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Title: Contamination and solid state welds.

Abstract

Since sensitivity to contamination is one of the verities of solid state joining, there is a need for assessing contamination of the part(s) to be joined, preferably nondestructively while it can be remedied. As the surfaces that are joined in pinch welds are inaccessible and thus provide a greater challenge, most of the discussion is of the search for the origin and effect of contamination on pinch welding and ways to detect and mitigate it. An example of contamination and the investigation and remediation of such a system is presented. Suggestions are made for techniques for nondestructive evaluation of contamination of surfaces for other solid state welds as well as for pinch welds. Surfaces that have good visual access are amenable to inspection by diffuse reflection infrared Fourier transform (DRIFT) spectroscopy. Although other techniques are useful for specific classes of contaminants (such as hydrocarbons), DRIFT can be used most classes of contaminants. Surfaces such as the interior of open tubes or stems that are to be pinch welded can be inspected using infrared reflection spectroscopy. It must be demonstrated whether or not this tool can detect graphite based contamination, which has been seen in stems. For tubes with one closedmore » end, the technique that should be investigated is emission infrared spectroscopy.« less

Authors:
Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
USDOE
OSTI Identifier:
908060
Report Number(s):
SAND2006-6203
TRN: US200722%%171
DOE Contract Number:
AC04-94AL85000
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; WELDED JOINTS; IMPURITIES; NONDESTRUCTIVE TESTING; SURFACE CONTAMINATION; GRAPHITE; DETECTION; Electric welding.; Welding.; Contamination.; Joining.; Material Science and Metallurgy-Working, Forming, Machining & Joining

Citation Formats

Mills, Bernice E. Contamination and solid state welds.. United States: N. p., 2007. Web. doi:10.2172/908060.
Mills, Bernice E. Contamination and solid state welds.. United States. doi:10.2172/908060.
Mills, Bernice E. Tue . "Contamination and solid state welds.". United States. doi:10.2172/908060. https://www.osti.gov/servlets/purl/908060.
@article{osti_908060,
title = {Contamination and solid state welds.},
author = {Mills, Bernice E.},
abstractNote = {Since sensitivity to contamination is one of the verities of solid state joining, there is a need for assessing contamination of the part(s) to be joined, preferably nondestructively while it can be remedied. As the surfaces that are joined in pinch welds are inaccessible and thus provide a greater challenge, most of the discussion is of the search for the origin and effect of contamination on pinch welding and ways to detect and mitigate it. An example of contamination and the investigation and remediation of such a system is presented. Suggestions are made for techniques for nondestructive evaluation of contamination of surfaces for other solid state welds as well as for pinch welds. Surfaces that have good visual access are amenable to inspection by diffuse reflection infrared Fourier transform (DRIFT) spectroscopy. Although other techniques are useful for specific classes of contaminants (such as hydrocarbons), DRIFT can be used most classes of contaminants. Surfaces such as the interior of open tubes or stems that are to be pinch welded can be inspected using infrared reflection spectroscopy. It must be demonstrated whether or not this tool can detect graphite based contamination, which has been seen in stems. For tubes with one closed end, the technique that should be investigated is emission infrared spectroscopy.},
doi = {10.2172/908060},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}

Technical Report:

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  • Transmission electron microscopy (TEM) was used to characterize the microstructures at and near the weld interface in upset welded Type 304L stainless steel test samples. Two sample configurations were examined in this study; upset welded cylinders prepared using a commercial resistance welder and cylindrical shaped samples welded in a Gleeble 1500 thermomechanical simulation device. The Gleeble samples evaluated were welded at 800 C, 900 C and 1,200 C with a 0.5 cm weld upset. The base microstructure of the samples varied with weld temperature. The lower temperature specimens contained a large free-dislocation density and distinct dislocation cells. The higher temperaturemore » specimens contained well-developed subgrains and a much lower free-dislocation density. The microstructure of the upset welded samples most closely resembled the 1,200 C Gleeble sample. No distinct bond line was observed by TEM in any of the specimens, i.e., diffusion and grain growth occurred across all weld interfaces. However, weld interfaces in both specimen configurations were characterized by the presence of 50--300 nm diameter particles spaced between 300 and 1,300 nm apart. Through the use of electron diffraction analysis and X-ray microanalysis two precipitate types were identified in both specimen configurations. A crystalline phase very similar to Mn{sub 1.5}Cr{sub 1.5}O{sub 4} and an amorphous phase enriched mainly in Si and Al were observed. Surface oxides and/or internal impurities may be sources for these precipitates. Future work will include a controlled study designed to determine the origin of the interface precipitates.« less
  • The microstructure of austenitic stainless steel welds can contain a large variety of ferrite morphologies. It was originally thought that many of these morphologies were direct products of solidification. Subsequently, detailed work on castings suggested the structures can solidify either as ferrite or austenite. However, when solidification occurs by ferrite, a large fraction of the ferrite transforms to austenite during cooling via a diffusion controlled transformation. It was also shown by Arata et al that welds in a 304L alloy solidified 70-80% as primary ferrite, a large fraction of which also transformed to austenite upon cooling. More recently it wasmore » suggested that the cooling rates in welds were sufficiently high that diffusionless transformations were responsible for several commonly observed ferrite morphologies. However, other workers have suggested that even in welds, delta ..-->.. ..gamma.. transformations are diffusion controlled. A variety of ferrite morphologies have more recently been characterized by Moisio and coworkers and by David. The purpose of this paper is to provide further understanding of the evaluation of the various weld microstructures which are related to both the solidification behavior and the subsequent solid state transformations. To accomplish this, both TEM and STEM (Scanning Transmission Electron Microscopy) techniques were employed.« less
  • Radioactive wastes, generated during years of nuclear materials production, will be vitrified in glass and sealed in canisters. These cylindrical canisters are fabricated from 0.375 inches (9.5 mm) thick Type 304L stainless steel plate and are 24 inches (61 cm) in diameter and 118 inches (3 m) tall with a forged nozzle. The canisters will be sealed by resistance upset welding a 5 inch (12.7 cm) diameter, 0.5 inch (1.27 cm) thick, slightly oversized plug into the nozzle. A parametric study recommended a range of production welding variables based on mechanical tests and metallography. Intentionally ``cold`` welds produced with lowmore » currents and short times exhibited insufficient interface length and lack-of-bonding. At very high currents, long weld times and low force, maximum heating occurred with significant melting at the top, which makes process stability a concern. All welds made between these extremes exhibited predominantly solid-state bonding. Little variation in microstructure between welds was found along much of the interface with changes in current, force and time. Hardness traverses across the welds showed higher values at the interface, indicative of the worked microstructure. Crevices formed at the top and bottom during plastic flow of the material, and grain sizes varied along the interface from differences in dynamic recrystallization and grain growth. The degree of melting at the top was the most significant difference among welds made within the recommended parameter range.« less
  • Investigations concerning the effect of atmospheric surface contaminants on the cohesion of silver in the solid state bonding of metals were conducted. Surface contaminants found by Auger electron spectroscopy were chlorine, sulfur, oxygen, and carbon, with the major contaminant being carbon. Examination of the diffusion behavior of the surface contaminants at elevated temperatures showed that oxygen and carbon were stable at the bonding temperatures. Chlorine was removed from the surface at low temperatures (100/sup 0/C), while sulfur reached a maximum surface concentration at 200/sup 0/C and started to decrease as the temperature was further increased. Reduction of the carbon levelmore » by ultraviolet cleaning did not change the bond strengths at the bonding conditions of 20 ksi and 160/sup 0/C. From these experiments, it was deduced that breaking through the contamination layer to provide intimate silver-silver contact is an important aspect of bonding.« less