Rapid Synthesis And Characterization Of Multi-Composite Ti(C,N) Cermet Powders

Ti(C,N)cermets are the preferred alternative materials for WC cemented carbide due to their hardness,high melting point,corrosion resistance,wear resistance and good thermal and chemical stability.In recent years,Ti(C,N)cermets have been widely used in tool and die materials.However,the core/rim structure due to the addition of secondary carbides has a influence on the toughness of the material.So it is very important and valuable to investigate the preparation of multi-composite Ti(C,N)cermets without a core/rim structure which are consists of multi-composite Ti(C,N)solid solutions and a binder phase.In this paper,the thermodynamics of carbothermal reduction(nitridation)process of each metal oxide is theoretically calculated.It is preliminarily deduced that the thermal reduction process of WO3 is WO3→WO2→W2C/WC,and the thermal reduction process of M0O3 is MoO3→MoO2→Mo2C.The final products of NiO and Co3O4 are Ni and Co respectively,and the thermal reduction process of Co3O4 is Co3O4→CoO→Co.Secondly,the effects of different compositions on the synthesis of composite Ti(C,N)cermet powders was studied.The results show that the order of the carbothermal reduction of three different components during the heating process is the same,which is TiO2→Ti4O7→Ti3O5→Ti(O,N)→Ti(C,N)→(Ti,W)(C,N)/(Ti,Mo)(C,N),and the final product powders are less than 1μm.Comparing with the synthesis of Ti(C,N)cermet powder without addition,W or Mo can reduce the carbothermal reduction temperature and accelerate the reaction process.The(Ti,W)(C,N)solid solution and the(Ti,Mo)(C,N)solid solution were respectively formed via spark plasma assisted carbothermal reduction-nitridation at 1450 ℃ with the components of adding W or Mo.In addition,the addition of W or Mo can also increase the wettability between the Ti(C,N)ceramic phase and the(Ni,Co)binder phase,and Mo can make the smaller particle size of the product powders which are only 200～400nm.Thirdly,Ultrafine(Ti,W,Mo)(C,N)-(Ni,Co)cermet powders have been synthesized by SPCRN reaction at 1400 ℃ for 10 min.During the process of preparing powders,the metal oxides were reduced by carbon black at low temperature.(Ti,W,Mo)(C,N)was fabricated in the following order,Ti02→Ti4O7→Ti3O5→Ti(O,N)→Ti(C,N)→(Ti,W)(C,N)→(Ti,W,Mo)(C,N).(Ti,W,Mo)(C,N)-(Ni,Co)cermet powders with the particle sizes of below 0.5pm were synthesized at 1350 ℃.The crystal structure analysis by the Rietveld method,HRTEM and SAED,as well as the elemental distribution analysis based on the mapping of the product powders further indicated that the pure(Ti,W,Mo)(C,N)-(Ni,Co)cermet powders were synthesized at 1400 ℃.Finally,the effect of different carbon sources on the synthesis of cermet powders was investigated.The temperature of carbothermal reduction-nitridation with C3N4 as the carbon source is higher than that with nano-carbon black as the carbon source,and the reaction process is slower.However,during the reaction process,nanotubes were formed in the products of carbothermal reduction-nitridation with C3N4 as the carbon source.The number of nanotubes increased first and then decreased with increasing temperature,and the nanotubes reached the maximum at 1200 ℃.While no nanotubes were formed in the products of carbothermal reduction-nitridation with carbon black as the carbon source,and the particle size gradually became even,and(Ti,W,Mo)(C,N)cermet powders could be prepared at a lower temperature.