Thermal Diffusion Behavior Of MC Promoted By C Vacancies And Application In Diamond Sinter

The residual from the process of industrial diamond sinter（PCD or PDC）causes problems,such as excessive expansion coefficient of metallic elements,soft spots and poor oxidation resistance.Here,in this paper,we tried to find an all-ceramic-based binder with low sintering temperatures for PCD（or PDC）.Carbides of transition metals,such as TiC,possess excellent physical and chemical properties and mechanical properties,and are widely applicated in engineering,in this case,they have significant potential acting as the candidate materials.However,the high sintering temperature,extreme high chemical stability and brittleness limit the application of these carbides.Therefore,how to remedy these deficiencies of TiC becomes a burning question.In response to these problems depicted above,this study adopts a strategy in introducing Carbon（C）vacancies to reduce the sintering temperature and improving its brittleness by combining with other strong transition metal carbides,nitrides and borides.In this paper,non-stoichiometric TiC_x（0.3≤x≤0.5）nano-powders with face-centered cubic structure and high concentration of C vacancy defect were synthesized by mechanical alloying（MA）based on first-principles simulation of the structure and properties of non-stoichiometric TiC_x（0≤x≤1）;The solid solution reactions between TiC_x and transition metal carbides（TaC,ZrC,B₄C）,borides（ZrB₂）and nitrides（AlN）,especially the diffusion reaction between TiC_x and TaC,as well as the diffusion reaction between TiC_x and AlN interface region,all of which were directed by C vacancy,were analyzed;The sintering temperature of transition metal covalent bond compounds is reduced via mass transfer between interfaces which was promoted by the emerge of C vacancies.The processes of multi-component composite sintering and adjusting the material structure,ensure the controllability on the mechanical properties of the material,and the fabrication of binder materials to the diamond sinter.The（TiNb）C_x,（TiV）C_x with the same face-centered structure and high C vacancies were synthesized by mechanical alloying using the non-stoichiometric TiC_x as the base phase.Finally,the Polycrystalline diamond composite（PDC）was prepared by the sintering of（TiNb）C_x with transition metal（W）.The first-principles simulation calculation predicted that the structure of 0.25≤x≤1would be stable in TiC_x,and the structural stability were enhanced with the increase of x value.In our experiment,The non-stoichiometric ratio TiC_x（0.3≤x≤0.5）nanometer powder with face-centered cubic structure and high concentration C vacancy defects was prepared via mechanical alloying（MA）.It could be sintered into a dense compact at a pressure of 5.5 GPa and a temperature range from 1200 to 1500°C.Under HTHP,the C vacancies promoted the reaction between TiC_x and TaC,ZrC to form a covalent bond compound with a uniform face-centered cubic structure alike to the structure of TiC.As well,under HTHP,theTiB₂ was produced both in the reaction between TiC_x and B₄C,and the reaction between TiC_x and ZrB₂.When the B₄C content is less than28%,all the TiC_x and B₄C were converted to TiB₂ and TiC,the formation of TiB₂increased the hardness of the sinter;The reaction between TiC_0.4 and ZrB₂ was accompanied with the formation of new phases of TiB₂,ZrC and ZrB,therefore,the addition of ZrB₂ or AlN promoted the formation of dense structure of sinter with fine and uniform crystal grains,and improved hardness and fracture toughness of the sinter.Using the TiC as the basal phase,a multi-component single-phase non-stoichiometric MC（In this paper,in the absence of specific cases,M represents the transition metal elements,C represents the C,N,B elements）powder was prepared by mechanical alloying method combined with transition metals（Nb and V）.Among them,（TiNb）C_0.5.5 exhibited the best performance at 5.5 GPa and 1600°C,and its vickers hardness and fracture toughness were 22 GPa and 7.2 MPa·m^1/2,respectively.A new type of all-ceramic binder was successfully prepared by the combination of TiC_x with multicomponent MC under a sintering condition,which confirmed the range of diamond sintering.Through the coordination of TiC_x and the MCs,the interface between diamond and binder was well bonded,that permitted high abrasive rate of the PDC prepared.