To cite this article: A.I. Khorev (2008) Complex alloying and heat treatment of titanium alloys, Welding International, 22:6, 364-368,
IntroductionThe currently available structural titanium alloys and filler materials ensure high reliability of welded structures.In future, advanced aircraft systems will be produced from titanium alloys with the strength level of 1100 MPa and the specific strengths of s B /g > 24 km, with considerably higher efficiency in comparison with aluminium alloys and steels. The welded structures will prevail in this area because they are characterised by higher technological properties in manufacture and by higher values of the coefficient of utilisation of the metal. Therefore, the level of the mechanical properties of the welded joints is the main factor which determines the prospects of using structural titanium alloys 1-3 .
Requirements imposed on titanium alloysThe following requirements are imposed on the currently available titanium alloys:-the tensile strength of semifinished products (sheets, plates, forgings, stamped products, etc) should not be lower than 1100 MPa;-the tensile strength of the welded joint s B w > 0.9 s B pm (s B w > 990 MPa); -the specific strength should be s B /g > 24 km (the commercial unit reflecting the length of the filament capable of holding its mass without fracture); -relatively low cost because of the cost of materials is one of the main components of the cost of the component as a whole;-universal nature in the manufacture of all types of semifinished products and production of all types (welded, brazed and monolithic) structure; -sufficient resources in the country and the possibility of large-scale production;-good weldability and technological efficiency in welding;-technological plasticity and the possibility of producing components of the required shape by hot, isothermal or cold stamping followed by heat treatment in dies or special devices;-high technological properties in heat treatment (energy requirement, labour content, complexity of the process); -high technological efficiency in machining of components.Specific strength is the main characteristic which determines the weight efficiency and a decrease in the weight of the structures.To obtain the required weight efficiency of the welded structure, two directions may be followed:-increase of the strength of the parent material at s B w / s B pm = 0.9; -increase of the value s B w / s B pm ; -at a specific strength of 24 km, the specific strength of the welded joint should be in the range 0.9-24 km, which corresponds to 21.6 km.If the ratio of the strength values of the welded joint and the parent metal is increased from 0.9 to 0.95 by improving welding, the given task may be solved at a specific strength of the parent material of 21.6/ 0.95 = 22.73 km. The strength of the ternary metal can be achieved in VT23 (VT23M) alloys in the annealed condition and the weight efficiency, required by the designer, can be reached.Special attention should be given by the designers and technologists to ...