Showing papers on "Metal matrix composite published in 1997"

The influence of tool coatings in machining of magnesium

Abstract: Magnesium is the lightest metal used in construction and therefore offers the greatest potential for weight reduction. The automotive industry in particular has an upcoming interest in the use of magnesium alloys. To observe the interactions between workpiece material and tool material and coating, respectively, turning experiments were carried out machining the alloy AZ91 HP. When machining magnesium dry, flank build-up due to adhesion between cutting tool and workpiece can occur at cutting speeds of vc = 900 m/min and more for uncoated and TiN-coated cemented carbide tools. Tools with either polycrystalline diamond (PCD) insert or coating can be used to reduce friction and adhesion in the tool-workpiece contact resulting in low machining forces as well as a superior surface quality even at high cutting speeds of vc = 2400 m/min. PCD coatings can also be applied to complex tool geometries. As tool wear can hardly be observed when machining magnesium alloys, a magnesium-based metal matrix composite (MMC) is machined to combine the adhesive effects of magnesium with the abrasive load caused by a reinforcement component. Excessive tool wear can be observed for TiN-coated carbides even at low cutting speeds of fvc = 100 m/min. PCD coatings show better results but cannot compete with tools having a PCD insert if a low film thickness is chosen.

Macro and micro scale modeling of thermal residual stresses in metal matrix composite surface layers by the homogenization method

Abstract: The modeling of thermal residual stresses generated in TaC/stellite and TiC/stellite composite surface layers produced by the oscillating electron beam remelting on low alloys steel is presented. The homogenization method is applied to analyze the real composite microstructures by utilizing the digital image-based (DIB) geometric modeling technique. Two scales of elastic stress analysis are studied: macroscopic one referring to the global structure of composite layer produced over the substrate of low alloy steel and microscopic, comprising the selected unit cell of composite microstructure.

Pulse‐Reverse Plating of Nanocomposite Thin Films

Abstract: A steady-state, pulse-reverse plating method has been developed which permits the enhancement of the particle concentration in electrodeposited metal matrix composite coatings. The procedure is demonstrated for the codeposition of nanosized, γ-alumina particles in a copper matrix.

Method of making a fibre reinforced metal component

Abstract: A ceramic fibre reinforced metal rotor with integral rotor blades is manufactured using a continuous strip of unidirectional ceramic fibres in a metal matrix. The continuous strip of ceramic fibres in a metal matrix is cut into a plurality of separate pieces of predetermined length. The separate pieces of ceramic fibres in the metal matrix are arranged alternately in a spiral, with separate pieces of unreinforced metal matrix in adjacent abutting relationship to form a ring which has a plurality of laminations. The ring of laminations of metal matrix composite pieces and unreinforced metal matrix pieces are arranged between an inner and an outer metal ring to form an assembly. The assembly is consolidated by hot isostatic pressing using radially applied pressure. The separate pieces of metal matrix composite provide compliance to reduce breaking or buckling of the fibres, and the pieces of unreinforced metal matrix prevents damage spreading between laminations.

Precipitation and dissolution kinetics in Al-Cu-Mg-Fe-Ni alloy 2618 and Al-alumina particle metal matrix composite

Abstract: The kinetics of precipitation and dissolution of precipitate phases in AA2618 and AA2618–alumina particle-reinforced metal matrix composite were studied using differential scanning calorimetry (DSC). Thermal effect peaks due to GPB (Guinier-Preston-Bagaryatskii) zone formation, GPB zone dissolution, formation of the θ ′ and S ′ phases, and the dissolution of the θ ′ and S ′ phases were identified. The kinetic parameters for GPB zone formation and dissolution reactions, calculated by using both the modified Avrami–Johnson–Mehl (AJM) equation and the Kissinger-type expressions, were comparable. GPB zone formation was found to be suppressed in the composite material while, on the other hand, GPB zone dissolution was enhanced.

Transient liquid-phase bonding of alumina and metal matrix composite base materials

Abstract: Transient liquid-phase (TLP) bonding of aluminium-based metal matrix composite (MMC) and Al2O3 ceramic materials has been investigated, particularly the relationship between particle segregation, copper interlayer thickness, holding time and joint shear strength properties. The long completion time and the slow rate of movement of the solid–liquid interface during MMC/Al2O3 bonding markedly increased the likelihood of forming a particle-segregated layer at the dissimilar joint interface. Preferential failure occurred through the particle-segregated layer in dissimilar joints produced using 20 and 30 μm thick copper foils and long holding times (≥20 min). When the particle-segregated layer was very thin (<10 μm), joint failure was determined by the residual stress distribution in the Al2O3/MMC joints, not by preferential fracture through the particle-segregated layer located at the bondline. Satisfactory shear strength properties were obtained when a thin (5 μm thick) copper foil was used during TLP bonding at 853 K.

Corrosion Protection of Aluminum Metal-Matrix Composites

Abstract: Corrosion protection of aluminum metal-matrix composites (MMC) by anodizing treatments was investigated Electrochemical behavior of MMC without protection also was investigated Electroch

Phase-stress partition during uniaxial tensile loading of a TiC-particulate-reinforced Al composite

Abstract: Using neutron diffraction, we measured during in situ loading the lattice elastic mean phase (LEMP) strains in the matrix and reinforcement of a 15 vol pct TiC-particulate-reinforced 2219 Al composite. From the strain components longitudinal to and transverse to loading, the in situ normal phase stresses (average normal stresses in the constituent phases) were obtained through Hooke’s law. The internal stress partition between the matrix and reinforcement, i.e., load sharing, can then be inferred. Internal stress development was also modeled using the finite-element method (FEM), showing good agreement with the experimental results. Both indicate that the relationship between the LEMP strains/phase stresses and the applied load noticeably deviates from linearity during composite microyielding, long before the nominal 0.2 pct proof stress is reached. The nonlinearity arises (despite the linear elastic relationship between phase stresses and LEMP strains) because the applied traction is not synonymous with the phase stresses, and the ratio of phase stresses may vary during loading. Notably, the morphology of the LEMP strain development with applied load differs in the directions parallel to or perpendicular to the load. The differences are explained by considering the evolution of local matrix plasticity. Thermal residual stresses and inelastic stress relaxation, driven by interfacial diffusion, are also discussed.

Tensile deformation and fracture behaviour of a titanium-alloy metal-matrix composite

Abstract: In this paper, the microstructure, tensile behaviour and quasi-static fracture characteristics of a Ti-6Al-4V alloy reinforced with discontinuous whiskes of titanium boride, are presented and discussed. Microstructural analysis of the composite revealed a non-uniform dispersion of the whisker reinforcements in the Ti-6Al-4V matrix. The elastic modulus of the composite was better than that of the unreinforced matrix. The ambient-temperature yield strength of the Ti-6Al-4V/TiB composite was higher than the yield strength of the unreinforced matrix. The strength decreased with increase in test temperature. The increased strength of the composite is rationalized in terms of concurrent and mutually interactive influences of mechanisms based on work hardening and the substructure that evolves from the presence of additional dislocations. The intrinsic mechanisms and micromechanisms governing the tensile fracture process are discussed.

Investigation of the precipitation kinetics in an A16061/TiB2 metal matrix composite

Abstract: The aging kinetics of AA6061 (Al−Mg−Si−Cu) based metal matrix composites (MMCs) containing TiB 2 -particles were investigated using hardness measurements, texture determination and electron microscopy. The samples were produced by an in-situ process. Two industrially manufactured in-situ composites with an AA6061 matrix and TiB 2 -particles (3.4 vol.%, 6.8 vol.% TiB 2 ) were studied at two different aging temperatures (160°C, 250°C) and compared to a similarly processed non-reinforced AA6061 alloy. An increasing volume fraction of TiB 2 correlated with changes in the aging response of the composites. Samples subjected to three aging times were selected for microstructure analysis in the TEM (10 min, 200 min, 1365 min, aging temperature 250°C). Special emphasis was laid on the investigation of the growth kinetics of metastable needle shaped matrix precipitates, which cause the increase in hardness. The TEM examinations of the MMCs substantiated that precipitate growth was accelerated in the presence of TiB 2 particles as compared to the unreinforced AA6061. These differences in kinetics were related to microstructural changes induced by the presence of the ceramic TiB 2 particles.

The processing and characterization of sintered metal-reinforced aluminium matrix composites

Abstract: The current investigation involves the fabrication and characterization of an aluminium metal matrix composite reinforced with sintered metal preforms. Two types of metallic preforms were used (steel and stainless steel) and a variety of squeeze casting conditions were investigated using systematic design-of-experiments techniques to determine the effect of casting conditions on the composite microstructure and mechanical properties. It was observed that a detrimental reaction phase containing iron, aluminium and silicon formed around the metallic preform particles, with a lower volume fraction of reaction phase forming at the lower melt casting temperature. This reaction phase appears to promote premature fracture by facilitating crack initiation and propagation. The stainless steel-reinforced composites had a smaller volume fraction of reaction phase and exhibited superior properties compared to the steel-reinforced composites.

Laser beam processing of a SiC particulate reinforced 6061 aluminium metal matrix composite

Abstract: SiC particulate reinforced 6061 Al metal matrix composites were laser beam cut using a 3kW continuous wave CO2 laser. The influence of laser processing parameters such as cutting speed, laser power, and shielding gas on the quality of the cuts were investigated. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to analyse the laser treated zone. Experimental results show that 6061 Al metal matrix composites can cut be successfully using laser. A number of Al4C3/Al4SiC4 plates were formed in the heat affected zones due to a chemical reaction between Si and Al that occurred during the laser processing.

Mechanism of film growth during anodizing of Al-alloy-8090/SiC metal matrix composite in sulphuric acid electrolyte

Abstract: Metal matrix composites (MMCs) consisting of Al-alloy 8090 reinforced with SiC particulate have previously proved to be susceptible to corrosion in chloride-containing environments. A study was carried out to investigate the possibility of anodizing the MMC for protection against corrosion. Sulphuric acid was found to be a preferred anodizing electrolyte for the composite, as it allowed a relatively thick anodic film to be formed on the surface. The investigation regarding the mechanism of film formation, performed on a scanning electron microscope, revealed that the thickness of the anodic film was non-uniform; however, the film–solution interface was relatively uniform compared with film–composite interface. Observation in the transmission electron microscope indicated that the pores in the anodic film which was formed, appeared round when they grew perpendicular to the surface and revealed elongated like "finger prints" when they developed at an angle on a rough surface, due to presence of SiC particles. The corrosion rate of the MMC, which was about 21 times the corrosion rate of ultra-pure aluminium in a chloride-containing environment, became negligible after anodizing.

Micromechanics for particulate reinforced composites

Abstract: A set of micromechanics equations for the analysis of particulate reinforced composites is developed using the mechanics of materials approach. Simplified equations are used to compute homogenized or equivalent thermal and mechanical properties of particulate reinforced composites in terms of the properties of the constituent materials. The microstress equations are also presented here to decompose the applied stresses on the overall composite to the microstresses in the constituent materials. The properties of a 'generic' particulate composite as well as those of a particle reinforced metal matrix composite are predicted and compared with other theories as well as some experimental data. The micromechanics predictions are in excellent agreement with the measured values.

A new aluminium silicon carbide formed in laser processing

Abstract: During laser processing to create an Al–SiCp surface metal matrix composite (MMC) layer on AA6061 Al alloy, needle-shaped particles were formed when a high laser energy input was used. Optical microscopy showed this phase to be similar to Al4C3 and Al4SiC4. Previous work was unable to identify the compound as one of those already known in the Al–Si–C system that included Al4C3, Al4SiC4, Al8SiC7, Al4Si2C5 and Al4Si3C6. Therefore, in the present work a phase identification was undertaken on the unknown, using transmission electron microscope (TEM) and the associated energy dispersion analytical X-ray (EDAX) system, together with X-ray diffractometry (XRD). This suggested that the phase was an aluminium silicon carbide having an hexagonal structure with a = 0.3316 and c = 2.1330 nm, which could be a metastable phase formed under the particular laser processing conditions used.

Temperature gradient transient liquid phase diffusion bonding: a new method for joining advanced materials

Abstract: A novel method for transient liquid phase (TLP) diffusion bonding of aluminium based materials has been developed which is capable of reliably providing excellent bonds with parent material shear strengths. This new method relies on imposing a temperature gradient across the bond line during TLP diffusion bonding and this leads to the formation of sinusoidal or cellular interfaces. Consequently, bond strengths are increased, possibly as a result of the higher metal–metal contact along the non-planar interfaces compared with the planar interfaces associated with either conventional TLP or solid state diffusion bonding processes. This paper describes the results achieved, implementing the new method and using copper interlayers, when joining Al–Mg–Si, Al–Li alloys, and an aluminium metal matrix composite with SiC particles. Patent protection has been filed in the UK under UK Patent No. 9709167.2.

Modelling central bursting in the extrusion of particulate reinforced metal matrix composite materials

Abstract: Elastic-viscoplastic damage constitutive equations for particulate reinforced metal matrix composite (MMC) materials have been used to investigate central burst formation in extrusion. The equations have been implemented into finite-element software with which extrusion processes for a range of area reductions and volume fractions of particulate reinforcement have been simulated. The analyses carried out have enabled an extrusion limit diagram to be established for a particle reinforced aluminium matrix composite. The results show that for volume fraction of reinforcement up to approximately 20%, the influence of the volume fraction of particle on central bursting is small compared with the process parameters area reduction and semi-cone die angle. Hence, the method of selection of process parameters to avoid central bursting in MMC materials is likely to be the same as that for monolithic materials. The results show that with increasing volume fraction of reinforcement, significant changes in the patterns of damage evolution occur, with increasing volume fraction leading to the development of damage in the central region of the extrudate that does not exist for lower volume fractions. However, increasing the volume fraction of reinforcement tends to decrease the level of surface damage developing within the extrudate.

Microstructure and properties of spray-deposited 2014 + 15 vol pct SiC particulate-reinforced metal matrix composite

Abstract: A metal matrix composite (MMC) of 2014 aluminum alloy reinforced with 15 vol pct SiC particulate was produced by the spray-forming-deposition process. The as-deposited preform revealed a high density and a homogeneous reinforcement distribution. Reactive products were not found on interfaces between the reinforcement and the matrix. Compared to the control alloy, the composite showed accelerated aging after solutionizing at 502 °C, while aging was retarded after solutionizing at 475 °C. Analysis indicated that the activation energy was almost the same for the aging process after different solutionizing treatments. This suggested that while the thermal barrier for the aging process was the same, other factors affecting the aging process should be considered. For example, the effective concentration of the precipitate forming elements possibly decreased after incompletely solutionizing at 475 °C. After heat treatment, the composite showed a tensile strength similar to the control alloy. The wear resistance of the composite improved considerably. The aging behavior of the composite was also studied using the nanoindentation technique. Steep gradient distribution of elastic modulus and hardness around the reinforcement SiC particulate was observed. Theoretical analysis showed that this could be attributed to the gradient distribution of precipitates, resulting from a gradient distribution of dislocation density around the SiC particulates caused by residual thermal misfit stresses.