激光成形修复TC4合金锻件的低周疲劳性能

采用激光成形修复技术制备了TC4合金锻件的面修复试样,对修复试样的显微组织、拉伸性能、低周疲劳性能进行了研究。激光修复区组织由粗大原始β柱状晶粒及晶内细长的α针及编织细密的α+β板条组织组成,热影响区组织呈现从锻件基体组织向修复区组织的连续变化,修复区与锻件基体为致密的冶金结合。对两组面修复试样分别进行去应力退火和去应力退火+喷丸处理后,测试获得了激光成形修复TC4合金锻件的低周疲劳曲线,由于面修复试样的拉伸性能与锻件相比强度高而塑性低,因此两组修复试样的疲劳寿命在低应变区高于TC4模锻件,此区强度对疲劳寿命起主要作用;而在高应变区低于模锻件,此区塑性对疲劳寿命起主要作用。修复试样经喷丸处理后,无论在高应变区还是在低应变区,其疲劳寿命都有所提高,并且在高应变区接近TC4模锻件水平,而在低应变区则高出模锻件一个数量级。

Low Cycle Fatigue Property of Laser Forming Repaired TC4 Forgings

Surface-repaired samples of TC4 forgings were prepared by Laser Forming Repair(LFR),and the microstructure,tensile property and low cycle fatigue property of the repaired samples were investigated.Microstructure of laser-repaired zone(LRZ) is typical Widmanstaten structure consisting of initial coarse columnar β grains,within which are fine acicular α and α+β basket weave structure,and there is a good metallurgical bonding between LRZ and the forging substrate.The heat affected zone(HAZ) presents a continuous change from the forging substrate microstructure to the repaired zone microstructure.The repaired samples were divided into two groups,and then they were treated by relief annealing(RA) and RA + shot peening(SP) respectively and their low cycle fatigue curves were obtained.It can be found that the fatigue life of the two groups is higher than that of the die forging in the area of low strain,but lower than that in the area of high strain.This is because the strength of the repaired sample is higher than that of forging,while the plasticity is poorer than the forging’s.The strength play a major role in fatigue life when samples are suffering a low strain,and the plasticity decides the fatigue life at high strain.It is shown that the fatigue life is improved by SP both at low strain and high strain.Moreover,the fatigue life of the LFRed samples with SP is close to the level of the forging at high strain,and longer than that of the forging at low strain by 1 order of magnitude.