Surface engineering of titanium by multi-interstitial diffusion using plasma processing

Abstract

Titanium and its alloys possess a range of highly interesting properties such as excellent corrosion resistance, high specific strength and biocompatibility, but suffers from poor wear resistance. The present work addresses plasma assisted surface treatment of CP 2 titanium using various combinations of oxygen and nitrogen, i.e. mixed interstitials. The sequence of controlled plasma nitriding and oxidizing treatments plays a significant role for the evolution of the hardness depth profiles and the development of the surface compound layer and the underlying diffusion/transition zone. Composition profiles of oxygen and nitrogen are obtained by GDOES; Mixed interstitial solubility of nitrogen and oxygen is found in both h.c.p. α titanium and in the compound layer. The combination of interstitials leads to larger case depth, in particular for the diffusion zone (expanded h.c.p. α titanium). Therefore, it highlights the advantages of combined nitriding and oxidizing compared to single nitriding treatments on the mechanical properties.

Low Temperature Nitriding of Metal Alloys for Surface Mechanical Performance

“…Accordingly, different scales have been considered to assess the gain in mechanical performance. Authors have been used extensively in both conventional micro-indentation [ 41 , 42 , 43 ] as well as instrumented nanoindentation [ 44 ]. It is important to take caution when comparing micro- and nano-indentation values as different tested volumes are considered.…”

“…Instrumented nanoindentation offers the possibility to assess both elastic and plastic changes in the subsurface by analyzing loading–unloading curves. Instead, a conventional micro indentation can be used only to assess the plastic response [ 42 , 43 ] unless the geometrical consideration of the Knoop mark can be considered. Most commonly, a sharp diamond indenter is used with a Vickers or Berkovich geometry (four-sided pyramid and three-sided, respectively).…”

“…Moreover, complex-shaped metal components are much cheaper than their equivalent ceramic ones. In this applicative domain, titanium alloys are by far the most interesting choice and can give rise to a tremendous amount of research (see, for example, [ 3 , 8 , 25 , 26 , 39 , 42 , 43 , 50 , 62 ]).…”

“…Moreover, it is of interest to deepen and smooth the mechanical gradient so as to avoid the ‘egg effect’ or a too-large mechanical contrast between the surface and the core. Combined treatments comprising plasma nitriding plus oxidation, for instance, are being proposed and are effective in smoothing the mechanical gradient while also deepening the influence of the treatment [ 42 , 43 , 75 , 76 ].…”

Relation between Mechanical Hardening and Nitrogen Profile of PBII Nitrided Titanium Alloy

“…The treatment of titanium and Ti-6Al-4V has been reported to allow for performance to be tailored, namely, corrosion [17,18], hardness [19,20] and wear [8,[21][22][23]. In previous works, commercially pure titanium was chosen to develop fundamental studies on the nitriding treatment influence on the mechanical properties as this avoids the complexity resulting from the dual α/β microstructure [24,25]. In the present paper, experiments have been conducted on Ti-6Al-4V alloy, which accounts for 50% of the titanium alloys market.…”