Study On The Preparation And Mechanical Properties Of Rare Earth Cerium Oxide Toughened WC/MgO Composites

Since the WC-based cemented carbide was first proposed to prepare by powder metallurgy,its high hardness,high wear resistance,and thermal stability have made it show its core competitiveness in the manufacturing field of cutting tools,mining tools,precision molds,wear-resistant parts,etc.In the development of WC-based cemented carbide,through the adjustment of the distribution ratio and the preparation process parameters,a variety of grades have been derived and a series of highly efficient tool materials and structural materials have been produced to adapt to different application occasions.Co,which provides toughness for the material,is an indispensable presence in traditional cemented carbides.However,Co is easy to soften at high temperatures.It also has high activity and poor corrosion resistance,which limits its performance.In addition,the cobalt mineral resources are unevenly distributed worldwide and the reserves are small.The cost of cobalt mining in China is high.Therefore,it is of great application value to explore the new WC cemented carbide that replaces Co with the comprehensive mechanical properties comparable to traditional cemented carbide.In recent years,there have been some theoretical foundations and practical preparation results for the WC/MgO composites by using inorganic metal oxide MgO instead of Co.Including the processing of raw material powders,the optimization of the distribution ratio,the determination of the sintering process route,etc.These results have been used as reference.This paper draws on the rare earth oxides that have been widely selected as additives in the field of industrial ceramics.This paper attempts to add CeO₂into WC/MgO and change the amount of CeO₂ and the process parameters.The changes of mechanical properties of WC/MgO composites with CeO₂ additives,the effects of CeO₂ on the phase,and the mechanism of action of rare earth additives were studied.The relationship between microstructure characteristics and properties of composites with different microstructure parameters and crack mode is analyzed,and the effect of crack deflection toughening caused by the second phase particles is discussed.As an applied basic research,this paper provides a theoretical method for selecting the optimization direction of performance in industrial production.It also provides ideas for the study of similar materials.The main results are as follows:1.WC-4.3wt%MgO-?0,0.05,0.15,0.25,0.5?wt%CeO₂ composites was prepared by high-energy ball milling method and hot-press sintering technology.The effects of CeO₂content on the phase composition,microstructure morphology,indentation crack pattern and mechanical properties were studied.The results show that CeO₂ can reduce the W₂C impurity phase peaks and hinders the decarburization process of WC.And it was found that Ce⁴⁺was partially reduced to Ce³⁺during the solid-phase sintering process,which was considered to be related to the increase of toughness.When CeO₂ is optimized to0.15wt%,it appears to refine the microstructure.WC grains tend to be rounded,the average grain size is the smallest,and the relative density is 96.979%.Surface indentation crack was judged as Palmqvist crack.Vickers hardness is 16.251 GPa and fracture toughness is 10.326 MPa·m^1/2?30 kgf?.The cracks are slender and curved.In addition to intergranular propagation path,some transgranular path and crack branches were also found.The highest flexural strength of 904.6MPa was obtained,which was significantly related to the relative density and the average grain size of WC.2.Based on the mass fraction of WC-4.3wt%MgO-0.15wt%CeO₂,the relationship between the structure densification and the temperature was investigated in the range of1580?-1720?,and the mechanical properties was also studied.The results show that WC grains coarsen with increasing temperature,but the relative densification is limited.The sample has good mechanical properties when the temperature is 1650?,f=96.979%,and the average grain size of WC is 1.674?m.CeO₂ can suppress the abnormal growth of grains during sintering,and also improve the dispersibility of MgO phase in matrix.According to the Arrhenius equation,the activation energy for grain growth during preservation is 459.13 kJ/mol,which is higher than that of pure samples without CeO₂.The tendency of CeO₂ to increase the activation energy is inferred from the decrease in the surface energy or the interfacial energy of WC/WC.3.A central composite experiment was designed for the temperature factor and preservation time factor.For the hardness response and fracture toughness response,it is determined that a quadratic polynomial regression model can be used.The least squares method gives the estimated coefficients of the terms in the regression equation.The regression equation and coefficients are tested for significance.Using the regular analysis method,it can be seen that the time factor has a greater impact on the performance response than the temperature factor by comparing the coefficients of the variables in the regular form equation.The surface properties of regression equations were explored using response surface method?RSM?.Constrain the value according to the actual situation,so as to obtain a reasonable implementation range of process parameters.