表面再结晶晶粒对涡轮叶片DZ4合金疲劳性能的影响

目的 了解表面再结晶晶粒影响涡轮叶片DZ4合金疲劳失效的机制,从而找出提高疲劳寿命的途径.方法 采用我国自主研发的涡轮叶片用定向凝固合金DZ4.对合金表面采用不同压力(0.1、0.3、0.5 MPa)进行喷丸处理,随后进行1220℃的热处理,合金表面塑性变形层发生再结晶形成再结晶晶粒.通过扫描电子显微镜等对不同条件下获得的再结晶微观组织进行观察分析.对于含表面再结晶层的DZ4试样和原始DZ4试样分别开展低周疲劳测试,以获得其循环变形行为和低周疲劳寿命.结果 在较低的喷丸压力下(如0.1 MPa),表层再结晶组织以离散的再结晶晶粒出现.在较高喷丸压力下(0.3 MPa和0.5 MPa),获得了完全的表面再结晶层,而且随喷丸压力的增大,再结晶层厚度增加.疲劳试验结果 显示,在较低喷丸压力(0.1 MPa)下获得的再结晶试样,其疲劳寿命比原始DZ4合金的明显降低;在0.5 MPa下获得的含再结晶层的DZ4试样,具有比原始DZ4合金更高的疲劳寿命.结论 定向凝固合金DZ4表面的再结晶层并不一定会降低其疲劳寿命.在较低喷丸压力(如0.1 MPa)及退火条件下形成的离散状再结晶晶粒对疲劳性能有害,疲劳寿命降低明显.在较高喷丸压力(如0.5 MPa)和退火条件下形成的致密细晶再结晶层,可提高DZ4合金的低周疲劳性能.晶体塑性模型有助于理解和预测再结晶层对疲劳性能的影响.

Effect of Surface Recrystallized Grains on the Fatigue Performance of Turbine Blade DZ4 Alloy

Objective To understand the effect of recrystallization ( RX) on the fatigue failure mechanism of turbine blade DZ4 al-loy, so as to develop a method to improve the fatigue life. Methods The domestic turbine blade DZ4 alloy was used. DZ4 was shot peened under different pressures (0.1, 0.3, 0.5 MPa), and heat treated at 1220℃ to generate surface recrystallization. The micro-structure of surface recrystallization was characterized by scanning electronic microscope (SEM). Fatigue testing was conducted on the raw DZ4 and surface recrystallized DZ4 alloy. Results Under lower pressure (e. g. 0.1 MPa), recrystallization occurred in form of discrete recrystallized grains, which remarkably reduced the fatigue life of DZ4. Under higher peening pressures (0.3 MPa and 0. 5 MPa) , fully recrystallized grains were observed and the recrystallized thickness increased with peening pressure. The fatigue life of RX-0. 5 MPa sample could be longer than that of raw DZ4 alloy. Conclusion Recrystallization did not necessarily reduce the fatigue life of DZ4 alloy. Under lower shot peening pressure (e. g. 0.1 MPa) and heat treatment, the discrete RX was the most detrimental to fatigue life. Under higher shot peening pressure (e. g. 0.5 MPa), the compact recrystallized layer with fine grain size was beneficial to the fatigue life of DZ4. Crystal plasticity model was helpful in understanding and predicting the influence of RX on fatigue property.