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

Author

Erhuvwu Joseph Oghnevweta, University of Wollongong

Year

2017

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials, Mechatronic and Biomedical Engineering

Abstract

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 Ti_100-xC_x (where x= 20, 30, 40, 50, 60, 70, 80) and Ti_100-xB_x (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 Ti_100-xC_x (x = 30, 40, 50, 60, 70) and Ti_100-xB_x (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.

Recommended Citation

Oghnevweta, Erhuvwu Joseph, Reaction sequences and mechanisms during controlled ball milling of titanium with carbon, boron and nitrogen, Doctor of Philosophy thesis, School of Mechanical, Materials, Mechatronic and Biomedical Engineering, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/42