新型镍基粉末冶金高温合金中γ'相扇形组织形成以及演化行为研究

MORPHOLOGICAL CHANGES BEHAVIOR OF FAN-TYPE STRUCTURES OF γ' PRECIPITATES IN NICKEL-BASED POWDER METALLURGY SUPERALLOYS

对新型镍基粉末冶金高温合金FGH98I进行不同工艺热处理,采用场发射扫描电镜和透射电镜等研究了合金中扇形组织的形成和演变.结果表明,FGH98I合金中扇形组织是由手指形二次γ'相枝晶和其间的γ基体组成,其形成具有择域特性,高度过饱和晶界的成分偏聚区可作为非均匀形核核心,通过自身浓度梯度扩散控制其长大、发展.标准时效处理使扇形组织长大和粗化,高温时效处理使扇形γ'相发生形态失稳,逐渐变成低能状态的稳定立方形状γ'相.

The variety and complexity of γ＇ phase morphological changes in heat treatment process of nickel-based powder metallurgy （P/M） superalloy, which contains high volume percentage γ＇ strengthening phase, is one of hot issues which material researchers focused on. γ＇ phase morphological changes have important effect on the strength, toughness, high-temperature creep and fatigue property of alloy. Based on the research of heat treameat process in the thirdly nickel-based P/M superalloy （FGH98I）, the researcher find that there are γ＇ fan-structure in solution heat treatment at different cooling rates, and follow-up treatment have obvious influence on γ＇ fan-structure morphology. Therefore, it is necessary to research scientifically and penetratingly on the formation conditions, formation mechanism, and the effects of different heat treatment process of γ＇ fan-structure which exist as a kind of special organization morphology. The formation and evolution of fan-type structure in a new type nickel-based P/M superalloy FGH98I was studied by means of FESEM and TEM. The results show that the fan-type structure in alloy FGH98I consists of finger-shaped γ＇ dendrites and the γ matrix between them. It forms only in a selection area characteristic, nucleates inhomogeneously in the chemical segregation area at different scales on highly supersaturated grain boundary and develops by own concentration gradient diffusion. The standard aging makes the fan-type structure growing up and coarsening. The γ＇ fingers become unstable, transforming into stable cubic shapeγ＇ in low-energy state after high-temperature aging.