Effect of duplex treatment of plasma nitriding on Micro structural and physical vapor deposition of Ti 6Al 4V

The purpose of the present paper was evaluation and comparison of Ti 6Al 4V alloy structural surface characteristics after both surface engineering processes comprised of plasma nitriding (PN) and a PN process followed by TiN PVD deposition, duplex process. PN treatment performed under gas mixture of N2/H2=4; at temperatures of 700, 750, 800 and 850°C for 10 h. To perform duplex process, a TiN layer deposited by catholic were plasma PVD on the surface of pre plasma nitrided samples. Structural characterization of surface and cross section performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microhardness testing methods. While TiN deposition was led to formation of only δ-TiN phase, three distinguished structure including of compound layer (constituted of δ-TiN and ε-Ti2N), aluminum-rich region and a diffusion zone, interstitial solid solution of nitrogen in titanium, were detected at the surface of plasma nitrided Ti 6Al 4V alloy. XRD patterns of duplex treated samples were indicated the simultaneous present of phases which formed during both processes. Although the structures obtained from each one of the processes alone were increased surface hardness, the hardness of outer surface produced by duplex process was significantly higher than plasma nitrided samples. Interdiffused interface of TiN layer (resulted of PVD process) with compound layer (caused by PN process) has been a significant role on the duplex coating performance. Increasing of plasma nitriding temperature, not only increased growth rate of TiN deposition by PVD process, but also improved homogeneity and continuity of TiN with compound layer.