The friction and wear properties of CaCO3 nanoparticles as additive in the titanium complex grease were studied by fourball friction and wear tester.The chemical states of the main elements on the wear scar surface of steel ball after test were analyzed by X-ray photoelectron spectroscopy(XPS),and the surface morphology of the wear scar of steel ball was observed by scanning electron microscope (SEM).The results show that the CaCO3 nanoparticles as additive in the titanium complex grease have obvious friction reducing and antiwear effect,which can reduce the average friction coefficient by 14.9% and the wear scar diameter by 35.1% compared with the pure titanium complex grease.Under the lubrication of the titanium complex grease with CaCO3 nanoparticles,a porous protective film composed of inorganic compounds,such as CaO decomposed by CaCO3 nanoparticles,TiO2decomposed by titanium complex grease,and Fe2O3 and FeO,is formed on the wear scar surface of steel ball.This protective film prevents the direct contact of the friction surface and has an effective friction reducing and antiwear effect.