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Discontinuous Inter-Granular Separations (DIGS) in the Gas Nitride Layer of ISS Race RingsThe starboard solar alpha rotary joint (SARJ) race ring on the International space station (ISS) failed due to severe spalling of the outer diameter, 45 degree (outer canted) nitrided surface. Subsequent analysis at NASA-KSC revealed that almost all of the debris generated due to the failure was nitrided 15-5 stainless steel. Subsequent analysis of the nitride control coupons (NCC) at NASA-JSC revealed the presence of discontinuous inter-granular separations (DIGS) in the gas nitride layer. These DIGS were present in the inter-granular networking located in the top 2 mils of the nitride layer. The manufacturer's specification requires the maximum white structure to be 0.0003 inches and intergranular networking below the allowable white structure depth to be cause for rejection; a requirement that the NCCs did not meet. Subsequent testing and analysis revealed that lower DIGS content significantly lowered the probability of nitride spalling in simulated, dry condition runs. One batch of nitride samples with DIGS content similar to the port SARJ (did not fail on orbit) which exhibited almost no nitride spalling after being run on one test rig. Another batch of nitride samples with DIGS content levels similar to the starboard SARJ exhibited significant nitride spalling on the same test rig with the same load under dry conditions. Although DIGS were not the root cause of starboard race ring failure, testing indicates that increased DIGS reduced the robustness of the gas nitride layer under dry operating conditions.
Document ID
20100011303
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Figert, John
(NASA Johnson Space Center Houston, TX, United States)
Dasgupta, Rajib
(NASA Johnson Space Center Houston, TX, United States)
Martinez, James
(NASA Johnson Space Center Houston, TX, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2010
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
JSC-CN-20048
Meeting Information
Meeting: MS&T''10
Location: Houston, TX
Country: United States
Start Date: October 17, 2010
End Date: October 21, 2010
Sponsors: American Ceramic Society
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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