Microstructure and Compressive Behavior of Ti-6Al-4V Alloy Built by Electron Beam Free-Form Fabrication

The paper presents the effect of layer deposition algorithms on the microstructure and the compressive behavior of the Ti-6Al-4V alloy built by the wire-feed electron beam free-form fabrication method. Patterns of the formation of pores and their shape changing under compressive loads were also investigated by computed tomography. The microstructure of the as-built samples consisted of columnar prior β grains with lengths of about several millimeters. Cross-sectional areas of the prior β grains did not depend from the metal cooling rate but were affected by the layer deposition algorithms. They were smaller and characterized by a wider range of the values when odd and even layers had been deposited perpendicular to each other. In this case, the prior β grains included predominantly the basket-weave Widmanstätten microstructure, while the α, α′, and residual β phases with different volume ratios presented after the parallel layer-by-layer deposition. The only reason for this feature could be the substrate surface conditions (waviness across the deposition path). The compression test results corresponded to the formed microstructure. The sample with the maximum amount of the martensitic α′ phase possessed the highest strength and the lowest ductility. On the contrary, the prevailed basket-weave Widmanstätten microstructure resulted in the improved toughness.