation of the strengthening phase at high stresses occurred at cryogenic temperatures, which has not been previously reported; and (iii) a strong orientation and phase dependence of the damage evolution during high-temperature deformation was observed. In the eutectic high entropy alloy transitions in the deformation mechanisms of the constituent phases were found to occur with increasing temperature, which lead to a new proposed alloy design strategy for optimising the high temperature properties. Further, the role of the phases is reversed at higher temperatures, i.e. the soft phase at lower temperature becomes the reinforcing phase when the temperature increases. The reported results will have a large impact on the development of accurate multi-scale models for property prediction, as well as development and optimization of complex materials which contribute to a sustainable society.
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| 4. |
- Jaladurgam, Nitesh Raj, 1993
(författare)
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Heterogeneous deformation of multi-phase engineering materials - an in-situ neutron diffraction study
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas turbines are complex power generation systems used in aerospace or land-based-power stations. Materials such as Ni-base superalloys are involved in the combustion zone of these machines, which continuously experiences harsh environments with loading at high temperatures. Moreover, the continuous demand for increasing operating temperature to achieve higher efficiencies and reduced emission levels opens the scene to new heat resistant materials like the state-of-the-art high entropy alloys (HEAs), which require a thorough understanding of the structure-process-property relationships. The microstructures of these advanced multi-phase, multi-component alloys are complex, and the deformation is generally heterogeneous both with respect to the different phases and to the crystallographic orientation within each phase. Hence, it is important to understand their behavior and performance during processing and service. In-situ neutron diffraction is a unique technique to probe the deformation behaviour during service/processing-like conditions, including plastic deformation at various temperatures, in order to provide insights into the structure-property relations. In the first part of this work the deformation mechanisms of a newly developed Ni-base superalloy was investigated using in-situ neutron diffraction and electron microscopy at room temperature. In addition, elasto-plastic self-consistent (EPSC) crystal plasticity simulations are used to obtain insights into the operating deformation mechanisms. In the second part, the as-cast eutectic high entropy alloy AlCoCrFeNi2.1 was studied using in-situ neutron diffraction at temperatures from 77 to 673 K. These investigations provide unique insights into the complex heterogeneous deformation behavior of these high-performance multi-phase engineering materials.
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| 5. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Load redistribution in eutectic high entropy alloy AlCoCrFeNi 2.1 during high temperature deformation
- 2022
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 22
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Tidskriftsartikel (refereegranskat)abstract
- The load redistribution between and within phases in eutectic high entropy alloy AlCoCrFeNi2.1 was measured using in-situ neutron diffraction during tensile deformation at 973 K. The load partitioning between phases is reversed compared to lower temperatures, with L12 becoming the stronger phase. The evolution of the orientation-specific stresses and strains in the L12 phase suggests that cube slip dominates the response. The low strength, internal load transfer and ideally plastic response of the B2 phase indicate a change in deformation mechanism compared to lower temperatures.
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| 6. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Macro- and micro-mechanical behaviour of a γ′ strengthened Ni-based superalloy at cryogenic temperatures
- 2021
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- In-situ neutron diffraction was performed during tensile deformation of Ni-base superalloy, Haynes 282, at 20, 100 and 300 K. Two distinct uni-modal microstructures with fine (20 nm) and coarse (200 nm) \(\gamma^\prime\) particles were investigated. On the macro-scale yield strength increased and ductility decreased with decreasing temperature, although most significant decrease in ductility occurred between 100 and 20 K. The work hardening differed between the two microstructures, but was independent of temperature for each microstructure. On the micro-scale intergranular elastic interactions mainly lead to a transfer of the load to grains with the $\left<200\right>$ parallel to the tensile axis. No further load re-distribution between matrix and particles occurred in the microstructure with fine \(\gamma^\prime\), where shearing of precipitates lead to co-deformation at all temperatures. In the coarse \(\gamma^\prime\) microstructure, the load was transferred intragranularly from matrix to particles, in addition to the intergranular load transfer. The particles initially behaved elastically while the matrix deformed plastically, but at higher stresses a change in load partitioning indicated that also the \(\gamma^\prime\) phase underwent plastic deformation as a result of the elastic stress build-up from the load partitioning. The tendency for, and effect of, plastic deformation of \(\gamma^\prime\) increased with decreasing temperature.
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| 7. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Microstructure-dependent deformation behaviour of a low γ′ volume fraction Ni-base superalloy studied by in-situ neutron diffraction
- 2020
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454. ; 183, s. 182-195
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Tidskriftsartikel (refereegranskat)abstract
- Ni-base superalloys are critical materials for numerous demanding applications in the energy and aerospace sectors. Their complex chemistry and microstructure require detailed understanding of the operating deformation mechanisms and interaction between the matrix and the hardening phase during plastic deformation. Here we use in-situ neutron diffraction to show that the dependence of the deformation mechanisms and load redistribution on $\gamma^\prime$ particle size in a Ni-base superalloy with a $\gamma^\prime$ volume fraction of around $20 \%$ can exhibit distinct differences compared to their high volume fraction counterparts. In particular, the load redistribution in the coarse microstructure occurs immediately upon yielding in the present case, whereas high $\gamma^\prime$ volume fractions have been observed to initially lead to shear mediated co-deformation before work hardening allows looping to dominate and cause load partitioning at higher stresses. The fine microstructure, on the other hand, behaved similar to high volume fraction alloys, exhibiting co-deformation of the phases due to particle shearing. A recently developed elasto-plastic self-consistent (EPSC) crystal plasticity model, specifically developed for the case of coherent multi-phase materials, could reproduce experimental data with good accuracy. Furthermore, the finite strain formulation of the EPSC model allowed deformation induced texture predictions. The correct trends were predicted by the simulations, but the rate of lattice rotation was slower than experimentally observed. The insights point towards necessary model developments and improvements in order to accurately predict e.g. texture evolution during processing and effect of texture and microstructure on component properties.
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| 8. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Temperature dependent load partitioning and slip mode transition in a eutectic AlCoCrFeNi 2.1 high entropy alloy
- 2021
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- Eutectic high entropy alloys are gaining increasing attention due to their excellent castability and combination of strength and ductility in the as-cast state. However, the detailed behavior of the nano-scale lamellar microstructure during deformation, and in particular the interaction between the phases, is not well understood. Here we use in-situ neutron diffraction during tensile testing over a wide temperature range (77–673 K) to obtain new insights into the temperature dependent mechanical interactions between and within phases during initial plastic deformation of an AlCoCrFeNi eutectic high entropy alloy. The load was transferred from the L1 to the B2 phase during the yielding process, and the changing load distribution within the L1 phase with increasing temperature strongly suggests that <110>{001} cube slip is activated at room temperature and above. This points towards alloying design for delayed octahedral-to-cube slip transition as a possible strategy for increasing the high temperature strength of material. 2.1 2 2
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| 9. |
- Munirathinam, Balakrishnan, et al.
(författare)
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Improved corrosion protection of titanium implant material by crystallographic texturing of Sr doped calcium phosphate electrodeposits
- 2019
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 675, s. 115-121
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline calcium phosphate (CaP) coatings can provide biocompatibility and corrosion protection to biomaterials upon implementation in the human body. While the long term stability of recently developed coatings in biological environment proves to be challenging, the present work tailors the surface by orienting the growth (crystallographic texturing) of strontium doped CaP coatings in order to increase their corrosion resistance. X-ray diffraction (XRD) as well as selected area electron diffraction patterns from transmission electron microscopy reveal that nanocrystalline CaP crystallizes in hexagonal hydroxyapatite structure preferentially oriented along the c-axis. Orientation distribution function obtained from XRD texture studies confirms the presence of a [0001] fiber texture and the estimated texture index indicates the evolution of texture with increasing deposition current density. Polarization studies point out that increasingly textured coatings decrease the corrosion current density by an order of magnitude (from 2.43 × 10 −7 to 3.46 × 10 −8 A cm −2 ). Impedance measurements confirm that oriented growth of film renders improved corrosion resistance. This study demonstrates that oriented growth of electrodeposited films strongly improves the corrosion performance of titanium, which can be employed in design and development of highly corrosion resistive implant materials.
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| 10. |
- Syed, Faisal Waqar, et al.
(författare)
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Hot deformation characteristics and microstructure evolution of Ti-5Al-3Mo-1.5V alloy
- 2021
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Ingår i: INTERNATIONAL JOURNAL OF ADVANCES IN ENGINEERING SCIENCES AND APPLIED MATHEMATICS. - : Springer Science and Business Media LLC. - 0975-5616 .- 0975-0770. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- A detailed investigation was conducted to study the concurrent effect of temperature and strain rate on the microstructure evolution in Ti-5Al-3Mo-1.5V dual-phase Titanium alloy. By applying varying strain rates from 10-3 to 10 s-1between 1098 and 1298 K at an interval of 50 K, isothermal compression characteristics and microstructural changes were recorded. The sizes of globules, concentrated predominantly at the lamellar kinks, were found to be inversely proportional to the strain rate. Further, a dynamic material model was employed to assess and plot the processing map displaying the safe hot working regime. The apparent hot-working activation energy in the alpha+ beta and beta phase field was 636 kJ/mol and 379 kJ/mol, respectively. A higher activation energy than the self-diffusion threshold of the alpha+beta and beta field was attributed to lamellae breakup and dynamic recrystallization in the respective phase fields. The microstructure analysis and identified softening mechanisms further helped in concluding the safe hot working regime to be 1248 K and 10(-3) s(-1).
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