Effect of heat treatment and laser multi-track overlapping on microstructure of a laser melting deposition TC18 titanium alloy

The effect of three different heat treatment processes and laser multi-track overlapping on the microstructure of laser melting deposition TC18 titanium alloy were investigated. The results show that, with the sequence of stress relieving annealing, isothermal annealing, double annealing, both the α phases at the grain boundaries and the α plates within the grains appeared to be coarsening gradually. The large columnar grains gradually split into smaller ones, and the shapes of other finer grains turned to be equiaxed. Because of the great temperature gradient and short interval time of remelting in the overlapping area of laser scanning, the large columnar grains were formed. While in the non-overlapping area, the lesser temperature gradient and longer interval time of remelting could not meet the standard for the epitaxial growth of columnar grains, so small grain cingulums were formed.