Influence of carburization on the structure and properties of functional diffusion coatings based on titanium carbide on TiC-WC-Co and WC-Co alloys

Abstract

The technology of applying diffusion titanium coatings from the medium of low-melting liquid-metal melts to hard alloys of the TiC-WC-Co and WC-Co types is described. It is shown that in the case of diffusion saturation of the surface layers of a hard alloy tool of the TiC-WC-Co and WC-Co types with titanium from the Pb-Bi-Li-Ti melt, preliminary carburization is an obligatory stage in the process of coating formation, and allows avoiding the formation of a decarburized zone under the diffusion layer. The effect of preliminary carburization on the phase composition of the coated hard alloy is shown. As a result of the phase analysis, it was revealed that the surface layer contains such phases as WC, TiC, Co 2 C, Co-C. In this case, titanium carbide TiC is formed due to the destruction of cobalt carbide upon further diffusion saturation with titanium. In the absence of carburization, the formation of a decarbidized layer was revealed, which differs from the coating and the base in lower microhardness, the drop in microhardness is about 1000 MPa. After carburization, there was a slight increase in the hardness of the coated parts from 89 to 91 HRA. Characteristics such as the microhardness of the carburization zone and its length depend on the temperature and duration of the preliminary carburization, as well as on the elemental composition of the material to be coated. Carburization was carried out in the temperature range from 950°C to 1150°C from 30 to 120 minutes. After saturation with carbon, the thickness of the carburization zone was from 2 to 25 μm, the microhardness from 16700 to 17150 MPa for the WC-Co alloy and from 18750 to 19200 MPa for the TiC-WC-Co alloy. The hardness of the layer under the coating ranged from 27000 to 28500 MPa for the TiC-WC-Co alloy and from 19300 to 23500 MPa for the WC-Co-type alloy.

Influence of diffusion alloying of structural steels by nickel and copper in the medium of low-melting liquid-metal solutions on their corrosion resistance

“…Diffusion alloying in the medium of low-melting liquidmetal solutions (DALLS) is considered as the most prospective TCT technology [13,14]. This technology allows to obtain defect-free coatings with homogeneous structure on the components with complicated shape, which are fabricated from structural steels, cast irons, hard alloys.…”

Features and regularities in formation of diffusion nickel-copper coatings on steels in the medium of low-melting liquid-metal solutions

“…Diffusion metallization as a kind of chemical and thermal treatment is used in machine-building not very widely; it is connected with insufficient information about the processes which are occurring during metallization, as well as with insufficient testing of the technologies. Thereby conduction of fundamental research of the processes and mechanisms of formation of diffusion coatings is rather actual [1][2][3][4][5][6][7][8][9]. This paper considers the features and regularities of formation of multi-component Ni-Cu based diffusion coatings, providing substantial improvement of operation properties of products which are working at impact and cyclic loads in the aggressive media.…”

“…This paper considers the features and regularities of formation of multi-component Ni-Cu based diffusion coatings, providing substantial improvement of operation properties of products which are working at impact and cyclic loads in the aggressive media. The method for diffusion alloying in the medium of low-melting liquid metal solutions (DALMLMS), which was developed by the authors, was used for applying of Ni-Cu coatings [1][2][3][4][9][10][11][12]. The passed investigations displayed that this method provides formation of homogenous defect-free coatings on products with extra complicated shape within the range from 10 minutes to 2 hours [10,12].…”

“…The method relates to chemical and thermal treatment, and adsorption and diffusion processes make the base of the mechanism of coating formation [1,4,[10][11][12]. However, the processes of mass transfer, activation of coated surface and adsorption have the decisive effect on the mechanisms of formation of diffusion-saturated (alloyed) layers as well as on their elementary, structural and phase composition and operating properties of coated products.…”

Влияние Комплексной Химико-Термической Обработки На Коррозионную Стойкость Стальных Изделий

“…При этом технологии ХТО можно разделить на две группы: 1) технологии, которые оказывают основное влияние на поверхностный слой изделия (например, азотирование), не позволяя получать диффузионные слои большой толщины; 2) технологии, позволяющие повысить одну характеристику, при этом, снижая другую (например, при цементации увеличивается твердость, но снижается коррозионная стойкость). Одной из перспектив-ных технологий ХТО является комплексная ХТО (КХТО), заключающаяся в совмещении цементации и диффузионного легирования в среде легкоплавких жидкометаллических растворов (ДЛЛЖР) [3,4,[9][10][11]. Технология ДЛЛЖР основана на явлении изотермического, селективного переноса элементов покрытия, растворенных в легкоплавком расплаве, на поверхность изделия с последующим диффузионным взаимодействием элементов покрытия с основным материалом изделия [4].…”