Microstructural phenomena associated with micrometeoroid impact craters in aluminum and stainless steel.

We explore the metallurgical and materials implications for hypervelocity impact crater formation in some representative materials exposed in space in low-Earth orbit. Radial cracks associated with small size (<0.2 mm) craters in anodized aluminum alloy illustrate the importance of impacting particle flux and size distributions. Novel sectioning and etching of selected craters in stainless steel bolt heads has illustrated the potential for detailed characterization of cracking, phase changes, and extreme deformation proximate to the crater wall while thin sections through the crater and selectively ion-milled to electron transparency have illustrated shock pressure effects on microstructures below the crater for the first time. The use of optical, acoustic, and electron microscopy is illustrated in the characterization of hypervelocity impact crater-related microstructures and these observations point to the essential role to be played by imaging techniques in understanding the environmental effects of space in low-Earth orbit on the behavior of materials and space structures. [ABSTRACT FROM AUTHOR]