THE DEFORMATION OF NIOBIUM SINGLE CRYSTALS

1967 ◽  
Vol 45 (2) ◽  
pp. 607-629 ◽  
Author(s):  
R. A. Foxall ◽  
M. S. Duesbery ◽  
P. B. Hirsch
Keyword(s):  
Shear Stress ◽  
Single Crystals ◽  
High Vacuum ◽  
Three Dimensional ◽  
Orientation Dependence ◽  
Ultra High Vacuum ◽  
Text Type ◽  
Dislocation Arrays ◽  
Critical Resolved Shear Stress ◽  
Twist Boundaries

Various orientations of single crystals of niobium, purified by ultra-high vacuum annealing, have been tested in compression at 295 °K and in tension at temperatures between 77 °K and 295 °K. The shear stress – shear strain curves show three-stage hardening in a manner similar to f.c.c. crystals. Analysis of the orientation dependence of the operative slip system suggests an asymmetry in the critical resolved shear stress for slip on {112} planes which increases with decreasing temperature. Explanations for this in terms of the various ways in which a [Formula: see text] type screw dislocation can dissociate have been proposed. It is found that dissociation on two {112} planes or composite dissociation on {110} and {112} planes leads to a satisfactory qualitative explanation of the experimental results.The dislocation distribution occurring as a function of strain has been studied for crystals of a single glide orientation deformed in tension at 295 °K. [Formula: see text] sections from crystals deformed into stage I contain clusters of primary edge dipoles. The density of secondary dislocations is low (~10%). Sections from crystals deformed into stage II were chosen such that the three-dimensional nature of the dislocation arrays could be investigated. The distribution shows strong similarities to those observed in copper crystals (Steeds 1966), i.e. edge multipole walls, tilt and twist boundaries. The density of secondary dislocations is high, being of the same order as the primary density.

Plastic Deformation of Ni3Nb Single Crystals

1998 ◽  
Vol 552 ◽  
Author(s):  
Kouji Hagihara ◽  
Takayoshi Nakano ◽  
Yukichi Umakoshi
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Single Crystals ◽  
Crystal Orientation ◽  
Strengthening Mechanism ◽  
Orientation Dependence ◽  
Slip Model ◽  
Compression Tests ◽  
Increasing Temperature ◽  
Critical Resolved Shear Stress

ABSTRACTTemperature dependence of yield stress and operative slip system in Ni3Nb single crystals with the DOa structure was investigated in comparison with that in an analogous L12 structure. Compression tests were performed at temperatures between 20 °C and 1200 °C for specimens with loading axes perpendicular to (110), (331) and (270).(010)[100] slip was operative for three orientations, while (010)[001] slip for (331) and {211} <10 7 13> twin for (270) orientations were observed, depending on deformation temperature. The critical resolved shear stress (CRSS) for the (010)[100] slip anomaly increased with increasing temperature showing a maximum peak between 400 °C and 800 °C depending on crystal orientation. The CRSS showed orientation dependence and no significant strain rate dependence in the temperature range for anomalous strengthening. The [100] dislocations with a screw character were aligned on the straight when the anomalous strengthening occurred. The anomalous strengthening mechanism for (010)[100] slip in Ni3Nb single crystals is discussed on the basis of a cross slip model which has been widely accepted for some L12-type compounds.

scholarly journals The orientation dependence of the strength of ice single crystals

2000 ◽  
Vol 46 (152) ◽  
pp. 41-44 ◽  
Author(s):  
Y. L. Trickett ◽  
I. Baker ◽  
P. M. S. Pradhan
Keyword(s):  
Strain Rate ◽  
Single Crystals ◽  
Axial Strain ◽  
Constant Strain Rate ◽  
Peak Stress ◽  
Deformation Mode ◽  
Orientation Dependence ◽  
Compression Tests ◽  
Ice Flow ◽  
Critical Resolved Shear Stress

AbstractSingle crystals with a wide variety of orientations were cut from large pucks of laboratory-grown ice. Constant-strain-rate compression tests were performed on the crystals either at an axial strain rate of 1 × 10−5 s−1at –20°C or at axial strain rates from 1 × 10−6 s−1 to 1 × 10−4 s−1 at –10°C. In agreement with previous studies of ice flow, the compression tests showed a linearly rising stress with increasing strain, followed by a sharply declining stress after reaching a peak. With further strain, the sharp decline in stress slowed and the flow stress approached a plateau that was only weakly dependent on strain. For all crystallographic orientations, it was found that Schmid’s (critical resolved shear stress) law was obeyed by the peak stress. Slip lines clearly showed that basal slip was the deformation mode.

Plastic Deformations in L10-Ordered Single Crystals with their c/a Ratios Less than Unity

2007 ◽  
Vol 561-565 ◽  
pp. 459-462
Author(s):  
Katsushi Tanaka ◽  
Hiromitsu Ide ◽  
Yoshinori Sumi ◽  
Kyosuke Kishida ◽  
Haruyuki Inui
Keyword(s):  
Shear Stress ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Room Temperature ◽  
The Other ◽  
Compressive Deformation ◽  
Positive Temperature ◽  
Plastic Deformations ◽  
Temperature Range ◽  
Critical Resolved Shear Stress

Compressive deformation of L10-ordered single crystals of FePd whose c/a ratio less than unity have been investigated from room temperature to 823 K. The results show that the critical resolved shear stress (CRSS) for octahedral glide of ordinary dislocations is smaller than that of super-lattice dislocations in all the temperature range investigated, that is the opposite sense to the case of Ti-56 mol% Al. The CRSS for ordinary dislocations virtually independent to the temperature. On the other hand, the CRSS for super dislocations exhibits a weak positive temperature dependence from room temperature up to 573 K and decreases in higher temperatures.

Room Temperature Deformation in “Soft” Orientation Nial Single Crystals

1990 ◽  
Vol 213 ◽  
Author(s):  
R.D. Field ◽  
D.F. Lahrman ◽  
R. Darolia
Keyword(s):  
Shear Stress ◽  
Elevated Temperature ◽  
Single Crystals ◽  
Room Temperature ◽  
Dislocation Motion ◽  
Temperature Deformation ◽  
Slip Planes ◽  
Schmid Factor ◽  
Critical Resolved Shear Stress ◽  
Active Slip

ABSTRACTA detailed study of deformation of NiAl single crystals in two soft orientations, <110> and <111>, has been conducted. The Schmid factor favors {100} slip in the former and {110} slip in the latter. Detailed dislocation analysis, critical resolved shear stress measurements, and slip trace analysis have been performed to determine the nature of dislocation motion and interactions in this material. Particular attention is given to prismatic loops formed during deformation, since the shapes of these loops reveal the active slip planes. Similar loop morphologies observed in elevated temperature [001] oriented tensile specimens are also discussed.

Accommodation of constrained deformation in f. c. c. metals by slip and twinning

1969 ◽  
Vol 309 (1499) ◽  
pp. 433-456 ◽  
Keyword(s):  
Shear Stress ◽  
Single Crystals ◽  
Plane Strain ◽  
Plane Strain Compression ◽  
Orientation Factor ◽  
Cubic Crystals ◽  
Constrained Deformation ◽  
Critical Resolved Shear Stress ◽  
Good Agreement ◽  
External Strain

The problem of accommodation of constrained deformation by slip and twinning has been analysed. The analysis is based on Taylor’s least work hypothesis. In this analysis, the operative combination of slip and twinning systems is found by minimizing the orientation factor M = (∑ i s i +α∑ i t i )/ ε , where s i and t i are the simple shears resulting from slip and twinning respectively, α is the ratio of the critical resolved shear stress for twinning against slip, and Ɛ is the external strain. Detailed calculations have been made for face-centred cubic crystals deformed by plane strain compression. Experimental observations on deformed single crystals of a Co–8% Fe alloy indicate good agreement with the analysis. Implications of the present study to the twinning observations of Heye & Wassermann on rolled Ag crystals are discussed.

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