Comparative research on cracking tendency in powder feeding laser cladding Stellite and NiCrSiB alloys

The comparative experimental researches demonstrated that laser cladding NiCrSiB alloy was of great tendency to cracking, with its microstructure mainly composed of small amount tough phases and a great deal of brittle disorder-distributed coarse hard phases. Laser cladding NiCrSiB + 50% Ni was a dendrite microstructure without cracks. Laser cladding Stellite 6 alloy was not sensitive to cracking, its microstructure consisted of tough dendrites and inter-dendrite eutectics. Cracks appeared in laser cladding layers of Stellite 6 plus over 18% of WC, their microstructures changed to be more brittle with more eutectics, more precipitated carbides and more complex shaped carbide precipitates. The basic reason for cracking is the big tensile stress induced in the cladding process, and the principal reason for cracking was attributed to the high brittleness of the as-clad layers due to the random shapes and disorder distribution of the hard phases in the microstructure. The method to decrease the cracking tendency was proposed to change the morphology of the strengthening phases, in which the hard phases precipitated dispersively within the microstructure and gradient distributed in the clad layers, in such a way the clad layer will be strong enough with good toughness and the tensile stress in the interface will be dramatically decreased at the same time.