| 1. |
- Hryha, Eduard, 1980, et al.
(författare)
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Carbon Control in PM Sintering: Industrial Applications and Experience so Far
- 2012
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Ingår i: Proc. of EURO PM2012 Congress & Exhibition, 16-19 September 2012, Basel, Switzerland. - 9781899072231 ; 1, s. 265-270
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Konferensbidrag (refereegranskat)abstract
- Challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have tried to address the problem, many of these have rarely come to reality and become an industrial practice.The purpose of this article is to summarize these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. Considering an industrial practice perspective, the paper ensures the PM Industry with a fresh new look into the understanding of the furnace operations and provides recommendations to improve the control of the furnace conditions. As an example, existing furnace installation utilizing Linde SINTERFLEX technology allows monitor and/or control the furnace atmosphere. Article describes reduction of oxides and carbon potentials to enable optimization of the production parameters.
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| 2. |
- Hryha, Eduard, 1980, et al.
(författare)
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Influence of the Steel Powder Type and Processing Parameters on the Debinding of PM Compacts with Gelatin Binder
- 2014
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Ingår i: Journal of Thermal Analysis and Calorimetry. - : Springer Science and Business Media LLC. - 1388-6150 .- 1588-2926. ; 118:2, s. 695-704
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Tidskriftsartikel (refereegranskat)abstract
- Binders present an important part of the powder metallurgy technology as they are vital to provide efficient powder agglomeration and/or lubrication during shaping. At the same time, they have to be easily removed from the compacts during initial stages of sintering without any harmful effect for the base material, as well as for the environment. Therefore, behavior of gelatin as a binder for stainless- and tool-steel gas-atomised powder compacts was studied by thermal analysis and electron microscopy. Thermal analysis showed that peak mass-loss occurred in the range between 340 and 370 C, depending on the base powder and heating rate. Risk for base powder oxidation at temperatures below 425 C was detected. Based on the obtained results, it is recommended to perform debinding at *425 C after applying a heating rate of around 7.5 C min-1. Only in this way efficient enough binder removal can be obtained concurrently to avoiding base powder oxidation.
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| 3. |
- Hryha, Eduard, 1980, et al.
(författare)
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Process Control System for Delubrication of PM Steels
- 2012
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Ingår i: Acta Metallurgica Slovaca. - 1335-1532 .- 1338-1156. ; 18:2-3, s. 60-68
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Tidskriftsartikel (refereegranskat)abstract
- Lubricants are important additive in powder metallurgy (PM) steels as they are needed to improve powder compressibility and reduce tool wear. Removal of the lubricant results in production of number of gas species that can have harmful effect on the base material. Current paper describes process gas monitoring system for delubrication control that is built on industrially available gas sensors. Experimental results indicate that accurate delubrication process control can be performed by utilizing only CO2 and O2 sensors. It is recommended to perform delubrication below 500°C in dry inert atmospheres in the case of modern ethylene bis stearamide based lubricants.
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| 4. |
- Nagaram, Anok Babu, 1987, et al.
(författare)
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Full Density Powder Metallurgical Cold Work Tool Steel through Nitrogen Sintering and Capsule-Free Hot Isostatic Pressing
- 2024
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Ingår i: Metals. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2075-4701. ; 14:8
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Tidskriftsartikel (refereegranskat)abstract
- Vanadis 4E (V4E) is a powder metallurgical cold work tool steel predominantly used in application with demand for wear resistance, high hardness, and toughness. It is of interest to have a processing route that enables full density starting from clean gas-atomized powder allowing component shaping capabilities. This study presents a process involving freeze granulation of powder to facilitate compaction by means of cold isostatic pressing, followed by sintering to allow for capsule-free hot isostatic pressing (HIP) and subsequent heat treatments of fully densified specimens. The sintering stage has been studied in particular, and it is shown how sintering in pure nitrogen at 1150 °C results in predominantly closed porosity, while sintering at 1200 °C gives near full density. Microstructural investigation shows that vanadium-rich carbonitride (MX) is formed as a result of the nitrogen uptake during sintering, with coarser appearance for the higher temperature. Nearly complete densification, approximately 7.80 ± 0.01 g/cm3, was achieved after sintering at 1200 °C, and after sintering at 1150 °C, followed by capsule-free HIP, hardening, and tempering. Irrespective of processing once the MX is formed, the nitrogen is locked into this phase and the austenite is stabilised, which means any tempering tends to result in a mixture of austenite and tempered martensite, the former being predominate during the sequential tempering, whereas martensite formation during cooling from austenitization temperatures becomes limited.
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| 5. |
- Manchili, Swathi Kiranmayee, 1987, et al.
(författare)
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Comparative study on the densification of chromium pre-alloyed powder metallurgy steel through nanopowder addition using design of experiments
- 2021
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Ingår i: Results in Materials. - : Elsevier BV. - 2590-048X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- There is a constant demand for high density press and sinter powder metallurgical components for automotiveapplications. Steel powder pre-alloyed with chromium is an attractive material for such applications, but newways to further increase the sinter density are required for successful processing of these powders to high density.Nanopowder could be used as a potential sintering aid in order to boost the densification of the steel powdercompact. In this study, steel powder pre-alloyed with chromium, without and with admixed nickel, is used as basepowder, to which nanopowder was added. Surface oxide removal, crucial for successful sintering of such mate-rials, was studied by thermogravimetry analysis in order to understand the influence of nanopowder addition onthe oxide reduction. Powder compacts containing nanopowder showed higher mass loss in comparison to the oneswithout nanopowder. Linear shrinkage obtained from dilatometric curves increased with the addition of nano-powder. To depict the influence of the critical parameters; sintering temperature, powder size, addition ofnanopowder and composition (with or without nickel), a design of experiment approach was applied. The criticalparameters were then adjusted at 2 different values (categorical parameters) and a‘full factorial design model’was used involving 16 experiments, with sinter density and hardness as output measures of the experimentsdetermined. The results were analyzed using polynomialfit to determine which of the parameter exerts themaximum influence. Presence of nickel increased the hardness whereas sintering temperature and presence ofnanopowder enhanced the sinter density. This led to the tentative design of optimum conditions that resulted inincrease in sinter density from 7.25 g/cm3(92.5% of the theoretical density) to 7.4 g/cm3(94% of the theoreticaldensity) with an addition of 5% nanopowder to Ni-containing grade when sintered at 1350 °C instead of 1250 °C.
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| 6. |
- Gruber, Hans, 1983, et al.
(författare)
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Effect of Powder Recycling on the Fracture Behavior of Electron Beam Melted Alloy 718
- 2018
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Ingår i: Powder Metallurgy Progress. - : de Gruyter. - 1335-8987 .- 1339-4533. ; 18:1, s. 40-48
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the effect of powder feedstock alterations during multicycle additive manufacturing on the quality of built components is crucial to meet the requirements on critical parts for aerospace engine applications. In this study, powder recycling of Alloy 718 during electron beam melting was studied to understand its influence on fracture behavior of Charpy impact test bars. High resolution scanning electron microscopy was employed for fracture surface analysis on test bars produced from virgin and recycled powder. For all investigated samples, an intergranular type of fracture, initiated by non-metallic phases and bonding defects, was typically observed in the regions close to or within the contour zone. The fracture mode in the bulk of the samples was mainly moderately ductile dimple fracture. The results show a clear correlation between powder degradation during multi-cycle powder reuse and the amount of damage relevant defects observed on the fracture surfaces. In particular, samples produced from recycled powder show a significant amount of aluminum-rich oxide defects, originating from aluminum-rich oxide particulates on the surface of the recycled powder. © 2018 H. Gruber et al., published by Sciendo.
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| 7. |
- Malakizadi, Amir, 1983, et al.
(författare)
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Effects of workpiece microstructure, mechanical properties and machining conditions on tool wear when milling compacted graphite iron
- 2018
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 410-411, s. 190-201
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to investigate the tool performance when machining compacted graphite iron (CGI) alloys. A comparison was made between solid solution strengthened CGI including various amounts of silicon (Si-CGI) and the pearlitic-ferritic CGI as a reference material. The emphasis was on examining the influence of microstructure and mechanical properties of the material on tool wear in face milling process. Machining experiments were performed on the engine-like test pieces comprised of solid solution strengthened CGI with three different silicon contents and the reference CGI alloy. The results showed up-to 50% lower flank wear when machining Si-CGI alloys, although with comparable hardness and tensile properties. In-depth analysis of the worn tool surfaces showed that the abrasion and adhesion were the dominant wear mechanisms for all investigated alloys. However, the better tool performance when machining Si-CGI alloys was mainly due to a lower amount of abrasive carbo-nitride particles and the suppression of pearlite formation in the investigated solid solution strengthened alloys.
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| 8. |
- Mehta, Bharat, 1993, et al.
(författare)
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Effect of precipitation kinetics on microstructure and properties of novel Al-Mn-Cr-Zr based alloys developed for powder bed fusion – laser beam process
- 2022
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 920
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the precipitation kinetics and resulting effect on microstructure and property of a family of novel high strength Al-Mn-Cr-Zr alloys designed for powder bed fusion – laser beam process. The alloys have been shown to be printable without solidification cracking along with high supersaturation of solutes in as-printed state. Upon direct ageing, two families of precipitates namely Al-Mn and Al-Zr are observed. Al-Mn containing precipitates, which are observed in as-printed condition as nanometric precipitates decorating special regions are seen to grow preferentially at grain boundaries, which is followed by growth in bulk of the sample. A possible explanation is suggested to be a higher diffusivity at grain boundaries leading to faster growth while depleting solutes around grain boundary region quickly. The Al-Zr precipitation, which normally follows bulk precipitation is observed to co-precipitate with Al-Mn precipitates. Optimised heat treatments are seen to achieve peak hardness of 143 HV at 623 K for 24 h and 142 HV at 648 K for 14 h as compared to 102 HV in as-printed condition for one of the alloys. This overall hardening effect is attributed majorly to Al3Zr nanoprecipitates along with semi-coherent Al12Mn precipitates.
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| 9. |
- Mehta, Bharat, 1993, et al.
(författare)
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Laser powder bed fusion of an al-mg-sc-zr alloy: Manufacturing, peak hardening response and thermal stability at peak hardness
- 2022
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- This study shows a rapid and systematic approach towards identifying full density and peak hardness for an Al-Mg-Sc-Zr alloy commonly known as Scalmalloy®. The alloy is tailored for the laser powder bed fusion process and has been shown to be printable with >99.8% relative density. The microstructure suggests Al grain refinement in melt pool boundaries, associated with formation of primary Al3 (Sc, Zr) particles during solidification. Peak hardening response was identified by heat treatment tests at 573,598 and 623 K between 0 and 10 h. A peak hardness of 172 HV0.3 at 598 K for 4 h was identified. The mechanical properties were also tested with yield and ultimate strengths of 287 MPa and 364 MPa in as-printed and 468 MPa and 517 MPa in peak hardened conditions, respectively, which is consistent with the literature. Such an approach is considered apt when qualifying new materials in industrial laser powder bed fusion systems. The second part of the study discusses the thermal stability of such alloys post-peak-hardening. One set of samples was peak hardened at the conditions identified before and underwent secondary ageing at three different temperatures of 423,473 and 523 K between 0 and 120 h to understand thermal stability and benchmark against conventional Al alloys. The secondary heat treatments performed at lower temperatures revealed lower deterioration of hardness over ageing times as compared to the datasheets for conventional Al alloys and Scalmalloy®, thus suggesting that longer ageing times are needed.
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| 10. |
- Mehta, Bharat, 1993, et al.
(författare)
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Microstructure, mechanical properties and fracture mechanisms in a 7017 aluminium alloy tailored for powder bed fusion – laser beam
- 2023
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 226
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Tidskriftsartikel (refereegranskat)abstract
- This study addressed a 7017 Al-alloy tailored for powder bed fusion – laser beam (PBF-LB) process. The alloy was prepared by mixing 3 wt% Zr and 0.5 wt% TiC powder to standard pre-alloyed 7017 grade aluminium powder. This made printing of the alloys possible avoiding solidification cracking in the bulk and achieving high relative density (99.8 %). Such advanced alloys have significantly higher Young's modulus (>80 GPa) than conventional Al-alloys (70–75 GPa), thus making them attractive for applications requiring high stiffness. The resulting microstructure in as-printed condition was rich in particles originating from admixed powders and primary precipitates/inclusions originating from the PBF-LB process. After performing a T6-like heat treatment designed for the PBF-LB process, the microstructure changed: Zr-nanoparticles and Fe- or Mg/Zn- containing precipitates formed thus providing 75 % increase in yield strength (from 254 MPa to 444 MPa) at the cost of decreasing ductility (∼20 % to ∼9 %). In-situ tensile testing combined with SXCT, and ex-situ tensile testing combined with fracture analysis confirmed that the fracture initiation in both conditions is highly dependent on defects originated during printing. However, cracks are deflected from decohesion around Zr-containing inclusions/precipitates embedded in the Al-matrix. This deflection is seen to improve the ductility of the material.
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