Sintered Metals & Ceramics: Possibly In Spyderco's Future?

[JD Spydo]

During my machine tool days I did a little studying on "SINTERED" metals and materials. Tungsten Carbide is what immediately comes to mind when I think of SINTERED materials. I'm sure that just like the super progress that ceramics has made in the world of abrasives>> and not to mention knife blades as well. I would be willing to bet that we might just see Sintered materials play a role in knife production down the road and have properties that would supersede the materials we currently use.

If Tungsten Carbide can hold together like it does then why couldn't a Sintered material be used as a space age knife blade? Or do any of you know about current studies or advances in Sintered materials.

I sure hope Cliff Stamp chimes in on this one or any of our other metallurgy savvy Forum Brothers who could shed some light on the subject.

Or even if there might be any super advances in ceramics we could talk about that also >> that is dealing with possible knife blades of the future.

Maybe even the General himself i.e. Sal Glesser might have something to let us in on pertaining to this subject>> I hope.

[Wanimator]

Have fun sharpening tungsten carbides.

[Blerv]

Insane wear resistance is possible with the ceramics of today. Unfortunately that's just part of what makes a good knife.

On paper something like obsidian is vastly superior to ancient bronze and irons. Problem was it had problems from durability to sharpening that made metals a welcome change.

[Wanimator]

^ I agree with Blerv.

[Hopsbreath]

Have fun sharpening tungsten carbides.

That was my first thought too. Drill bits and a wedding ring are my only experience with tungsten, but in those examples they just do not show wear...ever. Under no circumstance would I be interested in trying to sharpen a tungsten blade.

[Cliff Stamp]

Before you jump into ceramics and solid carbide blades there are a few options in what are only loosely steels :

-121REX
-MaxaMet

These are two steels which are capable of a working hardness of 70+ HRC with extreme carbide volumes and severe resistance to abrasive wear. However they are still steels and can still be worked with regular stones. I zero ground a 121-REX knife from Farid with a basic waterstone (700X Bester), mainly out of curiosity. These are among the strongest and most wear resistant steels available. They are not solid carbide, but they are much closer to it than something like S30V.

However, and this is where it gets a little interesting, even among the people who most strongly promote high carbide steels, most will back off from those materials in regards to advocating they are some kind of superior material. The carbide volume is so high that the ability to hold a high sharpness edge is fairly reduced. But if you are looking a holding a low sharpness for an extremely long time they are some fairly interesting choices. I am still trying to figure how how to sharpen them to optimize the performance but they can do some interesting things.

For example, take a S30V knife blade (or whatever you want) and draw it, edge down, along a sharpening stone - what happens? If you look at the edge now you will see it reflect light. Do that with a 70+ HRC 121 REX blade and very little happens, it is extremely resistant to being ground or impacted. A piece of solid carbide, or solid sintered ceramic takes this one step further.

In regards to grinding solid carbide or ceramic, diamond abrasives will cut them readily. The guy who sells Trend abrasives on YT always takes out carbide tools and shows how easy they grind on diamond abrasives. Diamond is as hard compared to carbide tools as they are to warm butter. The main issue in sharpening them is that they won't form that kind of fatigued burr that is popular in sharpening and the edge is much more likely to fracture than deform.

However, as an aside, from wading into the technical, you can buy a ceramic knife now for about $5. They may not come with a great sharpness, the edge angle may be too high, but diamond plates are now pretty cheap and ultra-fine pastes are common. There is no issue in sharpening them, people have got them face shaving sharp - again, you just can't rely on burr formation.

As another aside, something else you might want to look at at UHC steels in the ~67 HRC range. These are very low alloy (aside from carbon) steels which are capable of very high hardness and thus offer extreme resistance to deformation/rolling, but can still be ground on conventional abrasives, can be burr sharpened and can take a variety of finishes and are much tougher than the extreme steels like 121REX. There are also super alloys which use cobalt vs iron as the matrix to hold a huge volume of carbides and there are odd things like FerroTi which has a massive amount of Titanium Carbide (up to 45%), is again ~70 HRC, and uses steel just as the binder.

With all of these you start off by asking a simple question :

-what kind of performance do I want to increase in the knife

and from there you look what material and processing can improve it.

I have a friend who has a ceramic knife I gave him years ago. He loves it. He has never sharpened it and uses it all the time to cut up vegetables. I don't think he will ever sharpen it. It can't rust. It is very light. It isn't what I would call sharp, but tolerances for that differ wildly.

[JD Spydo]

Extremely interesting and enlightening Cliff. That puts a lot of perspective to what I was wanting to find out. So no matter how far up the ladder you go and with all new technologies aside there is always going to be trade-offs>> I hope I'm putting that across right.

With all the new "nanotech" research that has already come up with unbelievable lubricants and other marvels that makes our life easier. I'm still thinking that new metallurgical advances and new ceramics for all kinds of uses; I'm more than sure those technologies will be used in metals and ceramics soon if not already to some degree. I'm also more than sure we'll be seeing something down the road dealing with cutlery and other tool applications as far as advanced corrosion protection for instance.

One other sidebar are the extremely hard coatings that many of the knife companies have experimented with. Titanium Nitride, Boron Carbide and several other coatings you see on many machine tool end mills and other cutting tools. I'm sure that "coatings" will also be playing more of role in cutlery as well. Many metal coatings we see that knife industries have used up till now are somewhat merely aesthetic but some coatings actually have the ability to be used as a sharp cutting surface like the one that Buck did with their models 119 fixed blade and 110 folders a few years back>> the problem they had was that they couldn't get their end users to only sharpen one side. Just some thoughts as to where all of this might be going.

[Wanimator]

I have heard of Ceramic/steel combinations. But they were much to brittle for cutlery use, from what I've gathered and read.

[Cliff Stamp]

Titanium Nitride, Boron Carbide and several other coatings you see on many machine tool end mills and other cutting tools.

There has been more developed interest in this lately with use of titanium blades which are carbidized. They are pretty interesting in that the titanium will wear much faster than the solid line of carbide and thus as long as the cutting is on soft material (ropes, cardboard, etc.) you don't need to sharpen them at all, they will essentially cut forever. Now to be clear the sharpness isn't going to impress you if you are the type of person who uses a Sharpmaker when the knife doesn't shave, but for a lot of people who are just looking at having a knife that doesn't skid and is used to cut very harsh materials they are very attractive.

On the extreme end you can get diamond coatings on blades as well, these are much more wear resistant than the nitride coatings but there isn't any argument or data to show they would be of benefit on a blade over the standard carbide/nitride coatings. They are used in industry though, often they are used to actually coat carbide cutting tools. There are also solid diamond blades, but they are very thin and normally used to cut materials under very tight controls because they are made to optomize cutting ability and thus they are very thin and the apex is very narrow and the sharpness is an order of magnitude beyond steel.

In some cases we have to also step back and realize that the unknown is fairly difficult to predict. Just imagine talking to someone of last generation about sharpening when all they had seen was a benchstone and imagining all of what we have now with v-rods, jig based systems, and sharpening stones of all types of abrasives/bonds. There was a time, not very long ago when people would describe even S30V as being so difficult to grind/finish it was impossible to sharpen - but yet we now commonly work with steels which are much harder to grind/finish.

The abrasive technology development is huge because of the impact of better abrasives. Norton's development of SG abrasives to create an alumina based abrasive that actually sharpens itself as you use it to cut steel is the kind of thing that no one could imagine. The next step up in the TG wheels which allow an extremely high abrasive density combined with a very high bond strength (these are usually opposite) because of the shape of the abrasive (its like a bunch of worms vs cubes) produces some extremely high performance grinding tools :

-http://www.thegrindingdoc.com/files/cer ... wheels.pdf

At some stage we can maybe speculate, for example what would happen if we had a "smart" abrasive which could adjust its bond strength based on the load. Most of us have used stones at one point or another that are too hard or too soft. This is because the bond strength is adjusted for very high or low pressure applications accordingly. If for example you have a stone which works very well under the extreme pressure that is produced from putting a micro-bevel on a paring chisel, then it is going to be far too hard to use on the back of the same chisel.

After experimenting with stones a little, most people will have a collection of soft stones for when large contact areas are being used (because this means the pressure is very low) and then hard stones for when the contact area is small (as the pressure is very high then). In fact there are even companies that sell stones which are hard on one side and soft on the other with the same abrasive. This solution is however a bit awkward because different steels will need more/less pressure to cut as well and if you have a range of pressures you can end up with quite a range of stones.

For example, with the same 1 lbs load, this is the contact pressure produced :

-small detailed chisel / notching tool : > 100 psi

-narrow bevel on a knife : < 25 psi

-wide edge bevel on a knife : < 5 psi

-back of a plane : < 0.25 psi

If you have to work all of these tools, it isn't unreasonable that you might have a stone which works very well on each and has that nice gradual breakdown which is just strong enough to prevent excessive abrasive wear. If you try to use a stone which works well on the back of a plane it is likely to gouge insanely easy if you use it on the notching tool. Similar if you try a stone which works well on the notching tool it will likely be far too hard to cut well trying to flatten the back of a plane.

But imagine a stone which has a "smart" bond and it is able to respond to the pressure and just release fresh abrasive but not wear extensively. If this sounds crazy, well that is only because we can't think on how to do it yet. There are lots of smart materials which do similar things, there are ceramics for example which actually change their internal structure to absorb loads to keep them from fracturing. Who knows what we will have in the future - science can do wild and crazy things.

[SolidState]

Spyderco already uses sintered materials heavily. They have been doing it for years. If you're wondering if I have any knowledge in this arena - I worked for five years as a ceramics chemist who sintered powders for a living.

FWIW, any powder heated until it sticks together without properly melting is technically sintered. The sintering process happens at temperatures just below the melting point to lower the total surface energy of the material - large surface area = large surface energy. Sintering lowerers the surface energy, and products like ceramics are often sintered because their melting points make making a melt too costly or problematic for combining the elements in the desired fashion (keeping crystallites intact) and attaining the final desired structure.

To this end, virtually all of the CPM lines are sintered powders. Further the MIM process uses sintering so the handles on the original spyderflies and the Bi-fold are both sintered.

The short answer is that Spyderco has been doing this for years, and that powdered metallurgy allows for the refined grain structure by controlling the powder size going into the sintering operation. You should see the Hot Isostatic Presses (HIP) that Crucible uses. They are awesome!

[tvenuto]

Yea but are they "SINTERED"?

[JD Spydo]

Spyderco already uses sintered materials heavily. They have been doing it for years. If you're wondering if I have any knowledge in this arena - I worked for five years as a ceramics chemist who sintered powders for a living.

FWIW, any powder heated until it sticks together without properly melting is technically sintered. The sintering process happens at temperatures just below the melting point to lower the total surface energy of the material - large surface area = large surface energy. Sintering lowerers the surface energy, and products like ceramics are often sintered because their melting points make making a melt too costly or problematic for combining the elements in the desired fashion

To this end, virtually all of the CPM lines are sintered powders. Further the MIM process uses sintering so the handles on the original spyderflies and the Bi-fold are both sintered.

The short answer is that Spyderco has been doing this for years, and that powdered metallurgy allows for the refined grain structure by controlling the powder size going into the sintering operation. You should see the Hot Isostatic Presses (HIP) that Crucible uses. They are awesome!

Hey thanks for chiming in with that great up to date info "Solidstate">> And Cliff thank you as usual for your great input as well. Both you guys made some points I would like a little more clearity on if we can?

First of all CLIFF? You talked about a certain stone being soft on one side but yet hard on the other while being made of virtually the same material>> I'm not at all trying to say anything out of context but that's the way I understood it. For instance on my TORMEK unit ( low Speed Grinding Wheel used wet) has an abrasive stick that can change the properties of the grinding stone from coarse to fine by simply dressing the grinding stone on one side or the other of this abrasive stick. I've often wondered how that actually works>> but it indeed does. And I'm wondering if there are grinding stones that are actually Sintered?

And SOLIDSTATE? >> Glad you chimed in being you actually work in this arena and you've already given us some great input and easily understood as well. You stated that a Sintered material is a bonding process that takes place just short of actual melting temperatures>> I hope I understood you correct. With that being said I'm wondering what the main advantages are rather than just simply melting the materials anyway? I'm thinking that Sintering has superior properties in many respects?

[RadioactiveSpyder]

And diamond rods would still work just fine for sharpening, being the hardest natural substance known to man and all! .

Interesting thread and great contribution SolidState! Cheers, Radioactive :)

[JD Spydo]

And diamond rods would still work just fine for sharpening, being the hardest natural substance known to man and all! .

Interesting thread and great contribution SolidState! Cheers, Radioactive :)

You are right on both points RadioActiveSpyder This is developing into a very informative and enlightening thread. It's really cool that we have several IN HOUSE experts that chime in with timely, relative information in easy to understand format too.

I've heard that "Cubic Boron Nitride" is not too far from diamond on the Moh's Hardness Scale for what that's worth. But I don't know if it's got the right properties for a cutting edge. I have heard that it's abrasive properties are great and I'm looking forward to adding those CBN stones to my Sharpmaker kit.

And we can certainly talk about abrasives pertaining to the subject matter.

[SolidState]

And SOLIDSTATE? >> Glad you chimed in being you actually work in this arena and you've already given us some great input and easily understood as well. You stated that a Sintered material is a bonding process that takes place just short of actual melting temperatures>> I hope I understood you correct. With that being said I'm wondering what the main advantages are rather than just simply melting the materials anyway? I'm thinking that Sintering has superior properties in many respects?

Yeah, my name is Solidstate because I'm a solid-state chemist. You understood exactly correctly. Melting a material is shaking the atoms enough that they easily move around each other. Upon cooling, they tend to find optimal positions - we call this relaxing. If you reach temperatures just below the melting point, the atoms are still moving around a lot, but they will try to move to lower-energy positions. Sometimes, these lower-energy positions are between two larger particles (when I say large here, I mean multiple nano to micrometers). That will cause the particles to stick together and be sintered.

In the case of ceramics, sintering can often be achieved hundreds of degrees lower than the melting point. This can save ceramics companies a lot of money on energy for furnaces. Further, in ceramics, binders are often used to sinter powders at even lower temperatures than the pure ceramic will use. For example, I used to make new ceramic electronic materials from magnesium, zinc, tin and aluminum oxides. For me to make a melt, it would require over 1200 C, but a dense, sintered ceramic disc could be achieved at 900 Celsius. Often, I would find myself using a Hot Isostatic Press (HIP) to reach temperatures over 1000 Celsius and pressures of 20,000 atmospheres. That's about 300,000 PSI. The pressure is to force the particles together, and the heat is to get them sticky.

Often, when you melt things down, you will end up with the ability to make alloys and also large crystals, or simply dissolve elements into a molten liquid of metal. Sintering allows you to maintain small particle integrity and achieve a macroscale object (ceramic disc or knife blade) that has macroscopic integrity and near-ideal density. In the case of steel, people want certain optimal sizes of carbide particles for grain structure and wear resistance. Allowing for a melt may degrade the particles or cause them to grow larger than optimal for the application. Sintering allows you to stick the particles together without blending them or significantly changing their size. It gives you a lot of control of the microstructure of the steel, which is the magic to gaining macroscale properties. The control is easily lost to nature if you just let molten steel cool.

Ironically enough, Spyderco also plays with steel in which you let it cool from molten and let large crystallites grow. This is how they get the dendritic structures in the Serrata. One of the main reasons I love Spyderco is that they're at the top of the field in using modern solid-state chemistry and metallurgy, the other is that they're on top of the field in ergos too.

[Bill1170]

Hey Solidstate,

Since PM steels are sintered, do you know of any experiments being done with mixed powders? For example, if one were to to mix powdered alloys of two different compositions to obtain a combination of their properties in the resulting billet? I have no idea if this would work, and would like to hear your thoughts.

[3rdGenRigger]

My understanding is that the molten mix that's forced at high pressure through ceramic nozzles to create the powdered billets is already mixed...I could be wrong however and would love to know more about the process.

[Bill1170]

My understanding is that the molten mix that's forced at high pressure through ceramic nozzles to create the powdered billets is already mixed...I could be wrong however and would love to know more about the process.

Yes, the alloying elements in the molten mix are all melted together, and freezing them in small particles helps reduce segregation because it is fast freezing and because the particle size enforces an upper limit on the carbide size. My speculation is different than that, however.

Suppose you took powdered S90V and blended it with powdered M390? Each particle would contain only its own alloy, but the overall ingot would exhibit properties different from those of the two constituent alloys. What would occur at the boundaries of the different powder particles? I really don't know. It is just a thought exercise for now.

[3rdGenRigger]

I'll contemplate that with great interest.

[JD Spydo]

My understanding is that the molten mix that's forced at high pressure through ceramic nozzles to create the powdered billets is already mixed...I could be wrong however and would love to know more about the process.

Yes, the alloying elements in the molten mix are all melted together, and freezing them in small particles helps reduce segregation because it is fast freezing and because the particle size enforces an upper limit on the carbide size. My speculation is different than that, however.

Suppose you took powdered S90V and blended it with powdered M390? Each particle would contain only its own alloy, but the overall ingot would exhibit properties different from those of the two constituent alloys. What would occur at the boundaries of the different powder particles? I really don't know. It is just a thought exercise for now.

That is incredibly interesting "Bill1170">> it truly makes me want to go back to college and take another metallurgy class. I took a 101 course but this is all above and beyond that and it give me encouragement as to what great blades we'll have to look forward to down the SpyderRoad.

But I'm in no way ignoring what could be done in the ceramics world either. Just what has been done in the abrasives arena has taken many of us by leaps and bounds in the past 20 years or so. And it's kind of like what Cliff told us about in one of his previous posts talking about how abrasives and sharpening equipment has advanced exponentially in just a short time slot. It's truly mind bending trying to take in all the advances in technology in these areas of science. I think in most of our lifetimes we might even see abrasives that would make diamond not so important.