Ceramic harder than carbide?

P

Papa P

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May 13, 2016
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Is ceramic harder than carbide? Carbide edge blades usually have a hardness of 72 RC.
 
Generally speaking, yes. Ceramic rods and slabs are commonly used to sharpen blades.
 
Ceramic is harder, but more brittle. In my experience, ceramic blades lose their edge fairly quickly when subjected to light/medium use.
 
Depends on the type of ceramic and the type of carbide. There are some carbides that are harder than several type of ceramic, like Tungsten or Vanadium carbide, which are both very hard.

There are some types of ceramic that are harder than either of those though from what I know. "ceramic" is more a term describing the method of making something and its structure than an actual specific substance, like how "steel" is a broad concept/category for all of the different formulas as well.
 
The definitions of ceramics have changed greatly since early days. "carbides" such as tungsten carbides are made with tungsten carbide particles 'glued 'together with cobalt .Depending on type they vary with percentage of cobalt and size of carbides . Ceramics are sometimes "sintered " heated to bond the particles without a secondary 'glue'.
 
Charr said:
Depends on the type of ceramic and the type of carbide. There are some carbides that are harder than several type of ceramic, like Tungsten or Vanadium carbide, which are both very hard.

There are some types of ceramic that are harder than either of those though from what I know. "ceramic" is more a term describing the method of making something and its structure than an actual specific substance, like how "steel" is a broad concept/category for all of the different formulas as well.
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Absolutely correct!

Ceramic and carbide are very similar in the fact they are both sintered materials, just the base and binder are different, depending on their application or use.

As for hardness, tungsten carbide is measured in the Vickers scale, well beyond the range of the Rockwell C scale. If carbide is around 2,600 Vickers HV, think of it as roughly equivalent to 120Rc on the Rockwell scale. Good stuff.... I'm not positive which would be ultimately "harder", although my guess would be a ceramic - but it would be very brittle.
 
mete said:
The definitions of ceramics have changed greatly since early days. "carbides" such as tungsten carbides are made with tungsten carbide particles 'glued 'together with cobalt .Depending on type they vary with percentage of cobalt and size of carbides . Ceramics are sometimes "sintered " heated to bond the particles without a secondary 'glue'.
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You can also sinter some carbides, though Tungsten carbide has such a ridiculously high melting point (it doesn't technically melt, it usually just turns to gas), that you can only sinter it under very special conditions and it will usually only be possible in small amounts.

Generally, though, you are right. Most "Carbide" tools are made using Cobalt or a similar metal as the matrix with the carbide suspended in it.
 
Kyocera's website lists their ceramic blade (zirconium oxide) hardness to be 8.2 mohs. Not sure what that equates to in HRC.

I'm not sure where you got the HRC 72 though. Look at http://www.bladeforums.com/forums/s...based-on-Edge-Retention-cutting-5-8-quot-rope

The highest measured HRC is 65 for ZDP-189. Even Phil Wilson's custom knives are on the ragged edge of HRC 65 range. And he's perhaps the best, most at the extreme with heat treatment in the industry.
 
dsmegst said:
Kyocera's website lists their ceramic blade (zirconium oxide) hardness to be 8.2 mohs. Not sure what that equates to in HRC.

I'm not sure where you got the HRC 72 though. Look at http://www.bladeforums.com/forums/s...based-on-Edge-Retention-cutting-5-8-quot-rope

The highest measured HRC is 65 for ZDP-189. Even Phil Wilson's custom knives are on the ragged edge of HRC 65 range. And he's perhaps the best, most at the extreme with heat treatment in the industry.
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There are some steels that can reach as high as 72Rc, but they are never really taken to that, since they will have very little maintainable toughness and will be very brittle at that point.
CPM REX-121 is one the steels that can reach that high. It can max out between 70-72. For reference, the HRC scale only officially goes up to 70, but you can calculate beyond the boundary of the scale as well.

Most people would never want to make a blade out of a steel that was much higher than 65Rc at all. Rockstead will occasionally make ones that are up to 67-68 though.
 
I got the 72 RC from multiple custom knife makers who use the process of carbidizing, adhearing the carbide (tungsten or titanium) to one side of the edge of a blade. And Rex 121 is the only steel I have seen used to make a knife that goes beyond 70 RC.
 
Papa P said:
Does anyone know a Rockwell value that could be attributed to ceramics?
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Hi Papa P,

The alumina ceramic that we use for sharpening material is 9.2 on the Moh's scale. Technically a synthetic sapphire.

sal
 
I had to refresh my memory . Kyocera white blades are Zirconia .Their black blades are also zirconia but go through an extra process , Hot -Isostatic -Pressing ,making a stronger blade . Zirconia is very hard and wear resistant

Some of the "powder metal" steel blades also are made with HIP .
 
onespdfrk said:
Absolutely correct!

Ceramic and carbide are very similar in the fact they are both sintered materials, just the base and binder are different, depending on their application or use.

As for hardness, tungsten carbide is measured in the Vickers scale, well beyond the range of the Rockwell C scale. If carbide is around 2,600 Vickers HV, think of it as roughly equivalent to 120Rc on the Rockwell scale. Good stuff.... I'm not positive which would be ultimately "harder", although my guess would be a ceramic - but it would be very brittle.
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I'm pretty sure you can't have any material with higher HRC over 100 unless you have some fictional material like organic adamantium which harder and can bounce back the diamond indenter...
 
We made a knife about 20 years ago with magnesium scales and a HIP'ed Kyocera blade. Designed and made by Tak Fukuta. We made 500 pieces. I got some feedback that the ceramic blade was popular for chopping cocaine on a mirror. :rolleyes: Hard to find one these days.

sal
 
Papa P said:
I got the 72 RC from multiple custom knife makers who use the process of carbidizing, adhearing the carbide (tungsten or titanium) to one side of the edge of a blade. And Rex 121 is the only steel I have seen used to make a knife that goes beyond 70 RC.
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It's interesting to see what custom makers can do beyond "normal" production. I guess that's really akin to industrial diamond tipped bits and so forth. In my mind, that doesn't fit into what I would consider a steel blade though as they sound more like a coating. So normal sharpening would more likely pull the carbides off rather than sharpening them?
 
dsmegst said:
It's interesting to see what custom makers can do beyond "normal" production. I guess that's really akin to industrial diamond tipped bits and so forth. In my mind, that doesn't fit into what I would consider a steel blade though as they sound more like a coating. So normal sharpening would more likely pull the carbides off rather than sharpening them?
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That's pretty much how it works, but usually you sharpen the titanium side as well, allowing new carbides to take up the cutting edge.
The old carbides will likely already be largely stripped out because of the wear from use. That's what makes the blade dull over time.

I like carbide-titanium blades, but they aren't good for everything. They have good attributes and bad just like every other type of blade honestly.
 
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