Cheng Zhangjianing, Cao Xiaojian, Xu Xiaoli, Shen Qiangru, Yu Tianchong, Jin Jiang
College of Civil Engineering, Tongji University, Shanghai 200092, China.
School of Transportation & Civil engineering, Nantong University, Nantong 226019, China.
Materials (Basel). 2020 May 2;13(9):2107. doi: 10.3390/ma13092107.
The effect of nano grain surface layer generated by ultrasonic impact on the fatigue behaviors of a titanium alloy Ti3Zr2Sn3Mo25Nb (TLM) was investigated. Three vibration strike-numbers of 24,000 times, 36,000 times and 48,000 times per unit are chosen to treat the surface of TLM specimens. Nanocrystals with an average size of 30 nm are generated. The dislocation motion plays an important role in the transformation of nanograins. Ultrasonic surface impact improves the mechanical properties of TLM, such as hardness, surface residual stress, tensile strength and fatigue strength. More vibration strike numbers will cause a higher enhancement. With a vibration strike number of 48,000 times per square millimeter the rotating-bending fatigue strength of TLM at 10 cycles is improved by 23.7%. All the fatigue cracks initiate from the surface of untreated specimens, while inner cracks appear after the fatigue life of 10 cycles with the ultrasonic surface impact. The crystal slip in the crack initiation zone is the main way of growth for microcracks. Crack cores are usually formed at the junction of crystals. The stress intensity factor of TLM titanium alloy is approximately 7.0 MPa·m.
研究了超声冲击产生的纳米晶粒表层对钛合金Ti3Zr2Sn3Mo25Nb（TLM）疲劳行为的影响。选择每单位24000次、36000次和48000次三种振动冲击次数来处理TLM试样表面。生成了平均尺寸为30nm的纳米晶体。位错运动在纳米晶粒的转变中起重要作用。超声表面冲击改善了TLM的力学性能，如硬度、表面残余应力、抗拉强度和疲劳强度。更多的振动冲击次数会带来更高的提升。每平方毫米振动冲击次数为48000次时，TLM在10次循环下的旋转弯曲疲劳强度提高了23.7%。所有疲劳裂纹均从未处理试样表面萌生，而在超声表面冲击作用下，经过10次循环疲劳寿命后出现内部裂纹。裂纹萌生区的晶体滑移是微裂纹扩展的主要方式。裂纹核心通常在晶体交界处形成。TLM钛合金的应力强度因子约为7.0MPa·m。
