The steel industry is under siege: Carbon Fiber, Graphene and aluminium are rapidly making inroads into traditional automotive steel applications such as body in white, suspension, and even engine components. But, the recent unveiling of a new amorphous metal dubbed SAM2X5-630, could stall the trend in it’s tracks.
The search for increasingly versatile alloys of steel is driven not only by iron’s abundance and low cost but also the fact that steel is an exceptionally durable metal that can be alloyed with other materials to achieve specific properties.
Researchers are increasingly looking to amorphous steel as a source of new materials that are affordable to manufacture, incredibly hard, but at the same time, not brittle. The researchers believe their work on a steel alloy, named SAM2X5-630, is the first to investigate how amorphous steels respond to shock loadings.
SAM2X5-630 sets new standards.
A multidisciplinary team from the Universities of California, Southern California and the California Institute of Technology (CIT), described the material’s fabrication and testing in a recent issue of Nature Scientific Reports.
“Because these materials are designed to withstand extreme conditions, you can process them successfully under extreme conditions,” said Olivia Graeve, a professor of mechanical engineering at the Jacobs School of Engineering at UC San Diego, who led the design and fabrication effort. Veronica Eliasson, an assistant professor at USC, led the testing efforts.
To make the solid materials that constitute the alloy, Graeve and her team mixed MGMC with metal powders in a graphite mold. The powders were then pressurized at 100 mega-Pascals (the equivalent of 1000 atmosphere) and exposed to a powerful current of 10,000 Ampers at 630°C during a process called spark plasma sintering.
The spark plasma sintering technique allows for enormous time and energy savings, Graeve said. “You can produce materials that normally take hours in an industrial setting in just a few minutes,” she said.
The process created small crystalline regions that are only a few nanometers in size, with hints of structure, which researchers believe are key to the material’s ability to withstand stress. This finding is promising because it shows that the properties of these types of metallic glasses can be fine-tuned to overcome shortcomings such as brittleness, which have prevented them from becoming commercially applicable on a large scale, Eliasson said.
According to the researchers, the new steel alloy can withstand pressures of over 12.5 giga-Pascals (about 125,000 atmospheres) without permanent deformation. This is the highest impact resistance of any “bulk metallic glass”, a class of artificially generated materials first discovered in the 1960s that possess disproportionate strength, resilience, and elasticity due to their unusual chemical structure.
Typical metals and metal alloys have an organized, crystalline structure at the atomic level. Bulk metal glasses (BMGs, for short) are formed when metal and metal alloys are subjected to extreme heat and then rapidly cooled, exciting their atoms into disorganized arrangements, and then freezing them there.
SAM2X5-630 outperforms auto industry stalwarts.
In general, BMGs tend to be strong, resist scratching, tough to fracture, and highly elastic. One commercially available zirconium-based BMG is pound-for-pound twice as strong as titanium.
The Hugoniot Elastic Limit (the maximum shock it can take without irreversibly deforming) of a 1.5-1.8 mm-thick piece of SAM2X5-630 was measured at 11.76 ± 1.26 GPa.
For reference, stainless steel has an elastic limit of 0.2 GPa, while that of tungsten carbide (a high-strength ceramic used in military armor) is 4.5 GPa. This isn’t to say that SAM2X5-630 has the highest elastic limit of any material known; diamonds top out at a whopping 60 GPa, they’re just not practical for many real-world applications.
These properties were graphically demonstrated when engineers at USC tested the alloy by bombarding the material with 34 mm copper pellets fired from a from a gas gun at velocities up to 4,680 Km/hr. The material deformed slightly on initial impact but bounced back immediately afterward.
“The fact that the new material performed so well under shock loading was very encouraging and is an indication of future research opportunities,” said Professor Veronica Eliasson from the Department of Aerospace and Mechanical Engineering at USC.
With continuing research aiming to make the materials even more resistant to impact, the team believes that the resilience of the new alloy would find applications in shielding satellite casings from high-speed micrometeorite impacts and improving the strength of military armor.
As the automotive industry comes under increasing pressure to reduce weight and improve crash safety SAM2X5-630 will undoubtedly become the subject of new studies by the OEMs. Whether this new steel will be enough to ward off the advances being made by multi steels, aluminium, and carbon fiber is yet to be seen.