Research On The Properties Of Nanocrystalline Ti-B Compounds Films Applied To The Surface Of Titanium Alloy

Titanium and titanium alloys have a wide range of application in the chemical, petrochemical,aerospace and marine industries because of their excellent physical、chemical and mechanicalproperties. However, titanium and titanium alloys are restricted from industrial applications becauseof their poor corrosion resistance in reducing acid solution, poor high-temperature oxidationresistance and poor tribological properties, etc. Although, corrosion resistance, high-temperature andtribological properties are all belong to surface property, aim at such drawbacks, it is meaningful toimprove their corrosion resistance, high-temperature and tribological properties by surface modifiedtechnique.In the surface engineering applications, the compatibility between TiB/TiB₂and titanium alloy isgood, their differences in density are not significant. Also, the differences between them in linearexpansion coefficiency are within50%or less, the elastic modulus of TiB/TiB₂are4-5times higherthan the elastic modulus of titanium alloy. It is good to improve the hardness, tribological and otherproperties of titanium alloy.A series of films, such as nanocryatalline TiB₂film, nanocryatalline （Ti,Al）B₂film,amorphous-nanocrystalline TiBN film and amorphous-nanocrystalline （Ti,Al）BN film perpared onpure Ti substrates by glow discharge. Phase compositions and microstructure of the as-deposited filmswere characterized with X-ray diffractomety（XRD）, X-ray photoelectron spectroscopy（XPS）,transmission electron microscopy（TEM）, scanning electron microscopy（SEM） and energy-dispersiveX-ray spectroscopy（EDS）. The films were devoid of micro-cracks and pores, appears compact andquite well adhesived to the substrates. The film thickness was about10μm. The results showed thatall the films enhanced hardness and elastic effectively, particularly nanocrystalline TiB₂film. Thecritical load of binding force between films and suubstrate was above60N, which was about twice ashigh as actual sliding application.During corrosion test in3.5%NaCl solution, the corrosion resistence of amorphous-nanocrystalline TiBN and amorphous-nanocrystalline （Ti,Al）BN films were better than the corrosionresistence of nanocrystalline TiB₂and nanocrystalline （Ti,Al）B₂films, especially TiBN film.Addition of Al damaged the steady of passive film, reduced the corrosion resistance, but still betterthan the corrosion resistance of pure Ti substrate. In addition, there was active dissolve at0.25v and1.75v during tafel test which represented hydrolysis reaction of TiB₂and oxygen evolution reaction.During cyclic oxidation test at600℃and700℃in air, there were no obvious changes fornanocrystalline TiB₂and nanocrystalline （Ti,Al）B₂films, which meaned they had excellent high temperature oxidation resistance. Nevertheless, the amorphous-nanocrystalline TiBN andamorphous-nanocrystalline （Ti,Al）BN films showed poor high temperature oxidation resistance.During wear test at room-temperature. The results indicated that the friction coefficient increased withthe incraesed of load. Nanocrystalline TiB2film showed the best wear resistance. The main wearmechanisms of the films were abrasive wear and adhesie wear.