Investigation on K_IC of as-deposited Ti-6Al-4V alloy fabricated by laser solid forming

Samples of Ti-6Al-4V used in the test of plane strain fracture toughness (K_IC) test is fabricated by laser solid forming (LSF). Primary β grain, with a characteristic of epitaxial growth along the depositional direction, shows an average width of 100~400 μm and length of several centimeters. Within β grains, lathy α needles and fine-weaved dense Widmanstatten α+β laths are observed. K_IC≥52.6 MPa · m^1/2 reaches the forging standard. And as same as the tensile property of LSF Ti-6Al-4V sample, K_IC property presents remarkable anisotropism which is caused by the microstructure characteristic. Fine-weaved dense Widmanstatten α+β laths owns strong ability in anti-crack-propagation, in result, crack-propagation shows sentivites to β grain boundary. If crack propagation runs the direction perpendicular to β grain boundary, K_IC value reaches maximum; if crack propagation runs the direction along β grain boundary, the longer the boundary, the higher the K_IC value. It is more easier for crack propagation with a small angle between crack-propagation direction and β grain boundary(0-90°). The bigger angle and smaller β grain both result in difficulties in crack-propagation.