Preparion Of (Ti, M)C And Mechanical Properties Study Of (Ti, M)C Based On First Principles

TiC,with high strength,hardness,resistance to thermal shock,low price,and abundant resource,is recognized as a promising alternative to WC.Materials in which TiC is the hard phase,whereas Ni,Co,and some other metals are binder phase are called cermets.The typical core-rim structure of these materials is accounted for the lower fracture toughness of TiC-based cermets than that of WC-Co cermets which limits the wide application of TiC-based cermets.The toughness of TiC-based cermets can be improved by directly replacing TiC with?Ti,M?C,where M = W,Mo,V,Nb,and other metals,which can be prepared through solid solution pretreatment.As a result,materials with weak core-rim structures or no core-rim structures are obtained.Thus,the number of phase interfaces between the core phase and the rim phase is reduced,the adverse effects of the large composition gradient at the interface on the properties of cermets are weakened,and the toughness of TiC-based cermets is enhanced.Various methods,such as carbothermal reduction of oxides and pre-alloying method,have been developed to prepare solid solution carbides.Among these methods,carbothermal reduction of oxides is the most commonly used.However,using this method to prepare carbides excess free carbon is inclined to exist and this method requires complex,time-consuming,and high energy consuming.Therefore,preparation method for carbides with short procedures,low energy consumer and high purity of?Ti,M?C should be developed.In this study,three different types of carbides,namely,?Ti,M?C,where M = Mo,V,W,were prepared in an arc-melting furnace under argon-protected conditions.The effects of different contents of doping M on the crystal structure and mechanical properties of TiC and their reaction mechanisms,were investigated.The crystal structure of?Ti,M?C and the related mechanical constants were obtained by using the software Materials Studio?MS?on the basis of crystal structure of TiC.The essential effects of doping M with different contents on the material properties were explained at the electronic level.Our results show that the types and amounts of doping M may affect the crystal parameters,densities,mechanical properties of?Ti,M?C.However,the three different carbides?Ti,M?C possess the similar crystal structure as TiC,meanwhile the fracture mechanisms and reaction mechanisms of?Ti,M?C are also alike,but effect degrees of different types of doping M vary.The following results are obtained:?1?The relationship between the crystal parameter a of(Ti_1-xMo_x)C and the doping content of Mo is as follows: ?=4.329-0.0157x_Mo/Mo+Ti?x represents the atom ratio of doping Mo element to metal elements?,that is,a decreases linearly as the Mo content increases.The density of?Ti,Mo?C increases linearly with x,specifically from 5.21 g/cm³?x=0.1?to 6.89 g/cm³?x=0.5?,and the bending strength and hardness?Hv?increase at first and then decrease as the Mo content increases.Moreover,the hardness and bending strength of Ti_0.6Mo_0.4C belong maximum values of Hv?22.5 Gpa?and bending strength?576.8 Mpa?.With hot-pressed sintering being performed,the fracture modes of (Ti_1-xMo_x)C carbides are the mixture of trans-granular and inter-granular fracture and inter-granular fracture is the main mode.The nominal composition of Ti_0.5Mo_0.5C is selected as the subject,and the reaction mechanism of Ti-Mo-C system is examined.The results show that no new phases appear during the milling process.Furthermore,the reaction is composed of three parts for the arc-melting method to synthesize TiMoC₂: under high temperature,liquid Ti₂C,Mo₂C,Ti₂C and Mo₂C mixtures are formed,with reaction time prolonging,these mixtures disappear,and finally single pahse TiMoC₂ exists.The entire process finishes in 20³0 seconds.?2?The formation energy values of the(Ti_8-xMo_x)C₈?x=1⁴?carbides are less than 0,and the theoretical value of the crystal constants of(Ti_8-xMo_x)C₈ are slightly greater than the experimental values,with an error of less than 2%.The bulk modulus and shear modulus of Ti₅Mo₃C₈ are 287.05 and 220.39 Gpa,respectively.And using the empirical formula,its hardness reaches the highest value of up to 33.28 Gpa.Mo atom doping changes the bonding type and strength between the atoms inside the Ti-Mo-C carbides.Thus,hardness is altered.?3?The relationship between the crystal parameter a of the as-cast(Ti_1-xV_x)C?x=0.1–0.5?linearly decreases with the doping amount x of V,as demonstrated by ?=4.3293-0.0251x_V/V+Ti.The density of(Ti_1-xV_x)C increases linearly with the doping amount of V from 4.93 g/cm³?x=0.1?to 5.32 g/cm³?x=0.5?.The hardness and bending strength of(Ti_1-xV_x)C decrease firstly and then increase as the doping amount of V increases and their minimum values are 15.4 Gpa and 387.6 Mpa respectively,when x=0.3.The mechanical properties of Ti-V-C carbides are poorer than those of Ti-Mo-C carbides.The particle sizes of(Ti_1-xV_x)C carbides increase with the value of x.Two fracture modes,namely,inter-granular fracture and trans-granular fracture,are also observed.?4?The formation energy values of(Ti_8-xV_x)C₈?x=1⁴?carbides are less than 0.The calculated and experimental values of the crystal parameters are very close,with an error rate of 0.5%.The calculated and experimental values of the hardness of(Ti_8-xV_x)C₈ show the same variation trends which decrease and then increase as the doping content of V increases.Ti₅V₃C₈ belongs the lowest bulk modulus,shear modulus,and hardness and they are 270.57,181.25,and 23.21 Gpa,respectively.V atom doping changes the atomic bonding of the Ti-V-C carbides and thus affects their hardness.?5?The crystal parameters a of the as-cast(Ti_1-xW_x)C carbides linearly decrease with the doping content of W increasing,and the fitting relationship is expressed by ?=4.3327-0.0462x_W/W+Tia.The density of(Ti_1-xW_x)C increases linearly as the doping content of W increases from 6.15 g/cm³?x=0.1?to 10.30 g/cm³?x=0.5?.The hardness and bending strength of(Ti_1-xW_x)C increase as the doping content of W becomes bigger.Ti_0.5W_0.5C has the highest hardness and bending strength,26.2 Gpa and 589.5 Mpa,respectively.The average fracture particle size of(Ti_1-xW_x)C decreases as the doping amount of W increases.Therefore,grain refinement effect works in Ti-W-C system.?6?The formation energy values of the(Ti_8-xW_x)C₈?x=1⁴?carbides are less than 0.The crystal parameters of?Ti8-x Wx?C₈ carbides decrease as the doping content of W increases and shows a linear relationship.The theoretical and experimental values are very close,with an error rate below 1%.Moreover,the bulk modulus and shear modulus of the(Ti_8-xW_x)C₈ carbides increase gradually.The bulk modulus and shear modulus of Ti4W4C₈ are 317.19 and 241.69 Gpa,respectively.The estimated hardness is 36.49 Gpa.The theoretical and experimental hardness values of the carbides show the same variation trend.The G/B values of(Ti_8-xW_x)C₈ are higher than 0.57,which indicates brittleness.The W doping changes the bonding between atoms inside the Ti-W-C carbides.