Grain-boundary precipitation in Allvac 718Plus
- 作者：E.J. Pickering
- 关键词：Nickel alloys ; Crystal structure ; High-angle annular dark field (HAADF) ; Cellular growth ; Misorientation
- 刊名：Acta Materialia
- 出版年：2012
- 期刊代码：1_13596454
- 类别：ms
- 出版时间：April, 2012
- 卷：60
- 期：6-7
- 页码：2757-2769
- 文件大小：1939 K
摘要
Allvac 718Plus is a newly developed nickel-based superalloy designed to replace Inconel 718 in static and rotating applications in gas turbine engines. Fine 纬鈥?precipitates act as its principal strengthening phase and a second plate-like phase is generally present at grain boundaries. This has been reported to be the 未 phase (Niub>3 ub>Nb, D0ub>a ub>, orthorhombic), and is used to pin grain boundaries and improve resistance to intergranular fracture. In Allvac 718Plus non-uniform precipitation of a 未-like phase was observed along the grain boundaries; however, no relation was found between grain-boundary misorientation and the occurrence of precipitation. The crystal structure and chemistry of this phase was found to be different from the orthorhombic Niub>3 ub>Nb 未 phase reported previously in Inconel 718 and Allvac 718Plus. The true structure was found to be consistent with the hexagonal 畏-Niub>3 ub>Ti D0ub>24 ub> structure, but its chemistry was close to Niub>6 ub>AlNb with partial ordering of Al and Nb over the prototype Ti sites. It was found that the serrated boundaries observed in the alloy were a result of discontinuous precipitation of 畏-Niub>6 ub>AlNb, which was a predominant precipitation mechanism throughout the microstructure.