Showing papers on "Metal matrix composite published in 1999"

The fabrication, properties and microstructure of Cu–Ag and Cu–Nb composite conductors

Abstract: The properties and the microstructure of cold-drawn Cu–Ag and Cu–Nb composites have been investigated for their potential use as conductors in pulsed high field magnets. Cu–Nb and Cu–Ag are among the leading candidates for the 100T magnet to be built in cooperation between NHMFL and LANL. These conductors show a combination of high conductivity, high strength, adequate workability, and the final section size obtainable for the wire. The conductors are operated in the temperature range from liquid nitrogen to room temperature, and therefore the mechanical and electrical properties were measured at both −196 and +25°C. The 100T magnet requires conductors with various cross-sections. The conductors with small cross-sectional areas (6–12 mm 2 ) require higher strength. Thus, Cu–Nb composites with cross-sectional areas between 6 and 12 mm 2 were fabricated by bundling-and-drawing and characterized. The Cu–Ag composite was developed as one of the candidates for large cross-section applications. It was produced by casting, forging, rolling and cold drawing to a final cross-section of up to 45 mm 2 . In addition to the ability to fabricate coils for the magnet, we have considered the service life of the materials in regard to both cyclic loading and thermal fatigue. Examination of the initial portion of the stress–strain curve of cold-worked materials reveals that the internal stresses developed during the fabrication influence the mechanical response of the materials. Thus the properties of the drawn materials have been monitored as a function of cyclic loading and thermal annealing cycles. An important aspect of the selection of materials for high field magnets is the ability to obtain the material in large cross-sections and thus the work in this paper is concerned with the development of suitable production routes as well as the relationship between the structure and the properties of processed composites.

The microstructure and mechanical properties of TiC and TiB2-reinforced cast metal matrix composites

Abstract: TiC and TiB2 particles have been spontaneously incorporated into commercial purity aluminum melts through the use of a K-Al-F-based liquid flux that removes the oxide layer from the surface of the melt. The combination of spontaneous particle entry and close crystal structure matching in the Al-TiB2 and Al-TiC systems, results in low particle-solid interfacial energies and the generation of good spatial distributions of the reinforcing phase in the solidified composite castings. The reinforcement distribution is largely insensitive to the cooling rate of the melt and the majority of the particles are located within the grains. Modulus increases after TiC and TiB2 particle additions are greater than those for Al2O3 and SiC. It is thought that interfacial bonding is enhanced in the TiC and TiB2 systems due to wetting of the reinforcement by the liquid and particle engulfment into the solid phase. TiC-reinforced composites exhibit higher stiffnesses and ductilities than TiB2-reinforced composites. This has been attributed to stronger interfacial bonding in the Al-TiC system, due to the increased tendency for nucleation of solid on the particle surfaces.

The effect of particle shape on ductility of SiCp reinforced 6061 Al matrix composites

Abstract: To study the effect of particle shape on thermal residual stress and strain distributions in composites, five two-dimension SiCp/6061Al model composites reinforced with spherical, hexagon, square, triangle and shuttle-shaped particles, respectively were analyzed by finite element method (FEM). The results showed that the particle shape has a great effect on thermal residual stress and strain fields in composites. There are a residual plastic strain concentration in the matrix around a pointed particle corner and a serious residual stress concentration in the pointed particle corner. The two concentrations increase with decreasing pointed corner degree. When an external stress is applied, the plastic strain concentration in the matrix around the pointed particle corner and the serious stress concentration in the pointed particle corner which will fracture on a relative low level of applied stress can decrease ductility of the composite. Two 6061 aluminium alloy matrix composites reinforced with general SiC particles and blunted SiC particles were studied on the basis of the FEM analyses. It was found that most very pointed particle corners are eliminated after SiC particles being blunted. Replacing general SiC particles with blunted ones can reduce residual plastic strain concentrations in the matrix and serious residual stress concentration in the particle. Therefore, blunted SiC particles reinforced composite shows a higher ductility than general one. (C) 1999 Elsevier Science S.A. All rights reserved.

Fabrication process of metal matrix composite with nano-size SiC particle produced by vortex method

Abstract: The fabrication of metal matrix composite (MMCp) by vortex process is the general method due to the advantage of its convenience. However in the case of fine particles the surface property of the particle appears dominantly, especially in nano-size particles the agglomeration occurs and the fabrication of MMCp is reduced to be difficult. It is analyzed that the strength of the MMCp is dominated by the ascent of the dislocation density. Further, as the dispersion strengthening mechanism can be anticipated, dispersions of more fine particles into the matrix are required. In this study, the influences on various primary factors for solving an agglomeration problem are examined using SiC particles of 0.3 μm (the minimum diameter in the market) into 6061 Al alloy by the vortex method. From this study, the following results are obtained, (1) It is found that MMCp with no agglomeration can be fabricated by conducting the following procedure; pre-treatment, disagglomeration of powder, Ca addition and stirring in the semi-solid range. (2) It is deduced that the main factors of forming the agglomeration in the matrix of MMCp are the yield of SiO2 on the surface of SiC and the reduction of the void ratio of SiC powder.

Preliminary investigation on joining performance of SiCp-reinforced aluminium metal matrix composite (Al/SiCp–MMC) by vacuum brazing

Abstract: The present study has investigated the joining performance of SiC particulate reinforced aluminium metal matrix composite (Al/SiCp–MMC) by vacuum brazing process. After the joints brazed with Al–Si–Mg foil brazing filler metal at different brazing batches, both the mechanical properties and the microstructures of brazed joints were estimated. Moreover, the influence of SiCp size, SiCp volume percentage and the brazing parameters on bonding quality of the joints have also been discussed in detail. The results have revealed that the bonding quality either in SiCp/Al interface or in SiCp/SiCp interface belongs to weak bonding, and the results also show that under the same brazing parameters condition, the strength of brazed joints decreases along with increasing the SiCp volume percentage. In addition, the results also indicate that for a constant SiCp volume percentage the strength of brazed joints decreases when SiCp size increases. These results are very useful for the joining design of discontinuously reinforced metal matrix composites and further for the optimum design of composition of composites.

Reactions in the matrix and interface of the Fe–SiC metal matrix composite system

Abstract: Fe–SiC metal matrix composite (MMC) was produced by the use of hot isostatic pressing (HIP) or sintering for consolidation. The SiC in the MMC was in the forms of particulates and chopped fibers. The effect of exposure of the MMC to high temperatures for long time, up to 1.4×10 4 s, was obtained by heat treatment of the HIPed or sintered specimens. A small reaction zone of ∼0.5–1 μm, composed of iron silicides, was observed in specimens HIPed at 1173 K at a pressure of 150 MPa. Cursory mechanical tests indicate an increase in the ultimate tensile strength and the yield strength of 33.1 and 12.6% of the as HIPed specimens, respectively, when the SiC content was 3% by volume. C, originating from the SiC and dissolved in Fe, induces changes in the matrix when the MMC is exposed to high temperatures, leading to the formation of the familiar transformation products. Strengthening by modification of the Fe matrix under controlled conditions is a unique feature of the Fe–SiC MMC system. The kinetics of the reaction zone formation was investigated and it was found that its growth is diffusion controlled and occurs with an activation energy of 205.4 kJ mol −1 . The reaction zone might act as a diffusion barrier preventing fiber degradation as long as the conditions of thermal effects are reasonable, but exposure of the MMC to high temperatures for extended time can result in severe fiber damage. A mechanism is suggested for the reaction zone formation.

Effects of Si content on the microstructure and tensile strength of an in situ Al/Mg2Si composite

Abstract: Al/Mg2Si composites were in situ fabricated by the usual die-casting technique, and effects of the Si contents in the composites on microstructures and tensile strengths were investigated, Experimental results show that extra Si contents in Al/Mg2Si composites induce a ductile matrix and a uniform distribution of in situ particles. The refined microstructures lead to an obvious increase in both strength and ductility of the metal matrix composites (MMCs), The effects of extra Si on both the solidification process and fracture characteristics of the Al/Mg2Si composites were analyzed.

Indentation creep in a short fibre-reinforced metal matrix composite

Abstract: Creep properties of an unreinforced M124 (AlSi12CuMgNi) base alloy and an Al 2 0 3 (Saffil) fibre reinforced M124+s metal matrix composite (MMC) were investigated by indentation tests performed between 250 and 350°C. It has been found that the creep curve of the base alloy consists of two stages (transient and steady state), whereas the curve of the composite material contains a decelerating third stage as well. This creep behavior is correlated with the changes of the microstructure below the indenter during the deformation process. In the region of steady state creep the stress exponent and the activation energy was determined for both materials.

Elastic Phase-Strain Distribution in a Particulate-Reinforced Metal-Matrix Composite Deforming by Slip or Creep

Abstract: The macroscopic load-bearing capability of a composite is directly related to the strain partitioning due to load transfer between the component phases. Using neutron diffraction, the elastic mean phase strains were measured during in-situ loading of a Cu-15 vol pct Mo particulate metal-matrix composite (MMC) at 25 °C, 300 °C, and 350 °C. The degree of load sharing at each temperature was compared to finite-element (FE) results. The load transfer from the matrix to reinforcement is both qualitatively and quantitatively different at low and high temperatures. When the matrix creeps, load transfer is less effective than when the matrix deforms by slip; also, load transfer at elevated temperatures decreases with increasing applied stress.

Microstructure and mechanical properties of a high volume fraction SiC particle reinforced AlCu4MgAg squeeze casting

Abstract: The micro structure and mechanical properties of a high volume fraction SiC particle reinforced AlCu4MgAg alloy produced by squeeze pressurised infiltration of dense packed particle preforms were characterised. It was found that the addition of 60 vol.% 12 μm SiC particles eliminates the processing related intrinsic macrosegregation of the matrix alloy, induces coarse precipitates in as-cast matrix, but does not impede matrix grain growth. The SiC-Al interfacial chemical reaction is suppressed to a limited extent. In T6 condition, the interfacial intermetallics are largely dissolved and the matrix is decorated with fine and dense precipitates of θ′ and Q phases. The addition of SiC particles accelerates the age-hardening response of the matrix alloy. Mechanically, the stiffness, hardness, flexural strength, fatigue strength and abrasive wear resistance are substantially improved, together with significantly reduced fracture toughness and ductility in comparison with the matrix alloy. © 1999 Elsevier Science S.A. All rights reserved.

Fabrication of metal matrix composite automotive parts

Abstract: The present trend to make parts at or near net shape has brought powder metallurgy (PM) to the forefront and is being vigorously pursued by automotive design and materials engin-eers who are finding an increased application for this energy-and cost-saving process. Mixtures of four different compositions (15, 20, 25, 30% by weight) of SiC were prepared. By the PM technique, valves were fabricated by placing these powder mixtures in layers (one weight per cent along the stem and one along the base) in a die. Specimens ( φ15 × 30) were also prepared by the PM technique so that properties like compressive, tensile strength, etc. could be studied. A die was fabricated to cast valves through a liquid metallurgy route.

Microstructure and grain growth behavior of an aluminum alloy metal matrix composite processed by disintegrated melt deposition

Abstract: In this study, a silicon-carbide particulate (SiCp), reinforced aluminum alloy-based, metal-matrix composite was synthesized using disintegrated melt deposition. Microstructural characterization of the disintegrated melt deposition processed composite samples revealed the presence of columnar-equiaxed shaped grain structure, noninterconnected porosity associated with the reinforcing carbide particulates, improved interfacial integrity between the reinforcement and the aluminum alloy matrix coupled, and a near uniform distribution of the reinforcing SiC particulates in the alloy matrix. An examination of grain growth with the objective of delineating the effects of the silicon carbide particulates revealed a diminishing to minimal role of the reinforcing phase with an increase in temperature from 450 to 590 °C.

Microstructure of Cu–C interface in Cu-based metal matrix composite

Abstract: Existence of dilute copper–carbon solid solutions is one of the characteristic features of the interfaces of the metal matrix composites widely used in the electrical applications. Experimental high-resolution SEM study allows to visualize the formation of the interaction zone on carbon fibre. We model interstitial solid solutions formed in this interaction zone non-empirically within the embedded-cluster and supercell approaches. Atomistic approach allows selection of the geometry of the solid solution. Electronic structure studies show that the most favourable position of the carbon atom is shifted along the [110] direction from the centre of the octahedral position. Investigation of this physical phenomenon allows us to understand the nature of the chemical bonding in copper-based solid solutions with carbon.

Advances in the fabrication of titanium metal matrix composite

Abstract: This paper describes recent developments in the processing of continuous fibre reinforced titanium alloy metal matrix composite. Used selectively, MMCs can have a dramatic effect on performance and weight. They combine the exceptional strength and stiffness of a ceramic with the many advantages of a metal matrix, which include elevated temperature capability, impact resistance, and environmental stability. Titanium MMCs have passed through the initial material research stages and the basic mechanical performance criteria are now well established. Further progress towards commercial exploitation now depends on detailed process definition and cost reduction.

Addition of ceramic particles to TIG melted titanium surfaces

Abstract: A surface layer metal matrix composite has been developed by using a tungsten inert gas (TIG) arc with an operating current of 60 A. The 0·5 mm thick coating of a powder mixture containing 80 vol.-% titanium and 20 vol.-% 40 μm SiCp particles was pre-placed on commercially pure titanium surfaces using a suitable binder. The powder coating was then melted by traversing specimens beneath a Miller TIG arc using 110, 90, 55, and 45 MJ m-2 energy densities. Glazing at energy densities from 55 to 110 MJ m-2 completely dissolved the powder mixture and produced 1 mm deep hard (500 to 600 HV) layers which were free from pores, cracks, and cavities. The tracks had smooth and reflective surfaces. The microstructure developed in the tracks is dominated by the reaction of SiCp particles with the molten titanium layer to form titanium carbide (dendrites), Ti5 Si3, and titanium. Processing with 45 MJ m-2 energy density arc produced pores and cavities in the melt pool; the microstructure consisted of agglomerated...

Production of silicon carbide Al 2124 alloy functionally graded materials by mechanical powder metallurgy technique

Abstract: A mechanical powder metallurgy process involving a vibration stage before cold and hot compaction has been developed to manufacture functionally graded materials (FGMs). The microstructure and mechanical properties of SiCp/Al 2124 FGMs produced by this process have been studied. It was found that the vibration stage modified the SiC distribution from a layered structure to a smoothly changing SiC content with position in the sample. The vibration process also improved local homogeneity by breaking up the coarse SiC agglomerates which tended to form in high SiC content regions of the FGMs. Multilayered FGMs exhibited superior toughness to their metal matrix composite counterparts and there were indications that toughness was further enhanced in the continuous SiC gradient FGMs produced by the vibration stage.

Particulate refinement and redistribution during the axisymmetric compression of an Al/SiCp metal matrix composite

Abstract: Previous investigations have shown that the thermomechanical processing of Al/SiCp metal matrix composites (MMC) can reduce the size of SiC particles and yield a more homogeneous spatial distribution of particles. Both of the above microstructural features are conducive to improvements in the ductility and fracture toughness of MMC. This research was designed to measure the effectiveness of thermomechanical processing on the microstructure of an MMC by monitoring the change in SiC particle size and spatial distribution during the course of deformation processing. The MMC used in this investigation was the Al alloy 2618 reinforced with 14 vol% SiCp. Continuous and discontinuous axisymmetric compression tests were conducted, both at room and elevated temperatures. Optical and quantitative microstructural analysis was performed over many fields from each as-deformed specimen. This study finds that at elevated temperatures, a large number of fractured SiC particles corresponded with the macroscopic peak flow stress of the composite. Furthermore, the propensity for particulate fracture was most pronounced when specimens were deformed at room temperature, diminishing somewhat when specimens were deformed at elevated temperatures. However, deformation at elevated temperatures resulted in a more uniform spatial distribution of SiC particles within the matrix.