BS in Materials Engineering
Materials Engineering Department
Tensile coupons of Ti-6Al-4V were heat treated at varying annealing temperatures from 1200°F (648°C) to 1450°F (787°C) at 50°F (23°C) increments for 1 hour. The samples were air cooled to room temperature or furnace cooled to 800°F (426°C) followed by air cooling to room temperature. Four tensile coupons were treated at each annealing temperature and cooling rate. Alpha case was observed to form on the surface of the samples post heat treatment with a maximum depth of 25 µm (.001 in). Samples were tensile tested for their ultimate tensile strength, yield strength, and percent elongation. Samples across all annealing temperatures averaged an ultimate tensile strength of 920 MPa (133 ksi), a yield strength of 880 MPa (127 ksi), and a percent elongation of 15%. These values are higher than the given standards for annealed Ti-6Al-4V by 20 MPa, 50 MPa, and 5%, respectively. This is an offset of 2 to 5% for overall stress, and 50% for elongation. Micrographs of all samples showed equiaxed grains of primary alpha with transformed intergranular beta. The average grain size of primary alpha was 10 µm (4.0x10-4 in). These annealing temperatures, which fall under the martensitic starting temperature in the alpha-beta phase field, further relieve residual stresses in the material without compromising the morphology of the alpha-phase. The extent of annealing temperature within this range offers little difference to the strength of the material and microstructure given the hot worked and annealed samples.