Enhanced crystalline growth of Cr2AlC MAX phase coating by hybrid DCMS/HiPIMS

In this work, highly crystallized Cr2AlC MAX phase coatings were successfully fabricated on Ti-6Al-4 V substrate at a temperature as low as 480 ℃, by using a hybrid direct current magnetron sputtering (DCMS)/high power impulse magnetron sputtering (HiPIMS) technique. The focus of the research was to investigate the influence of substrate temperature and bias voltage on the microstructure and mechanical properties of the coating. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images revealed that coatings deposited within the temperature range of 480 ∼530 °C consisted of uniform, densely packed, and randomly oriented grains. Additionally, grazing-incidence X-ray diffraction (GIXRD) and high-resolution transmission electron microscopy (HRTEM) confirmed pronounced crystallinity in the Cr2AlC coating at a substrate temperature of 480 °C without utilizing any substrate bias. For reference, an amorphous Cr-Al-C coating was synthesized by hybrid DCMS/HiPIMS on Ti-6A1-4 V substrates at room temperature without intentional heating, followed by high temperature XRD analysis to elucidate its traditional phase evolution route. The results indicated that the amorphous Cr-Al-C phase began to transform to Cr2AlC at 570 °C. A continuous increase in Cr2AlC crystallinity was observed for temperatures between 570 and 700 °C, with the coating starting to decompose at 800 °C. Subsequently, OES and Langmuir probe techniques were employed to characterize the discharge plasma and establish the relationship between the hybrid DCMS/HiPIMS plasma and the structure of the as-deposited coating. According to our calculation model, it was found that ions/atoms bombardment induced a temperature increase of ∼122 °C on the growing coating surface, with contributions from Cr and Ar ions/atoms accounting for 64 % and 31 % of the total energy flux, respectively. These findings suggest that thermally activated adatom mobility enhancement could significantly benefit high-purity, low-temperature growth of Cr2AlC coatings.