Effects of HiPIMS discharges and annealing on Cr-Al-C thin films

Abstract

Cr2AlC coatings were synthesized by high power impulse magnetron sputtering (HiPIMS) from Cr2AlC compound target and subsequent thermal annealing in Ar atmosphere. The effect of HiPIMS duty cycle and substrate bias potential (UB) on the thin film composition were investigated. All initial Cr-Al-C coatings exhibit similar compositions close to the target stoichiometry, and dense and amorphous structure independently of the duty cycle. Meanwhile, Al deficiencies up to 15% are observed with UB increasing to −200 V. Based on the measured fraction of ionized metal species flux at the substrate, highly energetic bombardment of the coating with ionized inert gas and metal plasma species causes preferential resputtering of Al. Partially crystallized Cr2AlC thin films were obtained by annealing as-deposited Cr-Al-C coatings at 550 °C for 4 h. The annealed coating is made of an amorphous inner layer and a crystalline Cr2AlC outer layer. A higher annealing temperature of 650 °C led to complete transformation from amorphous phase to crystallized Cr2AlC, and to micro-cracking. These results indicate that the synthesis temperature of MAX phase could be reduced, and the annealing time increased, to obtain protective coatings of Cr2AlC on heat-sensitive components without alteration of the substrate metallurgical properties.