The Effects Of Cr, Ni And Mn On The Mechanical Properties Of Mo 2 FeB 2 Were Studied Based On The First Principle

With the deteriorating of oil and gas drilling conditions,the requirements for the working performance and working life of petroleum drill bit become more and more strict.As an im-portant part of the petroleum drill bit,the carcass with hard alloy has an important influence on its operating performance and working life.At present.WC-Co cemented carbide is widely used in the carcass of petroleum drill bit,but it tends to produce microcracks due to its poor fracture toughness,which seriously affects the working life of petroleum drill bit.Mo2FeB2-based cermet is a novel type of ternary boride with good mechanical properties,high temperature stability,excellent wear and corrosion resistance,and has been applied to injection mold,extrusion die and steel coating,etc.Thus,Mo2FeB2 cermet is considered as alternative materials for cemented carbide used in petroleum drill bits.However,Mo2FeB2 cermet has lower flexural strength and hardness than WC-Co cemented carbide.In order to improve the properties of Mo2FeB2 cermets,the alloying methods are commonly used in ex-periments(such as Cr,Ni,Mn,and V).In addition,the theoretical study on the effect of al-loying elements on the mechanical properties of Mo2FeB2 is still unclear.Therefore,the in-fluence of Cr,Ni and Mn on the mechanical properties of Mo2FeB2 has been studied by the first-principles calculation method in this article.Moreover,the stability relationship between Mo2FeB2,Mo2FeB4 and MoFe2B4 in the Mo-Fe-B system was also studied to ensure Mo2FeB2 is the most stable structure.The main research contents and conclusions are as follows:(1)In Mo2FeB2,Mo2FeB4 and MoFe2B4 three systems,Mo2FeB2 has the best thermody-namic stability and mechanical properties.Among them,the superior mechanical properties of Mo2FeB2 are mainly due to the strong B-Mo covalent bond,and the worse thermodynamic stability of Mo2FeB4 and MoFe2B4 is mainly due to the B-Mo,B-Fe and Fe-Mo antibonds.(2)Alloying elements Cr,Ni and Mn are prefer to replace the Fe site of Mo2FeB2,and at this time,Mo2FeB2 has better elastic modulus.Fe site doping can promote the bonding be-tween Fe,Mo and B in the Mo2FeB2,which can improve its mechanical properties.However,the worse mechanical properties of Mo site doping are mainly due to the Fe-TM ion bond.(3)By doping Cr and Mn at Fe site,the shear modulus,Young’s modulus and Vickers hardness of Mo2FeB2 can be improved,but it will increase Mo2FeB2’s brittleness.However,Ni doping will reduce its elastic modulus and Vickers hardness,but can improve its toughness.The mechanical properties’ enhancement of Cr and Mn doped Mo2FeB2 is mainly due to the strong covalent bond of Cr-B and Mn-B,while the plasticity’s improvement of Ni doped Mo2FeB2 is mainly due to the strong ionic bond between Ni,Mo and Fe.(4)By increasing the doping concentration of Cr and Mn,the shear modulus,Young’s modulus,Vickers hardness and brittleness of Mo2FeB2 can be further improved,but the pro-motion effects will decline when the doping concentration of Mn is too high.However,with the increase of Ni doping concentration,the effect is opposite to that of Cr and Mn doping,but its ductility can be further improved.The effect of alloying doping concentration on its mechanical properties is mainly due to that the bond strength of B-Cr and B-Ni decrease firstly and then increase with the increase of the Cr and Ni doping concentration,while the bond strength of B-Mn decreases with the increase of Mn doping concentration.