Ezzat S.Elshazly
,
M.El-Sayed Ali
材料科学技术（英）
The isothermal tetragonal-to-monoclinic phase transformation of 3 mol fraction Y2O3–ZrO2 ceramics containing different amounts of Al2O3 during ageing in water at 130℃ for periods of time up to 40 h was investigated to explore the effect of Al2O3 addition on this transformation. The propagation of the transformation into the specimen interiors was suppressed by the addition of Al2O3. The transformation kinetics showed a nucleation and growth mechanism on the specimen surface to be dominant in the low temperature ageing in water environment.
关键词:
Phase transformation
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null
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null
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null
Ming FANG
,
Qinghui LI
,
Fuxi GAN
材料科学技术（英）
The optical absorption properties of phase-change optical recording thin films subjected to various initialization conditions were investigated. The effects of initialization power and velocity on optical constants of the Ge2Sb2Te5 thin films were also studied. The energy gap of Ge2Sb2Te5 thin films subjected to various initialization conditions was also obtained. It was found that the optical energy gap of the Ge2Sb2Te5 thin films increased with either increasing initialization laser power or decreasing initialization velocity, with peak of 0.908 eV at laser power of 1000 mW or initialization velocity of 4.0 m/s, but the continued increasing initialization laser power or decreasing initialization velocity resulted in the decrease of the optical energy gap. The change of the optical energy gap was discussed on the basis of amorphous crystalline transformation.
关键词:
Phase transformation
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null
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null
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null
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Yutuo ZHANG
,
Chunli MO
,
Dianzhong LI
,
Yiyi LI
材料科学技术（英）
A model based on Avrami equation and Scheil’s additivity rule was proposed to simulate the phase transformation in plain carbon steels during continuous cooling in hot strip mill. In this model, a wide range of composition, cooling rate, primary austenite grain size and retained strain has been taken into account. It can be used to calculate the phase fraction transformed at different temperatures during continuous cooling. The phase equilibrium and transformation starting temperature can be determined by using Thermo-Calc and DICTRA. The simulated results containing the transformation at starting and finishing temperatures, Ae1 ,Ae3 and the maximum volume fraction for Q235B, were obtained. The calculated phase volume fractions are in good agreement with the experimental results.
关键词:
Phase transformation
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null
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null
Xin GAO
,
Yufeng ZHENG
,
Wei CAI
,
Su ZHANG
,
Liancheng ZHAO
材料科学技术（英）
The microstructure, phase transformation, compression property and strain recovery characteristics of equiatomic TaRu super high temperature shape memory alloy have been studied by optical microscope, XRD, DTA, compression tests and TEM observations. When cooling the alloy specimen from high temperature to the room temperature, (parent phase)→ (interphase)→ (martensite) two-step phase transformations occur. The microstructure at room temperature show regularly arranged band morphology, with the monoclinic crystal structure. The twinning relationship between the martensite bands is determined to be (101) of Type I. Reorientation and coalescence of the martensite bands inside the variant happened during compression at room temperature. The → reversible transformation contributes mainly the shape memory effect, with the maximum completely recovery strain of 2%.
关键词:
TaRu alloy
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null
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null
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null
Weiping SHEN
,
Fei WANG
,
Zhuohui WU
,
Changchun GE
材料科学技术（英）
This paper presents results of combustion synthesis (Self-Propagating High Temperature Synthesis, SHS) of Si3N4 under nitrogen with argon, hydrogen or ammonia. Higher percentages of α-Si3N4 content were obtained in large size cakes in SHS with hydrogen and ammonia than those with argon. Effect of the auxiliary gases for combustion synthesis of Si3N4 on α phase content, on phase transformation of α-Si3N4 to β-Si3N4 in SHS Si3N4 and on oxygen content in SHS Si3N4 were investigated.
关键词:
Combustion synthesis
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null
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null
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null
Wenchen XU
材料科学技术（英）
Hot compression tests were conducted on a Gleeble-1500 simulator to investigate the hot deformation behavior of BT20 Ti alloy (Ti-6Al-2Zr-1Mo-1V) in the temperature range from 550 to 1000℃ at constant strain rate in the range of 0.01~1 s-1, and then the optimum spinning temperature range was determined. Moreover, tube spinning experiments were executed to verify the reasonability of the optimum temperature range. The results show that the flow stress declines gradually with increasing deformation temperature and decreasing strain rate. In α+β phase region the dynamic recrystallization is the main softening mechanism and in β phase region the hot deformation softening is controlled by dynamic recovery. In α+β phase region with reducing strain rate dynamic recrystallization is fully developed. The optimum temperature of hot spinning is 850~900℃ and that of warm spinning is 600~650℃. Meanwhile, at the temperature above 600℃ tubular workpieces of BT20 Ti alloy have been spun without surface cracks and microstructure inhomogeneity, which proves that the optimum spinning temperature range obtained through hot compression experiments is reasonable.
关键词:
Dynamic recrystallization
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null
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null
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Zhenni ZHOU
金属学报(英文版)
The pearlite transformation in a Mo-containing iron alloy was investigated under 12~T magnetic field. The pearlite transformation was accelerated owing to the application of a strong magnetic field. Pearlite was of degenerated morphology without the presence of a strong magnetic field; but the degeneracy of pearlite is reduced when a strong magnetic field was applied, which may be attributed to the effect of strong magnetic field on faster carbon diffusion and less molybdenum segregation caused by a strong magnetic field.
关键词:
Steels
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Pearlite
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Phase transformation
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Strong magnetic field
Xianglong MENG
,
Wei CAI
,
K.T.Lau
,
L.M.Zhou
,
Liancheng ZHAO
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null
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null
材料科学技术（英）
The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys (SMAs) through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures (Ms) are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.
关键词:
TiNiHf alloy
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null
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null
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