Study On Microstructure And Properties Of TiC/Mo Composites

The pure molybdenum has its preferable properties such as high-temperature strength,electrical conductivity,thermal conductivity as well as the good resistance to thermal shock and thermal fatigue.Although the molybdenum has broad prospects of development,its brittleness at room temperature and oxidation resistibility need to be optimized.Additionally,to refine grain size for the above reason the spark plasma sintering?SPS?process is widely used to replace the traditional approach for its characteristic of rapid prototyping.In this paper,the discharge plasma method was used for sintering,and TiC and Cr elements were added to improve the related properties.In this paper,the Mo-5%TiC alloy and Mo-5%TiC-xCr?x=0.5,1.0,1.5wt%?alloy were densified by SPS and the microstructure,grain size and related properties were investigated.The result shows that the molybdenum-based alloy with minute grain size?less than 5?m?and uniform structure can be prepared by SPS method.The grain sizes of the alloy enlarged with the increase of Cr element.Particularly,alloy with 1.0wt%Cr addition possess the best compression strength,2156.87MPa.Its elastic deformation continuously improved with the increase of Cr,and the fracture mechanism changes from the original intergranular fracture to the intergranular and transgranular fracture.The time-varing oxidation mechanism and oxidation resistance of Mo-TiC alloy and Mo-TiC-Cr alloy were tested in different temperatures.The TiO2 particles formed on the surface of the Mo-TiC alloy have fluidity to some extent,which reduces the pores on the surface of the alloy and reduces the weight loss rate.There were MoO3 particles formed at 400?and 600?in the Mo-TiC alloy after high temperature oxidation.When the alloys oxidized at 800?,the volume fraction of the MoO3 increased.Further increasing the oxidation temperature to 1000?,the volume fraction of the MoO₃ decreased with the forming of TiO₂.The electrochemical corrosion test of the Mo-TiC alloys was conducted with different concentrations of Cl^-?0.25mol/L,1.0mol/L,1.5mol/L,2.0mol/L?and different PH values?8,9,10,11?.The equivalent electric circuits were simulated by the Tafel curves,Nyquist curves and Bode curves.The result showed that the electrochemical corrosion resistance of the Mo-TiC alloys increased with the increasing concentration of Cl^-.while the electrochemical corrosion resistance of the Mo-TiC alloys decreased with the increasing of PH values.Particularly,passivating phenomenon occurred in Mo-TiC alloys at PH 10 and 11.The friction and wear performence of the alloys were conducted in different loads?500g,1000g,1500g,2000g?and temperatures?25?,200?,400?,600??.The result showed that the friction coefficient of the alloys decreased first and then increased with the increasing of the load at room temperature.The surface of grinding defect showed the warp flakes that fell off with increasing load,which was significantly different from the friction mechanism in high temperature.The friction coefficient of the alloys increased at 200?for the formation of viscous phases,brittle MoO₃ phases formed along with continuous heating,which reduced friction and wear coefficient.In order to compare the differences in test performance between different molding processes,selective laser melting?SLM?technology was used to test the effects of different scanning speed and power of the laser on the microstructure and density.The results showed that the relative density of the alloys increased with the decreasing of the scanning speed,increased at first and then decreased with the increase power of laser.The number of powder layers had no effect on the performence of sample,but the hardness of the alloys showed anisotropy,the hardness perpendicular to the forming direction was higher,and the alloy prepared by SLM process showed better plasticity than SPS.