Microstructure and Properties of Laser Cladding Ni-based High-temperature Wear-resistant Alloy

IN718 is a nickel-based high-temperature alloy with economic performance that is widely used in manufacturing of hot-end components with ambient temperatures not exceeding 650 degrees C. Its structural composition includes the gamma phase as the matrix; the gamma '' phase is the main strengthening phase and the gamma' phase is an auxiliary strengthening phase. In response to the insufficient high-temperature wear-resistance of the nickel-based alloy valve-sealing surface of generator units operating in supercritical / ultra-supercritical environments, two improved nickel-based high-temperature wear-resistant alloy powders were prepared based on IN718 alloy by increasing its (Ti+Al) content to 6.6% and 7.6% to improve performance. The proportion of gamma' precipitate phases and some brittle and hard phases greatly improve the high-temperature wear-resistance of the alloy, meeting the manufacturing and remanufacturing requirements of nickel-based alloy valve-sealing surfaces in supercritical units. A nickel-based high-temperature wear-resistant alloy sample was prepared on 304 stainless steel substrate using laser cladding deposition technology. The room temperature tensile properties of the sample were tested using a universal testing machine. The wear resistance of the sample with (Ti+Al) content up to 6.6% was tested by a high-temperature friction and wear testing machine at room temperature and 700 degrees C. The microstructure of the IN718im2 laser cladding sample was studied using XRD and SEM. The phase proportions in IN718 and IN718im2 were calculated using JMatpro software. The results are presented as follows. When the (Ti+Al) content of IN718 alloy was increased to 7.6%, a large transverse crack appeared in the cladding layer. At this point, the SEM morphology of the sample surface showed a large number of delta phases and other brittle phases. The hardness values of the IN718im2 sample before and after heat treatment were 41.22 HRC and 55.6 HRC, respectively. When the (Ti+Al) content of IN718 alloy was increased to 6.6%, the initial average hardness of the laser cladding sample was 40 HRC, the tensile strength was 998 MPa, the elongation was 5.2%, the room temperature friction factor was approximately 0.75, and the wear was 0.327 5 mm(3) after 10 h of aging treatment at 700 degrees C. The average hardness was 54 HRC, the friction coefficient at 700 degrees C was approximately 0.35, and the wear was 0.024 mm(3). The proportions of gamma and gamma' phases were 18.19% and 53.5%, respectively. The wear resistance of the IN718im2 sample at 700 degrees C was better than that at room temperature because Nb, Ti, and Al promote in situ formation of a glaze layer, and Ti and Al promote high-temperature self-lubrication of the alloy. The content of (Ti+Al) in IN718im2 was much higher than that in IN718; the proportion of brittle and hard phases was also much higher. The SEM surface scanning results showed that the segregation of Al and Ti was relatively weak; Mo and Nb had obvious segregation, indicating that increasing the (Ti+Al) content within a certain range did not exacerbate segregation of Ti and Al. However, the cracks in the sample with a (Ti+Al) content of 7.6% indicate that excessive Ti and Al contents promote great precipitation of brittle phases and increase dislocation accumulation and stress concentration, leading to formation of cracks in the cladding layer. The results indicate that when the content of (Ti+Al) in IN718 alloy increases to 6. 6%, it has good laser cladding process performance and high-temperature friction and wear performance, suitable for use in manufacturing and remanufacturing of nickel-based alloy valve-sealing surfaces in supercritical / ultra-supercritical units, and providing a reference for development of nickel-based high-temperature alloys in laser additive manufacturing.