Effect of Size-refinement and Distribution of Lubricants on the Formation of Self-lubricating Films

Ni-based high temperature self-lubricating IS304(IS:Induction Sintering) composites with BaF_2/CaF_2 and Ag particles as lubricants were prepared by ball milling and induction sintering techniques.The microstructure of the IS304 composites is dense and the size of self lubricating particles is very fine.BaF_2/CaF_2 particles are in dimension of about 1μm and particles are less than 2μm respectively,while some BaF_2/CaF_2 particles are distributed in Cr_2O_3 particles.The synthesized IS304 composites exhibite high friction coefficient in the temperature range from room temperature to 250℃.However,the friction coefficient dramatically decreased at 280℃while the friction coefficient of coarse composites dramatically decreased at 330-350℃in the same test condition due to the formation of self-lubricating fluoride films.The fluoride films formed on the worn surface of synthesized composites is attributed to the size refinement and appropriate distribution of fluorides,which can lead to a higher temperature rise(flash temperature) at the instantaneous contacting surface.