中文摘要：

为了研究激光喷丸对IN718镍基合金微观组织特性的影响及其在高温下的稳定性,首先在常温下对标准拉伸试样关键区域进行激光喷丸处理,随后将喷丸样置于700℃下保温300 min,作为对比,分别测试了未喷丸样、喷丸样和喷丸高温保持样的表层残余应力和纳米硬度,并采用光学电镜和透射电镜对其微观组织特征进行观测。结果表明,激光喷丸后试样的表层出现了高幅值的残余压应力,最高值出现在喷丸中心,约为-706 MPa;激光喷丸后试样的表层硬度显著提高,平均纳米硬度提高了约67.4%;高温保持后试样的残余应力和纳米硬度均有不同程度的降低,但与未喷丸试样相比,强化增益效果仍然存在;显微组织观察结果显示,激光喷丸后,试样深度方向上晶粒形态均出现了显著的＂分层＂现象,塑性变形层晶粒细化明显,其影响深度可达80μm;保温后喷丸样晶界处可见析出条状δ相;TEM图像进一步表明,激光喷丸诱导的晶粒细化是条状孪晶和位错组织混合交织的结果;保温后喷丸样晶界处发现了沿同一方向向晶内延伸的位错阵列,这很好地验证了位错在高温下的活性,且是激光喷丸抑制晶粒在高温下快速增长的直接证据。

英文摘要：

The aim of this study was to investigate the effects of laser peening（LP） on the microstructure characteristics and high-temperature performance of IN718 nickel-based alloy. Firstly, LP process was performed on the standard tensile specimens at ambient temperature, and then the treated specimens were exposed at 700 °C for 300 min. We detected the surface residual stress and nano hardness on the untreated, the LPed and the heat-exposure specimens. The corresponding microstructures were also observed. The results indicate that high amplitude compressive residual stress distributes in the LP treated surface, the maximum value is –706 MPa, appearing in the central region of the LP area. LP process significantly increases nano hardness of the treated surface, and the average nano hardness is enhanced by 67.4%. Both the residual stress and nano hardness decrease after heat exposure; however, the strengthening effect still exists compared with the untreated specimens. An obvious ＂layer-separating＂ phenomenon occurs on the grain morphology in the depth direction after laser peening. The grain size in the plastic deforming layer is refined greatly, whose affecting depth reaches 80 μm. The precipitated δ phase is found in the grain boundaries for the heat-exposure samples. A further observation indicates that the interaction of mechanical twins and dislocation results in the grain refinement. After heat exposure, the single-directional-distributed dislocation array in the grain well verifies the dislocation activities, which confirms that LP can inhibit the grain growth of IN718 alloy at high temperature.