Coating AR parts

K

kouma

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Hello all,

I thought I would share this with you. I have been reading about people coating their critical AR parts with one of these popular coatings: Titanium Nitride (TiN), Titanium/Aluminum Nitride (TiAlN), and Chromium Nitride (CrN). Some of the benefits of such coatings include (http://www.warfrogindustries.com/home.html):

Hardness:
-Harder than carbide.
-Three times harder than hard chrome.
-Extremely strong adhesion.
-Molecular bond to substrate metal
-Performs extremely to prevent scratches

Natural Lubricity:
-Has high lubricity characteristics.
-Smooth operation of moving components.
-Naturally burnish/polishes itself. Basically the more you use it the smoother it gets.
-Low friction coefficient.

Advantages:
-Typically applied at (0.000118")
-Will not affect function in firearms with the highest tolerances.
-Wear resistance on precision components.
-Impervious to cleaning solvents and chemical


Below is a summary of the properties and major differences between each (http://www.acscoating.com/coating-details.aspx):

Titanium Nitride (TiN)
Color: Gold
Nano-hardness: 24
Thickness [um]: 1-7
Friction-(fretting): 0.55

Titanium Aluminium Nitride (TiAIN)
Color: Violet-Black
Nano-hardness: 28
Thickness [um]: 1-4
Friction-(fretting): 0.60

Chrome Nitride (CrN)
Color: Metal-Silver
Nano-hardness: 18
Thickness [um]: 1-7
Friction-(fretting): 0.30

TiN coating can be seen on barrels of high-end racer competition guns like STI DVC and SVI Infinity. TiN is usually the most popular due to its nice golden color. Below are two pictures I took from the Internet that shows TiN coating:

salient_arms_international_tier_one_1.jpg

STIDVC-LTD-lg.jpg


I opted to use TiAIN to preserve the tactical looks of my SIG716 and because it has the highest hardness out of the three, although any of the three are overkill for firearms. Here are the pictures of the results (Any smudges visible are just oil from soaking the parts in Fireclean):


 
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Perhaps some theoretical advantages.
That's assuming perfect surface prep and application/treatment.
At the end of the day, the time and money investment may or may not be worth the gain, perceived of otherwise.
I'd stick with factory standardized coatings. They get the job done, but to each his own.
I'd like to see some scientific real-world testing and comparisons before shelling out dough.
 
I recently got a nickel boron coated BCG, and it's way easier to clean compared to the standard coatings on my Daniel defense and Troy BCG's. And I mean way! Easier.... No scrubbing involved %95 of he carbon wipes right off with a rag

It also operates smoother then the regular coated one it replaced, and there are no wear marks on it like there was on the original one after the same amount of round s through it

For that reason I am also looking into having all my BCG parts coated

Please post where you had the costing done and what the cost was, I am very interested
 
I'm not jumping in the exotic coatings bandwagon myself. They don't make anything last any longer, probably the opposite. They just look nicer. The mil-spec parkerizing works just fine.


When you get into the extremely hard exotic coatings, you are crossing a treshold where you are having a BCG who's surface hardness is high enough to wear through the aluminum oxide (type3 hardcoat anodizing) layer of your upper and wear out anything it makes contact with. That includes your barrel extension.

Aluminium Oxide has a Mohs hardness of 9 in it's pure form (corundum, or Sapphire/Ruby) and Vickers hardness of 1500-1650HV, Titanium Nitride is 2300HV, Titanium Aluminium Nitride is 2800HV and Chromium Nitride is 1750HV.

Combine that to the fact that the aluminium oxide layer of hardcoat anodizing loses over 50% of it's friction resistance when sealed (our receivers are sealed), add the fact that 7075-T6 is a soft material, the fact that a surface coating's hardness is directionally proportional to the hardness of the host material, and you get a recipe for disaster.

Even if you just use a coated barrel in a handgun, the coating is still much harder than your slide and/or frame will ever be, and accelerated wear will occur. What do you think will happen to headspace over time with your coated bolt and uncoated barrel extension lugs?

These coatings are normally used for high speed drill bits and machining equipment for a reason.

A well-designed system uses two materials of similar or exact hardness to prevent wear. I don't care how shiny they got the bolt before coating it, it's a recipe for longterm problems and I'm all for longevity of a weapon system.



I would much rather have a standard, milspec parkerized BCG and as they say, this is a fix to a problem that doesn't exist. I'm steering clear off that ####.
 
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