Microstructural Evolution in the TC17 Titanium Alloy Processed During Laser Stereo Forming

In this paper, the microstructure evolution of TC17 titanium alloy prepared by laser stereo forming (LSF) was investigated. Forged TC17 plate was selected as the base material, and TC17 titanium alloy spherical powder with the size of 50-150 mu m was the candidate cladding material. The microstructure in deposited TC17 titanium alloy was consisted of three parts, namely fine grains at the bottom of the deposition area, coarse beta columnar crystals at the middle, while coarse beta columnar crystals or equiaxed crystals at the top. The microstructure is significantly affected by the thermal cycle history during the LSF process. At different locations of the deposited samples, the composition, morphology, size and volume fraction of the phases in the grains are discrepant, as the metastable beta phase and the acicular martensite (alpha ') structure were obtained at the bottom and in the middle, respectively. Due to thermal cycle during multi-layer deposition, the metastable beta phase will gradually evolved into alpha + beta phases. As the subsequent deposition process continued, the temperature in the middle of the deposition area decreased below the transformation point, and alpha ' is decomposed into alpha + beta. The precipitated alpha phase gradually grew up under the action of thermal cycle. Meanwhile, the fine secondary alpha phase precipitated from the metastable beta phase, and finally the coarser alpha lath and inter lath were obtained beta structure.

Automated summary

This paper investigates the microstructure evolution of TC17 titanium alloy prepared by laser stereo forming (LSF). The microstructure in deposited TC17 titanium alloy is significantly affected by the thermal cycle history during the LSF process. The metastable beta phase gradually evolves into alpha + beta phases due to thermal cycle during multi-layer deposition.