Showing papers on "Metal matrix composite published in 2003"

Friction stir processing: a novel technique for fabrication of surface composite

Abstract: A novel surface modifying technique, friction stir processing (FSP), has been developed for fabrication of surface composite. Al–SiC surface composites with different volume fractions of particles were successfully fabricated. The thickness of the surface composite layer ranged from 50 to 200 μm. The SiC particles were uniformly distributed in the aluminum matrix. The surface composites have excellent bonding with the aluminum alloy substrate. The microhardness of the surface composite reinforced with 27vol.%SiC of 0.7 μm average particle size was ∼173 HV, almost double of the 5083Al alloy substrate (85 HV). The solid-state processing and very fine microstructure that results are also desirable for high performance surface composites.

Effect of clustering on the mechanical properties of SiC particulate-reinforced aluminum alloy 2024 metal matrix composites

Abstract: Al 2024–SiC metal matrix composite (MMC) powders produced by centrifugal atomization were hot extruded to investigate the effect of clustering on their mechanical properties. Fracture toughness and tension tests were conducted on specimens reinforced with different volume fractions of SiC. A model was proposed to suggest that the strength of the MMCs could be estimated from the load transfer model approach that takes into consideration the extent of clustering. This model has been successful in predicting the experimentally observed strength and fracture toughness values of the Al 2024–SiC MMCs. On the basis of experimental observations, it is suggested that the strength of particulate-reinforced MMCs may be calculated from the relation: σ y = σ m V m + σ r ( V r − V c )− σ r V c , where σ and V represent the yield strength and volume fraction, respectively, and the subscripts m, r, and c represent the matrix, reinforcement, and clusters, respectively.

Wear performance of copper–graphite composite and a leaded copper alloy

Abstract: The wear behavior of new lead free metal matrix composite (MMC), centrifugally cast copper alloy graphite (C90300–10%graphite) composite (CG) is studied in comparison to a commonly used leaded copper (LC) alloy (18–22% Pb). Tribological tests were conducted with pins made from these materials and tested against a SAE 1045 steel counterface. The CG material showed higher wear resistance than the LC in the load range investigated (27–118 N). The CG and the LC showed similar friction coefficient (0.38) values at a low load of 27 N, where as at 118 N the CG had a slightly higher friction coefficient than the LC against the 1045 steel counterface. Transfer of material from the CG and the LC pins resulted in lowering the wear rate of the counterface as measured by the weight loss of the steel counterface. At the load of 27 N, the CG composite seems to be a viable substitute for the LC. For other loads modified versions of the CG are likely to provide optimum substitutes for the LC. Observations on structure, composition and morphology of surface, subsurface and wear debris was utilized in understanding the wear properties in each material.

Synthesis of ductile titanium-titanium boride (Ti-TiB) composites with a beta-titanium matrix: The nature of TiB formation and composite properties

Abstract: The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with β phase in the matrix by reaction sintering of TiB2 with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds of powder mixtures: (1) β-Ti alloy powders and TiB2; (2) α-Ti powder, a master alloy (Fe-Mo) powder containing the β-stabilizing elements, and TiB2; and (3) α-Ti powder, a β-stabilizing elemental powder (Mo or Nb), and TiB2. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at processing temperatures ranging from 1100°C to 1300°C. The morphology, size, and distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally packed mixtures led to the formation of a TiB monolithic layer around β grains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure factor for the β phase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables, and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.

The mechanical response of Al–Si–Mg/SiCp composite: influence of porosity

Abstract: The effect of porosity on the mechanical and fracture behaviour in Al–Si matrix alloy and composites reinforced with SiC particles of 10 and 20 vol.% in the as-cast state and after extrusion process has been studied. Matrix alloy and composites were fabricated by compocasting and extrusion. Samples were characterized by optical microscopy, image analyzer, scanning electron microscopy and tensile tests. The results demonstrate that hot extrusion considerably reduces the porosity, while size and distribution of the reinforcement particles are also affected. In the point of fracture behaviour, the existence of large porosity is more effective.

The microstructure and the thermal expansion characteristics of Cu/SiCp composites

Abstract: Copper/silicon carbide composites (Cu/SiC p ) were made by the powder metallurgy method. Electroless plating was employed to deposit a copper film on SiC p powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. Thermal expansion property of as-formed product was measured in the temperature range from 50 to 550 °C. The results showed that copper coating on silicon carbide particles could render uniform distribution of SiC p in the copper matrix. The composites exhibited positive thermal hysteresis behavior when cooled down from the peak temperature to room temperature, which can be explained in terms of the residual stresses and the interfacial bonding between copper and silicon carbide. The magnitude of this strain was a function of the SiC p volume fraction and the number of thermal cycles. The thermal expansion property of composites was measured and compared with those predicted from various theoretical models.

Interactions between tungsten carbide (WC) particulates and metal matrix in WC-reinforced composites

Abstract: A variety of experimental techniques have been used to investigate the interactions between tungsten carbide (WC-Co 88/12) particulates and the matrix in some new wear resistant cobalt-based superalloy and steel matrix composites produced by hot isostatic pressing. The results show that the chemical composition of the matrix has a strong influence on the interface reaction between WC and matrix and the structural stability of the WC particulates in the composite. Some characteristics of the interaction between matrix and reinforcement are explained by the calculation of diffusion kinetics. The three-body abrasion wear resistance of the composites has been examined based on the ASTM G65-91 standard procedure. The wear behavior of the best composites of this study shows great potential for wear protection applications.

The tensile response and fracture behavior of 2009 aluminum alloy metal matrix composite

Abstract: In this research paper the tensile properties and fracture characteristics of aluminum alloy 2009 discontinuously reinforced with silicon carbide particulates (SiC p ) are presented and discussed. The increased strength of the Al 2009/SiC p composite is attributed to the synergistic influences of residual stresses generated due to intrinsic differences in thermal expansion coefficients between the composite constituents, strengthening from constrained plastic flow and triaxiality in the ductile aluminum alloy metal matrix due to the presence of ceramic particle reinforcements. Fracture on a microscopic scale comprised of cracking of the individual and clusters of SiC particles present in the microstructure. Final fracture of the composite resulted from crack propagation through the matrix between the clusters of reinforcing SiC particles. The key mechanisms governing the tensile fracture process are elucidated.

Investigation of the Young's modulus of TiB needles in situ produced in titanium matrix composite

Abstract: In situ Ti/TiB composites with different volume fractions of discontinuous TiB reinforcements were produced by powder metallurgy. After compacting Ti� /TiB2 powders by hot unidirectional pressure, heat treatments led to the in situ formation of distinctive needles of TiB, randomly distributed in the titanium matrix. The Young’s modulus of TiB was evaluated using the ASW computation method and experimental Vickers micro-indentation. Three point bend tests were performed on Ti/TiB composites as a function of the TiB volume fraction in order to extract the Young’s modulus of TiB from the elastic properties of the composite. The different values obtained according to these three methods were discussed and compared with the literature. # 2002 Elsevier Science B.V. All rights reserved.

Titanium-titanium boride (Ti-TiB) functionally graded materials through reaction sintering: Synthesis, microstructure, and properties

Abstract: The study demonstrates an effective method to synthesize titanium-titanium boride (Ti-TiB) functionally graded material (FGM) tiles by exploiting the simultaneous TiB whisker formation in situ and the densification occurring during the reaction sintering process. The macrostructure of the graded material was designed to have a beta-titanium (β-Ti) layer on one side with the composite layers of Ti-TiB mixture having increasing volume fraction of the TiB through the thickness. The approach used an optimized tri-modal powder mixture consisting of α-Ti powder, a master alloy of the β-stabilizing-element powders (Fe-Mo), and TiB2. The structure and properties of both of these FGMs were systematically characterized by X-ray diffraction, electron microscopy, and microhardness measurements. Interestingly, it has been found that two different kinds of TiB whisker morphologies were observed in the FGMs. The Ti-rich layers were found to have large and pristine TiB whiskers uniformly distributed in the Ti matrix. On the other hand, the TiB-rich layer was found to have a network of interconnected and relatively smaller TiB whiskers appearing as clusters. The layers of intermediate TiB volume fractions were found to consist of both the morphologies of TiB. The effectiveness of the X-ray direct comparison method for the determination of volume fractions of phases in the FGM layers was also demonstrated. The Vickers microhardness level was found to increase dramatically from 420 kgf/mm2 in the β-Ti layer to 1600 kgf/mm2 in the TiB-rich layer. The elastic residual stresses retained in the graded layers after fabrication were determined based on an elastic multilayer model. The nature of microstructure, the hardness variation, and the distribution of residual stresses in these novel FGMs are discussed.

Study of electrical discharge grinding using metal matrix composite electrodes

Abstract: An investigation was made into the combined technologies of electrical discharge machining and grinding (EDMG). A metal matrix (Cu/SiC p ) electrode with a rotating device was made and employed to study the EDMG technology. It was found that 3–7 times the normal electrical discharge machining (EDM) material removal rate (MRR) could be achieved in EDMG under suitable conditions of electrode rotating speed, SiC p particle size and current. This novel achievement is attributed to the fact that, under appropriate conditions, the hump-shaped melted material created by the EDM mechanism is vulnerable to attack by the grinding mechanism during the EDMG operation, greatly increasing the removal rate. Conversely, under inappropriate conditions, in which hump-shaped material solidifies prior to the non-conductive ceramic particle grinding, the above function becomes negligible and results in much lower MRR.

Continuous Fiber Reinforced Titanium Matrix Composites: Fabrication, Properties and Applications

Abstract: Titanium matrix composites (TMCs) have been developed as high performance materials for light weight structural applications. The materials are comprised of a silicon carbide (SiC) fiber embedded in a titanium matrix, thus making use of the high strength of the SiC fibers, their high stiffness and creep resistance at elevated temperatures combined with the damage tolerance of titanium alloys. Since materials properties are closely related to the quality of the fabrication process, TMC processing is of major importance. Moreover, reinforcement-induced anisotropy of the material and thermal residual stresses formed during the consolidation process must be considered and understood for proper component design. Finally, modeling using FE methods reduces the time needed for component development and helps to elucidate failure mechanisms of the material.

Fabrication of nickel composite coatings reinforced with TiC particles by laser cladding

Abstract: Various weight ratios of TiC particulate nickel-based composite coatings were produced on carbon steel substrates by laser cladding The experimental results showed that the coating was uniform, continuous and free of cracks when a CaF2 flux was used Excellent bonding between the coating and the medium carbon steel substrate was ensured by the strong metallurgical interface The microstructures of the coating were mainly composed of γ-Ni dendrites, M23C6, a small amount of CrB, and dispersed TiC particles The morphologies of TiC particles changed from the globular, cluster to flower-like shape The volume fraction of TiC particles and the microhardness gradually increased from the bottom to the top of the coating, and the volume fraction of TiC particles increased with increasing of volume fraction of Ti and C The maximum microhardness of the coatings with 10, 15 and 20 wt% (Ti+C) in the preplaced alloy powder was approximately HV02750, HV02850 and HV02920, respectively, which was much larger than that of the steel substrate, HV02240

Rapid synthesis of Al2O3 reinforced Fe–Cr–Ni composites

Abstract: Short distance infiltration (sdi) was used to fabricate metal matrix composites (MMC) with very fine ceramic reinforcements. This ‘sdi-MMC’ process was used to synthesize a dense composite comprised of Fe–Cr–Ni/Al2O3. Fe2O3/Fe/Ni/Cr/Al powder compacts were rapidly heated to 900 °C and held at this temperature and a pressure of 20 MPa in air for 5 min. This thermomechanical treatment triggered the highly-exothermic thermite reaction between starting powders that, in turn, resulted in rapid in-situ formation of a composite comprised predominantly of γ(fcc) Fe–Cr–Ni, along with smaller amounts of α(bcc) Cr–Fe–Ni and α-alumina. SEM and TEM analyses revealed a microstructure consisting of a uniformly dispersed network of very fine (a few hundred nanometers) Al2O3 grains in a matrix of a fine-grained (=5 microns) metallic alloy. The dense composites exhibit average bend strength and toughness values of 1100 MPa and 18 MPa (m)1/2, respectively.

Improvement in mechanical properties of in-situ Al–TiB2 composite by incorporation of carbon

Abstract: In-situ TiB 2 reinforced aluminium composites have been successfully synthesized through chemical reactions between elemental Al, B and Ti materials. By incorporation of carbon into the in-situ reaction, the Al 3 Ti intermetallic phase was found to decrease via the formation of TiC and the decomposition of Al 3 Ti since TiC is more stable in the presence of carbon. Mechanical properties in terms of yield and ultimate tensile stresses and Young's modulus have been improved. Ductility in terms of elongation of the composite with the incorporation of carbon was found to increase by about 26% in comparison to the composite without carbon. The improvement in ductility may be associated with the decrease in the amount of Al 3 Ti and the increase in TiC particulates.

Multi-structure metal matrix composite armor and method of making the same

Abstract: A lightweight armor system may comprise multiple reinforcement materials layered within a single metal matrix casting. These reinforcement materials may comprise ceramics, metals, or other composites with microstructures that may be porous, dense, fibrous or particulate. Various geometries of flat plates, and combinations of reinforcement materials may be utilized. These reinforcement materials are infiltrated with liquid metal, the liquid metal solidifies within the material layers of open porosity forming a dense hermetic metal matrix composite armor in the desired product shape geometry. The metal infiltration process allows for metal to penetrate throughout the overall structure extending from one layer to the next, thereby binding the layers together and integrating the structure.