Fabrication of TiB whiskers reinforced Ti6242 matrix composites by direct laser deposition: Powder preparation, microstructure and mechanical property

Abstract

Direct laser deposition (DLD) technique has great potential in manufacturing titanium matrix composites (TMCs) components with complicated shape. The TiB whiskers reinforced Ti6242 matrix composites were fabricated from the premixed TiB2/Ti6242 powders via DLD technique. Quantitative characterization of the extent of mixing uniformity and the deformation rate of the ball milled TiB2/Ti6242 powders was performed so as to select the optimal ball milling parameters. The TiB2/Ti6242 powders with two different weight fractions of TiB2 (2 wt%TiB2/Ti6242 and 5 wt%TiB2/Ti6242) were used to obtain different distributions of TiB whiskers in the composites due to the change in the solidification path in DLD process. The TiB whiskers in the TMCs-Ⅰ obtained from the 2 wt%TiB2/Ti6242 powders exhibited a discontinuous network structure following solidification in hypoeutectic zone, while the TiB whiskers were randomly distributed in the TMCs-Ⅱ obtained from the 5 wt%TiB2/Ti6242 powders due to the solidification in hypereutectic zone. In comparison with the DLDed Ti6242, the α colonies and β grains of the TMCs-Ⅰ and TMCs-Ⅱ were significantly refined. In addition, both equiaxed and lamellar α phase were formed in the TMCs-Ⅱ, in which various orientation relationships (ORs) between TiB and α phase occurred and the presence or absence of OR between TiB and β phase was responsible for the different morphologies of α phase. The yield strength of the DLDed TMCs-Ⅰ and TMCs-Ⅱ increased by 10.7 % and 38.8 % in comparison with that of the DLDed Ti6242, and both the load-bearing strengthening and fine-grain strengthening effects effectively enhanced the strength of the composites.