MICROWAVE BRAZING OF METALS

Doug Kautz, Rajendra Vaidya, Patrick Hochanadel, Vivek Dave, Stan MorrowLos Alamos National Laboratory

Hugo HueyMicramics, Inc .

The use of microwaves as a heat source in brazing metals was investigated. Microwaveheating is attractive in a number of applications because of its flexibility with respect tocoupling through many different material types . In addition, proper selection of theappropriate materials can simplify the brazing equipment design . Microwave brazingcan also be used for brazing complex geometries and material combinations. Ourpreliminary trials focused on a variety of metal systems and braze filler materials . Thequality of the brazed joints was investigated using optical and scanning electronmicroscopy . The quality of the brazed joint was evaluated as a function of microwavepower, coupling coefficients, susceptor design, and brazement gaps . The brazing processwas also evaluated in terms of repeatability and ease of operation .

M ■

i crowave Brazi n

P resented by D . D . Kautz

M . S . Morrow , R .U . Vaidya , P . W . Hochanadel , andV .R . Dave - Los Alamos National Laboratory

and

H . H uey - Micramics, I nc .

2nd International Brazing an Soldering ConferenceSan Diego , California

February 200 3

T Los Alamos1

Outline

• Reasons for Wor k

• Equipment• Parameters Used

• Specimen Desig n

• Metallurgical Properties• Mechanical Properties

• Conclusions

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Reasons for Wor k

Why use Microwave Heat Source for Brazing ?

• Efficient heat source .• Localized heating source .• Allows the use of several different brazin g

atmospheres .• Can easily be configured for various geometries

and applications .

• Allows multiple assemblies to be brazed during asingle brazing furnace cycle .

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Microwave Furnace System• Power supplies have 6

kW total availabl epower .

• Output is typicallybalanced between thesupplies .

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• Aluminum chambe rmay be air or wate rcooled (neither used) .

• Alumina insulatin gfixtures used wit hsusceptors made fro mmaterials thermall yinteractive wit hm i c rowaves .

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Control cabinet and Furnace chamber withpower supply cerarnic insulatic»> and

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Specimen Desig n

• Materials :- 0 .003 " (0 .075 mm) thick foil of BAu -4 alloy (Aul8Ni) .- 0 .0025" (0 . 065 mm) thick foil of Ag31 Cu10Pd alloy .- 0 . 5" (12 .7 mm) diameter 304L stainless steel rod .- High temperature flux (AWS designation FB3D) .

• Joint Design :- Flat butt joint .- Filler and flux placed between specimens .- Self-weighting .- Susceptor centered on the butt joint .

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Brazing parameters

• 2 . 45 GHz microwave frequency .• 2 kW power during ~10 minute slope up t o

tem peratu re .• 1 kW power during the 10 minute soak tim e

at tem peratu re .

• Soak temperature : (~ 100 C over liquidus)- 1050 C for BAu -4 alloy .- 950 C for Ag31 Cu10Pd alloy .

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Metallurgical Properties of Brazed Joint s

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BAu -4 brazed joint

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Ag31 Cu10Pd brazed join t

• Finished braze joints compared very favorably withjoints produced by other means .

• Filler material wetting appeared excellent along bot hjoints .

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Mechanical Properties of Brazed Joint s

• Finished braze joints compared very favorably with jointsproduced by other means .

• Fracture surfaces indicated ductile failure of the brazingfiller metal .

• Joint design , while simple to fabricate was not a favorableconfiguration for brazing and testing .

• Approximate failure stress :- 37 .7 ksi (260 MPa ) for BAu -4 alloy joint .- 22 .5 ksi (155 MPa) for Ag31 Cu10Pd alloy joint .- Nominal 75 ksi (517 MPa) for 304L Stainless Steel .- Nominal 115 ksi (792 MPa) for BAu -4 alloy .- Nominal 54 ksi (374 MPa) for Ag31Cu10Pd alloy .

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BAu-4 Alloy

8000

7000

60005000~4000

03000

2000

1000

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Strain, %

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Ag3lCulOPd Alloy

5000

4000

3000

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1000

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Failure Surface s~;-, - ~y a , ~ ~r ~, ~ > °"~~ : •_ -~ a A n

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BAu-4 failure surface with flux inclusion Ag3lCulOPd failure surfac e

• Both brazes exhibited some flux inclusions .

• Both brazes exhibited a ductile failure morphology .

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Conclusions

• Microwave brazing appears to hold greatpromise as a method for heating ofmultiple specimens for brazing .

• Incremental increases in the power appliedto specimens will allow several joints to b ebrazed during one cycle .

• Quality of finished brazes is similar to tha tfound with other heating methods .

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