Solid Solution Effects Of Alloying VC,TiC On Microstructure And Properties Of WC-VC-TiC Cemented Carbides

Cemented carbides have well been recognized as hard and anti-wear materials for wide applications on industrial production.In present,to meet the particular requirements for services under extreme conditions,increasing strength,wear resistance,thermal fatigue resistance,thermal shock resistance,and corrosion resistance of cemented carbides become a hotspot of research in materials science community.Among great efforts to optimize the properties of cemented carbides,the attempts to improve the properties of cemented carbides by means of solid solution enhancement have drawn considerable attention.For example,?W,Ti?C solid solution could effectively resist the chemical corrosion and the diffusion wear in the steel cutting.?W,V?Csolid solution could improve the strength and high temperature hardness of the cemented carbides.However,there is few attention has been paid on the solid solution effects on the properties of?W,V,Ti?C cemented carbide by co-addition of VC and TiC in WC.Therefore,initially,the first-principles calculation was used to figure out the solid solution phase diagram of?W,V,Ti?C carbide.And corresponding mechanical properties of the carbide to phase diagram were calculated.Based on the first-principles calculations,we could target the components of the?W,V,Ti?C carbides with optimized mechanical properties.Subsequently,experiments were carried out to validate the results given by the first-principles calculation.We firstly synthesized the cemented carbides,where optimized mechanical properties could be achieved according to the solid solution phase diagram and mechanical property calculation.The constituents,microstructure,mechanical properties,corrosion resistance,friction and wear properties of as-prepared?W,V,Ti?C carbides were investigated in detail.Furthermore,the mechanism responsible for the strengthening of?W,V,Ti?C carbides by co-addition of VC and TiC in WC were clarified,and the correlation between mechanical properties and antiwear properties of as-prepared?W,V,Ti?C carbides were established.The main conclusions could be drawn as follows:?1?The results of the first-principles calculations show that the?W,V,Ti?C carbide with rich-V and rich-Ti constituents tend to crystallize into Face-Centered Cubic?FCC?structure,and the?W,V,Ti?C carbide with rich-W constituent tend to crystallize in Hexagonal-Close Packed?HCP?structure.From the calculated young's modulus and shear modulus,it can be seen that co-addition of TiC and VC in WC with small equal molar ratio can enhance mechanical performance of?W,V,Ti?C carbide.?2?Regarding binderless WC based cemented carbide,co-addition of VC and TiC in WC with equal molar ratio were fabricated,the content of addition varied from1 at.%to 5 at.%.Co-addition of VC and TiC in WC tend to form solid solution rather than composite.The solid solution effect in?W,V,Ti?C carbides was very significant for the enhancement of the mechanical properties of binder-free WC based cemented carbides.In particular,the hardness increased from 964.5 HV₁₀?without addition of VC and TiC?to 2533.4 HV₁₀?co-addition of 5 at.%VC and 5 at.%TiC?.The fracture toughness decreased slightly with the increase of the content of VC and TiC.Friction and wear tests in dry reciprocating sliding contact in ball-on-disk configuration were carried out in room temperature.The friction coefficient and wear rate of cemented carbide decreased with the increase of VC and TiC content.The wear rate decreased from 2.56×10^-3mm³/Nm?without addition of VC and TiC?to 4.6×10^-5mm³/Nm?co-addition of 5 at.%VC and 5 at.%TiC?,the wear resistance was improved by factor of 50.The wear mechanism for binder-free cemented carbides without or with lower content of VC and TiC was dominated by ploughing,adhesive wear and abrasive wear.The wear mechanisms for binder-free cemented carbides with high content of VC and TiC were grain pullout and surface cracking.?3?Regarding the cemented carbide with 8wt.%Co biner,co-addition of VC and TiC in WC with equal molar ratio were fabricated,the content of addition varied from1 at.%to 5 at.%.Co-addition of VC and TiC in WC tend to form solid solution rather than composite.This is similar with the binder-free cemented carbides.The results showed that grain size of?W,V,Ti?C carbides was refined,but the mean free path of cobalt phase was decreased.The hardness of as-prepared cemented carbides increased from 1709.3 HV₁₀?without addition of VC and TiC?to 2211 HV₁₀?co-addition of 4at.%VC and 4 at.%TiC?,the hardness was increased by 29.4%.The hardness of cemented carbides increased with the increase of the concentration of high VC and TiC,but the fracture toughness decreased.Friction and wear tests in dry reciprocating sliding contact in ball-on-disk configuration were carried out in room temperature.The friction coefficient of cemented carbide had poor correlation with VC and TiC content.However,the wear rate increased with the increase of VC and TiC content.The wear rate decreased from 9.91×10^-5mm³/Nm?without VC,TiC?to1.29×10^-5mm³/Nm?co-addition of 4 at.%VC,4 at.%TiC?,the wear rate was dropped by 87%.The wear mechanism for cemented carbides without or with lower content of VC and TiC was dominated by ploughing,Co-phase extrusion and smearing,and abrasive wear.The wear mechanism for cemented carbides with high content of VC and TiC was dominated by crushing of carbide grains and surface cracking.In addition,the corrosion resistance of WC-Co hardmetals was optimized by VC and TiC,and their corrosion resistance increased with the increase of VC and TiC content.