低成本细晶粒Mo2FeB2基金属陶瓷的制备及晶粒长大抑制机制研究

Mo2FeB2-based cermets by reaction boronizing sintering does not cotain the strategic Co and costly compounds of WC. In addtion, the mechanical properties compare favourably with the conventional WC-based hardmetals. Hence, Mo2FeB2-based cermets is a promising candidate for wear resistant applications. In this study, fined grain Mo2FeB2-based cermets was prepared by mechanical alloying and the two-step sintering with a low-cost raw material of MoFe, Fe and FeB powders. The phases variation during mechanical alloying was studied, and the effect of the powder particle size distribution, powder morphology, powder defect, formation of intermediate compound and the sintering process on the grain size distribution, microstructure, composition distribution and the mechanical properties were discussed. At the same time, we mainly investigated the evolutin of the solid skeleton and pore space, interface orientation relationship, evolution and influencing factors of microstructure during the two-step sintering. Based on these studies, the relationships between preparation technology, composition, microstructure and mechanical properties were established, and the mechanisms of grain refinement were obtained, which provided the theory foundation for the preparation of low-cost fined grain Mo2FeB2-based cermets with a better mechanical properties in a simple way.

反应硼化烧结的Mo2FeB2基金属陶瓷不含战略物质Co和贵重化合物WC且性能与常用硬质合金相当，因而作为工模具材料有着巨大的潜力和广阔的应用前景。本项目以廉价的FeB、FeMo、Fe粉等为原料，采用机械合金化的方法制备部分中间化合物，并用两步烧结法制备细晶粒Mo2FeB2基金属陶瓷。研究机械合金化过程中的物相变化规律；分析混合料的粉末粒度分布、粉末形貌、粉末缺陷、中间化合物的形成及主要烧结工艺参数对最终烧结体晶粒尺寸分布、显微组织、成分分布和力学性能的影响规律；重点研究两步法烧结过程中Mo2FeB2基金属陶瓷的固相骨架及孔隙的演变规律，细晶粒之间及大颗粒内部的界面取向特性，显微组织变化规律及影响因素；最终建立材料的成分、制备工艺、显微组织、界面微结构及性能的关系，并得到颗粒细化的机制。为在简单工艺条件下，制备结构合理、组织均匀、强韧性优良的细晶粒Mo2FeB2基金属陶瓷打下理论基础。

本项目提出了采用两步法烧结制备高性能的细晶粒Mo2FeB2基金属陶瓷的思想。首先探索了机械合金化过程中的物理和化学变化规律；研究了粉末在加热过程中的相变及显微组织演变规律；重点研究了两步烧结法中显微组织和孔隙的变化规律及温度T1、T2和保温时间t1和t2对金属陶瓷组织和性能的影响，发现当T1=1180℃、T2=1040℃、t1=20min、t2=20h时，金属陶瓷的组织明显细化，其抗弯强度从1909.1Mpa提高到2215.7Mpa，硬度从HRA90提高到HRA91；在高温液相烧结过程中，颗粒发生异常长大，二维形核机制是部分硬质相颗粒发生异常长大的主要原因。热等静压促进了硬质相颗粒的生长，当热等静压处理温度为1035℃时，金属陶瓷硬质相颗粒主要以颗粒合并的方式进行生长，当热等静压处理温度为1130℃时，溶解析出机制促进了颗粒的生长；系统研究了晶粒尺寸、粘结相含量、粘结相相组成对金属陶瓷断裂韧性的影响规律，发现粘结相的相组成对Mo2FeB2基金属陶瓷的断裂韧性有更加显著的影响，当粘结相为铁素体时，金属陶瓷的断裂韧性从14.2MPa·m1/2增加为28.5 MPa·m1/2，其增韧机制为硬质相颗粒与粘结相的沿晶断裂和粘结相的撕裂。另外运用固体与分子经验电子理论和第一性原理，研究了Mn添加剂对金属陶瓷力学性能的影响，结果表明Mn添加剂提高了硬质相的塑形和延展性，有利于金属陶瓷抗弯强度的增加，在此基础上提出了用固体与分子经验电子理论和第一性原理来指导金属陶瓷成分设计的构想。