One-step mechanosynthesis of nano structured Ti(CxN1−x) cermets at room temperature and their microstructure characterization

Nano structured Ti(Cx,N1−x) (x = 0.1–0.5 mol fraction) cermets are prepared at room temperature in a single step by ball-milling the stoichiometric mixtures of elemental α-Ti and graphite powders under nitrogen atmosphere. Within 1 h of milling (for x = 0.1), the α-Ti (hcp) phase partially transformed to metastable β-Ti (cubic) phase and the initiation of Ti(Cx,N1–x) (fcc) phase is noticed. Complete formation of Ti(C0.1N0.9) composition is observed after 5 h of milling and the other compositions are formed within 7 h of milling without any contamination either from the starting ingredients or from the milling media. Microstructure characterization of all unmilled and ball-milled powders is made by analyzing their respective X-ray diffraction (XRD) patterns employing the Rietveld structure refinement method. The microstructure of ball-milled samples is also characterized by high resolution transmission electron microscope (HRTEM). These analyses reveal the inclusion of both C and N atoms into the α-Ti lattice and confirm the average particle size of almost monodispersed spherical particles of Ti(Cx,N1–x) is ∼4 nm. The final compositions are also verified by energy dispersive X-ray (EDX) elemental analysis. Ti(Cx,N1–x) cermets are insulators and their optical band gap increases continuously from ∼4.58–5.38 eV with increasing C concentrations.

► α-Ti to β-Ti conversion is observed during 1 h of milling.
► Ti0.9C0.1N (fcc) phase is noticed to form after 1 h of milling.
► Lattice parameter of Ti(CxN1−x) increases according to Vegard's law.
► Particle size estimation of Ti0.9C0.1N from X-ray and HRTEM are in good agreement.