An investigation of the microstructure of body centred cubic metals after laser shock treatment

This paper reports on the metallographic and electron microscopic (SEM, TEM ) investigation of iron and molybdenum specimens which were shock treated i n a confined ablation mode using an excimer laser system (Working group: Dr . Lang, ATZ-EVUS, Vilseck). It is shown by different preparation and invest igation techniques (characterization of surface steps by DIG, study of ion polished cross sections by channelling contrast in a SEM, analysis of the m icrostructure by diffraction contrast in a TEM) that the shock induced chan ges of the microstructure and the associated strengthening depend on the ma terial being treated. In particular, the same laser treatment produces in i ron deeper deformation zones and higher increases in hardness compared with molybdenum. These features are correlated with a more pronounced formation of deformation twins in iron, although the shock deformation proceeds in b oth metals by the simultaneous action of dislocation slip and deformation t winning. Due to the extremely short duration of the laser induced pressure pulse, these investigations offer a unique access to studying the interacti on between dislocation slip and twinning during plastic deformation at high strain rates.