Hydrogen permeation resistance of plasma-sprayed Al2O3 and Al2O3–13wt.% TiO2 ceramic coatings on austenitic stainless steel

Al2O3 and Al2O3–13wt.% TiO2 ceramic coatings were prepared on 21Cr–6Ni–9Mn austenitic stainless steel substrates by plasma spraying. The phase contents and microstructures of the plasma-sprayed coatings were investigated by means of X-ray diffraction (XRD), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Also, the hydrogen permeation resistance was measured by thermal hydrogen charging. The results showed that plasma-sprayed Al2O3 and Al2O3–13wt.% TiO2 ceramic coatings can improve the hydrogen permeation resistance of 21Cr–6Ni–9Mn austenitic stainless steel effectively, and the hydrogen resistance efficiency of Al2O3 coating was higher than that of Al2O3–13wt.% TiO2 coating. Al2O3 coating displayed a denser structure than Al2O3–13wt.% TiO2 coating. The phase contents analysis revealed that the presence of the Ni(Cr, Fe, Ti)2O4 phase in the Al2O3–13wt.% TiO2 coating in addition to γ-Al2O3 and α-Al2O3. It was found that the bonding between the plasma-sprayed ceramic coatings and austenitic stainless steel substrates was mechanical rather than metallurgical.