Effect Of Vacancy On The Preparation And Properties Of Transition Group Metal Covalently Bonded Compound Composite Materials

Transition metal covalent bond compounds have better mechanical properties at a higher temperature.There are a large number of vacancy defects in non-stoichiometric compounds,and they are in a metastable state.The transition metal covalent bond compounds are added to form a solid solution with a single face-centered cubic structure.Its excellent mechanical properties have attracted attention,but the disadvantages of difficulty in sintering and low toughness limit its development and application.In this paper,the improvement of the shortcomings of transition metal compounds was the starting point.We added carbon fibers to prepare composite materials,explored the interaction between the anion vacancies of non-stoichiometric components and the surface of carbon fibers.,and analyzed the phase composition and microscopic morphology of the sintered body,as well as research on hardness,fracture and flexural strength.And the non-stoichiometric component TiC_0.4 was combined with VC and NbC for stacked sintering,it proved that the vacancy in the non-stoichiometric components played a positive role in the organic combination of the composite material interface area,which affected the mechanical properties of composite materials.We prepared TiC_0.4-carbon fiber composite sintered body.The experimental results showed that when the volume fraction of carbon fiber was 5vol.%,and sps was used for sintering at 1500℃,the mechanical properties of the sintered body were better.The hardness was 20.12 GPa,the toughness was 5.0 MPa·m^1/2,and the flexural strength was507.1 MPa.Because there were a large number of vacancy in the non-stoichiometric component,which had an interface reaction with the carbon fiber,so they were more closely combined.At the same time,the fiber debonded and pulled out,the crack deflected and bridged,which consumed fracture work and improved material performance.The TiC_0.4-NbC-carbon fiber composite sintered body and TiC_0.4-NbC-VC-carbon fiber composite sintered body were prepared,and we analyzed the influence of carbon fiber content and sintering temperature on composite materials.The results showed that the TiC_0.4-NbC-carbon fiber sintered body had better overall performance at 1500℃,with vickers hardness of 22.67 GPa,fracture toughness of 5.4 MPa·m^1/2,and flexural strength of584.8MPa.TiC_0.4-NbC-VC-carbon fiber sintered body had better overall performance at1500℃,with vickers hardness of 23.11 GPa,fracture toughness of 7.1 MPa·m^1/2,and flexural strength of 621.9 MPa.The laminated composite sintered bodies of NbC-TiC_0.4-NbC and NbC-TiC_0.4-VC were prepared.The experimental results showed that the existence of vacancy defects promoted the diffusion of atoms.In the NbC-TiC_0.4-NbC sample,the thickness and flexural strength of the diffusion layer between the two phases increase with the increase of temperature,which reached the optimal value of 236.9 MPa at 1600℃.In the NbC-TiC_0.4-VC sample,when the temperature increased,the thickness of the diffusion layer increased,and the diffusion capacity of V was better than that of Nb,the flexural strength increased with the increase of temperature.The best value is 307.8 MPa.