Microstructure And Properties Of In-situ Synthesized TiB₂ Steel Bonded Carbide By Microwave Sintering

Due to their high mechanical properties,well wear resistant performances and excellent machinability and heat-treatability,steel-bonded carbides had great potential in the field of engineering,such as industrial molds,measuring tools and wear-resistant materials.In this thesis,TiB₂ steel bonded carbides were synthesized in situ by microwave sintering.The effect of the TiB₂ contents?10%,20%,30%,40%?on the phase,microstructure and mechanical properties of steel bonded carbides were studied,compared with the samples prepared with additional TiB₂ particles.The friction and wear behavior of TiB₂ steel-bonded carbides was tested under different friction conditions.The influence of heat treatment on mechanical and friction and wear properties of Ti B₂ steel bonded carbide was also investigated.In addition,the microstructure and mechanical properties of Y₂O₃ doped TiB₂ steel bonded cemented carbide were researched.The results showed that both the in-situ synthesized and additional Ti B₂ steel-bonded carbides were mainly composed of?-Fe,TiB₂ and Fe₂B phases.The in-situ TiB₂particles are fine with a particle size of³?m.With increasing TiB₂ contents,the relative density of in-situ synthesized alloys increased at first and then remained unchanged.The relative density of additional TiB₂ alloys,however,increased first,and then decreased.Meanwhile,the microhardness and compressive strength of the two alloys increased as the TiB₂ content increased,but the bending strength decreased.The fracture mechanism of the in-situ synthesized steel-bonded carbides changed from ductile fracture to brittle fracture,while the fracture mechanism of the additional Ti B₂ alloy was brittle intergranular fracture.In-situ synthesis materials had higher performance than that of the additional TiB₂ steel-bonded carbide under the condition of the same TiB₂ content.The friction coefficient of the in-situ synthesis steel-bonded carbides with different TiB₂ contents was basically the same in the steady wear stage.As the TiB₂ contents increased,the wear volume gradually decreased and the wear resistance increased.By increasing loads and sliding rates,the friction coefficient of TiB₂ steel-bonded carbide decreased,and the depth and width of wear scar,wear volume and the wear rate increased.The main wear mechanism of steel-bonded carbide was adhesive wear and slight abrasive wear.The hardness and bending strength of TiB₂ steel-bonded carbides were improved after heat treated.The quenched steel-bonded carbides had highest hardness,but the tempered samples had highest bending strength.After heat treated,the wear resistance of TiB₂ steel-bonded carbide was enhanced,and both quenched and tempered samples exhibited well wear resistant performance.Adding nano-Y₂O₃ can promote the forming of TiB₂ particles and inhibit the forming of Fe₂B.As a result,the density,micro-hardness and bending strength of TiB₂ steel-bonded carbides were improved by adding Y₂O₃.They reached 6.58 g/cm³,556 HV_0.1and 675 MPa respectively as the addition of Y₂O₃ reached 0.25%.The results of friction and wear test indicated that the friction coefficient and the wear volume of TiB₂ steel-bonded carbide were reduced after adding nano-Y₂O₃ particles.The corrosion resistance and oxidation resistance were also improved by adding Y₂O₃ in the alloys.Nevertheless,the excessive addition of Y₂O₃ can lead to the increasing of sintering defects which will reduced the mechanical properties of steel-bonded carbides.