Indian Welding Journal

S. Sundaresan ¹

Affiliations
1 IIT, Madras, IN

Abstract

Although the importance of welding as a specialized branch of engineering science was realized in India only by the late 1950s, much progress has since been made in welding education and research.

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K. Keshava Murthy ¹, S. Sundaresan ¹

Affiliations
1 Department of Metallurgical Engineering, Indian Institute of Technology, Madras, IN

Abstract

The high strength-to-weight ratio of titanium alloys has contributed to their extensive use in the aerospace sector. More recently, however, their excellent resistance to corrosion and generally superior mechanical properties have resulted in their increasing use in the chemical industry as well as by the medical profession. Many of these applications involve welded joints and from this point of view the alpha-beta titanium alloys are considerably more difficult to join than the alpha or the beta alloys. Within the alpha-beta family, though many highstrength alloys have been developed to have greater fracture toughness than the standard alloy Ti-6AI-4V, their use has been limited because of poor weldability [1]. This is because of invariably low ductility in the as- welded condition and there is some evidence that, with the addition of increasing amounts of beta stabilizers, the ductility deteriorates further [2]. This has led to the design philosophy in the erstwhile Soviet Union involving the development of titanium alloys with moderate strength but appreciably greater ductility for welded fabrications subjected to complex stresses. While heavier cross-sections can be used for maintaining load-carrying capacity, the ductility would ensure satisfactory weldability [3].

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K. Keshava Murthy ¹, S. Sundaresan ¹

Affiliations
1 Dept, of Metallurgical Engg., Indian Institute of Technology, Madras 600 036, IN

Abstract

Tensile fracture of a-(5 titanium alloy weldments is sensitive to microstructure. Thus, though it occurs macroscopically at low ductility, it follows a void coalescence mechanism. The paper describes work in which the alloy Ti-6AI- 4V has been welded and heat-treated under different conditions. The role of the morphology and distribution of the a and p phases on the mode of tensile fracture has been discussed. Fracture toughness measurements of the fusion zone have shown that (i) the as-welded structure resists crack growth better than the base material; and (ii) post-weld treatment high in the (x-p field (say at 900°C) confers a further improvement over the as-welded level, while treatment at intermediate temperatures like 700°C could actually be detrimental. The paper explains the reasons for this behaviour in terms of microstructural features and scanning-electron fractographic observations.

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