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

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 (350 kHz 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 ± 0.1 eV and 73.1 ± 0.1 eV, respectively. The area fraction of the lower binding energy AlN bond (73.1 eV) increased with the AlN content in the cubic coating. The hardness was steadily increased from 11 GPa for VN to > 30 GPa for those V1 − xAlxN coatings with 0.48 ≤ x ≤ 0.57, among which the hardest V0.48Al0.52 N coating (> 40 GPa) showed a very dense, non-columnar, texture-free microstructure.