# Exotic body materials questions



## TigerhawkT3 (Sep 2, 2008)

I'm getting tired of seeing dents in flashlight bodies after a 2-3ft drop, even in 1AA lights with relatively little inertia. I was Googling for properties of other materials to see what came up. I was looking for strength, abrasion resistance, and thermal conductivity (for use with LEDs). Tungsten might be nice, if a little heavy, but info on the various alloys was too scattered for me to get a good grip on them. Tungsten carbide sounded good at first, but it's very brittle, so although it would be extremely scratch-resistant, a simple impact could chip it. Steels are strong and abrasion resistant, although not very good thermal conductors. Still, more mass and surface area might be able to offset that. I was looking into the various steel alloys, and I was really impressed by the D2 tool steel that's so popular in knife blades. Extremely strong, scratch-resistant, doesn't chip, all that jazz. The thing is, I don't know how practical it would be to work with. I know that Ti is a headache, and D2 is harder (AFAIK, which isn't very far  ). However, it's available in round rod, rectangle, etc., so it's presumably machinable by something.

BTW, D2 is around $35/foot in 5/8" round rod (onlinemetals.com). That sounds much cheaper than Ti or tungsten, which is a good thing in my book.

So, in a nutshell, D2 sounds like a pretty neat material for light bodies (except for the thermal management part - maybe the material surrounding the LE could be something softer but more conductive), but I've never seen it used. Can someone tell me why that is, so I can forget about it and move on?


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## DaFABRICATA (Sep 2, 2008)

Its hard to machine.
Tungsten is brittle.


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## AMRaider (Sep 2, 2008)

D2 is great for knives, but it is not as corrosion resistant compared to a lot of stainless steels. If it were to be used in a flashlight, I would advise to keep it away from water, especially salt water. There would be no question though.. your D2 flashlight would certainly "hold an edge"!

As for tungsten.. pure tungsten is more ductile than tungsten with impurities. I wouldn't worry about a tungsten flashlight cracking or breaking if it were made with relatively pure tungsten. The only problem is that your light would be extremely heavy for it's size since tungsten is so dense. Compared to aluminum, tungsten is about 7 times denser. My aluminum Arc6 is just over 2oz. If it were made of tungsten, it would weigh close to a pound. Not exactly pocket friendly hehe.


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## snarfer (Sep 2, 2008)

I was thinking about this too. It occurred to me that maybe it is not a matter of one single material, but a way of constructing that uses multiple materials together in order to have some desired properties. Here is an example of a Nokia phone concept that uses aluminum, rubber and plastic. 

I thought this was appropriate because a phone is one of those items that gets rough treatment similar to a flashlight. So you can see that first of all Nokia uses a corrugated aluminum, which would be light, have good heat conduction properties, and also have extra surface area for heat dissipation by virtue of the corrugations. Then it is paired with some durable plastic, which provides dent resistance and other desirable properties. 

I think the plastic really helps a lot with dent resistance actually. I remember seeing some documentation for a PVC honeycomb material used for boat building and other types of construction. Aluminum sheet laminated onto the PVC honeycomb was much more durable and resistant to denting than would be expected.


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## PhotonFanatic (Sep 2, 2008)

Tool steel is used to make tools, which means it is externally machined with diamond wheels. While one might be able to bore out tool steel, it would require some unusual tooling, or the use of EDM.

Seems to me that using something like 316SS, which is highly corrosion resistant, but combining it with a copper converter module makes more sense if one wants a durable, but still thermally efficient, flashlight. Still wouldn't be all that lightweight, however.

I am investigating using 6AL4V Ti and then having it Tungsten Carbide coated, then ground to a high polish. That would give a very strong shell for a light and then I would use the copper module for heat transfer.


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## Anglepoise (Sep 2, 2008)

Don't give up on Ti as a possibility. As long as it is left in a natural state,( no bead blasting etc ) it is tough and stainless and most importantly can be made to look like new again ( scratch removal) with a simple 5 minute rub using a Scotchbrite pad. Any type of steel will add considerably to the final weight, something you do not want.
Although thought of as a fad by some, Ti really has allot going for it as a flashlight material.


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## Rothrandir (Sep 2, 2008)

I cut tool steels fairly frequently on my lathe, they are hardened afterwards. They're honestly quite easy to work with.


I would not want to use it for a flashlight though...


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## StarHalo (Sep 2, 2008)

Titanium alloy body with Tungsten Carbide coat :thumbsup:

Now all we need is a thousand dollars to build it..


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## precisionworks (Sep 2, 2008)

"Tool steel" is a generic name for a broad family of high carbon ferrous materials. It includes A1 (air hardening, 100 carbon points), O1 (oil hardening, 100 carbon points), W1 (water hardening, 100 carbon points), etc. D2 is another member of the family, used where toughness, abrasion resistance (from the chromium content) and high Rockwell hardness are important. Cost of D2 Drill Rod (solid round section) is about 1/3 that of Ti64 solid rod in the same diameter.

D2 can be made many times harder than Ti64, *but it will rust overnight*.Ti64, as well as Commercially Pure Ti, are currently the best overall choice for lights (as well as knife handles, surgical screws/implants, aerospace parts, etc.) It isn't the hardest material in the world, but hardness is always in inverse proportion to toughness. It reacts with almost nothing, and is essentially rustproof as judged by a 240 hour salt water spray test ... not much that will withstand ten days of constant salt water spray. D2, in contrast, would have a nice brown rust coating after ten minutes:shakehead


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## LukeA (Sep 2, 2008)

precisionworks said:


> t reacts with almost nothing, and is essentially rustproof as judged by a 240 hour salt water spray test ... not much that will withstand ten days of constant salt water spray. D2, in contrast, would have a nice brown rust coating after ten minutes:shakehead



I think you mean 'corrosion resistant' instead of 'rustproof'. Titanium has no iron in it, and hence can't form iron oxide in the presence of oxygen.


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## KC2IXE (Sep 3, 2008)

Hey, how about inconel  ( as anyone who has had to machine the stuff shudders at the thought )

Hastaloy?


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## TigerhawkT3 (Sep 3, 2008)

Wow - I had no idea D2 was so vulnerable to corrosion. :huh: How is it protected in tools, knives, etc. - coated with something, I guess? What about the actual cutting edge? It just seems like it would defeat the purpose of having something very scratch-resistant and then coating it with some other material. One of the things I like about bare metal is that if it does get scratched, it doesn't contrast too much with the surrounding material and it can be sanded/buffed out.

KC2IXE, those are some cool alloys! Following links on Wikipedia, I arrived at Stellite. It's very difficult to machine, but looks like an ideal coating material. Wikipedia says it was used to line M60 barrels, but it doesn't specify whether it's the outside or the bore (or both). Stellite.com has a variety of lining services available, and it looks like they can handle complex areas (like for threads and such).

Mildly off-topic, I have this premonition that one day, we'll see some celebrity with an LED flashlight with a solid diamond heatsink... gem-quality, of course. :laughing: How's that for exotic?


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## precisionworks (Sep 3, 2008)

Bob Dozier was IIRC the first custom knife maker to use D2 on a large scale. D2 remains a popular material for custom knives, as well as some factory knives - but all makers caution that the blade needs to be wiped with an oily cloth after each use.

D2 is a "cold work" tool steel (as opposed to hot work). Cold work refers to any forming process that uses no heat, such as deep drawing and forming dies for sheet metal, cold drawing punches, hobbing and lamination dies, stamping dies, blanking dies, punches and shear blades, burnishing rolls, cold extrusion dies, slitting cutters, thread rolling and wire drawing dies, etc. In many of these uses, a lubricant is misted onto the metal being formed - some of that rubs off on the D2 die/punch/roll/slitter, and provides a degree of corrosion protection.

Until the invention of "rustless steel" in 1913, and going back to 1000 years BC, every iron or steel tool would rust - that was considered part & parcel of the package. Now everyone wants something tough, lighter than steel, and corrosion proof. Which is one reason that Ti is the material of choice in high end lights.


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## snarfer (Sep 4, 2008)

Actually use of diamond is not far-fetched at all. I saw a document from a Taiwanese company describing use of diamond film as integrated heat spreader within LED package.


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## Marduke (Sep 4, 2008)

KC2IXE said:


> Hey, how about inconel  ( as anyone who has had to machine the stuff shudders at the thought )
> 
> Hastaloy?



Or Haynes 230 :naughty:

I still want to try AL 2195, it would be a little bit lighter, but I'm not sure how well it would take a hardcoat


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## monkeyboy (Sep 4, 2008)

What about S30V? It's supposed to be similar to D2 but more corrosion resistant.


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