Mechanism of Cr2AlC as a diffusion barrier to retard degradation of NiCrAlY coatings on Ti65 alloy

• Cr 2 AlC effectively retarded the degradation of NiCrAlY coatings on Ti alloys. After oxidation, the degradation rate of NiCrAlY coating with Cr 2 AlC diffusion barrier was 45.2 %, while that of single NiCrAlY coating was as high as 83.8 %. • Due to the rapid loss of Al in Cr 2 AlC, which enhanced the metallurgical bonding between the coating and the substrate, the application of Cr 2 AlC diffusion barriers did not trigger coating spalling. • Due to the diffusion barrier effect of the Cr 2 AlC diffusion barrier on Ti, the mass gain during oxidation was effectively reduced. In the present work, Cr 2 AlC diffusion barrier was prepared to retard the degradation of NiCrAlY coatings on Ti alloys at high temperatures. As-deposited samples were vacuum annealed at 900 °C for 4 h to eliminate the defects in NiCrAlY coatings. After that, oxidation analysis was conducted at 800 °C in air for 500 h. Due to weak bonding of Al in Cr 2 AlC and high affinity of C and Ti, Cr 2 AlC quickly decomposed to α -Cr during annealing. The original Cr 2 AlC and decomposed α -Cr effectively prevented diffusion of Ti from substrate to NiCrAlY coating, which further improved oxidation resistance and inhibited degradation of NiCrAlY coatings. However, diffusion barrier effect was lost because α -Cr reacted with Ti in the substrate to form Cr 2 Ti. After oxidation, the degradation rate of NiCrAlY coating with Cr 2 AlC diffusion barrier was 45.2 %, while the degradation rate of single NiCrAlY coating was as high as 83.8 %. In general, the Cr 2 AlC diffusion barrier effectively suppressed the degradation of NiCrAlY coatings on titanium alloys.