微激光冲击DZ17G合金的表面完整性影响研究

Effects of micro-scale laser shock peening on surface integrity of DZ17G alloy

为了在不影响柱状晶组织的前提下改善DZ17G定向凝固合金的力学性能,采用微激光冲击强化方法进行表面处理,通过X射线衍射、扫描电子显微镜、透射电子显微镜和显微硬度计,测试分析微激光冲击对DZ17G定向凝固合金表面完整性的影响。试验结果表明:在水下无吸收保护层微激光冲击处理后,合金表面发生了烧蚀、熔融,1次冲击后形成光滑熔融区,但随着冲击次数增加而形成了大量微小烧蚀孔洞和难熔颗粒;表层组织仍由γ和γ′两相组成,柱状晶内形成了高密度位错和位错缠结,但未发生晶粒细化;硬度在深度上呈梯度分布,冲击1次后硬化层深度仅为100μm,表面硬度值达到503HV,提高了22.7%,而且硬度值和硬化层深度都随着冲击次数增加而增大。

Micro-scale laser shock peening is a surface treatment technology, which utilizes laser pulse with spot-size in micro-scale, low energy and short duration to induce shock wave acting on the metals.In order to improve mechanical properties of DZ17G directionally-solidified alloy without effects on the columnar crystals, micro-scale laser shock peening was suggested.The surface morphology, microstructure and micro-hardness were studied to analyze the effects on surface integrity by X-ray diffractometer, scanning electron microscope, transmission electron microscope and micro-hardness tester.The experiment showed that the alloy surface was ablated and melted by micro-laser shock peening underwater without ablating layer.There was smooth region generated with one laser impact, but the ablation degree increased with laser impacts, generating lots of ablation holes and infusible particles.The material still consisted of phases of γ and γ′.High-density dislocations and dislocation tangles were generated in material surface after μLSP, but without grains refined.The micro-hardness decreased with depth, with an affected depth of 100 μm and a maximal value 503 HV in the surface, increased by above 20%, under one laser impact.The micro-hardness and hardened layer depth increased with laser impacts.