Study On Development Of TiB₂-TiN-WC In-situ Reaction Self-lubricating Tool Materials And Friction Characteristic

The in-situ reaction of TiB2-TiN at high temperature can generate the TiO2 and B2O3 lubricating film,which can improve the lubrication problem at the tool-chip contact surface.But poor flexural strength and fracture toughness of TiB2-TiN were not suitable for dry cutting.The addition of metals and ceramics were propitious to improve the mechanical properties of multi-composite.It became the important direction of research and development of toughening and reinforcement TiB2 ceramic.TiB2-TiN-WC(BNC)in-situ reaction self-lubricating ceramic tool materials were fabricated using TiB2-TiN as matrix,WC as strengthening phase and(Ni,Mo)as sintering aids.The effects of the difference WC and(Ni,Mo)content and sintering process on the mechanical properties and microstructure of BNC self-lubricating ceramic materials were studied.The friction-wear test of BNC were also conducted at room temperature and elevated temperature and its tribological behaviors are analysed under different environmental conditions.The compositions content and sintering process of BNC were optimized,and their effects on the mechanical properties and microstructure were studied.It was shown that the proper content of WC can refine the matrix grains and enhance the fracture toughness of BNC composites by means of pulling out of grains.The metallic phase of(Ni,Mo)not only strengthened the bonding strength bewteen grain boundaries but also reduced the pores and micro-cracks were formed in BNC composite.BNC3 with the best mechanical properties was obtained when WC and(Ni,Mo)content were 20 wt.% and 8wt.% at 1650? under 30 MPa with a holding time of 50 minutes.It's Vickers hardness,flexural strength and fracture toughness were 18.55 Gpa?872.6 MPa and 7.1 MPa·m1/2,respectively.Friction and wear tests were carried out at room temperature and elevated temperatures by a reciprocating and a ball-on-plate configuration,respectively.The effects of sliding speed,applied load and environmental temperature on the tribological behaviors of BNC are studied.The results show that:the average friction coefficient of BNC0,BNC3 and BNC5 decrease with the increasing of sliding speed and applied load,but the wear rate increased.When the applied load is 50 N and sliding speed for 600r/min,the worn surface of BNC0,BNC3 and BNC5 composites are exists few Ti O2 and B2O3 lubricating film,and the BNC3 presented the bettertribological performance by contrast with BNC0 and BNC5.The friction chemical reaction was intensified as the temperature rises,and the lubricating film generated on the friction surface of BNC0 and BNC3 at 700?.The dominant wear mechanisms are transformed from abrasive wear and adhesion wear at room temperature and 400? to oxidation wear,mild adhesive wear and abrasive wear.