Journal of Materials Research and Technology (Jan 2022)
Comparative studies on the Ni60 coatings deposited by conventional and induction heating assisted extreme-high-speed laser cladding technology: formability, microstructure and hardness
Abstract
Extreme-high-speed laser cladding technology (EHLA), which can deposit coatings with high efficiency and excellent surface accuracy, has attracted great attentions recently. However, due to the high cooling rate and large overlapping ratio therein, the cracking tendency of hardfacing coatings cannot be reduced but even enlarged compared with that in the traditional laser cladding process, which limits its wider applications significantly. Aiming to above problems, an extreme-high-speed laser-induction hybrid cladding technology (EH-LIHC) was proposed in this paper. The Ni60 coatings were deposited by EHLA and EH-LIHC, and the formability, cracking behaviors, microstructure and microhardness distributions of different coatings were studied systematically. Results indicate that Ni60 coatings with low surface roughness of Ra <15.0 μm can be deposited by both EHLA and EH-LIHC. However, dense cracks form in the Ni60 coating by EHLA, whereas they are reduced significantly by EH-LIHC and eliminated absolutely at induction heating temperature T = 500 °C. Moreover, the increase of T in EH-LIHC shows little effect on the coating's dilution although the diffusion of Fe element is enlarged. Composite structures of the proeutectic γ-Ni dendrites, γ-Ni + Ni3B eutectics, and Cr7C3+CrB precipitates are generated in all Ni60 coatings. The grain size of the coating, and the content and distribution uniformity of the precipitates therein are all enhanced with the increase of T. Comparatively, its microhardness is little influenced, which is about HV900-960 at T = 300 °C∼500 °C, slightly lower than that in Ni60 coating by EHLA (HV970-1000). The EH-LIHC technology proposed in this paper provides a promising approach for preparing crack-free hardfacing coatings with high efficiency and high precision.
