L.T. Jiang

Residual microstructure associated with impact crater in Ti-6Al-4V meshes reinforced 5A06Al alloy matrix composite.

In this paper, TC4(m)/5A06Al composite was hypervelocity impacted by 2024 aluminium projectile with the diameter of 2mm and with the impact velocity of 3.5 km/s. The residual microstructure was observed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM). The TC4-Al interface before impact was composed of TiAl(3) phase and Ti(3)Al phase. Near the pithead, separation of TC4 fibers and Al matrix occurred along the impact direction. Around the middle of the crater, TC4 fibers were sheared into several sections. Near the bottom of crater, adiabatic shear band (ASB) occurred in TC4 fiber, while the angle between shear plane and cross section was 45°. The crack propagated along TC4-Ti(3)Al interface during impact and some Ti(3)Al phase at the TC4-Al interface transformed to amorphous with few nanocrystals after hypervelocity impact.

Microstructure and Mechanical Properties of High Densification Mo/Cu Composites

Microstructure and mechanical properties of the 55%, 60% and 67% Mo/Cu composites for electronic packaging application fabricated by a patent squeeze casting route have been investigated. The results show that Mo particles are homogeneously distributed in the matrix, and the Mo-Cu interfaces are clean, free from interfacial reaction products and amorphous layers. The densification of the Mo/Cu composites is higher than 99%. The as-received composites exhibit a Brinell hardness varying from HB178.1 to HB196.9 and an elastic modulus varying from 177GPa to 213 GPa. The tensile strength of the composites is higher than 480MPa. Moreover, the composites display favorable plasticity, while the elongation of the 55% Mo/Cu composite is as high as 5%. Obtaining high tensile strength and elongation in the composite is attributed to the high densification, as well as the clean and smooth Mo-Cu interfaces, both resulting from the cost-effective squeeze-casting technology.

SEM and TEM characterization of the microstructure of post-compressed TiB2/2024Al composite.

In the present work, 55 vol.% TiB(2)/2024Al composites were obtained by pressure infiltration method. Compressive properties of 55 vol.% TiB(2)/2024Al composite under the strain rates of 10(-3) and 1S(-1) at different temperature were measured and microstructure of post-compressed TiB(2)/2024Al composite was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). No trace of Al(3)Ti compound flake was found. TiB(2)-Al interface was smooth without significant reaction products, and orientation relationships ( [Formula: see text] and [Formula: see text] ) were revealed by HRTEM. Compressive strength of TiB(2)/2024Al composites decreased with temperature regardless of strain rates. The strain-rate-sensitivity of TiB(2)/2024Al composites increased with the increasing temperature. Fracture surface of specimens compressed at 25 and 250°C under 10(-3)S(-1) were characterized by furrow. Under 10(-3)S(-1), high density dislocations were formed in Al matrix when compressed at 25°C and dynamic recrystallization occurred at 250°C. Segregation of Mg and Cu on the subgrain boundary was also revealed at 550°C. Dislocations, whose density increased with temperature, were formed in TiB(2) particles under 1S(-1). Deformation of composites is affected by matrix, reinforcement and strain rate.

Microstructure characterization of Al matrix composite reinforced with Ti–6Al–4V meshes after compression by scanning electron microscope and transmission electron microscope

Compressive properties of Al matrix composite reinforced with Ti-6Al-4V meshes (TC4(m)/5A06 Al composite) under the strain rates of 10(-3)S(-1) and 1S(-1) at different temperature were measured and microstructure of composites after compression was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Compressive strength decreased with the test temperature increased and the strain-rate sensitivity (R) of composite increased with the increasing temperature. SEM observations showed that grains of Al matrix were elongated severely along 45° direction (angle between axis direction and fracture surface) and TC4 fibres were sheared into several parts in composite compressed under the strain rate of 10(-3)S(-1) at 25°C and 250°C. Besides, amounts of cracks were produced at the interfacial layer between TC4 fibre and Al matrix and in (Fe, Mn)Al(6) phases. With the compressive temperature increasing to 400°C, there was no damage at the interfacial layer between TC4 fibre and Al matrix and in (Fe, Mn)Al(6) phases, while equiaxed recrystal grains with sizes about 10 μm at the original grain boundaries of Al matrix were observed. However, interface separation of TC4 fibres and Al matrix occurred in composite compressed under the strain rate of 1S(-1) at 250°C and 400°C. With the compressive temperature increasing from 25°C to 100°C under the strain rate of 10(-3) S(-1), TEM microstructure in Al matrix exhibited high density dislocations and slipping bands (25°C), polygonized dislocations and dynamic recovery (100°C), equiaxed recrystals with sizes below 500 μm (250°C) and growth of equiaxed recrystals (400°C), respectively.

Mechanical Properties of Interpenetrating Graphite/2024Al Composites Produced by Improved Squeeze Exhaust Casting

The graphite/2024Al composites have been fabricated by improved Squeeze Exhaust Casting (SQEC) method. Two kinds of graphite preforms with porosities of 13% and 17% respectively were infiltrated with 2024Al (Al-5Cu-2Mg) alloy under the pressure of 73MPa. The disadvantages of traditional Squeeze Casting (SQC) were avoided and the distribution of aluminum alloy appeared homogenous 3D network in the composites. Flexural strength and Young’s modulus were determined at room temperature. Compared to graphite preform, the composites exhibited a significant enhancement of mechanical properties. The flexural strength and Young’s modulus of X-Y direction of G186/2024Al composites increased from 38.6MPa to 99.7MPa and from 10.1GPa to 19.7GPa, respectively. The fracture mechanism of the composites was discussed on the basis of fracture surfaces.

Influence of Deformation on Precipitation Behavior of 2024Al Alloy

In the present work, 2024Al alloy was rolled before solid solution, between solid solution and aging, and after aging treatments. Precipitation sequence in 2024 Al has not been altered by the rolling treatment. However, peak aging temperature of S’ phase was decreased from 264 to 254 oC, implying that the process of S’precipitation was accelerated by the deformation. After thermo-mechanical treatments, precipitates werefiner dispersed, and finest precipitate distribution was observed after treatment III (rolling between solid solution and aging), while precipitate size was all smaller than 240nm and more than 95% precipitates was smaller than 200nm. The highest dislocation density was found in 2024Al alloy after treatment III since the dislocations generated during deformation was slightly decreased during following low temperature aging treatment. Therefore, in order to improve the mechanical properties, it is suggested that the rolling treatment should be performed between solid solution and aging treatment.

Effects of Particle Size on Microstructure of the Matrix Alloy in Aluminum Matrix Composites

Aluminum matrix composites, reinforced by 0.15μm and 5μm Al2O3 particles with 40% volume fractions were fabricated by squeeze casting technique. The microstructure characterization near the interfaces of Al2O3p/1070Al composites was investigated by SADP and HREM techniques. Results showed that high-density dislocations were generated in the 5μm-Al2O3p/Al composite due to the thermal mismatch stress. In contrast, the matrix of the 0.15μm-Al2O3p/Al composite appeared to be nearly free dislocations and some “micro distortion areas” of 1-5nm were observed, which was attributed to the dispersion of fine sub-micron particles and uniform distribution of the stress near the interfaces.

Microstructures and Dynamic Compression Properties of a High Reinforcement Content TiB2/Al Composite

A high reinforcement content TiB2/2024Al composite with an average particle size of 8μm was fabricated by squeeze casting technology. The dynamic compression behaviors of the composite under varied strain rates were measured using split Hopkinson pressure bar, and its microstructure and fracture characteristic were examined. Resluts revealed that the composite was dense and homogenerous, and the TiB2-Al interface was clean without interfacial reactants. At high strain rate, the TiB2/Al composite showed insensitive to the strain rate, and both the flow stress and the elastic modulus improved little with an increase of the strain rate. The composite failed macroscopically in shear fracture and in split, which were caused by cracking of large reinforcement particles and interface failures under dynamic load.

Effect of Heat-Treatment on the Mechanical Properties of TiB2P/2024Al Composite

55vol% TiB2P/2024Al composite was fabricated by squeeze casting technology, and the effect of heat treatment on mechanical properties of the composites was studied by means of hardness measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile testing etc. Results show that heat treatment has remarkable influence on the hardness and the tensile strength of the composites. For TiB2P/2024Al composites, the composites aged at 130°C for 5h can obtain the highest hardness, and the composites peak-aged at 160°C and aged at 190°C for 24h can obtain the higher tensile strength, which is due to the type of precipitates in the composites. Considering the experimental error, heat treatments has no obvious effect on elastic modulus of the experimental composite.