Effects of thin hard film deposition on fatigue strength of AA7075-T6

Abstract

Thanks to their favorable strength-to-weight ratio, Aluminum-Zinc alloys are often used in high-performance industrial sectors. These alloys are characterized by poor erosion resistance, which could be increased by the deposition of thin films. For example, PVD (Physical Vapor Deposition) films can reduce wear and ensure appreciable performance in aggressive environments. This paper describes the effects of thin hard film deposition on the strength of AA7075 under cyclic loading. Uncoated samples and samples with a DLC (Diamond-Like Carbon) surface layer were tested with a rotating bending fatigue machine within the range of [Formula: see text]–[Formula: see text] cycles. Two regression models were tested to study the relationship between fatigue strength and number of cycles within the range considered. For the samples without the film, even a linear regression can be suitable. With regard to the fatigue strength of the samples with surface layer, a piecewise linear regression is suggested, although a high scatter of experimental data can be observed. Finite element (FE) modelling was used to calculate the stresses induced by bending moment. The bending stresses were added to the residual stresses induced by the film deposition. The maximum value was found beneath the sample surface. Therefore, crack nucleation is expected under the surface of samples with film. The fatigue cracks initiate at the surface in untreated samples.

Strength of notched Ti-6Al-4V specimens not subjected to solution treatment and over-aging under cyclic loading

“…The discrepancies may also be due to the assumptions made in the calculation including the absence of residual stresses after the creation of the notches. As known, residual stresses affect the fatigue life of components [33]. Even if the results of the step loading procedure and the estimation of the stress to failure with the Haigh diagram are quite similar, further investigations are needed.…”

Finite Element Analysis and Experiments for Predicting Fatigue and Rolling Contact Fatigue Behavior of Spur Gears

“…Therefore, low temperature coatings should be preferred, particularly if deposited on light alloys, as confirmed in a study on the contribution of type of coating and deposition temperature on 7075-T6 aluminum alloy [8]. The deposition of DLC coatings has been found to globally reduce the fatigue strength of 7075-T6 aluminum alloy within the number of cycles range 200,000-10,000,000 [9][10][11][12]. Another study which testifies to the doubtful contribution of PVD coatings on fatigue strength, better RCF strength, is presented in [13], where a more uniform damage-load diagram was obtained for uncoated spur gears compared to the coated components.…”

Impact of DLC Coating Deposition on the Fatigue Strength of Al-7075-T6 Aluminum Alloy

“…The fatigue strength of uncoated and DLC-coated Al-7075-T6 samples under rotating bending is described in [63]. Magnetron sputtering was used to deposit the DLC coating [64], with a maximum temperature of only 180 °C.…”