Brazing is a low-cost process used extensively in manufacturing and repair of component assemblies in the aerospace industry. For stainless steel joints requiring an airtight seal, the brazing metal Pd-Ni-Cr-Si-B (PalNiCro) is commonly applied. However the underlying mechanisms of the brazing process are not well understood, which has precluded optimization of the brazing parameters and reduced the cost-effectiveness of the production process. To address these issues, the role of processing conditions on the wetting characteristics of austenitic AISI 347 and martensitic AISI 410 stainless steel was studied in this work using PalNiCro as the brazing alloy. Sessile drop tests were conducted to assess the effect of time, temperature and surface roughness on the wettability conditions between the stainless steel substrate and brazement. The effect of time and clearance on the microstructure and hardness of the brazement was then examined. / A brazing temperature of 980ºC and a surface roughness from 600 grit SiC grinding paper were determined as the optimal wetting conditions. Under such conditions, the value of the equilibrium contact angle for the AISI 347 and AISI 410 stainless steels was determined to be approximately 10º after 100 seconds of melting. Examination of the brazements produced using optimized wetting conditions revealed the formation of borocarbide (Mx(C,B) y) and boride (MxBy) precipitates primarily confined to the grain boundaries and some locations within the interior of the grains, which resulted from the diffusion of boron from the brazing metal. The microstructure of the joint seam consisted of the three distinct regions: (1) a soft ductile nickel solid solution with dissolved palladium and chromium (hardness ~ 220 HV) and (2) palladium silicide (over 600 HV) surrounding (3) very hard Ni-rich islands (over 1000 HV) with the presence of nickel borides. An increase in brazing time showed a slight increase in the maximum brazing clearance (MBC) with also an increase in the diffusion layer for both AISI 347 and AISI 410. The volume fraction of the secondary phases within the joint seam exhibited marked increases up to a clearance of 150 mum with a decrease thereafter and an estimated value of 300 mum as the maximum attainable clearance.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.83862 |
| Date | January 2005 |
| Creators | Edelmann, Fabian |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Engineering (Department of Mining, Metals and Materials Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002271563, proquestno: AAIMR22643, Theses scanned by UMI/ProQuest. |
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