2, University of Houston, Houston, Texas, United States
The alloy composition Ti-6Al-4V, also known as Ti6Al4V is the workhorse alloy of the titanium industry. Its uses span aerospace airframes, engine components and also major non-aerospace applications in the marine, offshore and power generation industries due to its low density, high strength and excellent corrosion resistance. However, the properties of the alloy changes with oxygen content which remains dissolved at high temperatures and precipitate out to form oxides at low temperatures. Oxygen is detrimental to ductility of Ti-6Al-4V especially when it exceeds 0.33 wt.%, above which ductility drops rapidly and can be much lower than the corresponding ASTM specification of a minimum value of 10% . The oxygen in the alloy powder could be contributed from dissolved oxygen or adsorbed oxygen. Adsorbed oxygen is a function of the particle size and scales with decreasing dimensions of individual particles. Commercially available Ti6Al4V alloy powder size is large with size ranging from several tens to hundreds of microns. For increasing the overall strength of the alloy there is a need for decreasing oxygen content and particle size which in turn rises the cost significantly. Simultaneous improvements in mechanical properties of the alloy arising from the dispersion of hard particles, removal of oxygen, and grain size reduction can be achieved through the process of mechanical alloying of the alloy with oxygen scavenger element such as yttrium (Y). Use of Y to remove oxygen from Ti alloys have been demonstrated in prior work on consolidation of γTiAl dispersed with Y metal by ball milling .
In this work, Ti6AL4V-Y composite material was developed by consolidation of ball milled Ti6AL4V and Y powders. Ti based milling medium was used to avoid metallic elemental contamination and the powders were consolidated using spark plasma sintering (SPS). Structural characterization using Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDX) and X-ray diffraction indicated the formation of Y4Al2O9. This shows the oxygen scavenging effect of Y to form stable oxide by removing oxygen from Ti. Mechanical properties evaluation using nanoindentation and microhardness tests showed improved hardness in Y added composites.
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