Formation of carbonitride coatings on titanium by contact and noncontact methods
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FORMATION OF CARBONITRIDE COATINGS ON TITANIUM BY CONTACT AND NONCONTACT METHODS O. I. Yas’kiv, I. M. Pohrelyuk, V. M. Fedirko, and R. V. Proskurnyak
UDC 669.295:621.785
We study the procedures of thermodiffusion carbonitriding of titanium. It is shown that carbonitriding can be realized in the α-region of titanium and that it is possible to affect the surface quality of the coating and its properties by optimizing the temperature, time, and gas-dynamic parameters of carbonitriding and choosing the proper procedure of carbonitriding.
In recent years, significant attention of the researchers is given to multicomponent interstitial compounds of titanium (carbonitrides, carboxides, and oxynitrides). This is explained by the fact that their physicomechanical properties are better than the properties of binary compounds [1]. This is why they are more frequently used for the formation of functional coatings [2 – 4]. There are numerous technologies aimed the formation of coatings containing multicomponent titanium interstitial phases [5–7]. The procedure of thermodiffusion saturation can be regarded as the most universal, as far as the reproducibility of the results (independently of the structure and sizes of the components) and cost efficiency are concerned. Titanium is saturated from multicomponent media mainly by the method of gas saturation realized via the interaction of the gaseous phase containing the diffusants with the surface of the material. This procedure can be either “contact” (or, in other words, realized by the “powder method” because both the diffusant and the components of the remaining part of the saturating mixture are powders) and “noncontact.” In the contact method, the gaseous phase is generated in the immediate proximity of the saturated surface as a result of the interaction of powder particles of the diffusant (either in the free or in the bound state) with one of the gases of the saturating atmosphere. In the noncontact case, the gaseous phase is generated at a certain distance from the saturated object whose surface is not in contact with the diffusant and is surrounded solely by the gaseous phase containing a compound of this element. In both cases, the presence of activators in the saturating media is required. In view of the specific features of high-temperature behavior of titanium alloys and the operating conditions of products made of these alloys, the procedures of treatment of these materials must satisfy certain requirements. In particular, it is necessary to restrict the upper bound of the temperature of treatment, which should not be larger than the temperature of the polymorphic transformation (because this would deteriorate the mechanical properties of titanium and promote the embrittlement of the obtained coatings [8]), to guarantee high quality of the surface (depending on the temperature of the process and estimated according to its roughness), and form the surfaces of the same color because binary and ternary compounds are often used as decorative [9]. In what follows, we c
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