【作者】 李杰；

【导师】 宗亚平；

【作者基本信息】 东北大学 ， 材料学， 2011， 博士

【摘要】 颗粒增强铁基复合材料具有高强度、高刚度和优异的耐磨性能等一系列优点,是最具有工业研究价值的金属基复合材料之一。然而,多数文献报道都是研究某一种颗粒增强铁基复合材料性能,相互之间由于制备工艺的巨大差别结果没有可比性,还没有文献系统报道不同类型颗粒增强铁基复合材料制备、性能和模拟的对比研究。本文首先应用改进后的电流直加热动态热烧结工艺研究了保温时间对10%TiC/Fe复合材料性能的影响,考察该工艺是否同样适用于制备其它不同类型颗粒增强铁基复合材料,然后制备了八种不同类型陶瓷颗粒(Cr3C2、SiC、TiC、Ti(C,N)、Si3N4、B4C和A12O3)增强铁基复合材料,考察了复合材料的力学性能和磨损性能,初步探索了不同类型颗粒混合增强作用,研究了强化粒子含量对不同类型复合材料性能的影响,同时,应用Eshelby等效夹杂力学模型模拟了不同类型复合材料的力学性能,揭示了不同类型铁基复合材料的强化机理,探讨了粒子含量对不同类型复合材料性能的影响,为颗粒增强铁基复合材料的发展提供必要的实验数据和理论参考依据。研究保温时间对10%TiC/Fe复合材料性能影响的结果表明：当保温时间少于200s时,材料烧结不充分,缺陷较多,材料的性能较低；保温时间为200s时,TiC颗粒与铁基体没有明显的界面反应,界面结合良好,材料的性能最高；随着保温时间的延长,TiC增强颗粒与铁基体发生剧烈的界面反应,并发生了不同程度的分解,产生了大量的枝条状石墨割裂了基体的连续性,导致性能降低。TiC/Fe和SiC/Fe复合材料均在保温时间为200s获得最佳性能,这验证了不同粒子增强铁基复合材料的最佳制备工艺是基本相同的,表明了电流直加热动态热压烧结工艺很好的稳定性和适应性。八种陶瓷颗粒对铁基复合材料力学性能影响的研究表明,SiC增强颗粒对改善铁基复合材料抗拉强度的作用最好,Cr3C2颗粒次之,TiC和Ti(C,N)颗粒的强化效果第三,A1203颗粒的增强效果最差。不同类型复合材料的显微组织观察表明,10%Ti(C,N)/Fe和10%TiC/Fe复合材料中,没有观察到增强粒子与基体界面处明显的界面反应,腐蚀后的基体显微组织为铁素体；而10%Cr3C2/Fe和10%SiC/Fe复合材料中,SiC和Cr3C2增强颗粒与基体有一定的界面反应,并且在基体中产生了一定数量的珠光体；而其它四种复合材料中,腐蚀后的基体显微组织为铁素体,并且粒子与基体的界面处存在一定孔洞、微裂纹等缺陷。研究得出的机理解释为：SiC和Cr2C3两种粒子与铁基体发生了一定的界面反应增加了界面结合力,有利于载荷传递增加复合材料强度,而且分解产生一定的珠光体又显著增加铁基体本身的强度,因此复合材料的强度提高很多,同时,SiC颗粒的断裂韧性比Cr2C3显著高而热膨胀系数低,具有最高的热导率,这些综合因素贡献的结果导致了SiC粒子具有最好的强化效果；另一方面,其他A1203等四种强化粒子不仅不具有产生珠光体提高基体本身强度的强化作用,而且由于粒子低的导电性和表面化学惰性使材料制备困难,产生界面显微缺陷导致复合材料的最终强度很低。SiC/Fe、TiC/Fe、Cr3C2/Fe和Ti(C,N)/Fe四种铁基复合材料磨损性能的研究结果显示：不同类型铁基复合材料均表现出很好的耐磨性能,磨损量均是经淬火+低温回火后的#45钢在对照磨损条件下的磨损量的15%以下；Ti(C,N)增强颗粒对改善铁基复合材料磨损性能的作用最强,SiC增强颗粒次之,TiC增强颗粒第三,Cr3C2虽然提高硬度和强度显著但改善耐磨性效果最差；颗粒增强铁基复合材料的耐磨性与材料硬度没有直接对应关系,与基体界面可经受一定变形量的强化粒子,例如Ti(C,N)对复合材料耐磨性的提高作用最显著。由本研究中混合增强铁基复合材料的初步实验结果得出：在含有Cr3C2颗粒的混合增强复合材料中,其它类型颗粒的加入促进Cr3C2颗粒更好地溶入铁基体,有效强化复合材料；而在含有SiC颗粒的混合增强复合材料中,其它粒子的加入加剧SiC与基体的界面反应,导致复合材料的性能不突出。增加混合粒子中SiC颗粒的粒度后,混合增强铁基复合材料的致密度、硬度、抗拉强度和耐磨性能均得到了提高,展现出良好的研究价值,但目前试验数量还没有实现性能的最优化。本文利用Eshelby等效夹杂力学模型模拟了不同类型铁基复合材料的应力-应变曲线,结果表明：10%SiC/Fe和10%Cr3C2/Fe复合材料应力-应变曲线的模拟结果明显低于实验结果,10%TiC/Fe和10%Ti(C,N)/Fe复合材料的模拟结果与实验结果吻合良好,而其它四种粒子增强复合材料的模拟结果均高于实验结果,因此本研究又进一步计算了不同颗粒类型增强铁基复合材料中基体的受力情况。模拟研究表明：TiC/Fe和Ti(C,N)/Fe复合材料的强化机理以增加粒子承担载荷的方式为主；而SiC/Fe和Cr3C2/Fe复合材料的增强机理除载荷传递外,还存在强化粒子显著提高铁基体本身强度的作用；而其它四种粒子增强复合材料中的陶瓷颗粒虽然通过传递载荷强化了复合材料,但其降低了基体本身的强度,所以最终复合材料的强度相对于纯铁基体的强度差别很小。模拟结果与试验结果的规律符合,对揭示材料强化机理和解释试验现象提供了理论支持。试验得出全部八种复合材料的屈服强度和抗拉强度均在颗粒体积分数为10%时达到最大值的重要结果,而模拟结果显示各种复合材料的屈服强度随着颗粒体积分数的增加呈现逐渐上升的趋势,结合显微组织观察,研究得出的机理解释是：当颗粒体积分数小时,增强颗粒较少,载荷传递的增强效果低,复合材料的强度低；增强颗粒体积分数为10%时,载荷传递增强效果增加,而增强颗粒仍然分布均匀,没有微观裂纹降低强度的有害作用,因此复合材料强度最好；增强颗粒的体积分数进一步提高到15%时,虽然载荷传递增强效果有所增加,但粒子团聚现象显著发生,局部微观裂纹的出现对强度的损害超过了增强的作用,因此复合材料的强度变低。更多还原

【Abstract】 Particulate reinforced iron matrix composite, which has high strength, high stiffness and high wear resistance properties, is one of the metal matrix composites with potential value of industrial applications. However, investigations in the literature have been focused on individual sole type of particle reinforced iron matrix composites respectively and the results have no comparability each other to evaluate different reinforcements due to the enormous difference on preparation technology and on materials microstructure. It is significant to conduct systematically an investigation with respect to preparation, properties and modeling of iron matrix composites reinforced by different types of ceramic particles.First, the improved specimen current heating dynamic hot press sintering technology was applied to study the effect of the holding time on properties of10%TiC/Fe composite to investigate whether the technology is equally applicable to the preparation of iron matrix composites reinforced by other types of reinforcing particles rather than SiC reinforcement. Then, tensile properties and wear performance of the iron matrix composites reinforced by different types of ceramic particles (Cr3C2、SiC、TiC、Ti(C,N)、Si3N4、TiB2、B4C and Al2O3) prepared by the same technology were studied experimentally as well as to examine the effect of different types of mixed particles and the influence of reinforcing content. Moreover, the mechanical properties of different types of composites were simulated by Eshelby equivalent inclusion mechanical model to reveal the strengthening mechanisms of different types of iron matrix composites in order to provide necessary experimental data and theoretical fundament for the development of particle reinforced iron matrix composite.The study on the influence of holding time on properties of10%TiC/Fe composites indicated that the sintering of the composite is insufficient with lots of defects in microstructure and the properties of the composites are low if the holding time is less than 200s. When the holding time is200s, it is shown that TiC particles have no reaction as well as good bond with the iron matrix by sufficient sintering, so the composite exhibited excellent properties. As the increase of holding time further, TiC particles would react with the iron matrix severely to produce graphite plates by TiC decomposing into iron matrix to disserve its continuity, and this results in a decrease in the properties of the composite. The properties of both TiC/Fe and SiC/Fe composites can achieve optimal when the holding time is200s, which implies that the best preparation parameters for the eight types of composites are same and the specimen current heating dynamic hot press sintering technology has good stability and flexibility.The investigation on the effect of eight types of ceramic particles on mechanical properties of iron matrix composites showed that SiC reinforcing particles present the strongest effect on improving strength experimentally, and Cr3C2reinforcing particles take the next best effect with the AI2O3reinforcing particles being the worst. It was seen by microstructure observations that the TiC and the Ti(C,N) particles have no reaction with the iron matrix to leave a pure Ferrite microstructure of the matrix, whereas the Cr3C2and the SiC particles took a slight reaction with iron to form some Pearlite in the matrix. The rest types of composites not only have pure Ferrite microstructure in the matrix but also have some micro-voids and micro-cracks at the interfaces between the reinforcing particles and the matrix. It is concluded that the slight reaction between Cr3C2or SiC reinforcing particles and the iron matrix increases the interfacial bonding, which is beneficial to raise the strength of composites as well as the reactive product, Pearlite, increases matrix strength to enhance the composites. The SiC has higher fracture toughness than the Cr3C2, as well as low coefficient of thermal expansion and highest thermal conductivity and those also help the SiC become the best reinforcing particles in the investigation. The TiC and the Ti(C,N) particles do not react with the matrix to produce Pearlite and do not result in micro defects in the matrix neither so that their strengthening effect is moderate. On the other hand, the other four types of reinforcing particles such as AI2O3not only didn’t increase matrix strength by producing Pearlite but also results in the interface micro defects due to their low electric conductivity and chemical inertness, which make them poor types as the reinforcing particles.The iron matrix composites reinforced by different types of ceramic particles (SiC, TiC, and Ti(C,N)) were selected to investigate the effects of reinforcing particles on wear behaviors. It is shown that the wear loss of all the iron matrix composites is less than15%of that of typical carbon tool steel. The Ti(C,N) particles presented the strongest effect on improving the wear resistance among the four types of investigated ceramic particles and the effect of the other reinforcing particle types on wear property falls a series of SiC, TiC and Cr3C2from high to low. It was surprisingly noticed that there is no clear relationship between the wear performance and hardness of the composites. The reinforcing particles such as Ti(C,N) particles which are endurable to a certain deformation on the interfaces can improve wear resistance more significantly.The preliminary results of the iron matrix composites reinforced by mixed types of ceramic particles showed that the addition of other types of ceramic particles helps Cr3C2particles be dissolved in the iron matrix to strengthen the composites. The addition of other types of particles results in intensive interface reaction between the SiC particles and the iron matrix to lower properties of the composite. The relative density, hardness, tensile strength and wear resistance of the mixture reinforced composites can be all improved if SiC particle size is increased. This is an interesting phenomenon and is worthwhile for a further research.The stress-strain curves of the different iron matrix composites were simulated by Eshelby equivalent inclusion mechanical model to reveal strengthening mechanisms. The results showed that the stress-strain curves by the modeling agree well with those of the experiments on TiC/Fe and Ti(C,N)/Fe composites, but the modeling results are much lower than the experiments on SiC/Fe and Cr3C2/Fe composites, and the modeling results are much higher than the experiment on the other composites. Further more, stress in matrix of the iron matrix composites reinforced by different types of particles has been calculated. The modeling results suggested that the strengthening mechanism in10%TiC/Fe and10%Ti(C,N)/Fe composites chiefly relies on load sharing of the reinforcements only, while the strengthening mechanisms in the SiC/Fe and Cr3C2/Fe composites rely not only on load sharing of the reinforcement but also on increasing matrix strength. The other composites are strengthened by load sharing of the reinforcement but the matrix strength is lowered due to micro defects so that the strength of the composites is almost the same as that of the iron matrix alloy. The modeling offers a good support to interpret the experiments. The tensile strength and yield strength of all the eight types of composites showed a maximum value at10%volume fraction of reinforcing particles experimentally whereas the yield strength should be increased continuously with the increase of the volume fraction by the modeling. The theoretical analysis and microstructure observations were carried out to suggest a good explanation for the experiments:When the reinforcement volume fraction is low, the effect of load sharing mechanism is insufficient and composite strength is low. When the reinforcement volume fraction achieves to10%, the strengthening of load sharing mechanism is increased meanwhile the reinforcements are still distributed homogeneously with no harmful effect on the strength. When the volume fraction is further increased up to15%for example, the reinforcement distribution is uneven with many clusters, which have weak bond with the matrix to contribute nothing in load sharing effect and break the continuity of the matrix to lower matrix strength because of the micro-cracks between the particles in the clusters, so that the composite strength is lower than that of the10%fraction composite.更多还原