Study On Microstructure And Properties Of Non-magnetic TiC-based Cermets

In the thesis,the effect of 2~8 mol% Mo or WC addition on microstructure,and magnetic and mechanical properties of TiC–40N i cermet was investigated,and then the effect of 2~8 mol % WC addition on microstructure,and magnetic and mechanical properties of non-magnetic TiC–6Mo–40Ni cermet was investigated.Additionally,strengthening and magnetic transformation mechanisms of cermets were discussed.The main conclusions were as follows:TiC ceramic grains were no longer characteristic of square in two dimensions,and they were finer in size with the addition of Mo.TiC ceramic grains were significantly refined when Mo content was higher than 2 mol%.Room-temperature saturation magnetization,remanence and maximum susceptibility of cermets decreased with the increase of Mo content.Cermets became non-magnetic at room temperature at 6 and 8 mol% Mo,whose Curie temperature was about 195 and 158 K,respectively.This was mainly attributed to that the total amount of non-ferromagnetic solutes Ti and Mo in their Ni-based binder phase was above critical value which made binder phase non-magnetic at room temperature.Transverse rupture strength and hardness of cermets reached its maximum at 6 mol% Mo,mainly due to significant refinement of ceramic grains and high solute amount in binder phase.TiC ceramic grains were no longer square in two dimensions with the addition of WC.However,ceramic refinement effect of WC addition was weaker than that of Mo addition,and the addition of WC made inner rim of ceramic grains more thick.Some fine undissolved WC particles might be present in cermets when WC content was too high.Cermets kept ferromagnetism at room temperature regardless of WC content.This was mainly attributed to that the total amount of non-ferromagnetic solutes Ti and W in their N i-based binder phase was below critical value which made binder phase non-magnetic at room temperature.Transverse rupture strength of cermets was relatively high at 4~6 mol% WC addition,mainly because ceramic grains were refined in some degree.Hardness of cermets increased with the increase of WC content,mainly because the high solubility of WC in ceramic grains led to the increase of the volume fraction of ceramic grains.In addition,transverse rupture strength of WC-containing cermets was lower than that of Mo-containing cermets,when Ti N content was the same.For non-magnetic TiC–6Mo–40Ni(mol%)cermet,the thickness of inner rim of ceramic grains and the total amount of solutes in binder phase increased with the addition of WC.Room-temperature saturation magnetization,remanence and maximum susceptibility of cermets decreased and then increased with the increase of WC content,and they had the minimum at 6 mol% WC,and room-temperature saturation magnetization and remanence tended to zero.Cermets had a higher transverse rupture strength at 4~6 mol% WC.One of main reasons was better solid solution strengthening effect of their N i-based binder phase.On the whole,the higher WC content,the lower hardness of cermets,mainly because the solute amount in their binder phase increased with the increase of WC content,leading to the decrease of the volume fraction of ceramic grains.