Effect Of Transition Metal Elements On The Stability Of (Zr,W)C Solid Solution And The Second Phase Precipitation

As a carbide ceramic material used in deep space,electronics,machinery,laser,nuclear reaction and other scenarios as engineering structural materials,it is destined to be required by related industries to have a series of excellent properties.In addition to high temperature resistance,it is often necessary to maintain properties such as high hardness,high strength,high toughness,friction resistance,and corrosion resistance.However,the current carbide ceramics still have the problems of poor fracture toughness and difficulty in sintering.Therefore,the preparation of composite ceramic materials with high toughness and good hardness characteristics has important research significance.This topic mainly uses transition metals to induce the in-situ precipitation of the second phase in（Zr,W）C solid solution.This method can avoid the problems of poor bonding strength and low dispersion at the interface between the matrix and the second phase caused by the direct addition of the second phase.In order to achieve the purpose of making up for the inherent low toughness defects of ceramics,this research hopes to prepare a composite ceramic with high hardness and high fracture toughness.Through first-principles analysis of structural stability,ease of formation and mechanical properties to further narrow the scope of the experiment.Finally,the sintering preparation process and the influence of different transition metal content on the microstructure and mechanical properties of（Zr,Me,W）C ceramics are explored.By analyzing the precipitation mechanism of the second phase,a controllable structure morphology and excellent mechanical properties can be obtained.First-principles calculations are used to perform cut-off energy testing,geometric optimization,energy band and density of states calculations,binding energy and formation energy calculations,and mechanical properties prediction for each product.The main conclusion drawn is that the systems with higher thermodynamic stability are mainly Ti,Nb and V.It is speculated that the addition of these transition metals can promote the sintering densification process to a certain extent.Adding Nb and Mo can improve the toughness of the material.Adding Ti,V and Cr can improve the hardness and wear resistance of the material.Among them,Ti series and V series not only have a relatively high hardness matrix,but also have two high toughness precipitate phases,W and VW.Therefore,it can be predicted that the materials of these two systems may have the characteristics of high hardness and high toughness at the same time.In the experimental part,we first explored the ball milling process and sintering process that can prepare high-density samples.Then,on this basis,the changes of the precipitated phases of the three systems of Ti,Hf,and V were explored.At the same time,according to the current results,a better Ti system was selected for in-depth research on the amount of introduction.The results show that with the increase of Ti content,the precipitated product of the second phase changes from W and W₂C to W and（Zr,Ti）C solid solution phase.The density of the samples is above 99%.As the amount of Ti added increases,the phenomenon of spot-like W crystal grains precipitated inside the crystal grains also increases.When the amount of Ti added is 0.4mol,the density is 99.7%,the Vickers hardness is 24.68GPa,and the fracture toughness is 5.76MPa·m^1/2.