Research On The Properties Of Large Scale Ti-6Al-4V Made By Selective Electron Beam Melting

Compared with the additive manufacturing technology using laser as energy,selective electron beam melting(SEBM)is under the environment of high vacuum which is suitable for the manufacturing of refractory rare metal parts.It has a lot of advantages,such as a high energy density,a high scanning speed,controlled powder bed temperature,small stress in components.Selective electron beam melting was point by point scanning and layer by layer accumulation,which is important to ensure the consistency of structure and properties in components.The height of sample is about a few millimeters in the reports of selective electron beam melting titanium alloy,the properties along the height direction of large sample was rarely involved.In this paper,the samples(12 mm x 300 mm height)were fabricated when Arcam A2 fabricated large parts,which were treated by hot isostatic pressing(HIP),the structure and properties of as-built sample and HIP samples were studied.The density of the as-built sample is 4.388 g/cm~3,which was 99%of the theoretical density.The directions of original β columnar crystals were parallel to the direction of deposition,which of the bottom of were larger than the top of the sample.The structure in the original coarse β columnar crystals were very small,the thickness of α lamellar at top,middle,and bottom of sample were 1.15μm,1.00μ.m and 0.79μm respectively.The reduction of area at top of sample reached to 52%,which of middle and bottom were 39%and 34%respectively.After hot isostatic pressing process,the density of the samples increased to 99.9%of the theoretical density,and the defects in samples were eliminated.The hot isostatic pressing process was near the phase transition point for 2 hours,the thickness of a lamellar at top has grown up to 4.93μm,the bottom of which has grown up to 4.56μm,which was about 5 times larger than the as-built sample.Because of a lamellar growing up,the yield strength and tensile strength has decreased by about 10%of as-built,and elongation and reduction of area of top has increased by about 1%,but the middle and bottom of sample has increased by more than 40%.The heterogeneity of structure and mechanical properties of top and bottom of sample was related to the homogeneity of performance,the microstructure and mechanical properties of samples has become consistent after treated by hot isostatic pressing.This study is very vital to improve the forming process of SEBM and improve the stability of the parts fabricated by SEBM.