Although the element we call Titanium was first discovered by Reverend William Gregor in 1790, in England, we use the name which was coined by the German chemist Martin Heinrich Klaproth, who independently discovered the element five years later. This is fortunate for many reasons, not the least of which is that Gregor's name of choice was “Manacannite,” which is, to say the least, not nearly as cool as “Titanium”. I mean, seriously, imagine posting a WTB for a “Ma-PD-S”. Just doesn't have the same ring to it as “Ti-PD-S” does it? Obviously, everyone else back in the day felt the same, as the name “titanium” was adopted despite the credit for the first discovery of the element justly being given to Rev. Gregor.
But it's also fortunate because it is so apropos. The actual metal wasn't isolated and purified from one of its ores until 1910 by Matthew Hunter, so there was no way that Klaproth could have known how appropriate his name actually was, but, honestly, if you had to imagine a metal of the Gods, a metal fit for the Titans of Greek mythology, in your wildest dreams you would probably not come up with a list of attributes that would be much more amazing than the actual attributes of titanium and its alloys. No other metal can boast the combination of attributes (or even a fraction of them) that titanium has. Titanium is:
At 4.54 g/cc titanium is only 56 percent the density of steel, and only 68 percent more dense than aluminum. Few metals are lighter than titanium. And yet it is also very strong:
Only the so-called “superalloys” of steel have greater ultimate yield strength than the titanium alloys but this comes at the price of significantly greater weight. When strength-to-weight ratio is considered, nothing beats any of the titanium alloys, which have the highest strength-to-weight ratio of any of todays structural metals. Moreover, titanium has also what is sometimes termed “toughness”. It resists stress-reversal fracturing and the consequent development of brittleness under repeated stresses and impacts. This is why it is the metal of choice for use in such components as the landing struts of Navy aircraft fighter jets, which get slammed down into the deck upon every landing. Part of titanium's toughness and durability comes from it's flexibility:
Titanium has a “stiffness” (modulus of elasticity) which is about half that of steel and yet it will retain it's shape over a larger percentage of its stress range than many other metals. In other words, where other metals would undergo permanent deformation, titanium will spring back. This, combined with its lower stiffness, is part of what makes it so tough and durable. If you remember that stupid child's story about the oak tree and the reed and the wind coming and, oh look, the reed bends but the oak tree doesn't, and, haha, the oak tree gets broken and falls but the reed is still alive. Yeah. That one. You can tell I like that story, can't you? I mean, seriously, who would want to be a reed when you could be an oak tree? The oak tree lives for like a hundred years and the reed only lives one. The oak tree is up high, in the air and the sun light, and reaches deep into the mysteries of the rich moist earth. The reed is a surficial thing, neither high, nor deep. The oak tree provides acorns--food and shelter. It's a majestic thing. Nothing against the reed, but, whoop-de-do! So the reed survives a rare storm and the oak does not? So what? The oak tree couldn't have all its other properties if it were as flexible as the reed. It's a small price to pay!
But I digress. Or actually, I don't, because if you remember that story, then, actually, titanium IS that impossible combination: the strength of the oak and the flexibility of the reed both! As I said, metal of the Gods.
I might as well have put corrosion “IMMUNE”, because there is very, very little that will corrode titanium. Or rather, I should say, there is very, very little that will corrode titanium-dioxide, since bare titanium itself is actually very reactive, and achieves its corrosion resistance by forming an oxide layer in air almost instantaneously, and it is this oxide layer which protects the rest of the bulk metal. This oxide layer is so corrosion resistant, that even after 4000 years submerged in the ocean, the sea water would still have only affected the metal to a thickness of a sheet of paper. It resists corrosion from most oxidizing acids, from all body fluids and substances, from fruit and vegetable juices, and from most other organic compounds. Only Fluorine ions will cause significant local corrosion to titanium.
Titanium is also very high on the Galvanic Series. i.e. it is a very noble metal, and will not suffer galvanic erosion in an electrolyte (such as sea water).
However, when heated to very high temperatures in air, titanium will burn away before melting (this is part of the reason why it took so long to be extracted from its ores). However, that said, it's important to note that titanium (and especially titanium alloys) retains its strength to much higher temperatures than most other metals:
As Don's Trial by fire: Haiku from the ashes thread can attest, titanium can take quite a lot of heat! An aluminum light in a house fire would probably have deformed, and would certainly have had its chem-coted interior ruined, if not its anodizing. The Haiku, on the other hand, was only in need of a bit of mild cleaning with soap and water and a scrub pad. The o-ring channels, the threads, the body, everything was pretty much structurally untouched by the house fire, not to mention the battery exploding inside of it! Titanium retains its strength at temperatures where many other metals become weak. This is yet another reason, above and beyond its high strength-to-weight ratio and corrosion resistance, that titanium alloys are often the metals of choice for use in jet engine turbine parts (although, at this point, superalloys of steel with nickel have the highest operating temperatures and strengths of any metals yet devised.)
Despite its high strength, titanium is non-magnetic and that can be a decided advantage in many situations.
Titanium conducts both heat and electricity relatively well. It's a metal, after all! And all metals are good conductors of heat and electricity compared to materials classed as semi-conductors or insulators. So, while it's true that among metals, titanium is a relatively "poor" conductor, and that it's easy, looking at tables of conductivity, to think that titanium is "awful" or "horrible" as a conductor, it's also equally true and quite a bit more relevant that for many purposes, including for flashlights, that any metal, including titanium, will conduct both heat and electricity more than well enough, and that its resistance is negligible compared to all the other resistances involved! Obviously, you wouldn't use titanium for house wiring, nor for the fins of a baseboard heating unit, but where other factors dictate its use, such as in heat-exchangers in a nuclear power plant, or in a flashlight body, the metal can acquit itself well enough in terms of both heat and charge conduction, as long as the demands placed upon it aren't too severe. For a detailed analysis of the electrical and thermal performance of titanium in flashlights, please see my LunaSol 20 thread, or posts #75 through #82 in this thread.
In other contexts, however, such as in a machining cutting or drilling operation, where there is greater heat buildup in a smaller area over a shorter time span, the relatively poor conductivity of titanium compared to other metals shows up quite clearly. See below.
No other metal comes close to being as inert and biocompatible as titanium. Certain grades of stainless steel are acceptable substitutes where cost prohibits the use of titanium, but titanium is clearly the best. It is hypoallergenic and inert in the human body and will not cause any kind of reaction or rejection, nor will it corrode or erode, and bone is happy to grow around and fuse with titanium. It is the only truly biogenic metal. Hence its use in dental implants, joint replacements, and so on. But it is also used for these same reasons in jewelry by people who have reactions to other common jewelry materials.
Unlike aluminum which expands like crazy when heated, titanium does not. It has a fairly low coefficient of thermal expansion which makes it attractive for use in combination with ceramics, glass (e.g. flashlight lenses), and other composites.
Amenable to Decorative Treatments
Titanium can easily be anodized by flame or by soaking in an acidic solution with an applied, and spectacular patterns and colors can be achieved as a result. (One example would be ukmidnite's anodised McGizmo clips). The colors generated from the anodization layer are due to constructive and destructive interference between the light reflected from the top surface of the oxide layer, and the next layer down, and this can actually be tuned with voltage, and all of this is possible because the oxide layer is clear with a high index of refraction. See below.
Titanium can also be beadblasted in varying shades of light to dark-gray.
And titanium can also have very tough scratch-resistant coatings applied to it, such as TiN, AlTIN, and diamond coatings. To this end titanium is often used to make machining tips.
Yeah. Really. Titanium is the ninth most abundant element in the earth's crust. It's high price comes not from its rarity, but from the difficulty of extracting it from its ores, i.e. from its compounds.
THE OXIDE FILM OF THE METAL OF THE GODS
But this consideration forces me to back up a bit and talk about the oxide film that develops on titanium. Again, it's just frigging ridiculous how amazing this metal is! I mean, as if all the previous attributes weren't enough, it's like the gods sitting around in round table throwing out ideas were like, yeah, but, really, that's just not enough. We want this metal to have a really great oxide. We want the tarnish itself to be godlike. And it is! Why? Well, because it is:
Titanium dioxide has wonderful optical properties, and in its form and structure as the very thin protective layer around the pure bulk titanium of a titanium metal part it is clear with a very high index of refraction. It's part of why titanium is so lustrous and beautiful. In other metals, they are lustrous and beautiful when they are NOT tarnished, after you clean and polish them, or just after the object has been minted (hence the expression “mint” in reference to the highest possible grade of coin condition). As most metal objects sit around in air and moisture, they tarnish, and look anything other than “mint”. Not so with titanium. When someone buys one of Don's lights and puts it safely away, untouched in a drawer and then decides to sell it five years later, it comes out of the drawer looking every bit as beautiful and perfect as it did when it went in. The oxide layer starts out at about 2 or 3 nanometers thick and grows only very, very slowly. And even as the layer slowly and incrementally increases in thickness, it does not reduce the luster or beauty of the object one bit! I carried my LunaSol 20 almost every single day for four years and it is no less beautiful and lustrous as my brand new Haiku. In some ways, it even looks prettier. It's very subtle, but it seems to me to be “whiter” or brighter, somehow (possibly this is just due to the smoothing out of machining grooves, though). It certainly has many many fine scratches on it (but no deep or gross scratches), but with titanium, this does not make the surface look dull or less beautiful. It just gives it a patina; it just gives it character. I wish I could say the same for my platinum ring, which after 13 years just looks scratched up. I recently decided that I had waited more than long enough and that if the thing didn't have the nice “platinum gray” patina by now, it never would have it. So it's at the jewelers being polished even as I write this. This is another part of the reason why titanium is seeing more and more use as jewelry! But I digress . . .
Yes, the OXIDE itself is in fact conductive. Bulk titanium dioxide powder, pressed into a rod and sintered is actually conductive. It is considered a semiconductor, since its conductivity is much lower than that of metals, but is still far from being an insulator. This might sound a bit unimpressive, except when you consider that the oxides of many metals are outright insulators. The oxide of aluminum, for example, is one of the best insulators known to exist! However, metals with insulating oxide layers will still conduct in macroscopic metal to metal contact joints because the surfaces are not perfectly flat at an atomic level, and so, microscopically, the oxide layers are punctured through in many places and the conduction happens in these metal to metal “bridges”. Moreover, if the layer is thin (20 nm average thickness or less) then conduction will happen due to the tunneling effect at voltages greater than 30 mV even without metal bridges. Greater pressure will create more actual metal-to-metal contact and thus lower resistance. This is why contact resistance is always a function of pressure.
But, it gets better! Bulk titanium dioxide is one thing, but the oxide film on our beloved titanium gadgets actually has a very low resistivity for metal to metal contact joints! Even without metal to metal bridges or tunneling it passes current through the junction quite well, thank you very much! There is no oxide layer that will form on one of Don's titanium flashlights to increase contact resistance in the circuit path because the oxide layer IS already conductive. And its already there.
And . . . yes, it gets better still! The oxide film will conduct nicely in metal-to-metal contact joints but it will NOT conduct into electrolyte solutions, or not at all well at any rate. In other words, it will not conduct into sea water, for example. Poseidon clearly put in a few requests for the characteristics of this metal in the design phase! I mean, seriously! I ask you, how much better could it really get?
Yeah. Titanium just feels really, really, REALLY good. Part of this, at least for me, is the density--more dense than aluminum, less dense than steel--it seems to hit the sweet spot. It's got heft and substance, but it doesn't feel dense and overly heavy for its size. Another part of this incredible tactile experience is the heat conductivity, and again, it's in a sweet spot--significantly more heat conductive than plastic, but less conductive than bare aluminum. When you pick up a titanium light, cool or warm, it feels good. It just feels good.
But, part of this is also because the oxide film has a nice tactile feel. This is not usually the case, to say the least! Tarnished silver is no longer smooth feeling, and it's obviously not shiny and beautiful to the eye. Bare aluminum sitting in the open air is not only dull and lacking luster, it is also not the best feeling thing to handle. Not so titanium. No, its oxide layer looks AND feels great!
SO IT'S GOOD IN FLASHLIGHTS?
So, yes, by now I hope I have answered the obvious question “why the hell use this stuff in a flashlight?” Because, clearly we don't need incredible strength, nor high temperature resistance, nor many of the other of titanium's properties. However, what we do need is a durable, long-lasting, ever-beautiful, maintenance-free, great feeling and performing flashlight body and head. Titanium gives us all that and more. I don't think people realize just how many issues can arise electrically with aluminum to aluminum joints. It's why the Arc AAA experienced the so-called "crimp ring problem": the current path went from the aluminum body, through aluminum threads, into the head, and then through an aluminum to aluminum contact joint with the light engine. And well, aluminum to aluminum joints are just plain prone to developing high contact resistance. And this is exactly what happened to many Arc AAA's, mine included. My titanium Sapphire GS, on the other hand, will have no such issues! And since a titanium body flashlight is one thing, through and through, you can, if you desire, smooth out and polish away any unsightly damage. As I posted in my LunaSol 20 review, you can take a light that looks like this:
and with some time and a bit of elbow grease, make it look like this:
There's no anodizing to chip off and there's no chem-cote interior to harm. It is one thing, through and through. A titanium flashlight is forever. You can carry it day in and day out, drop it, damage it, and it will still look great, or can be made to look great again with a little bit of elbow grease.
WHY IS IT SO EXPENSIVE?
I've heard people say before to me that the notion that titanium is somehow difficult to machine is a myth, that it's just not true, that it's not much harder to machine than steel. I wondered about this at the time it was said to me, but having no information to contradict it, I kept my silence and made a mental note to look into it at some point. Well, I have, and I can tell you in no uncertain terms that titanium is significantly more difficult to machine than steel, and WAY more difficult to machine than aluminum. Here are relevant excerpts from Titanium: A Technical Guide, by Matthew J. Donachie:
http://www.candlepowerforums.com/vb/images/misc/quote-left.png) 0% 50% no-repeat transparent;"> When machining conditions are selected properly for a specific alloy composition and processing sequence, reasonable production rates of machining for titanium and its alloys can be achieved at acceptable cost levels. Table 10.1 shows machinability comparisons of several titanium alloys with other materials (higher numbers indicate improved/lower-cost machin-ability). Success in machining titanium depends largely on overcoming several of its inherent properties, which are described in the following sections.
Heat Conduction. Titanium is a poor conductor of heat. Heat, generated by the cutting action, does not dissipate quickly. Therefore, most of the heat is concentrated on the cutting edge and the tool face. Tool life is adversely affected.
Alloying Tendency. Titanium has a strong alloying tendency, or chemical reactivity, with materials in the cutting tools at tool operating temperatures. This causes welding to the tool during the machining operation and consequent galling, smearing, and chipping of the machined surface, along with rapid destruction of the cutting tool.
Elastic Modulus. Titanium has a lower elastic modulus than steel and superalloys and thus has more "springiness" than these metals. The result is greater deflections of a workpiece. Proper backup may be required to improve stiffness. Rigidity of the entire system is consequently very important, as is the use of sharp, properly shaped cutting tools. Greater clearances of cutting tools are also required due to these deflections.
Surface Damage Susceptibility. Titanium and its alloys are susceptible to surface damage during machining operations; this is particularly true during grinding. Titanium alloys are less forgiving of surface defects in fatigue-limited operations than are some metals. Care must be exercised to avoid the loss of surface integrity, especially during grinding, because even properly conducted grinding operations can result in surfaces that appreciably lower fatigue life. Maintaining a sharp tool during machining is very critical to optimize fatigue life in titanium.
Work Hardening Characteristics. The work hardening characteristics of titanium are such that its alloys demonstrate a complete absence of "built-up edge." The lack of a built-up edge ahead of the cutting tool causes changes that result in an increase in heat on a very localized portion of the cutting tool. High bearing forces are also produced, and the combination of heat and force results in rapid tool breakdown.
So, 300/18 is 16.667. Ti-6-4 is nearly 17 times more expensive to machine into a given part than aluminum is! And this is on top of the already increased expense of the initial material cost itself.