PSI - Issue 36

Victor Shapovalov et al. / Procedia Structural Integrity 36 (2022) 262–268 V. Shapovalov, I. Protokovilov, V. Porokhonko / Structural Integrity Procedia 00 (2021) 000 – 000

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Figure 6 shows fractographs of samples after impact tests. Initial inspection of fracture surfaces at low magnification (×100) showed the following. The nature of fracture of the base metal is transcrystalline (Fig. 5 a). The fracture surface is matte. The main crack develops strictly perpendicularly to the applied load, mainly by grain body. The nature of fracture of the weld metal and HAZ, transcrystalline, mixed-type (Fig. 5 d, g). Fracture surfaces are matte-shiny, but there is more of a matte component. The main crack changes its direction in the process of development. Further studies were carried out at higher magnifications. It was found that the base metal fracture pattern is transcrystalline, ductile, with a dimpling surface (Fig. 5 b,c). The weld and HAZ metal are characterized by similar mixed-type transcrystalline fracture with areas of both ductile (dimple) and brittle (cleavage facets and quasi cleavage) fractures (Fig. 5 e, f, h, i). But, it should be noted that, compared with the HAZ, the fracture surface of weld metal had dimples and facets of a larger size, which indicates a significant grain growth in this zone. In general, it can be assumed that the branching of cracks in the weld and HAZ metal contributed to the fact that the crack required more energy for its propagation, therefore, the impact toughness value increased compared to the base metal, where fracture occurred without branching. 4. Conclusions A technology and conditions of electroslag welding of Ti-6Al-4V alloy slabs with a thickness of 100 mm has been developed. The technology provides: - dense structure of welded joint without macro and micro defects; - the gas composition of the weld metal meets the requirements of the standard, which indicates the reliable protection of the weld metal from atmospheric gases contamination; - the tensile strength of the weld metal is about 90 % of the strength of the base metal and impact toughness is 1.6 times higher. The mechanical properties of the welded joint are primarily related to the grain size and microstructure of weld metal and HAZ, which are formed under conditions of a low cooling rate and high heat input used for the ESW process. References Paton, B., Yushchenko, K., Kozulin, S., Lychko, I., 2019. Electroslag welding process. Analysis of the state and tendencies of development (Review). The Paton Welding Journal 10, 33 – 40. Yushchenko, K., Lychko, I., Kozulin, S. et al., 2018. Application of welding in construction. The Paton Welding Journal 9, 23 – 27. https://doi.org/10.15407/tpwj2018.09.05 Kaluc, E., Taban, E., Dhooge, A., 2006. Electroslag welding process and industrial applications. Metal Dunyasi 152(13), 100 – 104. Yushchenko, K., Kozulin, S., Lychko, I., Kozulin, M., 2014. Joining of thick metal by multipass electroslag welding. Ibid. 9, 30 – 33. https://doi.org/10.15407/tpwj2014.09.04 Paton, B., Dudko, D., Palti, A. et al., 1999. Electroslag welding (Prospects of development). Avtomatich. Svarka 9, 4 – 6 [in Russian]. Shcherbinin, E., Kompan, Ya., 2005. MHD Technologies of Electroslag welding and melting of Titanium alloys for aerospace industry, The 15th Riga and 6th Pamir Confrerence on fundamental and applied MHD 287 – 290. Devletian, J., Chen, S.J., Wood, W., et al., 1990. Fundamental aspects of electroslag welding of titanium alloys. Recent trends in welding science and Technology, S.A.David and J.M.Vitek, eds., ASM International 419 – 424. Chen, S.J., Devletian, J.B., 1990. Microstructure and mechanical properties of electroslag welds in Ti-6A1-4V alloy. Weld. J. 69 (9), 319 – 324. Protokovilov, I., Porokhonko, V., Petrov, D., 2013. Technological peculiarities of electroslag narrow-gap welding of titanium. The Paton Welding Journal 1, 34 – 38.