Reaction sequences and mechanisms during controlled ball milling of titanium with carbon, boron and nitrogen

The primary aim of this research was to develop fundamental understanding on the reaction sequences and mechanisms during controlled ball milling of titanium powder with carbon (graphite), boron (amorphous), and nitrogen gas, respectively. A series of magnetically controlled ball milling experiments was performed on compositional mixtures of Ti100-xCx (where x= 20, 30, 40, 50, 60, 70, 80) and Ti100-xBx (where x= 40, 45, 50, 55, 60, 65, 70, 75) and Ti34B66, under high purity Helium gas, with the external temperature of the vial monitored using pyrometer. Likewise, reactive ball milling of titanium powder in nitrogen gas was performed using the same milling conditions, with the initial nitrogen pressure continuously monitored. Small amounts of Ti-C, Ti-B and Ti-N milled powders were taken out before and after ignition in an air-tight glovebox filled with Helium and then characterized using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FSEM), Transmission Electron Microscopy (TEM) combined electron diffraction, High Resolution Transmission Electron Microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Aberration Corrected Scanning Transmission Electron Microscopy (STEM) combined with electron energy loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDS). XRD analysis of the milled powders of Ti100-xCx (x = 30, 40, 50, 60, 70) and Ti100-xBx (x = 45, 50, 55, 60, 65, 70, 75) and Ti34B66 mixtures revealed the formation of TiC and, TiB and/or TiB2 after detection of a sharp temperature rise corresponding to an exothermic ignition event, while the reaction of Ti80C20 and Ti20B80 was found to progress gradually to form TiC and TiB2 respectively without evidence of a sharp ignition point. For the Ti-N milled products, the XRD analysis revealed both Ti and a small amount of TiN, (about 2.5at.%, as evidenced by SEM-EDS) before ignition. After ignition, TiN together with significant proportions of unreacted Ti was found.