超声辅助钛合金激光沉积成形试验研究

Experimental Study on Ultrasonic-Assisted Laser Metal Deposition of Titanium Alloy

借鉴超声振动在铸造、焊接、熔覆等领域中的作用,将超声振动引入钛合金激光沉积成形系统中,利用超声作用细化晶粒,均匀组织成分,减小试件的残余应力,从而解决成形件变形开裂的难题。针对成形系统的结构特点,搭建了超声振动系统,进行了超声振动辅助钛合金沉积成形试验。通过观察沉积试件的微观组织和对试件残余应力的测试,发现超声振动使试件熔覆层中的晶粒得到细化,使功能梯度材料试件中的TiC硬质相弥散均匀;并且能够减小试件的残余应力。测试结果表明超声空化或机械效应可以打碎由初生枝晶交错连接形成的固态结晶网,从而细化了晶粒,同时使继续结晶时熔体得到补充,减小了枝晶间产生的拉应力;另外超声波在熔池中的搅拌声流将使硬质相运动到熔池各处,使之分布更为均匀,在一定程度上减少了相与相之间凝固收缩应力的不同而产生的凝固应力。

To solve the bottleneck problem of deformation and cracks of laser metal deposition（LMD） parts and improve their mechanical properties,ultrasonic vibration is introduced to the LMD of titanium alloy processes to refine the grain size and to reduce residual stress based on its significant effect in the fields of casting,welding and laser cladding.So the paper applies ultrasonic vibration system to fabricate the samples and analyses its effect on its macroscopical appearances、microstructure and residual stress by experiments.The results show that the cladding layers thickness and the grain size change smaller,and also the reinforcement phase TiC in functionally graded materials samples is more uniform dispersion by metallographic photos.In addition,the residual stress is reduced,which shows that cavitation and mechanical effect of ultrasound break the solid crystal net connected by primary dendrite and refine the grain,and also the melt get supplement so as to the tensile stress is reduced.On the other hand,stirring acoustic stream in the molten pool make the reinforcement phase distribution uniform to reduce the solidification stress for different interphase solidification shrinkage stresses.