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Posted (edited)

I read that a layer of nickel placed between the cladding and core of a laminated knife acts as a stop to carbon migration.

Can anyone tell me to what extent is this true? 

I ask because I see lots of pictures of sanmai with a layer of nickel, almost all of which display, to a greater or lesser extent, the "shadow" that carbon migration throws on both sides of the weld.

 

Edited by Dan P.

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I have always been told that pure nickel will stop carbon migration, and Verhoeven says it will, but hopefully Jerrod will step in soon with the metallurgist's perspective.  I was told it had to be pure nickel, not an alloy like 15n20 or L6.  I think the idea is that since nickel does not form carbides or have the interstitial spaces in its crystal structure for carbon that iron does, the rate of migration is slow enough to be effectively nil.

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Posted (edited)

Thanks Alan. 

I have read the same, and yet I see many pictures (mostly on instagram) where nickel has been used and where the characteristic shadow of carbon migration can be seen.

Perhaps it is something else? Nickel migration? Ha ha.

 

Edited by Dan P.

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Dan,

Do they state that nickel was used? 

Can we trust that they actually KNOW what they are using? I have seen some use 203E as pure nickel or 316 stainless and claim the same or as Alan says L6 or 15N20.

Maybe they mistake a bright line as nickel rather than decarb or borax flash or other phenomenon?

 

Over the years I more and more take what people say at less than face value.

Ric

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Sadly, after a brief search I cannot find any evidence as to why Ni should block carbon diffusion.  The pure Ni lattice is a face center cubic structure, just a touch smaller than Fe (3% smaller atomic diameter).  If I think about it when I get more time I will look further.  This does not appear to be something that has been rigorously studied though.  I've only checked my 2 primary text books at this point, so I may find something that explains it later.  

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Posted (edited)
18 hours ago, Richard Furrer said:

Dan,

Do they state that nickel was used? 

Can we trust that they actually KNOW what they are using? I have seen some use 203E as pure nickel or 316 stainless and claim the same or as Alan says L6 or 15N20.

Maybe they mistake a bright line as nickel rather than decarb or borax flash or other phenomenon?

 

Over the years I more and more take what people say at less than face value.

Ric

In the instances I'm thinking of, the use of pure nickel was stated, but my fairly loosely held belief that carbon migration happened is circumstantial, if that is the right turn of phrase.

I have also not used nickel for this purpose myself, so my authority on the subject is nonexistent, except that I am quite familiar with what carbon migration/diffusion looks like.

I figured, like everything, given time and temperature the carbon will find a way to a state of entropy, and that to whatever degree nickel is effective, it is not absolutely effective.

 

 

Edited by Dan P.

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Ooh, a bladesmithing urban myth!  I think this calls for a grant-funded study...

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59 minutes ago, Jerrod Miller said:

Sadly, after a brief search I cannot find any evidence as to why Ni should block carbon diffusion.  The pure Ni lattice is a face center cubic structure, just a touch smaller than Fe (3% smaller atomic diameter).  If I think about it when I get more time I will look further.  This does not appear to be something that has been rigorously studied though.  I've only checked my 2 primary text books at this point, so I may find something that explains it later.  

I would be very eager to hear any further thoughts you might have on the matter Jerrod. 

There are notions floating about in the knife making world whose origins I sometimes wonder about. 

 

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5 minutes ago, Alan Longmire said:

Ooh, a bladesmithing urban myth!  I think this calls for a grant-funded study...

Bigly!

 

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I can't remember where, but I recall hearing/reading a source I trusted that made the claim that it worked.  I definitely want to dig deeper.  I'm just way too busy lately and I know it is going to take a while to find the hard data, if it exists.  Surely Kevin Cashen has looked at this?  If so, I would totally trust what he found.  

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i dont see anything specific on his site and his contact link is down i should have an email around here some were but i might wait till hes back from adventure down under before i bend his ear on this i am curious now

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I first heard about it from Howard Clark.  This has been discussed here before, a Google search of the site for 'carbon migration' should take you to the relevant posts (sorry, my bandwidth here is next to zero or I'd go looking myself).

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I did a site search, but didn't find anything conclusive in the first several hits.  This one was close, and this one mentions an article by Verhoeven and Howard Clark (with this link).  Perhaps someone can track down the full article?  

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I'm not smart enough to interpret this exactly, but on a hunch I looked at solubility of carbon in pure nickel, and maybe carbon just doesn't go into solution in nickel until it reaches a much higher temperature than what we usually work with? I know the attached reference starts at 700C (a touch over 1200F), but that doesn't mean the migration is significant at that temp. It's just where the formula starts. Keep in mind, I really do no nothing about this and my metallurgy knowledge is minimal at best. Like I said, it was just a hunch as I'm slowly learning more.

https://aip.scitation.org/doi/abs/10.1063/1.1702064

 

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It would be nice to have access to that paper too.  As it stands, I can't see a good (believable) correlation between that and the BCC Fe values in my book.  (there is a difference of 11 orders of magnitude, I don't trust that; I must be missing something).  

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The original paper is "Carbon Diffusion between the Layers in Modern Pattern-Welded Blades".  I've found two possible sources for it:

https://www.sciencedirect.com/science/article/pii/S1044580398000357

https://www.researchgate.net/publication/222074204_Carbon_Diffusion_Between_the_Layers_in_Modern_Pattern-Welded_Damascus_Blades

Maybe that will be useful.
 

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2 hours ago, GEzell said:

The original paper is "Carbon Diffusion between the Layers in Modern Pattern-Welded Blades".  I've found two possible sources for it:

https://www.sciencedirect.com/science/article/pii/S1044580398000357

https://www.researchgate.net/publication/222074204_Carbon_Diffusion_Between_the_Layers_in_Modern_Pattern-Welded_Damascus_Blades

Maybe that will be useful.
 

The first link is the same link I posted, and the second is the same paper on another site.  Both links require payment for the article.  

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I have gone through both the PDF and print versions of Verhoeven (they are slightly different), and there is no mention of nickel being a barrier to carbon migration.  Really cool stuff about how diffusion works, but nothing on what might inhibit it.  Sigh...  Too bad Howard doesn't hang around here these days. :(

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I talked with someone who knows about these things, and this is what they said....

"I think because as an alloying element, nickel is substitutional, taking the place of one or more iron atoms in the cube. But, as a pure metal, the nickel stays arranged as a body centered cube regardless of temperature, rather than changing to face centered austenite as iron does, which is what allows the carbon to move through the cube. The interstitial spaces are more open in austenite, so the carbon can get through to saturate it. But because the pure nickel does not change to face centered, and remains body centered cubic, there is no room for the carbon to move through."

Makes sense to me, but it's way above my pay grade.  This is what he remembers of information given to him from Mr V...

 

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55 minutes ago, GEzell said:

But, as a pure metal, the nickel stays arranged as a body centered cube regardless of temperature, rather than changing to face centered austenite as iron does,

This is inaccurate.  Pure nickel is FCC.  

56 minutes ago, GEzell said:

which is what allows the carbon to move through the cube.

This is also not accurate.  Carbon diffuses through BCC iron (steel), just slower.  Heat (energy) is the primary driving force to the rate of diffusion.  

There is enough room in the iron BCC lattice for C, and enough room in the nickel FCC lattice for carbon.  

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So this an example of why I originally asked this question (photo attached)

It’s w/i, nickel and silver steel. The dark shadow at the edge of the w/i is something I’ve always understood to be carbon migration. Perhaps it’s something else. 

This mixture swapping w/i for m/s also shows a faint shadow on the m/s side, albeit less than without the nickel.

This blade took maybe two welding heats, and otherwise was not held at high temperatures for long periods. 

Any thoughts?

DA017521-56BA-4D77-81F4-3BDBA5B01DB5.jpeg

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Here’s the m/s, ni, carbon mix. (Photo attached) There’s a faint shadow on the m/s

Perhaps it’s not carbon migration at all? 

The flux used was borax/boric acid/sal ammoniac/iron powder. 

2B299747-DE0D-4DA6-ACBB-5E40DE58A3A4.jpeg

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On 3/19/2018 at 1:02 AM, Richard Furrer said:
1 hour ago, Dan P. said:

Here’s the m/s, ni, carbon mix. (Photo attached) There’s a faint shadow on the m/s

Perhaps it’s not carbon migration at all? 

The flux used was borax/boric acid/sal ammoniac/iron powder. 

2B299747-DE0D-4DA6-ACBB-5E40DE58A3A4.jpeg

no answers....but a few thoughts. Borax definitely gives some kind of visual residual when its used in welding as would pure iron powder and certainly cast iron powder (both of which are added to flux and both of which work well) . the other posibilities are some kind of alloy banding segregation at the weld boundary, I wonder about some alloys being concentrated at the surfaces of the material ,  when iron is differentially oxidised away around them (just an idea...not fact necessarily ).....and the obvious one is carbon migration. surly carbon migration through nickel would be easy to see under a good microscope? it would be easy enough to eliminate some of the variables by dry welding the material and using Pure iron whith known chemistry as a material (its really nice in san mai).   To Me it looks like C migration and I love the look.

 

 

my other thought is how thick are those lines, wide on the diagonal but very thin Nickel and V thin carbon migration or whatever it is...

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2 hours ago, owen bush said:

 

my other thought is how thick are those lines, wide on the diagonal but very thin Nickel and V thin carbon migration or whatever it is...

Very thin for sure, but the received wisdom is that -if- it is carbon migration it should not be there at all with nickel. 

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It certainly looks like carbon migration to me, especially in the wrought iron.  

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