Materials Science, Vol. 39, No. 3, 2003 LAWS OF FORMATION OF OXYCARBIDE LAYERS ON TITANIUM IN CARBON- AND OXYGEN-CONTAINING MEDIA I. M. Pohrelyuk, O. I. Yas’kiv, V. M. Fedirko, and S. V. Huryn UDC 620.194: 621.795 We established the laws of changes in the phase composition of surface layers in the course of saturation of titanium from graphite in static argon atmosphere and dynamic vacuum (1.3–133.3 Pa) at 950 – 1100° C. We showed that the composition of the oxycarbide phase de- pends on the saturation temperature and oxygen partial pressure in the gaseous oxygen-contain- ing environment. Owing to the thermodiffusive saturation of titanium alloys in active environments, in particular, nitrogen-, carbon, and boron-containing media, one succeeds in forming hardened surface layers with coatings of various structures and, hence, with various properties. Mainly due to the chemical affinity of titanium for oxygen, which is inevitably present in the environment, this saturation is accompanied by the appearance of heterophase coat- ings with oxygen-containing phases. Until recently, such a result of treatment was evaluated negatively, as a forced one, caused by the complexity of controlling the quality of the environment and phase formation, or evi- dent reject in the course of chemical heat treatment. However, a series of the latest investigations demonstrates better operating characteristics of multicomponent compounds like titanium oxynitrides, oxycarbides, etc. [1, 2]. To reach the given operating properties of these coatings on titanium alloys, it is useful to develop methods for clear identification of such coatings, to study the laws of their formation, and to establish relationships between their composition and physicochemical characteristics. In what follows, we describe some laws and features of formation of oxycarbide phases in the surface layers of titanium in the course of saturation from a carbon- and oxygen-containing environment. Experimental Technique We preliminarily ground specimens of commercially pure VT1-0 titanium of size 15 × 10 × 1 mm to R a = 0.4 μm. Further, they were subjected to thermodiffusive carburization from graphite in an argon atmosphere (0.1 MPa) and vacuum (1.3– 133.3 Pa), where the oxygen partial pressure varied from 0.2 to 200 Pa. Saturation was carried out at 950 – 1100° C for 5 h. We analyzed the phase composition of the obtained coatings on a DRON-3.0 X-ray diffractometer in CuK α -radiation under a voltage U = 30 kV and a current I = 20 μA. The tube was focused using the Bragg – Brettano scheme. The measurements were carried out with a scanning step of 0.05° and an exposure at a point of 4 sec. Results and Discussion To form carbide layers on titanium alloys, graphite is the optimal medium [3, 4]. The phase composition of surface layers of the specimens depends substantially on the temperature of their treatment (within the range 950 – 1100°C) due to the evolution of the carbide phase during saturation. For example, in the case of carburiza- tion of VT1-0 titanium from graphite in argon at 950°C, titanium dioxide TiO 2 in rutile modification is formed Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Translated from Fizyko-Khimichna Mekhanika Mate- rialiv, Vol. 39, No. 3, pp. 81 – 84, May – June, 2002. Original article submitted August 8, 2002. 400 1068–820X/03/3903–0400 $25.00 © 2003 Plenum Publishing Corporation