Crack Initiation Mechanism of Ti65 Titanium Alloy Fabricated by Laser Deposition Manufacturing

Abstract

In order to produce complex Ti65 alloy structural parts at reduced cost and shorter lead times, samples were fabricated using laser deposition manufacturing (LDM). The microstructure and mechanical properties of specimens produced under 2 kW (low power) and 5 kW (high power) laser settings were compared. Samples fabricated at higher power exhibited better tensile strength and ductility, whereas low-power samples showed a more pronounced tendency to crack. This cracking behavior is attributed to the distinctive chemical composition of Ti65 alloy and the specific laser power settings, which govern the as-deposited microstructure and, consequently, its mechanical properties. In the as-deposited Ti65 alloy, silicides precipitated along α/β interfaces and within the β phase, with larger and more numerous silicides observed in low-power samples. During the LDM process, β-stabilizing elements (W, Zr, Ta, and Nb) tended to concentrate in these silicides, with greater enrichment in the low-power samples, thus causing excessive silicide formation. This increased silicide precipitation, combined with a lower concentration of β-stabilizing elements in the α and β phases, reduced both ductility and strength in the low-power samples. In contrast, high laser power accelerated the dissolution of silicides and enhanced the β-stabilizing elements’ solid solution in the α and β phases, resulting in better formability and improved room-temperature tensile properties.