Composition Design,Microstructure Control And Properties Of WCoB-TiC Based Cermets

WCoB based cermets have high hardness,wear resistance and high temperature oxidation resistance,and have low reaction rates with non-ferrous metals such as copper and zinc,and are especially suitable for non-ferrous metal processing tools.At present,WCoB-TiC based cermet materials prepared by WC-Co-TiB₂ initial powder system not only have low raw material cost,save strategic tungsten resources,but also in-situ TiC ceramic phase can improve the toughness of materials to a certain extent.A common raw material for preparing high-performance WCoB-based cermets.However,the WCoB-TiC based cermet prepared by the powder system is brittle,and the strength and toughness are still insufficient.How to effectively improve the toughness of WCoB-TiC based cermet materials has become a key issue to be solved in the current research of WCoB-TiC based cermet materials.From the research and development progress of ternary boride-based metal ceramics,the influence of main components?including binder phase content and Mo/B atomic ratio?,alloying elements and metal carbides on the microstructure and properties of Mo₂FeB₂ and Mo₂NiB₂ based cermets larger.However,there are few reports on WCoB based cermets in these aspects,so it is necessary to systematically study the influence of main component content,alloying elements and metal carbides on the microstructure and properties of WCoB based cermets.In view of this,this paper focuses on the influence of composition on the microstructure and properties of WCoB-TiC based cermets.Before the specific experiment,we used part of the theoretical calculation based on the first principle of density functional theory to guide the experimental operation.First-principles calculations show that both WCoB and W₂CoB₂ systems are brittle materials,of which W₂CoB₂ has good thermodynamic stability and comprehensive mechanical properties.The alloying elements Ni and Cr will be preferentially doped at the Co atom position of W₂CoB₂,and the alloying elements Ni and Cr can be used to increase the bulk modulus of the material,and then the bulk of the material will increase with the increase of the alloying element content.The modulus is reduced.Trace Ni doping can increase the hardness of the material,while Cr can effectively improve the toughness of the material.The main components?initial Co content and W/B atomic ratio?have a great influence on the microstructure and mechanical properties of WCoB-TiC based cermets.When the initial Co content is changed to increase the W₂CoB₂ content in the hard phase,the material hardness increases.With the increase of initial Co content,the hardness and flexural strength of WCoB-TiC based cermet increased first and then decreased.When the initial Co content was 18.2 wt.%,the hardness was 91.6 HRA,and the initial Co content was 19.6 wt.The highest flexural strength is 853.6 MPa at%.In addition,the mass growth of WCoB-TiC based cermets at high temperature oxidation conforms to the parabolic oxidation kinetics model.The hardness and flexural strength of WCoB-TiC based cermets increase first and then decrease with the increase of W/B atomic ratio.When W/B atomic ratio is 0.6,the highest hardness is 92.3HRA.At this time,the content of hard phase W₂CoB₂ is also The maximum value.When the W/B atomic ratio is 0.5,the WCoB-TiC based cermet has the maximum bending strength and the maximum fracture toughness,which are 853.6 MPa and 11.48 MPa·m^1/2,respectively.The alloying elements Ni and Cr have a great influence on the microstructure and mechanical properties of WCoB-TiC based cermets.With the increase of the Ni content,the wettability of the liquid bond relative to the hard phase during the reaction boride sintering is improved,and the white hard phase particles are refined,which is advantageous for the improvement of the flexural strength and the fracture toughness.Although Cr doping reduces the density of WCoB-TiC based cermets,a small amount of Cr can refine the hard phase grains,thereby improving the overall mechanical properties of WCoB-TiC based cermets.The proper amount of Ni-Cr co-doping is an effective method to improve the mechanical properties of WCoB-TiC based cermets.When the Ni and Cr contents are 2.3 wt.%and 2.0 wt.%,the hardness,flexural strength and fracture toughness of WCoB-TiC-based cermets reach the maximum values of 92.5 HRA and912.3 MPa and 12.56 MPa·m^1/2,respectively.The grain growth inhibitors VC and Cr₃C₂ have a great influence on the microstructure and mechanical properties of WCoB-TiC based cermets.VC mainly reacts with W₂CoB₂ and TiC to form M₃B₂ and?Ti,W,V?C solid solution,and aggregates at W₂CoB₂/Co and TiC/Co interface,which reduces the interfacial energy,resulting in a decrease in the solubility of W₂CoB₂ in the binder phase.The driving force of the W₂CoB₂ particles is reduced,thereby refining the crystal grains.Cr₃C₂ is mainly dissolved in the binder phase,resulting in a decrease in the solubility of W₂CoB₂ in the binder phase,which reduces the driving force of the W₂CoB₂ particles and refines the grains.Appropriate amount of VC/Cr₃C₂ composite addition can further inhibit the growth of hard phase grains in WCoB-TiC based cermets,thus improving the mechanical properties of the materials.When the VC and Cr₃C₂ contents are 0.4 wt.%and 0.5 wt.%,respectively,the sample has a maximum hardness of 93.8 HRA,and when the VC and Cr₃C₂ contents are 0.4 wt.%and 0.3 wt.%,the bending strength and fracture toughness reached the maximum values of 1108.3 MPa and 14.96 MPa·m^1/2,respectively.