Raman spectroscopy sheds new light on TiC formation during the controlled milling of titanium and carbon

Abstract

A magneto ball mill was used to mill titanium and carbon elemental powder mixtures with compositions of Ti 50C 50 and Ti 60C 40 under a helium atmosphere. Previous studies on the milling of titanium and carbon powder mixtures have reported a sudden increase in the temperature of the milling vial, which occurs after a specific milling interval, referred to as t ig [Z.G. Liu, J.T. Guo, L.L. Ye, G.S. Li, Z.Q. Hu, Appl. Phys. Lett. 65 (1994) 2666–2668; G.B. Schaffer, J.S. Forrester, J. Mater. Sci. 32 (1997) 3157–3162; N.Q. Wu, S. Lin, J.M. Wu, Z.Z. Li, Mater. Sci. Technol. 14 (1998) 287–291; Z. Xinkun, Z. Kunyu, C. Baochang, L. Qiushi, Z. Xiuqin, C. Tieli, S. Yunsheng, Mater. Sci. Eng. C 16 (2001) 103–105; C. Deidda, S. Doppiu, M. Monagheddu, G. Cocco, J. Metastable Nanocryst. Mater. 15/16 (2003) 215–220]. This sudden temperature increase has been found to correspond to the formation of TiC via a rapid, highly exothermic reaction. In these cases, XRD analysis did not detect TiC in powder sampled before t ig. These results, combined with those from studies suggested that the milling period prior to t ig represents an incubation period during which the powders become mechanically activated and that no reaction between the starting powders occurs during this time [L. Takacs, J. Solid State Chem. 125 (1996) 75–84; B.K. Yen, T. Aizawa, J. Kihara, J. Am. Ceram. Soc. 81 (1998) 1953–1956; M. Puttaswamy, Y. Chen, B. Jar, J.S. Williams, Mater. Sci. Forum 312–314 (1999) 79–84; G.B. Schaffer, P.G. McCormick, Metall. Transact. A 23A (1992) 1285–1290; M. Mingliang, L. Xinkuan, X. Shenqui, C. Donglang, Z. Jingen, J. Mater. Process. Technol. 116 (2001) 124–127]. In the current investigation a sudden increase in the temperature of the milling vial was also observed after a specific milling duration of t ig. XRD analysis of powder sampled before t ig did not detect TiC, whilst for powder sampled after t ig, XRD analysis indicated that the powder had almost completely transformed into TiC. However, Raman spectroscopy showed the formation of non-stoichiometric TiC in Ti 50C 50 and Ti 60C 40 powders sampled before t ig. It is believed that the current, and many previous XRD analyses did not detect the formation of TiC prior to t ig either because the TiC grain size was too small and/or the phase represented too small a volume fraction of the powder samples to be detected by the XRD method employed. These Raman spectroscopy results suggest that a significant component of the heat generated at t ig may be due to a combination of growth of TiC accompanied by consumption of unreacted Ti and carbon, and/or recrystallisation of the TiC formed prior to t ig, rather than the direct formation of TiC.