Papers by Keyword: Powder Metallurgy (PM)

Abstract: The article’s primary purpose is to give a technological assessment of manufacturing complex-shaped parts using powder metallurgy. The process is considered in the example of a complex-shaped product consisting of several elements manufactured separately from the Fe-C-Cu powder mixture and then combined into a single structure. The joining was carried out by impregnation of porous structural elements with the fusion of copper-containing material. It has been demonstrated that the infiltration process is affected by many factors: porosity of structural elements, wettability of their pore channels, fluid flowability of the infiltrating material, and other factors. The research was carried out on the mass products - centrifugal pump stages for oil production. The elements compaction was carried out on hydraulic press at a pressure of 500 MPa, which ensured the average density of the parts after sintering up to 7.8-8.4 g/cm³. During sintering and impregnation, various types of defects of the pieces were detected, which were caused by the excessive thickness of the infiltrating material, different densities of the walls, and insufficient wettability in the connection zones of the elements.The investigations have shown that manufacturing complex components by prefabricating single elements and their subsequent sintering combined with infiltration is feasible. It can be done in a chamber furnace as well as with belt sintering. However, it is necessary to carefully prepare the mold before sintering, choose the infiltrating agent, and analyse possible disadvantages.

Abstract: The benefit of pre-sintered machining is to avoid machining difficulty of sintered parts especially hardenable PM steels. Pre-sintering treatments of green PM part at temperatures lower than the normal sintering temperature of 1120 °C result in green strength improvement high enough for machining. In this study, the influences of various pre-sintering temperatures and several machining conditions on machined surface quality of pre-sintered PM samples were investigated. The pre-sintered samples were machined by a turning process using a carbide cutting insert with varied cutting speeds at a fixed feed rate and depth of cut without cutting lubricant. Chromium alloyed PM steel (Astaloy^® CrM) powder samples with (0.5 wt. %C) and without graphite (0 wt. % C) additions mixed with 1 wt. % of zinc stearate were prepared as green parts by cold compaction in a cylindrical die with diameter of 30 mm. Green density was about 7.00 g/cm³ and height of each sample was controlled by hydraulic pressure and powder weight of 80 g/sample. The green samples were treated by pre-sintering treatment before machining testing. Surface quality of each machined sample was evaluated by average surface roughness and surface texture by SEM analysis and the appearance of outlet edge breakout. The experimental results revealed that the pre-sintered samples with graphite addition showed better surface quality in terms of surface roughness and surface texture and small outlet edge breakout appearance. Moreover, at high pre-sintering temperatures of 900 and 1,000°C, the samples showed similar average surface roughness under the same turning conditions. The obtained surface textures were better than those of the samples pre-sintered at 700 and 800°C. The outlet edge breakout could not be found in the graphite-added samples pre-sintering at 1,000°C.

Abstract: Magnesium (Mg) has a great potential to be used in various field of work since it is lightweight and has low density properties. However, its application is limited due to its poor properties for Mg has a relatively low strength. Improvement is made by mixing Mg with calcium (Ca) as composite element for it is lightweight and non-toxic. In this research, Mg is prepared with different weight percentage (0, 0.5, 1, 1.5, 2 wt. %) of Ca with pure Mg as reference prepared by powder metallurgy (PM) method to study the mechanical properties. Morphological analysis carried out by optical microscope shows increase grain refinement with the increase of calcium content in Mg-Ca composites. The phase transition upon addition of Ca is determined using XRD method detects formation of Mg₂Ca. Range from 1.78 g/cm³ to 1.83 g/cm³, the density of each sample composite increase. While porosity profiles show inverse characteristics upon addition of Ca. Microhardness strengths also intensifies up to 193.20 MPa as more Ca content added in.

Abstract: Having the benefit of lightweight and low density makes magnesium (Mg) a good element with high potential to be used in various field of work. Yet, its application is limited for Mg is relatively low in term of strength. Hence, calcium (Ca) is chosen to be mixed with Mg as additional element for it is lightweight and non-toxic. In this research, Mg is prepared with different weight percentage (0, 1, 2 wt. %) of Ca via powder metallurgy (PM) method. The effect of sintering was investigated by focusing on the microstructure and properties of sintered sample. The samples were sintered at two sintering temperature (500 and 600 °C) in argon atmosphere. Morphological analysis carried out by optical microscope shows increase pores refinement with the increase of sintering temperature together with calcium content in Mg-Ca composites. Results show that the grain size and hardness of the samples increase as sintering temperature increase.

Abstract: Al-Cu alloy and its matrix composites reinforced with different volume fractions of short carbon fibers covered by copper have been produced by powder metallurgy method and heat treatment. The effects of the fiber volume fraction and load applied on the wear and friction behaviors of the composites were investigated. The results showed that the Cf/Al-Cu composites had better mechanical and tribological properties compared to Al-Cu alloy. The applied load did not obviously affect the wear resistance and friction coefficient.

Abstract: Ti metal matrix composites (Ti–MMCs) reinforced by vapor grown carbon nanofiber (VGCF) and graphite particle (Gr) were prepared via powder metallurgy and hot extrusion. Ti with 0~0.4wt% VGCF/Gr mixture powders were consolidated by using spark plasma sintering (SPS) at 800 °C. Hot extrusion was then performed at 1000 °C with an extrusion ratio of 37:1. Microstructures and mechanical properties of the as-extruded Ti composites were investigated. Tensile strength of Ti–VGCF/Gr composites was steadily augmented when additions of VGCF/Gr were increased from 0.1 to 0.4 wt%. YS and UTS were increased 40.2% and 11.4% for Ti–0.4wt%VGCF as compared to pure Ti, while those values were 30.5% and 2.1% for Ti–0.4wt%Gr. The strengthening mechanism including grain refinement, carbon solid solution strengthening and dispersion hardening of TiC/carbon was discussed in detail.

Abstract: Production of tungsten-copper composites includes compaction and sintering of tungsten powder, then infiltration of copper melt within the tungsten skeleton. Sintering of tungsten compacts usually requires a temperature range of 1800 to 2200°C. This means, this process not only needs advanced heating equipments and high expenses but also may cause formation of defects such as structural heterogeneities, cracks and distortions. In this research the required sintering temperature was reduced to 1500°C by increasing compaction pressure. Also the relation between compaction pressure applied through a cold isostatic press (CIP), and green density of the compacted tungsten powder was established. In addition, the effect of various pressures on densification of tungsten compacts during sintering at moderate temperature, i.e. 1500°C was studied, and the optimum structure for infiltration was chosen. Then by infiltrating Cu melt into the optimized W-skeleton, composites of W-Cu having a density of 17.2 gr/cm3 were produced. This method of production provides an innovative technique for obtaining a desired density of infiltrable skeleton, sinterable at a lower temperature than the temperatures used for the conventionally packed W-compacts without introducing structural inhomogeneities during sintering. Study of some characteristics of the optimized composite produced by the above technique satisfied the requirements for production of W-Cu composites having all the specifications given for these types of composites produced at higher temperatures than 1500°C.

Abstract: Copper-based composite now is a potential material for various applications, while powder metallurgy processing technique is an alternative for high temperature processing materials and net shape component. In this research, Cu-based composite containing 10-50 vol% SiC fibers was fabricated by employing the powder metallurgy route. The mixtures of SiC fibers and Cu particles were blended in a ball milling machine with the addition of ethanol at 150rpm. Then, the mixtures were uniaxially compacted into a ɸ13.5mm cylindrical pallet and followed by sintering in vacuum furnace from 800-950°C for 4 hours. The density of the composite decrease with increasing SiCf and density as high as 87% for 10vol% SiCf/Cu matrix sintered at 800°C had been achieved. The Vickers hardness of 774MPa also had been achieved for 10vol% SiCf/Cu matrix but sintered at 900°C.

Abstract: Metal matrix-particulate composites fabricated by using powder metallurgy possess a higher dislocation density, a small sub-grain size and limited segregation of particles, which, when combined, result in superior mechanical properties. The present study aims to develop iron based silica sand nanoparticles composites with improved mechanical properties. An iron based silica sand nanoparticles composite with 5, 10, 15 and 20 wt.% of nanoparticles silica sand were developed through powder metallurgy technique. It was observed that by addition of silica sand nanoparticles with 20 wt.% increased the hardness up to 95HRB and tensile strength up to 690MPa. Sintered densities and electrical conductivity of the composites were improved with an optimum value of 15 wt.% silica sand nanoparticles. Proposed mechanism is due to diffusion of silica sand nanoparticles into porous sites of the composites.

Abstract: The sintering and dissolution process (SDP), in which NaCl is used as space holder, was used to produce open-cell Ag foams with various pore sizes. The content, size and shape of NaCl particles dictate the pore architecture of the foams. The yield strength of Ag foams decreases with increasing porosity. Of equivalent porosity, the yield strength of the foams with larger pore size is also higher than the foams with smaller pore size.