Fe element promotes the transformation from columnar to equiaxed grains and the formation of ultrafine microstructure of Ti-6Al-4V alloy by laser wire deposition

Abstract

Controlling the columnar to equiaxed grains transformation is the main method for improving the mechanical properties of Ti alloys by additive manufacturing. The effects of different Fe contents on the grain morphology, microstructure, and mechanical properties (including hardness and strength) of Ti-6Al-4V produced by laser wire deposition were studied. Columnar β grains in the deposit were transformed into equiaxed grains by the addition of Fe. Iron caused the formation of the ω and TiFe phases, which promoted the formation of a uniform ultrafine microstructure. The dispersed TiFe acted as a nucleation site for the α phase and promoted the formation of the nanometer-scale α phase. Iron played the role of solid solution strengthening, fine grain strengthening, and dispersion strengthening in the deposit. Additionally, it significantly improved the mechanical properties of the deposit. The average hardness of the deposit gradually increased, and the hardness distribution gradually homogenized as the Fe content increased. The compressive strength of the deposit was as high as 2830 MPa, and the compressive plastic deformation reached 43% by adding 3.3 wt% Fe.