Titanium Armor 2
As just noted in Titanium Armor I, titanium alloys have exceptionally poor thermal properties. This is the primary factor which gives rise to its signature problem in ballistic applications: Adiabatic shear plugging and discing failure. To make matters worse, this characteristic problem is exacerbated when titanium is used in thin plates suitable for body armor.
To put it as simply as possible, plugging and discing 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 that 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 not an insurmountable challenge. We’ve devoted a lot of time and effort to the problem, and we’ve cracked it.
The solution involves a bit of engineering aikido: 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 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 2796 fps and M855 at over 3100 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 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 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.
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.
The Mantis Titanium Armor Plate is the ultimate general-purpose body armor plate.
 This is, in large part, why we have metal matrix composites, or MMCs. Copper — which already has a thermal conductivity roughly 20 times greater than titanium’s — is often reinforced with diamond grit for use in high performance heat-sinks. And although we mentioned that stiffness is not amenable to improvement via alloying strategies, metals like steel and aluminum are sometimes, however rarely, reinforced with ceramic particles or whiskers for improved stiffness in niche aerospace applications. MMCs such as those, and in a general sense, can’t be called “alloys,” and they’re almost always very brittle. A titanium MMC would likely be both very brittle and exorbitantly expensive — and either factor alone would be sufficient to obviate its use in armor, given the wide availability of strong, brittle, ultra-stiff, and inexpensive ceramics.