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Title: Microstructural evolution of single Ni 2TiAl or hierarchical NiAl/Ni 2 TiAl precipitates in Fe-Ni-Al-Cr-Ti ferritic alloys during thermal treatment for elevated-temperature applications

Abstract

Precipitate features, such as the size, morphology, and distribution, are important parameters determining the mechanical properties of semi- or fully-coherent precipitatehardened alloys at elevated temperatures. In this study, the microstructural formation and evolution of recently-developed Fe-Ni-Al-Cr-Ti alloys with superior creep resistance have been systematically investigated using transmission-electron microscopy (TEM), scanning-electron microscopy (SEM), and atom-probe tomography (APT). These alloys were designed by adding 2 or 4 weight percent (wt. %) Ti into a NiAl-hardened ferritic alloy with a nominal composition of Fe-6.5Al-10Cr-10Ni-3.4Mo-0.25Zr-0.005B in wt. %. These alloys were, then, subjected to a homogenization treatment at 1,473 K for 0.5 hour, followed by aging treatments at 973 K for 1 ~ 500 hours. In the homogenization-treated case, both alloys contain a primary L21-type Ni 2TiAl precipitate, but with the distinct size and morphology of the precipitates and precipitate/matrix interface structures. In the subsequent aging treatments, the 2 wt. % Ti alloy establishes a hierarchical-precipitate structure consisting of a fine network of a B2-type NiAl phase within the parent L2 1-type Ni2TiAl precipitate, while the 4 wt. % Ti alloy retains the single Ni 2TiAl precipitate. It was found that the hierarchical structure is more effective in remaining the coherent interface during themore » growth/coarsening of the precipitate. The formation of the different types of the precipitates, and their effects on the microstructural evolution are discussed, and the driving forces for these features are identified from the competition between the interface energy and elastic interactions due to the lattice misfit and misfit dislocations.« less

Authors:
 [1];  [1];  [2]; ORCiD logo [3];  [1]
  1. Univ. of Tennessee, Knoxville, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1394435
Alternate Identifier(s):
OSTI ID: 1397790
Grant/Contract Number:
AC05-00OR22725; 09NT0008089; FE0005868; FE-0011194
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 127; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Song, Gian, Sun, Zhiqian, Poplawsky, Jonathan D., Gao, Yanfei, and Liaw, Peter K.. Microstructural evolution of single Ni2TiAl or hierarchical NiAl/Ni2 TiAl precipitates in Fe-Ni-Al-Cr-Ti ferritic alloys during thermal treatment for elevated-temperature applications. United States: N. p., 2017. Web. doi:10.1016/j.actamat.2017.01.011.
Song, Gian, Sun, Zhiqian, Poplawsky, Jonathan D., Gao, Yanfei, & Liaw, Peter K.. Microstructural evolution of single Ni2TiAl or hierarchical NiAl/Ni2 TiAl precipitates in Fe-Ni-Al-Cr-Ti ferritic alloys during thermal treatment for elevated-temperature applications. United States. doi:10.1016/j.actamat.2017.01.011.
Song, Gian, Sun, Zhiqian, Poplawsky, Jonathan D., Gao, Yanfei, and Liaw, Peter K.. Sat . "Microstructural evolution of single Ni2TiAl or hierarchical NiAl/Ni2 TiAl precipitates in Fe-Ni-Al-Cr-Ti ferritic alloys during thermal treatment for elevated-temperature applications". United States. doi:10.1016/j.actamat.2017.01.011. https://www.osti.gov/servlets/purl/1394435.
@article{osti_1394435,
title = {Microstructural evolution of single Ni2TiAl or hierarchical NiAl/Ni2 TiAl precipitates in Fe-Ni-Al-Cr-Ti ferritic alloys during thermal treatment for elevated-temperature applications},
author = {Song, Gian and Sun, Zhiqian and Poplawsky, Jonathan D. and Gao, Yanfei and Liaw, Peter K.},
abstractNote = {Precipitate features, such as the size, morphology, and distribution, are important parameters determining the mechanical properties of semi- or fully-coherent precipitatehardened alloys at elevated temperatures. In this study, the microstructural formation and evolution of recently-developed Fe-Ni-Al-Cr-Ti alloys with superior creep resistance have been systematically investigated using transmission-electron microscopy (TEM), scanning-electron microscopy (SEM), and atom-probe tomography (APT). These alloys were designed by adding 2 or 4 weight percent (wt. %) Ti into a NiAl-hardened ferritic alloy with a nominal composition of Fe-6.5Al-10Cr-10Ni-3.4Mo-0.25Zr-0.005B in wt. %. These alloys were, then, subjected to a homogenization treatment at 1,473 K for 0.5 hour, followed by aging treatments at 973 K for 1 ~ 500 hours. In the homogenization-treated case, both alloys contain a primary L21-type Ni2TiAl precipitate, but with the distinct size and morphology of the precipitates and precipitate/matrix interface structures. In the subsequent aging treatments, the 2 wt. % Ti alloy establishes a hierarchical-precipitate structure consisting of a fine network of a B2-type NiAl phase within the parent L21-type Ni2TiAl precipitate, while the 4 wt. % Ti alloy retains the single Ni2TiAl precipitate. It was found that the hierarchical structure is more effective in remaining the coherent interface during the growth/coarsening of the precipitate. The formation of the different types of the precipitates, and their effects on the microstructural evolution are discussed, and the driving forces for these features are identified from the competition between the interface energy and elastic interactions due to the lattice misfit and misfit dislocations.},
doi = {10.1016/j.actamat.2017.01.011},
journal = {Acta Materialia},
number = C,
volume = 127,
place = {United States},
year = {Sat Jan 07 00:00:00 EST 2017},
month = {Sat Jan 07 00:00:00 EST 2017}
}

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Cited by: 6works
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  • A series of alloys has been exposed at 1200/degree/C in atmospheres of controlled oxygen and sulfur potentials, after preoxidation in air or in impure argon. The corrosion behavior is interpreted on the basis of phase-stability diagrams. The presence of iron and nickel-rich spinel particles in the outer layers of the initial oxide scale plays an essential role in resistance to sulfur attack. When the oxygen potential is sufficiently low, these spinels are reduced to a mixture of chromium oxide and an Fe-Ni alloy. The latter can then form sulfides which are liquid at high temperatures and accelerate penetration of sulfurmore » into the underlying metal. 30 refs.« less
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  • The operating slip systems and flow behavior of single crystalline Al{sub 66.8}Ti{sub 27.4}Fe{sub 5.8}, a two phase Ll{sub 2}+Al{sub 2}Ti materials, was investigated as a function of temperatures using specimens with compressive axes near [001], [{bar 1}3], [{bar 1}2], [{bar 1}33]. The materials shows a very limited compressive ductility, and fracture occurs by cleavage along planes of low indices, such as (011), (001), (013) and (111). Slip occurs exclusively on the octahedral slip systems at low temperatures, and on both octahedral and cube systems at high temperatures. A transition in operating slip systems from octahedral slip to cube slip, similarmore » to the one seen in Ni{sub 3}Al-type alloys, occurs as the temperature increases and as the orientation of the specimens change from near-[001] to near-[{bar 1}11]. The transition in slip system is attributed to the hardening effect of the Al{sub 2}Ti precipitates, rather than to the anisotropy of APB energy on cube and octahedral slip planes of the matrix. Because of the large hardening effect of the Al{sub 2}Ti, the two phase material is substantially stronger than single Ll{sub 2} phase materials. The shape (but not the level) of the flow stress-temperature curve for the two phase material resembles that of the single phase Ll{sub 2} material at low and intermediate temperatures. At high temperatures, however, the flow stress of the two phase material exhibits a sharp decrease, a feature which is not observed in the single phase Ll{sub 2} materials and can be correlated with a continuous dissolution of the Al{sub 2}Ti precipitates at high temperatures.« less