Recycling of waste Ti machining chips by planetary milling: Generation of Ti powder and development of in situ TiC reinforced Ti-TiC composite powder mixture

The present paper reports the synthesis of in-situ TiC reinforced Ti-TiC composite powder mixture from waste Ti chips by high energy planetary milling. First, we synthesize Ti powder from waste Ti chips by planetary milling for 2.5 h and then Ti and graphite powder mixtures (Ti/C weight ratios of 100/6 and 48/12) are milled for 12 h to obtain in-situ TiC reinforced Ti-TiC composite. The both milled Ti and Ti-TiC composite powder mixtures are characterized by XRD, SEM, FESEM and TEM. It has been found that Ti powder of size 5-10 mu m with crystal size of 10-20 nm are obtained after 2.5 h of milling. Faster rate of formation of TiC is evident from XRD spectra at high Ti content (Ti/C weight ratio = 100/6) than low Ti content (Ti/C weight ratio = 48/12). The contamination issue during synthesis of Ti powder and also during milling of Ti and graphite are discussed. It has also been observed that rate of oxidation reduces during milling of Ti + graphite than milling of pure Ti chips as graphite forms a layer around Ti particle and prevents oxidation. An average particle size of 5 gm is obtained after milling Ti + C powder mixture for 12 h (Ti/C weight ratio 48/12), whereas average size of 15 gm is obtained for Ti/C weight ratio of 100/6. (C) 2017 Elsevier B.V. All rights reserved.