In situ nitridation of titanium–molybdenum alloys during laser deposition
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In situ nitridation during laser deposition of titanium–molybdenum alloys from elemental powder blends has been achieved by introducing the reactive nitrogen gas during the deposition process. Thus, Ti–Mo–N alloys have been deposited using the laser engineered net shaping (LENSTM) process and resulted in the formation of a hard α(Ti,N) phase, exhibiting a dendritic morphology, distributed within a β(Ti–Mo) matrix with fine scale transformed α precipitates. Varying the composition of the Ar + N2 gas employed during laser deposition permits a systematic increase in the nitrogen content of the as-deposited Ti–Mo–N alloy. Interestingly, the addition of nitrogen, which stabilizes the α phase in Ti, changes the solidification pathway and the consequent sequence of phase evolution in these alloys. The nitrogen-enriched hcp α(Ti,N) phase has higher c/a ratio, exhibits an equiaxed morphology, and tends to form in clusters separated by ribs of the Mo-rich β phase. The Ti–Mo–N alloys also exhibit a substantial enhancement in microhardness due to the formation of this α(Ti,N) phase, combining it with the desirable properties of the β-Ti matrix, such as excellent ductility, toughness, and formability.
KeywordsPole Figure Powder Feedstock Orientation Imaging Microscopy Octahedral Interstitial Site Equiaxed Morphology
This work has been supported by the ISES contract awarded to the University of North Texas by the US Air Force Research Laboratory, AFRL contract number FA8650-08-C-5226, with Dr. Jay Tiley as the program manager. The authors also gratefully acknowledge the Center for Advanced Research and Technology (CART) at the University of North Texas.