Mechanical, anti-oxidation and cutting performance of AlBCCrNbSi high entropy nitride coatings with various substrate bias

Abstract

The (AlBCCrNbSi)N coatings were synthesized through magnetron sputtering under various substrate biases, followed by a comprehensive analysis of their structural, mechanical, and oxidation resistance properties. X-ray diffraction analysis reveals that coatings deposited at biases ranging from 0 V to −150 V exhibit an amorphous structure, which is attributed to severe lattice distortion caused by small boron and nitrogen atoms. As the substrate bias is increased to −200 V and − 250 V, a transition to a nanocrystalline face-centered cubic (FCC) structure is observed. The cross-sectional morphology of the coating transitions from a fibrous structure to a granular structure with increasing bias, suggesting densification of the microstructure. The maximum hardness (22.5 GPa) and Young's modulus (193.5 GPa) are attained at −150 V, which is attributed to the densified structure and the presence of the amorphous phase. In addition, the oxidation resistance of the coatings is markedly improved at −150 V, with the thinnest oxide layer (114 nm) recorded after annealing at 1000 °C for 5 h. Transmission electron microscopy analysis reveals a multi-layered oxide structure, characterized by a dense surface oxide layer and an extended amorphous layer restricts oxygen diffusion. Besides, cutting tests indicate that the coating deposited at −150 V exhibits superior wear resistance compared to titanium nitride (TiN) and is comparable to titanium aluminum nitride (TiAlN), while also demonstrating enhanced oxidation resistance at elevated temperatures. In addition, this study quantitatively analyzes lattice distortion to elucidate the mechanisms driving the amorphous-to-nanocrystalline transition with increasing substrate bias in (AlBCCrNbSi)N coatings. The lattice distortion induced by boron and nitrogen atoms promotes the formation of an amorphous structure at low bias and improves oxidation resistance. These results demonstrate the significance of optimized substrate biasing in enhancing the structural, mechanical, and anti-oxidation properties of (AlBCCrNbSi)N coatings for cutting tools.