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Title: Grain Growth and Precipitation Behavior of Iridium Alloy DOP-26 During Long Term Aging

Abstract

The influence of long term aging on grain growth and precipitate sizes and spatial distribution in iridium alloy DOP-26 was studied. Samples of DOP-26 were fabricated using the new process, recrystallized for 1 hour (h) at 1375 C, then aged at either 1300, 1400, or 1500 C for times ranging from 50 to 10,000 h. Grain size measurements (vertical and horizontal mean linear intercept and horizontal and vertical projection) and analyses of iridium-thorium precipitates (size and spacing) were made on the longitudinal, transverse, and rolling surfaces of the as-recrystallized and aged specimens from which the two-dimensional spatial distribution and mean sizes of the precipitates were obtained. The results obtained from this study are intended to provide input to grain growth models.

Authors:
 [1];  [1];  [1];  [1];  [1]
  1. 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
OSTI Identifier:
1361356
Report Number(s):
ORNL/TM-2017/109
DOE Contract Number:
AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Pierce, Dean T., Muralidharan, Govindarajan, Fox, Ethan E., Cox, Victoria A., and Geer, Tom. Grain Growth and Precipitation Behavior of Iridium Alloy DOP-26 During Long Term Aging. United States: N. p., 2017. Web. doi:10.2172/1361356.
Pierce, Dean T., Muralidharan, Govindarajan, Fox, Ethan E., Cox, Victoria A., & Geer, Tom. Grain Growth and Precipitation Behavior of Iridium Alloy DOP-26 During Long Term Aging. United States. doi:10.2172/1361356.
Pierce, Dean T., Muralidharan, Govindarajan, Fox, Ethan E., Cox, Victoria A., and Geer, Tom. Mon . "Grain Growth and Precipitation Behavior of Iridium Alloy DOP-26 During Long Term Aging". United States. doi:10.2172/1361356. https://www.osti.gov/servlets/purl/1361356.
@article{osti_1361356,
title = {Grain Growth and Precipitation Behavior of Iridium Alloy DOP-26 During Long Term Aging},
author = {Pierce, Dean T. and Muralidharan, Govindarajan and Fox, Ethan E. and Cox, Victoria A. and Geer, Tom},
abstractNote = {The influence of long term aging on grain growth and precipitate sizes and spatial distribution in iridium alloy DOP-26 was studied. Samples of DOP-26 were fabricated using the new process, recrystallized for 1 hour (h) at 1375 C, then aged at either 1300, 1400, or 1500 C for times ranging from 50 to 10,000 h. Grain size measurements (vertical and horizontal mean linear intercept and horizontal and vertical projection) and analyses of iridium-thorium precipitates (size and spacing) were made on the longitudinal, transverse, and rolling surfaces of the as-recrystallized and aged specimens from which the two-dimensional spatial distribution and mean sizes of the precipitates were obtained. The results obtained from this study are intended to provide input to grain growth models.},
doi = {10.2172/1361356},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}

Technical Report:

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  • This report summarizes results of studies conducted to date under the Iridium Alloy Characterization and Development subtask of the Radioisotope Power System Materials Production and Technology Program to characterize the properties of the new-process iridium-based DOP-26 alloy used for the Cassini space mission. This alloy was developed at Oak Ridge National Laboratory (ORNL) in the early 1980`s and is currently used by NASA for cladding and post-impact containment of the radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for interplanetary spacecraft. Included within this report are data generated on grain growth in vacuum or low-pressuremore » oxygen environments; a comparison of grain growth in vacuum of the clad vent set cup material with sheet material; effect of grain size, test temperature, and oxygen exposure on high-temperature high-strain-rate tensile ductility; and grain growth in vacuum and high-temperature high-strain-rate tensile ductility of welded DOP-26. The data for the new-process material is compared to available old-process data.« less
  • Weld metal grain structure and mechanical properties of the Ir-0.3% W alloy (DOP-26) doped with 60 ppM Th and 50 ppM Al have been investigated by use of a gas tungsten arc (GTA) welding process. The fusion zone grain structure is strongly influenced by heat input and puddle shape and therefore by the bead width. With increasing bead width from 2.5 to 3.7 mm, the grains in the fusion zone show a sharp change in growth direction near the centerline region and develop a fine columnar structure with grains growing parallel to the welding direction. Mechanical properties of the weldsmore » and base metal were characterized by tensile and impact tests from 650 to 1150/sup 0/C. The ductility and fracture behavior of DOP-26 welds are sensitive to weld bead width, postweld heat treatment, and weld-test orientation.« less
  • DOP-26 iridium alloy cups are used for fuel cladding for radioisotope power systems. The cups are deep drawn and recrystallized prior to final fabrication operations. This study characterizes the plastic deformation of cups during a sizing operation following the recrystallization heat treatment. The purpose of the sizing operation is to achieve the specified roundness, diameter, and radius dimensions of the cup. The operation introduces various levels of plastic strain in the cup. Plastic strain can be a cause of inhomogeneous or abnormal grain growth during subsequent exposure to elevated temperature during the service life of the fueled clad. This ismore » particularly true in the case of cups which have irregularities in the cup walls from the deep drawing operations. Diameter and roundness measurements were made on two cups both before and after sizing. Plastic strain levels were calculated using the ABAQUSTM finite element software. The calculated plastic strain levels in both cups were below 0.025, a value shown to be below the critical strain for abnormal grain growth during a simulated service exposure. The calculated maximum plastic strain was found to increase with increased applied sizing load and was not sensitive to the input value for the clearance between the cup and the sizing die. The calculated geometry of the sized cups was in good agreement with the measurements on the finished cups.« less
  • The basic purpose of this paper is to provide a literature review relative to fabrication of the General Purpose Heat Source (GPHS) that is used to provide electrical power for deep space missions of NASA. The particular fabrication operation to be addressed here is arc welding of the GPHS encapsulation. A considerable effort was made to optimize the fabrication of the fuel pellets and of other elements of the encapsulation; that work will not be directly addressed in this paper. This report consists of three basic sections: 1) a brief description of the GPHS will be provided as background informationmore » for the reader; 2) mechanical properties and the optimization thereof as relevant to welding will be discussed; 3) a review of the arc welding process development and optimization will be presented. Since the welding equipment must be upgraded for future production, some discussion of the historical establishment of relevant welding variables and possible changes thereto will also be discussed.« less