Depends on the type of milling you want to use. In high-energy milling you will have oxidation of titanium particles. Similarly TiO will oxidize to TiO2 when milled with high energy. Therefore, I would recommend using protective atmosphere.

As for the milling balls, always use high quality defect-free milling balls. As it will significantly reduced possibility for contamination.

Otherwise, big companies that manufacture mills, they typically provide conditions (cups, balls, temperature, seals, rotational velocity) that are to be used with their equipment for certain application.

Be very careful when opening the milling cup with fine powder in it. It may produce flames. You should use inert atmosphere and glove box.

No one industrially mills titanium. There's no sound economical reason to do so and the problem of oxidation has yet to be handled properly. Oxidation issues are the limiting factor in large scale, low cost production of titanium powders in general, Titanium is a black hole as far as impurities, it sucks up anything, O, C, Fe, Cr, W and this enhances an always green problem of ball milling: materials contamination. 

the main problem is cold welding, metal particles under ball milling tend to weld to each other rather than  to fracture especially if subjected it to continuous milling without breaks. this give the metal heat that promotes welding to the ball milling media and between the particles. some people use  reagents like stearic acid  and alchols to minimize welding.  others use cryo milling (milling under liquid nitrogen). glove box is necessary for charging and discharging the samples to avoid metal oxidation. 

after all we can say grain size  in nanometer rather than particle size, since ball milling can produce particles that in micrometers but have nano grains 

Oxidation is a major problem for Ball Milling methodology

Titanium can pick up interstitial elements very easly. Milling in a protective atmosphere is mandatory (e.g. Argon). high energy milling can promote cold welding as well because Ti is ductile, if you want to reach nanoscale particle maybe milling fragile TiH2 particles cold be a good idea, with hydride decomposition second step . On the other hand HDH Ti powder shows higher amount of oxygen in finer particles, mainly under 50 microns, in increase drastically in nanoparticle. If you aim at working with nanostructured material you do not even need nanoparticle, but micro particles with nanograins. ball-to-powder ratio used to be the most effective parameter in high energy milling processes.

Is there any liquid (can be used for ball milling) which can stop the oxidation of titanium ?

Is there any liquid which can stop the oxidation of titanium during ball milling?

Is there any liquid which can stop the oxidation of titanium during ball milling

You can use hexane, since there is no oxygen in this chemical compound. Prefere cyclohexane which is more stable (closed ring structure). Always use that with inert atmosphere (Argon), since it is flammable. Milling power and time must be controlled to avoid titanium carbide formation.

I also performed some ball milling in air of Fe powder and subsequent sintering in argon gave the FeO,Can any one suggest to tackle this problem of oxidation.