[b]Metallurgical Bond Strength?[/b]

[beagh]

Hello All

I am interested in determining the metallurgical bond strength of a metal-metal composite wire. The wire consists of a silver core and nickel-cobalt-chromium-molybdenum (MP35N) outer layer.

1) Does anyone know if there is an existing test procedure avalibale to test the metallurgical bond strength of wires?
2) I believe the answer to the above question is negative which brings me to my second queation. Is it possible to etch a nickel-cobalt-chromium-molybdenum alloy away from a silver core?

All response are greatly appreciated

Kind Regards
PM

 

[Goahead]

The bond strength cannot be higher than the strength of the weakest element (silver). Can you judge on the quality of the metallurgical bond by regular metallographic examination of longitudinal sections?

http://www.welding-advisers.com/

 

[beagh]

It is possible to examine the bond strength qualitatively by examing cross sections, however I am interesting in measuring the bond strength quantitatively to access the influence of drawing parameters such as die angle and reduction ratio.

To this end I am wondering if it is possible to remove the outer core of the wire using an etching method or alternative process.

 

[metengr]

You don't mention in your post the outer diameter of the composite wire, and the relative diameters between the two materials. Perhaps you could devise a simple bend test to evaluate the shear strength of the bond between the silver core and MP35N outer layer?.

A tensile fiber and shear stress could be calculated based on the bend radius. Destructive examination of specimens after bend testing would reveal bond integrity, as described by Goahead, and some degree of bond strength between the two materials.

 

[metman]

Once upon a time we furnace brazed 321 S.S. bars with Gold/Nickle brase alloy in Hydrogen atmosphere(as I recall the braze temperature is above 1900 deg F). The bars were end loaded by standing them vertically with weights on top of three pair of bars.

The finished brazed bars were machined and tensile tested. I don't recall the numbers but the failure occurred in the parent metal and metallographic evaluation showed obvious diffusion between the parent bars.

 

[beagh]

The diameter of the wire varies from 1.27mm to 0.0254mm but initially I am hoping to conduct tests on slightly larger radii (3mm). The centre core varies between 5% and 35% of the total diameter of the wire

In response to 'Metenger' I would think that a bend test might be the way to go..although I am not so convinced that this test is suitable for small wire?

In response to 'Metman' could you please shed more light on the test method..i do not fully understand. Were the bars loaded in compression before the tensile test? If so why? Are there any relevant publications i might look at?

 

[metman]

beagh: The bars were loaded with weights to achieve maximum diffusion of Gold/Nickel Braze alloy into the base metal, 321 S.S. during the hydrogen brazing cycle.

Picture three pillars or columns of 1" (25.4 mm) square X 8" (101.6 mm)long. Each column contains 2 pieces of 1"square X 4" long bars of 321 S.S. with a foil of Au/Ni alloy sandwiched inbetween each set of 2 pcs of S.S. On top of the three pillars, positioned in a triangle, a weight is applied of about 50-75 lbsf. Therefore the compressive stress is not large but adequate to promote diffusion bonding during the braze cycle.

After the three pillars were brazed, each one was machined to make 3 tensile test specimen. These three specimen were pull tested and the failure occured in the base metal because of the extent of difussion bonding between each set of two bars and the braze alloy.

I believe my boss, Richard (Dick)Preston -- now deceased) wrote an article for Machine Design or some such magazine. I will do a Google search.