The Structural Control and Characterizations of Titanium Alloy Films Based on SZMs
Supervisor:yang yan qing
Because of the high mechanical strength,excellent thermal stability,good corrosion resistance and intrinsic biocompatibility,titanium alloys have been widely used in the aerospace and biomedical industry.As one of the most typical metallic materials,titanium alloy films have received lots of attentions recently.Magnetron sputtering process is often used for preparing films because of its ability of refining and homogenizing coating structures,producing nanocrystallites with superior properties and promising good adhesions between film and substrate.It is well known that the film structure is of great importance because it determines the film properties.However,the structures of titanium alloy films are seldom studied as so far.Compared with bulk materials,the sputtered films have completely different structural properties,such as texture growth,nanocrystalline growth and high intrinsic stress owing to the non-equilibrium deposition process.These structural features depend process parameters,such as substrate temperature,working pressure,sputtering power and substrate bias.The Structure Zone Models provide important guidelines for systematizing both the experimental results and the dependence of film structures on process parameters.Based on these models,we studied the structures of Ti-6Al-4V、Ti-5Al-4Mo-4Cr-2Zr-2Sn、Ti-6Al-7Nb and Ti-Mo alloy films prepared by magnetron sputtering,respectively.The main results are showed as follows:(1)The Ti-6Al-4V alloy films show a transition from a columnar growth with(0002)texture to an equiaxial growth with random orientation as the substrate temperature rises from100°C to 500°C.A schematic diagram based on the Structure Zone Model is established to describe the structure evolution as a function of substrate temperature.(2)Based on the Structure Zone Models,we studied the texture,morphology and residual stress of Ti-6Al-7Nb films which are controlled by a combined effect of substrate temperature and particle bombardment.Nanoindentation results show that the texture strengthening contributes to the improvements of the film hardness.(3)We investigated the phase and morphology evolutions of Ti-15 wt.%Mo and Ti-30wt.%Mo alloy films when the substrate temperature rises from 50°C to 300°C.Ti-15 wt.%Mo alloy films keep a metastableβgrowth only at 50°C and 100°C,while Ti-30 wt.%Mo alloy films keep aβgrowth at the whole temperature range.The two films both have a zone 1growth at the low substrate temperature range.As the temperature rises to 300°C,Ti-15 wt.%Mo alloy films change into a noncolumnar growth with rough surface,while Ti-30 wt.%Mo alloy films change into a dense and columnar zone 2 growth which is accordance with the SZMs.The comparison between EDS and XPS results shows an enrichment of Ti on the oxide surface layer for all films.(4)We investigated the phase,morphology,and texture in Ti-17 alloy films as a function of substrate temperature from 125°C to 530°C.The films show a metastableβ-Ti growth at125°C and a phase evolution with the increasing T_s.When the substrate temperature rises to530°C,the films show anα+βdual-phase growth.Based on the Structure Zone Models,the films show a morphology transition from zone 1 to zone T.Besides,the films show a random growth at 125°C,and a change into texture growth as the substrate temperature rises.