Effect of Zirconia ALD coating on stress corrosion cracking of AZ31 alloy in simulated body fluid

In the last years, magnesium (Mg) and its alloys have been widely studied as materials for temporary implant devices. However, one of the main limitations that hampers its use in these applications is the occurrence of corrosion-assisted cracking phenomena, such as stress corrosion cracking (SCC) and corrosion fatigue (CF), in presence of the simultaneous action of corrosive human-body-fluid and mechanical loadings. This work aims to provide some improvements in the field, assessing the effect of a 100nm thick zirconia coating produced by means of atomic layer deposition (ALD) on the SCC susceptibility of AZ31 alloy. Slow strain rate tests (SSRT) have been carried out with an applied strain rate equal to 2.6 10^-6 s^-1, and the samples were immersed in simulated body fluid at 37 °C for the whole duration of the tests. The presence of the coating has revealed to provide a reduction in the SCC susceptibility, measured by means of the ISCC indexes. In addition, to provide an explanation of the observed behavior, corrosion experiments (potentiodynamic polarization curves and hydrogen evolution experiments) have been carried out.