Investigation of characteristics of Cu based,Co-CrC reinforced composites produced by powder metallurgy method

This study was carried out to assess the contribution of Co and CrC reinforcement particles to Cu main matrix powders by powder metallurgy (P/M) method as well as to mechanical properties, abrasion resistance and microstructure properties. For this purpose, the matrix material Cu powders, Co and CrC reinforcement particles, of which the weight percents are as follows: 5% (2% Co + 3% CrC), 10% (4% Co + 6% CrC) and 15% (6% Co + 9% CrC), were added. The samples were produced by cold pressing at room temperature and 450 MPa pressure, using the P/M method. Microstructure characterization of composite samples was performed by SEM-EDS and XRD analysis. Mechanical characterization of composite samples was carried out by analyzing the data of density determinations, hardness measurements, abrasion resistance tests and tensile tests. As a result of this study, it was observed that as the reinforcement ratio increased, the relative density of the samples decreased while the hardness of the samples increased. As a result of the findings obtained from the analysis of the tensile tests and other tests performed, it was clearly seen that the reinforcement particle ratio of wt. 10% was the optimum reinforcement ratio for this study.     

Studies on wear rate and micro-hardness of the Al/Al2O3/Gr hybrid composites produced via powder metallurgy

Micro-structural characterization of the composites has revealed fairly uniform distribution and some amount of grain refinement in the specimens. Further, it was observed that the micro-hardness improve when increasing the milling time and the reinforcement content due to presence of hard Al₂O₃ particles. Was also observed a low wear rate exhibited by the Al/Al₂O₃/Gr hybrid composites due to presence of Al₂O₃ and Gr which they acted as load bearing elements and solid lubricant respectively. The observed wear rate and micro-hardness have been correlated with microstructural analyses.     

Wear resistance of silicon infiltrated B4C/BN composites

The B₄C/BN composites were fabricated by hot-pressing process. In this research, the silicon infiltration process was applied to improve the surface hardness and wear resistance of the B₄C/BN composites. The phase composition, microstructure, Vickers hardness and wear resistance of the silicon infiltrated B₄C/BN composites were investigated and compared with the hot-pressed B₄C/BN composites. XRD analysis results of the silicon infiltrated specimens showed that the resultant coating was mainly composed of silicon carbide and silicon. The Vickers hardness of the silicon infiltrated B₄C/BN composites was significantly improved in comparison with the hot-pressed B₄C/BN composites. The Vickers hardness of the silicon infiltrated B₄C/BN composites achieved to 12-16 GPa. The wear resistances of the silicon infiltrated B₄C/BN composites were also significantly improved in comparison with the hot-pressed B₄C/BN composites. SEM micrograph of silicon infiltrated specimens showed that the thickness of silicon carbide and silicon coating was about 200-300 μm, which significantly improved the surface hardness and wear resistance of the B₄C/BN composites.     

In-situ Forming Composite Coating by Laser Cladding C/B4C

B₄C and graphite(C) mixed powders were clad by laser at the surface of Ti–6Al–4V alloy in N₂ environment. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray energy dispersive spectroscopy (EDS) were used to analyze the composite coatings. It was found that TiC, TiB, TiN, and TiB₂ which were comprised of the coating were hard strengthening phases in-stiu formed. The microstructure of the coating were mainly dendrites and whiskers-like crstals in white light area. When the mass ratio of graphite is up to 40%, the micro-hardness of coating in specimen A was up to 1245 HV_0.2, which was much greater than that of the substrate. The hardness of Ti–6Al–4V alloy was only 360 HV_0.2. The micro-hardness of the coating in specimen B was from 1060 HV_0.2 to 1358 HV_0.2. The hardness of specimen B was about three to four times greater than that of the substrate. However, the residual graphite in the coating acted as a lubricant, which increased the wear resistant property of the laser cladding coating. The wear resistant property of specimen B was 4 times as great as that of the substrate. It was twice as great as that of specimen A.     

B4C/Al Composites Processed by Metal-assisted Pressureless Infiltration Technique and its Characterization

In order to improve the wettability between Al melt and B₄C ceramic preform during fabricating B₄C/Al composites by pressureless infiltration technique, trace amount of Ti particulates with high melting point was added into the starting materials as infiltration inducer. A simple and cost-effective method, metal-assisted pressureless infiltration technique, was developed to fabricate light-weight B₄C/Al composites. The microstructure, phases, and mechanical behavior of B₄C/Al composites were characterized by SEM, XRD, and mechanical property test. The density of the as-fabricated B₄C/Al composites was about 2.75 g/cm³ and the relative density of this kind of composites was over 97%. The as-fabricated B₄C/Al composites exhibited rather well wear resistance. The flexural and compressive strengths of the as-fabricated B₄C/Al composites were about 200 MPa and 670 MPa, respectively.     

Reciprocal sliding wear behaviour of B4C particulate reinforced aluminum alloy composites

Aluminum based composites reinforced with B₄C particles were prepared by cryomilling and subsequent hot pressing steps. The cryomilled powders dispersed with 5 wt.% or 10 wt.% B₄C particles were hot pressed under a pressure of 600 MPa at 350 °C. Microstructural studies conducted on the composites indicated that homogeneous distribution of the B₄C particles in the Al matrix and a good interface between them had been achieved. According to the results of reciprocating wear tests carried out by utilizing alumina and steel balls, wear resistance increased with increasing B₄C particle content.     

Production and characterization of boron carbide and silicon carbide reinforced copper-nickel composites by powder metallurgy method

In this study, composite samples were produced by reinforcing boron carbide and silicon carbide particles in different rates by weight into copper-nickel powder mixture using powder metallurgy method. The prepared powder mixtures were cold pressed under 600 MPa pressure and pelletized. The pelletized samples were then sintered in an atmosphere-controlled furnace. Scanning electron microscopy to determine the microstructure of the produced samples and x-ray diffraction method analysis to determine the phases forming in the structure of the produced samples were used and microhardness was taken to determine the effect of boron carbide and silicon carbide on hardness. In addition to that, the mechanical properties the transverse rupture strength were investigated using three-point bending tests. The corrosion tests were performed potentiodynamic polarization curves of the samples in 3.5 % sodium chloride solution. The highest hardness value was measured as 162 HV 0.05 in the sample reinforced with 10 % boron carbide. As the amount of silicon carbide increased, the corrosion resistance of the composite increased. Moreover, as the amount of boron carbide increased, the corrosion resistance of the composite decreased. Load-contact depth values were examined, copper-nickel+10 % silicon carbide has the highest peak depth of 48.12.     

Abrasive wear behavior of various reinforced AA6061 matrix composites produced with hot pressing process: A comparative study

The effects of various reinforcements (boron carbide ‐silicon carbide‐alumina) with constant volume fraction (20 %) on the abrasive wear properties of AA6061 matrix composites produced with hot pressing process were investigated. The wear tests were carried out using a pin‐on‐disk wear tester by sliding at sliding speeds of 1.2 m/s against silicon carbide paper. Applied normal loads have 5, 10 and 15 N magnitude at room temperature. The wear morphologies of the worn surfaces were analyzed using a scanning electron microscope in order to examine the wear characteristics and to investigate the wear mechanisms. The effects of reinforcement type on the wear behavior of AA6061 matrix composites were observed. Results exhibited that the optimum wear resistance obtained with the boron carbide reinforced composite parts. All reinforced samples showed better wear resistance compared to as‐received samples in all the studied conditions. Scanning electron microscope characterization showed that test specimens have complex combination of wear mechanisms on the worn surface.     

B_4C增强铝基复合材料力学性能有限元模拟

建立了颗粒增强铝基复合材料的轴对称单胞模型,并通过有限元方法模拟了B_4C颗粒增强5083铝基复合材料的力学性能和微观应力分布。结果表明,模拟结果与实验结果吻合较好,模拟椭球体颗粒增强复合材料的抗拉强度为485 MPa,而实验值为477 MPa,相对误差仅为1.7%。颗粒形状对复合材料微观应力场有很大影响:圆柱体颗粒的尖角处容易造成应力集中,而球体颗粒界面处应力分布较为均匀。在一定范围内,复合材料的弹性模量和抗拉强度随着B_4C颗粒体积分数的增加而增加。在颗粒体积分数不变的情况下,不同长径比的颗粒沿复合材料受力方向定向排列时,颗粒的长径比越大,复合材料的弹性模量、强度等力学性能也越高。     

Processing of B4C Particulate-reinforced Magnesium-matrix Composites by Metal-assisted Melt Infiltration Technique

In fabricating magnesium-matrix composites, an easy and cost-effective route is to infiltrate the ceramic preform with molten Mg without any external pressure. However, a rather well wettability of molten Mg with ceramic reinforcement is needed for this process. In order to improve the wettability of the metal melt with ceramic preform during fabricating composites by metal melt infiltration, a simple and viable method has been proposed in this paper where a small amount of metal powder with higher melting point is added to the ceramic preform such that the surface tension of the Mg melt and the liquid-solid interfacial tension could be reduced. By using this method, boron carbide particulate-reinforced magnesium-matrix composites （B4C/Mg） have been successfully fabricated where Ti powder immiscible with magnesium melt was introduced into B4C preform as infiltration inducer. The infiltration ability of molten Mg to the ceramic preform was further studied in association with the processing conditions and the mechanism involved in this process was also analyzed.     

Preparation of super-high strength nanostructured B4C reinforced Al-2Cu aluminum alloy matrix composites by mechanical milling and hot press method: Microstructural,mechanical and tribological characterization

In this research, super-high strength nanostructured B₄C reinforced Al-2Cu aluminum alloy matrix composites produced by mechanical milling and hot press method. Nanostructured Al-2Cu powder containing 4, 6 and 10?wt.% B₄C reinforcement particles synthesized using a high-energy attritor under argon atmosphere. Results showed that with increasing the content of B₄C particles the matrix grain size decreased. Since the compressibility of mechanically milled powders is very low, hot press processing used for consolidation of nanostructured Al-2Cu/B₄C powders. The hot pressed Al-2Cu/10?wt.%B₄C nanocomposite, when tested in compression, exhibited extremely high strength (1.1?GPa) which is 735?MPa higher than that of coarse grain Al-2Cu sample. Moreover, the hardening capacity (H_c) of hot pressed nanocomposites decreased with the increase in the content of B₄C particles. According to Orowan strengthening mechanism, since B₄C particles act as a barrier to the dislocations movement, the increase of B₄C particles leads to the increase of barriers and as a result, Δσ_Orowan increases. Therefore, the strength of composite increases but work hardening capacity (H_c) decreases. The results of wear test indicated that wear rate and friction coefficient declined gradually as the B₄C particles fraction increased. Based on this result, hot-pressed sample containing 10?wt.% B₄C showed the lowest wear rate and friction coefficient (1.9?×?10^?5 mm³/m and 0.48 respectively).     

Dry wear properties of A356-SiC particle reinforced MMCs produced by two melting routes

SiC particle reinforced metal matrix composites (MMCs) were produced by a common liquid phase technique in two melting routes. In the first route, 5, 10, 15 and 20 vol% SiC reinforced A356-based MMCs were produced. In the second route, an Alcan A356 + 20 vol% SiC composite was diluted to obtain 5, 10, 15 and 20 vol% SiC MMCs. In both cases the average particle size was 12 μm. The composites that produced by two different routes were aimed to compare the dry wear resistance properties. A dry ball-on disk wear test was carried out for both groups of MMCs and their matrix materials. The tests were performed against a WC ball, 4.6 mm in diameter, at room temperature and in laboratory air conditions with a relative humidity of 40–60%. Sliding speed was chosen as 0.4 m/s and normal loads of 1, 2, 3 and 5 N were employed. The sliding distance was kept at 1000 m. The wear damage on the specimens was evaluated via measurement of wear depth and diameter. A complete wear microstructural characterization was carried out via scanning electron microscopy. The wear behaviors were recorded nearly similar for both groups of composites. Diluted samples showed lower friction coefficient values compared with the friction coefficient values of the vortex-produced composites. This was attributed poor bonding between matrix and particles in the vortex-produced composites associated with high porosities. But, in general, diluted Alcan composites showed slightly lower wear rate relationship with the particle volume percent and applied load when compared with vortex produced materials.     

Pressureless sintering of B4C whisker reinforced Al2O3 matrix composites

Al₂O₃-B₄C whisker composites have been successfully densified by pressureless sintering. Low oxygen partial pressures, below 10 atmospheres, were determined to be suitable for the composite densification, and the maximum densities were achieved at 1800°C for 60 minutes. The B₄C whiskers were screened classified into five size fractions and the effect of size and size distribution on the densification were studied. The small whiskers with a narrow size distribution (–325+400 mesh) yielded the highest density results. The maximum value of relative densities was 98%, 97%, 94% and 89% at 10, 20, 30 and 40 vol % B₄C whiskers, respectively. Addition of B₄C between 5 and 15 vol% proved to be a sintering aid to the alumina densification via mechanisms other than being a grain growth inhibitor. An increased fracture toughness up to 6.2 MPa·m was achieved in the composites containing 10–20 vol% B₄C whiskers.     

Production of superplastic aluminium composites reinforced with Si3N4 by powder metallurgy

Superplastic aluminium composites were processed from these fine aluminium powders of less than 20 m and reinforcements of either Si₃N₄ whiskers or Si₃N₄ particulates by hot extrusion at temperatures between 733 and 793 K with a reduction ratio of 1001. The dispersion of the reinforcements was homogeneous, and the size of the grains of this matrix alloy after extrusion was fine, at less than 3 m for the composites reinforced with either Si₃N_4W or Si₃N_4P. All composites showed large superplastic elongations of more than 300% in a relatively high strain-rate range from 4×10^–22 s^–1 at testing temperatures between 788 and 833 K. These superplastic composites also exhibited excellent mechanical properties at room temperature, which are supposedly attributable to both the homogeneous dispersion in reinforcements and the fine-grained structures.     

Microstructural studies and wear assessments of Ti/TiC surface composite coatings on commercial pure Ti produced by titanium cored wires and TIG process

Tungsten Inert Gas (TIG) process and titanium cored wires filled with micro size TiC particles were employed to produce surface composite coatings on commercial pure Ti substrate for wear resistance improvement. Wire drawing process was utilized to produce several cored wires from titanium strips and titanium carbide powders. Subsequently, these cored wires were melted and coated on commercial pure Ti using TIG process. This procedure was repeated at different current intensities and welding travel speeds. Composite coating tracks were found to be affected by TIG heat input. The microstructural studies using optical and scanning electron microscopy supported by X-ray diffraction showed that the surface composite coatings consisted of α′-Ti, spherical and dendritic TiC particles. Also, greater volume fractions of TiC particles in the coatings were found at lower heat input. A maximum microhardness value of about 1100 HV was measured which is more than 7 times higher than the substrate material. Pin-on-disk wear tests exhibited a better performance of the surface composite coatings than the untreated material which was attributed to the presence of TiC particles in the microstructure.     

Investigation of mechanical and tribological behaviors of multilayer graphene reinforced Ni3Al matrix composites

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni₃Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface.     

Processing of Al/B4C composites by cross-roll accumulative roll bonding

In the present study, Al/B₄C composites were successfully produced in the form of sheets, through accumulative roll bonding (ARB) and cross-roll accumulative roll bonding (CRARB) processes. The CRARB process was performed in two steps. In the first step, the strips were roll-bonded with a draft percentage of 66% reduction, while in the second step the strips were roll-bonded with a draft percentage of 50%. The results indicated that the dispersion of the B₄C particles in the CRARB process is more homogeneous than the ARB process. In addition, the tensile strength of the CRARBed composite is higher than that of the ARBed composite.     

Experimental investigation on mechanical behaviour,modelling and optimization of wear parameters of B4C and graphite reinforced aluminium hybrid composites

Aluminium alloy (AA) 6061 and 7075 were reinforced with 10 wt.% of boron carbide (B₄C) and 5 wt.% of graphite through liquid casting technique. The Scanning Electron Microscope (SEM) and Energy Dispersive Spectrum (EDS) were used for the characterization of composites. The wear experiment was carried out by using a pin-on-disc apparatus with various input parameters like applied load (10, 20, and 30 N), sliding speed (0.6, 0.8, and 1.0 m/s) and sliding distance (1000, 1500, and 2000 m). Response Surface Methodology (RSM) using MINITAB 14 software was used to analyse the wear rate of hybrid composites and aluminium alloys. The worn surfaces of hybrid composites and base alloys were studied through SEM and EDS systems and some useful conclusions were made.     

Development of Ni-base metal matrix composites by powder metallurgy hot isostatic pressing for space applications

In this work, near-net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) of Ni-base metal matrix composite (Ni-MMC) was developed to improve the hardness and wear properties of turbopumps mechanical seals. Silicon carbide (SiC) and titanium diboride (TiB₂) fine powders were used as reinforcements with different ratios to improve the hardness and consequently the tribological properties of the developed Ni-MMC material. Powder characterisation was performed on the blended powders to check the homogeneity of the mixed powders. The hot isostatically pressed (HIPed) Ni-MMC microstructures were analysed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The HIPed material showed a fully dense microstructure with a continuous network of ceramic reinforcement particles at the prior particle boundaries (PPBs). Furthermore, microhardness tests were performed on IN625, IN625-SiC and IN625-TiB₂ to understand the impact of the reinforcement on the microhardness. It was demonstrated that the volume percentage of ceramic reinforcement in the IN625 matrix plays a crucial role in achieving higher hardness by increasing the fraction of hard phases appearing in the microstructure of the developed Ni-MMC material. The final part of the work focuses on the canister design and manufacture of a near-net-shape (NNS) mechanical gas seal using IN625 based MMC to demonstrate the feasibility of manufacturing mechanical seals through the NNS PM HIP technique. Overall, IN625 based MMCs resulted in a drastic improvement in tribological properties if compared to the base material. Furthermore, the employment of the PM HIP consolidation technique resulted in a fully dense and homogeneous microstructure, highlighting the potentials of PM HIP in the generation of novel composite materials.     

Investigation of microstructure and wear behaviors of al matrix composites reinforced by carbon nanotube

In this study, the effect of CNT amount in Al-CNT composites produced by adding carbon nanotube (CNT) to 7075 Al alloy in various amounts on microstructure and wear behaviors of aluminum matrix composites was investigated. CNT was added to 7075 Al alloy powder at five different amounts. The powders were mechanically milled for 2 hours. Mechanical milled powders were cold pressed and then pre-shaped by hot pressing. Pre-shaped samples were sintered for 1 hour under 10^?6 millibar in 580°C. Microstructure examinations, hardness measurements, and wear tests were carried out. The results show that CNT's in the microstructure were agglomerated as nanotube amount increases and there was no uniform distribution. The highest hardness value was obtained in AMC reinforced with 1% CNT while it is seen that hardness of the composite decreases and weight loss increases as CNT amount increases.