Study On Adhesion Of Interlayer In Magnetron Sputtered Coatings To High-Speed Steel And Magnesium Substrates

The study was laid a strong emphasis on adhesion of interlayer to high-speed steel(HSS) and magnesium substrates. Influences of ion clean on surface of the HSS and magnesium substrates were investigated by SEM, Profile meter and Scratch test. Adhesion of Cr interlayer to substrates after various ion clean processes was evaluated. The interface between interlayer and substrate were observed and analyzed by TEM and EDS. Then the key to improve adhesion of interlayer to magnesium substrate were discussed from perspectives of crystallography match and mechanic match.The results indicated that: ion clean does not affect the adhesion of interlayer to HSS as much as its adhesion to magnesium. An overhigh voltage in ion clean result a severe damage for substrate surface; Whereas a lower voltage result an incomplete cleaned surface. Both of them are harmful for improvement of adhesion. Owing to there's no great changes for morphology of substrates, It's unnecessary to have a long time ion clean, because the sputtered particles from targets begin to deposit on substrate. In the experiments carried out in this study, the optimum ion clean process for HSS is -400 V, 30 min, but for magnesium -300 V, 20 min. The TEM images for interface between interlayer and substrate indicate that the adhesion mechanism for Cr interlayer to HSS, AZ31 magnesium is mainly physical bonds which caused by the gradient, mixing interface by ion implantation, mechanical bonds caused by microcosmic rough substrate surface after ion clean also has contribution to adhesion. Zr, Al interlayers were used to investigate how to obtain a strong adhesion on magnesium substrate. Zr interlayer, which is similar with Cr interlayer in lattice type and lattice constant, shows the comparative adhesion compared with Cr interlayer. But Al interlayer, which is similar with Cr interlayer in hardness, shows a much stronger adhesion than Cr interlayer. To obtain a strong adhesion for coatings on magnesium substrates, elastic modulus does not affect the adhesion as much as hardness. The match between hardness of HSS and magnesium is the key to obtain a strong adhesion.