准β热处理工艺对TC4-DT钛合金裂纹扩展行为的影响

Fatigue Crack Propagation Behavior of TC4-DT Alloy with Quasi-β Heat Treatment

研究了准β热处理工艺窗口参数(保温时间和加热温度)对损伤容限型TC4-DT钛合金的疲劳裂纹扩展行为的影响,并采用金相显微镜(OM)和扫描电镜(SEM)从显微组织、裂纹扩展路径及断口形貌进行了分析对比。结果表明:随着保温时间从5 min延长至15 min,原始β晶粒尺寸从130μm增大到230μm,转变点处ΔKt由17.5 MPa·m^(1/2)增大至19.4 MPa·m^(1/2),当10 MPa·m^(1/2)≤ΔK≤20 MPa·m^(1/2)的低应力范围,裂纹扩展速率降低;随着加热温度从988℃升高至998℃,原始β晶粒尺寸从130μm增大至240μm,转变点处ΔKt由17.5 MPa·m^(1/2)增大至18.0 MPa·m^(1/2),转折点前的裂纹扩展区的裂纹扩展速率降低;当温度继续升高至1008℃时,原始β晶粒尺寸增大至400μm,转折点处ΔKt增大至20.5 MPa·m^(1/2),裂纹扩展速率在转折点附近降低,但在ΔK≥20.5 MPa·m^(1/2)的较大应力区域时,裂纹扩展速率无明显变化;温度升高或保温时间延长,裂纹扩展路径曲折度增加,二次裂纹数量增多、深度增加,断口表面粗糙度降低。

Influence of holding time and heating temperature of quasi-13 heat treatment on fatigue crack propagation behavior of TC4- DT alloy was studied. Microstructure, fatigue crack propagating path and morphology were observed by metallurgical microscope （OM） and scanning electron microscope （SEM）. When the heating time increased from 5 min to 15 rain, the 13 grain size increased from 130 to 230 μm, the value of the turning point AKt increased from 17.5 MPa-m1/2 to 19.4 MPa.m1/2 , and while the fatigue crack propaga- tion rate decreased. When heating temperature increased from 988 to 998 ℃ , the β grain size increased from 130 to 240 μm, the value of AKt increased from 17.5 to 18.0 MPa＇m1/2 , fatigue crack propagation rate decreased in the condition of △K≤ △Kt. When heating temperature increased from 998 to 1008 ℃ , the β grain size increased to 400 μm, the value of AKt increased to 20.5 MPa-m1/2 , fa- tigue crack growth rate decreased nearby AKt. The crack propagation path became more tortuous, secondary crack became more and deeper, the roughness of fracture surface decreased when temperature and holding time increased.