Pretreatment Influence on Titanium Surface Properties After Gas Nitriding
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JMEPEG DOI: 10.1007/s11665-017-2934-x
Pretreatment Influence on Titanium Surface Properties After Gas Nitriding I.M. Pohrelyuk, S.M. Lavrys, O.M. Sakharuk, I.V. Stasyshyn, and O.V. Penkovyi (Submitted January 25, 2017; in revised form June 20, 2017) Influence of an initial mechanical treatment (grinding, polishing) on geometry and physical–mechanical parameters of a commercially pure titanium (Grade 2) surface after thermodiffusive saturation by nitrogen was studied. Microstructure analysis has shown that mechanism of formation and growth of a nitride film depends on the initial mechanical treatment. Nitriding under temperature of 750 °C does not influence practically the quality of ground surfaces and decreases it on one class for polished one. For higher saturation temperatures, surface quality has little dependence from the initial treatment. The best set of geometry and physical–mechanical characteristics belongs to the surface, which was initially polished and nitrided subsequently under 750 °C temperature, which provides its high wear resistance. Keywords
mechanical treatment, nitriding, roughness, structuralphase state, surface topography, titanium
Therefore, the aim of this paper is to evaluate the influence of the initial mechanical treatment (grinding, polishing) on geometrical and physical–mechanical parameters of the technically pure titanium (Grade 2) surface quality after the thermodiffusion saturation by nitrogen.
1. Introduction 2. Equipment and Research Methods Commercially pure titanium is widely used in a chemical industry and medicine due to high specific strength (Ref 1, 2), corrosion resistance (Ref 3) and biocompatibility (Ref 4). However, it possesses a disadvantage: a low wear resistance (Ref 5-9). In order to solve these problems, one uses a thermochemical treatment, in particular, surface thermodiffusion saturation by nitrogen (gas nitriding) which allows receiving a surface layer with high antifriction properties and hardness (Ref 10-12), without compromising such important material properties as corrosion resistance and biocompatibility (Ref 13-15). Nitriding forms a changed layer on the surface, which characteristics depend considerably on technological parameters (temperature, time, nitrogen partial pressure). From the other side, surface initial geometric and physical–mechanical characteristics, which are set by an initial mechanical treatment, define area of active surface, which interacts with an interstitial element (nitrogen), and thus the thickness of hardened layer, its structure, phase composition, the magnitude and distribution of residual stresses, etc. (Ref 16-24). Info about influence of a thermochemical treatment process on surface properties is extremely important in cases when service conditions allow using elements with hardened surfaces without its further treatment (finishing) as it will make it possible to predict operational properties of the hardened surface (wear resistance, corrosion resistance, etc.).
I.M. Pohrelyuk, S.M. Lavrys, O.M. Sakharuk, and I.V. Stasyshyn,
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