Hao WANG
,
T.S.YEN
,
Hanrui ZHUANG and Weiying SUN (State Key Lab. on High Performance Ceramics and Superfine Microstructure
,
Shanghai Institute of Ceramics
,
Chinese Academy of Sciences
,
Shanghai
,
200050
,
China)
材料科学技术（英）
The sintering processes of Re-(α' + β')-sialon composites (Re=Sm, Dy, Yb) have been investigated by using a specially designed high temperature dilatometer. The initial densification of various samples starts at about 1200℃, and the maximum shrinkage rate of these sialon composites occurs at about 1500℃. The light rare earth sialon has a noticeably tower densification temperature and a higher final shrinkage. The sirtering kinetics of Re-(α' +β')-sialonare much more complex. The Kingery's liquid phase sintering model appears to be applicable,but the mechanism of mass transport in stage two appears to be changeable. The controlling factor shiffs from solution-precipitation to diffusion when densification process proceeds from the earlier part to the later part of this stage.
关键词:
Hao WANG
,
Xiaoping SONG
,
Xiangdong YAO
,
Haifeng ZHANG
,
Zhuangqi HU
材料科学技术（英）
The crystallization behavior and crystallization kinetics of (Cu60Zr30Ti10)99Sn1 bulk metallic glass was studied by X-ray diffractometry and differential scanning calorimetry. It was found that a two-stage crystallization took place during continuous heating of the bulk metallic glass. Both the glass transition temperature Tg and the crystallization peak temperatures Tp displayed a strong dependence on the heating rate. The activation energy was determined by the Kissinger analysis method. In the first-stage of the crystallization, the transformation of the bulk metallic glass to the phase one occurred with an activation energy of 386 kJ/mol; in the second-stage, the formation of the phase two took place at an activation energy of 381 kJ/mol.
关键词:
Bulk metallic glasses
,
null
,
null
Hao WANG
材料科学技术（英）
Semisolid metal forming has now been accepted as a viable technology for production of components with complex shape and high integrity. The advantages of semisolid metal forming can only be achieved when the feedstock material has a non-dendritic semisolid structure. A controlled nucleation method has been developed to produce such structures for semisolid forming. By controlling grain nucleation and growth, fine-grained and non-dendritic microstructures that are suitable for semisolid casting can be generated. The method was applied to hypoeutectic and hypereutectic Al-Si casting alloys, Al wrought alloys and a Mg alloy. Parameters such as pouring temperature, cooling rate and grain refiner addition were controlled to achieve copious nucleation, nuclei survival and dendritic growth suppression during solidification. The influences of the controlling parameters on the formation of semisolid structure were different for each of these alloy groups. The as-cast structures were then partially remelted and isothermally held. Semisolid structures were developed and followed by semisolid casting into a stepped die.
关键词:
Semisolid processing
,
null
,
null
,
null
