材料期刊网

采用XRD、SEM、EDS和Image-Pro Plus金相分析等方法测定了GH3625合金热挤压管材在不同冷变形量ε下经过800℃时效后δ相的析出含量,研究了冷变形对δ相的析出规律及析出动力学的影响.结果表明,δ相首先在形变孪晶界、晶界以及变形带上形核并析出,随后在晶内形核长大,并且随冷变形量的增加,δ相在变形带上析出量增加;随冷变形量的增加,δ相的形貌从针状向棒状或颗粒状转变;随着时效时间的延长,δ相的平均尺寸不断增大,长大规律符合LSW理论.当时效温度为800℃时,δ相的析出含量与时效时间的关系满足Avrami方程,且随冷变形量的增加,δ相的含量增加,时间指数n减小,δ相析出速率α增加,冷变形促进δ相的析出.Nb的溶质拖曳与δ相的钉扎共同作用抑制晶粒长大.(Σ)=35％时,合金的硬度随保温时间的延长而增加,(Σ)≥50％时硬度未发生明显变化.

GH3625 alloy is a wrought nickel-based superalloy mainly used in aeronautical,aerospace,chemical,nuclear,petrochemical,and marine applications industry due to its good mechanical properties,processability,weldability and resistance to high-temperature corrosion on prolonged exposure to aggressive environments.However,in medium and high temperature environment during longterm service,the γ" is a metastable phase,easily transformed into stable δ phase,or δ phase directly formed in the y matrix so that alloy performance was deteriorated,leading to the result of alloy failure.At the present work,mass fraction of δ phase in GH3625 superalloy hot-extruded tube cold deformed to different reductions and then aged at 800 ℃ for different times,were measured by XRD.The effect of cold deformation on the law and kinetics of δ phase precipitation was investigated by SEM,EDS and ImagePro Plus metallographic analysis.The results show that δ phase first precipitates at the deformation twin and grain boundaries as well as deformation bands,and then precipitates in the grains.The amount of δ phase at the deformation bands increases with the increase of cold deformation.The morphologies of δ phase change gradually from needles to spheroids or rodlike with increasing cold deformation.With the extend of ageing time,the average size of δ phase increases which grows according to LSW theory.At 800 ℃,the relationship between the precipitation content of δ phase and ageing time follows Avrami equation.As cold deformation increases,the content of δ phase increases,the time index n decreases,whereas the δ phase precipitation rate increases.Cold deformation promotes the precipitation of δ phase.The solute drags of Nb in soild solution and pinning of δ phase inhibits the grain growth during ageing process of cold deformed GH3625 superalloy hot-extruded tube.The hardness of the alloy increases with the extension of the holding time at ε =35％ but no obvious change at ε≥50％.