短时超温对定向凝固DZ125合金微观组织和拉伸性能的影响

Overheating Effect on Microstructure and Tensile Property of Directionally Solidified DZ125 Superalloy

超温是航空发动机涡轮叶片一种常见的服役损伤形式,然而目前国内针对涡轮叶片用定向凝固高温合金在超温条件下的微观组织与力学性能的研究还比较有限。以定向凝固DZ125合金为研究对象,研究了DZ125合金在1100~1270℃温度范围内热处理3 min^2 h的微观组织退化规律,并开展了1100~1240℃温度范围内的拉伸性能测试。结果表明:1100~1230℃温度范围内γ′相短时间便大量溶解,温度超过1160℃时仅5 min后γ′相体积分数便进入稳定状态。随着超温温度升高,γ′相溶解加剧,直至1230℃下枝晶干γ′相完全溶解。温度超过1240℃时残余共晶γ′相开始回溶,1245℃时富Hf元素的MC2碳化物发生初熔。同样超温热暴露参数下空冷后的γ′相体积分数比水冷样品高约10%。由于超温导致的γ′相大量溶解,使得DZ125合金的拉伸屈服强度从1100℃下的129 MPa降到了1240℃的7 MPa,抗拉强度则从168 MPa降到了24 MPa。超温使得DZ125合金微观组织迅速退化,进而导致力学性能的大幅度降低。

Overheating is a common service damage form for aero-engine turbine blades,while limited domestic studies focused on the effect of overheating on the degradation of microstructure and mechanical properties of directionally solidification superalloy.In this paper,microstructural characterization was conducted in a widely used directionally solidification superalloy DZ125 after overheating at 1100 ℃ to 1270 ℃ for 3 min to 2 h;tensile tests were also carried out at 1100 ℃ to 1240 ℃.The results showed that the γ’phase dissolved rapidly between 1100 ℃ and 1230 ℃.When the temperature exceeded 1160 ℃,the volume fraction of γ’ phase reached steady state after only 5 min as the overheating temperature rose,more γ’ phase dissolved and γ’ phase in the dendrites completely dissolved at 1230 ℃.The residual eutectic γ’ phase began to dissolve at 1240 ℃.The MC2 carbides with Hf enrichment suffered incipient melting at 1245 ℃.In addition,cooling method also affected the volume fraction of γ’ phases,air cooling always resulted in a 10% higher of volume fraction than water cooling at the same overheating temperature.Because of γ’ dissolution,the tensile properties gradually weakened with overheating temperature increasing from 1100 ℃ to 1240 ℃:the yield strength of DZ125 alloy decreased from 129 MPa at 1100 ℃ to 7 MPa at 1240 ℃,and the corresponding tensile strength decreased from 168 MPa to 24 MPa.Serious microstructural degradation of DZ125 alloy caused by overheating led to a significant damage of mechanical properties.