Effects Of Ge On The In-situ Synthesis And Mechanical Properties Of Ti₃SiC₂/Al₂O₃ Composites

Owing to the Ti₃Si C₂/Al₂O₃ composites has a good mechanical properties,Ti₃Si C₂/Al₂O₃composites are considered as ideal structural materials.However,Ti C and Ti Si₂ typically coexist during the synthesis of Ti₃Si C₂/Al₂O₃ composites through an in-situ reaction,which adversely affects the mechanical properties of the resulting composites.In this study,Ti₃Si C₂/Al₂O₃ composites were prepared via in-situ hot pressing sintering,Ge was used as a sintering aid.The effects of Ge doping on the in-situ reactive preparation and mechanical properties of Ti₃Si C₂/Al₂O₃ composites were studied by experiments and calculations.Ti₃Si C₂/Al₂O₃ composites were prepared via hot pressing sintering at 1350?,1400?,1450?,1500?,and 1550?under 30 MPa for 1.5h.The Al₂O₃:Ti₃Si C₂volume ratio(fabricated via in-situ reaction;molar ratio of Ti:Si C:C=3:1:1)was 6:4.Ge was doped to form3Ti/1Si C/1C/x Ge mixtures,where x=0,0.1,0.2,0.3,0.4,and 0.5 mol.The results show that the addition of Ge inhibits the formation of impurity phase,and improves the purity,mechanical properties of Ti₃Si C₂/Al₂O₃ composites.The sample prepared at 1450?with 0.3 mol Ge addition showed the best comprehensive properties,whose flexural strength,fracture toughness,and microhardness were 640.2 MPa,6.57 MPa.m^1/2,and 16.21 GPa,respectively.It can be seen from the XRD patterns,TEM,and EDS,the properties of composites are improved due to the Ge replaced some of the Si atoms to compensate the evaporation loss of Si to form Ti₃(Si_1-xGe_x)C₂,which showed a crystal structure similar to that of Ti₃Si C₂.Furthermore,the molten Ge accelerated the diffusion reaction of the raw materials,increasing the overall density of the Ti₃Si C₂/Al₂O₃ composites.In order to further study the effect of Ge doping on the preparation and properties of composites,the experimental results were calculated and verified by first-principles.The results showed that the density of state of Ti₃(Si_0.75Ge_0.25)C₂ solid solution formed by Ge replacing part of Si was similar to that of Ti₃Si C₂ and slightly skewed to the left,which indicates the stability of Ti₃(Si_0.75Ge_0.25)C₂ structure to a certain extent.The Gibbs free energy of Ti₃Si C₂/Al₂O₃composites was negative at 1350?to 1550?,and the minimum at 1450?.The values of elastic modulus of solid solution of Ti₃(Si_0.75Ge_0.25)C₂ was between Ti₃Si C₂ and Ti₃Ge C₂,there was no phenomenon of solution strengthening or weakening.