IN-SITU HIGH TEMPERATURE EBSD ANALYSIS OF THE EFFECT OF A DEFORMATION STEP ON THE ALPHA TO BETA TRANSITION IN ADDITIVE MANUFACTURED Ti-6Al-4V

摘要

Additive Manufacture (AM) of Ti-6Al-4V generally leads to an undesirable microstructure with a non-random texture. The alpha texture is inherited from large columnar β grains that grow across the deposited layers with a strong preferential <001> growth direction. It has been found in AM that the application of a surprisingly small amount of plastic strain to each layer, by methods such as in-process rolling, can disrupt the columnar growth and produce a more randomly orientated, fine equiaxed β grain structure, and consequently a refined final microstructure and far weaker alpha texture. The origin of this interesting effect was investigated by direct in-situ observation of the formation of new β grain orientations, within the retained deformed beta, and their growth on reheating near to the transus temperature, by EBSD analysis. This analysis has shown that α colonies twin during deformation, which generates new beta orientations during reheating.