Stainless Bronze - possible? Alternatives perhaps?

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Tiffany
Posts: 4
Joined: Thu May 22, 2014 10:47 am

Stainless Bronze - possible? Alternatives perhaps?

Unread post by Tiffany » Fri May 23, 2014 9:19 am

Short version:
I've been planning on getting into metalsmithing to be able to make rings and such. I don't really want to bore you with all the details or anything but since gold is so expensive and PVD's, even something like TiN or ZrN(C) will eventually wear off under years of heavy use, I figure the only real solution is to use an alloy and the only promising alloys seem to be some derivatives of copper like manganese bronze, silicon bronze, C954 aluminum bronze but even those with their superior corrosion resistance are probably going to leave a green mark on your finger or smell like vinegar from the chemical reaction with heavy use. It really makes me wonder though why something like a stainless brass/bronze doesn't exist.

The main question I've actually registered to ask is if you could add a significant enough (minimum of 10.5%) level of chromium to bronze (or a similar copper alloy) so the chrome oxide would do for bronze what it does for iron in stainless steel and essentially create a stainless bronze.
Long version:
First before I get into all of the complicated details allow me to explain the situation: I'm looking to get into metalsmithing to make my own unique custom jewelry because it seems like it would be a fun and rewarding hobby.

I've never really been a fan of white/grey metals. My only real love when it comes to metals are the ones in the red yellow (Au) spectrum:
Image

Essentially, gold. The ideal color being the color in the center here:
Image

So now that we have established the color we have to get into the specifics of things. Gold has all of the properties as a noble metal and availability that it's clearly the best choice at this point but let's face it: gold is expensive. It may not tarnish but the materials for a single ring would set you back some $300-600, if not more, and I've never personally cared about the prestige of jewelry. I know that it is important to some people that their piece of jewelry is expensive and they can proudly wear it as a status symbol. Personally, I worry about something that expensive being stolen or losing it. For me, jewelry is all about aesthetics: "Does it look beautiful?," not "is it expensive?." For instance, I would choose moissanite over diamond any day because it's far more brilliant regardless of the status quo where everyone thinks diamond is the must-have gemstone. And of course rather than an obscenely expensive ruby I'd go with a red (pyrope) garnet instead - they're dirt cheap and still very beautiful.

But beyond that, it also needs to be functional. Nobody likes gold plated jewelery that wears down or chips on them revealing a different metal underneath. It's cheap and it's really not desirable. So it needs to be both the color of gold and also functionally similar in that it won't tarnish nor reveal a different color after heavy wear, or damage, and it can't smell or leave a mark on your finger.

What I'm after isn't just the color gold. PVD's, even something like TiN or ZrN(C) (where the amount of carbon is used to adjust the color) will eventually wear off under years of heavy use or potentially get scratched. I figure the only real solution is to use an alloy and the only promising alloys seem to be some derivatives of copper like manganese bronze, silicon bronze, or C954 aluminum bronze; but, even those with their superior corrosion resistance are probably going to leave a green mark on your finger or smell like vinegar from the chemical reaction with heavy use. I suppose you could perhaps use something like C954 aluminum bronze with a ZrN(C) PVD to help negate ever noticing if it wears down or becomes scratched.

Choosing the gold color almost feels like self flagellation at this point as working with something as popular and readily available as stainless steel or titanium which are already well established would be a far easier task. Even silver, really. It's far cheaper than one would imagine despite its grouping as a precious noble metal and listed commonly right along with gold - you can get a silver coin on eBay for $6-12. Heck, I saw a set of ten 90% silver dimes going for just $20 yesterday.

So this leads me to the question: Surely someone else before me has thought of this and felt the same way. So why doesn't something like a stainless bronze exist?

Let's look at another stainless metal: stainless steel. Steel is essentially iron and carbon, what makes it "stainless" steel is a minimum of 10.5% chromium. So, shouldn't we be able to add a significant enough (minimum of 10.5%) level of chromium to bronze (or a similar copper alloy) so the chrome oxide would do for bronze what it does for iron in stainless steel and essentially create a stainless bronze?

I admittedly don't know much of anything about metallurgy. But, maybe one of you guys can help me out.

Darryl was kind enough to send out a mail to the guild's jewelers and metallurgists asking this very question (short version), but I figured that it might be good to have it here officially on the forum.

Here is a reply from Herb:
Herb wrote: It seems she is asking for alloys that are used in the electronics business.
Some of these corrode, but not all.
I could suggest she look at thermocouple tables, or go the web sites of Isabellenhuette, Dillenburg, Germany.
They probably make half of the thermocouple wire used in the world.
They build their own ingots, produce wire and foil, and sell thermocouple wire and precision resistors.
Herb

Martin Pansch
Posts: 312
Joined: Thu Feb 14, 2013 10:44 am
Location: Young America, MN

Re: Stainless Bronze - possible? Alternatives perhaps?

Unread post by Martin Pansch » Fri May 23, 2014 6:27 pm

Tiffany,

When it comes to material science it is tough to beat Herb's opinion. You might ask the people of the Society of North American Goldsmiths.

It sounds like you are on the same quest as alchemists have pursued for centuries. Gold from lead (or other non-gold metal). Unless you have a philosopher stone or basilisk powder (see On Divers Arts) it might be tough get exactly what you are looking for. I've got to think that if there was a practical, economical gold replacement that someone would be making and using it.

There are some copper alloys that are high in chromium (0.6 to 1.2) and resistant to corrosion but I don't know how resistant. Or how much of it's copper color it retains.

http://www.copper.org/resources/propert ... om_cu.html

I am not a metallurgist but the way it has been explained to me it that the chromium makes stainless steel resistant to rust is by precipitating on the surface of steel. So the stainless steel will have a surface that is mostly or all chromium. This is accomplished by passivating it in an acid. The acid eats away the iron and leaves the chromium. This is why you can actually get some rust on stainless when you grind, drill or weld on it and not re-passivate that area.

If you find a copper alloy with the 10.5% chromium that you would probably need to passivate it similarly to get it stain resistant. This will leave a layer of chromium on the surface. It might only be a few angstroms thick but I think it would push the look of your finished piece towards the white and shiny end of the spectrum.

Depending on how long your quest takes that price of gold might end up seeming more reasonable. Good luck and let us know what you find.

Tiffany
Posts: 4
Joined: Thu May 22, 2014 10:47 am

Re: Stainless Bronze - possible? Alternatives perhaps?

Unread post by Tiffany » Sat May 24, 2014 1:58 am

I have contacted Isabellenhütte Heusler of course. I am awaiting their reply. I'll let you guys know if they come up with anything.

That's good information about chromium, Martin - thanks for that. So it looks like that idea is likely off the table.

Here's a thought that occurred to me: The ceramic-like materials that are deposited using PVD such as TiN and ZrN(C)... is it possible to actually have a piece of solid, say... TiN? I assume that it's not but the materials themselves - TiN & ZrN(C) sound like they do what I'm after. The only problem is that they're only deposited as a thin film rather than being the actual material itself.

As a last resort something like C954 aluminum bronze with a ZrN(C) PVD that is then gold rolled? I don't know.

What are your thoughts on the durability of gold-filled/rolled gold for jewelry in general? I know that gold plating is absolutely terrible and I've heard that rolled gold jewelry isn't much better despite its promises otherwise.

Martin Pansch
Posts: 312
Joined: Thu Feb 14, 2013 10:44 am
Location: Young America, MN

Re: Stainless Bronze - possible? Alternatives perhaps?

Unread post by Martin Pansch » Sat May 24, 2014 3:32 pm

Jewelry and exotic alloys? Now I am really outside my comfort zone of being a old country "hacksmith" (in training.)

Both titanium nitride and zirconium nitride are very hard ceramics. They are very hard and smooth. It is why they do so good as a coating for drill bits, medical implants and the like. The upshot is that even if you were to get a solid block of either of them you couldn't work them like a metal. They would probably explode into tiny sharp bits o' shrapnel. You could try to grind them but it would probably be harder than most grinders you took to them.

A quick search of the interweb shows some mention of powdered metallurgy done with TiN. Typically this means you pack a powder of TiN really tightly into a mold and heat it up until it fuses. It doesn't go liquid so it is a sintered more than a truly solid object. Same thing is done in making some bronze bushings. Problem is this heating is done in a neutral gas environment, and you need really precise heat control and the like so it sort of limits it to industrial applications.

I have seen titanium used for jewelry and knife fittings that were made into incredible colors through heat, much like temper colors. I believe a straw/goldish color would be possible. Though once again it would only be a surface color and hard use of it would lead to scratches that would show through to the tasty titanium center.

Is a limit to how thick of a layer of TiN or ZrN can be laid down? There is probably a standard amount for drill bits, etc. based on economics but if you go to the coater and ask them to lay it as thick as possible that might minimize the issues of the surface abrading and showing the metal beneath. I am sure it will cost more. Hopefully not as much and making it of gold. Maybe get a piece coated and give it the Samsonite Luggage test to see how durable it is.

I am certainly not the right one to opine about the durability of any type of jewelry. Unless dog tags count? No? Maybe one of the jewelers in the Guild is reading and will give us the benefit of their wisdom.

Good luck.

Tiffany
Posts: 4
Joined: Thu May 22, 2014 10:47 am

Re: Stainless Bronze - possible? Alternatives perhaps?

Unread post by Tiffany » Sun May 25, 2014 8:06 am

In terms of how thick they can do TiN, this is from a website that offers the service: 0.01 to 10 μm (typically 2 to 5 μm). The coating is cost is something like $2 according to this page, so practically dirt cheap.

That brings another thought across my mind then and perhaps any jeweler here could answer it, but I imagine if you used a PVD like TiN wouldn't it make it impossible to insert gemstones since you wouldn't be able to bend the little metal nibs that hold them in?

And while I'm asking jewelers questions I may as well ask about gold itself: What is the lowest gold content that you can go before the alloy essentially loses its functional properties you would expect in gold jewelry? I think most jewelry tends to be in 14k (41.5% non-gold) while the lowest you can even label as gold is 10k (58.3% non-gold) and the lowest karat gold alloy I can find prices on is 6k (75% non-gold).

Tiffany
Posts: 4
Joined: Thu May 22, 2014 10:47 am

Re: Stainless Bronze - possible? Alternatives perhaps?

Unread post by Tiffany » Tue May 27, 2014 7:15 am

I got a reply back from Isabellenhütte Heusler. They told me that they don't have anything like what I'm describing.

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