Microstructure and wear-resistance of the CoCrFeNiMo high entropy alloy coatings by modulated arc currents using plasma transferred arc weld technique

Abstract

High entropy alloys have been regarded as a promising material for wear-resistant coating application. However, the efficient production of high entropy alloy coatings (HEACs) remains an obstacle for their industrial implementation. In this study, the CoCrFeNiMo HEACs with the thickness of ∼4 mm and robust metallurgical bonding were successfully manufactured on the Q345 steel substrate through the plasma transferred arc welding (PTAW) technique. The influence of the varying PTAW arc current (130 A, 180 A, and 230 A) on the microstructure, tribology behavior and wear-resistance of CoCrFeNiMo HEACs was systematically investigated. With the increasing arc current, along with the higher dilution rate, the content of Fe in PTAW-coatings apparently increases from 21.07 at. % (130 A) to 47.60 at. % (180 A), and finally to 55.76 at. % (230 A). The microstructure of PTAW-coatings consists of the primary phase (dendritic region) and the $\sigma$/FCC dual-phases eutectic (inter-dendritic region). However, the primary phase gradually changes from $\sigma$ to FCC phase with the increasing PTAW arc current. Nanoindentation test shows that the hardness of σ-phase, σ/FCC eutectics and FCC phase are 19.91 GPa, 10.71 GPa and 5.34 GPa, respectively. The dry sliding friction and wear tests indicate the improved wear-resistance as the PTAW arc current decreases from 230 A to 130 A. The coefficient of friction (COF) decreases from 0.75 to 0.64, the average hardness increases from 316 HV to 661 HV, and the wear rate reduces from 5.65 $\times$ 10⁻⁴ mm³ $\bullet$ Nm⁻¹ to 2.42 $\times$ 10⁻⁴ mm³ $\bullet$ Nm⁻¹. Meanwhile, the wear mechanism gradually changes from a combination of adhesive wear, oxidative wear and abrasive wear to the dominant abrasive wear due to the changed constituent phases.