Wang Shiyuan, Li Hangyue, Bowen Paul
College of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China.
School of Metallurgy and Materials, University of Birmingham, Birmingham, B15 2TT, UK.
Materials (Basel). 2019 Oct 24;12(21):3487. doi: 10.3390/ma12213487.
The effects of influential fatigue testing factors, including loading schemes (e.g., traditional load shedding and staircase load increasing), morphology of crack starters, and precracking approaches on the near-threshold fatigue crack growth behaviors for a near lamellar γ-TiAl alloy (Ti-45Al-2Mn-2Nb-1B) were investigated at room temperature and 650 °C. The results showed that the measured fatigue threshold values in lamellar γ-TiAl alloys are very sensitive to the applied testing procedures. For example, the staircase load-increasing method yielded smaller threshold values. When such a load-increasing method was used, the threshold values were measured either from a notch machined by electro-discharge machining or prepared by a compression-compression fatigue loading. Moreover, some differences could be seen with respect to the morphologies of the crack starters. Most of the above influences are associated with the brittle nature of the material and the characteristics of the lamellar microstructures, and closure effects are primarily induced by crack wake roughness or unbroken ligaments.
研究了包括加载方案（如传统的降载和阶梯式加载）、裂纹起始形态和预裂纹处理方法等影响疲劳试验的因素对一种近片层状γ-TiAl合金（Ti-45Al-2Mn-2Nb-1B）在室温及650℃下近门槛疲劳裂纹扩展行为的影响。结果表明，片层状γ-TiAl合金中测得的疲劳门槛值对所采用的试验程序非常敏感。例如，阶梯式加载方法得到的门槛值较小。当采用这种加载方法时，门槛值是通过电火花加工加工的缺口或通过压缩-压缩疲劳加载制备的缺口来测量的。此外，关于裂纹起始形态可以观察到一些差异。上述大多数影响与材料的脆性本质和片层微观结构的特征有关，而闭合效应主要是由裂纹尾迹粗糙度或未断裂的韧带引起的。
