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Rings from titanium alloy Ti6Al4V used for making pressure vessels for launch vehicles are studied after annealing and after solution treatment and aging. The mechanical characteristics of the rings after quenching and aging do not always have the specified values, especially in thicker sections. The studied rings are of two sizes and have a final wall thickness of 30.5 and 17.5 mm. The effect of the temperatures of solution treatment and aging, of the quenching rate, and of the section thickness on the mechanical properties is studied, and the process is updated to provide the required properties. INTRODUCTIONTitanium alloy Ti6A14V is a promising material for the aerospace industry due to its high specific strength. The alloy is used for making fuel tanks of launched vehicles and satellites. The tanks are fabricated by welding domes and rings that are delivered in two conditions, namely, after annealing or after quenching and aging. The process of production of rings in annealed condition is relatively simple and well developed. The process of production of rings in quenched and aged condition is more complex and requires optimization with respect to several parameters in order to provide the specified mechanical properties, especially in the case of large sections. For this reason, quite a number of works have been devoted to determining the optimum conditions for the production of rings starting with melting of the alloy and ending with the heat treatment of ready articles [1,2]. The final mechanical properties of titanium alloys are determined by the morphology of the products of the martensitic transformation and of the decomposition of a¢-martensite during aging. Due to the low thermal conductivity of titanium the occurrence of these processes and hence the formation of the specified properties depends substantially on the sizes of the section.The aim of the present work was to optimize the heat treatment process (solution treatment and aging) in the production of rings from titanium alloy Ti6Al4V. METHODS OF STUDYWe obtained titanium alloys by the vacuum arc remelting (VAR) process with a cold compacted electrode. We used several remelting operations to control the content of gases and impurities in the ingot. The ingot was forged and rolled to the required ring sections. The preform was subjected to deformation (upsetting and drawing) to provide good results after the heat treatment. The rolled rings were subjected to a heat treatment involving solid solution treatment and aging. We studied rings of two sizes having a diameter of about 1.2 m and a wall thickness h = 17.5 and 30.5 mm. A typical production cycle included double VAR, forging, pancaking and piercing, saddling, ring rolling, solution treatment, measurement of the mechanical properties of specimens and rings, ultrasonic inspection, proof machining, and final inspection.The chemical analysis of the alloy was performed by the method of optical emission spectroscopy. The content of the gases (oxygen) was analyzed by the Leco method. The mechanical...

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