Graphene-coated Si₃N₄ Nanoparticles Dispersion Strengthened And Modified Tial Matrix Composite

TiAl alloy is expected to replace the traditional Ni-based alloys as a new generation of high-temperature structural materials due to its low density,high strength,good high temperature strength and creep resistance.However,the inherent shortcomings such as low fracture toughness and poor plasticity at room temperature of TiAl alloy limit its further development and application.The inoculation method by adding ceramic particles could realize a significant grain refining,as well as the intracrystalline strengthening induced by the ceramic inoculate and the in-situ nanoparticles(NPs).It can achieve high-efficiency and low-cost toughening of TiAl alloy.In this project,two processes,high-energy ball milling and vacuum rapidly quenched,were used to synthesize graphene-coated silicon nitride nanoparticles(Si₃N₄-graphene nanoparticles,SGP)and Ti₂Al C-Ti₂Al N/TiAl inoculant ribbons,which were added to TiAl alloy.In the alloy matrix,Si C-Ti₂Al N/TiAl composite and Ti₂Al C-Ti₂Al N/TiAl composite were prepared.The phase composition and microstructure characteristics of the two composite materials were investigated,and the distribution of the reinforcement in the matrix and the mechanism of matrix refinement were studied.Through the mechanical property test at room temperature and high temperature,the strengthening and toughening mechanisms of the two materials are studied,and the conclusions obtained are as follows:Both SGP particles and Ti₂Al C-Ti₂Al N ribbons can refine the TiAl alloy structure,but SGP particles show a better refinement effect.After adding SGP particles to the TiAl matrix,the in-situ synthesized Si C and Ti₂Al N reinforcement phases uniformly dispersed in the matrix,the average grain size of the alloy is refined to about 40?m,and the average lamellar spacing is reduced to 30 nm.After the 1.0%Ti₂Al C-Ti₂Al N/TiAl ribbon was added to the TiAl matrix,the grain size of the matrix was slightly refined,but the average lamellar spacing has no change.The reinforcement phase in composite is consistent with that observed in the ribbon.And the microstructure deteriorates significantly with the increase of the amount of thin ribbons added.At room temperature,the compressive strength and ductility of Ti₂Al C-Ti₂Al N/TiAl-based composites are not significantly improved compared to the matrix.The yield strength of Si C-Ti₂Al N/TiAl composites continues to increase with the increase in the amount of SGP added,which is significantly higher than that of the TiAl matrix,while the ultimate compressive strength and compressive fracture strain show a trend of increasing first and then decreasing.When the amount of SGP particles added was 1.0%,the Si C-Ti₂Al N/TiAl composites showed the best plastic-strength matching,yield strength of about 1520.2 MPa,ultimate compressive strength of about 2545.4 MPa,and compressive fracture strain of16.0%.Under the high temperature conditions of 1273K?1473K,the peak stress of Si C-Ti₂Al N/TiAl composite is significantly higher than that of the base alloy.The room temperature mechanical properties of the two composite materials are mainly enhanced by the solid solution strengthening of interstitial nitrogen atoms,fine grain strengthening of the TiAl matrix,and dispersion strengthening of the second phase particles.