Material property modification via ion implantation and its effects on strength and compressibility

Material properties under high pressure, temperature, and strain are affected by the presence of impurities and defects, leading to changes in compressibility, strength, phase transition pressure, etc. To investigate some of these effects, we developed a method for implanting He ion gas bubbles throughout metal samples. This allows us to modify the metal starting impurity and introduce a large number of dislocation pinning sites without a significant change in microstructure. It is expected that doping will lead to material hardening, although the amount is predicted to depend on He bubble density and size.

The He implantation is performed at the Center for Accelerator Mass Spectrometry, by using a volumetric raster scan of a metal foil and varying the energy, He bubbles of varying sizes can be implanted within a ~10-50 um horizon. Due to the heat generated by the ion deposition process, a cooling stage was developed, which allows for an increase in bubble density as well as a decrease in bubble size by restricting He ion mobility through the metal in a controllable manner. The He bubble distribution is evaluated with TEM. The foils are then used in target fabrication for our experiments on the National Ignition Facility (NIF). The experimental strategy for the targets differs depending on the type of data to be acquired. Here, we will discuss their application in strength Rayleigh-Taylor (RT) experiments and planned equation of state (EOS) experiments. Several strength RT experiments have been performed on Pb, using multiple implantation levels and comparing to pure Pb. EOS experiments are currently being developed, using a novel two-part design. Overall, the implantation methodology combined with shock-ramped experiments gives us a new way to look at how nanoscale changes in material composition affect overall behavior under high-rate, laser-generated compression.