Dislocation reactions at γ/γ′-interfaces during shear creep deformation in the macroscopic crystallographic shear system (001)[110] of CMSX6 superalloy single crystals at 1025°C

1998 ◽  
Vol 246 (1-2) ◽  
pp. 133-142 ◽  
Author(s):  
M. Kolbe ◽  
A. Dlouhy ◽  
G. Eggeler
Keyword(s):  
Single Crystals ◽  
Creep Deformation ◽  
Shear Creep ◽  
Crystallographic Shear ◽  
Shear System

scholarly journals How Nanoscale Dislocation Reactions Govern Low- Temperature and High-Stress Creep of Ni-Base Single Crystal Superalloys

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 134 ◽  
Author(s):  
David Bürger ◽  
Antonin Dlouhý ◽  
Kyosuke Yoshimi ◽  
Gunther Eggeler
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
High Stress ◽  
Shear Stresses ◽  
Creep Tests ◽  
Shear Creep ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Crystallographic Shear ◽  
Shear System

The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750 °C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [ 01 1 ¯ ] ( 111 ) and [ 11 2 ¯ ] ( 111 ) . These two shear systems share the same glide plane but differ in loading direction. The [ 11 2 ¯ ] ( 111 ) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [ 01 1 ¯ ] ( 111 ) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior.

Derivation of Polycrystal Creep Properties From the Creep Data of Single Crystals

1977 ◽  
Vol 44 (1) ◽  
pp. 73-78 ◽  
Author(s):  
T. H. Lin ◽  
C. L. Yu ◽  
G. J. Weng
Keyword(s):  
Single Crystals ◽  
Creep Deformation ◽  
Tensile Loading ◽  
Present Theory ◽  
Sole Source ◽  
Stress And Strain ◽  
Creep Data ◽  
Stress Strain ◽  
Macroscopic Stress ◽  
Additional Constant

A method developed for calculating the polycrystal stress-strain-time relation from the creep data of single crystals is shown. Slip is considered to be the sole source of creep deformation. This method satisfies, throughout the aggregate, both the condition of equilibrium and that of continuity of displacement as well as the creep characteristics of single crystals. A very large three-dimensional region is assumed to be filled with innumerable identical cubic blocks, each of which consists of 64 cube-shaped crystals of different orientations. This region is assumed to be embedded in an infinite elastic isotropic medium. This infinite medium is subject to a uniform loading. The average stress and strain of a cubic block at the center of the region is taken to represent the macroscopic stress and strain of the polycrystal. This method is self-consistent and considers the heterogeneous interaction effect of the creep deformation of all slid crystals. The macroscopic stress-strain-time relations of the polycrystal were calculated for three tensile loadings, one radial loading, and two nonradial loadings of combined tension and torsion. The numerical results given by the present theory agree well with those predicted by the so-called “Mechanical Equation of State.” The creep strain components calculated by the present theory for the case of a constant tensile loading followed by an additional constant tensile loading are found to be considerably higher than those predicted by von Mises and Tresca’s theories. These results agree well qualitatively with experimental results.

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