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...
Nickel-based superalloy Inconel 625 is widely used in aeronautical, aerospace, chemical, petrochemical and marine applications due to its good mechanical properties, weldability and resistance to high temperature corrosion on prolonged exposure to aggressive environments. It is a solid solution strengthened medium strength superalloy, which contains chromium, molybdenum and niobium as alloying additions. Considering the chemistry and specification requirements of the alloy, it was processed through vacuum induction melting (VIM) process followed by electro slag remelting (ESR) route to obtain alloy with controlled gas and inclusion contents. Homogenisation cycle was selected and was carried out at 1170°C temperature to obtain uniformity in chemistry and microstructure. Chemical homogeneity was confirmed through analysis of samples from top, middle and bottom of the secondary ESR ingot. Hot working range was decided considering the flowability of superalloy and the same was carried out under close monitoring of temperature and with specified amount of reduction per stroke. Intermediate reheating and reduction during forging was noted to be an important aspect so to avoid cracking during forging. Processing parameters were established to obtain forgings of different thicknesses with sound ultrasonic quality. Microstructure analysis revealed single phase austenitic grain structure with ASTM grain size no. 4-7, confirming that material has undergone sufficient amount of mechanical working. Mechanical testing was carried out and the mechanical properties were found to be meeting the requirement. Present paper provides details of melting process selection, thermomechanical processing and characterization of the superalloy to achieve the targeted mechanical properties.
Ti6Al4V owing to its high specific strength and Inconel-718 due to its high strength and oxidation resistance at elevated temperatures, have been used in Reusable Launch Vehicle-Technology Demonstrator (RLV-TD). Achieving required properties in large cross-section aerospace quality forgings of these alloys is challenging and has not been reported earlier. Hence, thermo-mechanical processing cycles have been devised to realize forgings of ~1400 mm length in these alloys and successfully used in RLV-TD. Forgings of these alloys having desired microstructures and ultrasonic quality of Class-A1 as per AMS 2630 B standard have been realized. This article discusses the processing challenges and solutions thereof.
TP 2230standards. Most of the products were indigenously developed to meet products of global standards. The contribution of MIDHANI titanium alloys as import substitutes for the year 2006-07 has been to the tune of Rs. 3569 lakhs.Titanium alloys can be classified as alpha, alpha beta and beta alloys. MIDHANI manufactures all three variants. Titanium and titanium alloys find extensive application in aerospace industries due to their superior strength to weight ratio (specific strength). Application of MIDHANI alloys include marine and petro chemical industries, aerospace, nuclear, power and bio medical. MIDHANI Titan 12, 14, 15 etc. commercially pure grades of titanium are known for their excellent corrosion resistance. Titan 21 ELI, Titan 31 ELI, BT 14 are meant for cryogenic applications. BT9, BT 5-1, BT 3-1, GTM-Ti-64, OT 4-1 etc. are used for making blade, disc and various components of turbo engine of Aircraft. PT-1M and PT-7M grades were indigenously developed for marine applications.Titan 31 is extensively used for space components such as gas bottles, rings and other structural members of space vehicle and satellite. In continuation of its contribution to strategic sectors, the developments undertaken for the year 2006-07 include, Ø Highly cold workable beta titanium alloy Titan 42 for aerospace application.Ø Highly corrosion resistant Titanium-Tantalum-Niobium grade TITANB for nuclear applications. MANUFACTURING FACILITIESMIDHANI has facilities for processing of titanium and titanium alloys to the tune of 200T per annum. Company has the facilities for ingot making to finish mill products including bars, plates, sheets, strips, wires, gas bottles, welded tubes and rings. MeltingMIDHANI sources titanium sponge and master alloys from external resources like Japan, Russia, CIS countries and China. Titanium sponge is compressed in a 3000T Press to make brick like compacts. These compacts are welded together in a plasma welding unit to get an electrode of 1.4T to 6.0T. Figure 1 depicts entire process flow for the production of titanium ingots and mill products.
The alloy 44Ni-14Cr-2.6Nb-1.7Ti-1.5Mo-0.3V-Fe is derived from the family of super alloys 706 and 718 compositions. It is a precipitation hardenable alloy with its primary constituents consisting of Niobium and Titanium. A balanced content of Nickel, Chromium and Aluminium in alloy 706 provides good hardenability and resistance against oxidation and corrosion. Further modified 706 with Molybdenum and Vanadium improve its high temperature capabilities. Modified 706 displays excellent mechanical properties in combination with good fabricability compared to structurally complex 718. This alloy finds application in aerospace field requiring high strength and ease of fabrication. The present paper describes the manufacturing practice adopted and presents mechanical properties evaluated on various products.
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