GH2909低膨胀高温合金热处理中的组织演变行为

Microstructure Evolution of GH2909 Low Expansion Superalloy During Heat Treatment

采用SEM、TEM、EPMA及萃取相分析等多种手段相结合对GH2909低膨胀高温合金在标准热处理过程中的组织演变规律进行分析。结果表明,锻态GH2909合金中主要析出相是块状和短棒状含Si的Laves相,Laves相在980℃固溶过程中逐渐发生部分回溶,两阶段固溶后短棒状Laves相基本消失。标准热处理后GH2909合金晶界上出现颗粒状的G相呈断续排列,晶内有盘片状ε相大量析出。基体中有细小的、以Ni和Ti为主要元素的γ′相,结构式为Ni_(2.26)Fe_(0.16)Co_(0.50)Nb_(0.62)Ti_(0.43)Al_(0.02)。GH2909合金中的Laves相、ε相、G相均为富Nb、富Si相,萃取相分析结果表明GH2909合金中30%左右的Si元素在标准热处理后以析出相形式存在,GH2909合金的组织控制中应关注Si元素的作用。

GH2909 alloy is a low expansion superalloy developed on the base of GH2907 alloy.The mass fraction of Si is increased to accelerate the precipitation ofεphase,which improves resistance to stress-induced oxidative brittleness at grain boundaries.Increasing the mass fraction of Si also complicates the types of precipitates,and there is a long-time argument for determining precipitates in GH2909 alloy.The mechanical property is closely related to microstructure and precipitate.This work investigated the microstructure evolution of GH2909 low expansion superalloy during standard heat treatment by SEM,TEM,EPMA,and micro-chemical phase analysis.The Laves phase is the predominant phase in the wrought GH2909 alloy,according to the study.In the GH2909 alloy,the Si-rich Laves phase has a blocky form and a short rod shape.In solution treatment,the Laves phase dissolves gradually.After twostage solution treatment,the short rod-shaped Laves phase almost completely dissolves.Slow cooling is needed to avoid re-precipitation of short rod shape Laves phase during solution treatment because Laves phase is sensitive to the cooling rate.Discontinuous G phase particles decorate grain boundaries after normal heat treatment,and a sizable discal phase precipitates in the matrix.There is also a fine phase rich in Ni and Ti in the matrix with the chemical formula Ni_(2.26)Fe_(0.16)Co_(0.50)Nb_(0.62)Ti_(0.43)Al_(0.02).In the GH2909 alloy,the Laves phase,G phase,andεphase are high in Si and Nb.During precipitation,these phases compete for Si and Nb elements.Furthermore,the micro-chemical phase analysis results demonstrate that 30%of the Si in the GH2909 alloy is finally precipitated.As a result,Si should be given special consideration in the microstructure control of the GH2909 alloy.