目的 研究激光辅助氮化过程中,氮化层的开裂行为.方法 利用CO2激光辅助氮化的方法在钛合金表面制备氮化钛涂层,观察氮化层的宏观、微观形貌,分析组织结构特征,测定氮化层残余应力,研究基体厚度、激光扫描工艺参数对氮化层表面形貌和裂纹情况的影响.结果 钛合金经单道或多道激光氮化后,表面形成非均匀氮化钛层,其显微结构为沿主干轴交叉生长的枝状晶组织,存在数量和尺寸不等的显微裂纹.较薄试样经单道激光氮化后,表面呈现较低的残余压应力状态,较厚试样则以拉应力为主;试样经多道激光氮化后,整个氮化区表面均呈现残余压应力状态.结论 枝状氮化层与基体组织高度结合,不易脱落,但受基体约束作用,氮化层内的拉伸热应力导致其冷却过程中形成微裂纹.随着试样厚度和氮化面积的增加,较高的热应力使得裂纹密度和裂纹尺寸增加,严重影响氮化层的质量.残余应力是热应力和相变应力叠加的结果,对于多道激光氮化工艺而言,大面积氮化使得相变压应力增加,同时后热效应使得热应力降低,最终呈现出残余压应力状态.
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