| With the continuous development of modern society,people have higher and higher requirements for materials in various aspects,and the advantages of traditional materials in certain properties have become less and less obvious.Particle-reinforced aluminum-based composites are widely used in aviation,because of their unique advantages,such as high specific strength,high specific stiffness,good electrical and thermal conductivity,wear resistance and corrosion resistance,easy preparation,process design,and good cost control.Aerospace,automotive industry,electronic components and other fields.In recent years,the demand for lightweight development and energy saving and emission reduction has placed high demands on the heat resistance of aluminum alloys.Finding suitable reinforcing particles to develop heat-resistant aluminum-based composite materials has attracted more and more attention.Titanium nitride(TiN)has the advantages of high melting point,high hardness,low thermal expansion coefficient,and good lattice matching relationship with the aluminum matrix,etc.It is a potential enhanced particle in aluminum alloy.However,the prone interfacial reaction between TiN and A1 is a long-standing problem.The coarse slab-shaped TiA13 produced seriously affects the comprehensive properties of the composite,which further limits the processing and application of TiN-reinforced aluminum-based composites.Therefore,it is of great significance to reduce the conversion of TiN in the aluminum melt and to prepare TiN reinforced aluminum-based composites with good microstructure properties and no by-products.Based on the previous research of the research group,this paper systematically studies the effects of liquid-solid reaction temperature,reaction time,and the proportional relationship between TiN and C on the conversion rate of TiN by rationally designing the reaction conditions to obtain the optimal process.The nano-Al4C3,AIN and sub-micron TiN particle-reinforced aluminum-based composites were prepared by combining the micro-interface reaction of TiN and aluminum matrix in the liquid-solid reaction process.XRD,DSC,SEM,and TEM are used to systematically study the composite material,and the relationship between room temperature and high temperature(350℃)mechanical properties and the structure and particle content of the material is analyzed;at the same time,(TiN+C)/Al Insufficient system,B element was introduced into TiN/Al system to transform coarse TiAl3 into TiB2 phase which is more thermodynamically stable.The interfacial reaction of TiN in aluminum melt was systematically studied by means of detection.In addition,the response law between the mechanical properties and the microstructure distribution of the(TiN+TiB2)/Al system is studied in this paper,and the influence of reaction conditions on the properties of composite materials is revealed.The main research work of this thesis is as follows:(1)Effect of C on the conversion behavior of TiN in aluminum.the thesis studies the TiN transition process in the system for(TiN+C)/Al system through various analysis methods.Through Gibbs free energy calculation,DSC thermal analysis,XRD,and microscopic observation analysis,it was found that as the liquid-solid reaction temperature increases,the TiA13 in the melt continues to increase,and alumina particles will be formed after the reaction temperature reaches 800℃,which will continue to rise.At high temperatures,both the particle size and content of alumina increase.The liquid-solid reaction temperature was set to 700℃.The experiment found that the conversion rate of TiN remained stable within 1.5h,and the conversion rate increased when the reaction time was extended;the reaction time and temperature were determined,and the reaction in a short time(1h)Under the conditions,with the increase of C content,the conversion rate of TiN showed a trend of first decrease and then increase,but under long-term(2h)reaction conditions,the content of C had no significant effect on the conversion rate.(2)Preparation of nano-aluminides and submicron TiN particles reinforced aluminum-based composite.Based on the analysis of the conversion conditions of TiN,the extruded Al-5TiN-0.6C composites with liquid-solid reaction at 670℃ for 2h were taken as the research object.The micro-interface reaction of TiN in Al melt was used to obtain nano-AlN and AI4C3 studies.The effect of particle content on the properties of composite materials is shown.The results show that the increase in the content of conversion-enhancing particles significantly improves the room temperature and high temperature strength of 350℃.The high-temperature strength and elongation at 350℃ are 151 MPa and 7%.(3)Effect of N-B complex on the transformation behavior of TiN in aluminum.In order to make up for the deficiency of(Al-TiN)/C system,the residual TiA13 phase in the material is eliminated.Based on the related research of the research group,the element B was introduced into the TiN/A1 system through the N-B complex,and TiAl3 was transformed into thermodynamically stable TiB2 particles.The effects of liquid-solid reaction time,reaction temperature,and B/Ti ratio on TiN conversion were systematically studied.The experimental results show that the particle size of the originally coarse TiA13 phase gradually decreases with the introduction of the B element.When the B/Ti ratio reaches 2:1,the conversion of TiN is completely suppressed,and TiAl3 is not formed.Through TEN analysis,it was found that a large amount of shell-AIN exists around TiN particles in the composite.The analysis suggests that a dense AIN shell hinders the contact between TiN and aluminum,thereby preventing the reaction of TiN. |
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