激光熔覆修复对TC4钛合金疲劳裂纹扩展速率的影响

Effect of Laser Clad Repair on Crack Growth Rate of TC4 Titanium Alloy

为了研究激光熔覆修复对TC4钛合金疲劳裂纹扩展速率的影响,采用激光熔覆技术,通过逐层堆积TC4钛粉,对TC4钛合金板表面凹槽进行修复。利用光学显微镜和扫描电镜分别观测试样的微观结构和疲劳断口,采用疲劳裂纹扩展实验测定试样裂纹长度与循环次数,利用修正的七点递增多项式拟合法获得每组3个试样在相同裂纹长度下的疲劳裂纹扩展速率。实验结果表明:激光修复区由β晶粒和沿晶界连续分布的α相组成,属于典型的魏氏组织,热影响区由等轴的α晶粒和β转变组织组成,属于典型的双态组织;同母材相比,激光熔覆修复件疲劳裂纹扩展速率显著降低。TC4钛合金熔覆修复件抗疲劳裂纹扩展能力的提高归因于魏氏组织断裂韧性高和双态组织优异的综合力学性能。

To investigate the effect of laser clad repair on crack growth rate of TC4 titanium alloy,surface groove of TC4 titanium alloy plate was repaired by adding TC4 titanium power layer by layer based on laser cladding technology.The microstructure and fracture surface morphology were characterized by optical microscopy and scanning electron microscopy,respectively.Fatigue crack growth experiment was used to obtain the crack length and cycle number.A modified incremental polynomial method was used to obtain the fatigue crack propagation rates of three samples per group under the same crack length.Experimental results indicated that the laser repairing zone was composed ofβgrains andαphase precipitating along the grain boundary,which belonged to typical Widmannstatten.The heat effect zone consisted of equiaxedαgrains andβtransformed structure,which was known as two-state structure.Comparing with the original sample,the fatigue crack growth rate of the laser cladding repaired samples was obviously decreased.The improvement of fatigue crack growth rate resistance for laser cladding repaired TC4 titanium alloy was attributed to a combination of high fracture toughness of Widmannstatten and the comprehensive mechanical properties of two-state structure.