Flow Behaviour of Ti-6Al-4V Subjected To Step Temperature Isothermal Forging

Three different samples of Ti -6Al-4V of size 10mm diameter x15mm height compressed at a strain rate of 102 sec -1 in a 100KN servo hydraulic machine (DARTEC, UK make) with three different initial temperatures. First specimen of Ti-6Al-4V was compressed at an initial temp 1123K from initial length 15 mm to 10mm then the temperature was reduced to 1073K and compressed to a length of 7 mm now the temperature further reduced to 1023K and comprised to 3mm.The set of 2 more compressions were repeated at two more progressively decreased temperatures. Flow behavior of the specimens was observed at different stages of compression. Softening parameter has been calculated after a strain of approximately 0.4(compression at each step of temperature). Higher softening parameters were obtained at the compressions with initial temperatures 1073K and 1023K.This indicates the grain refinement. At 1123K the Softening parameters are lower indicates grain growth at higher temperature. Microstructures have been observed at the end of final compression. As huge strain imposed on the specimen reduced the grain size from 16 μm to approximately 8 μm, which is suitable for super plastic deformation and also improved strength Keywords— flow curves, grain refinement, step temperature isothermal forging, softening parameter.