Gang Wang
材料科学技术（英文）
The hot deformation behavior of a Ti-47Al-2Cr-2Nb-0.2W-0.15B (at.%) titanium aluminide alloy fabricated by pre-alloyed powder metallurgy has been investigated by using the hot compression tests in the temperature range from 950°C to 1300°C and at the strain rates between 10-3 s-1 and 10 s-1. The processing maps have been established to evaluate the optimum hot processing conditions and reveal the instability regions. It is found that the flow stress of the investigated alloy is a strong function of the temperature and the strain rate. The investigated alloy has the optimum hot-working condition at 950°C and 10-3 s-1, since the material undergoes dynamic recrystallization to produce a fine-grained microstructure. At 1250°C and 10-3 s-1, the
alloy exhibits superplastic deformation. At 1300°C and 10-1 s-1, the cyclic dynamic recrystallization with high temperature grain coarsening takes place. The material undergoes flow instabilities at lower temperatures and higher strain rates, as predicted by the instability criterion. The processing maps demonstrate that the strain significantly affected the instability regions. The manifestations of the instabilities have been observed in the form of microvoids, wedge cracks, and surface fractures.
关键词:
Titanium aluminide
Gang Wang
,
Zbigniew H. Stachurski
金属学报(英文版)
doi:10.1007/s40195-016-0369-2
The homogeneous plastic flow in bulk metallic glasses (BMGs) must be elucidated by an appropriate atomistic mechanism. It is proposed that a so-called concordant shifting model, based on rearrangements of five-atom subclusters, can describe the plastic strain behaviour of BMGs in a temperature range from room temperature to the supercooled liquid region. To confirm the effectiveness of the atomic concordant shifting model, a comparative investigation between the vacancy/atom model and the concordant shifting model is carried out based on the estimation of the strain rate deduced from two models. Our findings suggest that the atomic concordant shifting model rather than the vacancy/atom exchange model can well predict the large strain rate in the superplasticity of BMGs.
关键词:
Bulk
,
metallic
,
glasses
,
Superplasticity
,
Vacancy/atom
,
exchange
,
model
,
Atomic
,
concordant
,
shifting
,
model
,
Strain
,
rate
Gang Wang
,
Vladimir D.Krstic
材料科学技术（英文）
The effect of Y2O3 and the total oxide volume fraction (Y2O3+Al2O3) on density and mechanical properties of low temperature (1770~1940℃) pressureless sintered β-SiC ceramics were presented. The optimum temperature for pressureless sintering of β-SiC was found to be 1850℃ and the optimum content of Y2O3 in the oxides was found to be between 40 and 57 wt pct. The highest sintered density was achieved by adding oxides at 14 vol. pct. Both of the highest strength and fracture toughness were achieved at 14 vol. pct oxide addition and yttria concentrations between 40 and 57 wt pct in the oxides. Hardness, on the other hand, was found to be the highest for samples with 14 vol. pct oxide addition and 64 wt pct Y2O3 in oxides.
关键词:
Y2O3
,
null
,
null
,
null
