DD9单晶高温合金拉伸性能各向异性

TENSILE ANISOTROPY OF SINGLE CRYSTAL SUPERALLOY DD9

采用OM,SEM和TEM研究了[001],[011]和[111]取向第三代单晶高温合金DD9组织,在拉伸试验机上测试了3种取向760和1100℃下的拉伸性能.结果表明,在垂直于晶体生长方向的截面上,[001],[011]和[111]取向DD9合金铸态枝晶形貌、热处理态γ'相形状不同;随着温度的升高,合金的抗拉强度与屈服强度降低,各向异性减弱;除1100℃下[001]取向屈服强度略低于[011]取向,[001]取向DD9合金抗拉强度与屈服强度分别高于[011]和[111]取向合金;[001],[011]和[111]取向DD9合金760℃下拉伸断口呈类解理特征,1100℃下断口为韧窝断裂特征;760℃下DD9拉伸试样在基体通道内含有浓密的位错,[001]取向在γ'相内出现了层错,1100℃下[001]与[111]取向在基体通道内和γ'相内累积了大量浓密的位错网,[011]取向出现了大量的形变孪晶带.

The Ni-based single crystal superalloys are widely used in key hot section parts of advanced aero engine due to the superior high temperature mechanical properties. Multi-axial stresses resulting from complex temperature and stress state happen frequently in blades during service, thus the mechanical properties of three orientations need to be studied. However, most of these works are conducted in the first and second single crystal superalloys and there is rare report concerning the third single superalloys. Therefore, in this work the microstructures and tensile properties of the third generation single crystal superalloy DD9 with [001], [011] and [111] orientations were investigated by OM, SEM, TEM and tensile testing machine at 760 and 1100 ℃. The results show that ascast dendritic structures and heat treated γ＇ of DD9 alloy with three orientations are different on the section perpendicular to the crystal growth direction. With rising of temperature, the ultimate tensile strength and yield strength decrease and tensile anisotropy drops obviously. The ultimate tensile strength and yield strength of DD9 alloy with[001] orientation are higher than those with [011] and [111] orientation except that the yield strength with [001] orientation is slightly lower than that with [011] orientation. With temperature increasing, the fracture characteristic transforms from quasi-cleavage at 760 ℃ to dimple at 1100 ℃. At 760 ℃, very high density dislocations appear in the matrix channels with [001], [011] and [111] orientations, but some stacking faults are present only in γ＇ particles with [001] orientation. At 1100 ℃, the high density dislocation networks resulted in the matrix channels and particles of the alloy with [001] and [111] orientations, while a large number of deformation twins are found in samples with [011] orientation.