High Entropy Alloys Binded Novel Ti(C,N)-based Cemented Carbides

Covalent compounds have been widely used in the field of engineering technology duo to high heat resistance,high hardness,and high strength of resistance at high temperatures.In this paper,the structural properties,elastic properties,and the phase transitions of the TiC and TiN,and non-stoichiometric TiC_x and TiN_x compounds were simulated by density functional theory and accelrys materials studio.We demonstrated how to build the structure model of the non-stoichiometric TiC_x and TiN_x by CASTEP software.Using the CASTEP module of accelrys materials studio,the electronic band structure and state density were calculated.At the same time,Phase formation energy and vacancy formation energy of TiN_x and TiC_x were also calculated.The mechanical properties of the non-stoichiometric compounds mediated by C and N vacancy defects have been predicted.Calculations showed that Ti-C and Ti-N bonds decreased and Ti-Ti bonds increased with reducing the content of C/N in the non-stoichiometric compounds.The metallicity of the TiC_x and TiN_x compounds increases due to that the metallic bond energies of Ti-Ti are very low and this easily leads to fracture.The hardness and sintering temperature of TiC_x and TiN_x decrease and fracture toughness increase because the structural energy is very lower.However,it has little effect on the hardness.TiN_0.3 nanocrystalline powders were prepared by mechanical alloying.The structure and mechanical properties of the sintering and interfacial reactions between TiN_0.3 and AlN were studied.Layered sintering between TiN_0.3 and AlN were conducted by spark plasma sintering?SPS?.The experiment results show that the N vacancy deficients strengthen the Ti-Ti metallic bonds in the TiN_x compounds leading to the weakening of the covalent bonds.The interfacial reactions between TiN_0.3 and AlN happen and reactions form complex interfacial structure.The interfacial reaction zone consists of a continuous stoichiometric TiN layer and a multi-phase region close to TiN_0.3 with re-formed AlN grains distributed in TiN_x matrix.Interface reaction and reaction degree were controlled by the concentration of the N vacancy deficient and temperature.The interfacial reaction between TiN_0.3 and AlN occurs at the high N vacancy concentration and high temperature and the system keeps equilibrium in at the low N vacancy concentration.The mechanical properties of TiN_0.3/AlN composite were improved by the interface reaction between TiN_0.3 and AlN.The high pressure high temperature sintering?HPHT?showed that the vickers hardness and the fracture toughness reached 24 GPa and 8MPa×m^1/2,respectively when the content of AlN are 24 wt.%and 12 wt.%,respectively.In order to improve hard toughness and high temperature oxidation resistance of the covalent bond composite material.Three kinds of high entropy alloys were produced by MA.The structure and the mechanical properties of three kinds of high entropy alloys were studied.The results show that the three kinds of high entropy alloys present good high temperature stability and good mechanical properties.High entropy alloys was suitable as replacements for Co,Ni as a bond phase,and synthesis of new types of cemented carbide materials.The microstructure,high temperature oxidation resistance and mechanical properties of Ti?C,N?based cemented carbide were studied and compared with the traditional Co,Ni as binder of Ti?C,N?,the fracture toughness and high temperature oxidation resistance of high entropy alloys as binder of Ti?C,N?based cemented carbide whether it was improved.The experimental results show that high entropy alloys was melted to form the melt at high temperature sintering and scattered in the grain boundary of the hard phase and high entropy alloys.The grains were firmly cohere together,so the strength of cemented carbide was increased.At the same time,with the increase of the content of high entropy alloys,the growth of grain is blocked,slows down,The hardness and toughness of Ti?C,N?based cemented carbide were improved.The properties of the new Ti?C,N?based cemented carbide were mediated by adding WC and AlN.The experimental results show the hardness of Ti?C,N?cemented carbide was improved obviously and the fracture toughness was obviously enhanced when only adding WC.After adding AlN,the hardness of Ti?C,N?based cemented carbide was greatly improved.The values of fracture toughness were lower than that of compounds added WC.This is due to that the sintering character of AlN is very bad.Therefore,the content of AlN should be strictly controlled.Adding AlN and WC together,the density of Ti?C,N?based cemented carbide was improved and the number of voids were also reduced significantly.With the increase of adding content of AlN,the hardness was gradually enhanced,the toughness decreased to some extent.The amount of AlN should be controlled when adding WC and AlN together.When different contents of AlN were added into the Ti?C,N?based cemented carbide,the value of the toughness of Ti?C,N?based cemented carbide reaches the maximum at 2 wt%content of AlN.