Laser-directed energy deposition of CoCrFeNiTi high entropy alloy coatings: effects of powder geometry and laser power

CoCrFeNiTi high entropy alloy (HEA) has been extensively studied to serve as coating materials on complexly shaped parts of equipment used in industries such as oil, gas, and mining due to its high hardness, excellent wear resistance, and good high-temperature stability. Laser-directed energy deposition has potential to fabricated HEA caotings due to its advantages of excellent metallurgical bonding, high coating density, suppressed element segregation, and the capability of thick coating deposition. However, limited investigations have been conducted on the effects of input parameters (such as powder geometry and laser power) on the mechanical properties of laser DED fabricated CoCrFeNiTi high-entropy alloy coatings. In this study, CoCrFeNiTi HEA coatings have been fabricated on Ti substrates from spherical-shaped and irregular-shaped powders under different levels of laser power. The effects of powder geometry and laser power on molten pool thermal characteristics (including temperature, cooling rate, and solidification time), phase constitution, microstructure, and mechanical properties of hardness and wear resistance have been investigated. Under the same laser power, the utilization of irregular-shaped powders resulted in uniform microstructures and higher hardness. For the coatings fabricated from spherical-shaped powders, the increase of laser power could improve the microhardness and wear resistance. For the coatings fabricated from spherical-shaped powders, the increase of laser power could increase the microhardness. However, the wear resistance is increased and then decreased due to the increase in friction of coefficient.