一种[011]取向镍基单晶合金拉伸蠕变中的组织演化

在1040℃,137MPa下对011]取向镍基单晶合金进行蠕变曲线测定,采用SEM观察热处理及蠕变后样品不同晶面的组织形貌,研究了011]取向镍基单晶合金在蠕变期间的组织演化特征,并分析了组织演化的规律及影响因素。结果表明:取向差为4°的011]取向镍基单晶合金经完全热处理后,组织是立方γ′相以共格方式嵌镶在γ基体相中,并沿<100>取向规则排列;在拉伸蠕变期间,合金中γ′相转变成与001]取向平行的纤维状筏形组织。由于施加拉伸载荷,使立方γ′相中的(100)晶面及γ基体相承受挤压力,可排斥较大半径的Al、Ta原子,而在(001)晶面产生较大的晶格扩张应变,可诱捕较大半径的Al、Ta原子,因而促使γ′相沿001]取向定向生长成为纤维状筏形组织。在外加应力作用下,不同晶面γ′/γ两相界面的应变能密度变化是促使发生元素扩散和γ′相定向粗化的驱动力。

Microstructure Evolution of a [011] Orientation Single Crystal Nickel-Base Superalloy during Tensile Creep

By means of measuring creep curves under the applied stress of 137 MPa at 1040 oC and observing the microstructure by SEM after the alloy was heat treated and crept,the microstructure evolution of 011] orientation single crystal nickel-base superalloy during tensile creep was investigated,and the effect factors of the evolution regularity was analyzed. Results show that,after full heat treatment,the microstructure of 011] oriented single crystal nickel-base superalloy consists of the cubic γ′ phase embedded coherently in the γ matrix,regularly arranged along the <100> orientation. During tensile creep,the cubicγ′ phase in the alloy is transformed into the strip-like rafted structure along the direction parallel to 001] orientation. In the action of the applied tensile stress along the 011] orientation,the extrusion stress is applied on the γ phase and (100) crystal plane of the cubic γ′ phase to generate the constricted strain of the lattice,which may exclude the Al and Ta atoms with bigger radius. Whereas,the expanding lattice strain appearing on the (001) crystal plane of the cubic γ′ phase may trap the Al and Ta atoms with bigger radius. Therefore,the cubic γ′ phase is directionally grown into the strip-like rafted structure along the 001] orientation. In the action of the applied stress,the change of the strain energy density in the different interfaces of the cubic γ′/γ phases is thought to be the driving force of the element diffusion and the directional coarsening of γ′ phase.