Phase and Residual Stress Evaluation of Dual-Phase Al70Cr30N and Al80Cr20N PVD Films

Abstract

We investigated arc ion-plated Al70Cr30N and Al80Cr20N thin films deposited with three different bias voltages (50 V, 100 V, and 150 V) to study crystal phase stabilities, residual stresses, and mechanical properties. Commercial compositions of AlxCr100–xN coatings typically range from x = 50 to 70 where the cubic face centered crystal phase occurs. The present study focuses on films near the solubility limit of Al in the cubic Cr(Al)N lattice around 70 at.%, above which hexagonal AlN (h–AlN) starts to form in significant amounts. Residual stress values are obtained by two methods: grazing incidence diffraction with the wholepattern fitting and the conventional side inclination method (sin2Ψ method). When multiple phases are present in the film, wholepattern fitting turns out to be particularly effective and a comparison of both measurement methods will be discussed. The Al70Cr30N films consist of the cubic phase with crystallite sizes of about 70 nm for all bias voltages. Compressive stress increased with bias voltage from about 3 to almost 6 GPa and coatings become brittle. Al80Cr20N films showed a different dependence on bias voltage. Using 50 V bias voltage in deposition, the major phase is h–AlN phase with a crystallite grain size of < 30 nm and (0002) preferred orientation. With increasing bias the cubic phase is stabilized also reaching about 70 nm crystallite size. In general, the compressive residual stress was significantly lower than for Al70Cr30N films for the same bias voltages which may be a result of the presence of the hexagonal phase. Wear and scratch tests confirmed higher ductility of the Al80Cr20N variants but reduced resistance of the films in impact wear testing.

Quo Vadis: AlCr-Based Coatings in Industrial Applications

“…Coatings with a higher Al content, deposited using Al 85 Cr 15 and Al 90 Cr 10 , formed dual-phase structures at bias voltages higher than 40 V [66]. The influence of phase structure on the stress state has been exemplified in the direct comparison of (Al 80 Cr 20 )N coatings, which had lower compressive stress values relative to (Al 70 Cr 30 )N. This effect was attributed to stress relief through the presence of hexagonal phases in the former case [88].…”

“…Dual-phase coatings with Al concentrations of more than 70 at.% have been reported as monolayer coatings [88,90,94,95], as well as multilayers [66,96]. The coatings are characterised by relatively low hardness compared with fcc (Al,Cr)N, lower oxidation resistance than fcc (Al,Cr)N with a high Al content, but also with the positive effect of exhibiting lower stress.…”

“…The combination of fcc (Al,Cr)N with hcp (Al,Cr)N was investigated to address the potential for adapting stress, hardness and wear properties [88,96].…”