Microstructure and mechanical properties of in-situ dual ceramic phase synergistic strengthened CoCrMoNbTi(B4C)x high entropy alloy coating. (June 2023) - He, Longjun
Highlights: An in-situ dual ceramic phase strengthened CoCrMoNbTi(B4C)x HEA coating was developed via Laser cladding. After composition optimization, the phase structure of the HEA coating consisted of BCC solid solution matrix, TiC and TiB ceramic phase. Owing to the in-situ generation of ceramic particles, the structure of the alloy transformed from dendritic structure to equiaxed crystal structure. The grain refinement effect of this alloy was very obvious (close to two orders of magnitude), and the average grain sizes reached submicron level. The properties of alloy in-situ generating ceramic phase were superior to those of the original HEA, such as the nano hardness, Young's modulus, etc. Abstract: CoCrMoNbTi high entropy alloy coating with boron carbide (B4C) addition is prepared on titanium alloy substrate via laser cladding. The influences of B4C content on solidification microstructure, solid phase transformation and structure as well as the resultant mechanical properties of the high entropy alloy are investigated. With B4C addition, the original dendritic columnar grains transform into the finer and more uniform equiaxed crystal structure. By increasing the content of B4C, the solid phase evolution follows three steps: BCC1 + BCC2 → BCC1 + BCC2 + TiC → BCC1 + BCC2 + TiC + TiB, and the mechanical properties of the coating section vary correspondingly. The nano-hardness (H) and Young's modulus (E) of the CoCrMoNbTi(B4C) 0.6 coating are enhanced to 10.75 GPa and 240.35 GPa, compared to the original CoCrMoNbTi coating (H = 6.83 GPa and E = 168.88 GPa). The strengthening mechanisms are mainly grain boundary strengthening, dislocation strengthening, dispersion strengthening, precipitation hardening and solid solution strengthening.