Study Of Transition Elements Doped WCoB Based Cermets By First-principle Calculation And Experiment

With the development of information technology and material research,the transitional "trial and error" method has appeared a series of disadvantages,such as long research time and high costs.Based on the "Materials Genome Initiative" and material design method,different transition elements doped ternary boride cermets are studied by first-principle calculation to replace WC-Co based cermets.Spark plasma sintering is adopted to study the phase evolution,microstructures and mechanical properties in different sintering stages.Different Cr doping content is used to verify the conclusions of first-principle calculations.Ternary borides show high hardness and high melting point among hard materials.By solving the poor sinterability of binary boride,ternary borides are fabricated by"reaction bronzing sintering".Based on periodic table of the elements,26 ternary borides in ICSD are calculated by first-principle calculation to get the mechanical properties,ductility and hardness.Among them,WCoB,MoCoB,Mo2FeB2 and Mo2NiB2 show enormous potential for further studies.WCoB are chosen as the research target due to the high hardness and high mechanical properties.The first-principle calculations are adopted to study the effect of V(3s24p63d34s2)doped WCoB and W2CoB2.V doping leads to the decreasing of stability of WCoB and W2CoB2,which are harder to form by simple substances.The weaker B-V covalent bonds and W-V metallic bonds contribute to the increasing of ductility and decreasing of mechanical properties and hardness.The first-principle calculations are adopted to study the effect of Cr(3s23p63d54s1)doped WCoB and W2CoB2.Cr doping contributes to the increasing of stability of WCoB and W2CoB2,which is in thermodynamic stable states.Cr doping leads to the decreasing of mechanical properties and the increasing of ductility,which can be attributed to the hybridization between 2s(B)-3d(Co,Cr)-5d(W)orbitals.The low content of Cr doping contributes to the increasing of hardness.The first-principle calculations are adopted to study the effect of Mn(3d54s2)doped WCoB and W2CoB2.Mn doped structures are in thermodynamic stable states and the stability increases slightly.Due to the weaker B-Mn covalent bonds,Mn doping leads to the decreasing of mechanical properties and hardness.When the Mn doping content reaches the maximum value,the mechanical properties and ductility increase slightly after sharply dropping.The comparison of the results of V,Cr,Mn doped WCoB and W2CoB2 is adopted to analyze the suitable doping element and hard phase.The Cr,Mn doped WCoB and W2CoB2 show high stability and relatively high mechanical properties.Cr,V doped WCoB and W2CoB2 show high ductility.By adopting four hardness models,the low content Cr doped WCoB shows the highest hardness value.Therefore,Cr doped WCoB is the suitable choice to improve the mechanical properties of WCoB based cermets.The first-principle calculations are adopted to study the mechanical properties and electronic structure of WCoB and Cr doped WCoB under high pressure.The W4Co4B and W4Co3CrB4 are stale below 170GPa.High pressure leads to the decreasing of lattice constants and the increasing of mechanical properties.High pressure contributes to the increasing of ductility and harness.The delocalization of electrons in the bonding region increases and hybridization decreases under high pressure.All structures are para-magnetism under different pressure,which is nearly zero.The WCoB based cermets are sintered among 600?-1200? by SPS to study the microstructure and phase evolution.The WCoB hard phase is generated by Co2B at 1000*by solid phase reaction with lots of pores and low relative density.The liquid phase appears at 1150? with high density.The Vicker's hardness and transverse rupture strength(TRS)reach the maximum value of 1262 Hv0.5 and 1212 MPa at 1200? and 1170?,respectively.Different Cr doping content of WCoB based cermets are sintered among 1150?-1200? at liquid phase sintering stages.Cr doping contributes to the decreasing of density and TRS,which is attributed to the increasing of unreacted W phase and the decreasing of wettability.The residual Cr of binder phase forms Cr enrichment zones under high doping content,which leads to the decrease of mechanical properties.Cr doping leads to the increase of hardness,and the maximum value is 1751Hv0.5.Based on Rietveld structure refinement and EDS analysis,the hardness is determined by 0.025Kg load.The variation trend is consistent with theoretical hardness models,which verifies the conclusion of first-principle calculation.