Characterizing Defects In Metals Using PALS

Machines with moving parts develop wear and tear after some time of operation. Sometimes defects are on the surface, and thus are visible with the naked eye or with a microscope. However, some defects are seated below the surface and are unnoticeable by the human eye or by a microscope. One way of probing materials for these defects is by way of Positron Annihilation Lifetime Spectroscopy (PALS). This sensitive technique was applied to characterize atomic-scale defects in aluminum and copper samples, as well as steel bearing raceways of different levels of usage. Measurements on aluminum and copper were performed before and after annealing near the melting point. Results show that average positron lifetime decreases significantly after annealing. Then steel bearing raceways were subjected to PALS measurements before and after mechanical testing. Results show an average increase in the positron lifetime of tested bearings as compared to the as-fabricated bearing.

Autorentext

Jason Lavaska Calloo was born on October 17th, 1987 in the Parish of Saint Ann, Jamaica. In August 2011 he completed his Masters in Physics at Miami University. Under the mentorship of Dr. Herbert Jaeger, he used the sensitive technique of Positron Annihilation Lifetime Spectroscopy to characterize atomic-scale defects in steel, copper and aluminum