Graded Al-AlN, TiN, and TiAlN multilayers deposited by radio-frequency reactive magnetron sputtering

Graded layers and multilayers have been reported to improve surface properties of steel tools. Our study was aimed at defining the appropriate processing parameters for deposition of graded Al-AlN and AlN-TiN-TiAlN multilayers on silicon, glass, and M2 steel tools. The layers were deposited by r.f. reactive magnetron sputtering using dual cathode targets, Ti and Al. The ratio of nitrogen flow to nitrogen plus argon flow (f_N2/f_(N2+Ar)), r.f. power, and bias voltage (V_B) were used as the processing parameters. These parameters may be varied continuously, thus allowing the formation of a graded structure. The layers were characterized with regard to structure, composition, and mechanical properties using Fourier transform IR (FTIR) spectrometer, X-ray diffractometry, Auger electron spectroscopy microscope, Vickers microhardness tester, and scratch tester (testing adhesion). The reactive sputtered AlN layers displayed oriented (101̄1) or (0002) crystalline structure dependent on the gas pressure, while the graded Al-AlN layer had an oriented (0002) AlN structure and a randomly oriented Al structure with (0002) the highest peak. FTIR spectra of AlN thick layers showed sharp and intense absorbance bands at 1025cm^-1, 930cm^-1, and 544cm^-1. However, peaks related to thin films were seen to be broadened and shifted compared with those of thick films. The TiN and TiAlN layers displayed (111) oriented crystalline structures of δ-TiN and high microhardness and adhesion characteristics. The relationship between the processing parameters and the structure of the layers formed is presented and discussed.