Influence of the conditions of saturation of titanium from graphite in vacuum on the structural state of surface layers
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INFLUENCE OF THE CONDITIONS OF SATURATION OF TITANIUM FROM GRAPHITE IN VACUUM ON THE STRUCTURAL STATE OF SURFACE LAYERS V. M. Fedirko, S. V. Huryn, I. M. Pohrelyuk, and O. I. Yas’kiv
UDC 669.295:620.196
We study the influence of temperature and time factors in the course of saturation of VT1-0, OT4, and VT14 titanium alloys from graphite in vacuum on the process of phase formation of surface layers. An increase in the temperature from 900 to 1000°C and in the saturation time (to 23 h) favors the transformation of binary compounds (titanium oxide and carbide) into TiC xOy-type carbooxides, which leads to the additional hardening of surface layers. We have established the dependence of the composition of triple compounds on the parameters of treatment. The carbon component in carbooxides is directly proportional to the temperature and time parameters, while the oxygen component is in inverse proportion to them.
In order to form carbooxide coatings, one simultaneously saturates the surface layer of titanium alloys with carbon from graphite in oxygen-containing media of dynamic vacuum or a static argon atmosphere. Saturation from graphite in a static argon atmosphere was studied in [1]. In the present paper, we investigate the saturation of titanium alloys from graphite in dynamic vacuum (rarefied air) and compare it with saturation in a static argon atmosphere. Procedure of Investigations We tested specimens made of titanium alloys [commercially pure VT1-0 α-titanium, OT4 pseudo-α-alloy, and VT14 ( α + β ) -alloy], 10 × 15 × 1 mm in size. The specimens were polished to R a = 0.4 µm, washed in alcohol, and dried. Saturation from graphite was carried out in rarefied air (1.3 Pa) at 900 and 1000°C for 1 – 23 h. The phase composition of the surface layer of these specimens was determined on a DRON-3.0 X-ray diffractometer in monochromatic CuKα-radiation with focusing of the tube by the Bragg – Brettano scheme. The voltage on the anode of the X-ray tube was 30 kV, and the current was 20 mA. The binary phases (titanium carbide and oxide) were identified by the values of interplanar spacings. Titanium carbooxide was identified by comparing the diffractograms obtained with a standard diffractogram constructed according to the model of structure developed by Levi et al. [2]. The surface hardening was evaluated by the microhardness on a PMT-3M instrument under a load on the indenter of 0.49 and 0.98 N. We found changes in the mass of the specimens after treatment by weighing on a Voyager balance of the firm “OHAUS” to an accuracy of ± 0.1 mg. Results and Discussion In the course of treatment at a temperature of 900°C, the mass increment of the specimens increases with time (Fig. 1, curves 1 – 3). Note that unalloyed VT1-0 titanium and OT4 alloy are saturated most intensely. As Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 75 – 78, July – August, 2004. Original article submitted April 20, 2004. 518
1068–820X/04/4004–0518
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