HOkay, sometimes I lose track of the confusion that's propagated about this
material, and the common uses of the term "ceramic," as well as the vague
terms used in metallurgy to describe WC and TaC, which are interstitial
carbides. On top of it all, the metalworking- and other industrial fields
have added their own jargon. This is going to be one of my lengthy
dissertations, so I'll apologize in advance and warn off anyone who doesn't
really give a damn. On the other hand, they may find this interesting,
because it's the result of research I did on the history of carbide tools in
1977, plus years of exposure as Materials Editor of American Machinist, and
more recently as Tooling Editor of Machining magazine. You won't see it put
together quite this way anywhere else, I believe.
The term "ceramic" is old and vague as hell. It can include any non-metallic
material, or compound of a metal and a non-metallic material, that's hard
and brittle. You will sometimes see plain sand- and lime-putty mortar, which
has a compression strength of only 75 - 350 psi, described as a "ceramic" in
the building-restoration literature. This is not as ridiculous as it sounds;
when lime putty (hydrated lime, Ca(OH2)) picks up CO2 from the atmosphere,
it becomes CaCO3 -- limestone. That fills the bill: non-metallic and
somewhat hard, somewhat brittle. As reconstituted limestone goes, lime
mortar pretty lousy, but it's still within the definition. The definition of
"ceramic" actually is that broad. Fine-clay dishware is generally described
as "ceramic," as another example.
There is no absolute technical definition, although engineers of advanced
ceramics from around the world got together in 1993 and wrote one for their
own use. It doesn't apply to anything we're interested in. It applies only
to the newest, most advanced engineering ceramics. In Europe, engineers
define plain glass as a ceramic. We're not interested in that definition,
What we're interested in is something that will help us sort out the often
contradictory uses of the term in industry. Here's a good one from
"Industrial ceramics are commonly understood to be all industrially used
materials that are inorganic, nonmetallic solids. Usually they are metal
oxides (that is, compounds of metallic elements and oxygen), but many
ceramics (especially advanced ceramics) are compounds of metallic elements
and carbon, nitrogen, or sulfur."
There's tungsten carbide for you: a metal (tungsten) compounded with carbon.
It's hard, it's brittle, it's refractory, and it doesn't even melt like a
metal. That's a ceramic. The bonding of W and C fit well within the more
technical chemical definitions, which allow for both ionic and covalent
bonds, plus various combinations thereof.
WC is a particular type of ceramic: an interstitial carbide. Here's
"Interstitial carbides are derived primarily from relatively large
transition metals acting as a host lattice and the small carbon atoms
occupying interstices of the close-packed metal atoms...Several have
industrial importance, including tungsten carbide (WC) and tantalum carbide
(TaC), which are used as high-speed cutting tools because of their extreme
hardness and chemical inertness."
Now for some background on the confusing, often contradictory uses of the
Back in the 1920s, some Germans came up with a way to make tools out of this
hard stuff by mixing some WC powder and some cobalt powder, and then
pressing and sintering them together into a composite material. It was NOT a
compound. The carbide particles remained distinct in the composite. It was
something like concrete in that regard.
At about the same time, Philip McKenna (Kennametal) was experimenting with
WC for cutting tools, too, trying to make them out of solid WC. You do this
by taking straight WC powder and pressing it, and then sintering it at
extremely high temperatures. I think WC sinters at around 4700 deg. F. Very
difficult, and quite expensive (what do you make the pressing tools out of,
for example?). He made the WC into billets and then sliced them into cutting
tools with diamond saws.
McKenna had some success but the result was too brittle and too expensive.
It *was* capable of handling higher temperatures than the German stuff, and
it was harder. But it was a no-go commercially. (Aside: the US Army is
making big pieces of solid tungsten carbide again, much like McKenna's
billets he made in the 1920s. Only the Army is using it for artillery
So McKenna reverted to the German method, and these carbide/cobalt (and
sometimes nickel) composites became available around the world, and were
commonly called "cemented carbides." The cement, also known as the matrix,
is the cobalt.
First terminology problem: People got sloppy and started dropping the
"cemented" part of "cemented carbide." It was just "carbide," or "tungsten
carbide." Only it wasn't, really. It was some tungsten carbide mixed with
some metal and sintered into a composite material.
Second terminology problem: Metallurgists are more contrary than chemists,
and they sometimes call tungsten carbide "metallike," or even a "metal."
Chemists object. Metallurgists don't care. Machinists wind up confused. It's
metallike, only it allows almost no slippage of crystals along slip planes:
it has virtually no ductility, in other words. It behaves like a ceramic. It
fits the definitions of ceramics that chemists and other scientists use.
Metallurgists still don't care. They have their own little world.
Third terminology problem: As newer ceramics came into play in the emerging
world of "hard materials," they, too, got mixed with metal binders or
matrices to form composites, and were given the name "cermets." Snappy,
descriptive, and neat. However, somebody forgot about
tungsten-carbide/cobalt composites. They're cermets, too. Marketing people
in the cutting tool business didn't care. They had a snappy new name to
apply to their new products, and they weren't going to let lowly old
tungsten carbide horn in on the action. Machinists wind up confused. Tool
companies don't care.
So, does that help? There are no WC tools on the market that I know of.
They're all cemented, metal-matrix composites made of ceramic WC, refractory
metals, and sometimes odds and ends of other metals and ceramic compounds. A
pure mass of WC is a pretty rare thing, and is not used for cutting tools
today. It never was, except for some experiments.
'Sorry for the length. I didn't have time to write it shorter. <g>
Excellent dissertation and very helpful. Thank you.
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
I'm not at all sure why women like men. We're argumentative, childish,
unsociable and extremely unappealing naked. I'm quite grateful they do though.
I am going to delete some of your material here in the interest of
length. Your discussion covers most of the vagueness of the term
"ceramic" and I doubt if we would have any disagreement if we had the
opportunity to spend a couple hours in a face to face discussion of
I am a research chemist and spent the first 15 years of my career in
the metallurgy research laboratory of a large corporation. What the
hell it was the General Electric Research Laboratory. The second 18
years I was at the same facility and although still dealing with the
metallurgists and ceramists I also had to contend with a bunch of
organic chemists. Ceramics was my second major in a PH.D. program at
the University of Illinois.
We probably made more cemented carbides than any other company and at
the time I started we were in the midst of developing the production
of synthetic diamonds. None of cemented carbide research or the
synthetic diamond research was done in our Ceramics Laboratory.
Yes the term is vague, widely used and widely miss-used. The following
information on ceramics is blatantly copied in part from the
"Encyclopedia of Chemistry" edited by G.L.Clark a well-known chemist
and one of my U of I professors. Parts of the stuff below was authored
by A.I. Andrews head of the Ceramics Department at the U of I and one
of my committee members.
**An all-embracing definition is rather difficult because it includes
what appears by a cursory examination to cover widely diverse areas. A
recent committee of the American Ceramic Society defined ceramics to
include those industries which manufacture products by the action of
heat on raw materials, most of which are of an earthy nature, in which
the chemical element silicon together with its oxide and complex
compounds known as silicates occupy a predominant position.
They go on to say "It is much easier to understand the scope of the
ceramic industry by a consideration of specific products. It may be
divided into seven major areas:"
For brevity's sake the areas are listed here by title only without
expansion...Structural clay products, Whitewares, All varieties of
glass products, Porcelain enamel products, Refractories, Cemented
materials such as Portland cement, & Abrasive materials such as
alumina, silicon carbide. ***
Now I can see a quick Ah Hah from Ed but would hasten to point out
that although cemented WC certainly fits in some of those categories
it is not specifically mentioned in the definitions. In addition
Cermets, Refractorys, & Abrasives are covered separately in the
My problem with calling WC a ceramic probably comes from the viewpoint
of a chemist tainted by a long association with a bevy of ceramists
and metallurgists. Here is my reservation in a nutshell...Would one
call the following compounds ceramics: iron carbide, aluminum carbide,
iron oxide, calcium oxide, calcium carbide, silicon dioxide,
molybdenum sulfide, etc. If it is a single compound I would be very
hesitant to call it a ceramic. So by my definition one needs two or
more compounds along with some interaction so as to not have a simple
mixture to get a ceramic. WC (to me) is a chemical compound (it is a
carbide) as is e.g. SiO2 an oxide and not a ceramic. Quartz might give
me some hemming and hawing as one could consider it a glass which sort
of puts it in the ceramic category.
Cemented carbides fall very nicely into the category of "Cermets"
which is from my point of view a better and more descriptive and well
If the question had been "cemented WC" I probably wouldn't have made
the same comment but when the topic was WC it created all sorts of
misgivings to let that go by as a ceramic. Actually I am crotchety
enough in my old age so I still consider cemented carbides as cermets
not ceramics but how one classifies them probably depends a great deal
on one's background.
To repeat... Ed's excellent dissertation is deleted for brevity. It
certainly exhibits why there are differences of opinions even by those
actively working in the field which I haven't done for almost 18 years
No need to apologize. Your points are well taken,interesting, &
Both great dissertations. Thanks for another interesting discussion.
Tim (TOP-posting for brevity)
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms
However -- *why* did you quote the whole thing yet again? You
did not need to quote it all -- it was all out there in the newsgroup
still, and any *reasonable* newsreader could have followed a link back
from your article.
Instead, you quoted 143 lines, with no need at all. That does
not qualify as "brevity" in my book.
*This* is why people object to top posting. Once someone does
that, they seem to feel no need to trim excess quoted material.
If you *must* top-post -- *please* trim most of the quoted
Email: < email@example.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
You'll note, however, that handbook descriptions of ceramics sometimes note
that diamond technically falls within their definitions of "ceramics." It's
not included in the common explanations because of convention, not because
of some technical exclusion.
In the US, it's conventional to include only compounds among the ceramics.
In Europe, that's not necessarily so. Again, it's more a matter of technical
However, that's just industry convention and internal definitions. For
example, WC is listed as a ceramic in the NIST ceramics database.
Again, conventions, not technical exclusions. For example, your "single
compound" [I assume you mean "two-component" compound] definition runs into
a big problem with the fact that the overwhelming volume of engineering
ceramics (sometimes called "technical ceramics," especially in Europe) is
two-component compounds: silicon nitride; silicon carbide; aluminum oxide;
and zirconium oxide. Together, that group is the one usually called the
conventional "engineering ceramics" in engineering.
The definitional problem you're raising is similar to the one that those
engineers who got together in 1993, as I mentioned, were facing. The newest,
highest-performing engineering ceramics are mostly complex compounds.
They're used primarily in electronics and in aerospace. However,
two-component ceramics are the dominant ones in industry, and no one that I
know of would reject, say, silicon nitride or zirconium oxide as major
As for iron carbide, iron oxide, etc.: iron carbide most definitely is
considered a ceramic carbide in engineering. Iron carbide, along with
chromium carbide and vanadium carbide (the dominant one in terms of
performance) are the ceramic carbides that make up a percentage of the
better high-speed steels. In the very high-performance HSS, such as CPM Rex
121, they make up over 30% of the total mix, and they're very important to
the materials' properties.
Iron oxide is one that tests the definitions. Red rust (Fe2O3) meets some
peoples' definitions but not others'. It would be interesting to see what
its properties were if it were compacted and sintered. Black rust, on the
other hand (Fe3O4), the tenacious stuff that often tends to hang on when we
strip red rust off of steel with phosphoric acid, is sometimes called the
"ceramic form" of iron oxide. Now, since you're a chemist, I should say that
I'm aware there are two different forms of Fe3O4, and that only one of them
meets this definition (magnetite). But the point is that some iron oxides
exhibit ceramic properties, and are justly called "ceramic" by the common
Cemented carbides, definitely. But "cermet" is a marketing term, not a
You're right, they definitely are cermets, or metal-matrix ceramic/metal
composites, if you want to get precise. They most definitely are NOT
ceramics! They CONTAIN ceramics, in a mechanical mixture of metal and
ceramic powders that is sintered into a solid mass. Their properties fall
somewhere between the properties of ceramics and metals. But that's due to
the mechanical mixture, and their properties adhere to the law of mixtures,
as it's known in materials science.
But "carbide" tools, or "WC" tools, are neither carbides, nor tungsten
carbide, nor ceramics.
Let's make sure we're clear on this: WC is a ceramic. Tools are not made of
pure WC, any more than a "fiberglass" Corvette body is made of pure glass.
Cemented carbides are metal-matrix composites that *contain* WC. I hope we
have agreement at least on the point that "carbide" tools are not ceramics.
They're mixtures of ceramics and metal(s).
I'm sure your definitions are considered the more useful ones in the
technical end of your former business, Don. That's perhaps a good chemist's
definition. But it is a minority position within industry. The mainstream
definition *within engineering* doesn't think much of including hardened
lime putty among ceramics, but the people who make decorative ceramics, and
who call themselves ceramicists, probably would disagree. The word
"ceramics" comes from the Greek word for "potter's clay." A lot of different
people, in diverse arts and industries, believe their definition is the
correct one. <g>
But within mechanical engineering and the closely related arms of materials
science, tungsten carbide, silicon carbide, tantalum carbide, vanadium
carbide, aluminum oxide, etc. are all mainstream engineering ceramics.
It *is* a matter of definition. But consider the relevant issues in
mechanical engineering, or most other aspects of engineering: these
materials are all hard as hell; they non-ductile; they're highly refractory;
they're compounds of metals (iron, aluminum tungsten) or metalloids (boron,
silicon) and non-metals (oxygen, carbon, nitrogen, etc.); and they're
generally quite inert. Those are the properties
that are relevant, and they're the ones that fit the mainstream, engineering
definition of ceramics -- including tungsten carbide. The fact that some
include these materials in their definitions of ceramics and others do not
is a matter of convention and tradition more than of some chemical
definition. And that's true because there is no precise chemical definition
of a ceramic.
(remove "3" from email address for email reply)
This portion of your excellent discussion is what does it for me,
the fact that cemented carbides are composed to some large degree
of cobalt metal means that I would tend to shy away from the
'ceramic' label. Though I have to agree that the issue is a
confusing one - here the thing's name really depends on who
is doing the describing: physicist, ceramist, chemist, machinist,
================================================= please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
So would I. Cemented carbide cutting tools are NOT ceramics. They *contain*
ceramics, especially WC and TaC.
That was my main point. <g>
Another good point. Note Don's hesitations, based on the definitions he
accepts as a chemist.
The problem is, chemists don't have a hold on the definitions. They have
never bothered to make a precise, technical definition of ceramics, because
it's not really a technical term.
Engineers of advanced ceramics have created a definition for their own use,
back in 1993, as I mentioned. But they freely acknowledge that the
definition is only for their purposes, to help avoid confusion within their
own field. They're not trying to convince the world that they have the
Actually the cobalt content of cemented tungsten carbide is small
compared to the WC and other carbides. The reason cobalt is used is
that it wets the surface of WC and doesn't run wild dissolving the
carbide. Nickel or iron or a lot of other elements would be cheaper.
How you label these materials certainly will depend on your
background. I thought Ed and I might agree but it ain't gonna happen.
That makes no difference because we are both correct in the
environment in which we work.
Oh, I don't think we disagree, Don. I'm just being contrary. <g>
In trying to clarify something like this it's often more important to
identify the points of disagreement than those of agreement. I don't write
to explain things to people like you, who know more about the chemistry of
it than I'll ever know. I write to make as clear as I can the things that
are relevant and distinctive to the machinists and people with an
applications-engineering interest in materials.
So don't think we really disagree. My point there was that your
understanding of ceramics is based on a chemist's needs and understanding,
which is at the opposite pole from a ceramicist's needs and understanding.
People who do metalworking with these materials are somewhere in the middle
of those two extremes.
Tungsten carbide is a misunderstood material, lost in jargon and convention
within the metalworking trades. I've tried to deal with that and explain it
to a magazine audience for roughly 30 years, although not quite in the terms
we've been using here. Having your POV on it is extremely helpful -- for the
contrasts more than the similarities, actually. One could make a case that
it's a lack of confrontation between the different views on this subject
that have helped to muddy the waters over the last 80 years.
Now, if we had a potter here on the NG, we'd really be able to put some
perspective on it. <g>
Or maybe the guy we heard about who was supposedly caught stealing ceramic
tool bits back when they were still quite a new thing. Supposedly when
they checked his house, they found that he'd tiled his bathroom floor with
them. Probably an urban myth, but quite a story, especially when they
used to cost about 10X what they do today.
Delete 1 from address - munged to avoid spam and worse
On 6 Feb 2004 17:29:55 -0800, firstname.lastname@example.org
Just put it in the "FM" category.
"To be civilized is to restrain the ability to commit mayhem.
To be incapable of committing mayhem is not the mark of the civilized,
merely the domesticated." - Trefor Thomas
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