孔挤压强化对航空Ti-4Al-5Mo-5V-6Cr-1Nb钛合金微观组织及疲劳性能的影响

Effects of hole expansion strengthening on microstructure and fatigue properties of aviation titanium alloy Ti-4Al-5Mo-5V-6Cr-1Nb

摘要:

为提高航空Ti-4Al-5Mo-5V-6Cr-1Nb钛合金中心孔试样的疲劳性能，采用开缝芯棒对其板材中心孔进行了孔挤压强化实验，分析了孔挤压强化对合金微观组织和疲劳性能的影响，揭示了孔挤压强化的抗疲劳增益效果和微观机制。结果表明，孔挤压强化层由靠近孔边缘的晶粒细化区域和远离孔边缘的变形区域组成，变形程度呈梯度分布。孔壁内侧残余压应力层深度达2000 μm，最大残余压应力达-700 MPa，强化层深度达100 μm，最高硬度值为380 HV0.1，比基体硬度值提高20%。孔挤压强化显著提高合金的疲劳寿命和降低疲劳寿命分散性，中值寿命和平均寿命分别提高2.74倍和2.53倍，变异系数从48.7%降至29.6%。残余压应力场和强化层能有效抑制孔壁内表面疲劳裂纹的产生，使疲劳裂纹萌生从表层转移至亚表层，辉纹更细密，辉纹间距从1.94 μm降低至0.92 μm。

Abstract:

To enhance the fatigue performance of the central hole specimen of the aviation titanium alloy Ti-4Al-5Mo-5V-6Cr-1Nb, hole extrusion strengthening experiment was conducted on the center hole of its plate using a slotted mandrel. The effects of hole extrusion strengthening on the microstructure and fatigue performance of the alloy were analyzed, and the anti-fatigue enhancement effect and microscopic mechanism of hole extrusion strengthening revealed. The results showed that the hole extrusion strengthened layer with a gradient distribution of deformation degree consisted of a grain refinement zone near the hole edge and a deformation zone away from the hole edge. The depth of the residual stress layer on the inner side of the hole wall was 2000 μm, and the maximum residual stress was -700 MPa. The depth of the strengthened layer was 100 μm, and the highest hardness value was 380 HV0.1, which was 20% higher than the hardness value of the matrix. The fatigue life and fatigue life dispersion of the alloy was significantly improved after hole extrusion strengthening, with the median life and average life increasing by 2.74 times and 2.53 times, respectively, and the coefficient of variation decreasing from 48.7% to 29.6%. The residual stress field and strengthened layer effectively suppressed the initiation of fatigue cracks on the inner surface of the hole wall, shifting the initiation of fatigue cracks from the surface to the subsurface, resulting in finer striations with a striation spacing decreasing from 1.94 μm to 0.92 μm..