Reactive Spark Plasma Sintering (SPS) of Nitride Reinforced Titanium Alloy Composites (Postprint).

摘要

Coupled in situ alloying and nitridation of titanium--vanadium alloys, has been achieved by introducing reactive nitrogen gas during the spark plasma sintering (SPS) of blended titanium and vanadium elemental powders, leading to a new class of nitride reinforced titanium alloy composites. The resulting microstructure includes precipitates of the delta-TiN phase with the NaCl structure, equiaxed (or globular) precipitates of a nitrogen enriched hcp alpha(Ti,N) phase with a c/a ratio more than what is expected for pure hcp Ti, and fine scale plate-shaped precipitates of hcp alphi-Ti, distributed within a bcc Beta matrix. During SPS processing, the delta-TiN phase appears to form at a temperature of 1400 degrees C, while only hcp alpha(Ti,N) and alpha-Ti phases form at lower processing temperatures. Consequently, the highest microhardness is exhibited by the composite processed at 1400 degrees C while those processed at 1300 degrees C or below exhibit lower values. Processing at temperatures below 1300 degrees C, resulted in an incomplete alloying of the blend of titanium and vanadium powders. These delta-TiN precipitates act as heterogeneous nucleation sites for the alpha(Ti,N) precipitates that appear to engulf and exhibit an orientation relationship with the nitride phase at the center. Furthermore, fine scale alpha-Ti plates are precipitated within the nitride precipitates, presumably resulting from the retrograde solubility of nitrogen in titanium.