Study On Preparation, Structure, Mechanical Properties And Oxidation Process Of Non-stoichiometric Ti(Zr)C

TiC and ZrC have been widely used in many fields because of their excellentphysical and chemical properties. In this thesis, bulk nanostructured (NC)/ultra-finegrained (UFG) TiCx, ZrCxand TixZr1-xC were sintered by Spark Plasma Sintering (SPS)and high pressure sintering (HPS), sintering and densification is enabled at lowtemperature with good mechanical properties,The nonstoichiometric TiCx/ZrCxnanopowders were synthesized by ball milling withpure metal powders of Ti/Zr in organic solvents. The influence of rotational speed，milling time, type of organic solvents and doses of organic solvent on the preparation ofnano carbide powder were studied.Bulk ultra-fine grained TiCxhaving relatively high density was sintered at1300℃byspark plasma sintering (SPS) technology, the average grain sizes from250to300nm. Bythe adjusting of the milling duration, TiCxwith different carbon content were obtained bysintering the TiCxnanopowders. The ordered carbon vacancies in the sintered TiCxwithlow carbon content are achieved simultaneously during the sintering process, forming acubic Ti2C type ordering phase. The hardness increased with the increase of carboncontent in nonstoichiometric TiCx, the values of the highest hardness is17.9GPa, and sodid the compressive strength, the highest compressive strength is3.2GPa. ZrC wassintered at1200℃, the average grain sizes is about100nm, the values of the hardness is16GPaPrior to sintering under3GPa at different temperatures, the TiCxnanopowders weretreated at800℃for30min in vacuum for degassing, the TiC0.85sintered at1100℃withaverage grain sizes is about100nm, the values of the Vickers hardness reached26Gpa,the average grain size increase with increase the temperature and the hardness decrease.Compared with sintered TiC0.85by SPS, high pressure sintering can improve the hardnesssignificantly, and reduce the sintering temperature. ZrC was sintered in the same waywithout vacuum degassing, fracture morphology analysis show that the sintered ZrCcontained a lot of pores, the values of the Vickers hardness only16GPa. The complete solid solutions of TixZr1-xC were fabricated by SPS with sintering theTiCx-ZrCxcomposite nanopowders, we got the solid solution phase diagram ofTixZr1-xC.During the process of sintering, TixZr1-xC solid solution with ZrC rich andTixZr1-xC solid solution with TiC rich were first formed, and then a single phase wasobtained by increasing the temperature. The hardness of single phase solid solution washigher than that of not complete solid solution, and then the elastic modulus is lower. Dueto the restriction of grain growth of TiCxand ZrCxto each other, the average grain sizeswere at the range of100nm to400nm for TixZr1-xC sintered at1800℃, the values of theVickers hardness was up to24GPa, the values of the fracture toughness was up to6.9MPa m1/2.We investigated the oxidation of sintered TiCx, ZrCxand TixZr1-xC in the air.Compared with the stoichiometric TiC and ZrC, TiCxand ZrCxwith ordered carbonvacancies have lower initial temperatures of oxidation. Basing on the analyses, we believethat the reason is the TiC and anatase TiO2with low lattice mismatch. In the air oxidationprocess of ZrC0.6with ordered carbon vacancy, ZrC0.6O0.4formed at first, increasing theoxidation temperature, the tetragonal phase ZrO2was observed, and then orthogonal phaseZrO2appeared. The mutual solutions of TixZr1-xC have better antioxidant capacity thanTiC and ZrC.