skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The yield strength anomaly of single-slip-oriented Fe-Al single crystals

Abstract

Many features of the well-documented yield strength anomaly in B2-structured Fe-Al alloys have been successfully described or predicted by the vacancy-hardening model (George EP, Baker I. Philos Mag 1998;A77: 737). Interestingly, the model does not predict any orientation dependence for the yield anomaly. Here, we examine this by measuring the yield stress of three different single-slip-oriented Fe-43Al single crystals as a function of temperature. It was found that the critical resolved shear stress of all the alloys decreased rapidly with temperature from 77 K to {approx}300 K, showed a plateau from 300 K to 723 K, increased to a peak at 873 K, and then decreased again with further increase in temperature. While neither the low-temperature strength (<300 K) nor the temperature of the yield stress peak depended on the orientation (in agreement with the vacancy-hardening model), the yield stress in the plateau region around room temperature did.

Authors:
 [1];  [1];  [2];  [3]
  1. Dartmouth College
  2. University of New South Wales
  3. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931581
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Intermetallics; Journal Volume: 15; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALLOYS; MONOCRYSTALS; ORIENTATION; SHEAR; YIELD STRENGTH

Citation Formats

Wu, D., Baker, I., Munroe, P R, and George, Easo P. The yield strength anomaly of single-slip-oriented Fe-Al single crystals. United States: N. p., 2007. Web. doi:10.1016/j.intermet.2006.03.007.
Wu, D., Baker, I., Munroe, P R, & George, Easo P. The yield strength anomaly of single-slip-oriented Fe-Al single crystals. United States. doi:10.1016/j.intermet.2006.03.007.
Wu, D., Baker, I., Munroe, P R, and George, Easo P. Mon . "The yield strength anomaly of single-slip-oriented Fe-Al single crystals". United States. doi:10.1016/j.intermet.2006.03.007.
@article{osti_931581,
title = {The yield strength anomaly of single-slip-oriented Fe-Al single crystals},
author = {Wu, D. and Baker, I. and Munroe, P R and George, Easo P},
abstractNote = {Many features of the well-documented yield strength anomaly in B2-structured Fe-Al alloys have been successfully described or predicted by the vacancy-hardening model (George EP, Baker I. Philos Mag 1998;A77: 737). Interestingly, the model does not predict any orientation dependence for the yield anomaly. Here, we examine this by measuring the yield stress of three different single-slip-oriented Fe-43Al single crystals as a function of temperature. It was found that the critical resolved shear stress of all the alloys decreased rapidly with temperature from 77 K to {approx}300 K, showed a plateau from 300 K to 723 K, increased to a peak at 873 K, and then decreased again with further increase in temperature. While neither the low-temperature strength (<300 K) nor the temperature of the yield stress peak depended on the orientation (in agreement with the vacancy-hardening model), the yield stress in the plateau region around room temperature did.},
doi = {10.1016/j.intermet.2006.03.007},
journal = {Intermetallics},
number = 2,
volume = 15,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Single crystals of binary Ti[sub 3]Al and ternary Ti[sub 3]Al-V alloys with the D0[sub 19] structure were deformed in compression at 20-900 C. Slip systems of the (10[bar 1]0)< 1[bar 2]10 >-type and the (11[bar 2]1)< [bar 1][bar 1]26 >-type were observed in these alloys throughout the entire temperature range depending on orientation, but the (11[bar 2]1)< [bar 1][bar 1]26 >-slip was limited to orientations near [0001]. The basal (0001)< 1[bar 2]10 >-slip was also activated in quenched Ti[sub 3]Al. The CRSS for the (10[bar 1]0)< 1[bar 2]10 >-slip in the binary and ternary alloys decreases monotonically with increasing temperature.more » In the ternary alloy the CRSS for the (10[bar 1]0)< 1[bar 2]10 >-slip shows a violation of Schmid's law, while the binary alloy obeys the CRSS law. When Ti[sub 3]Al is deformed by (11[bar 2]1)< [bar 1][bar 1]26 >-slip the CRSS for the slip exhibits an anomalous peak in the temperature-CRSS curve but the addition of vanadium suppresses the extent of the anomalous strengthening.« less
  • The {bar 1}{bar 1}26{r{underscore}angle}(11{bar 2}1) pyramidal slip in Ti{sub 3}Al shows the so-called yield stress anomaly. A marked change in dislocation configuration is observed in the temperature range concerned; dislocations observed at the lowest temperature of the range, {minus}70 C, are ordinary pairs of edge c+a/2 superpartial dislocations coupled by antiphase boundaries (APBs) while at the other extreme temperature 700 C, pairs of unlike superpartials coupled by APBs are observed. The change in dislocation configurations is interpreted as resulting from immobilization of edge c+a/2 superpartial segments by climb dissociation onto the basal plane.
  • Cyclic deformation behavior of Cu-30% Zn single crystals oriented for single slip was studied at constant plastic shear strain amplitudes ({gamma}{sub pi}) in the range of 3.8 {times} 10{sup {minus}5}--6.4 {times} 10{sup {minus}3} in order to understand systematically the fundamental fatigue behavior of low stacking fault energy materials. Results indicate that the cyclic hardening behavior strongly depends on the strain amplitude applied. For low strain amplitudes ({gamma}{sub pi} < 3 {times} 10{sup {minus}4}), cyclic saturation occurred after an initial cyclic hardening stage, but for high strain amplitudes ({gamma}{sub pi} {ge} 6.0 {times} 10{sup {minus}4}) saturation could not be reached untilmore » fatigue failure. The initial cyclic hardening rate ({theta}{sub 0.2}) was found to decrease with increase in the applied strain amplitude. Slip bands were found to behave very similarly to Jueders band appearance at the beginning as well as in the middle stage of cyclic deformation. Particularly, the similarity of the cyclic hardening behavior at low and high strain amplitudes to the work hardening response in stages I and II of tensile deformation of the same alloy has been pointed out. Cyclic stress was further decomposed into two terms, the effective stress and the internal stress, and both were found to increase continuously with cyclic deformation. It has been demonstrated that the activities of secondary slips played an important role in the continuous cyclic hardening at high {gamma}{sub pi}. A comparison of the present result with previous relevant work on both wavy and planar slip materials has been attempted. The transition of wavy slip mode to planar slip mode of Cu-Al and Cu-Zn alloys has been discussed in terms of the electron-atom ratio and the critical value of the ratio for such a transition is found to be 1.18--1.19 for both alloys.« less
  • The dislocation structures of Cu-30% Zn single crystals cyclically deformed at {gamma}{sub pi} = 3.8 {times} 10{sup {minus}5}--6.4 {times} 10{sup {minus}3} were studied through transmission electron microscopy in order to understand the cyclic deformation mechanisms of the material. It has been shown that the fatigue dislocation structures have two basic configurations depending on the strain amplitude applied. At low strain amplitudes ({gamma}{sub pi} < 3 {times} 10{sup {minus}4}), the dislocation structure is characterized by dislocation segments and multipoles, very similar to that formed in stage 1 of tensile deformation in the same material. At high strain amplitudes ({gamma}{sub pi} >more » 3.0 {times} 10{sup {minus}4}), however, the dislocation structure is dominated by planar dislocation loops and tangles, in this case a small amount of dislocation multipoles and a special zigzagged structure are also detected. Secondary slips were found to be activated from a very low strain amplitude ({gamma}{sub pi} = 3.8 {times} 10{sup {minus}5}). This behavior is attributed to (1) the lower stress for dislocation generation compared with cyclic flow stresses and (2) heterogeneous deformation at low strain amplitudes that results in a weak effect of local latent hardening. Cyclic deformation mechanisms at low and high strain amplitudes have been discussed in terms of the motion of dislocation multipoles and the dislocation reactions between the primary and secondary slip systems. The critical strain amplitude for the transition of the deformation mechanisms has been also theoretically determined to be 3 {times} 10{sup {minus}4}, in good agreement with results on the cyclic deformation response and the features of dislocation structures. The formation of specific dislocation structures such as the zigzagged structure has been discussed with detailed dislocation mechanisms.« less
  • The authors have successfully produced a single crystal of austenitic stainless steel which is a typical single-phase structural material. In the present study, the austenitic stainless steel single crystals oriented for single slip were cyclically deformed in order to investigate both the change in the hysteresis loop shape and the cyclic hardening behavior. The prediction of fatigue crack initiation is discussed from the view point of the change in {beta}{sub E} value.