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PM technique has been applied for some products in the autoindustries due to unique functions and cost saving. The wear resistance of PM steel parts is one of the most significant surface properties. Nitriding and carburizing processes consist of exposing metallic materials to nitrogen and carbon to improve their surface hardness and wear resistance. In this research, the partially diffusion prealloyed powders, Ultrapac LE, containing Fe-4Ni-1.5Cu-0.5Mo with 0.2% graphite and two different densities were sintered at 1120 °C for 30 min. Depending on the applied pressures during cold pressing, two different porosities of 14.11 and 10.26 vol.% were obtained. Some specimens were carburized and some others were nitrided in cyanate liquid salt bath. The pin-on-disc wear test and hardness test were used to evaluate the surface behavior of specimens. The results showed that the wear resistance increased by nitriding and carburizing processes and the effect of nitriding is more than carburizing on wear resistance. In the case of materials studied, except for 4 h nitrided specimens, other specimens with higher porosity level showed better wear resistance. In these specimens, large pores entrapped the wear debris and created a densified layer. It prevented the formation of large abrasive agglomerates. For the carburized specimens, wear mechanisms were affected by the brittle fracture caused by abrasive wear. So, wear resistance did not increase significantly. In this investigation, abrasive, plastic deformation and oxidation wear were observed as wear mechanisms. 相似文献
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《粉末冶金学》2013,56(5):566-571
AbstractThe effect of prepassivation of prealloyed powder of 316L stainless steels on pore morphology and powder particle shape was investigated. Image analysis technique was used to study the effect of prepassivation, compaction and sintering temperature on the pore morphology of powder metallurgy 316L stainless steels. Porosity, dimension and morphology of the pores were characterised by means of four basic parameters: fraction of surface porosity, equivalent circle diameter, shape factor and elongation factor. In addition, SEM macrographs of powder particles were also investigated by applying the image analysis technique. The Feret’s average diameter and elongation factor were employed to describe the size and roundness of powder particles respectively. Annealing treatment reduced the equivalent circle diameter of pores and simultaneously improved fshape and felong towards higher values. It was proposed that the prepassivation treatment reduced irregularity of powder particles through elimination of sharp corners of powder particles by exposure to acid environment. 相似文献
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蔡幼庆 《安徽工业大学学报》1993,(1)
本文研究了Fe-P-C三元系粉末合金经不同温度淬火及不同温度回火后的组织和性能。试验结果表明:临界区热处理与常规温度处理相比,硬度略有升高,冲击韧性有较大增加。本文并对强韧化机理进行了探讨。 相似文献
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多孔结构和轻质是粉煤灰陶粒的基本特征 ,它们影响混凝土拌和物的工艺性能 ,本文试验研究了陶粒混凝土拌和物的坍落度及其损失、离析性和减水剂的塑化效果。 相似文献
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The aim of the work was to find out how the modification of surface treatment and microstructures affect the fatigue characteristics of the considered sintered materials.Two different systems were prepared:as-sintered and shot peened prealloyed sintered(Astaloy CrL based)steels with addition of 0.5%and 0.7%C.Sintering was carried out in laboratory tube furnace in an atmosphere of pure gases 75%N2+25%H2.The sintering temperature was 1180-C and sintering time was 60 min.Heating and cooling rates were 10-C/min... 相似文献
17.
Residual porosity in ferrous powder metallurgical alloys induces the phenomenon of localized yielding, or first yielding, during tensile testing. This gives rise to the existence of a true (E1) and apparent (E2) Young’s modulus. The true Young’s modulus is similar to the dynamic modulus (Ed) determined by the acoustic resonance method, whereas the apparent Young’s modulus is lower than both E1 and Ed. For alloys with hard microstructures the apparent Young’s modulus turned out to be about 6% lower than the true Young’s modulus and a negligible influence of matrix hardness and pore morphology was highlighted. However, for ferritic or ferritic–pearlitic materials this difference was higher, ranging between 14 and 31% and it decreases as pore roundness is increased. For austenitic AISI 316L alloys both E1 and E2 are lower than Ed because of the presence of oxides on the powder surface, which favour early decohesion at the necks during tensile testing. 相似文献
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Lin Hua Xunpeng Qin Huajie Mao Yumin Zhao 《Journal of Materials Processing Technology》2006,180(1-3):174-178
This paper analyses the basic aspects of plastic deformation behaviours of compressible sintered powder materials, such as plastic volume change, mass constancy, small Poisson's ratio and the effect of hydrostatic pressure on yield. Based on the uniaxial compression tests using sintered powder copper as a model material, the true stress–strain equation, a generalized yield criterion and some plastic constitutive equations for compressible sintered powder materials are proposed. The proposed generalized yield criterion can depict both the initial yield and successive yield of compressible sintered powder materials in the form of unified yield function, and reflect comprehensively the effects of initial density and deformation strengthening on yield of compressible sintered powder materials as well. Experiments show that the generalized yield criterion can be applied to materials with various densities from loose powder to fully dense metal. 相似文献
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