Space exploration is not what you might call a safe line of work. Among the threats, space debris is a real concern. This debris continuously encircles the Earth, trapped in a “low-earth-orbit” (LEO). Collisions with this debris can be problematic both to satellites and manned space vehicles. In a worst-case scenario, this could result in a cascading collision.
As reported in Materials Views, “While eliminating this threat is virtually impossible, spacecraft shields can be developed that mitigate the impact of small projectiles, protecting vital electronics and hull integrity.” The ability to deflect this type of impact is not a trivial task. The “hypervelocity” impacts require advanced materials to successfully withstand the impact without adding excessive weight.
The advanced material must satisfy a number of criteria for properties. Among these are low density, high hardness, and high toughness. Bulk metallic glasses (BMGs) are good candidates for the job. They meet the requirements for strength and weight while maintaining good formability. They can be configured for use in cellular or composite forms.
Bulk metallic glasses are amorphous metals. It is very “unusual” for metals to be amorphous. All pure, elemental metals have a crystalline structure in a solid state. When metals are mixed together as an alloy - such as in brass or stainless steel - they still have a crystalline structure.
What makes BMGs unique is that they are often a special mixture of metals that has atoms of vastly different size. This can “confuse” the atoms so that they cannot arrange into an orderly pattern found in crystalline materials. Depending on the alloy, the metal can be made amorphous by special processing in limited quantities.
Usually rapid cooling is used to make metallic glasses. Early alloys required cooling rates from the liquid state on the order of a million degrees per second. BMGs being developed today can be cooled more slowly, but large parts (think centimeters) are still not practical. Fortunately, the properties for these materials can make up for some of that.
Glass isn’t the first material you might think of for taking a hypervelocity hit. As it turns out, glass might be a good option, as long as it’s metal.
Images Courtesy of Materials Views