Solidification Effect on the Microstructure and Mechanism of Laser‐Solid‐Forming‐Produced Flame‐Resistant Ti–35V–15Cr Alloy

Abstract

Ti–35V–15Cr alloy has become an indispensable material in aerospace industry due to its excellent flame‐resistance properties. Herein, the block and thin‐wall Ti–35V–15Cr samples are built by laser solid forming (LSF) under the same processing parameters, and the evolution of solidification microstructure is investigated. This work focused on the effect of molten pool solidification parameters and complex thermal cycling conditions on the morphology of β grains and the substructure in the grains. The microstructure of LSF‐produced Ti–35V–15Cr block sample mainly consists of epitaxial columnar dendritic grains, whereas that of the deposited thin‐wall sample is mainly composed of near‐equiaxed grains together with subgrains formed in the near‐equiaxed grains. Such different microstructure results from extremely sensitive thermal behavior condition in LSF process. The simulated thermal behavior characteristics using finite element method illustrate that the thermal cycles during block deposition are very complex and the temperature gradient at the last solidification in block deposition is much higher than that in the deposition of thin‐wall samples, resulting in significantly different solidification microstructure between thin‐wall and block samples.