Characterization of mechanically alloyed and pressureless sintered Al-7 wt% Si-2 wt% LaB6-2 wt% (MoSi2, WSi2) hybrid composites

The purpose of this research is to investigate the dual effect of silicide (MoSi₂ or WSi₂) and LaB₆ reinforcing particles on the microstructural and mechanical properties of Al-7 wt% Si (Al7Si) matrix. Hypoeutectic Al7Si blends prepared from elemental Al and Si powders were mechanically alloyed (MA’d) for 12 h in a planetary ball mill (at 300 rpm). Afterwards, 2 wt% silicide reinforcements (MoSi₂ or WSi₂) with various particle size distributions (micron, bimodal, submicron) were separately added into these MA’d Al7Si powders together with 2 wt% of LaB₆ particles. Powders having compositions of Al7Si, Al7Si-2 wt% LaB₆, Al7Si-2 wt% LaB₆-2 wt% MoSi₂ and Al7Si-2 wt% LaB₆-2 wt% WSi₂ were milled for 30 min using a high-energy ball mill (at 1200 rpm) in order to obtain homogeneous distribution throughout the microstructure. Compositional, microstructural and mechanical characterization studies were performed on the sintered samples. The results showed that high-energy ball milling ensured the homogeneous distribution of micron-sized MoSi₂ and WSi₂ particles within the matrix rather than those of bimodal and submicron-sized ones. Micron-sized MoSi₂ and WSi₂ reinforced hybrid composites displayed dramatically higher hardness and wear resistance than those of composites reinforced with different size of MoSi₂ and WSi₂ particles. The striking point of the study was the remarkably higher hardness and wear resistance properties of the hybrid composites compared to those of un-reinforced and only LaB₆-reinforced ones. As a conclusion, hybrid composites extremely displayed promising mechanical properties.     

Microstructure,mechanical and tribological properties of TiAl-based composites reinforced with high volume fraction of nearly network Ti2AlC particulates

TiAl-based composites reinforced with different high volume fractions of nearly network Ti₂AlC phase have been successfully prepared by mechanical alloying and hot-pressing method. Their microstructure, mechanical and tribological properties have been investigated. Ti₂AlC network becomes continuous but the network wall grows thicker with increasing the Ti₂AlC content. The continuity and wall size of the network Ti₂AlC phase exert a significant influence on the mechanical properties. The bending strength of the composites first increases and then decreases with the Ti₂AlC content. The compressive strength of the composite decreases slightly compared to the TiAl alloy, but the hardness is enhanced. Due to the high hardness and load-carrying capacity of the network structure, these composites have the better wear resistance. And this enhancement is more notable at low applied loads and high Ti₂AlC content. The mechanisms simulating the role of network Ti₂AlC phase on the wear behavior and the wear process of TiAl/Ti₂AlC composites at different applied loads have been proposed.     

Influence of B4C on the tribological and mechanical properties of Al 7075–B4C composites

In the present investigation, the influence of B₄C on the mechanical and Tribological behavior of Al 7075 composites is identified. Al 7075 particle reinforced composites were produced through casting, K₂TiF₆ added as the flux, to overcome the wetting problem between B₄C and liquid aluminium metal. The aluminium B₄C composites thus produced were subsequently subjected to T6 heat treatment. The samples of Al 7075 composites were tested for hardness, tensile, compression, flexural strengths and wear behavior. The test results showed increasing hardness of composites compared with the base alloy because of the presence of the increased ceramic phase. The wear resistance of the composites increased with increasing content of B₄C particles, and the wear rate was significantly less for the composite material compared to the matrix alloy. A mechanically mixed layer containing oxygen and iron was observed on the surface, and this acted as an effective insulation layer preventing metal to metal contact. The coefficient of friction decreased with increased B₄C content and reached its minimum at 10 vol% B₄C.     

Microstructure and abrasive wear behaviour of B<Subscript>4</Subscript>C particle reinforced 2014 Al matrix composites

In this study, the microstructure and abrasive wear properties of varying volume fraction of particles up to 12% B₄C particle reinforced 2014 aluminium alloy metal matrix composites produced by stircasting method was investigated. The density, porosity and hardness of composites were also examined. Wear behaviour of B₄C particle reinforced aluminium alloy composites was investigated by a block-on-disc abrasion test apparatus where the samples slid against the abrasive suspension mixture (contained 10 vol.% SiC particles and 90 vol.% oil) at room conditions. Wear tests performed under 92 N against the abrasive suspension mixture with a novel three body abrasive. For wear behaviour, the volume loss and specific rate of the samples have been measured and the effects of sliding time and the content of B₄C particles on the abrasive wear properties of the composites have been evaluated. The dominant wear mechanisms were identified using SEM. Microscopic observation of the microstructures revealed that dispersion of B₄C particles was generally uniform while increasing volume fraction led to agglomeration of the particles and porosity. The density of the composite decreased with increasing reinforcement volume fraction but the porosity and hardness increased with increasing particle content. Moreover, the specific wear rate of composite decreased with increasing particle volume fraction. The wear resistance of the composite was found to be considerably higher than that of the matrix alloy and increased with increasing particle content.     

Preparation and mechanical properties of ZrB<Subscript>2</Subscript>-based ceramics using MoSi<Subscript>2</Subscript> as sintering aids

ZrB₂ (zirconium diboride)-based ceramics reinforced by 15vol.% SiC whiskers with high density were successfully prepared using MoSi₂ as sintering aids. The effects of sintering condition and MoSi₂ content on densification behavior, phase composition, and mechanical properties of SiC_w/ZrB₂ composites were studied. Nearly, fully dense materials (relative density >99%) were obtained by hot-pressing (HP) at 1700°C–1800°C in flow argon atmosphere. The grain size of ZrB₂ phase in the samples sintered by HP at 1700°C–1800°C were very fine, with mean size below 5 μm. Mechanical properties (such as flexural strength, fracture toughness, and Vickers hardness) of the sintered samples were measured. The sample with 15vol.% MoSi₂ addition sintered by HP at 1750°C displayed the best mechanical properties.     

Preparation and mechanical properties of ZrB2-based ceramics using MoSi2 as sintering aids

ZrB₂ (zirconium diboride)-based ceramics reinforced by 15vol.% SiC whiskers with high density were successfully prepared using MoSi₂ as sintering aids. The effects of sintering condition and MoSi₂ content on densification behavior, phase composition, and mechanical properties of SiC_w/ZrB₂ composites were studied. Nearly, fully dense materials (relative density >99%) were obtained by hot-pressing (HP) at 1700°C–1800°C in flow argon atmosphere. The grain size of ZrB₂ phase in the samples sintered by HP at 1700°C–1800°C were very fine, with mean size below 5 μm. Mechanical properties (such as flexural strength, fracture toughness, and Vickers hardness) of the sintered samples were measured. The sample with 15vol.% MoSi₂ addition sintered by HP at 1750°C displayed the best mechanical properties.     

SiC晶须与Si_3N_4颗粒强韧MoSi_2复合材料

采用湿法混合和热压工艺制备了不同Si3N4(p)和SiC(w)体积含量的MoSi2基复合材料,研究了复合材料的显微组织,晶粒大小,硬度、断裂韧性和抗弯强度.结果表明,复合材料的晶粒比纯MoSi2明显细化,且随着强化相添加量的增加而减小,抗弯强度和断裂韧性均大幅度提高,其中MoSi2-20%SiC(w)-20%Si3N4(p)复合材料具有较好的综合力学性能,断裂韧性和抗弯强度分别427 Mpa和10.4 Mpa·m1/2.复合材料的强化机制为细晶强化和弥散强化,韧化机制为细晶韧化和裂纹偏转与分支韧化.     

Abrasive wear of FeCr (M7C3–M23C6) reinforced iron based metal matrix composites

Abstract

The effects of volume fraction, particle size, and sintered porosity of FeCr (M₇C₃–M₂₃C₆) particulates on the abrasive wear resistance of powder metallurgy (PM) Fe alloy metal matrix composites have been studied under different abrasive conditions. It was seen that the abrasive wear rate of the composites increased with an increase in the FeCr volume fraction in tests performed with 80 grade SiC abrasive paper, but it decreased for tests conducted with 220 grade SiC abrasive paper. Furthermore, the wear rates decreased with an increase in FeCr size for composites containing the same amount of FeCr. Hence it is deduced that Fe alloy composites reinforced with larger size FeCr particles are more effective against abrasive wear than those reinforced with smaller ones. At the same time the results show that the beneficial effects of hard FeCr particulates on wear resistance far outweighed the detrimental effects of sintered porosity in the PM metal matrix composites. In addition, the fabrication of composites containing soft particles such as graphite or copper favours a reduction in the coefficient of friction, and increases the matrix hardness of the composite. For this reason graphite and copper were used in the matrix in different amounts to test their effect on the wear resistance. Increase in graphite and copper volume fraction allowed the formation of additional phases, which had high hardness and wear resistance. It was also found that the wear rate of the composites decreased considerably with graphite and copper addition.     

Particle effects on friction and wear of aluminium matrix composites

Particle effects on friction and wear of 6061 aluminium (6061 Al) reinforced with silicon carbide (SiC) and alumina (Al₂O₃) particles were investigated by means of Vickers microhardness measurements and scratch tests. Unreinforced 6061 Al matrix alloy was also studied for comparison. To explore the effect of heat treatment, materials subjected to three different heat treatment conditions, i.e. under-aged, over-aged and T6, were used. Multiplescratch tests using a diamond and a steel indentor were also carried out to simulate real abrasive wear processes. Vickers microhardness measurements indicated that T6 heattreated composites had the highest hardness. Single-scratch tests showed that the variation of friction coefficient was similar to that of Vickers hardness and the peak-aged composites exhibited the best wear resistance. The wear rate of fine particle-reinforced composites was mainly affected by hardness. However, the wear rate of large particle-reinforced composites was influenced by both the hardness and fracture of the particles.     

Hybrid effect of nanoparticles with carbon fibers on the mechanical and wear properties of polymer composites

Polyetheretherketone (PEEK) composites reinforced with carbon fibers (CFs) and nano-ZrO₂ particles were prepared by incorporating nanoparticles into PEEK/CF composites via twin-screw extrusion. The effects of nanoparticles on the mechanical and wear properties of the PEEK/CF composites were studied. The results showed that the incorporation of nano-ZrO₂ particles with carbon fiber could effectively enhance the tensile properties of the composites. The tensile strength and Young’s modulus of the composites increased with the increasing nano-ZrO₂ content. The enhancement effect of the particle was more significant in the hybrid reinforced composites. The compounding of the two fillers also remarkably improved the wear resistance of the composites under water condition especially under high pressures. It was revealed that the excellent wear resistance of the PEEK/CF/ZrO₂ composites was due to a synergy effect between the nano-ZrO₂ particles and CF. CF carried the majority of load during sliding process and prevented severe wear to the matrix. The incorporation of nano-ZrO₂ effectively inhibited the CF failures through reducing the stress concentration on the carbon fibers interface and the shear stress between two sliding surfaces. It was also indicated that the wear rates of the hybrid composites decreased with the increasing applied load and sliding distance under water lubrication. And low friction coefficient and low wear rate could be achieved at high sliding velocity.     

Al-based nanocrystalline composites by rapid solidification of Al-Ni-Sm alloys

Nanophase composites (Al-based materials with α-Al particles dispersed in an amorphous matrix) can be produced by melt spinning and annealing Al₈₈Ni_{12 − x}Sm_x (x = 2 to 10 at%) master alloys. The structures and the thermal stability of the ribbons obtained, asquenched and after annealing, are characterised by X-ray diffraction and differential scanning calorimetry. The mechanical properties of these composites, including hardness and abrasive wear resistance, are measured as a function of the volume fraction of α-Al nanocrystals in the amorphous matrix. The properties of these nanophase composites are compared with other industrial alloys in the aluminium family and show an exceptional hardness and wear resistance.     

Characterization of microstructure and properties of Al–Al<Subscript>3</Subscript>Zr–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

Aluminium-based metal matrix composite strengthened by in situ Al₂O₃ and Al₃Zr particles were synthesized by powder metallurgy route. Phase analysis by X-ray diffraction and scanning electron microscopy revealed that the reaction between Al and ZrO₂ produced Al₂O₃ and Al₃Zr phases in the sintered composites. The hardness of the composite is a strong function of sintering temperature as well as the volume fraction of reinforcements. The dry sliding wear test results clearly indicated that increasing the volume fraction of zirconia particles in the composite improved the wear resistance. Microcutting, ploughing, delamination and oxidation were the main mechanisms of wear.     

Microstructure and abrasive wear characteristics of in situ vanadium carbide particulate-reinforced iron matrix composites

In this work, in situ synthesis with infiltration casting and subsequent heat treatment was applied to fabricate vanadium carbide (V₈C₇) particulate-reinforced iron matrix composites. The microstructure and wear-resistance of V₈C₇ particulate-reinforced iron matrix composites with different volume fraction were studied using scanning electron microscopy, X-ray diffraction, and wear testing. The V₈C₇ particles were uniformly distributed in the matrix, and the size of the V₈C₇ reinforcement was 2–12 μm. The relative wear resistance of the composites initially increases decreases with higher V₈C₇ volume fractions. The best wear resistance of the composites was 21.2 times higher than that of gray cast iron under a 20 N load. This was achieved at 24% V₈C₇ volume fraction. Wear of the composites manifests as grooves, broken carbide particles, and re-embedment of wear debris.     

Properties of NbC-TiAl and TiB2-TiAI composites produced by plasma transferred arc process

Intermetallic compound based composites (IMCs) consisting of particles of NbC and TiB₂ in Ti-36 wt-%Al (NbC-TiAl and TiB₂-TiAl respectively), with varying volume fraction of reinforcing particles, were produced by a plasma transferred arc process. In NbC-TiAl IMCs, the hardness and 0·2% compressive proof stress increased steadily with increasing volume fraction of NbC whereas the tensile strength was lower than that of the unreinforced TiAl regardless of the volume fraction of NbC. In TiB₂-TiAl IMCs, the hardness and 0·2% compressive proof stress exhibited maximum values at a volume fraction of 5 vol.-%TiB₂. The maximum tensile strength of ～500 MN m^?2, which is almost twice that of the unreinforced TiAl, was obtained at a volume fraction of 5 vol.-%TiB₂. The initial improvement of mechanical properties due to the addition of TiB₂ was considered to be caused by the reinforcing effect of the TiB₂ particles, grain refinement, and the disappearance of γ grains in 3–5 vol.-%TiB₂-TiAl IMCs. The deterioration of the mechanical properties observed for a volume fraction of >5 vol.-%TiB₂ may be attributed to the increase in the amount of y grains with increasing volume fraction of TiB₂ particles from 7 to 15 vol.-% and the increase in coarse TiB₂ particles that can act as crack initiation sites in tensile tests.

MST/3434     

Effect of dual size particle distribution on processing and properties of AZ91D/SiCp magnesium matrix composites prepared by rotation cylinder method

Abstract

Spiral fluidity and hardness and wear experiments were carried out to investigate the effect of dual size (5 and 50 μ m) SiC particle distributions on the fluidity, hardness, and wear resistance of Mg - 9.1Al - 0.7Zn (wt-%) alloy containing 10 vol.-% SiC particles, with the aim of tailoring properties to specific applications. Although a decrease in the fluidity of the composites is observed, as expected, in the presence of SiC particles, the fluidity of the composites with dual size particle distributions was in some instances better than that of composites containing the same volume fraction of single size particles. The hardness and wear resistance of the composites with dual size distributions were weakly dependent on the mixing ratio. In terms of complete molten processing and tailored mechanical properties, the optimum mixing ratio of 5 and 50 μm particles appears to be 1:2.     

Influence of the hard coated B4C particulates on wear resistance of Al–Cu alloys

In the present study, sliding wear tests were carried out on different sizes and volume fractions of coated B₄C particles reinforced 2024 aluminum alloy composites fabricated by a squeeze casting method. Microstructural examination showed that the B₄C distributions were generally homogeneous in the matrix while some particle clusterings were observed at relatively high particle containing composites. As compared to the 2024 Al matrix alloy, the hardness of the composites was found to be greater. It is observed that the wear resistance of the composites was significantly higher than that of the unreinforced aluminum alloy, and increased with increasing B₄C particles content and size. The hard B₄C particles act as a protrusion over the matrix, carries a major portion of the applied load and protect the abrasives from penetration into the specimen surface. Combination of rough and smooth regions is distinguished on the worn surface of the composites. The depth and number of grooves in composites decreased with increasing volume fraction of B₄C particles, and the worn surfaces of composites were relatively smooth.     

Al-5Cu/B4Cp composites: The combined effect of artificially aging (T6) and particle volume fractions on the corrosion behaviour

In this study, the Al–5Cu matrix composites reinforced with different boron carbide (B₄C) particle volume fractions have been successfully produced by the hot-pressing method. Then, the artificially aging (T6) was applied to the composites for increasing their mechanical properties. The combined effect of the T6 heat treating and the B₄C particle volume fraction on the corrosion behaviour of the composites were investigated by potentiodynamic scanning (PDS) technique under aerated and deaerated 3.5% NaCl marine environments. The effect of the T6 treating on the hardness and corrosion susceptibilities of the composites were also evaluated microstructurally to contribute to their industrial use and production processes. The microstructural characterization of the composites was carried out by using a scanning electron microscope (SEM) with an attached energy dispersive spectrum (EDS) and X-ray diffraction (XRD). It was found that the corrosion susceptibilities of the composite have been interestingly decreased with increasing the B₄C particle volume fraction in the matrix while the T6 treatment enhances the pitting susceptibility of the composites. The reason of the behaviour has been discussed in details the text.     

Tribological investigation of Zamak alloys reinforced with alumina (Al2O3) and fly ash

ABSTRACT

In this study, zinc aluminum alloy (Zamak) (ZA-27) composites reinforced by different weight fractions of fly ash, alumina (Al₂O₃), or both particles were produced using compo-casting technique. The composites were subjected to hardness and wear tests. The hardness of the composites increases with increase of the weight fractions of reinforcements. In wear test, the composites were examined under dry sliding conditions using pin on disc apparatus. The wear results revealed that the wear resistance increases with increase of the weight fractions of reinforcements. However, the effect of fly ash particles on the wear resistance of the produced composites is more statistically significant than the effect of Al₂O₃ particles. The morphology of the composites was examined using scanning electron microscopy (SEM) after the test. The SEM images revealed the existence of adhesion and delamination wear mechanism.     

Microstructural, mechanical and wear behavior of A390/graphite and A390/Al2O3 surface composites fabricated using FSP

In the present investigation, A390/graphite and A390/Al₂O₃ surface composite (SC) layers were fabricated using friction stir processing (FSP). The effect of tool rotational and traverse speeds on the microstructural, mechanical and wear characteristics of the surface layers was studied. The results revealed that increasing the tool rotational speed increases the hardness of the composite layers. The traverse speed has less significant influence on the hardness of the composite layer than the tool rotational speed. The A390/Al₂O₃ surface composites exhibited higher hardness than the A390/graphite surface composites. The surface composites exhibited better wear resistance than the matrix alloy. The A390/Al₂O₃ surface composites exhibited lower wear rates than the A390/graphite surface composites. Increasing the tool rotational reduces the wear rate of both A390/Al₂O₃ and A390/graphite surface composites.     

Production and properties of SiCp-reinforced aluminium alloy composites

A vacuum infiltration process was developed to produce aluminium alloy composites containing various volume fractions of ceramic particles. The matrix composites of aluminium with 9.42 wt%Si and 0.36 wt%Mg containing up to 55 vol% SiCp were successfully infiltrated and the effect of infiltration temperature and volume fraction of particle on infiltration behaviour was investigated. In addition to aluminium powder, magnesium was used to improve the wetting of SiC particles by the molten aluminium alloy. The infiltration rate increased with increasing infiltration time, temperature and volume fraction of particle, but full infiltration appeared at the optimum process parameters for the various volumes of fraction composite compacts. In addition, the microstructure, hardness, density, porosity and wear resistance of the composites were also examined. It is observed that the distribution of SiC particles was uniform. The hardness and density of the composite increased with increasing reinforcement volume fraction and porosity decreased with increasing particle content. Moreover, the wear rate of the composite increased with increasing load and decreased with increasing particle content.