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Title: Dissolution kinetics of {delta} phase and its influence on the notch sensitivity of Inconel 718

Abstract

The dissolution kinetics of {delta} phase in Inconel 718 at 980 deg. C, 1000 deg. C and 1020 deg. C and its influence on high temperature notch sensitivity have been studied using a quantitative X-ray diffraction (XRD) method and high temperature stress rupture life tests of notched specimens. The amount of {delta} phase decreases gradually during holding time at 980 deg. C, 1000 deg. C and 1020 deg. C. The {delta} phase will be fully dissolved in the austenitic matrix at 1020 deg. C for more than 2 h. A certain amount of {delta} phase still exists after holding at 980 deg. C and 1000 deg. C for times up to 6 h; the amount remaining are 3 wt.% and 0.6 wt.%, respectively. The dissolution rate remains at a high level at the beginning, and then decreases gradually with an increase of holding time. A dynamic equilibrium state can be approached after holding at 980 deg. C for more than 30 min and at 1000 deg. C for more than 2 h. The alloy with {delta} phase amounts higher than 0.62 wt.% does not exhibit notch sensitivity, whereas serious notch sensitivity exists if the concentration is below 0.43 wt.%.

Authors:
 [1];  [2];  [2];  [2];  [2]
  1. State key Laboratory of Metastable Materials Science and Technology, Yanshan University, 066004, Qinhuangdao (China). E-mail: dayongcai@sina.com.cn
  2. State key Laboratory of Metastable Materials Science and Technology, Yanshan University, 066004, Qinhuangdao (China)
Publication Date:
OSTI Identifier:
21003534
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 58; Journal Issue: 3; Other Information: DOI: 10.1016/j.matchar.2006.04.020; PII: S1044-5803(06)00121-5; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AUSTENITIC STEELS; DISSOLUTION; INCONEL 718; NOTCHES; RUPTURES; SENSITIVITY; THERMAL STRESSES; X-RAY DIFFRACTION

Citation Formats

Cai Dayong, Zhang Weihong, Nie Pulin, Liu Wenchang, and Yao Mei. Dissolution kinetics of {delta} phase and its influence on the notch sensitivity of Inconel 718. United States: N. p., 2007. Web.
Cai Dayong, Zhang Weihong, Nie Pulin, Liu Wenchang, & Yao Mei. Dissolution kinetics of {delta} phase and its influence on the notch sensitivity of Inconel 718. United States.
Cai Dayong, Zhang Weihong, Nie Pulin, Liu Wenchang, and Yao Mei. Thu . "Dissolution kinetics of {delta} phase and its influence on the notch sensitivity of Inconel 718". United States. doi:.
@article{osti_21003534,
title = {Dissolution kinetics of {delta} phase and its influence on the notch sensitivity of Inconel 718},
author = {Cai Dayong and Zhang Weihong and Nie Pulin and Liu Wenchang and Yao Mei},
abstractNote = {The dissolution kinetics of {delta} phase in Inconel 718 at 980 deg. C, 1000 deg. C and 1020 deg. C and its influence on high temperature notch sensitivity have been studied using a quantitative X-ray diffraction (XRD) method and high temperature stress rupture life tests of notched specimens. The amount of {delta} phase decreases gradually during holding time at 980 deg. C, 1000 deg. C and 1020 deg. C. The {delta} phase will be fully dissolved in the austenitic matrix at 1020 deg. C for more than 2 h. A certain amount of {delta} phase still exists after holding at 980 deg. C and 1000 deg. C for times up to 6 h; the amount remaining are 3 wt.% and 0.6 wt.%, respectively. The dissolution rate remains at a high level at the beginning, and then decreases gradually with an increase of holding time. A dynamic equilibrium state can be approached after holding at 980 deg. C for more than 30 min and at 1000 deg. C for more than 2 h. The alloy with {delta} phase amounts higher than 0.62 wt.% does not exhibit notch sensitivity, whereas serious notch sensitivity exists if the concentration is below 0.43 wt.%.},
doi = {},
journal = {Materials Characterization},
number = 3,
volume = 58,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • The precipitation of intermetallic phases in Inconel 718 has been extensively studied. It has been found that the major intermetallic phases that precipitate in the austenite matrix are the metastable {gamma}{double_prime} (DO{sub 22} structure) and {gamma}{prime} (L1{sub 2} structure) phases and the equilibrium {delta} (DOa structure) phase. The {delta} phase can form during processing or during services. The precipitation of {delta} phase during aging has been studied in the solution treated Inconel 718. However, there are only a few studies on the precipitation of {delta} phase in cold rolled Inconel 718. R.P. Singh et al. found that more of themore » {delta} phase precipitated in the 50% cold rolled material compared to the 30% cold rolled material at lower temperatures, but they did not give information on the precipitation of {delta} phase in cold rolled Inconel 718 at higher temperature. The {delta} phase has a big influence on mechanical properties in Inconel 718. Therefore, it is necessary to measure the volume fraction of {delta} phase. Usually, the volume fraction of {delta} phase was measured by quantitative metallographic techniques and quantitative chemistry phase analysis. In the present work, the volume fraction of {delta} phase in cold rolled Inconel 718 at 910 C for different time is measured by X-ray diffraction techniques, and the influence of cold rolling on the morphology and the volume fraction of {delta} phase is investigated.« less
  • The hot working characteristics of {delta} phase in the delta-processed Inconel 718 alloy during isothermal compression deformation at temperature of 950 deg. C and strain rate of 0.005 s{sup -1}, were studied by using optical microscope, scanning electron microscope and quantitative X-ray diffraction technique. The results showed that the dissolution of plate-like {delta} phase and the precipitation of spherical {delta} phase particles coexisted during the deformation, and the content of {delta} phase decreased from 7.05 wt.% to 5.14 wt.%. As a result of deformation breakage and dissolution breakage, the plate-like {delta} phase was spheroidized and transferred to spherical {delta} phasemore » particles. In the center with largest strain, the plate-like {delta} phase disappeared and spherical {delta} phase appeared in the interior of grains and grain boundaries.« less
  • Inconel 718, a Nb-modified nickel-base superalloy has been widely used in gas turbine and related applications due to its good mechanical properties and structural stability at elevated temperatures ({approximately}650 C). The mechanical properties of Inconel 718 depended on the austenite grain size and the size, morphology and content of {delta} phase, {gamma}{double_prime} and {gamma}{prime} phases. In a previous study, the {delta} phase content in Inconel 718 was measured by X-ray diffraction techniques. However, it was difficult to measure the content of {gamma}{double_prime} and {gamma}{prime} phases. M.G. Burke and M.K. Miller determined the composition of the {Upsilon} matrix by using analyticalmore » electron microscopy and atom probe field ion microscopy. Their results indicated that the composition of the {Upsilon} matrix changed due to the formation of the various precipitates. The variation in the composition of the {Upsilon} matrix affected the lattice constant of {Upsilon} phase, then the content of {delta} phase, {gamma}{double_prime} and {gamma}{prime} phases was thought to be associated with the lattice constant of {Upsilon} phase. In this paper, the lattice constant of {Upsilon} phase and the content of {delta} phase in Inconel 718 aged at 910 C for different times after cold rolling are measured by X-ray diffraction techniques. The lattice constant of {Upsilon} phase as a function of the content of {delta} phase, {gamma}{double_prime} and {gamma}{prime} phases is derived.« less
  • Systematic research has been undertaken on the effect of cold rolling on the precipitation kinetics of {delta} phase in INCONEL 718. Above 910 C, cold rolling promotes the precipitation of {delta} phase. Below 910 C, the precipitation of {delta} phase is still preceded by the {gamma}{double_prime} precipitation in cold-rolled INCONEL 718. Cold rolling promotes not only the precipitation of {gamma}{double_prime} phase but also the {gamma}{double_prime} {r_arrow} {delta} transformation. The relationship between the weight percentage of {delta} phase and aging time follows the Avrami equation. Below 910 C, as cold rolling reduction and temperature increase, the time exponent (n) decreases, whereasmore » the rate of {delta} precipitation increases. The apparent activation energy of {delta} precipitation varies in the range of 1113 to 577 kJ/mol for 25 to 65% cold-rolled INCONEL 718 and decreases as cold rolling reduction increases. Precipitation-time-temperature (PTT) diagrams have been determined for the four cold-rolled INCONEL 718. The noses of the PTT curves are located at about 910 C. These curves are shifted significantly to longer times as cold rolling reductions decrease.« less
  • The effects of solution and intermediate heat treatments on the notch stress-rupture properties of Inconel 718 were investigated using commercial quality barstock. It was determined that a solution heat treatment of 1038$sup 0$C for as short a time as 20 min could render this alloy notch-sensitive by solutioning extensive quantities of the orthorhombic Ni$sub 3$Nb delta phase. Restoration of notch ductility subsequent to 1038$sup 0$C (20 min) solution heat treatment was accomplished by the insertion of a 917$sup 0$C (10 h) intermediate heat treatment, prior to aging, during which significant quantities of the delta phase were precipitated. This intermediate heatmore » treatment was not successful in restoring notch ductility to specimens which had been given longer, 1 h, solution heat treatments at 1038$sup 0$C. A 954$sup 0$C (3 h) intermediate heat treatment was also not successful in restoring notch ductility to specimens solution heat treated for 20 min at 1038$sup 0$C. It was confirmed that the most important factors controlling the notch-rupture ductility in Inconel 718 are the size, quantity, and distribution of the delta phase. The grain size of the material did not directly control the notch properties. (auth)« less