【作者】 宾仕博；

【导师】 邢书明；

【作者基本信息】 北京交通大学 ， 载运工具运用工程， 2014， 博士

【摘要】 为解决颗粒增强钢基复合材料制备过程中颗粒分布不均匀和界面结合弱化两大技术问题,本文提出了一种颗粒增强钢基复合材料制备新工艺——消失模液锻工艺。该工艺利用消失模(泡沫载体)携带增强颗粒,在载体消失过程实现增强颗粒的添加,利用钢液充型包裹捕捉作用实现增强颗粒均匀混入钢液,然后在压力作用下凝固成形,最终得到钢基体内部含有均匀分布的抗磨颗粒、组织细密、界面结合良好的颗粒增强复合材料。实验研究了增强颗粒均匀分布于钢基体的制备工艺条件。采用颗粒平均分散系数表征和评价增强颗粒在钢基体的分布状态,并通过图像分析软件和Matlab统计软件计算各工艺条件下的平均分散系数。平均分散系数越小,颗粒分布越均匀。以TiC增强ZG55SiMn为例,通过正交实验得到TiC颗粒均匀分布的最优工艺为：液锻比压80MPa、冷却速度24.5K.s"1、充型速度107.6mm.s-1、颗粒体积分数10%。在此工艺条件下成形TiC/ZG55SiMn复合车轮制件,通过室温拉伸实验、耐磨性能实验和硬度测试实验对复合材料进行性能测试。实验结果为：TiC/ZG55SiMn复合材料的抗拉强度为525-560MPa,与未经TiC颗粒增强的钢基体抗拉强度相比有所下降,但硬度达到HRC58.1,较未经TiC颗粒增强的提高了60%-70%；单位长度的磨损量为3.57×10-9Kg.m-1,仅为未经TiC颗粒增强的20%～25%；比模量为6.84MPa.m3.Kg-1,较未经TiC颗粒增强的提高了5%。研究了附带增强颗粒泡沫载体气化消失行为,建立了金属模腔加压充填条件下载体消失产生的气隙压力和气流速度的计算公式；研究了增强颗粒与钢液的作用行为,提出了增强颗粒进入钢液的条件、颗粒在钢液不团聚条件和颗粒最终被凝固界面捕获而均匀分布在钢基体的条件；研究了制备工艺参数对颗粒分布和界面结合的影响规律。研究了在TiC颗粒均匀分布最优的工艺参数条件下,不同的冷却速度(2K.s-1、6K.s-1、15.8K.s-1、24.5K.s-1)、不同的颗粒体积分数(2%、5%、10%、15%)和不同的液锻比压(40MPa、60MPa、80MPa、100MPa)对TiC颗粒分布的影响规律。采用光学显微镜(OM)和扫描电镜(SEM)观察TiC颗粒在钢基体中的分布情况。实验结果表明TiC颗粒易沿着充型方向发生团聚,后充满部位的TiC颗粒浓度比先充满的大。TiC颗粒随冷却速度增大分布越均匀；当颗粒体积分数小于10%时,TiC颗粒随颗粒体积分数增大分布越均匀,但当颗粒体积分数大于10%以后,TiC颗粒随颗粒体积分数增大而变得不均匀；随液锻比压增大TiC颗粒分布越均匀,当液锻比压大于100Mpa以后,随液锻比压变化TiC颗分布变化不明显。通过扫描电镜观察拉伸试样断口处和磨损实验试样表面TiC颗粒的剥落情况,研究不同液锻比压对界面结合的影响作用。实验结果表明在较低的液锻比压条件下,界面结合不好,界面附近存在微孔,TiC颗粒与钢基体脱离或被拔出,保持着圆整的颗粒状。说明,在较低的应力下裂纹即可沿着界面脱离方向扩展,最后连接在一起造成材料的脆性断裂。随着液锻比压的增大,界面结合良好,其断裂机制是TiC颗粒碎化,形成裂纹,然后沿着界面处扩展,最后引起界面撕裂。裂纹扩展过程需要在钢基体中产生大量的局部塑性变形并消耗大量的应变能,界面有足够的强度,复合材料可承受更大的外加载荷。通过电子显微探针(EPMA)和X射线衍射分析(XRD),研究Ni包覆TiC颗粒对界面的影响作用。实验结果表明,经8%Ni包覆的TiC颗粒与钢基体的界面区域主要物相为Fe3Ni2,界面影响区域厚度范围约为0.5-1.5μm,界面结合不是简单的机械镶嵌而是发生了一定化学反应的冶金结合。Ni的加入促进钢液合金元素向TiC颗粒相周围的扩散,增大TiC颗粒表面能,降低颗粒与钢熔体的润湿角,最终形成Fe-Fe3Ni2-TiC阶梯式连续界面,改善了界面润湿性和结合强度,性能得到改善。更多还原

【Abstract】 To resolve the two key technique issues of particle uneven distribution and weak interface bonding during the fabrication of particle reinforced steel matrix composites (PRSMCS), a novel technology named Lost Foam Liquid Forging(LFLF) was proposed in this paper. The technology makes particles getting into molten steel equably come true by the interaction of foam carrier with molten steel, then solidified under applied pressure, and finally obtains the PRSMCS with the uniform distribution of particle, compact structure and excellent interface bonding.This paper researched the preparation process of PRSMCS with uniform distribution of reinforced particle. Distribution of particle in steel matrix was characterized with the mean dispersion coefficient, which was gained by use of image analysis software and Matlab statistical software. The smaller of mean dispersion coefficient, the more equably distribution of particle in steel matrix. The orthogonal experiment for preparing composite of TiC/ZG55SiMn was carried out. When the specific pressure is at80MPa, cooling velocity at24.5K.s-1, filling velocity at107.6mm.s-1and TiC particle volume fraction at10%, the most uniform distribution of TiC particle in steel matrix was gained. Specimens were sampled from the composite of TiC/ZG55SiMn fabricated by the above optimal technical parameters, and to be subjected to tensile test, wear test and hardness test successively. The experimental results show that tensile strength of TiC/ZG55SiMn is525-560MPa, which is smaller than that of steel matrix without TiC particle reinforced; Hardness of TiC/ZG55SiMn is58.1HRC, which is improved by60%～70%compared with that without TiC particle reinforced; wearing capacity of unit length is3.57X1O-9Kg.m-1, which is only20%-25%of that without TiC particle reinforced; specific modulus is6.84MPa.m3.Kg-1, which is improved by5%compared with that without TiC particle reinforced.The gasification behaviors of foam carrier with particle-reinforcement was studied in LFLF, and the computational formula of airflow pressure and airflow velocity in metal cavity were established; The interaction behavior of particle with molten steel was studied, the conditions for particle getting into molten steel, distributing equably in molten steel, and being captured by solidification interface were discussed; In addition, the influence rules of technical parameters on particle distribution and interface bonding were also investigated. Effects of different cooling velocity(2K.s-1,6K.s-1,15.8K.s-1,24.5K.s-1), different particle volume fraction(2%,5%,10%,15%), and different specific pressure(40MPa,60MPa,80MPa,100MPa) on TiC particle distribution were analyzed in the case of the above optimal technical parameters for fabricating TiC/ZG55SiMn. Distribution of TiC particle in steel matrix was investigated by optical microscope(OM) and scanning electron microscope(SEM). The experimental results show that it’s easy to make TiC particle aggregation in the direction of mold filling of molten steel, and the concentration of TiC particle in the subsequent full of part is greater than that in the first full of part. TiC particle distributes more equably with the increase of cooling velocity; when particle volume fraction is lower than10%, TiC particle distributes more equably with the increase of particle volume fraction, but the situation is opposite when particle volume fraction exceeds10%. TiC particle distributes more equably with the increase of specific pressure, but the change trend is not obvious when specific pressure exceeds100Mpa.Effect of different specific pressure on interface bonding was analyzed by means of observing fracture morphology of tensile sample and surface appearance of wearing sample by SEM. The experimental results show that on the condition of low specific pressure, there are micro-pores on the interface, and TiC particles on the fracture which is separated or pulled out from steel matrix. It proves that the unbound region of interface leads to cracks, then grow up and hold together, which causes brittle fracture of composite, so the interface bonding is poor on the condition of low specific pressure. With the increase of specific pressure, cracks come from TiC particle fragmentation but not interface, and there are lots of strain energy will be consumed during the crack propagation process, which causes local plastic deformation in steel matrix. So it’s achievable for excellent interface bonding as specific pressure increases and composite can bear more applied load.Effect of TiC particle coated with8%Ni on interface bonding was analyzed by means of EPMA and XRD. The experimental results show that the main phase on the interface between TiC particle coated with8%Ni and steel matrix is Fe3Ni2, the combination of interface is not simply mechanical setting but metallurgical bonding with a certain of reactions. The addition of Ni accelerates diffusion of alloying element from steel matrix to TiC particle, increases the surface energy of TiC particle, reduces the wetting angle of TiC particle between steel matrix, and forms the continuous interface in the form of Fe-Fe3Ni2-TiC, so the wettability and bonding strength of interface were enhanced, and the mechanical performance was improved accordingly.更多还原