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Dheerendra Kumar Dwivedi A. Sharma T. V. Rajan 《Materials and Manufacturing Processes》2005,20(5):777-791
In this paper, the influence of silicon particle morphology on mechanical properties of two piston alloys has been reported. Alloys having nominal composition Al-12%Si-1%Ni-0.8%Cu-0.6%Mg (LM13) and Al-17%Si-1%Ni-0.8%Cu-0.6%Mg (LM28) were prepared by melting and casting. The morphology of silicon crystals was changed using additives during the melt treatment and subsequently by heat treatment. Mechanical properties such as hardness, ductility, and tensile strength of experimental alloys were tested. Test results showed that the melt treatment and heat treatment of both the alloys increased the tensile strength, hardness, and ductility. However, the influence of melt treatment on mechanical properties was not as significant as that of heat treatment. Tensile strength and ductility of LM13 was found to be higher than the LM28 alloy under similar conditions. Hardness of LM28 was higher than the LM13 alloy. Optical and SEM studies showed a change in eutectic silicon morphology on melt treatment of LM13. However, change in morphology of primary silicon particles was not significant as for LM28. Heat treatment of both alloys caused spheroidization and better distribution of eutectic silicon crystals. Sharp-edged primary silicon particles were rounded off after the heat treatment of LM28. Scanning electron microscopy (SEM) of tensile fractured surfaces was carried out to study the influence of microstructure on fracture mode. Heat treatment of both alloys promotes dimple fracture. However, as-cast and melt-treated alloys show predominantly cleavage fracture. 相似文献
33.
The propagation of short cracks in the neighbourhood of grain boundaries have been investigated using a technique were the crack is modelled by distributed dislocation dipoles and the plastic deformation is represented by discrete dislocations. Discrete dislocations are emitted from the crack tip as the crack grows. Dislocations can also nucleate at the grain boundaries. The influence on crack growth characteristics of the distance between the initial crack tip and the grain boundary has been studied. It was found that crack growth rate is strongly correlated to the dislocation pile-ups at the grain boundaries. 相似文献
34.
How does snow's anisotropic directional reflectance affect the mapping of snow properties from imaging spectrometer data? This sensitivity study applies two spectroscopy models to synthetic images of the spectral hemispherical-directional reflectance factor (HDRF) with prescribed snow-covered area and snow grain size. The MEMSCAG model determines both sub-pixel snow-covered area and the grain size of the fractional snow cover. The Nolin/Dozier model analyzes the ice absorption feature that spans wavelength λ≅1.03 μm to estimate snow grain radius when the pixel is fully snow-covered. Retrievals of subpixel snow-covered area with MEMSCAG are progressively more sensitive to the HDRF as grain size decreases, solar zenith angle increases, and fractional snow cover increases. The model overestimates snow cover in the forward reflectance angles by up to +20% and underestimates it in the backward reflectance angles by as much as −15%. Grain size retrievals from both MEMSCAG and Nolin/Dozier are more sensitive to anisotropy as grain size and solar zenith angle increase. MEMSCAG retrievals of grain size are insensitive to snow-covered area. The largest inferred grain sizes occur around a peak in the backward reflectance angles and the smallest generally occur at the largest view angles in the forward direction. Retrievals of albedo from MEMSCAG and Nolin/Dozier are similarly sensitive to anisotropy, with albedo errors up to 5% for a 30° solar zenith angle and up to 10% at 60°. The albedo differences between the two models are less than 0.015 for all grain sizes and solar zenith angles. 相似文献
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钼对钨-镍-铁高比重合金性能和组织的影响 总被引:1,自引:0,他引:1
在95wt%W-3.5wt%Ni-1.5wt%Fe粉末混合料中加入纯钼粉,经成型烧结后,发现当钼的加入量超过1wt%时,能提高合金的强度,而合金的延伸率、截面收缩率及密度降低,合金的钨晶粒细化;钼溶解在基体相及钨相中,有固溶强化的作用。 相似文献
38.
在利用高分辨电子显微术研究 Si_3N_4结构过程中,有了新的发现。这些发现包括纳米级裂纹、超结构、纳米畴和辐射损伤等。纳米级裂纹是晶粒中纳米大小的裂纹,它可能是导致穿晶断裂的裂纹。超结构可能影响Si_3N_4晶粒的力学性能,我们在研究中发现了三种超结构。纳米畴是晶粒中一种新的结构缺陷,在研究中我们发现了两种这类畴。也研究了辐射损伤,发现 α-Si_3N_4比β-Si_3N_4更易于受到辐射损伤,这说明β-Si_3N_4比α-Si_3N_4结构更稳定。还仔细地研究了 Si_3N_4陶瓷的晶界,结果指出,晶界工程对于改善 Si_3N_4陶瓷的力学性能是强有力的手段。 相似文献
39.
《Materials and Manufacturing Processes》2007,22(6):710-714
The effect of SiO2 addition on densification and grain-growth behavior of 8YSCZ/SiO2 composites was investigated using high purity 8 mol% yttria-stabilized cubic zirconia powders (8YSCZ) doped with 0, 1, 5, 10 wt% SiO2. The specimens were sintered at 1400°C for 1 hour. It was seen that the sintered density increased with SiO2 content up to 1 wt% and further increase in SiO2 content led to a decrease in density. The enhanced density with increasing SiO2 content up to 1 wt% could be mainly attributable to liquid phase sintering. For grain growth measurements, the specimens sintered at 1400°C were annealed at 1400, 1500, and 1600°C for 10, 50, and 100 hours. The experimental results showed that the grain growth in 8YSCZ/SiO2 composites occurred more slowly than that in undoped 8YSCZ. Also, the grain growth rate decreased with increasing SiO2 content. The grain growth exponent value and the activation energy for undoped 8YSCZ were found to be 2 and 289 kJ/mol, respectively. The addition of SiO2 raised the grain growth exponent value to 3, and activation energy for the grain growth process was increased from 289 to 420 kJ/mol for the addition of SiO2 from 0 to 10 wt%. 相似文献
40.
《Materials Science & Technology》2013,29(12):1802-1808
AbstractIn the present research, a combined forward extrusion–equal channel angular pressing was developed and executed for the deformation of a plain carbon steel. In this method, two different deformation steps, including forward extrusion and equal channel angular pressing, take place successively in a single die. The deformation process was performed at different deformation start temperatures (800, 930 and 1100°C). Three-dimensional finite element simulation was used to predict the strain and temperature variations within the samples during deformation. With microstructural observations and the results of finite element simulation, the main grain refinement mechanisms were studied at different deformation temperatures. The results show that the forward extrusion–equal channel angular pressing is effective in refining the ferrite grains from an initial size of 32 μm to a final size of ~0·9 μm. The main mechanisms of grain refinement were considered to be strain assisted transformation, dynamic strain induced transformation and continuous dynamic recrystallisation, depending on the deformation temperature. 相似文献