Effect of particle cracking on the strength and ductility of Al-SiCp powder metallurgy metal matrix composites

The effects of particle cracking on the strength and ductility of Al-SiCp metal matrix composite material (MMC) was investigated. The composite was manufactured using a simple powder metallurgy (PM) technique of hot pressing followed by hot extrusion. Also, the effects of reinforcement weight fraction and strain rate variations on the strength and ductility of the same composite were examined. It was found that particle cracking plays a significant role in controlling the mechanical properties of the composite. It was shown that particle cracking is possible in an MMC material made with a low strength matrix (commercially pure aluminum), and increases with the increase of reinforcement weight fraction, applied strain rate, and amount of plastic deformation. The yield strength increases as a function of reinforcement weight fraction and to a lesser extent as the strain rate increases. The tensile strength increases at low SiCp weight fractions, then remains constant or decreases as more particles are added to the matrix.     

Some aspects of machining cast Al-SiCp composites with conventional high speed steel and tungsten carbide tools

An attempt was made to evaluate machining of eutectic Al-Si (LM6) and hypoeutectic Al-Si (LM25) alloys reinforced with 10, 15, and 20% SiCp of two particle sizes using conventional high-speed steel (HSS) and tungsten carbide (WC) tools by varying cutting speed, feed, depth of cut, and environment. Machining of metal matrix composites (MMCs) is a difficult task using HSS and WC tools. The tool life of both these conventional tools was observed to decrease with increasing percentage and coarseness of SiCp in the composites. Tungsten carbide tools had a longer tool life than HSS under all the different conditions studied. Contrary to the known phenomenon of enhanced tool life in machining monolithic alloys with the use of cutting fluid, the tool life of WC/HSS tool in machining composites with cutting fluid was only 10 to 20% of that without cutting fluid.     

Micropatterns of W-Cu composites fabricated by metal powder injection molding

The metal powder injection molding (MIM) process has been applied to fabricate micropatterns of W-Cu composites. A 150μm×150μm×300 μm column array patterned lost plastic mold was used as the mold insert. Several parameters were examined to overcome limitations of lost plastic molding such as low plastic strength, unvented blind hole structure and parting line. Molding temperature was a more dominant factor than molding pressure for the complete filling of feedstock into the micro patterns. The intrinsic defects originating from the lost plastic mold could be eliminated by the re-injection molding of the disc-shaped green part in a vacuum. The final micropatterns of W-Cu composite were fabricated by sintering at 1100°C and 1300°C for 1 h.     

WCp/Fe metal matrix composites produced by laser melt injection

Laser melt injection (LMI) was used to produce WC particles (WC_p) reinforced metal matrix composites (MMCs) layer on the mild steel. During the LMI process, different parameters were applied, and the processing window of this technique was obtained. The MMCs layers were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM result reveals that none macro-defects except few pores can be found in the MMCs layer, and the WC_p distribute uniformly in the layer. In addition, some new phases can be found in the MMCs layer, where Fe₃W₃C is the predominant phase. At the same time, the amount of dissolved WC_p plays a key role in the microstructure of the MMCs layer. The WC particle dissolved into the melt pool leads to the appearance of reaction products in the matrix, such as various primary Fe₃W₃C dendrites, and the liquid WC remained on the solid WC particle results in the formation of a thicker reaction layer.     

激光-TIG复合熔注制备WCp／Al复合材料层的微观组织

采用激光-TIG复合熔注工艺,在铝合金表面制备WCp/Al表而复合材料层.通过优化激光功率、TIG电流、扣描速度和送粉率等工艺参数,可以捩得0.5～4.3 mm厚的表面复合材料层.采用XRD、SEM、EDS等手段对表面颗粒强化层的微观组织和成分进行研究.结果表明:熔注层基体的微观组织为过共晶组织;熔注层不同位置的过共晶相具有不同的形貌,熔池上部主要为含有十字花状、鱼骨状、蝶状先共晶相(W1-xAlx)Cy的过共晶组织,而底部的先共晶相呈现块状形态.     

Effect of rolling and heat treatment on tensile behaviour of wrought Al-SiCp composites prepared by stir-casting

Al 6061- and Al 7108-SiCp composites (Al-PMMC) were prepared by stir-casting with SiCp size of 8 and 15 μm and volume fraction (Vf) of 0–20%. These composites were then subjected to successive hot rolling at 450 °C using a strain rate of 1 s⁻¹ while the intermediate period of heating between each two successive rolling steps was 1 min to 1 h. Tensile test was conducted on the as-rolled composite strips with 3.0, 1.1 and 0.4 mm thicknesses using 81, 94 and 98% reductions, subsequently, with a tensile rate of 10 MPa s⁻¹. Different tensile properties including ultimate tensile strength UTS, Young's modulus and elongation, were determined. The tensile behaviour was analysed in view of matrix alloy type and SiCp size and Vf. The effect of T6 treatment on the microstructure and tensile properties was also presented. Generally, successive hot rolling resulted in decreasing casting defects such as void and SiCp agglomeration present in the as-cast composites and hence enhanced mechanical properties were achieved. Almost 240 and 390% improvement in ultimate tensile strength (UTS) for 6061 and 7108 composite was obtained, respectively. The improvement in strength was remarkable for composites rolled to 0.4 mm. Annealing improved the elongation% at break of the 10–15% Vf composite more than 3 times. UTS of rolled composite was enhanced by T6 treatment at 176 °C and 120 °C for 6061 and 7108 composites. The effect of T6 treatment on the composite tensile behaviour was discussed.     

Debinding injection molded materials by melt wicking

For metal and ceramic injection molding procedures which use wax binders in the production of powder-based parts, melt wicking is commonly employed to debind the components prior to sintering. Because debinding is often a time-consuming procedure, the influence of such process variables as powder size, part height, green density and temperature have been investigated to reduce the amount of time required for debinding by melt wicking.     

Microstructures and wear resistance of large WC particles reinforced surface metal matrix composites produced by plasma melt injection

Large WC particles (− 840 μm-+ 420 μm) reinforced surface metal matrix composites (SMMCs) were produced using plasma melt injection (PMI) process on a Q235 (similar to ASTM A570 Gr. A) low carbon steel substrate. Microstructures of the SMMC were observed using scanning electron microscope (SEM), and the composition was determined with energy dispersion spectroscopy (EDS). Phases were analyzed with X-ray diffraction. Micro-hardness of the SMMC was tested. Wear losses of the SMMC layer were evaluated under dry friction conditions and compared with those of the substrate material. The results show that the large WC particles are caught by crystallized metal and stay in the upper part of the SMMC layer, and there is only a little melting on the outer surface. No sinking down of WC particles occurs. The SMMC layer is well bonded to the substrate, and the interface is crack free. The wear resistance of the Q235 substrate is greatly improved with large WC particles injected.     

Application of ball-milled powder mixture to intermetallics coating through reaction synthesis

The application of ball-milling for reactant powders to improve the intermetallic coating reaction was examined. Ni-50 at.% Al powder compacts milled at three different ball-to-powder weight ratios in a planetary mill were analyzed by differential scanning calorimetry (DSC) and coated onto mild steel through the reaction synthesis in a hot press. The effects of ball-milling on the coating reaction in the hot press were compared with those in the reaction synthesis in DSC. The experimental results show that the particle size of the elemental powders was decreased by ball-milling, and that the coating reaction in the hot press was enhanced by ball-milling for the reactant powders, unlike the reaction synthesis in DSC. This improvement was attributed to the increase in the density of the reactant compact by the load applied during the reaction.     

W-ZrC composites prepared by reactive melt infiltration of Zr2Cu alloy into partially carburized W preforms

W-ZrC composites without residual WC have been prepared for the first time by reactive infiltration at 1300 °C for 1 h in vacuum using a molten Zr₂Cu alloy and a newly designed partially-carburized W powder as raw materials. The as-synthesized composites consist of two major phases of W and ZrC, in which the content of W is 65 vol%. The reaction time needed to produce a fully densified W-ZrC bulk ceramic is distinctly shortened by this means, as contrasted with conventional WC/W or WC preforms. The microstructural evolution during reactive melt infiltration is investigated to obtain a better understanding of reaction mechanisms and mechanical properties of the W-ZrC composites derived by infiltrating Zr₂Cu alloy into partially carburized W preforms. The flexural strength, Young's modulus and fracture toughness for the W-ZrC composite are 554 MPa, 339 GPa and 9.7 MPa·m^1/2, respectively.     

Specific features of cast high-entropy AlCrFeCoNiCu alloys produced by ultrarapid quenching from the melt

Results of studying structural and phase transformations that occur in the cast high-entropy equiatomic AlCrFeCoNiCu alloy after ultrarapid quenching from the melt in an inert atmosphere (RQM) and various isothermal treatments are presented for the first time. The investigations have been performed using analytical, transmission and scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction structure and phase analyses, as well as measurements of the nanohardness, microhardness, and elastic moduli. It has been found that an ultrafine-grained structure is formed in this alloy during RQM. Already during quenching and, especially, during subsequent annealing, the alloy undergoes decomposition, which is accompanied by the precipitation in the bcc (B2) matrix of some nanosized phases, predominantly of equiaxed morphology, both atomically ordered (B2) and disordered (A2), with various chemical compositions. All nanophases are multicomponent solid solutions and are enriched in a few elements, which leads to a pronounced nanomodulation of the elemental and phase compositions over the alloy bulk, identified, in particular, from the presence of satellites in the vicinity of some reflections in selected-area electron diffraction patterns.     

Hybrid control of graphite cast iron structure by partial melt treatment process

The Modified Inmould Process, which forms a cast iron-graphite hybrid alloy with a spheroidal/flake graphite structure (SG/FG), has been developed by the author.^1-3 Though this process can easily control the transitional structure of SG/FG, there are some mild restrictions caused by rapid collision during the mixing of molten metals in the mould on pouring. In this study, a new experimental process was designed to solve this difficulty. The plate-like mould cavity was separated into a reaction chamber (RC) and a product cavity by a thin dam. An alloy of FeSiMg for spheroidization of base molten metal was prepared in the reaction chamber. Molten metal was poured up from the bottom of the product cavity and a part of it flowed over the dam into the reaction chamber. After being spheroidized in the reaction chamber, spheroidal graphite (SG) iron melt flowed backward into the product cavity. The density of SG molten iron with a higher carbon equivalent value is generally lower than that of flake graphite (FG) molten metal. Thus SG molten metal moved into the upper end of the product cavity by replacement of the base metal, while the base metal remained stationary at the lower end of the cavity. As a result of the phenomena of flow, movement and replacement between mutual melts, a SG/FG transitional layer structure was formed, downward, throughout the cast product.     

Microstructure of reaction zone in WCp/duplex stainless steels matrix composites processing by laser melt injection

The laser melt injection (LMI) process has been used to create a metal matrix composite consisting of 80μm sized multi-grain WC particles embedded in three cast duplex stainless steels. The microstruture was investigated by scanning electron microscopy with integrated EDS and electron back-scatter diffraction/orientation imaging microscopy. In particular the search of the processing parameters, e.g. laser power density, laser beam scanning speed and powder flow rate, to obtain crack free and WC_p containing surface layer, has been examined. Before the injection of ceramic particles into remelted surface layer, the influence of processing parameters of laser surface remelting on the microstructure and properties of selected duplex steels was also investigated. Although after simple laser surface remelting the austenitic phase is almost not present inside remelted layer, in the case of LMI the austenite was observed in vicinity of WC particles, due to increase of carbon content acting as austenite stabilizer. The diffusion of carbon in the reaction zone results also in a formation of W₂C phase in the neighborhood of WC particles with a strong orientation relationship between them. The maximum volume fraction of the particles achieved in the metal matrix composite layer was about 10% and a substantial increase in hardness was observed, i.e. 575 HV0.2 for the matrix with embedded particles in comparison to 290 HV0.2 for untreated cast duplex stainless steels.     

ZrC-W复合材料的无压反应浸渗制备工艺

以WC粒径为4μm气孔率为55％的多孔WC为预制体,Zr2Cu合金为浸渗剂,采用低温反应浸渗工艺制备了ZrC-W复合材料,系统研究了反应浸渗温度和时间对复合材料的物相组成及显微组织的影响规律.结果表明,随浸渗温度的升高,WC与Zr2Cu合金的反应程度增加,即生成的ZrC和W的含量增加,WC的残留量减小,当浸渗温度超过1500℃时,残留的WC转变为W2C相.随浸渗时间的延长,ZrC和W的含量增加,WC的残留量减小,ZrC的点阵常数增大,并出现W2Zr、Cu5Zr等中间反应相.     

WCp/Ti-6Al-4V graded metal matrix composites layer produced by laser melt injection

The laser melt injection (LMI) process was explored to produce WC particles (WC_p) reinforced Ti-6Al-4V metal matrix composites (MMC). In particular monocrystalline WC powder was used as injection particles to avoid the intercrystalline cracking often observed in granular or cast WC_p reinforced MMC. WC_p were injected into the extended part of the melt pool just behind the laser beam. The process allowed for the minimization of the WC_p dissolution caused by the direct irradiation of the laser beam, and the decomposition reaction between WC_p and Ti melt. Different parameters were applied, and a processing window of LMI was obtained. WC_p exhibit a graded distribution along the depth direction of the MMC layer. New phases such as TiC and W₂C are observed in the MMC layer, in which TiC is the predominant phase. TiC grains present a continuous decrease in both amount and size with the distance from the surface to the bottom of the MMC layer. Two types of reaction layers around WC_p can be distinguished, namely an irregular reaction layer and a cellular reaction layer. The growth and final morphology of reaction layers are most likely being dominated by the composition of the neighbouring melt pool. A gradual hardness distribution in the depth direction of the composites layer is observed. Moreover, the transition from the MMC layer to the substrate also exhibits a gradual change in the hardness.     

Highly dense,inexpensive composites via melt infiltration of Ni into WC/Fe preforms

Traditionally, WC-based composites use Co as the metal binder phase to consolidate using liquid-phase sintering with a small percentage of Co, but a potentially lower cost binder phase can be made with a different approach when using large amount of metal binder phase. FeNi as a metal binder material is much cheaper than Co. WC can be liquid-phase sintered and melt infiltrated with FeNi, but by making FeNi in situ, costs lower even further. Composites of WC-(Fe-Ni) were made by first pressing a mixture of WC and Fe powders and subsequently melt infiltrating Ni in an amount corresponding to less volume than the porosity of the preform to ensure high WC content. The research objective was to make highly dense composites via melt infiltration with a low-cost metal binder phase in situ. This method has the potential to make fully dense composites, rather than hardmetals, with suitable properties at lower costs. The density and hardness are 97.4%TD and 6.72 GPa, respectively.     

Microstructure evolution of grey cast iron powder by high pressure gas atomization

The grey cast iron powders were prepared by high pressure gas atomization. Calculation results show that the cooling rates of droplets of grey cast iron reach to 10⁴ to 10⁶ K s^?1 in the experiments. Microstructures of atomized grey cast iron powders with different diameters were characterized by X-ray diffraction, optical microscopy and scanning electron microscopy. Microstructures of powders under 38 μm in diameter are mainly γ-Fe and a little α-Fe. With the increase of powder diameter, content of γ-Fe phase gradually decreases, while content of α-Fe phase increases. When the diameter is over 150 μm, powders are completely composed of α-Fe phase. By measuring the spatial variation in microstructural scales within powders, the results show the lamellar spacing increases with the increase of powder diameter. As the powder size is larger than 106 μm, the increase trend of the lamellar spacing becomes smaller.     

粉末冶金法制备纳米颗粒增强Cu基复合材料

采用粉末冶金方法,以SiC、SiO2、Al2O3和AlN等纳米颗粒为增强相,制备出Cu/SiC、Cu/SiO2、Cu/Al2O3和Cu/AlN等铜基纳米复合材料;研究了各增强相的含量对复合材料的显微组织和性能的影响,比较了不同纳米颗粒对铜基复合材料的增强效果.结果表明,Cu基纳米复合材料随增强相质量分数的增加,密度降低,电阻率略有升高,强度和硬度先升高后降低;退火温度曲线表明,复合材料的软化温度都达到700℃以上,远高于纯铜的软化温度(150℃),大大提高了材料的热稳定性;通过比较得知,在质量分数相同时,所采用的各增强相纳米颗粒对铜基体的增强效果相近.