Studying Plasticity in Hard and Soft Nb–Co Intermetallics

Abstract

It is shown that micropillar compression can be used to study the plastic flow behavior of both a hard, brittle cubic Laves phase, NbCo2, and a related monoclinic compound, Nb2Co7, which is known to be softer, but is also brittle and has, so far, only been prepared in a fine‐grained form. Flow in the Laves phase occurs at a shear stress of 3.1 GPa on the $\left\langle {0{\bar {1}}{\bar {1}}} \right\rangle ${111} slip system, consistent with previous observations and estimates from hardness measurement. Micropillar compression and electron microscopy of single crystals of Nb2Co7 indicates that flow takes place parallel to the (001) plane, with $\left\langle {100} \right\rangle $ and $\left\langle {110} \right\rangle $ type Burgers vectors, at a critical resolved shear stress between 0.1 and 0.5 GPa. It is shown that this is much less than predicted by hardness measurements, consistent with the idea that the hardness of plastically anisotropic materials is determined by flow on the hardest operating slip system.

On the structure of defects in the Fe7Mo6 μ-Phase

“…2.379 ± 0.004 Å (for the calculation of the error see below), which corresponds neither to the shift measured experimentally in this study (2.74 ± 0.01 Å) nor to values reported for Laves phases before [21,23,26,[28][29][30][31][32][33][34]. As this vector is not a full translational vector of the crystal, it would create a visible distortion of the shifted crystal, if a lower part of the crystal remains underneath the stacking fault (not shown).…”

“…Above 0.6 Tm, plastic deformation by dislocation slip and to a lesser degree by mechanical twinning has been observed [22,25,29,37,38]. The twinning system is of {111}<112>-type [31] and dislocation slip is based on dislocation with a 1/2<110> Burgers vector in cubic or 1/3<11-20> in hexagonal notation on either (111) or {0001} planes, respectively [21]. Where plastic deformation was achieved at room temperature (RT) or below, it was accommodated mainly by {111}<112> twinning, e.g.…”

Microcompression of brittle and anisotropic crystals: recent advances and current challenges in studying plasticity in hard materials

“…4. [34] Only a few years after its first use, the microcompression technique was made even more powerful in unraveling deformation mechanisms by enabling experiments at elevated temperatures. [35,36] In nanoindentation, the related nanomechanical method based on the same equipment, publications are currently rising every year with respect to the development of high-temperature capability and the limit is being pushed toward 1000°C, reaching application temperatures of turbine materials.…”

“…Selection of hard crystals tested by microcompression. ZrB 2 , [87] Mo 2 BC, [85] WC, [21] Fe 3 Al, [88] Co 3 (Al,W), [89] CMSX-4, [36] Si, [31] GaAs, [2] InSb, [90] Al 2 O 3 (unpublished), MgO, [25] (Fe,Ni) 2 Nb, [30] (Mg, Al) 2 Ca (courtesy of C. Zehnder), Nb 2 Co, [34] AlN, [91] GaN, [92] doped ZrO 2, [93] LiF, [94] Al 7 Cu 2 Fe, [95] FeZn 13 , [96] Cu 6 Sn 5 , [24] either conventional or high resolution, is easily performed after compression by the site-specific FIB milling and where necessary further thinning of a transparent membrane from the micropillar (see Figs. 3, 4, 6, and 10, for examples).…”

Deformation at ambient and high temperature ofin situLaves phases-ferrite composites

“…This behavior may result from a size effect in the plastic behavior of the C14/36 FeZrCr Laves phases. Indeed, the impact of size reduction on the plastic behavior of some Laves phases has already been evidenced by nanoindentation of micropillars [24]. The main result of the present study is first to reveal the effect of lamella size on the mechanical behavior of the Fe–Zr–Cr Laves phase–ferrite composites.…”