Microstructure, chemical states, and mechanical properties of magnetron co-sputtered V1 − xAlxN coatings

Abstract

Wear-resistant vanadium-containing nitride hard coatings are of special interest for tooling applications. We deposited V1−xAlxN coatings by reactive magnetron co-sputtering from vanadium and aluminum targets, which were independently driven by dc and pulsed dc (350kHz and 75% duty) power supplies, respectively. Over the range of x=0–0.62, all V1−xAlxN coatings were supersaturated cubic solid solutions stabilized in the metastable B1 structure. X-ray diffraction and transmission electron microscopy (TEM) studies revealed no evidence of the hexagonal AlN phase. In the cubic V0.38Al0.62N coating, however, interconnected AlN-rich and AlN-deficient domains were identified by elemental mapping in the scanning TEM mode. Regarding the growth structure, the V0.48Al0.52N and V0.43Al0.57N coatings exhibited a dense and fibrous one, while the V0.38Al0.62N coating exhibited a porous and columnar one with many through-thickness cracks. In the cubic V1−xAlxN coatings with a high amount of AlN (x≥0.52), X-ray photoelectron spectroscopy analysis revealed two distinct AlN states centered at 73.4±0.1eV and 73.1±0.1eV, respectively. The area fraction of the lower binding energy AlN bond (73.1eV) increased with the AlN content in the cubic coating. The hardness was steadily increased from 11GPa for VN to >30GPa for those V1−xAlxN coatings with 0.48≤x≤0.57, among which the hardest V0.48Al0.52N coating (>40GPa) showed a very dense, non-columnar, texture-free microstructure.