Showing papers on "Metal matrix composite published in 2012"

Production and wear characterisation of AA 6061 matrix titanium carbide particulate reinforced composite by enhanced stir casting method

Abstract: Metal matrix composite (MMC) focuses primarily on improved specific strength, high temperature and wear resistance application Aluminium matrix reinforced with titanium carbide (Al–TiC p ) has good potential The main challenge is to produce this composite in a cost effective way to meet the above requirements In this study Al–TiC p castings with different volume fraction of TiC were produced in an argon atmosphere by an enhanced stir casting method Specific strength of the composite has increased with higher % of TiC addition Dry sliding wear behaviour of AMC was analysed with the help of a pin on disc wear and friction monitor The present analyses reveal the improved specific strength as well as wear resistance

Fabrication of aluminum-alumina metal matrix composites via cold gas dynamic spraying at low pressure followed by friction stir processing

Abstract: Cold gas dynamic spraying at low pressure (1 MPa gage or 150 psig) was used to fabricate Al–Al2O3 metal matrix composite (MMC) coatings onto 6061 Al alloy. The powder contained Al powder admixed with −10 μm Al2O3 in fractions up to 90 wt.%. Scanning electron microscopy (SEM), Vickers microhardness testing, and image analysis were conducted to determine the microstructure, properties, and volume fraction of reinforcing particles in the coatings. The coatings were then friction-stir processed (FSP) at tool rotation speeds of 894 or 1723 RPM using a flat cylindrical tool. The Al2O3 content and hardness of the final MMC coatings increased with increasing fractions of Al2O3 particles in the feedstock powder, resulting in a maximum Al2O3 content of 48 wt.% and a hardness of 85 HV of the as-sprayed coating when 90 wt.% Al2O3 was used in the feed powder blend. After FSP, the hardness of the MMC increased to a maximum of 137 HV. The as-sprayed coatings contained Al2O3 particles that were segregated between the Al particles, and FSP was effective in dispersing these Al2O3 particles and decreasing their mean free path. It was suggested that this re-distribution and Al2O3 particle size refinement during FSP improved the hardness of the MMC coatings.

Microstructure and wear properties of laser-deposited functionally graded Inconel 690 reinforced with TiC

Abstract: Functionally gradient material (FGM) can be tailored to the structural requirements of the final product. In this study, titanium carbide (TiC) reinforcement particles were embedded in Inconel 690 with laser direct deposition to build functionally gradient metal matrix composites (FGMMCs). The microstructures of the MMC and distribution of TiC particles were characterized with an optical microscope, SEM and X-ray diffraction. There was a near absence of internal voids in the deposited TiC-Inconel 690 MMC. With the volume percentage of TiC particles in the depositions varied from 0 to 49%, a drastic evolution in the microstructure was observed and the presence of TiC particles over 30% yielded a refinement of the matrix microstructure and introduction of a finely dispersed crystalline phase. High-temperature dissolution of TiC was not detected under the conditions used. Micro-hardness and wear resistance tests showed a significant improvement with increased TiC content.

Three dimensional (3D) microstructure-based modeling of interfacial decohesion in particle reinforced metal matrix composites

Abstract: Modeling and prediction of the overall elastic–plastic response and local damage mechanisms in heterogeneous materials, in particular particle reinforced composites, is a very complex problem. Microstructural complexities such as the inhomogeneous spatial distribution of particles, irregular morphology of the particles, and anisotropy in particle orientation after secondary processing, such as extrusion, significantly affect deformation behavior. We have studied the effect of particle/matrix interface debonding in SiC particle reinforced Al alloy matrix composites with (a) actual microstructure consisting of angular SiC particles and (b) idealized ellipsoidal SiC particles. Tensile deformation in SiC particle reinforced Al matrix composites was modeled using actual microstructures reconstructed from serial sectioning approach. Interfacial debonding was modeled using user-defined cohesive zone elements. Modeling with the actual microstructure (versus idealized ellipsoids) has a significant influence on: (a) localized stresses and strains in particle and matrix, and (b) far-field strain at which localized debonding takes place. The angular particles exhibited higher degree of load transfer and are more sensitive to interfacial debonding. Larger decreases in stress are observed in the angular particles, because of the flat surfaces, normal to the loading axis, which bear load. Furthermore, simplification of particle morphology may lead to erroneous results.

Cold spray blended Al+Mg17Al12 coating for corrosion protection of AZ91D magnesium alloy

Abstract: Commercially pure aluminum and aluminum blended with 50 vol.% and 75 vol.% of the intermetallic Mg 17 Al 12 compound feedstock powders were successfully deposited onto as cast AZ91D magnesium substrate using a cold spray process that was employed at low working gas pressure and temperature. The microstructure, mechanical performance and corrosion resistance properties of the Al coatings with and without reinforcement particles were investigated and discussed. The results show that under the same deposition conditions, the coating porosity level can be significantly decreased by adding hard particles into the pure aluminum feedstock. Although, only a small fraction (less than 10 vol.%) of the Mg 17 Al 12 particles was retained in the coatings, the hardness, was increased from 47 ± 5 HV 0.1 to 58 ± 3 HV 0.1 , while the bonding strength was 2 to 3 times higher than the pure Al coating. The spherical Mg 17 Al 12 particles play a role similar to that of the hard ceramic reinforcement particles in the metal matrix composite (MMC) coatings. Electrochemical corrosion experiments also demonstrated that the composite coatings have similar electrochemical characteristics to the bulk Al, and they can provide suitable protection for the as cast AZ91D magnesium material.

Production of high strength Al–Al2O3 composite by accumulative roll bonding

Abstract: Recently accumulative roll bonding has been used as a novel method to produce particle reinforced metal matrix composites. In this study, aluminum matrix composite reinforced by submicron particulate alumina was successfully produced and the effects of number of ARB cycles and the amount of alumina content on the microstructure and mechanical properties of composites were investigated. According to the results of tensile tests, it is shown that the yield and tensile strengths of the composite are increased with the number of ARB cycles. Scanning electron microscopy (SEM) reveals that particles have a random and uniform distribution in the matrix by the ARB cycles and a strong mechanical bonding takes place at the interface of particle-matrix. It is also found that the tensile strength of the composite, as a function of alumina content, has a maximum value at 2 vol.%, which is 5.1 times higher than that of the annealed aluminum.

Effect of heat input on the microstructure of in-situ synthesized TiN–TiB/Ti based composite coating by laser cladding

Abstract: In situ synthesized TiN and TiB particulate-reinforced metal matrix composite coating was formed on Ti-3Al-2V alloy by laser cladding with a Ti/h–BN powder mixture. The phase structure, microstructure, microhardness and wear performance of the composite clad layer were analyzed by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), micro-hardness tester and wear testing machine. It has been found that the clad layer mainly consisted of α-Ti, TiN and Ti4N3−x at the laser power density of 120 W/mm2; While, TiB and TiN were synthesized at the laser power densities of 150 and 180 W/mm2. TiN and TiB were compared with dendrite and needle platelet type microstructures. The microhardness of laser clad layer was 800–1200 HV0.3 which was about 5 times of the substrate. The lost height of the substrate is almost 2 times of the clad layers.

Preparation method of graphene reinforced metal-matrix composite

Abstract: The invention discloses a preparation method of a graphene reinforced metal-matrix composite, which comprises the following steps of: firstly, dispersing the graphene oxide on the surface of the flaky metal powder; and then obtaining the graphene/metal composite powder through the reducing treatment; and at last, carrying out densification treatment by adopting a powder metallurgic technology to obtain the compact graphene reinforced metal-matrix composite. The flaky metal powder has the plane two-dimensional form, is inclined to the directional piling to form a laminated structure, and is helpful for inducing the graphene orientation distribution and giving play to the reinforcing effect. The preparation method disclosed by the invention is simple and feasible, is capable of regulating the graphene content and is suitable for preparing the massive composite.

Effect of Mn addition on the microstructure and tensile properties of Al–15%Mg2Si composite

Abstract: This research was carried out to investigate the influence of different concentrations of Mn (0.5, 1, 2, 3 and 5%) on the microstructure and tensile properties of Al–15 wt.%Mg 2 Si metal matrix composite. Microstructural examination was carried out using optical and scanning electron microscopy (SEM). The results depicted that 1 wt.% Mn addition changes the morphology of primary Mg 2 Si from irregular to polyhedral shape and its average particle size decreases from 40 μm to 12 μm. Cubic morphology of particles was also observed by the addition of 2% Mn. Further addition of Mn (>2%) did not significantly change the size or morphology of the primary Mg 2 Si. Microstructural studies also showed that Mn addition changes the morphology of the eutectic Mg 2 Si phase from flake-like to rod-like. Tensile properties of specimens with different Mn contents were also investigated. The results of tensile testing revealed that optimum Mn level for improving both UTS and elongation values is 2 wt.%. At higher Mn concentrations, an intermetallic phase (Al 6 Mn) introduced on eutectic cell boundaries appears to be the main reason for slight reduction in tensile properties. A study of the fracture surfaces via SEM revealed a brittle mode of failure in Mn free composite. However, the addition of 2 wt.% Mn changes the fracture mode to ductile by increasing fine dimples and reducing the number of decohered particles thereby increasing the composite ductility.

Microstructure and tribological properties of laser-clad Ni–Cr/TiB2 composite coatings on copper with the addition of CaF2

Abstract: In this study, Ni–Cr/TiB2 metal matrix composite (MMC) coatings with the addition of a little CaF2 (2 wt.%) were successfully fabricated on a Cr–Zr–Cu alloy substrate by laser cladding process with powder mixtures of Ni, Cr, TiB2 and CaF2 as the precursor materials. The MMC coatings were free of defects and the interfacial substructure between the MMC coatings and the copper substrate was epitaxial, with excellent bonding by the strong metallurgical interface. The microstructure, phase and tribological properties were investigated by means of optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM), as well as dry sliding wear test. Results show that the influence of TiB2 on the microstructure and tribological properties of the coatings was significant. The microstructure of the coatings was mainly composed of dendrites, cystiform-dendrites and particles. The dendritic microstructural features of the MMC coatings could be changed into particles by increasing TiB2 to 20 wt.%. The laser-clad Ni–Cr/TiB2 MMC coatings on copper with the addition of CaF2 exhibited higher microhardness and better wear resistance than pure copper substrate. The highest microhardness was up to 946 HV0.1 which was improved 8 times compared to the original substrate. The friction coefficient of the laser-clad Ni–Cr–20 wt.%TiB2–2 wt.%CaF2 coating was reduced significantly to about 0.24, and a relatively smooth wear surface could be observed.

Microstructure and mechanical property of nano-SiCp reinforced high strength Mg bulk composites produced by friction stir processing

Abstract: Friction stir processing has been applied to fabricate SiC–Mg bulk composites in this study. AZ63 magnesium alloy, a kind of commercial engineering materials, was selected as base metal. SiC nanoparticles with average size of 40 nm were selected as reinforced particles. After being ultrasonic dispersed in ethanol and friction stir processed with base metal, the SiC particles were uniformly dispersed. Friction stir processing without filling any particles was also applied to base metal as a comparison group. Microstructure evolution was observed by optical microscope and scanning electron microscope. Fine and uniform nugget zone were found both in comparison group and composite. The phases of the material were determined by X-ray diffraction. Transmission electron microscopy observation was conducted to study the condition of SiC nanoparticles. SiC particles were found both inside the grain and at the grain boundary. No micro-sized particle agglomeration was observed in the composite. Vicker hardness and tensile test were carried out to study the mechanical properties of the composite. The average Vicker hardness of the base metal, comparison group and composite were 80 Hv, 85 Hv and 109 Hv respectively. The ultimate tensile strength of the composite reached 312 MPa. Compared with 160 MPa of the as-casted Mg alloy, 263 MPa of the comparison group, the effect of nanoparticles on strength increase was significant.

Microstructure evolution and mechanical properties of dissimilar friction stir welded joints between AA1100-B4C MMC and AA6063 alloy

Abstract: The feasibility of dissimilar friction stir welding (FSW) between the AA1100-16 vol.% B4C metal matrix composite and the AA6063 alloy has been evaluated. The effect of the welding parameters on the interface bonding, joint microstructure and mechanical properties was investigated. The results revealed that all dissimilar joints produced under welding conditions investigated were stronger than the base materials of the Al-B4C composite. Analysis of the Mg concentration and the B4C particle distribution indicates that good material mixing and seamless bonding was achieved around the interface between the Al-B4C composite and the Al 6063 alloy during FSW. The electron backscatter diffraction analysis (EBSD) shows that during dissimilar FSW, there was a gradual microstructural evolution on both material sides, resulting in a variety of grain structures in the different weld zones. In the weld zones of FSW joints, the materials underwent dynamic recovery and recrystallization to different extents depending on their thermal mechanical history. The grain refinement of both materials in the nugget zone was observed. It is recommended that the 6063 aluminum alloy should be fixed on the advancing side and the use of an appropriate offset to the 6063 aluminum side is preferred.

Fabrication of High-Strength Al/SiC p Nanocomposite Sheets by Accumulative Roll Bonding

Abstract: Accumulative roll bonding (ARB) was successfully used as a severe plastic deformation method to produce Al-SiC nanocomposite sheets. The effects of process pass and amount of SiC content on microstructure and mechanical properties of the composites are investigated. As expected, production of ultrafine grain structures by the ARB process as well as nanosize particulate reinforcements in the metal matrix composite (MMC) resulted in excellent mechanical properties. According to the results of the tensile tests, it is shown that the yield and tensile strengths of the composite sheet increased with the number of ARB cycles without saturation at the last cycles. Scanning electron microscopy (SEM) revealed that the particles had a random and uniform distribution in the matrix by the last ARB cycles, and strong mechanical bonding takes place at the interface of the particle matrix. Transmission electron microscopy (TEM) and the corresponding selected area diffraction (SAD) demonstrate ultrafine grains with large misorientation in the structure. It is also shown that by increasing the volume fraction of particles up to 3.5 vol pct, the yield and tensile strengths of the composite sheets increased more than 1.3 and 1.4 times the accumulative roll-bonded aluminum sheets, respectively.