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

Title: Structural transformation and improved ductility in ordered FeCo and ZrCo intermetallics

Abstract

Using the first-principles calculations, we find that Fe-Co has a tendency for a structural transformation to a lower symmetry sheared L10 phase under the applied shear stresses. This tendency for structural transformation can have a significant influence on the mechanical properties of FeCo, as it might be closely connected with the intrinsic brittleness of Fe-rich and stoichiometric FeCo alloys and with the improved ductility of Co-rich FeCo alloys. We suggest that improved ductility in Co-rich FeCo alloys may originate from transformation toughening due to the B2-L10 structural transformation near the regions of high stress concentration, as the stress energy is fully dissipated by the decrease in the electronic energy due to the structural phase transformation into a lower energy structure. Similarly, in ZrCo, our first-principles calculations find that a B2-B33 martensitic phase transformation can occur under the applied shear stress, which may contribute to the good ductility of this alloy, despite the fact that ZrCo is a strongly ordered line compound.

Authors:
 [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931520
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 2006 MRS Fall Meeting, Boston, MA, USA, 20061127, 20061201
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COBALT ALLOYS; IRON ALLOYS; ZIRCONIUM ALLOYS; BRITTLENESS; DUCTILITY; PHASE TRANSFORMATIONS; STRESSES; INTERMETALLIC COMPOUNDS

Citation Formats

Krcmar, Maja, Fu, Chong Long, and Morris, James R. Structural transformation and improved ductility in ordered FeCo and ZrCo intermetallics. United States: N. p., 2007. Web.
Krcmar, Maja, Fu, Chong Long, & Morris, James R. Structural transformation and improved ductility in ordered FeCo and ZrCo intermetallics. United States.
Krcmar, Maja, Fu, Chong Long, and Morris, James R. Mon . "Structural transformation and improved ductility in ordered FeCo and ZrCo intermetallics". United States. doi:.
@article{osti_931520,
title = {Structural transformation and improved ductility in ordered FeCo and ZrCo intermetallics},
author = {Krcmar, Maja and Fu, Chong Long and Morris, James R},
abstractNote = {Using the first-principles calculations, we find that Fe-Co has a tendency for a structural transformation to a lower symmetry sheared L10 phase under the applied shear stresses. This tendency for structural transformation can have a significant influence on the mechanical properties of FeCo, as it might be closely connected with the intrinsic brittleness of Fe-rich and stoichiometric FeCo alloys and with the improved ductility of Co-rich FeCo alloys. We suggest that improved ductility in Co-rich FeCo alloys may originate from transformation toughening due to the B2-L10 structural transformation near the regions of high stress concentration, as the stress energy is fully dissipated by the decrease in the electronic energy due to the structural phase transformation into a lower energy structure. Similarly, in ZrCo, our first-principles calculations find that a B2-B33 martensitic phase transformation can occur under the applied shear stress, which may contribute to the good ductility of this alloy, despite the fact that ZrCo is a strongly ordered line compound.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • Intermetallics, which are ordered alloys, have excellent high temperature strength. Unfortunately a universal problem facing intermetallics is the lack of ductility. This program attempted to look at some novel solutions for enhancing ductility in intermetallics. Deformation twinning has been demonstrated in TiNi to be responsible for its ductility. This was a surprising result since twinning was not believed to occur readily in ordered alloys. Furthermore the twinning occurred on a (114) plane which had not been previously observed. Research into determining the mechanisms for twinning in ordered alloy and understanding how twinning enhances the ductility of intermetallic was studied. Martensiticmore » transformations in many intermetallics also provides a possible means of enhancing ductility. The detwinning of martensite twins or transformation induced martensite provides a mechanism for accommodating large strains. It is known that a metastable martensitic phase may be created by quenching a non-stoichiometric NiAl alloy. This presents the potential of substantial ductility in NiAl. Investigation of the martensitic phase transformation and its effect on the ductility of NiAl alloys was investigated.« less
  • Intermetallics, which are ordered alloys, have excellent high temperature strength. Unfortunately a universal problem facing intermetallics is the lack of ductility. This program attempted to look at some novel solutions for enhancing ductility in intermetallics. Deformation twinning has been demonstrated in TiNi to be responsible for its ductility. This was a surprising result since twinning was not believed to occur readily in ordered alloys. Furthermore the twinning occurred on a (114) plane which had not been previously observed. Research into determining the mechanisms for twinning in ordered alloy and understanding how twinning enhances the ductility of intermetallic was studied. Martensiticmore » transformations in many intermetallics also provides a possible means of enhancing ductility. The detwinning of martensite twins or transformation induced martensite provides a mechanism for accommodating large strains. It is known that a metastable martensitic phase may be created by quenching a non-stoichiometric NiAl alloy. This presents the potential of substantial ductility in NiAl. Investigation of the martensitic phase transformation and its effect on the ductility of NiAl alloys was investigated.« less
  • Employing ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the <111> slip on both {l_brace}110{r_brace} and {l_brace}112{r_brace} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stressesmore » near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.« less
  • Employing ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the <111> slip on both {l_brace}110{r_brace} and {l_brace}112{r_brace} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stressesmore » near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.« less
  • This paper provides a brief review of recent research on the effect of test environment on ductility and fracture in ordered intermetallics. A number of intermetallics including FeAl, Fe{sub 3}Al, Co{sub 3}Ti and Ni{sub 3}Al alloys show distinctly room- temperature lower ductilities when tested in air than in vacuum or controlled environments. The environmental embrittlement involves the reaction of water vapor in the air with reactive elements (such as aluminum) in the intermetallics and the resulting generation of atomic hydrogen that drives into the metals and promotes brittle fracture along grain boundaries or cleavage planes. It has been demonstrated that,more » in some alloy systems, the embrittlement can be alleviated or totally eliminated by alloying additions. The test environment can also affect the ductility of ordered intermetallics at elevated temperatures, but the embrittling mechanism and agent are quite different. The study of environmental effects has led to better understanding of brittle fracture and low ductilities, thereby providing a new direction for alloy design of ductile ordered intermetallics for structural use. 72 refs., 13 figs., 2 tabs.« less