Rust wars! Blade coatings testing...

aarongough

aarongough

Joined
Mar 12, 2013
Messages
1,167
Hey guys!
I'm shortly about to tackle something I've wanted to do for a while, pitting a bunch of different blade coatings head-to-head to see what the outcomes are, and to decide what my blade coating of choice will be going forward!

I've been talking to different coatings suppliers for a few months, and after much wrangling I got 16 prototype blades coated with 4 different PVD coatings. I also kept aside a few blades that I coated in-house with Cerakote and an uncoated blade for a baseline, which I will be doing up with a 600 grit satin finish before the testing starts.

All blades are made from A2 tool-steel, heat-treated to 62.5HRC.

All blades that are PVD coated were prepped by sanding them to 400 grit, then blasting them with a 50/50 mixture of 120 grit aluminum oxide media and 60-120 mesh glass beads, this leaves a really nice smooth feeling matte texture on the blade, very similar to how the touchpad on a Macbook feels actually. I did half the overall blades with an alternate surface prep of just 120 grit aluminum oxide blasting, but that surface prep is a little too coarse and doesn't feel great to the touch (like fine sandpaper), so I'm excluding it from the test.

The Cerakote blade was prepped using my tried and true method: sanded to 400 grit, blasted with 120 grit aluminum oxide at 90PSI until matte, sprayed with a 19:1 ratio mixture of Graphite Black Cerakote, then baked at 250ºF for 2 hours. This coating has gone out on a lot of knives and has performed very well so far. It will serve as a point of known performance in the test.

My goal with this test is to find something that performs better than Cerakote in every way, if possible. I want it to hold up to heavy use (like splitting wood) better, while also offering longer-lasting corrosion resistance. Cerakote is very, very, corrosion resistant when the coating is new, but once you've put it through heavy use several times the coating is likely scraped away in places and this defeats the corrosion resistance in those areas...

The coatings under test will be:

* A2 Uncoated
* Cerakote (Graphite Black)
* Chromium Nitride monolayer (CrN)
* Tungsten Carbide Carbon monolayer (WCC)
* CrN + WCC dual layer PVD
* CrN + DLC dual layer PVD

Chromium Nitride, WCC and DLC are all coatings that are used commonly in industry. DLC is used commonly on cutting tools, injection molds and so on. WCC is used on sliding parts that have to be run dry, like slides in injection molds. WCC seems to be used less in North America, but more in Europe for some reason.

DLC is a coating that most of us are familiar with and it sets a pretty high bar! The DLC coating that I've had done is a dual layer coating with Chromium Nitride underneath for added corrosion resistance. The DLC came out this time with a little bit of a rainbow sheen to it, but my coating provider has promised me the next batch can be done without that. They will also be doing the next batch with a thicker Chromium Nitride underlayer and a thicker DLC layer, so if the next batch comes from them it should actually outperform the DLC seen in this test!

Chromium Nitride is essentially a very thin layer of Chrome, like you'd see on a car, that is also nitrided which makes it very, very, hard (much harder than the blade steel itself). It has the highest substrate adhesion of any of the coatings, and also excellent corrosion resistance, which is why it's used as an underlayer in a few cases.

I've had a number of customers request a coating that is more 'natural' looking, so I'm looking at offering Chromium Nitride coated blades in addition to whatever black coating I choose, provided that Chromium Nitride performs as hoped.

The test procedure:

I plan to put the blades through a number of stages of testing:

1) Assembly testing (is it possible to assemble the knives using epoxy without marking the finish?)
2) Initial appearance (how much do I like the appearance of the coatings?)
3) Light use testing (how well does the coating hold up to light use like cutting cardboard, woodcarving, etc...)
4) Heavy use testing (how well does the coating hold up to heavy use like batoning firewood, using the windowbreaker, etc...)
5) Corrosion resistance testing (given that the blade has now seen some use, how well does it protect from corrosion?)
6) Abuse testing (how well does it hold up to opening cans and other abuses like that)

I would love your guys input on any additional things you think should be done, and also if you have ideas about the specifics of given tests!

For the corrosion resistance test I was planning to wrap the blades in towels that have been soaked in salt water, then leaving them in a sealed container for a few days, but if you guys have alternate ideas I am open to them!

Without further ado here are some photos of the coatings as they were received from the suppliers, you can click on the images to see the full-res photos:











 
Last edited:
My initial impression is that overall Cerakote still looks the best when it's a fresh coating. It has a really nice even satin black that's pretty hard to beat.

The other coatings are very 'dry' when they come from the suppliers. They're so clean that any fingerprint shows up on them as an oily spot, much like a fresh acid etched finish actually.

To counteract this I have tried lightly oiling them the same way I would with an acid etched finish, and it had a similar effect! The coatings all darkened up significantly. The DLC coating went completely black and now looks every bit as good as the Cerakote finish. The others are still a dark grey rather than fully black which is not ideal...

The chromium nitride is a beautiful satin chrome appearance, I really like it! It doesn't work all that well with my handles that have two colors (black & green for instance) but it looks great with solid colors. I had a number of customers that were after a more 'high visibility' knife for hunting use, so the CrN paired with Blaze Orange handles might be just the ticket for that!

I won't have much opportunity to get started with the testing until sometime late next week because I'm working on machining handle scales, but I figured I would get this thread rolling in advance!

-Aaron
 
This should be interesting and I look forward to the results, but I'm surprised you are testing on machined blades rather than a bunch of much cheaper coupons.
 
You might try industrial hard chrome plating. It will probably hold up as well or better than anything.
 
aarongough said:
I had a number of customers that were after a more 'high visibility' knife for hunting use...
Click to expand...

If that is the case then don't use a black or grey coating on the blade. In the dark it would be much easier to find a reflective steel blade then a black one.

I know you are doing the coating for rust prevention, but even with a coating on the blade the the most important part of the knife, the edge, will be un-coated and will be subjective to rust.

Honestly if you used S35V, CPM154, N690 etc. you would need no coating for protection from rust with a few seconds of wipe down.

I powdercoat and use cerakote on blades and truth be told if they get used the coatings do wear and you have to clean them just a much as if they were bare steel to keep away the corrosion from the edge as well as the areas that are worn.

Coated blades do look good, but those good looks soon fade over time as the coating is scratched and worn and there is nothing the owner can do to fix that other then a complete strip of the blade.

I also find when a blade is coated the owner often does not pay attention to cleaning as well because they believe it is protected from corrosion, then they end up with rusted edges more due to not oiling their blades edges for maintenance.

No matter what coating you use with an A2 blade it will have to be maintained the same coated or not.

With the use of Frog Lube or WD40 Corrosion inhibitor rust really is no longer a worry with my A2 blades.
 
daizee said:
This should be interesting and I look forward to the results, but I'm surprised you are testing on machined blades rather than a bunch of much cheaper coupons.
Click to expand...

These blades are all rejects from my process, something minor is wrong with them that is enough to stop them going out to a customer... It's a good thing though as it lets me test real coatings on real blades in real situations which is nice!
 
Bill DeShivs said:
You might try industrial hard chrome plating. It will probably hold up as well or better than anything.
Click to expand...

Good idea! There's a plating place down the street that I should chat to... my concern with that is that I know it's not the most environmentally friendly process, but I'll go have a look and see what their operation looks like.
 
AVigil said:
If that is the case then don't use a black or grey coating on the blade. In the dark it would be much easier to find a reflective steel blade then a black one.

I know you are doing the coating for rust prevention, but even with a coating on the blade the the most important part of the knife, the edge, will be un-coated and will be subjective to rust.

Honestly if you used S35V, CPM154, N690 etc. you would need no coating for protection from rust with a few seconds of wipe down.

I powdercoat and use cerakote on blades and truth be told if they get used the coatings do wear and you have to clean them just a much as if they were bare steel to keep away the corrosion from the edge as well as the areas that are worn.

Coated blades do look good, but those good looks soon fade over time as the coating is scratched and worn and there is nothing the owner can do to fix that other then a complete strip of the blade.

I also find when a blade is coated the owner often does not pay attention to cleaning as well because they believe it is protected from corrosion, then they end up with rusted edges more due to not oiling their blades edges for maintenance.

No matter what coating you use with an A2 blade it will have to be maintained the same coated or not.

With the use of Frog Lube or WD40 Corrosion inhibitor rust really is no longer a worry with my A2 blades.
Click to expand...

I definitely plan to try out some stainless steels mid next year to see if they can replace A2. CPM154 in particular I have high hopes for as a really nice 'all round' steel, we'll see how the testing goes though.

I have one blade in DLC from another manufacturer which was what prompted this testing, I have batoned with that blade a fair amount and the coating was not affected at all, only thing that touched it in the end was sandpaper! If I can get similar performance from a coating for my blades I would be very happy... I really like the look of coated blades personally. A coating combined with a stainless steel in the future could be pretty amazing! Though I think A2 will be hard to replace in terms of raw toughness and edge retention...
 
I love A2 and use it all the time and it performs well at 60 rc and with cryo. 3V does even better.

Todays high alloy stainless would be considered "magic" if a blade traveled back in time, they are that good. :)
 
AVigil said:
I love A2 and use it all the time and it performs well at 60 rc and with cryo. 3V does even better.

Todays high alloy stainless would be considered "magic" if a blade traveled back in time, they are that good. :)
Click to expand...

Yes I agree that modern powder metal stainlesses are pretty amazing! I have used CPM154 previously on a few test blades and I really liked how it performed!
 
Adding to the salt water towel wrap, I'd be interested to see the blade only partially wrapped. That is, leaving a portion exposed to the salty, humid air in the container.

As AVigil notes, I presume that the sharpened edge will be uncoated. I would be interested to see if any corrosion "creeps" underneath the coated portion, or causes separation of the coating.

Lastly, I'd also be very interested to know about any cost comparisons. It doesn't need to be precise quote, but I have no concept of if these procedures add $10 or $100 to a knife.
 
FunkCoaster said:
Adding to the salt water towel wrap, I'd be interested to see the blade only partially wrapped. That is, leaving a portion exposed to the salty, humid air in the container.

As AVigil notes, I presume that the sharpened edge will be uncoated. I would be interested to see if any corrosion "creeps" underneath the coated portion, or causes separation of the coating.

Lastly, I'd also be very interested to know about any cost comparisons. It doesn't need to be precise quote, but I have no concept of if these procedures add $10 or $100 to a knife.
Click to expand...

I will definitely be interested as well to see if any corrosion creeps under the coating! I haven't seen that at all with Cerakote, but I have no idea if the others will be different.

Leaving a portion of the blade exposed is an interesting idea. I could perhaps leave a portion of the tip exposed while the rest of the blade is wrapped? In that case I would definitely need to heat the container I think... Not sure if that's getting outside the realm of a reasonable test though, I will take feedback on that!

Costs on the PVD coatings vary a bit:

DLC was $30/each for the prototype blades, going down to about $18/each once I'm giving them a batch of 50 or more at a time.

Cerakote cost is a little hard to figure, but doing it yourself requires a fair whack of cash up-front as you need a decent compressor, sandblasting cabinet, HVLP spray gun, and an oven to bake it on. Cost of the paint on a per-knife basis would only be a few dollars, but then the prep time adds a fair bit of labor cost to each. I would say that prepping a knife and spraying it with Cerakote takes me around 45-60 minutes for each knife when I'm working on a batch of 24. That includes all prep steps like sandblasting and so on.

Cost for the WCC/CrN coatings is also a bit hard to determine. That coating provided did not do those coatings on a per-part basis, instead I had to pay for them to run a whole vacuum chamber. Running the vacuum chamber is $600 and I think I can fit about 50 or so knives in the chamber. The dual layer coatings requires payment for two chambers as they run each coating separately. So that one would work out to something like $24 per knife if I was doing 50 knives per chamber.
 
God knows I hate oxidization! Results should be very telling...I'll make a batch of popcorn in anticipation.
 
I should also note that there's still prep time on my end for all the PVD coatings: the blades have to be sanded to 400 grit, then blasted...

Also worth noting that these coatings companies really don't seem to like doing onsie-twosie type stuff. They barely wanted to talk to me even when I was saying 50-100 blades per month!
 
Just include a bottle of Frog Lube with each knife and skip the coating :)

I have been using Frog Lube and WD 40 corrosion rust inhibitor and they both are amazing at keeping corrosion away.

You can basically stop worrying about corrosion with a simple wipe of the blade.
 
AVigil said:
Just include a bottle of Frog Lube with each knife and skip the coating :)

I have been using Frog Lube and WD 40 corrosion rust inhibitor and they both are amazing at keeping corrosion away.

You can basically stop worrying about corrosion with a simple wipe of the blade.
Click to expand...

That approach works for sure! I do like the look of coated blades personally though, we'll see how the testing turns out!
 
This.


AVigil said:
Just include a bottle of Frog Lube with each knife and skip the coating :)

I have been using Frog Lube and WD 40 corrosion rust inhibitor and they both are amazing at keeping corrosion away.

You can basically stop worrying about corrosion with a simple wipe of the blade.
Click to expand...
 
You must log in or register to reply here.
Back
Top