Abstract
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.
Highlights
Due to their high strength, good machining performance and low cost, steels are widely used in industrial fields of petroleum, coal, train and automotive manufacturing [1,2]
Owing to the formation of coatings completely relying on the input of laser energy, defects—such as cracks, holes and excessive heat-affected zone caused by excessive heat input or uneven energy density—often appear in the microstructure of coating [14,15,16,17]
The results revealed that as the powder feeding speed increased from 200 mg/s to 500 mg/s, the tendency to form equiaxed/coaxial regions in the coating zone decreased, and the distance between the dendritic arms at the bottom of the coating decreased from 1.12 μm to 1.02 μm
Summary
Due to their high strength, good machining performance and low cost, steels are widely used in industrial fields of petroleum, coal, train and automotive manufacturing [1,2]. When repairing the defense-grade ultra-high strength steel by laser cladding, the formation of non-tempered martensite adversely affected the mechanical properties of the part, and the subsequent heat treatment may cause other harmful effects [18]. This greatly limits the application of laser cladding. In order to motivate the effect of the powder feeding rate, in terms of the amount of powder materials and the speed of powder particles, the powder feeding system was modified in the present study, i.e., a convergent-divergent Laval nozzle structure was used in replacing the cylindrical tube to accelerate powder particles to a high speed during the laser cladding process. The influence of high-speed powder feeding on the microstructure, phase composition, microhardness and wear resistance of laser cladded coatings on the surface of 27SiMn steel substrate is comprehensively discussed
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