High-entropy alloys are unusual in more ways than one. Because several elements share the crystal lattice almost equally, the atoms interfere with one another’s movement, producing severe lattice distortion, sluggish diffusion, and what materials scientists call the cocktail effect, in which the mixture behaves in ways its individual components do not predict. When such an alloy is designed around elements with high heats of combustion, notably titanium and zirconium, it becomes an energetic structural material: a substance that can hold together as a structural component and, under violent impact, fragment and react with oxygen to release substantial chemical energy. That dual personality is precisely what makes these alloys interesting for impact applications, since they deliver both kinetic penetration and a secondary thermal and overpressure effect that conventional penetrators cannot provide.

The team fabricated three candidate alloys, TiZrWV, TiZrNbWV, and TiZrNbV, using vacuum arc melting. High-purity raw materials were weighed in equiatomic ratios, melted under strong electromagnetic stirring, and remelted six times, with each melt held liquid for twenty minutes to ensure chemical homogeneity. The ingots were then rapidly solidified under argon-assisted forced convection and machined into cylindrical specimens by wire electrical discharge machining. Tungsten was added to boost solid-solution strengthening, while niobium and vanadium were introduced to stabilize the solid-solution phases and refine the grains. The choice of composition was deliberate: each alloy represents a different balance between strength, ductility, and reactivity.

Quasi-static compression tests on an MTS Landmark universal testing machine, run at strain rates of 0.001 and 0.01 per second, revealed a clear hierarchy of mechanical behavior. TiZrNbWV emerged as the strongest of the three, with a yield strength rising from 1418 to 1469 megapascals as the strain rate increased, and a fracture strength reaching 2000 megapascals at the higher rate while still sustaining a fracture strain of roughly thirteen percent. Its yield strength exceeded that of TiZrWV by more than twenty-five percent under identical conditions. TiZrNbV, by contrast, showed the best plastic deformation capability and the highest quasi-static fracture strength, climbing from 1960 to 2021 megapascals, while TiZrWV sat in the middle with intermediate values in both categories.

Scanning electron microscopy of the fractured specimens explained these differences at the microstructural level. TiZrWV failed through quasi-cleavage planes characteristic of brittle fracture. TiZrNbWV displayed a layered, stepped surface with folds and tear ridges, indicating a mixed brittle-ductile process in which crack propagation was accompanied by significant plastic flow. TiZrNbV showed river-like patterns and abundant ductile dimples of moderate depth, the signature of fracture driven by the nucleation, growth, and coalescence of microvoids. In all three alloys, cracks tended to propagate along shear planes oriented at roughly forty-five degrees to the compression axis, and bright flashes of light were recorded at the fracture surfaces, evidence that even slow, quasi-static loading can trigger measurable energy release.

Dynamic compression on a split Hopkinson pressure bar pushed the strain rates into the 1000 to 3100 per second range and exposed pronounced strain-rate strengthening in every alloy. TiZrWV saw its yield strength jump by more than fifty percent relative to its quasi-static values, reaching 1723 megapascals at a strain rate of 2105 per second, while TiZrNbWV reached 1967 megapascals at nearly 3000 per second. The relative strengthening followed the order TiZrWV, then TiZrNbV, then TiZrNbWV, a pattern the authors attribute to the different ways niobium and tungsten contribute to baseline strength and strain-rate sensitivity. Under the microscope, the dynamically fractured specimens told an even more dramatic story: all three alloys developed localized molten structures on their fracture surfaces, from large melted blocks in TiZrWV and TiZrNbWV to fine molten droplets and flow traces in TiZrNbV, confirming that adiabatic heating during high-strain-rate shear had raised local temperatures high enough to melt metal.

The centerpiece of the study was a series of ballistic experiments in which cylindrical flat-nosed projectiles of each alloy were fired from a 14.5-millimeter-bore ballistic gun at a novel three-layer spaced target: a five-millimeter-thick 2A12 aluminum front plate, a 1.6-millimeter circuit board populated with conventional electronic components, and a three-millimeter aluminum rear plate, with 100-millimeter gaps between layers. A high-speed camera running at 30,000 frames per second captured the impacts at velocities ranging from roughly 548 to 1012 meters per second. The results showed a striking division of labor. Penetration of the front aluminum plate was dominated by kinetic effects, with classic plug-shear failure and circular perforation, and many reactive fragments passed through unreacted, producing only weak flashes. The main energy-release reactions occurred later, when the fragmented projectile struck the rear circuit board, shattered further, and generated a high-temperature fragment cloud that reacted violently with atmospheric oxygen.

To quantify this behavior, the researchers introduced two optical indicators drawn from the high-speed imagery: flash duration, which reflects how long the energy release persists, and flash intensity, a normalized grayscale measure of instantaneous emission. TiZrNbWV proved the most persistent reactor, with flash durations reaching 73.92 milliseconds at high impact velocity, nearly eighteen times its low-velocity value. TiZrWV followed with a maximum of 55.08 milliseconds, while TiZrNbV lasted only 15.02 milliseconds even at 984 meters per second, showing little sensitivity to velocity. The intensity picture inverted at different speeds: at low velocities TiZrNbV produced the highest peak flash intensity and the steepest rise, indicating strong instantaneous release, whereas at high velocities TiZrWV delivered the most intense and rapid response. TiZrNbV’s intensity curves at 856 and 984 meters per second even showed a bimodal profile, attributed to secondary fragmentation generating a second wave of reactions.

The damage left behind on the targets provided macroscopic confirmation of these differences. The third-layer aluminum plates perforated by TiZrWV and TiZrNbWV projectiles bore irregular, jagged, tear-like holes with rough boundaries, consistent with dispersed fragment populations and sustained, spatially nonuniform loading. The TiZrNbV projectile, with its better deformability and shorter energy-release duration, left a comparatively regular circular perforation with smooth edges, indicating a more concentrated residual fragment population. At the highest velocities, all three alloys produced a quasi-detonation phenomenon, in which extensive fragmentation enlarged the reactive surface area and triggered intense thermochemical release within a very short time, and in several cases energy release continued behind the fully perforated target as a pronounced post-penetration effect.

The authors are careful to note the limits of the work. The ballistic tests covered a restricted velocity range, and flash duration and intensity are image-based comparative parameters rather than direct measurements of absolute energy, so the quantitative link between microstructure, fragmentation, and reaction kinetics remains to be established. Even so, the study delivers a practical design guideline: TiZrNbWV suits applications demanding high structural strength, strong penetration, and sustained post-impact energy release; TiZrWV fits scenarios that prize rapid, intense release under high-velocity impact; and TiZrNbV offers a balance of deformability, concentrated penetration, and fast response. By turning the fleeting glow of an impact into numbers, the work gives designers of energetic structural materials a quantitative language for tuning composition to the mission at hand.

Subject of Research: Mechanical properties and impact-induced energy release of TiZr-based high-entropy alloy projectiles against multi-layer circuitry targets

Article Title: Mechanical properties of reactive high-entropy alloys and energy-release characteristics of projectiles impacting a multi-layer circuitry target

Article References: Shi, Z., Wu, C., Qiao, W., Mao, L., Pang, Z., & Liu, J. (2026). Mechanical properties of reactive high-entropy alloys and energy-release characteristics of projectiles impacting a multi-layer circuitry target. Mechanical Sciences, 17(2), 901-916. https://doi.org/10.5194/ms-17-901-2026

Image Credits: AI Generated

DOI: 10.5194/ms-17-901-2026

Keywords: high-entropy alloys, energetic structural materials, TiZr-based alloys, ballistic impact, energy release, vacuum arc melting, split Hopkinson pressure bar, flash duration, flash intensity, penetration mechanics, strain-rate strengthening, multi-layer target