Effect of Si3N4 content on microstructure and frictional-wear properties of MoNbTaWTi refractory high entropy alloy composite coatings

Abstract

To address the shortcomings of the Ti-6Al-4 V alloy, characterized by low surface hardness and inadequate friction and wear properties, a composite coating of in-situ TiN reinforced MoNbTaWTi refractory high-entropy alloy was developed using laser cladding technology on Ti-6Al-4 V substrate. The effects of different Si3N4 contents on coating organization and wear resistance are discussed. Analysis through X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) revealed that the composite coating primarily consisted of the body-centered cubic (BCC) phase and an in-situ TiN enhanced phase. Notably, at a Si3N4 content of 2.0 wt%, the average microhardness at the coating's top surface reached 808.67 HV0.1, surpassing that of the substrate by 2.33 times. The friction coefficient was reduced to 0.3009, representing only 59.01 % of the Ti-6Al-4 V substrate. Furthermore, the wear weight loss measured at 0.4×10−2 mm3 was a mere 22.35 % of the Ti-6Al-4 V substrate, with the wear area accounting for only 0.27 % of the Ti-6Al-4 V substrate. Results demonstrated that utilizing the in-situ reaction between Ti element and Si3N4, the in-situ generated TiN reinforced phase significantly enhanced the hardness and wear resistance of the coating.