BS in Materials Engineering
Materials Engineering Department
An alloy was fabricated with Ti-6Al-4V and Nb powder using laser deposition (LD) to form a compositional gradient. The gradient was deposited, starting with Ti-6Al-4V powder, onto a forged Ti-6Al-4V substrate in an Argon environment. Niobium (Nb) composition increased by 4-at.% with each layer deposited until the composition reached 100-at.% Nb. This process yielded steep thermal gradients and affected the microstructure and mechanical properties across the compositional gradient. To observe the microstructural changes in the alloy, an etched gradient was viewed with optical microscopy at 1000x, where the grain structure was observed to be an acicular α phase at 100-at.% Ti-6Al-4V. As the at.% of Nb increased, the amount of β- Ti increased, the grain size decreased and the porosity increased. The 100-at.% Nb layers also exhibited porosity between layers. XRD scans of the LD Ti-6Al-4V indicated much less β-Ti present compared to the forged substrate. A peak shift in BCC with increasing Nb represented a gradual transition from β-Ti to Nb. A decrease in HCP peak intensities and increase in BCC indicated the decreasing amount of α-Ti and increasing amount of Nb along the gradient, where at 55-60 at.%, α-Ti was observed to be negligible. Microhardness was also used to probe the uniformity within layers and the change in strength across layers. A large variance was present in the layers of 50-90 at.%, while a general decrease in hardness was observed with the addition of Nb.