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

• Published in: Surface & coatings technology 2020-10, Vol.399, p.126141, Article 126141
• Main Authors: Ougier, Michaël, Michau, Alexandre, Schuster, Frédéric, Maskrot, Hicham, Schlegel, Michel L.
• Format: Article
• Language: English
• Subjects: Aluminum; Annealing; Bombardment; Composition; Cr2AlC coating; Crack initiation; Crystallization; Engineering Sciences; Fracture mechanics; HiPIMS; Magnetron sputtering; MAX phase; Metallurgy; Microcracks; Microstructure; Phase transitions; Protective coatings; Rare gases; Stoichiometry; Substrate bias potential; Substrates; Thin films
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126141

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. •Amorphous Cr-Al-C thin films were deposited from Cr2AlC compound target by HiPIMS.•Duty cycle has no effect on the composition of Cr-Al-C in the investigated range.•Increasing substrate polarization results in Al-deficient films.•Structure evolution of Cr-Al-C coatings upon annealing temperature was studied.•Micro-cracking is observed for coated Zr-based substrates annealed above 600 °C.