Microstructure and fracture property of electron beam rapidly manufactured TC4 alloy

Microstructure and fracture morphologies of as-deposited TC4 samples fabricated by rapid manufacture of electron beam selective melting (EBSM) were observed and analyzed by a digital microscope and a scanning electron microscope respectively. The influence of different build geometries and load directions on the fracture properties was studied. The results indicate that fracture properties of vertical samples are influenced by columnar crystals and characterized by its anisotropy. The fracture toughness (K-IC) in the deposition direction of vertical samples is 94. 94MPa . m(1/2) which is greater than that in the electron beam scanning direction (85. 33MPa . m(1/2)) and the elongation (delta) of 3% is very low; a morphology has some influence on the fracture properties. The elongation (delta) and fracture toughness (K-IC) in horizontal samples with lamellar a colony are greater than that in vertical samples with crossed acicular a, and the maximum is 14. 5% and 101. 45MPa . m(1/2), while the ultimate tensile strength (sigma(b) ) and the yield strength (sigma(0.2)) are lower; furthermore, the fracture of EBSM-TC4 samples consists of different sizes of dimples and circuitous tearing ridges. So the fracture method is characterized by ductile dimple-based intergranular fracture and the circuitous degree of tearing ridges as well as size and depth of dimples on the fracture morphologies of horizontal samples are greater than that in vertical samples.