【作者】 石金磊；

【导师】 严红革；

【作者基本信息】 湖南大学 ， 材料加工工程， 2011， 硕士

【摘要】 功能梯度材料是一种综合性能优异的先进材料,其性能沿梯度方向连续变化,因而适用于在厚度方向上对性能有不同需求的工程构件。此类材料性能的梯度变化是由其不同位置处的化学成分、微观组织不同造成的。目前用于制备功能梯度材料的方法主要有粉末冶金法、离心铸造法、热喷涂、浸渗法和电磁相分离法等。本论文探索了喷射沉积技术在梯度复合材料中应用的可行性,采用课题组自行设计的喷射沉积装置成功地制备了6066Al/SiC_P梯度复合材料,并对其进行了微观组织分析和性能检测。结果表明:SiC颗粒增强相的质量分数在沉积坯中沿沉积方向从底部到顶部由0%逐渐增加到30%,从而证实了喷射沉积法制备梯度复合材料的可行性。论文开展了梯度复合材料沉积坯热致密化工艺的研究,提出了利用阶梯式压头对坯料进行致密化的新工艺,通过实验摸索出了适合于6066Al/SiC_P梯度复合材料致密化的工艺参数。结果表明:在压制温度为580℃、压制压力为220MPa、保压时间为10min的工艺参数下,采用阶梯式压头进行热模压致密化,可以将沉积坯的相对密度提高到99%以上。阶梯式压头热模压工艺可以有效地消除沉积坯中的孔隙,改善基体与增强颗粒间的界面结合情况,提高材料的致密度,特别适用于在较小的压制压力下对较大尺寸的坯料进行热模压致密化。经热致密化后,复合材料中SiC增强颗粒的浓度依然呈梯度分布。梯度复合材料的力学性能沿梯度方向呈现变化,在SiC颗粒浓度为15mass%时力学性能最高,达到428MPa。论文对比了致密化前后材料组织性能的变化并对其进行了分析讨论。初步探讨了阶梯式压头在热模压致密化过程中的机理,就坯料在致密化过程中的受力状态进行了分析讨论,指出了阶梯式压头致密化的优势,为进一步的研究打下了基础。采用喷射沉积法制备SiC颗粒增强铝基梯度复合材料的工作尚未有类似报道。与其他方法相比,采用喷射沉积法制备的梯度复合材料具有组织细小、SiC增强颗粒在高度方向上呈连续梯度分布且可控性强,特别适合于制备大尺寸的梯度复合材料坯件。更多还原

【Abstract】 Functionally gradient materials (FGMs), a new class of advanced and innovative materials which are capable of providing superior and reliable performance, are actively being sought for engineering devices that are subjected to two distinct service conditions on two opposite sides across the thickness direction. In a functionally graded material the properties change gradually with position. The property gradient in the material is caused by a position-dependent chemical composition, microstructure or phase composition. The processing techniques developed for preparing FGMs include powder metallurgy, centrifugal casting, thermal spraying, infiltration processing, electromagnetic separation, etc.This thesis explored the feasibility of spray deposition in preparing functionally graded composites. The 6066Al/SiC_P graded composites were successfully prepared via the spray deposition system. This system was developed by our research team. The microstructure and mechanical properties of the preform were characterized. The results revealed that the SiC_P weight fraction of the as-deposited preform from the top to the bottom ranges almost continuously from 0 to 30%. This result indicated that spray deposition is a reliable approach in producing the FGMs.Densification was conducted on the spray deposited graded composites in this thesis. A novel technique named as stepped force plug pressing was developed. The optimized processing parameter appropriated for 6066Al/SiC_P was obtained through experiments. The results showed that the relative density of the composites was above 99% after densification with the stepped force plug pressing in the processing parameter of 580℃, 220MPa and 10min pressure retaining. The stepped force plug pressing showed excellent perfermence in eliminating the porosity in the preform and improve the interface between the matrix and the reinforcement particles. It is applicable to densify larger preform with less pressure. The SiC particles in the preform still presented a graded feature after densification. The tensile strength of the graded composite varied with different SiC percentage and achieved a peak value 428MPa at 15mass% SiC weight percentage. The results and discussions were given about the different structures and properties between the spray deposited preform and densified composites. The mechanism of the stepped force plug pressing and the stress of the preform during the densification were simply analyzed. The advantages of this novel densification technique were presented, which laid a foundation for its further development.There was no similar report in researchs about SiC_P reinforced aluminum matrix graded composites preparing via spray deposition. Compared with graded composites preparing by other techniques, spray deposited graded composites have advantages of fine grain and easy in controlling. Spray deposition was especially suitable in preparing large graded composites.更多还原