铸造铁硼耐磨合金中Fe2B原子掺杂韧化及其抗磨料损伤行为

Hard phase is an important constituent phase in the wear resistant cast alloy。Besides high hardness,the enough toughness of hard phase is also the foundation of the wear resistant alloy with an excellent superior wear resistance.It has significance in science and practical use for further improving the wear resistance of the alloy to investigate an improvement of hard phase's toughness and its effect on the behavior change of anti-abrasive damage behavior of Fe2B before and after toughening. This project proclaimed the essential reason of hard phase's brittleness based on prophase theoretical calculations, and taking higher brittle Fe2B hard phase in Fe-B cast alloy as the object of study, the academic thoughts of toughening Fe2B by adoping atom to improve the wear resistance of the alloy was determined. The main research contents were determined as follows: The effect of adoping atom on the solidification process and phase compositions of Fe-B alloy and its distribution state would be investigated; the variation characteristics of crystal lattice parameters of Fe2B and the toughness and other mechanical properties of different oriented Fe2B would be investigated and based on the theoretical calculations the the toughening mechanism of Fe2B would be studied;on the basis of the improvement of the toughness of Fe2B, the fundamental cause of the change of the anti-abrasive damage behavior of Fe-B cast alloy would be investigated, and the synergistic action mechanism of Fe2B and matrix on the wear of Fe-B alloy would be further revealed; at the same time the contribution degree of toughening Fe2B to improving the wear resistance of Fe-B alloy would be clarified. It has significant reference value to investigate the project for toughening hard phases in other casting alloys.

硬质相是铸造耐磨合金中的重要组成相，除需保证高硬度外其具有足够韧性也是合金具有良好耐磨性的基础。研究耐磨合金中硬质相韧性改善及对其抗磨料损伤行为变化的影响，对于进一步提高合金耐磨性具有重要的科学意义和实用价值。本项目基于前期理论计算所揭示的硬质相产生脆性的本质原因，以铸造铁硼合金组织中脆性较大的硬质相Fe2B为研究对象，确定通过原子掺杂技术改善Fe2B韧性进而提高合金耐磨性的学术思想。主要研究内容为：掺杂原子对铁硼合金凝固过程和组相构成的影响及其平衡分配特征；掺杂前后Fe2B的晶格参数、不同取向Fe2B韧性及其它力学性能的变化特征，并基于理论计算研究原子掺杂韧化机制；基于 Fe2B的韧性改善,研究铁硼合金抗磨料损伤行为变化的根本原因，进一步揭示硬质相与基体对合金抵抗磨损的协同作用机制，阐明Fe2B韧化对合金耐磨性改善的贡献程度。通过该项目的研究对其它耐磨合金硬质相韧化具有重要的参考价值。

铁硼合金是一种新型的金属耐磨材料，与传统的铁碳合金相比，铁硼合金中硬质相Fe2B的硬度更高，且硼化物的体积分数和金属基体中的碳含量可以独立控制，兼顾合金的硬度和韧性。因此，铁硼合金应用研究具有重大工程价值。然而，铁硼合金中硼化物韧性较差，在磨损过程中，容易发生断裂和破碎，极大地降低了材料的耐磨性，因此改善铁硼合金中Fe2B韧性是当前的首要问题。.本课题通过向Fe-3.0 wt% B合金中添加一系列的Cr元素，研究了Fe-3.0 wt% B合金中Fe2B以及合金的组织结构、力学性能以及耐磨性能的变化规律，并利用理论计算和实验表征手段解释了Cr元素掺杂后的作用机理，得到以下主要结果：.1）当Cr添加量在0-2.5 wt%时，Fe-3.0 wt% B合金的组织变化不明显。Cr添加后，容易富集在硼化物晶粒内，且随Cr含量增加，马氏体和硼化物中Cr浓度均呈线性增长。随着Cr含量不断增加，铸态铁硼合金的硬度逐渐升高，热处理态合金以及硼化物的硬度变化不明显；铁硼合金和硼化物的断裂韧性均先升高后降低，在Cr含量为2.0 wt% 处分别取得最大值4.704 MPa∙m1/2和30.4 MPa∙m1/2。.2）第一性原理计算和HRTEM分析结果表明，Cr原子添加后，硼化物中沿[002]方向的B-B共价键键长缩短，成键电子密度增大，化学键强度增大，硼化物的断裂韧性提高；当Cr含量为2.5 wt%时，由于硼化物晶粒内部晶格畸变累积而形成缺陷，导致断裂韧性反而降低。.3）随着Cr含量的增加，Fe-3.0 wt% B合金中两体和三体磨料磨损失重均先降低后升高，2Cr试样的磨损失重最小，与硼化物断裂韧性变化规律一致。在两体磨损过程中，硼化物起到抵抗磨料切削作用，对两相交互作用（负值）起到决定性作用；硼化物断裂韧性提高明显降低了断裂和破碎现象，从而提高合金耐磨性。三体磨损过程中，合金主要损失机制为短程切削和疲劳剥落，且磨料颗粒对试样表面产生强冲击作用，磨损表面及亚表层中硼化物破碎严重；破碎的硼化物难以发挥其硬质相作用，对合金三体磨损耐磨性反而不利；随着硼化物韧性不断提高，铁硼合金三体磨损耐磨性提高明显。.本课题通过Cr掺杂有效改善了硼化物断裂韧性，提高了铁硼合金磨料磨损耐磨性，并解释了硼化物的韧化机理，为铁硼合金的改良开发和工程应用奠定了基础。