Spark plasma sintering of graphitized multi-walled carbon nanotube reinforced Ti6Al4V

Graphitized multi-walled carbon nanotubes (MWCNTGr) reinforced Ti6Al4V (Ti64) matrix composites prepared via the powder metallurgy route were synthesized by spark plasma sintering (SPS) technique. 1, 2 and 3 wt% MWCNTGr were dispersed in the Ti64 matrices by adapted high energy ball milling (HEBMA). Composite powder mixtures were sintered in vacuum at constant applied pressure, heating rate and isothermal holding time of 50 MPa, 100 degrees C/min and 5 min respectively. The sintering temperature was varied between 850 and 1000 degrees C. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the as-received MWCNTs, MWCNTGr, admixed composite powders and the bulk sintered composites. MWCNTGr evolution during graphitization treatment, dispersion in Ti64 matrix and in the sintered composites was analyzed using the characteristic Raman peak intensity ratio (I-D/I-G). The relative density of the sintered MWCNTGr/Ti64 composites was enhanced with increased sintering temperature, but deteriorated with increased wt% MWCNTGr in the metal matrix. Vickers microhardness of the consolidated composites improved with increasing sintering temperature and weight fractions of MWCNTGr over that of the unreinforced matrix alloy. The formation of crystalline TiC interfacial product during composite powder processing and consolidation is also discussed.