Amorphous steel powder metallurgy alloy has highest impact resistance
April 13, 2016
Source: ASM International
The University of California San Diego announces that a team of engineers has developed and tested SAM2X5-630, a type of amorphous steel with a record-breaking ability to withstand impact without deforming permanently. To make the solid materials that comprise the alloy, Prof. Olivia Graeve and her team first mixed iron and other powders in a graphite mold. The powders were then pressurized at 100 MPa or 1000 atmospheres, and exposed to a powerful current of 10,000 amperes at 1165°F during a process called spark plasma sintering.
The process creates an amorphous structure that contains small crystalline regions that are only a few nanometers in size. Researchers believe that these small regions are key to the material's ability to withstand stress. This finding is promising because it shows that the properties 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.
Researchers at the University of Southern California, led by Prof. Veronica Eliasson, tested how the alloy responds to shock without undergoing permanent deformation by hitting samples of the material with copper plates fired from a gas gun at 500 to 1300 meters per second. The material did deform on impact, but not permanently.
The Hugoniot Elastic Limit is defined as the maximum shock a material can take without irreversibly deforming. The limit of a 1.5-1.8 mm-thick piece of SAM2X5-630 was measured at 11.76 GPa. By comparison, stainless steel has an elastic limit of 0.2 GPa, while that of tungsten carbide is 4.5 GPa.
The primary focus of future research efforts on these alloys is increasing the weight of the materials to make them more resistant to impacts.
In addition to Prof. Graeve and Prof. Eliasson, co-authors include Prof. Gauri R. Khanolkar and Prof. Andrea M. Hodge at USC, Prof.Michael B. Rauls at Caltech, and Prof. James Kelly from the Department of Mechanical and Aerospace Engineering at UC San Diego.
This research was supported by the Defense Threat Reduction Agency, grant HDTRA1-11-1-0067.
The full study "Shock Wave Response of Iron-based In Situ Metallic Glass Matrix Composites," published on March 2, can be found online at http://www.nature.com/articles/srep22568
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