粉末高温合金中SiO2夹杂物与基体的界面反应机理及对其变形行为的影响

Interface Reaction Mechanism Between SiO2 and Matrix and Its Effect on the Deformation Behavior of Inclusions in Powder Metallurgy Superalloy

通过人工植入夹杂物的方法,采用SEM、EPMA、TEM、纳米压痕和微纳CT研究了FGH96粉末高温合金中30和60μm SiO2夹杂物在粉末态、热等静压(HIP)和热挤压(HEX)过程中形貌、尺寸以及化学成分的演变规律,深入揭示了SiO2夹杂物与基体发生界面反应的机理,定量研究了夹杂物在粉末态、HIP态以及HEX态下尺寸的变化,表征了夹杂物在挤压棒材中的三维形貌。结果表明,在粉末态时,夹杂物呈长条状或板条状;在HIP过程中,夹杂物与基体发生了置换反应,形成了内部Ti O2、外部Al2O3并弥散分布于γ基体的复合夹杂物,确定了形成氧化物的物相种类,揭示了界面反应机理,同时,30μm SiO2周围未出现γ’相贫化区,60μm SiO2周围形成了γ’相贫化区,合金基体较γ’相贫化区具有较高弹性模量和纳米硬度,γ’相贫化区为软化区,反应后30和60μm SiO2夹杂物尺寸分别约为35和75μm,体积得到进一步增大;在挤压过程中,60μm SiO2由于贫化区的存在表现出与30μm SiO2不同的变形行为,并通过SEM观察统计的夹杂物尺寸与理论计算和微纳CT测试结果进行了对比验证。

Powder metallurgy(P/M)Ni-based superalloy has been the most important material for high-temperature structural application in turbine disc owing to its good tensile and creep properties.However,the inclusions in P/M superalloy have an important impact on the safety and reliability of superalloy.By means of implanting SiO2 inclusions artificially,the evolution rule of morphology,size and chemical composition of 30 and 60μm inclusions in FGH96 superalloy during powder,hot isostatic pressing(HIP)and hot extrusion(HEX)processes was investigated by SEM,EPMA,TEM,nanoindentation and MicroCT.The interfacial reaction mechanism between inclusions and matrix alloy was revealed deeply,the size change of inclusions during different stages was studied quantitatively,and the 3 D morphology of inclusions was characterized.The results show that the inclusions in powder stage are long stripe or plate-likeshape,the displacement reaction happened in the process of HIP,which produced the composite inclusions with Ti O2 inside and Al2 O3 outside dispersed uniformly in theγmatrix,and the phase types of oxides were confirmed,furthermore,the reaction mechanism was figured out.Meanwhile,the denuded zone ofγ’phase appeared around the inclusions with the dimension of 60μm,but not 30μm.The alloy matrix had higher elastic modulus and hardness than the denuded zone ofγ’phase,implying that the denuded zone was softened zone.After the reaction,the dimension of inclusions became larger,the average size of 30 and 60μm inclusions were 35 and 75μm,respectively.During the HEX,owing to existence of the denuded zone,60μm inclusions had different deformation behaviors with 30μm inclusions,and the dimension of inclusions obtained from statistics by SEM was used to contrast and validate with the results from formula calculation and Micro-CT.