Microstructure characterization of laser solid forming Ti-6Al-4V alloy by high power

The microstructure characterization of laser solid forming (LSF) Ti-6Al-4V alloy by high power was investigated, the mechanism of the microstructure formation by high power LSF was revealed, and the differences and reasons of microstructure forming were analyzed compared with the low power LSF. The results indicate that because of lower temperature gradient and higher speed of solidification by high power, the macrostructure consists of three sections: bulky columnar crystal, small bamboo-like columnar crystal and equiaxed grains. The layer band exists in each deposited layer. But only the bulky columnar crystal through multiple layers grows epitaxially from the substrate along the deposition direction by low power LSF. The microstructure within layer band consists of colonies of Widmanstätten α lath outlined in retained β, while the microstructure between the layer bands consists of basketweave Widmanstätten α lath, and some of them are spheroidized into equiaxed α lath. Compared with typical microstructure by low power, the length-width ratio of the α lath decreases obviously, and no needle α lath exists.