The coal mine machinery and equipment are susceptible to wear failure and their service life is reduced because of the harsh working conditions, including high speed, heavy load, vibration, impact, and so on. Preparing wear-resistant coating on worn parts' surface is one of the most economical and efficient approaches to address the challenge of wear failure of coal mine machinery and equipment. The laser cladding technology has the benefits of fast heating speed, small heat-affected zone of the substrate, small thermal deformation of the workpiece, fine grain size, compact microstructure and low dilution rate of the coating, and metallurgical bonding between the coating and the substrate, which can efficiently enhance the workpiece's surface hardness and wear resistance. Thus, the laser cladding technology has a broad use prospect in the field of coal mine machinery production, maintenance, and remanufacturing. The Fe-based alloy powder has exceptional qualities of low cost and excellent anti-wear properties, and it is always employed in the repair and remanufacturing applications of coal mine machinery and equipment. Thus, the microstructure and tribological properties of Fe-based coating fabricated using laser cladding technology on the 27SiMn steel surface are studied. This offers a theoretical basis for Fe-based alloy powder's application in the coal mine machinery and equipment.
Fe-based alloy powder is produced on the surface of 27SiMn steel using the laser cladding equipment. The spot size, laser power, scanning speed, lap rate, and powder feeding rate are 15 mm×2 mm, 3000 W, 6 mm/s, 45%, and 30 g/min, respectively. The phase compositions and morphologies of the Fe-based alloy powder and coating are examined using an X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The changes in microhardness are measured using the hardness tester, and the substrate and coatings' tribological properties at room temperature are analyzed by the friction and wear tester .
From the coating surface [Fig. 2a)], the dendrite is presented in the microstructure. The growth changes of the microstructure in the molten pool zone during laser cladding are presented in Fig. 2(b), and the cellular structures are generated in the bonding area between the coating and the substrate. The Cr and Mo elements are enriched around the grain boundary and the Fe element is presented in the grain (Fig. 3). From Fig.4, the Fe and Cr elements are changed visibly in the bonding zone between the coating and the substrate. It implies that the Fe and Cr elements' mutual diffusion has happened. This element diffusion phenomenon demonstrates that the Fe-based alloy powder and substrate are melted during the process of laser cladding because of the laser beam's action. The coating's XRD analysis result is demonstrated in Fig.5, and the coating comprises of the body-centered cubic α-Fe phase and (Fe-Cr) solid solution phase. The coating's microhardness is demonstrated in Fig.6. The coating area's average microhardness is (652.62±49.00)HV, and the average microhardnesses of the heat-affected zone and the substrate are (515.29±82.00)HV and (292.68±19.00)HV, respectively. The coating's average microhardness is about 2.1 times that of the substrate. In Fig. 7(a), the average friction coefficients of the coating and the substrate are 0.3265 and 0.3344, respectively. The wear volumes of the coating and the substrate are 2.77×10-4 mm3 and 1.2×10-2 mm3, respectively (Table 4 and Fig. 8). The wear rates of the coating and the substrate are demonstrated in Fig. 7(b). Compared with the substrate's wear rate, the coating's wear rate decreases by 97%. Figure 9 demonstrates the wear morphologies of the coating and the substrate. The substrate's wear is more serious, and the coating's wear track is relatively smooth.
In this research, the microstructure and tribological properties of Fe-based coating fabricated using laser cladding technology on the 27SiMn steel surface are studied. The primary phases of laser cladding Fe-based coating contain the α-Fe phase and (Fe-Cr) solid solution phase. The coating surface microstructure is composed of dendrite structure, which is dense and uniform, without visible cracks or other defects. The cross-sectional microhardness shows a gradient change. The coating's average hardness is about 2.1 times that of the substrate. The substrate's wear rate is 70.8×10-7 mm3·N-1·m-1, and the coating's wear rate is 1.634×10-7 mm3·N-1·m-1. The wear mechanisms of the substrate are primarily adhesive wear and abrasive wear, while the coating's wear mechanisms are primarily abrasive wear, and oxidation wear exists in both the substrate and coating.
