In order to improve the wear resistance of 27SiMn steel substrate, Fe-based alloy coatings were prepared by laser cladding technology in the present study. In comparison to the conventional gravity powder feeding (GF) process, high-speed powder feeding (HF) process was used to prepare Fe-based alloy coating on 27SiMn steel substrate. The effect of diversified energy composition of powder materials on the microstructure and properties of coatings were systematically studied. X-ray diffractometer (XRD), optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the phase structure and microstructure of Fe-based alloy coatings, and the hardness and tribological properties were measured by the microhardness tester and ball on disc wear tester, respectively. The results show that the microstructure of conventional gravity feeding (GF) coatings was composed of coarse columnar crystals. In comparison, owing to the diversification of energy composition, the microstructure of the high-speed powder feeding (HF) coatings consists of uniform and small grains. The total energy of the HF process was 75.5% of that of the GF process, proving that high-efficiency cladding can be achieved at lower laser energy. The refinement of the microstructure is beneficial to improve the hardness and wear resistance of the coating, and the hardness of the HF coating increased by 9.4% and the wear loss decreased to 80.5%, compared with the GF coating. The wear surface of the HF coating suffered less damage, and the wear mechanism was slightly adhesive wear. In contrast, wear was more serious in the GF coating, and the wear mechanism was transformed into severe adhesive wear.
Self-lubricating NiCrBSi-Ni/MoS 2 coatings are prepared on 304 stainless steel by pre-placed laser cladding, in which Ni/MoS 2 is almost completely decomposed and the Cr x S y antifriction phase is in situ generated. Meanwhile, (Cr, Fe) 2 B and (Cr, Fe) 7 C 3 are generated from the molten pool as a result of oversaturated B and C atoms in γ-Ni and the diffusion of Fe atoms. Therefore, the composite coatings are mainly composed of γ-(Ni, Fe), (Cr, Fe) 2 B, (Cr, Fe) 7 C 3 , and Cr x S y . When compared with the substrate, the wear rate of the coatings with 20 wt-% Ni/MoS 2 is reduced by 21.16%, owing to the Cr x S y lubricating phase, while it is reduced by 25.61% for the coatings with 5 wt-% Ni/MoS 2 , owing to blocky (Cr, Fe) 2 B or (Cr, Fe) 7 C 3 hard phases. The wear mechanism of the coatings is adhesive wear and oxidative wear.
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