Help with solid state diffusion bonding temperature selection

[PValBlanc]

Hi, This would be my first time posting on these forums, and I need some help. I've my share of experience with liquid-state torch fired mokume, and am setting up to try my hand at kiln fired solid-state diffusion bonding instead. I've found most of the information I need except one vital detail. I can't seem to find any guidelines on how to select temperature for bonding. 

Let's start simple here and suppose a sterling silver/copper billet. 

Sterling melts at 893 C

Copper melts at 1083 C

Sterling is a hypoeutectoid alloy at 17.5% copper

The Eutectic point of silver/copper is at 28.1% copper and around 790 C 

So here's the question. Do I want to be heating my billet a little under the melting point of sterling, seeing as it is the lowest melting point? Should I be heating a little under the eutectic point? Not sure if the eutectic point is relevant if nothing is hitting liquidus. Perhaps none of the above? 

Any advice would be greatly appreciated. I can't get my hands on the midget/fergusson books, and most other sources I find all take for granted you've got the basics figured out. 

Cheers -Pat.

[teenylittlemetalguy]

We sound like we are at eye exact same place. I just finished my temp control and have made one mostly unsuccessful run.

i have been told by a pro that they set it about 50deg f cooler than eutectic.  The reason is if there is any melt at all the resulting alloy could mix in ANY proportion along the melt line so you must protect for the lowest melt point.

another thing I learned is that solid state billets are fragile until about 50% consolidated by forging.

 

 

[Glenn]

Do I want to be heating my billet a little under the melting point of sterling, seeing as it is the lowest melting point? Should I be heating a little under the eutectic point?

I can't get my hands on the midget/fergusson books,

Have you tried heating the billet to a little under the melting point of sterling? How did it work out for you?

Did you try heating a little under the eutectic point?  How did that work out for you?

What success or problems did you have with each?

Have you tried inter library loan for the midget/fergusson books? Was the library able to get them for you?

[PValBlanc]

Thanks! In my experience any form of mokume billet is prone to failure until about 66% reduction. Or rather, you can't be sure your firing was successful until you've reduced about 2/3. 

 

I guess the one thing bugging me about the whole question surrounding the eutectic point, is it shouldn't be a concern if nothing melts. And if you're heating up to say 840C in a controlled heating kiln (I'm using the my knifemaking heat-treating kiln), you're still 50 degrees under the melting point. There's no reason for it to melt, unless your kiln is unreliable, or your alloy proportions are off.

That said, how long did you soak your billet at temperature for in your mostly unsuccessful run? Inderstand ss diffusion bonding soaking times can be as long as 8 hours.

I did check the libraries Glenn, and it doesn't seem to be an option.  And while I do understand the value of experimentation, this is something that people have done before, and so clearly, answers exist. I apologize if my question is too basic and as such has attracted such an aggressive response. It was not my intention to frustrate anyone. 

The question just didn't have a definitive answer within the forum thread, and seemed like a pertinent one, both for me or anyone browsing the forums in the future. 

[Glenn]

Your first question posted on the forum contained highly technical data. This would only come from reading or experience using a very controlled set up. I ask to see which you were using, and the results, no aggression intended. Many times a question with details  as to the set up will allow us to jump ahead to YOUR level of knowledge rather than trying to start at the beginning only to find we are talking will under your skill and expertise.

 

 

Edited October 4, 2015 by Glenn

[PValBlanc]

Ah, I misinterpreted the tone here. Sorry. 

Essentially, I haven't attempted a billet in the kiln yet (as I feel I lack this basic piece of information) and as a thouroughly scrapped mokume billet is usually a lot of money down the drain, I'd rather do my homework first. 

So long story short, my experience is limited to torch fused billets so far. Kiln, torque plates, steel foil, charcoal and all is covered. I just need a working idea of how to determine temperature to bond two given metals (i have phase diagrams for most of the relevant ones).

Edit: I failed to specify, the kiln is a knifemaker's electric kiln, quite precise for temperature control, but on the poor side for atmospheric control (hence, wrapping the billet and torque plates in a steel foil bag filled with charcoal,to cut oxidation).

[teenylittlemetalguy]

Pv, my billet was in 10+hours. I am pretty certain it is clamping issue. I will retry soon. I am also experienced with TLP welds and making the change to solid state, I agree that diffusion welds need to be consolidated but I have had good luck withTLP and only consolidating 35% or so. Sounds like the solid state welds need a little more than that. Which is not what I expected.

I keep getting forbidden on posts but would love to compare notes with you

 

[teenylittlemetalguy]

Since I seem to be able to post now... 

The whole point of staying below the eutectic point is to insure it is not a TLP weld.

Because of entropy IF anything melts then the resulting alloy can be ANY ratio. Just because you have 50/50 Au/ Cu does not mean that the alloy is 50/50 unless you melt it all and know that there is no other possible combonation.

[PValBlanc]

Can't be time then. Clamping issues huh. What kind of Torque Plates are you using? Your average torque plates release pressure fairly early in the firing process because of thermal dilation. You can build Torque plates to counteract this. 

Essentially, you want your bolts to be made of a steel with a significantly lower coefficient of thermal expansion than your billet and plates. Bolted in the middle of the plates you use a die with a rectangular cavity in which to fit your billet and a punch to fit the billet. The punch needs a higher coefficient of expansion than the billet and die. The result is maintained pressure on all three axis' on your billet. It also cuts down on oxidation.

tis a pain to make though.

[timgunn1962]

Ferguson gives 600-700 degC, 60 minutes and a Nitrogen atmosphere for Fine Silver/Copper. There's no figures for Sterling Silver/Copper.

[teenylittlemetalguy]

No problem making a torsion plate, I was just excited and hurried it. I have some from TLP that would have worked but were all bigger than my container. I will now just make a bigger container. I don't want to use ss foil.

i have some friends that do a lot of diffusion welding and I have been meaning to ask if they have a simple temp chart. Will let you know what they say.

[PValBlanc]

teeny, Cool, I'll be sure to keep an eye on the thread. 

Timgunn: That's interesting, I'll have to make due with the charcoal and foil variant of reducing atmosphere, I don't have the means for nitrogen. That said it shouldn't be a problem. 700 is a nearly a full 100 degrees below eutectic, so it shouldn't be an issue either way, sterling and fine silver should both behave similarly at those temperatures. 

Thanks for the tip, if nothing else pops up, I'll know to start the tests below eutectic rather than below liquidus. Between you and teeny, I've got two opinions pointing in that direction. 

[teenylittlemetalguy]

my buddy referenced the Steve Midgett book. it has a small chart that says 1360f for 8-10hrs for;

Silver to Copper, nickel silver, bronze, kuromido and shakudo. 

 

Edited October 6, 2015 by teenylittlemetalguy

[PValBlanc]

Well under eutectic. Perfect. All the info so far points in the same directions. Thanks a lot. This will be a great help.

[teenylittlemetalguy]

happy to help. would love to see what you make. 

[Frosty]

Pat: I'm wondering what you're using for torsion plates. Steel has a much lower expansion coefficient than any of the other metals you're listing in your billet. How can pressure possibly decrease when the billet is expanding farther and faster than the bolts?

Frosty The Lucky.

[PValBlanc]

Currently, spme fairly basic torque plates without the die and punch section, but lower expansion bolts than the plates themselves. I don't remember the specific steels, I just trusted the machinist who made them with that.

How pressure can decrease anyways? That's a good question, although testing has shown it does, according to James Binnion's team anyways. 

He's written some papers on the thermal expansion mismatch torque plates for the santa fe symposium if you want a expert's opinion. I'll proceed to go reread those, because your question, sir frosty, may well kerp me up all night if I don't find the answer

[Adler Sochi]

Hello everyone! I am new here, but looking for the same answers as Pat does, ...temperatures and time for the electric kiln and to use it with precious metals.

 One jeweler told me that steel foil bag filled with charcoal also making it hotter, ..don't know how much hotter. I wonder if it also has to be considered while setting up temperature.

[teenylittlemetalguy]

Welcome Adler. Where are you located?

the additional heat is fairly inconsequential. The charcoal is there to absorb oxygen before the copper can get it and form an oxide that blocks the weld. What metals are you planning to weld?

[Adler Sochi]

I am in Seattle WA,  and I would like to try silver, gold(yellow, red, white), palladium possibly platinum.

...do I need to practice on silver/copper combination first?
... would it be the same temperatures and time for gold as well as for copper?

 

 

 

 

[teenylittlemetalguy]

Seattle? cool you are close. 

have you done any Mokume before? It is not really easy to get good results and there is actually a lot of wasted material learning Mokume. I would highly recommend not starting with precious metals. 

copper and nickel or copper and brass is a good place to start. I am told 1360f for 8-10hrs is a good place to start for copper/ nickel. 

copper/ brass 1580f for 8-10 hrs.

I stay away from precious metals other than silver as I am not doing much jewelry. someone else may have advise on those. 

[Adler Sochi]

I haven't done anything yet, just trying to get as much info as possible, so I don't repeat mistakes on which someone already learned. I have enough silver to practice on, just need to know what would be a better metal closer in speks to gold to practice on.

[teenylittlemetalguy]

there is a steep learning curve for Mokume, any practice is better than none. try out silver. there will not be much difference when you get to gold except temps. 

[Adler Sochi]

Do you mean to try combination of silver and copper, ...so what is the temps and time for this combo?

[teenylittlemetalguy]

Do you mean to try combination of silver and copper, ...so what is the temps and time for this combo?

yep. 1360f for 8-10 hrs is what they recommend in steve midgetts book.