Effects of Ti Content on Hardness and Wear Resistance of CoCrFeNiTi High-entropy Alloy Coatings

High-entropy alloys (HEAs) are composed of five or more elements with an atomic percentage between 5% and 35%, and their corresponding coatings with excellent performance and strong adaptability can be prepared by laser cladding technology. Laser cladding technologies can reduce the cost and increase the value of the HEAs for industrial applications. First-principles calculations are based on density functional theory (DFT) and are widely used in material research. Recently, this method also has been applied to predict the properties and analyze the mechanisms of HEAs, especially in the strengthening mechanisms of mechanical properties and wear resistance, which can reduce uncertainties and improve the efficiency in the development of HEA systems. With the above methods, High-entropy alloy laser cladding coatings with high industrial application value can be designed and synthesized by considering the effects of Ti content on the microstructure and properties of the coatings. In this paper, CoCrFeNiTix HEA coatings were prepared on the surface of the Q235 steel by laser cladding technology. The models of CoCrFeNiTix HEA face-centered cubic (FCC) structure solid solutions were constructed By the special quasi-random structure (SQS) method and the mechanics and formation properties of the alloys with different Ti contents were predicted through first-principle calculations. The microstructure, microhardness, and wear resistance of the coatings were characterized and studied. The strengthening mechanism of wear resistance was elucidated by experiment and first-principles calculations. The calculation results showed that the solid solution phases of CoCrFeNiTi HEAs had high shear modulus and low formation energy, and their shear modulus and formation energy gradually increased and the phase stability of FCC solid solution decreased with increasing Ti content. The experimental results indicated that CoCrFeNiTi0.1 adopts an FCC phase, CoCrFeNiTi0.3 exhibits an FCC phase and a tetragonal FeCr phase, and CoCrFeNiTi0.5 adopts an FCC phase, a tetragonal FeCr phase, and a rhombohedral NiTi phase. The FCC phase, tetragonal FeCr phase, rhombohedral NiTi phase, and hexagonal CoTi phase are all observed in the CoCrFeNiTi0.7 HEA. CoCrFeNiTix HEAs exhibited a dendritic structure, in which Ni and Ti were enriched in the interdendritic regions, and Cr and Fe were centered in the dendrites. With increasing Ti content, the dendrite spacing of the alloy decreases, the secondary dendrite arm is more developed, and the element segregation phenomenon is alleviated, the microhardness gradually increased, the friction coefficient, wear rate, and mass loss continued to decrease, and the wear resistance increased significantly, which was consistent with the calculation results. The main wear mechanism of the coatings was abrasive wear, accompanied by partial adhesive wear in the alloys with low content of Ti. The increase in Ti content aggravated the lattice distortion and promoted the precipitation of hard phases (such as σ-phase), thus enhancing solid solution strengthening and precipitation strengthening, hindering the development of cracks, increasing the resistance of dislocation motion and the slip difficulty, and improving the comprehensive wear resistance, with the small wear area. The hardness and wear resistance of the CoCrFeNiTix HEA coatings were significantly improved with increasing Ti content. The CoCrFeNiTi0.7 laser cladding coating exhibited a great industrial application value. © 2023, Chongqing Wujiu Periodicals Press. All rights reserved.