G.S. Wang

Low-cycle fatigue behavior of Al-based composites containing in situ TiB2, Al2O3 and Al3Ti reinforcements

Abstract Aluminum-based composites reinforced with in situ TiB 2 and Al 2 O 3 particles were prepared through reactive hot pressing of TiO 2 , Al and B powders. Brittle Al 3 Ti blocks were also formed in situ when the B/TiO 2 molecular ratio is smaller than 2. The low-cycle fatigue behavior of in situ composites under total strain-controlled conditions at room temperature was investigated. The results showed that the composite reinforced with in situ TiB 2 and Al 2 O 3 particles exhibits a relatively stable cyclic response at low total strain amplitudes. At higher total strain amplitudes, cyclic softening from the onset of deformation was observed. However, the presence of Al 3 Ti blocks led to a very slight cyclic hardening followed by softening at total strain amplitude of 0.4%. Moreover, the intermetallic Al 3 Ti blocks reduced the fatigue life of in situ composites as they promoted microscopic cracking during cyclic deformation. Finally, the fatigue life data of in situ composites can be described by the Coffin–Manson relationship.

Microstructure and properties of SiCw/6061 aluminium alloy composites after compression at temperatures around solidus of matrix

Abstract The effect of compressive deformation at temperatures around the solidus of the matrix on the microstructure and properties of SiCw/6061 aluminium alloy composites was investigated. It was found that the temperature, strain rate, and amount of deformation affect whisker distribution and breakage, densification and uniformity of composites, and SiCw/matrix alloy interfacial bonding. The microstructural evolution due to compression affects the properties of the composites, which is considered to be the most important aspect for evaluating high temperature plastic forming of the composites. The optimum parameters for compressive deformation were determined by analysing the microstructure and the properties of the composites.

Microstructure and Tensile Properties of Al Hybrid Composites Reinforced with SiC Whiskers and SiC Nanoparticles

2024Al hybrid composites reinforced with 20vol% SiC whiskers and 0vol%, 2vol%, 5vol% and 7vol% SiC nanoparticles respectively, were fabricated by squeeze casting technique. The results show that the reinforcements distribute homogeneously in the matrix of the as-cast composites. Hot extrusion leads to a directional distribution of the SiC whiskers and a more homogenous spatial distribution of the SiC nanoparticles in the composites. Tensile test indicates that the tensile strength and modulus of the composites increase with increasing content of the nanoparticles and raises further after extrusion.

Effect of aging treatment on mechanical properties of (SiCw+SiCp)/2024Al hybrid nanocomposites

2024Al based composites reinforced by a hybrid of SiC whisker and SiC nanoparticle were fabricated by a squeeze casting route. In the (SiCw+SiCp)/Al composites, the volume fraction of SiC whisker is 20% and that of SiC nanoparticle is 2%, 5% and 7%, respectively. The as cast composites were solution treated followed by aging treatment. The experimental results show that the SiC nanoparticles are more effective in improving the hardness and tensile strength of the composites than SiC whiskers. The hardening kinetics of the composites is enhanced by reinforcements addition and the peak aging time is 4-5 h. The hardness of all the hybrid composite decreases at the initial aging stage, suggesting that dislocation recovery softening process coexists with precipitation hardening. DSC study shows that the GP zone formation of the hybrid composites is suppressed.

Investigation of compression of SiCw/6061Al composites around the solidus of the matrix alloy

Abstract Compression test of SiCw/6061Al at the temperatures around the solidus of matrix alloy has been studied. Compression flow stress increases with increasing strain rate according to a power law σ=K ϵ m . At temperatures lower than the solidus of matrix, the m value is 0.32 and the activation energy of deformation is almost the same as that of aluminum self-diffusion, indicating a dislocation motion controlled by lattice diffusion deformation mechanism of the composite. At temperatures slightly higher than the solidus of the matrix, the m value is 0.5 and the activation energy of deformation is much higher than that of the self-diffusion of aluminum, indicating a grain boundary and interfacial sliding deformation mechanisms of the composite.

Wearing resistance of in-situ Al-based composites with different SiO2/C/Al molar ratios fabricated by reaction hot pressing

Abstract The in-situ Al-based composites with different SiO 2 /C/Al molar ratios were fabricated by reaction hot pressing. The dry sliding wear characteristics of the composites were investigated using a pin-on-disc wear tester. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to investigate the surface composition and its morphology. The results show that when the SiO 2 /C/Al molar ratio is 3:6:9, more in-situ synthesized Al 2 O 3 and SiC along with Si particles are produced, and Al 4 C 3 is prevented completely from the Al–SiO 2 –C system. Thereby, a significant improvement of wear resistance is obtained. When the sliding velocity increases from 0.4 to 1.6 m/s, the wear loss decreases gradually. With increasing the normal load, the wear loss increases as well. Ploughing, craters and micro-grooving are observed as dominant abrasive wear mechanisms. Whereas, when a high velocity is employed, only the oxidation mechanism controls the wear behavior of the composites.

High Temperature Mechanical Behavior and Microstructure of α-Si3N4w/4032Al Composite Fabricated by Squeeze Casting

The effect of compressive deformation parameters such as temp erature and strain rate on the microstructures and the mechanical behavior of -Si3N4 whisker reinforced 4032 aluminum alloy composite was investigated. The compressive temperatures involve below and above the solidus temperature of the -Si3N4w/4032Al composite, which was determined by Differential Scanning Calorimeter (DSC). The results show that the flow stre ss of the -Si3N4w/4032Al composite are much higher than that of the unreinforced 4032Al alloy at w temperatures, but this difference becomes quite small at higher temperatures. Flow st ress of the composites enhances with decreasing compressive temperature and increasing strain rate. Strain softening appears during compressive deformation in all the testing conditions. Microstructure observations by SEM and TEM indicate that the rotation and breakage of the whiskers toget her with the dynamic recovery of matrix alloy during compressive deformation are responsible for all the mechanical behavior indicated above. In addition, there are interfacial reactions between th matrix alloy and the Si 3N4 whiskers due to segregation of the alloy elements near the matr ix/reinforcement interfaces. The compressive deformation mechanisms of the -Si3N4w/4032Al composite are also discussed preliminarily. Introduction Aluminum composites reinforced with ceramics whisker exhibit a uniq ue combination of high specific strength and modulus [1]. Among various reinforcements, sili con nitride is widely used because of its high modulus and strengths, excellent thermal resistance, and good compatibility with the aluminum matrix. Compressive deformation is a valuable way to study the plastic deformation of metal matrix composites. There have been some reports about the compressive deformation behavior of the SiCw/Al composites [2,3]. However, almost all the re s arches about the plastic deformation behavior have been carried out by tensile tests at el ev t d temperatures [4-6], and no research has been reported about the compressive deformation of the Si 3N4w/Al composites. The focus of this study is mainly on the compressive characteristics and the effects of deformation parameters on the microstructure and compressive deformation behavior of the Si 3N4w/Al composites. Experimental Materials and Procedures -Si3N4w/4032Al composites with 20% volume fraction of the reinforcement wer e fabricated by squeeze casting. The 4032 alloy was selected as the matrix with the composition shown in Table 1. The reinforcement materials were -Si3N4 whiskers with an average diameter of 0.5 m and an average length of 20 m. The solidus temperature of the composite was determined by using D SC at different heating rates. Compressive deformation behavior of the com posite at elevated temperatures was studied by using a Gleeble1500 Thermal Simulat or. The deformation temperatures are from 500 C to 580 C, and the strain rates used in the compressive tests are from 0.094 s to 1.00 s. The microstructure of the composites compressed in different condi tions was observed by means of SEM and TEM. Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 249, pp 239-244 doi:10.4028/www.scientific.net/KEM.249.239

Deformability of a SiCw/6061Al composite during high strain rate compression at elevated temperatures

The deformability of SiCw/6061Al composite during high strain rate compression has been investigated at elevated temperatures around the solidus of the matrix alloy. The results show that the maximum deformability was obtained at 580°C which is near the solidus of the matrix. Analysis of the results indicates that the composites deformed at 580°C have the largest strain rate sensitivity (m value) and the lowest threshold stress, both of which lead to the maximum deformability. Microstructure observation shows that microcracks were formed at the interfaces in the composites deformed at 540°C and 620°C, whereas, in the composite deformed at 580°C, microcracks were rarely found because of the low stress concentration at the interfaces due to the presence of a small amount of liquid. It is suggested that the presence of an adequate amount of liquid phase gives rise to the effective accommodation required for grain boundary sliding for the composite, and thus directly affects the deformability of SiCw/6061Al composite.

In situ (α-Al2O3+ZrB2)/Al composites with network distribution fabricated by reaction hot pressing

In situ (α-Al2O3+ZrB2)/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis (DTA) was used to study the reaction mechanisms in the Al–ZrO2–B system. X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX) were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechanical properties was investigated. The results show that the optimum sintering parameters to complete reactions in the Al–ZrO2–B system are 850°C and 60 min. In situ-synthesized α-Al2O3 and ZrB2 particles are dispersed uniformly around Al particles, forming a network microstructure; the diameters of the α-Al2O3 and ZrB2 particles are approximately 1–3 μm. When the size of Al powder increases from 60–110 μm to 150–300 μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of reinforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of the in situ (α-Al2O3–ZrB2)/Al composites from Hv 163 to Hv 251.

Preparation and Characterization of Diamond/Cu Composites

Diamond/Cu composites from the direct combination of diamond and Cu show low thermal conductivities due to weak interface. And copper coating is coated on diamond particle surfaces to modify and enhance the interface wetting between diamond and copper through electroless plating. Copper matrix composites reinforced with copper-coated diamond particles were produced by powder metallurgy. A high thermal conductivity of 370 W/m/K was achieved in the 30vol.%Cu-coated diamond/Cu composites. The lowest CTE is 9.65 × 10−6K−1. The greatly enhanced thermal conductivity is ascribed to the copper coating. Copper coating on diamond particles is therefore an effective way to enhance the thermal conductivity of diamond/Cu composites.