Intermetallics. Metal molecules? Need clarification. 3

[Greenleader]

I know conventional steel has no molecules, as the type of bond the atoms have is crystalline.
However, since my recent melt result, I have been trying to understand exactly what type of structure/bond intermetallics have.
As I read it, 2 metals form a covalent bond, i.e. molecular. Is that an accurate assumption?

The term "intermetallic" seems to be one of those terms that are thrown around too much also. Like "nano structures", etc.
Kind of hard for a comic book metallurgist to pin it down.
Thanks.

 

[metengr]

http://www.knovel.com/web/portal/basic_search/display?_EXT_KNOVEL_DISPLAY_bookid=1090

 

[metengr]

Greenleader;
Typically, I don't make sales pitches because I am not in sales. If you join TMS, you have access to materials reference books in the Knovel E-library. There is a 4 volume set on Intermetallic Compounds, of which volume 2 is listed above. If you don't want to join TMS, locate the above books at a university library or obtain a subscription with Knovel directly. They also have many other good books.

 

[Greenleader]

Thank you met, as usual.
Some folks are labeling carbides as intermetallics, and such.

 

[tomwalz]

Not sure I have heard much about labeling carbides as intermetallics. They do talk about a wetting binder. (That is why Cobalt is so widely used in spite of cost and health issues.)

I do talk about intermetallics in brazing tungsten carbide. When you section a joint and you can see a distinct area between the carbide and the braze alloy that is often described as an intermetallic.

I discuss this in terms of cleanliness and surface preparation. (I work mostly in brazing followed by failure analysis.) The surface of tungsten carbide needs to be clean and chemically receptive to the braze alloy. If it forms an intermetallic you have a good, strong join.

A wettable surface is one on which the braze alloys flows out well. A properly wettable surface is one on which the braze alloy flows out well and forms a chemical (intermetallic) bond as well as a physical bond.

Three things here. 1. Intermetallic as it applies to making carbide 2. Intermetallic as it applies to brazing carbide 3. Intermetallic as it applies to carbide failure (carbide welding – and at least two kinds of that.

That’s the way I see it. Not sure how right I am or how clearly I have explained it. If you want to call I would be happy to talk to you. Depending on your area of interest I could refer you to others as well.

By the way, really good question.

Thanks,
Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[pwtomlin]

A conventional alloy, like steel, has a metallic bond that is characterized by an "electron cloud" where electrons are not strongly associated with a particular atomic nuclei.

Intermetallics contain bonds that are partially metallic, partially covalent, and partially ionic. This mixed bonding is much more directionally dependent than metallic bonding and it results in a more rigidly ordered structure. In conventional alloys, there is often a wide range of composition allowed whereas in intermetallics it is a narrow band around a particular stoichiometric ratio.

A carbide is, by definition, not an intermetallic. However, if you are talking about steel microstructures I could see there being some confusion about whether a particular phase is a carbide or an intermetallic.

 

[illium98]

Good question. All answers on point. Carbides, intermetallics. It does get a little fuzzy. Also, bonds in ceramics (primarily ionic but also to a significant extent covalent).

Regardless of the nature of the bond, I would try to avoid speaking of molecules whenever possible unless you are talking about gasses or organic chemistry.