Development, Processing and Characterization of Gradient Micro-Porous Metals through Blended Elemental Powder Metallurgy

The research into alloys, specifically titanium and aluminum alloys (Ti-Al), has a rapidly growing technological importance. The combined research into Ti-Al alloys in the field of powder metallurgy have promise of fabricating a part with high compressive strength, low relative density and material properties in addition to being a cost-effective process. Titanium and aluminum are known to have a high affinity for oxygen. The problem of oxidation, due to storage or processing, on the titanium and aluminum must be studied prior to any fabrication. A hypothesis was made that a mixture of Hydrofluoric Acid and Nitric Acid (known as Kroll reagent) could remove oxides on the powders before the powder metallurgy (P/M) process. Optimization of the P/M process was achieved using two weight percentages of titanium and aluminum elemental powders to test for the presence of gradient phases post sintering. After samples of Ti-Al alloys were created using exclusively titanium and aluminum powders, porous metallic foams were created using the P/M space holder technique with sodium chloride (NaCl) as the space holder. Metallographic, morphology and pore sizes were evaluated using Scanning Electron Microscopy (SEM) and optical microscopy. An Energy Dispersive Spectroscopy (EDS) attached to the SEM and X-Ray Diffraction (XRD) was used to evaluate impurity content and diffusion. The cleaning procedure was analyzed using EDS to show that there was a 70% to 100% increase in oxygen after the procedure. This showed that the hypothesis concerning oxide removal was not proven. XRD analysis shows that TiAl, Ti3Al, TiAl3, TiO, TiO2, Al2O3 were present in varying intensities. Using NaCl as a space holder showed that there was little to no diffusion that occurred and large amounts of oxides were produced.