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Formation of Oxynitride Layers on Titanium Alloys by Gas Diffusion Treatment
I. Pohrelyuk,O. Yaskiv,O. Tkachuk,이동복 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.6
Titanium alloys were oxynitrided in controlled nitrogen-oxygen gas atmospheres between 650 °C and 950 °C for 5 h to 10 h with two different techniques of gas diffusion treatment. One technique was performed in an oxygen-containing (oxygen amount ≥ 0.4 %) nitrogen environment. The other technique was performed in a deoxygenated (oxygen amount < 0.01 % to 0.0005 %) nitrogen environment with subsequent cooling in an oxygen-containing nitrogen environment (with an oxygen pressure of 1 Pa). The surface microhardness of oxynitrided samples increased due to the strengthening effect of titanium oxynitrides (TiNxOy). The maximum microhardness of the titanium oxynitrides was obtained with a near-equiatomic composition of nitrogen and oxygen in TiNxOy under optimal oxygen partial pressure and temperature-time conditions.
Formation and Oxidation of Nitrided layers formed on Titanium alloys by Gas Nitriding
Li Chen,I. Pohrelyuk,O. Yaskiv,O. Tkachuk,Dong-Bok Lee 한국표면공학회 2010 한국표면공학회 학술발표회 초록집 Vol.2010 No.5
As a result of the nitrogen interaction during gas nitriding, a titanium nitride layer was formed, followed by an interstitial solution of nitrogen in the hcp α-itanium. The phase composition at the outmost nitrided surface layer of Ti-6Al-4V alloy is TiN and Ti₂N. In the Ti-N compound layer, Ti₂N is the major phase and TiN is the minor one. Al exists as dissolved ions at the top surface of the Ti-N compound layer. Nanoindentation microhardness testing was conducted on the nitrided titanium alloys to analyze their hardness evolution in relation to the nitriding processing parameters and alloy composition. It was found that themicrohardness increases due to the strengthening effect of interstitial nitrogen and the formation of nitrides. When the nitrided Ti-6Al-4V titanium alloy was oxidized at 600℃ and 700℃ for 10 hrs in air, the nitrided alloys oxidized slightly. Above 800℃, they oxidized fast and microcracking developed on the nitride surface. The microhardness of the surface layers was very high, and it decreased through the diffusion zone to approach the base microhardness of the matrix. Nitriding and oxidation increased the surface microhardness due to the strengthening effect of interstitial nitrogen and oxygen as well as the formation of titanium-nitrides and -oxides. The microhardness of the nitrided alloys increased with the increase of the oxidizing temperature.
열확산처리 공정에 의한 순수 타이타늄의 표면특성 향상 연구
정현경 ( Hyeon Gyeong Jeong ),이동근 ( Dong Geun Lee ),( O. Yaskiv ),이용태 ( Yong Tai Lee ),허보영 ( Bo Young Hur ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.9
The thermo-chemical treatment (TCT) process was applied to achieve surface hardening of CP titanium. The following three different surface modification conditions were tested so that the best surface hardening process could be selected:(a) PVD, (b) TCT+PVD, and (c) TCT+Aging+PVD. These specimens were tested and analyzed in terms of surface roughness, wear, friction coefficient, and the gradient of hardening from the surface of the matrix. The three test conditions were all beneficial to improve the surface hardness of CP titanium. Moreover, the TCT treated specimens, that is, (b) and (c), showed significantly improved surface hardness and low friction coefficients through the thickness up to 100㎛. This is due to the functionally gradient hardened surface improvement by the diffused interstitial elements. The hardened surface also showed improvement in bonding between the PVD and TCT surface, and this leads to improvement in wear resistance. However, TCT after aging treatment did not show much improvement in surface properties compared to TCT only. For the best surface hardening on CP titanium, TCT+PVD has advantages in surface durability and economics.