Papers by Keyword: S-Phase

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Authors: Jérôme Majimel, G. Molénat, F. Danoix, D. Blavette, Gilles Lapasset, M.J. Casanove
Authors: Thomas Bell
Abstract: The present paper reviews the scientific development of our understanding of S-Phase. It is now known that S-Phase formation is an example of para equilibrium phenomena. A necessary but not sufficient condition for S-Phase formation is the presence of an fcc structure at least in part with structure in the starting alloy. An essential requirement is for a nitride forming element to be present particularly Cr. After surface engineering with carbon, nitrogen or carbon and nitrogen to generate supersaturated solid solutions, the various tribological, corrosion, mechanical and microstructural studies are reviewed for the various alloy systems. The current industrial status of S-Phase technology on an international basis is examined and the potential for its acceptance in china is discussed.
Authors: Abbas Saeed Hakeem, Raja Muhammad Awais Khan, Moath Mohammad Al-Malki, Faheemuddin Patel, Akolade Idris Bakare, Sadaqat Ali, Stuart Hampshire, Tahar Laoui
Abstract: The development of SiAlON-based ceramics has shown great impact in the field of cutting/drilling tool industry and other engineering applications. It is highly desirable to cut-down the cost of the cutting tools by increasing their service lifetime. Potential ways to improve tool life is by preparing these SiAlON-based ceramics adopting non-conventional synthesis routes and by using different precursors. The present study reports the results of synthesis of SiAlON-based nano-ceramics via spark plasma sintering (SPS) technique. Generally, metal nitride and metal oxide precursors are used for synthesizing self-reinforced SiAlON ceramics. In this work, nano-sized metallic precursors including amorphous-Si3N4 and crystalline β-Si3N4, SiO2, AlN and Al2O3 were used, which could be a novel way to synthesize SiAlONs at low temperatures with enhanced performance. The properties of these SiAlONs are tailored by optimizing the synthesis parameters. The synthesized samples were characterized by X-ray diffraction and field emission scanning electron microscopy to study the effect of processing parameters on microstructure, density and hardness.
Authors: Seong Taek Lim, Yong Yun Lee, Il Sang Eun
Abstract: An effort has been made to present optimum alloy designs of commercial 7175 and 7050 type alloys to be used in thick forgings with proper microstructures and properties. The effects of changing alloy constitutions, primarily [Zn+Mg+Cu] and Zn:Mg ratio, on the evolutions of the coarse equilibrium phases and age hardening response are investigated. As a result, equilibrium phases (M,T,S) are evolved depending on alloy constitutions and cooling rate following solutionizing. The formation of the T- and S-phases is effectively controlled in the novel alloys (dilute and with high Zn:Mg ratio). In the slow quench, the redesign promotes homogeneous precipitation of η-phases, leading to higher mechanical properties than conventional alloys. The novel alloys provide microstructural homogeneity and extended heating range, ensuring 7xxx thick forging applications.
Authors: Yang Yu Su, Fan Shiong Chen, Liu Ho Chiu, Heng Chang
Abstract: In this study, the plasma nitrocarburizing has been used to treat AISI 316 austenitic and AISI 410 martensitic stainless steels. Treated specimens were characterized by means of morphological analysis, surface microhardness measurement, and resistivity measurement. Plasma nitrocarburizing at low temperature (420°C) produced a single phase nitrided layer of nitrogen and carbon expanded austenite (S phase) on the specimen surface, which considerably improved the resistivity property of AISI 316 austenitic stainless steel.
Authors: Jolanta Baranowska, Vicente Amigó
Abstract: The results concerning gas nitriding of sintered stainless steel are presented in the paper. The samples made of 316L steel were gas nitrided at temperatures between 400-550°C. The microstructure of the layer was investigated by means of light and atomic force microscopy. The phase composition was identified using X-ray diffraction. Moreover, tribological and corrosion properties of the samples were evaluated. It was demonstrated that in case of gas nitriding it is possible to obtain nitrided layers also inside open pores, which can be beneficial for corrosion response of nitrided sintered austenitic stainless steel applied in corrosive environments.
Authors: Dao Kui Xu, Paul A. Rometsch, Hua Chen, Barry C. Muddle
Abstract: In this work, the influence of multi-step solution (MSS) treatments on the constituent particle dissolution, overheating and associated quench cracking behaviour in room temperature water-quenched 7150 Al alloy has been investigated. For comparison, the microstructure and quench cracking behaviour of single step solution treated samples water-quenched from 505°C were also investigated. Based on optical microscopy of differently quenched samples, the quench cracking mode and the influence of overheating of constituents on the quench cracking behaviour have been demonstrated. The results reveal that the constituent particles can be effectively dissolved in the MSS-505°C samples. When the quench temperature of MSS-505°C samples is equal to or higher than 485°C , macro quench cracks can be clearly observed. Moreover, the density and length of the quench cracks increase with increasing quench temperature. Etched microstructures indicate that the quench crack propagation mode is intergranular. However, for samples directly heated to 505°C , typical overheating can be observed at the triple junctions and these regions preferentially act as crack propagation routes.
Authors: Paweł Kochmański, Jolanta Baranowska
Abstract: The paper presents results of research on nitrided layers on precipitation hardened stainless steel, known also as 1RK91 (Sandvik NanoflexTM). Samples were subjected to low temperature nitriding. The influence of nitriding parameters on nitriding kinetics was investigated. The nitriding process was carried out in a mixture of NH3 50% and products of its dissociation as well as in 100% ammonia atmosphere at temperature range 425-475°C. To investigate the kinetics of nitrided layer formation, the nitriding time changes between 2 and 8 h. The obtained diffusion layers were examined using the following methods: light and scanning electron microscopy, XRD phase analysis. The distribution profiles of selected chemical elements were acquired using optical spectrometry GDOES.
Authors: Seong Taek Lim, Yong Yun Lee, Il Sang Eun
Abstract: Recent 7xxx aluminum alloys have been designed for the finite use of thick semiproduct with contolled amount of constituent phases which mostly evolve during ingot preheat. In this study, the effects of constitutional change and preheat conditions of 7175 and 7050 type alloys on the evolution of constituent phases [M-, T-, S-phase and dispersoid] are presented. The constiuents evolve depending on the constitutional effect, primarily the change of Zn:Mg ratio, preheat condition comprising temperature and cooling rate following preheat. T- and M-phase are reprecipitated during cooling after preheat, depending on the alloy constitutions. S-phase is evolved depending on the constitution and preheat temperature, rather than preheat cooling rate. Prominent precipitation temperature interval of constituents are discussed in view of quaternary phase evolutions. In addition, evolutions of dispersoids together with M-phase are discussed. Specific alloy designs and preheat conditions could provide controlled microstructures for the thick 7xxx semiproducts.
Authors: Paweł Kochmański, Jolanta Baranowska
Abstract: The paper presents results of research on nitrided layers on Sandvik NanoflexTM precipitation hardened stainless steel. The influence of process parameters on nitriding kinetics and structure of the layers was investigated. The gas nitriding process was conducted in a mixture of ammonia 50% and products of its dissociation, as well as in 100% ammonia atmosphere at temperature range 400500°C and time between 2 and 8 h. The obtained diffusion layers were examined using the following methods: light and scanning electron microscopy, XRD phase analysis and EDS chemical analysis. Mechanical properties were tested with hardness measurements. It was found that kinetics depends on treatment temperature and nitrogen potential of the atmosphere. Moreover, treatment conditions affecting Sphase formation and expanded martensite in nitrided layers are discussed.
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