Making weld joints of dissimilar titanium alloys under low-temperature superplasticity conditions

M.X. Mukhametrakhimov


Experimental studies of the solid-phase weldability of VT6 and VT14 industrial titanium alloys are carried out in the temperature range of low-temperature superplasticity (SP). In welding of dissimilar titanium alloys a significant reduction of the process temperature can be achieved by alloying with Mo. The use of an ultrafine grained (UFG) sheet of VT14 alloy, which is alloyed by Mo to stabilize the β-phase allows, enables to localize the deformation at the junction zone due to a significant difference between the flow stresses of the interlayer and sheets to weld. As a result, a structural laminate of sandwich type is obtained that contains two interfaces between the alloys VT6 and VT14. As the studies have shown, when approaching the junction zone from VT6 alloy, some small Mo content is detected and at the junction plane this content increases to the value typical for the base composition of VT14. Mechanical tests show that the pressure welding of sheet billets in different combinations results in a high level of mechanical properties and quality of the joints. For a comparative analysis, VT6 sheet billets without any intermediate sheet were joined under the same conditions. Mechanical tensile tests showed that there is a small delamination between the titanium sheets in the failure zone. A quality solid-phase joint in this case can be obtained by increasing the pressure and prolonging the time of process. It can be concluded, therefore, that obtaining high-quality solid-phase joints of dissimilar titanium alloys depends not only on the size of the intermediate sheet grains, but also on the chemical and phase composition of material in the joint zone.

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