Numerical analysis and experimental research of cracking controlling in laser cladding with unidirectional powder feeding and bidirectional scanning

A new craft of laser cladding called as unidirectional powder feeding and bidirectional scanning is developed to solve the cracking of cladding coats. The stress field of laser cladding is numerical calculated. The results show that the cladding coat is in tension stress state after traditional craft of unidirectional powder feeding and unidirectional scanning. Stress is concentrated in the top of cladding coat and the joint of coat and matrix. And the value of stress is comparatively high. It is an important reason that results in the cracking of cladding coat. After the bidirectional scanning, there is no concentrated stress in the top of cladding coat and the maximum value of tension stress inside cladding coat is only about 1/10 of the stress value after unidirectional scanning. The craft of unidirectional powder feeding and bidirectional scanning is adopted in the experiment of cladding with the Ni60 alloy powder on the surface of 45 steel. Twelve samples are cladded by different laser power, powder feeding speed and scanning craft in experiment. Experimental results show that there isn´t any crack in the samples that cladded by bidirectional scanning. It must be pointed out that cracking of multi-pass overlapped cladding coats is also avoided by the new cladding craft. Metallographic structure of multi-pass overlapped cladding coats is inspected. And the inspection results show that there is not any crack or air hole inside the cladding coats. The state between every pass of cladding coat is metallurgical combination. It is proved that bidirectional scanning craft is reliable and effective for cracking controlling.