Objective Inconel 625 is one of the main materials for jet engines and various industrial gas turbines with a stable structure and an excellent performance. It is used in extreme environments with high temperature and wear. The service environmental conditions of components have become more severe with the rapid development of the marine and aerospace industries. Moreover, the demand for higher-performance Inconel 625 components has increased. Particle-reinforced Inconel 625 metal matrix composites can improve the strength and wear resistance of materials, which has become a research hotspot in the recent years. However, only a few studies have been published on the effects of different amounts of reinforcing phase on the matrix, especially on the microstructure and friction and wear properties. The advantages of WC are high hardness and low coefficient of thermal expansion. It can also easily be wetted by molten metal and is an ideal material for improving the wear resistance of components. As a reinforcing phase, WC can meet the requirements of components under high-wear conditions, such as in gas turbines. WC-12Co with a particle size of 45-100 μm was selected for use in this study. Cobalt has excellent thermodynamic properties, which prevents laser from directly acting on WC, thus relieving WC melting, maintaining the particle integrity, and improving the composite properties. WC-12Co particle-reinforced Inconel 625 metal matrix composite coatings were prepared herein by laser cladding. The effects of the WC-12Co particles with mass fractions of 5%, 10%, and 15% on the microstructure and wear resistance of the Inconel 625 matrix were studied, which have a high reference value for component repair technology and material selection in practical industrial applications.
Methods The Inconel 625/WC-12Co composite coatings were prepared by laser cladding in argon atmosphere. The microstructure, phase composition, microhardness, and friction and wear properties of the composite coatings were obtained by metallographic and scanning electron microscopy (SEM), X-ray diffraction (XRD), and microhardness and ring-block wear testers, respectively. The width and depth of the wear marks were measured by a white light interference 3D surface profiler, and a three-dimensional model was established. The effects of different WC-12Co additions (with mass fractions of 5%, 10%, and 15%) on the microstructure and wear resistance of the Inconel 625 matrix were obtained according to the abovementioned characterization and analysis.
Results and Discussions The WC-12Co particle-reinforced Inconel 625-based composite coatings were successfully prepared by laser cladding. The composite coatings with different WC-12Co contents were analyzed by XRD, SEM, microhardness, and friction and wear properties. The results are as follows:
1) After the WC-12Co addition, the microstructure was refined and accompanied by the precipitation of NbC, M23C6, and other carbides. The content and kinds of carbides also increased with the increase of the WC-12Co content.
2) Most WC-12Co kept their complete form and were uniformly distributed in the coatings. Some were decomposed or melted at the edge. The unmelted WC-12Co in the coatings inhibited the growth of coarse columnar crystals. The equiaxed and short columnar crystals were dominant around the WC-12Co. More Mo and Nb elements were found in the matrix intercrystalline. The higher the addition amount, the higher the content of the two elements, indicating that the two elements segregated at the grain boundary.
3) The composite coating microhardness gradually increased with the increase of the WC-12Co content. Compared with the pure Inconel 625 (264 HV0.2), the average microhardness of the composite coatings was 274 HV0.2, 289 HV0.2, and 308 HV0.2 respectively. The increase of the microhardness was caused by the eutectic precipitation, fine grain strengthening, and secondary phase strengthening.
4) The mass loss, wear rate, wear width, and depth of the composite coatings significantly decreased, and the wear rate decreased from 10.5004×10-4 to 0.5768×10-4 mg·m-1, indicating that the WC-12Co addition can significantly enhance the wear resistance of Inconel 625. Adhesive and abrasive wears occurred alternately in the friction and wear process. Due to the extremely high hardness of the WC-12Co particles, the duration of the abrasive wear increased when the amount of WC-12Co was high, and the strengthening effect of the carbides precipitated from the grain boundaries reduced the wear of the Inconel 625 matrix, significantly improving the wear resistance.
Conclusions The WC-12Co particle-reinforced Inconel 625 metal matrix composite coatings were prepared by laser cladding. The WC-12Co addition significantly affected the microstructure and the wear resistance of the Inconel 625 matrix. The composite coating microstructure was refined; carbides, such as NbC and M23C6, were precipitated at the grain boundaries; and equiaxed and short columnar crystals were dominant around the WC-12Co. The augmentation of the WC-12Co content significantly improved the microhardness and the wear resistance of the composite coatings. In summary, adding WC-12Co particles can refine the microstructure of the Inconel 625 matrix and improve its hardness and wear resistance.
