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Title: Mechanical properties as an indicator of interstitials in niobium for superconducting accelerator cavities

A preliminary investigation was conducted into the feasibility of using simple mechanical properties experiments to evaluate interstitial impurity uptake from processing environments. Two types of tests were examined: tensile tests and complex modulus measurements using a dynamic mechanical analyzer (DMA). For the tensile tests, samples were cut from a single crystal of niobium, with the same orientation, and then prepared following different procedures. Significant differences were observed during tensile tests, with yielding strength and strain-to-failure clearly related to interstitial uptake. When the strain rate was reduced by an order of magnitude, the strain-to-failure was reduced by 18 % indicating that interstitial hydrogen is responsible for this behavior. For the complex modulus measurement, polycrystalline samples from different locations of two different ingots were examined at a frequency of 1.0 Hz while the temperature was increased at the rate of 1.0 °C per minute. Anaelastic peaks were found for C, N, and O in all samples, but the lower limit of the system did not allow for detection of a peak for H. It is concluded that mechanical properties could be developed as a measurement tool to guide the development of processing methods for producing reduced interstitial content material, but additional research, andmore » uncertainty analysis, is required for these tools to be reliable in this application.« less
Authors:
;  [1] ;  [2]
  1. Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, US (United States)
  2. Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, US (United States)
Publication Date:
OSTI Identifier:
22492686
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1687; Journal Issue: 1; Conference: Ingot niobium summary workshop, Newport News, VA (United States), 4 Dec 2015; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; ACCELERATORS; CAVITIES; DATA COVARIANCES; FAILURES; HYDROGEN; IMPURITIES; INDICATORS; INTERSTITIALS; MECHANICAL TESTS; MONOCRYSTALS; NIOBIUM; PEAKS; POLYCRYSTALS; STRAIN RATE; SUPERCONDUCTING CAVITY RESONATORS; TENSILE PROPERTIES; YIELD STRENGTH