题目: New approach to introduce L12-ordered precipitation to alumina-forming austenitic heat-resistance steels

　　报告人: 赵冰冰

　　       上海交通大学材料学院高性能金属材料研究所

　　地点：李薰楼249会议室

　　时间：2015.08.24 （周一）上午10：00

　　报告摘要：

Alumina-forming austenitic (AFA) heat-resistance steels firstly developed by Yamamoto et al. at Oak Ridge National Laboratory have been reported as a new promising class of steels with potential for use in high temperature applications in recent years. The superior oxidation resistance of AFA steels in water vapor at elevated temperatures results from the formation of an alumina protective scale, which is much more stable than the conventional chromia scale. The creep resistance of AFA steels is improved mainly by precipitation strengthening. Besides modifying the typical existing precipitates, introduction of coherent L12-ordered precipitate is highly desired. L12-ordered phase gamma prime (g’) is the most important precipitate for high-temperature strengthening in Ni-based superalloys. It is well-known that g’-Ni3Al precipitates can be introduced into AFA steels by increasing the Ni content or addition of Ti element, based on previous knowledge. In the present work, we demonstrate that addition of 2.8 wt. % Cu to an alumina-forming austenitic (AFA) stainless steel promotes the formation of an L12-ordered phase with the dominating elements Ni, Cu and Al, instead of B2-NiAl and Cu-rich phases as demonstrated by some previous works. Owing to the similar size and distribution of MC carbides in the alloys with and without Cu, the creep resistance improvement of the AFA steel was associated with the occurrence of coherent L12-ordered Ni-Cu-Al precipitates. Systematic phase equilibrium calculation in the Fe-Ni-Cu-Al quaternary system by JMatPro shows that Cu is an L12 structure stabilizing element, which increases the precipitation temperature of the L12 phase from the g matrix. This opens up new opportunities to promote the formation of L12-ordered phase in Fe-based austenitic heat-resistance steels and benefit high-temperature mechanical properties.