Chengbao Liu Jian Shen Jian Zhang Langhong Lou
材料科学技术（英文）
A nickel base single crystal (SC) superalloy was directionally solidified using liquid metal cooling (LMC) process at various withdrawal rates. The microstructure was refined as increasing the withdrawal rate from 3 to 12 mm/min. However, higher withdrawal rate of 15 mm/min induced the formation of stray grains. Size and volume fraction of the eutectics were found to decrease with the increasing in withdrawal rate. After solution heat treatment at 1250°C, un-dissolved eutectic was observed in specimens. High temperature creep rupture life was observed to be very sensitive to the fraction of these remaining eutectics. Creep rupture tests at 1000°C/235 MPa showed that refined microstructure and low fraction of the remaining eutectic lead to significant improvement of the rupture life.
关键词:
Eutectic
,
single crystal superalloy
,
liquid-metal-cooling
,
withdrawal rate
Guanghui MENG
,
Xin LIN
,
Weidong HUANG
材料科学技术（英文）
Based on the Jackson and Hunt’s analysis, the selection of lamellar spacing in regular eutectics was reexamined at low velocity. The isothermal assumption was released and the effective interface undercooling was determined by the weighted average of the eutectic phases. It is found that the lamellar spacing minimized the effective interface undercooling depends only on the intrinsic characteristics of a given system at a fixed velocity. In addition, the selection of lamellar spacing is related to the relationship between the average interfacial undercoolings of the eutectic phases and the lamellar spacing. The selected lamellar spacing obviously deviated from that predicted by the Jackson and Hunt’s analysis if the variation of the average interfacial undercoolings of the solid phases with the lamellar spacing was markedly different at a constant growth rate.
关键词:
Solidification
,
null
,
null
,
null
杨金华
,
刘占军
,
王立勇
,
郭全贵
,
宋进仁
,
刘朗
新型炭材料
通过加热TiB2及 ZrB2粉末与等静压炭块至共熔点以上的方法制备出新型炭/陶复合材料涂层 TIB、ZRB-1与ZRB-2。结果表明,所制自生复合材料涂层的表层与内部结构明显不同,表层由B掺杂的高度有序石墨构成,内部由TiB2-C或ZrB2-ZrC-C合金组成。 TIB、ZRB-1与ZRB-2涂层中石墨的d002值分别为0.3359、0.3360与0.3354 nm,接近或等于单晶石墨的d002值(0.3354 nm),表明高度有序石墨结构的形成。3种涂层内部石墨的拉曼光谱中D峰、D'峰明显,2D峰强度低及G峰向高波数偏移,这些特征是由石墨碳网格结构中B掺杂所致。此外,ZrB2粒径小有利于涂层表层应力的释放。
关键词:
石墨
,
陶瓷
,
涂层
,
自生复合材料
