Abstract This study analyzes the influence of Cr content on hardness H, elastic modulus E and fracture toughness KIC of the M2B boride by means of nanoindentation experiments. Additionally, properties of the Fe3(C,B) phase are determined. Samples of the M2B phase are casted and microstructurally characterized by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. At a Cr content higher than 14.7 atom% the M2B phase transforms from tetragonal into orthorhombic structure. The tetragonal M2B type possesses an optimum of H (21 ± 1 GPa), E (373 ± 6) GPa and KIC (3.5 ± 0.7 MPa m ) at 4–5 atom% Cr. The hardness, modulus and toughness of the orthorhombic M2B phase increase with Cr content and reach values of H = 27 ± 0.7 GPa, E = 473 ± 9 of and KIC = 3.26 ± 0.8 MPa m at maximal investigated Cr content of 55 atom%. The hardness of the M2B phases decreases around 2.3–3.2 GPa as a function of indentation depth, which is known as the indentation size effect. Hardness and fracture toughness of M2B phase outperform conventionally used M7C3 carbides and are similar to MC-carbides. Findings can be used in novel alloying approaches in order to optimize the performance and reduce cost of tool steels.

中文翻译：

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添加 Cr 提高四方晶系 (Fe,Cr) 2 B 和正交晶系 (Cr,Fe) 2 B 相的硬度、模量和断裂韧性

摘要 本研究通过纳米压痕实验分析了Cr含量对M2B硼化物硬度H、弹性模量E和断裂韧性KIC的影响。此外，还确定了 Fe3(C,B) 相的特性。M2B 相的样品被浇铸并通过扫描电子显微镜、能量色散光谱和 X 射线衍射进行微观结构表征。在 Cr 含量高于 14.7 原子% 时，M2B 相从四方结构转变为正交结构。四方 M2B 型在 4-5 原子% Cr 下具有最佳的 H (21 ± 1 GPa)、E (373 ± 6) GPa 和 KIC (3.5 ± 0.7 MPa m )。正交 M2B 相的硬度、模量和韧性随着 Cr 含量的增加而增加，并在最大研究的 Cr 含量为 55 原子％时达到 H = 27 ± 0.7 GPa、E = 473 ± 9 和 KIC = 3.26 ± 0.8 MPa m。作为压痕深度的函数，M2B 相的硬度在 2.3-3.2 GPa 左右下降，这被称为压痕尺寸效应。M2B 相的硬度和断裂韧性优于常规使用的 M7C3 碳化物，并且与 MC 碳化物相似。研究结果可用于新型合金化方法，以优化工具钢的性能并降低成本。