Synthesized Nonstoichiometric TiC_x And TiN_x Powders By Ma And Study Of The Powders Sintering Property

Titanium carbide (TiC) and Titanium nitride (TiN) are widely used because they possess many excellent physical and chemical properties. Nevertheless, the high melting point and difficulty for sintering limit their application. Therefore, reducing the sintering temperature of TiC and TiN is an issue for the widely application of refractory compounds. The TiC_x and TiN_x powders fabricated by means of MA were sintered by vacuum hot-pressing sintering. The sintered samples possess excellent mechanical properties.The structural stability of TiC_x and TiN_x were calculated using the first-principle study. The results showed that the structural stability of TiC_x and TiN_x decreased with the C and N content reduce, but in the range of x between 0.25¹, the phase formation energy were negative. Which means TiC_x and TiN_x could maintain the NaCl structure in the range of x between 0.25¹.The mixed powders of TiC and Ti were mechanical alloyed to synthesize nonstoichiometric TiC_x. An X-ray diffractometer (XRD) and a sanning electron microscope (SEM) were used to analyze the structures and observe the morphologies of the milled powders. The TiC_x powder fabricated by means of MA was sintered at 1500℃under vacuum and at the pressure of 40 MPa. The fracture surfaces of the sintered samples were investigated by SEM and the mechanical properties were tested. The results showed that with the C content increased the lattice constant of TiC_x and the recrystallization temperature of TiC_x increase, the grain size of the sintered sample decrease. The bond density of Ti-C, hardness, fracture toughness and bending strength increased. The mechanical properties for the sintered sample of the TiC and Ti powders mixed as 1:0.3 molar ratio milled for 20 h are optimum. The microhardness, fracture toughness and bending strength are 2575.92 Hv, 4.74 MPa·m^1/2 and 433.1 MPa, respectively.TiN_x was synthesized by MA titanium and urea. Combination differential scanning calorimetry (DSC) and fourier transformation infrared (FTIR) technology were used to analyze the decomposed products of urea. XRD, raman spectroscopy and field emission scanning electron microscope (FESEM) were used to analyze the structures and investigate the morphologies of the milled powders. A transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS) were used to observe the micro-morphology and analyze the component of the powders. Ti and urea mixed as 4:1 molar ratio milled for different time was sintered at 1500℃under vacuum at the pressure of 22.5 MPa. The mechanical properties of the sintered samples were also tested. The results showed that the decomposed products of urea were NH3 and HNCO. The reaction efficiency increased with the Ti content increase. The reaction process was a solid-gas reaction process. The oxidation temperature of TiN_x was decreased compared with that of TiN. TiC or TiOx are not found in the milled powders. The phase composition for the sintered samples of the powders milled more than 20 h are only TiN_x. The sintered sample of the powders milled for 50 h possesses the optimal mechanical properties, the hardness, fracture toughness and the bending strength are 2186 Hv, 7.03 MPa·m^1/2 and 307.6 MPa.Synthesis TiC_x and TiN_x nano-powders by means of MA can reduce the sintering temperature and improve the mechanical properties of the sintered sample. It is significant for the application of TiC and TiN and it also provide the scientific basis study for manufacturing refractory compound tools.