Deformation behaviour of recrystallized Ni3Al

Deformation behaviour of the recrystallized Ni₃AI with non-stoichiometric and stoichiometric compositions have been investigated. Recrystallization microstructures in non-stoichiometric Ni₃AI are composed of the Ll₂ ordered and a small amount of the f c c disordered . It is shown that the large elongation of non-stoichiometric Ni₃AI is due to -phase existing at recrystallized t'- grain boundaries. Recrystallization microstructures in stoichiometric Ni₃AI are confirmed to be a single phase of . Coarse-grained stoichiometric Ni₃AI shows considerable ductility, although the fine-grained compound is brittle. The ductility may be related to the low yield strength in the coarse-grained samples.     

Growth of recrystallising grains in boron doped Ni76 Al24

Abstract

Cold rolled boron doped Ni₇₆ Al₂₄ was partially recrystallised at 850, 875, and 900°C. The recrystallised volume fraction and the interfacial area between recrystallised and unrecrystallised parts were determined as functions of time. The analysis of results showed the growth rates of recrystallised grains to be dependent on temperature, but independent of time. The activation energy for the transformation was 168 kJ mol^-1 and that for growth was 87 kJ mol^-1. The activation energy for growth was much less than that for diffusion and was dependent on the degree of cold working. This has been attributed to the strong interaction of boron with the structural defects produced by cold working.     

Geometry and grain size effects on the fracture behavior of sheet metal in micro-scale plastic deformation

The demand on micro-parts is significantly increasing in the last decade due to the trend of product miniaturization. When the part size is scaled down to micro-scale, the billet material consists of only a few grains and the material properties and deformation behaviors are quite different from the conventional ones in macro-scale. The size effect phenomena occur in micro-scale plastic deformation or micro-forming and there are still many unknown phenomena related to size effect, including geometry and grain size effects. It is thus critical to investigate the size effect on deformation behavior, especially for the fracture behavior in micro-scale plastic deformation. In this research, tensile test was conducted with annealed pure copper foils with different thicknesses and grain sizes to study the size effects on fracture behavior. It is found that flow stress, fracture stress and strain, and the number of micro-voids on the fracture surface decrease with the decreasing ratio of specimen size to grain size. Based on the experimental results, dislocation density based models which consider the interactive effect of specimen and grain sizes on fracture stress and strain are developed and their accuracies are further verified and validated with the experimental results obtained from this research and prior arts.     

Non-equilibrium grain boundary co-segregation of Boron and Magnesium in Ni3Al

The non-equilibrium grain boundary co-segregation of boron and magnesium in Ni₃Al–B–Mg alloys was determined by Auger electron spectroscopy (AES) in conjunction with ion sputtering in a cooling rate range of 0.05–269 K/s from temperatures of 1023, 1223 and 1373 K. The analytical expressions of diffusion rate equations describing non-equilibrium segregation process based on the concept that mobile solute-vacancy complexes migrating to grain boundaries is responsible for non-equilibrium grain boundary segregation of solute atoms in an alloy was used to simulate well the experimental results. The diffusion coefficients for boron atoms, boron-vacancy complexes, magnesium atoms and magnesium-vacancy complexes were determined, and the binding energy of boron-vacancy and magnesium-vacancy complexes was estimated.     

Effect of the ferrite grain size on the deformation and fracture characteristics of a structural steel

Strength of Materials -     

取向电工钢的低温拉伸变形和断裂行为

测量了普通取向电工钢室温至300℃的拉仲性能并观察了拉伸断口形貌.对比分析和定量计算表明,随着拉伸温度的升高P原子在晶界偏聚的程度逐渐降低,使得断口形貌的沿晶特征减弱、解理特征增强.拉伸温度超过100℃以后沿晶断裂特征消失,基体的屈服强度逐渐低于解理强度,使得断口形貌解理特征减弱、韧窝特征增强,至190℃转变成完全的韧窝断口.在100℃-160℃范围内拉伸变形时位错滑移会拖曳柯垂尔气团随之迁移,造成了随温度升高延伸率下降,且屈服强度的降幅减缓.