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Enhancement of hardness, modulus and fracture toughness of the tetragonal (Fe,Cr)2B and orthorhombic (Cr,Fe)2B phases with addition of Cr.

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Title: Enhancement of hardness, modulus and fracture toughness of the tetragonal (Fe,Cr)2B and orthorhombic (Cr,Fe)2B phases with addition of Cr.
Authors: Lentz, Jonathan1 Lentz@wtech.rub.de, Röttger, Arne1, Großwendt, Felix1, Theisen, Werner1
Source: Materials & Design. Oct2018, Vol. 156, p113-124. 12p.
Subjects: Hardness, Fracture toughness, Elastic modulus, Borides, Nanoindentation tests, Orthorhombic crystal system
Abstract: This study analyzes the influence of Cr content on hardness H, elastic modulus E and fracture toughness K IC of the M 2 B boride by means of nanoindentation experiments. Additionally, properties of the Fe 3 (C,B) phase are determined. Samples of the M 2 B 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 M 2 B phase transforms from tetragonal into orthorhombic structure. The tetragonal M 2 B type possesses an optimum of H (21 ± 1 GPa), E (373 ± 6) GPa and K IC (3.5 ± 0.7 MPa m ) at 4–5 atom% Cr. The hardness, modulus and toughness of the orthorhombic M 2 B phase increase with Cr content and reach values of H = 27 ± 0.7 GPa, E = 473 ± 9 of and K IC  = 3.26 ± 0.8 MPa m at maximal investigated Cr content of 55 atom%. The hardness of the M 2 B 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 M 2 B phase outperform conventionally used M 7 C 3 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. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:This study analyzes the influence of Cr content on hardness H, elastic modulus E and fracture toughness K IC of the M 2 B boride by means of nanoindentation experiments. Additionally, properties of the Fe 3 (C,B) phase are determined. Samples of the M 2 B 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 M 2 B phase transforms from tetragonal into orthorhombic structure. The tetragonal M 2 B type possesses an optimum of H (21 ± 1 GPa), E (373 ± 6) GPa and K IC (3.5 ± 0.7 MPa m ) at 4–5 atom% Cr. The hardness, modulus and toughness of the orthorhombic M 2 B phase increase with Cr content and reach values of H = 27 ± 0.7 GPa, E = 473 ± 9 of and K IC  = 3.26 ± 0.8 MPa m at maximal investigated Cr content of 55 atom%. The hardness of the M 2 B 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 M 2 B phase outperform conventionally used M 7 C 3 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. [ABSTRACT FROM AUTHOR]
ISSN:02641275
DOI:10.1016/j.matdes.2018.06.040