Fabrication and mechanical properties of FeAl/TiC composites

1　INTRODUCTIONOver the past few decades, considerable inves tigations have been carried out to identify alterna tive binders for cermets in order to improve theirmechanical properties and also to overcome certainshortcomings, such as high cost and density, lowoxidation and corrosion resistance, and environ mental toxicity[1, 2]. Iron aluminides are of particu lar interest due to their low cost and density, highspecific strength, environmental friendliness andexcellent oxidati…     

Magnetic and mechanical properties of FeSi alloys with high Si content

The chemical vapor（CVD） deposition-diffusion method was applied to prepare FeSi alloys with high silicon content up to 6.5%. In spite of various deposition and post-annealing, the sample remains α-Fe bcc structure. The cross section of the composition was analyzed to evaluate the Si content and distribution before and after annealing. The results show that the soft magnetic properties are improved by increasing the silicon content. For the samples containing about 6.5% Si, the coercivity decreases to 60 from 237.3 A/m of the original. It is also obtained that, in addition to the Si content, Si distribution has a large influence on the core loss due to the effect of resistivity. The micro-hardnesses were also evaluated along the cross-section after various annealings.     

Fabrication and mechanical properties of MWCNTs-reinforced aluminum composites by hot extrusion

Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void formation and carbide formation of the composites.In the present work,multi-wall carbon nanotubes(MWCNTs)aluminum composites were produced.High-energy ball milling with the aim at developing well-dispersed MWCNTs Al composites was followed by cold compaction,sintering,and hot extrusion at 500 ℃.Different amounts of stearic acid as processing control agent(PCA)is used in order to minimize cold welding of the Al particles,and to produce finer particles.Differential scanning calorimetry(DSC),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray diffraction(XRD)were employed to analyze the MWCNTs,the aluminum powder,and the composites' microstructural behavior.The hardness and tensile properties of the composites are also evaluated.The results showed 500％ increase in yield stress after the addition of 1 wt％ MWCNTs in Al-MWCNTs based composite.The ball-milling time of 4 h is found to be sufficient as excessive milling time destroys a vast number of MWCNTs.     

Microstructure and properties of submicron-scale TiC particle reinforced titanium matrix composites prepared by shock wave consolidation

Submicron-scale TiC particle reinforced titanium matrix composites (TMCs) were prepared by shock wave consolidation technique at detonation speed of 2500-5000m/s. The microstructures were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The compressive strength and hardness values of the composites were also determined. The results show that the composites have higher compressive yield strength and hardness values than hot-rolled pure titanium. Twins in the microstructure of TMCs show that titani-um particles undergo plastic deformation during consolidation process. The fine grains with size less than 1 μm often locate in the boundaries among the titanium particles. TiC particles seem to keep unchanged during the consolida-tion. These bring about the increase in strength and hardness for the composites. The detonation speed of 3200 m/s is proper parameter for compacting powder in the present work.     

Effect of rare earth Pr on microstructure and mechanical properties of Al2O3-SiO2（sf）/Al-Si composites

The Al₂O₃-SiO₂(sf) (volume fraction, 20%)/Al-12.6Si metal matrix composites(MMCs) with or without rare earth Pr addition were fabricated by infiltration squeeze method. Effect of Pr addition on microstructures and fractographs of Al-Si MMCs was investigated by SEM and TEM. Tensile properties at room temperature and 200 °C were tested. It is shown that the addition of Pr is favorable to produce uniform microstructures and modify the eutectic Si crystal effectively. Compounds/intermetallics with high content of Pr are formed at the interface between short fiber and matrix. Yield strength(σ_0.2), ultimate tensile strength(σ_b) and fracture elongation of Al-Si MMCs are improved by adding suitable amount of Pr. Compared with those values of Al-Si based MMC at 200 °C, σ_0.2 and σ_b of MMC with 0.29% Pr are increased by 33% and 55%, respectively. The tensile fracture surface of Al-Si MMCs with Pr addition presents ductile fracture features.     

Effect of carbon content on microstructure and property of TiC/Ti-6Al-4V composites

TiC reinforced Ti-6Al-4V matrix composites were fabricated by consumable arc-melting technology utilizing the reaction between titanium and graphite. The phase composition, microstructure and hardness of the TiC/Ti-6Al-4V composites were investigated by XRD, SEM and hardness testing equipment, respectively. The results show that the reinforcements are distributed uniformly in the matrix alloy. With the carbon content of the composites increasing from 0.15% to2.0%, the morphology of TiC transforms from particle into short-bar shape or chain-type consisting of featheriness or wheat-shape and finally into dendritic. Simultaneously, the hardness of the composites increases. The formation mechanisms of TiC can be analyzed as follows： the growth of dendritic primary TiC before the peritectic reaction is dominated by the solute concentration gradient, after peritectic reaction, the nucleation and growth of TiC in β-Ti leads to its forming of short-bar shape. The dendritic TiC mainly is distributed in the matrix grain, but the short-bar shape TiC mainly segregates at the grain boundary, especially at the triangular grain boundaries.     

Effects of Ce and Ti on the microstructures and mechanical properties of an Al-Cu-Mg-Ag ahoy

The effects of Ce and Ti additions on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy have been studied, It has been shown that either Ce or Ti can decrease the as-cast grain size of the Al-Cu-Mg-Ag alloy, increase the nucleation ratio for Ω phase as heterogeneous nucleation centers, inhibit the growth of Ω phase during aging, and thus increase the volume fraction and decrease the spacing of Ω phase. These microstructures increase the yield strength and tensile strength. However, if both Ce and Ti are added to the alloy, they form （Ce,Ti）-contained compounds and increase the grain size during casting, but have no effects on the nucleation and the growth of Ω phase during aging. The alloy containing both Ce and Ti has a relatively lower Vicks hardness and strength compared to the alloy containing either Ce or Ti.     

Microstructure and electric properties of Sip/Al composites for electronic packaging applications

Sip/1 199, Sip/4032 and Sip/4019 environment-friendly composites for electronic packaging applications with high volume fraction of Si particles were fabricated by squeeze-casting technology. Effects of microstructure, panicle volume fraction, panicle size, matrix alloy and heat treatment on the electrical properties of composites were discussed, and the electrical conductivity was calculated by theoretical models. It is shown that the Si/Al interfaces are clean and do not have interface reaction products. For the same matrix alloy, the electrical conductivity of composites decreases with increasing the reinforcement volume fraction. As for the same panicle content, the electrical conductivity of composites decreases with increasing the alloying element content of matrix. Panicle size has little effects on the electrical conductivity. Electrical conductivity of composites increases slightly after annealing treatment. The electrical conductivity of composites calculated by P.G model is consistent with the experimental results.     

Effect of coating thickness on microstructures and mechanical properties of C/Cu/Al composites

The different copper coatings with thickness varying from 0.3 lain to 1.5 lain were deposited on carbon fibers using either eleetroless plating or electroplating method. The coated fibers were chopped and composites were fabricated with melting aluminum at 700 ℃. The effect of the copper layer on the microstructure in the system was discussed. The results show that the copper layer has fully reacted with aluminum matrix, and the intermetallic compound CuAl2 forms through SEM observation and XRD, EDX analysis. The results of tensile tests indicate that composites fabricated using carbon fibers with 0.7-1.1 lain copper coating perform best and the composites turn to more brittle as the thickness of copper coating increases. The fracture surface observation exhibits good interface bonding and ductility of the matrix alloy when the thickness of copper coating is about 0.7-1.1 μm.     

Effect of Y2O3 on microstructure and mechanical properties of hypereutectic Al-20%Si alloy

The effect of Y203 on the microstructure and mechanical properties of the hypereutectic Al-20%Si（mass fraction） alloy was investigated. The results show that, with the addition of Y203 into the Al-P-Ti-TiC modifier, the average size of primary silicon in the Al-20%Si alloy modified by Al-P-Ti-TiC-Y203 modifier （approximately 15μm or less） is significantly reduced, and the morphology of eutectic silicon changes from coarse acicular and plate like to refined fibrous. The Brinell hardness （HB189） and tensile strength （301 MPa） of Al-20%Si alloy modified by the Al-P-Ti-TiC-Y2O3 increase by 11.6% and 10.7%, respectively, for the alloys aider heat treatment.     

Preparation and mechanical properties of SiC／2024 composite by semisolid casting

A SiC/2024 composite was made by semisolid casting.The wetting between SiC and Al matrix is improved by treating SiC particles at a high temperature,coating K2ZrF6,and adding Mg to the Al melt,An effective way to remove the gas around SiC particles was also found.Microstructures were observed under optical microscope(OM) and scanning electron microscopy(SEM).The results show that SiC particles and Al matrix are well bonded and no gaps or cavities around the particles are observed.SiC particles distribute homogeneously in the Al matrix.The existence of SiC particles results in the increase of wear resistance and strength.     

Preparation and mechanical properties of TLCP/UP/GF in-situ hybrid composites

One kind of novel reactive thermotropic liquid crystalline polymer-methacryloyl copolymer （LCMC） containing polyester mesogenic units was synthesized. Its structure, morphology and properties were investigated systemically by Ubbelohde viscometer, differential scanning calorimetry （DSC）, Fourier transform infrared spectroscopy （FTIR）, wide-angle X-ray diffractometry （WAXD） and polarizing optical microscopy （POM）. The results indicate that it is one kind of nematic thermotropic liquid crystal polymer （TLCP）. The impact strength, bending strength and the morphologies of impact fracture surface of LCMC, unsaturated polyester （UP） and glass fiber （GF） in-situ hybrid composites were studied by Izod impact tester, universal testing machine and scanning electron microscopy （SEM）, respectively. The results show that the impact and bending strength of composites containing LCMC are improved, especially the composites containing 5% LCMC increases most obviously. These results with SEM results reveal that LCMC plays an important role in the improvement of interfacial adhesive between matrix and fiber.     

Friction and wear properties of mullite／ZrO2／Al2O3 composites

The friction and wear properties of ZrO2 and ALO3 cooperatively toughened mullite composites-mullite/ZrO2/Al2O3(MZA) were studied. The tribological tests were performed in a line-reciprocating tribometer using a GCr15 steel ball on a MZA disk under different dry reciprocating sliding conditions at room temperature. A wide range of normal loads and sliding speeds were chosen to investigate the relationship between the wear mechanisms of MZA and the testing conditions. The wear mechanism diagram of MZA is constructed, it contains two typical regions. It suggests that the wear mechanisms of MZA in each of the region change from one to another depending on the wear conditions. In the mild wear region, the wear rate of MZA is 10^-6 mm^3/m, and the wear mechanism of MZA is plastic deformation accompanied by a little micro-cracking. In the severe wear region, the wear rate of MZA is 10 5 mm^3/m and the dominant wear mechanism in this region is brittle fracture.     

Effect of rare earth La_2O_3 on the microstructure and mechanical properties of TiC/W composites

In this study, La2O3 was investigated as an additive to TiC/W composites. The composites were prepared by vacuum hot pressing, and the microstructure and mechanical properties of the composites were investigated. Experimental results show that the grain size of the TiC/W composites is reduced by TiC particles. When 0.5 wt.% La2O3 is added to the composites, the grain size is reduced further. According to TEM analysis, La2O3 can alleviate the aggregation of TiC particles. With La2O3 addition, the relative density of the TiC/W composites can be improved from 95.1% to 96.5%. The hardness and elastic modulus of the TiC/W 0.5 wt.% La2O3 composite are little improved, but the flexural strength and the fracture toughness increase to 796 MPa and 10.07 MPa·m1/2 respectively, which are higher than those of the TiC/W composites.     

Effect of alumina short fiber and air-cooling processing on solidification microstructure and tensile properties of Al2O3/Al-15Si composites

The effect of microstructure variation by addition of alumina short fiber and optimization of tensile properties by air-cooling processing in Al2O3/Al-15Si composites were studied.The results show that in Al-015Si alloy matrix composites with 14% and 30%(volume fraction)fiber,the primary silicon is hardly refined,but the eutectic silicon is effectively refined and granulated.Granulation of some eutectic silicon mainly happens in fiber segregation areas.Refining and granulation of the eutectic silicon are related to the physical constraint arising from the fiber,After the 30%Al2O3/Al-15Si composite was remelted and air-cooled,the number of the eutectic silicon on the surface of the fiber increases,which results in the improvement of fiber/matrix interface and tensile properties for the as-cast composite,Air-cooling processing may be reliable for the optmization of the microstructure and properties of fiber reinforced hypereutectic Al-15Si alloy composites.     

Friction and wear properties of pitch／resin densified carbon—carbon composites used for airbrakes

By use of X-ray diffractometry and scanning electron microscope(SEM),the friction and wear results obtained from MM-1000 dynamometer tests of CVI pitch/resin C/C composites were analyzed.By investigating the factors that affected the friction and wear properties,such as matrix carbon,applcation environment,graphitization degree and brake pressure,etc,friction and wear mechanism of carbon materials were probed.The results indicate that pitch densified CVI initially treated composite is more graphitizable with its graphitization degree up 59 62%,and which results in uniform small debris easier to generate,more smooth friction curves with the coefficient of 0.3-0.4 and relatively higher wear and mass loss,compared with CVI/resin C/C composites.It was further proved by SEM observation that tribological behavior of C/C composite was system dependent.Factors determining the friction and wear properties such as the size of debris and its influence on friction and wear,brake pressure,graphization degree and debris bilm formation interacted and affected each other.The friction and wear mechanism of C/C composites under different high temperature treatments needs further research.