【作者】 王芳；

【导师】 聂金凤；

【作者基本信息】 南京理工大学 ， 材料工程（专业学位）， 2019， 硕士

【摘要】 陶瓷颗粒增强铝基复合材料具有高的比强度、耐磨性、低的热膨胀系数以及低密度等特性在航空及航天、汽车机械等领域具有广阔的应用前景。在众多陶瓷颗粒中,TiC、TiB₂颗粒以其高的弹性模量、高硬度、低密度以及与α-Al良好的晶格匹配关系而得到广泛使用。目前这类材料存在的关键问题是增强相在基体上呈聚集分布,这对材料的力学性能和耐腐蚀性能产生不利的影响。针对上述问题,可采用变形的方式对材料进行处理。因此,研究该材料在变形过程中的组织演变、力学性能和耐腐蚀性能具有重要的意义。本文采用熔体原位自生方法制备Al-5%TiB₂/TiC铝基复合材料,分别选用热轧、高压扭转、叠轧的方法对其进行变形处理,采用光学显微镜、扫描电镜、电子背散射衍射技术和透射电镜表征分析了不同变形状态下复合材料的微观组织演变规律,利用硬度、单轴拉伸实验和电化学分析测试手段对其力学性能和腐蚀性能进行了测试。主要结论如下:（1）热轧制对Al-5%TiB₂/TiC铝基复合材料微观组织及力学性能的影响。在300℃下对材料进行了压下量分别为20%、40%、80%和90%的轧制变形处理,结果表明:随着压下量的增大,增强颗粒趋于弥散分布,晶粒沿轧制方向不断被拉长细化。硬度和抗拉强度随着压下量的增加不断提升,当变形90%时分别达到60HV、186MPa,相比铸态分别提升了40%、142%,这主要由增强相的弥散分布、晶粒的细化以及位错的塞积造成的。同时,研究了上述不同变形量下材料在3.5wt.%NaCl溶液中的腐蚀行为,发现材料的耐腐蚀性呈现先升高后降低的趋势,但均好于铸态材料。其中,下压量为20%时具有最优的耐蚀性,这归因于增强颗粒的弥散分布带来的转移电荷电阻的增大以及增强相与基体结合界面密实度的增加。（2）高压扭转对Al-5%TiB₂/TiC铝基复合材料微观组织及力学性能的影响。通过高压扭转对材料进行了1转、2转和5转的变形处理,结果表明:随着转数的增加增强颗粒的分布愈发弥散,α-Al晶粒得到不断细化获得了超细晶铝基复合材料,5转时晶粒细化至295nm。硬度和抗拉强度也在不断的提高,5转时分别提高到92HV、212 MPa,相比铸态分别提升了113%和175%。分析认为高压扭转后材料的强化机制主要有弥散强化、细晶强化和位错强化,并且通过定量计算表明前两者增加显著,特别是弥散强化的贡献值增加显著,对强度的提升起着至关重要的作用。（3）累积叠轧制备6063Al/Al-TiB₂/TiC层状复合材料及其组织性能的研究将Al-TiB₂/TiC复合材料和6063Al进行1到3道次的叠轧处理构筑了层状铝基复合材料,结果表明:获得了界面结合良好、增强颗粒弥散分布的Al/Al层状材料,随着道次的增加,α-Al晶粒沿轧制方向伸长不断被细化。材料的硬度和抗拉强度随道次的增加而不断的增加,三道次时,6063Al和Al-TiB₂/TiC的硬度值分别达到113HV、60HV,Al/Al层状材料的抗拉强度值提升到256MPa,相比铸态Al-TiB₂/TiC复合材料提高了232%。该层状铝基复合材料的强度贡献主要来源于增强相的弥散分布、时效析出强化、位错强化以及与Al/Al界面处背应力之间的交互作用。更多还原

【Abstract】 Aluminum matrix composites（AMCs）reinforced by ceramic particles have excited great interest in automotive industry,aerospace and defense application for their high specific strength,good wear resistance,excellent dimensional stability and superior damping capacity.TiC and TiB₂ particles are widely used for their high elastic modulus,high hardness,low density and good lattice matching relationship withα-Al.At present,the main problem of this kind of materials is that the reinforcing particles aggregate seriously in the matrix,which influence the mechanical properties and corrosion resistance of the composites seriously.It has been found that the following deformation can improve the problem to some extent.Therefore,it is of great significance to study the microstructure evolution,mechanical properties and corrosion resistance of the materials during the deformation process.Al-5%TiB2/TiC aluminum matrix composites were prepared through in situ melt reaction of Al-Ti and Al-B-C alloys and subsequent the hot rolling,high pressure torsion and accumulative roll-bonding method were used to improve the microstructure and mechanical properties.The microstructure evolution of the composites were characterized using optical microscope,scanning electron microscopy,electron back scattering diffraction technology and transmission electron microscopy.Finally,the mechanical properties and corrosion resistance performance were evaluated by the hardness,uniaxial tensile tests and electrochemical analysis method.The main conclusions can be drawn as follows:（1）Effect of hot rolling on microstructure and mechanical properties of Al-5%TiB2/TiC aluminum matrix composites.The hot rolling deformation were conducted at 300℃and the reduction were 20%,40%,80%and 90%,respectively.The results show that both the microstructure uniformity and mechanical properties of the composites were significantly improved with increasing rolling reduction.The hardness and tensile strength of the composites with 90%rolling reduction reached 60HV and 186MPa respectively,which were 40%and 142%higher than as cast one.It was considered that the increase of the strength was caused by the dispersion distribution of the reinforcing phase,the refinement of grain and the plugging of dislocation.At the same time,the corrosion behavior of the material in 3.5wt.%NaCl solution with different reduction were studied.It was found that the corrosion resistance of the composites with increasing deformation increased firstly and then decreasing to some extent,which are still better than that of the as-cast one.The optimal corrosion resistance is obtained when the reduction is about20%,which is attributed to the increase of the transfer charge resistance caused by the dispersive distribution of the reinforced particles and the improvement of the interface between the particle and the Al matrix.（2）Effect of high pressure torsion on microstructure and mechanical properties of Al-5%TiB2/TiC aluminum matrix composites.The materials were severely processed by high pressure torsion for 1,2,5 turns.The results show that the TiC and TiB₂ particle aggregates were significantly dispersed.Meanwhile,theα-Al grains were also refined during the severe plastic deformation and an ultrafine-grained structure with an averageα-Al grain size of²45nm was obtained after 5 turns.Due to the loading transfer strengthening,grain boundary strengthening and dislocation strengthening by the HPT processing,the hardness and tensile strength increased to 92HV and 212MPa after 5revolutions,respectively,which were 113%and 175%higher than the as-cast one.The quantitative calculations show that the contribution of dispersion strengthening increases significantly which plays the most important role.（3）Study on the preparation,microstructure and properties of 6063Al/Al-5%TiB₂/TiC layered heterogeneous composites processed by accumulative roll-bonding.The 6063Al/Al-5%TiB₂/TiC composites with layered structure were prepared by accumulative roll-bonding from 1 to 3 cycles.The results show that the composites with good interfacial bonding and dispersive distribution of reinforced particles were obtained.The hardness and tensile strength of the composites increased with increasing cycles.The hardness values of 6063Al and Al-5%TiB₂/TiC reached to 113HV and 60HV,respectively,and the tensile strength value of the composite reached 256MPa after three cycles,which is 232%higher than that of as-cast Al-5%TiB₂/TiC composite.The improvement of the strength can be attributed to the combination of the load transfer strengthening of reinforced particles,precipitation strengthening,dislocation strengthening and the back stress strengthening.更多还原