Crystal structure and composition dependence of mechanical properties of single-crystalline NbCo2 Laves phase

Luo, Wei; Kirchlechner, Christoph; Zavašnik, Janez; Lu, Wenjun; Dehm, Gerhard; Stein, Frank

doi:10.1016/j.actamat.2019.11.036

Cited by 35 publications

(12 citation statements)

References 36 publications

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“…This implies reduction of the Peierls stress [384] as had already been suggested as explanation for the abovedescribed behavior of MgZn 2 [5]. Strength (by micropillar compression tests [364]) and toughness (by microcantilever bending tests [393]) of NbCo 2 were also studied as a function of composition using the same diffusion couples. The critical resolved shear stress behaves very similar to the hardness with highest values in the central region of the C15 homogeneity range and a decrease when approaching the off-stoichiometric boundaries, which is explained by the reduction of the shear modulus and [378], dislocation density d [378], and dislocation velocity v (399°C) [377] also exhibit extrema at the stoichiometric composition (adapted with permission from [5]).…”

Section: Plastic Deformationmentioning

confidence: 59%

“…stacking fault energy [364]. The microcantilever bending tests revealed a linear elastic fracture behavior for all compositions.…”

Section: Plastic Deformationmentioning

confidence: 85%

“…Successful direct observation of synchroshear-induced stacking faults in Laves phases by high-resolution scanning transmission electron microscopy (STEM) was reported for the first time by Chiswick et al [356]. Since then synchroshear-induced stacking faults in different deformed C14 and C15 Laves phases were observed by various authors [361][362][363][364]. Figure 19 shows a synchro-Shockley dislocation in C14 HfCr 2 Laves phase with the dislocation core in the center of the image as explained in the figure caption [356].…”

Section: Plastic Deformationmentioning

confidence: 93%

“…A chance to study plastic deformation of such brittle phases at room temperature came up with the establishment of micromechanical testing methods in materials science, see, for example, [370]. Micropillar compression tests of single-crystal cubic C15 and hexagonal C14 and C36 Laves phases revealed the occurrence of plastic deformation by basal and, in case of the hexagonal crystals, also nonbasal, prismatic and pyramidal slip [364,[371][372][373][374]. An example for a plastically deformed C14 NbCo 2 micropillar is shown in Fig.…”

Section: Plastic Deformationmentioning

confidence: 99%

“…In order to study in a systematic way the dependence of mechanical properties of single-crystalline Laves phases on composition, crystal orientation, and crystal structure, Luo et al [364,384,[392][393][394] focused on the binary system Co-Nb, in which the Laves phase NbCo 2 exists as stable phase with C36, C15, and C14 structure in adjacent phase fields (from approximately 24.0 to 25.0, 25.0 to 34.3, and 35.5 to 37.0 at.% Nb, respectively). By producing diffusion couples, they obtained several hundred lm thick layers of Laves phase covering the entire homogeneity ranges of the three polytypes.…”

Section: Plastic Deformationmentioning

confidence: 99%

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Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

2020

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Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function of the involved elements is often lacking. It is one of the two main goals of this review to summarize the knowledge for some selected respective topics with a certain focus on non-stoichiometric, i.e., non-ideal Laves phases. The second, central goal of the review is to give a systematic overview about the role of Laves phases in all kinds of materials for functional and structural applications. There is a surprisingly broad range of successful utilization of Laves phases in functional applications comprising Laves phases as hydrogen storage material (Hydraloy), as magneto-mechanical sensors and actuators (Terfenol), or for wear- and corrosion-resistant coatings in corrosive atmospheres and at high temperatures (Tribaloy), to name but a few. Regarding structural applications, there is a renewed interest in using Laves phases for creep-strengthening of high-temperature steels and new respective alloy design concepts were developed and successfully tested. Apart from steels, Laves phases also occur in various other kinds of structural materials sometimes effectively improving properties, but often also acting in a detrimental way.

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Section: Plastic Deformationmentioning

confidence: 59%

“…stacking fault energy [364]. The microcantilever bending tests revealed a linear elastic fracture behavior for all compositions.…”

Section: Plastic Deformationmentioning

confidence: 85%

Section: Plastic Deformationmentioning

confidence: 93%

Section: Plastic Deformationmentioning

confidence: 99%

Section: Plastic Deformationmentioning

confidence: 99%

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Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

2020

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Determination of the Rate Dependence of Damage Formation in Metallic‐Intermetallic Mg–Al–Ca Composites at Elevated Temperature using Panoramic Image Analysis

Medghalchi,

Zubair,

Karimi

et al. 2023

Adv Eng Mater

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We study a cast Mg‐4.65Al‐2.82Ca alloy with a microstructure containing an α‐Mg matrix, reinforced with a C36 Laves phase skeleton. Such ternary alloys are targeted for elevated temperature applications in automotive engines, since they possess excellent creep properties. However, in application, the alloy may be subjected to a wide range of strain rates, and thus accelerated testing is often essential. It is, therefore, crucial to understand the effect of such rate variations. Here, we focus on their impact on damage formation. Our analysis is based on high resolution panoramic imaging using scanning electron microscopy, combined with automated damage analysis using deep learning for object detection and classification (YOLOv5). We find, that with decreasing strain rate the dominant damage mechanism for a given strain level changes: at a strain rate of 5•10‐4/s, the evolution of microcracks in the C36 Laves phase dominates damage formation. However, when the strain rate is decreased to 5•10‐6/s, interface decohesion at the α‐Mg/Laves phase interfaces becomes equally important. We also observe a change in crack orientation, indicating an increasing influence of plastic co‐deformation of the α‐Mg matrix and Laves phase. We attribute this transition in the leading damage mechanism to thermally activated processes at the interface.This article is protected by copyright. All rights reserved.

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Tailoring the Plasticity of Topologically Close‐Packed Phases via the Crystals’ Fundamental Building Blocks

et al. 2023

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Brittle topologically close‐packed precipitates form in many advanced alloys. Due to their complex structures, little is known about their plasticity. Here, a strategy is presented to understand and tailor the deformability of these complex phases by considering the Nb–Co µ‐phase as an archetypal material. The plasticity of the Nb–Co µ‐phase is controlled by the Laves phase building block that forms parts of its unit cell. It is found that between the bulk C15–NbCo2 Laves and Nb–Co µ‐phases, the interplanar spacing and local stiffness of the Laves phase building block change, leading to a strong reduction in hardness and stiffness, as well as a transition from synchroshear to crystallographic slip. Furthermore, as the composition changes from Nb6Co7 to Nb7Co6, the Co atoms in the triple layer are substituted such that the triple layer of the Laves phase building block becomes a slab of pure Nb, resulting in inhomogeneous changes in elasticity and a transition from crystallographic slip to a glide‐and‐shuffle mechanism. These findings open opportunities to purposefully tailor the plasticity of these topologically close‐packed phases in the bulk by manipulating the interplanar spacing and local shear modulus of the fundamental crystal building blocks at the atomic scale.

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Crystal structure and composition dependence of mechanical properties of single-crystalline NbCo2 Laves phase

Cited by 35 publications

References 36 publications

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

Determination of the Rate Dependence of Damage Formation in Metallic‐Intermetallic Mg–Al–Ca Composites at Elevated Temperature using Panoramic Image Analysis

Tailoring the Plasticity of Topologically Close‐Packed Phases via the Crystals’ Fundamental Building Blocks

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