Effects of the Alloy Composition on Phase Constitution and Properties of Laser Deposited Ni-Cr-B-Si Coatings

Three Ni-Cr-B-Si hardfacing alloy powders with different Cr contents and Si to B ratios were deposited at cladding speeds of 5-40 mm/s on steel substrate using laser beam and the alloy composition-phase formation-properties relationships in the deposits were studied using several experimental techniques. Two general groups of compositions could be defined in this alloy system; the high-alloy grades characterized by numerous Cr boride precipitates, a low Si/B ratio and substantial Ni-B-Si eutectics, and the low-alloy grades with very little Cr boride precipitates, a high Si/B ratio and limited amounts of interdendritic eutectics. The findings confirmed that phase formation of Ni-Cr-B-Si laser deposited coatings primarily depends on the Cr content and Si/B ratio with the former controlling the amount of Cr-rich precipitates and the latter influencing the nature of the eutectic structures. In addition, it is shown that both Cr-rich precipitates and eutectic structures contribute to the functional properties of the coatings such as hardness and cracking susceptibility. The correlation between phase constitutions produced by different compositions and the hardness/cracking tendency is established and discussed.