Effect Of Physical Metallurgical Factors On Microstructure,magnetic And Mechanical Properties Of Ti(C,N)-based Cermets

With the rapid development of industry and technology,demand for high-performance and non-magnetic materials is increasing.Ti(C,N)-based cermets have good wear resistance,good corrosion resistance,a small amount of scarce strategic resources,as well as low cost.Therefore,if Ti(C,N)-based cermets possess non-magnetism,they will be promising materials for non-magnetic tools and dies and non-magnetic wear-resistant parts.In this paper,a series of Ti(C,N)-based cermets were prepared by powder metallurgy method,and the effect of Mo,Mo2 C,WC,Cr3C2,nano-TiC,VC,Cr and graphite(C)additions on microstructure,magnetic and mechanical properties of TiC–10TiN–15/30Ni(mol%)cermets was investigated.The main conclusions were as follows:Addition of Mo has good suppression effect on ferromagnetism of TiC–10TiN–30Ni,TiC–10TiN–4C–30Ni,and TiC–10TiN–4C–15Ni cermets,room-temperature(RT)saturation magnetization Ms,remanence Mr and initial susceptibility ?ini decreased with increasing Mo content.When Mo content was 8 mol%,cermets were paramagnetic at RT,and Curie temperature Tc of the former two groups of cermets was 115 K and 194 K,respectively.The effect of Mo2 C addition on magnetization of TiC–10TiN–30Ni cermets was similar to that of Mo addition,and cermets with 6 mol% Mo2 C was non-magnetic at RT.Addition of WC has weak suppression effect on ferromagnetism of TiC–10TiN–30Ni and TiC–10TiN–4C–15/30 Ni cermets,which could not make these cermets be non-magnetic at RT.For TiC–10TiN–6WC–4C–15/30 Ni cermets,with further addition of Cr3C2,Ms,Mr and ?ini decreased,and cermets with 1.5 mol% Cr3C2 were non-magnetic at RT.For TiC–10TiN –6WC–4C–30Ni cermets,RT Ms,Mr and ?ini decreased with increasing nano-TiC content,and when nano-TiC content exceeds a certain value,cermets transformed to be non-magnetic at RT.Tc of cermets with 7.5 and 10.0 mol% nano-TiC content was 210 K and 78 K,respectively.Addition of C enhanced ferromagnetism of TiC–10TiN–6Mo–15/30 Ni cermets,and cermets with more than 2 mol% C became ferromagnetic at RT.Addition of WC,Cr or VC further reduced magnetization of RT non-magnetic TiC–10TiN–6Mo–30Ni cermets.Tc of cermets without WC,Cr and VC was 250 K,Tc of cermets with 6 mol% WC or 6 mol% Cr addition was below 10 K,and that with 1 mol% VC addition was 117 K.Ti(C,N)ceramic grains in experimental cermets did not contain ferromagnetic Ni,except that in cermets with high Cr content.Consequently,magnetic properties of cermets,especially intrinsic Ms and Tc,were primarily dependent upon composition and lattice structure of their Ni-based binder phase.Solution behavior of solute elements in Ni-based binder phase was investigated by thermodynamic calculation and experiment.Ferromagnetism of experimental cermets became weakened with the increase of Ti,Mo,W,Cr,V content in Ni-based binder phase,and cermets transformed to be non-magnetic at RT,when the total content of solute elements in their Ni-based binder phase exceeded critical values,which made Ni-based binder phase be non-magnetic at RT.This phenomenon was in agreement with that of Ni-based binary alloy.According to the band theory,when atoms of Ti,Mo,W,etc.are dissolved in Ni,their valence electrons are transferred into spin-down band of Ni atoms,leading to the weakening of magnetic exchange interaction between Ni atoms,thus lowering magnetic moment,and consequently suppressing ferromagnetism of Ni matrix.Addition of nano-TiC increased Ti content in binder phase and weakened ferromagnetism of cermets.Addition of C decreased Ti,Mo contents in binder phase,which enhanced magnetization of cermets.Appropriate addition of Mo,Mo2 C and WC improved bending strength of cermets,which was mainly attributed to refinement strengthening because of the refining of Ti(C,N)ceramic particles,and enhanced solid solution strengthening effect with the increase of solute element contents in binder phase.Small addition of Cr3C2 refined ceramic particles,and improved bending strength and hardness of cermets.Small addition of nano-TiC improved bending strength of cermets,mainly due to the refinement of ceramic particles and the increase of solute element contents in binder phase.When C content was low,ceramic particles distributed uniformly,thickness of rim phase was moderate,and bending strength of cermets was high.RT non-magnetic cermets with excellent mechanical properties were prepared by multi-alloying.For instance,bending strength and hardness of TiC–10TiN–6Mo –30Ni–1VC cermet,whose Tc was 117 K,reached 2673 MPa and 88.9 HRA,respectively.