Titanium Armor in Detail
Background and Development of the Mantis Titanium Armor Plate.
The first titanium alloys — including the famous Ti6Al4V, which now accounts for more than 50% of total titanium production — were developed in the USA in the late 40s. Shortly after their development, a military assessment noted that these new alloys showed promise at defeating small arms projectiles. Despite numerous subsequent investigations, experiments, and studies over the 1950s and 60s — which included the development of extremely strong titanium alloys — titanium body armor was issued to US or NATO soldiers only once: River boat crews in Vietnam were issued a light titanium-nylon flak jacket, which was not intended to stop high-velocity projectiles. This was little more than a slightly lighter derivative of WWII’s steel-nylon aircrew flak jacket, and very few units were produced.
Resurgence in the US as an armor material:
Over the ten-year period from roughly 1996-2006, titanium enjoyed a small resurgence in the US as an armor material: Several private US companies examined monolithic titanium body armor plates on a prototype or experimental basis, the Army Research Labs investigated hot pressing titanium metal powders in 2005, and the very first versions of DragonSkin’s namesake armor vest made use of titanium-ceramic composite armor tiles. Ultimately, none of these efforts met with much success. (Though it bears noting that later versions of DragonSkin did not use titanium, and that an improved version of ceramic DragonSkin has recently been re-launched by Stealth Armor Systems.)
The extensive use of titanium as a body armor material by the Soviets.
The Soviets, in contrast to the Americans, made extensive use of titanium as a body armor material. In 1979, shortly after the initiation of the Soviet-Afghan war, the 6B2 armor vest was issued to troops on the ground in Afghanistan. The 6B2 consisted of an array of titanium alloy plates, each just 1.25mm thick, bonded to 30 layers of twill-weave aramid. The shell was made of nylon, with Velcro fasteners — and it’s worth noting that Velcro was a very new material at the time, so its appearance on Soviet vests led to speculation as to the vest’s origins. Total system weight was 4.8kgs, including front and back portions. Protection from shrapnel and low-velocity rounds was deemed adequate, but the 6B2 was completely incapable of stopping high-velocity aimed projectiles. In fact, it reportedly could not stop 7.62x39mm rounds fired from distances of 300-500 meters. The 6B2 was therefore much like the Vietnam-era flak jacket in many respects, even in appearance, but markedly heavier.
6B3TM Armor Vest
The 6B2 was quickly replaced in service by the 6B3TM, a still heavier version, where the thickness of the titanium plates was increased to 6.5mm. This change increased the weight of the vest to 12kg. It was then changed again, in the 6B3TM01, to a version with front plates which were 6.5mm thick, and rear plates which were 1.25mm thick.  This final version was roughly 9kg in total weight. Having said all of that, it is exceedingly unlikely that 6.5mm-thick plates of titanium would stop 7.62x39mm or 5.56x45mm rounds at anywhere near muzzle velocity — but they would have done the job at engagement distances of 200-500+ meters.
6B4 Armor Vest
In 1985, midway through the war, the 6B4 was introduced. This was an armor vest made of boron carbide and aramid, similar to those issued to certain soldiers in Vietnam, doubtless of much greater protective ability than the titanium armor vests which preceded it. Ceramic strike faces feature heavily in subsequent models of Soviet and Russian armor — though, until quite recently, body armor in Russia often comprised titanium and steel portions. This appears to have been eschewed entirely in recent years; the most advanced Russian model at present, the 6B46 “Granite 5a” armor plate, appears to be made entirely of silicon carbide over aramid.
Mechanical and Ballistic Properties of Selected Titanium Alloys used in Modern Armor Systems:
Ti6Al4V is an alpha-beta titanium alloy comprised of 90% Ti, 6% Al, and 4% V. It has a density of 4.43g/cm3, a hardness of 334HB, a yield strength of 880MPa, tensile strength of 950MPa, charpy impact at 17 J, and elongation at 14% in 2″. It has a shear strength of just 550MPa.
Russian “armor-grade” titanium is a beta-titanium alloy comprised of 3% Al, 5.15% V, 3.65% Cr, with trace amounts of boron, zirconium, and molybdenum. It has a hardness of 387HB, and a density of 4.62 g/cm3. Its other properties are unknown, but it is not unreasonable to assume that it possesses greater yield strength and tensile strength than Ti6Al4V, an inferior charpy impact strength, and inferior elongation.
Adjusted for weight, the US Army Research labs have determined that the ballistic performance of Ti6Al4V is superior by roughly 7% to that of the aforementioned Russian alloy. Adjusted for weight, I repeat. As Ti6Al4V is about 5% lighter, what this means is that the two alloys perform nearly identically at equivalent thicknesses. The differences in mechanical properties are apparently not of great importance; the lighter alloy performs better largely on account of its lightness.
It needs to be said that the Russian alloy was tested by US Military research labs, who are not exactly a neutral and unbiased third-party in this matter, nor were the alloys tested against every projectile — they were tested only against steel FSPs. It could well be that Russian side-by-side experiments have their alloy outperforming Ti-6-4 when testing against a qualitatively different threat, e.g. lead-core ball projectiles.
Adiabatic shear plugging
In any case, it’s clear that both titanium alloys possess a great strength-to-density ratio, and both are comparable in hardness to rolled homogenous armor (RHA) steel. What is not made clear from a cursory glance at those mechanical properties is titanium’s propensity to fail via plugging, which markedly reduces its utility as a standalone armor material. When a titanium alloy plate is struck by a high velocity projectile, shear strain, strain rate, and temperature can rise to very high values over a very small surface area. Titanium’s relatively poor shear strength, combined with its very poor heat transfer properties, make it inherently susceptible to fail catastrophically in such situations via a phenomenon known as adiabatic shear plugging. This problem becomes almost insurmountable when titanium alloy armors are used at low thicknesses — thicknesses typical of body armor!
Almost insurmountable, but not totally insurmountable.
The Development of High-Performance Titanium Body Armor Systems:
Plugging and discing can occur when any ductile material is struck at a high velocity and rapidly deforms. When the material is unable to dissipate the heat generated by the impact and by very rapid deformation, the region around the impact site will exhibit local thermal softening and rapid crack formation. When thermal softening outpaces the strain-hardening effect, you get a transition from ductile to brittle behavior, and this typically results in the ejection of a disc or plug of material from the target. This is a fast process, which happens within microseconds of the initial impact. What it looks like is illustrated in the image below:
Where (a) is a plugging, (c) is discing, and (b) is a brittle fracture mode common to high-strength/low-ductility beta-titanium alloys, which is very much reminiscent of the fracture conoid in ceramic materials.
Because of their susceptibility to plugging and discing, thin plates (< 1”) of titanium armor generally perform substantially worse than an equal weight of armor steel. Thick plates of titanium armor alloys are, however, far less susceptible to shear failure, and are much superior to RHA in vehicular armor applications. (But as they’re also much more expensive, they are used only in extremely rare and unusual cases.)
This raises a fairly obvious question: “Is it possible to design a titanium alloy with better thermal properties?” The disappointing answer to this question is no. Although it’s trivially easy to make a pure metal stronger or tougher via alloying strategies, it’s extremely difficult to improve that metal’s thermal properties or its stiffness. A metal’s thermal response — much like its stiffness — depends almost entirely on its chemical nature. As a general rule, these properties can’t be improved by tinkering with alloying elements. In fact, it’s possible to go a step further and posit another general rule: When it comes to thermal conductivity, alloys are almost universally inferior to the pure metals they’re derived from.
This all means that it’s quite a challenge to use titanium in body armor applications — or in any high-impact application where a low plate thickness is called for.
But, again, it was not an insurmountable challenge. We have devoted a lot of time and effort to the problem, and we have cracked it.
The solution involved accepting the plug as a momentum-capture mechanism: If we can’t prevent adiabatic shear failure, we can work with it and turn it to our advantage. Because the plug typically has a substantially larger diameter than the projectile, and because it’s ejected from the plate at a much lower velocity than the projectile, it can reliably be caught by a relatively thin UHMWPE plate backer.
This is how the Mantis Titanium armor plate was born, and is illustrated in the image below:
So now we have a plate which features, among other things, a titanium alloy strike-face and a UHMWPE composite backer.
When stuck by a sufficiently potent rifle round, (1) the incoming projectile will be disrupted on the strike face, (2) a disc or plug with a higher diameter and lower velocity than the projectile will be ejected from that titanium strike face, and (3) the UHMWPE backer will catch the plug or disc without undue difficulty. In short, the system functions as an elegant momentum trap.
In testing, it has stopped all RF2-style threats, including M80 Ball at 2800 fps, M855 at over 3100 fps, and .22-250 at 4330 fps.
This represents an entirely new type of armor plate.
Though it shares certain performance and design characteristics with ceramic armor plates, it’s also obviously different in many respects. The Mantis titanium armor plate is optimized for ruggedness and reliability. The strike-face doesn’t crack or shatter upon impact; instead, ballistic damage is highly localized. The titanium strike-face isn’t ruined upon impact from low-velocity frag or pistol rounds up to .44 Magnum; at worst, it’s marked, but not fractured. And, much unlike ceramic plates, there should be absolutely no concerns about durability in harsh conditions or if handled roughly.
And although its durability and multi-hit performance bring steel armor plates to mind, the Mantis titanium armor plate has a vastly better performance-to-weight ratio, it’s not especially vulnerable to M193 (or similar rounds) at any reasonable velocity, and there is no bullet frag or “spall” problem — because, as with a ceramic plate, the threat is stopped inside the plate rather than on its surface.
This plate offers the best of both worlds:
In many respects, as the product description page covers in more detail, this plate offers the best of both worlds: The reliable multi-hit performance and toughness of steel body armor, with the performance-to-weight characteristics of ceramic armor.
The alloy used in the Mantis Titanium Armor Plate is a grade with moderately high static hardness but exceptional toughness, ductility, and dynamic performance at high strain rates We have found that this translates to optimal performance against rifle ball rounds, including steel-core ball rounds like M855. We are experimenting with higher-hardness alloys for Level IV protection, and anticipate that a titanium-faced Level IV plate will be released eventually — though it will be substantially heavier than the plate we have available now, which we believe represents an ideal balance of performance, cost, and weight.