Diamonds are not forever: hypersonic impact turns ultra-hard composite into graphite shock absorber

Diamonds have a reputation for permanence, but a new experiment has shown that even the hardest naturally occurring material can surrender within microseconds. Researchers at Texas A&M University College of Engineering and Rice University forged an ultra-hard diamond composite and then fired aluminum projectiles at it at more than eight times the speed of sound. On impact, portions of the diamond composite transformed into graphite, a substantially softer form of carbon that acted as an instant shock absorber, absorbing, dissipating and redistributing the kinetic energy delivered by the projectiles. The study, published in Materials Today, reveals how ultra-hard materials behave under extreme shock and mechanical stress, and the team says the knowledge could help engineers design next-generation shielding and protective materials for aviation, defense and space technologies.

The work was supported by the Air Force Office of Scientific Research and was led on the Texas A&M side by Aniket Mote, a doctoral candidate of mechanical engineering, and Thomas Lacy, a professor of mechanical engineering. The researchers set out to answer a deceptively simple question: can the behavior of materials subjected to extreme conditions be replicated and studied in a controlled setting? In this case, that meant investigating hypersonic impact on a diamond-composite target. What they captured went beyond a record of damage. “We captured a phase change in the material and recorded how the material transitioned from one state to another,” Lacy said. The intense shockwaves generated by the aluminum projectiles rapidly reorganized the diamond composite’s rigid internal structure, transforming portions of it into graphite.

The practical significance of that observation lies in timing and mechanism. “The phase change happens almost instantly, and it could help guide the development and design of materials that can better withstand extreme environments,” Lacy said. For hypersonic and space vehicles, the team suggests the knowledge could unlock resilient materials capable of enduring the brutal shockwaves and mechanical stresses experienced during high-speed flights. In defense applications, the findings could aid the development of shielding and protective materials engineered not only to withstand intense impacts but to manage the transfer of energy through a target, potentially softening or perhaps even neutralizing serious blows. “The diamond-to-graphite transformation could help guide the design of next-generation materials for extreme environments, to serve national and global research interests,” Lacy said. “The project gives us a new view of how ultra-hard materials behave under hypersonic impacts,” Mote added.

The violent forces that power, yet devastate, modern aircraft, spacecraft and defense systems share a single brutal reality: they depend on materials that can fracture, deform or fail in a fraction of the time it takes to blink. Amid crushing pressures, searing temperatures and hypersonic speeds, engineers are left racing to understand what happens to materials in those fleeting moments between impact, shock and failure. The diamond-to-graphite transformation provides a rare window into those moments, because the researchers observed the material transitioning from one state to another rather than simply recording how a diamond composite behaves and changes under extreme shock. By collapsing its atomic grid into softer graphite, the composite’s transformation helped absorb and dissipate kinetic energy at a microstructural level.

Before the target could face the gun, it had to be built. Diamonds are forged from carbon under extreme conditions and are prized for a crystalline carbon structure that makes them the hardest naturally occurring material known. Yet synthesizing bulk diamonds from smaller diamond grains has been a longstanding challenge for engineers and materials scientists. Traditional techniques use heat and pressure to fuse smaller diamond grains together, but at the extremes diamonds break down and melt. To overcome this, the Rice University researchers mixed two additional ingredients with the smaller diamond grains and used spark plasma sintering to consolidate the mixture into a composite. “Cubic boron nitride and cobalt were added to the mixture, to help bind and stabilize it,” Mote said. The result was a dense, tough, bulk material that locked smaller diamond particles into place.

With the composite in hand, the evaluation moved to a two-stage light gas gun. “A two-stage light gas gun can be used to launch projectiles at hypervelocities to evaluate ultra-high-rate material behavior of a target,” Lacy said. Moments before a test, the laboratory falls into a poised silence as the Texas A&M and Rice University teams work through their safety checklist before unleashing aluminum rounds traveling roughly 6,500 miles per hour toward the diamond composite target. The countdown begins, then launch. Within microseconds, the aluminum projectiles barrel down the gun and impact the target in a cascade of pressure, shock and heat. “Impact phenomena are measured and characterized using state-of-the-art diagnostic equipment,” Lacy said. Lining the length of the gun are high-speed cameras and ultra-fast sensors that recorded the violent impact of two experiments.

The two tests differed in scale and speed. “In the first test, we launched a cluster of 1 millimeter aluminum ‘buckshot’ projectiles traveling at nearly Mach 7.5. And in the second test, we fired a single, large 4 millimeter aluminum projectile at speeds approaching Mach 8.45,” Mote said. When the researchers reviewed the footage and analyzed the diamond composite target under a microscope, they made a remarkable discovery. “We found that portions of the diamond composite had transformed into graphite,” Lacy said. “It was exciting to observe this phase change in real time.” The observation led the team to a blunt conclusion: diamonds are not forever when impacted at speeds over eight times the speed of sound.

Capturing this transformation required more than an innovative material. It required a facility capable of re-creating the extreme conditions responsible for it: the Texas A&M University Hypervelocity Impact Laboratory, or HVIL. Located on the Texas A&M-RELLIS innovation and technology campus, the HVIL serves as a premier aeroballistics laboratory, housing a 45-foot-long two-stage light gas gun designed to blast targets with projectiles that travel upward of 29,000 miles per hour, then dissect the impact with an arsenal of sophisticated diagnostics. “At the HVIL, we have a high throughput capability and are among the world’s leaders in the number of shots performed annually,” Lacy said. “The HVIL’s capabilities enable us to characterize, test and model extreme transient variations in temperature and hypervelocity loading,” Mote said.

The laboratory’s role extends beyond a single experiment. Collisions there are not spectacles but surgical strikes into the unknown of extreme physics and materials sciences, intended to pioneer and fuel breakthroughs in engineering and national security. Because of its state-of-the-art capabilities, the HVIL underscores Texas A&M’s commitment to pushing the boundaries of science, engineering and education. “Our external collaborations help serve the national interest by exploiting the expertise of researchers with markedly different backgrounds,” Lacy said. For students, the lab offers a rare kind of education, where classrooms give way to impactful discoveries and applications. “It’s a one-of-a-kind training and experience,” Mote said. “Running a gun lab, we are motivated to be as operationally safe as possible while training the next generation of engineers and scientists.”

Among the countless impacts and materials studied inside the HVIL, the diamond-to-graphite transformation delivers a simple but profound insight: even the hardest materials are capable of change. While the diamond’s transformation into graphite marked the end of this experiment, for the team and the research community at large it could usher in the beginning of a new era of materials built to survive the impossible. At Texas A&M, researchers are developing new materials, discovering how they behave and how they might be built to endure, at the very edge of possibility. The study, published in Materials Today under the title “Diamond-to-graphite transformation under hypersonic impact,” appeared on 6 August 2026, and its authors suggest that understanding when and how this transformation happens carries significant practical potential for materials designed to withstand extreme environments.

Subject of Research: Diamond-to-graphite phase transformation in an ultra-hard diamond composite under hypersonic projectile impact

Article Title: Forging diamonds, firing hypersonic projectiles, forming graphite

Article References: Forging diamonds, firing hypersonic projectiles, forming graphite. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: diamond composite, graphite, hypersonic impact, phase transformation, shock absorber, two-stage light gas gun, spark plasma sintering, cubic boron nitride, cobalt, Materials Today, Hypervelocity Impact Laboratory, protective materials