低碳钢表面激光直接镀Ti层中裂纹形成的研究

STUDY ON CRACKS IN LASER DIRECT-CLADDED TITANIUM LAYER ON LOW CARBON STEEL

在不添加中间层的基础上,通过调控激光熔覆工艺在低碳钢表面获得均匀、无裂纹、Ti含量超过99%的镀Ti层,并采用数值方法模拟激光熔覆过程,分析了镀Ti层内的温度场和应变场.结合实验和模拟结果、相图和EDS分析,发现熔覆过程中镀Ti层和基体间形成可能由TiFe、共晶金属间化合物(TiFe+β-Ti)和少量α-Ti组成的界面层,该界面层具有本征脆性,极易形成裂纹,且此裂纹无法消除;镀Ti层内裂纹产生的根本原因是在脆性温度区内产生的拉伸应变超过了金属的临界塑形.可通过减少线能量而减少裂纹驱动力,从而消除镀Ti层内的裂纹,获得均匀、无裂纹的镀Ti层.

By adjusting laser power and nozzle speed in laser cladding technology,crack-free titanium layer with even thickness and titanium mass percentage over 99%,was obtained on the substrate of low carbon steel without any intermediate layer when heat input was between 12—20 J/mm.The temperature field and the mechanical strain were simulated.Together with phase diagram and EDS,it was found that an interface zone,consisted of TiFe,（TiFe＋/3-Ti） eutectic com- pound and a-Ti,was formed between the titanium layer and the substrate.The interface zone is brittle and cracks occur in it.In titanium layer crack also occur if the mechanical strain exceeds the critical plasticity of metal.By reducing heat input,the mechanical strain decreases,thus a crack-free titanium layer with even thickness can be obtained.