Development of thermal protection systems is one of the important engineering problems that should be solved at development of reusable space vehicles. Metal panels of thermal protection systems should consist of separate tiles with individual fastening to load-carrying structure of space vehicle, with surface density of not more than 10 kg/m 2 , capable of withstanding multiple long flights and providing temperature lowering from 1100 ºC on the outer wall to 200 ºC on the inner wall. The work shows the results on development of the technology of vacuum diffusion welding of a three-layer honeycomb panel from experimental powder alloy YuIPM-1200. Technological samples of three-layer honeycomb panel were made from this alloy, and their testing was performed in the working temperature range. 7 Ref., 11 Figures. K e y w o r d s : thermal protection systems; metal three-layer panel, powder high-temperature alloy, vacuum diffusion welding, thermal cycling tests Received 06.10.2016 Figure 11. Appearance of mock-up lower (a) and upper (b) skins before thermal cycling (1) and after 11 thermal cycles (2)

A complex of properties of aluminium alloy 2219 welded joint, made by single-pass welding with a non-fusible electrode along and across the rolled product, and heat-treated to the state T62, in liquid amyl and its vapors at a temperature of 50 °C for 45 days was investigated. Characteristics of plasticity and strength of 2219 alloy welded joints are as follows: in the longitudinal (D) direction – yield strength of the welded joint is (301–317) MPa, of the base metal (295—297) MPa, strength limit of the welded joint (409–415) MPa, of the base metal (422–425) MPa, elongation is (4.0–5.8)% and (17.6–19.1)%, respectively; in the transverse (P) direction – the yield strength of the welded joint is (309–331) MPa, of the base metal (304–307) MPa, the yield strength of the welded joint (392–414) MPa, of the base metal (428–433) MPa, elongation is (2.1–3.3)% and (12.6–15.0)%, respectively. The strength coefficient of welded joints in the longitudinal direction is 0.96, in the transverse – 0.94. Welded joints in the above environment are resistant to corrosion cracking and intergranular corrosion, resistance against exfoliating corrosion is evaluated by grade 2. Resistance of 2219 alloy in T62 state in amyl corresponds to the resistance group «stable», in amyl vapors – the group “highly resistant”. After aging in amyl and amyl vapors, the strength grades of the base metal samples and welded joints in both directions are almost unchanged, the plasticity parameters change ambiguously: the yield strength of the base metal increases by ~ (5–6)%, of welded joints decreases by ~ (6–7)%, the relative elongation of the base metal is reduced by ~ (5–16)%, of welded joints by about ~ 20 %. Independently of the direction of welding relative to metal’s rolling, samples’ fractures are mostly viscous. After the exposing in amyl, the coefficient of the strength of welded joints in the longitudinal and transverse directions is the same and equal to 0.91, after the influence of amyl vapors, it is 0.95 in the longitudinal direction and 0.96 in the transverse direction.

The problem of effect of solidification rate on structure of weld metal of scandium-containing aluminium alloys is considered. Peculiarities of scandium precipitation from melt in solidification of aluminium alloys under non-equilibrium conditions, simulating fusion welding, are investigated. Procedure of investigations has been developed and confirmed experimentally. Advantage of offered procedure over the existing ones consists in the fact that it allows simulate almost all the methods of fusion, from argon arc non-consumable electrode welding to electron beam welding. It is shown that the procedure satisfies the put aims completely. Microstructural investigations of ingots in height showed that within the interval of solidification rates from 10 3.3 to 10 2.5 °C/s the change of form of solidification occurs from dendritic to subdendritic ones. It was found that at rates of solidification, commensurable with solidification of weld metal, up to 0.41 % Sc can be contained in solid solution of alloys. When applying the highly concentrated power sources, such as electron beam, it is possible to reach the similar value also in welds. In arc methods of welding approximately 0.3 % Sc can be assimilated in solid solution of weld metal. It was found that it is necessary to provide its content in weld metal at the level of 0.35-0.40 wt.% to maximization of effect from alloying of welds with scandium. In this case the increase in mechanical properties of weld metal is provided both by refining of its crystalline structure, and also by hardening the solid solution by scandium. 7 Ref., 3 Tables, 4 Figures.

Structural transformations and formation of chemical inhomogeneity in the weld and HAZ metal in fusion welding of complex alloy of V96 type were studied. It is shown that under the influence of welding heat, partial melting of the alloy phase components proceeds in the heat-affected zone with formation of structures of eutectic origin in the form of extended interlayers along the grain boundaries, causing metal embrittlement. Scandium addition to the alloy enables reducing the solidification processes and degree of segregation along the grain boundaries, as well as localizing partial melting of the grains without formation of coarse eutectic interlayers.

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