Deuterium Retention In Tungsten And Tungsten Carbides Irradiated With D Ions

Abstract

Depth profiles of D atoms and D₂ molecules in tungsten and chemical vapor deposited (CVD) tungsten carbides W₂C and WC exposed to D plasma at temperatures in the range 340 to 670 K or implanted with 6–10 keV D ions at 300 and 650 K have been determined using secondary ion mass spectrometry (SIMS) and residual gas analysis (RGA) measurements in the course of surface sputtering. The deuterium inventory has depended strongly on the structure of the materials investigated. In polycrystalline hotrolled W exposed to D plasma the deuterium has been retained in the bulk of the material as D atoms at intrinsic defects (grain and block boundaries, dislocations, etc.), whereas in the bulk of W single crystals also exposed to the D plasma the deuterium has not been found. In W single crystals and hot-rolled W samples implanted with 6 keV D ions at 300 K the deuterium is retained as D atoms both in the ion stopping zone and at depths up to several urn. Besides, in the stopping zone the deuterium has been additionally accumulated in the form of D₂ molecules. After D ion implantation at 650 K the D₂ molecules have not been observed in the W samples and deuterium is trapped solely in the form of D atoms in the implantation zone. There are at least two types of ion-induced defects which are responsible for trapping of D in the W samples: (i) D₂ filled microvoids localized in the implantation zone and (ii) dislocations which are distributed from the surface to depths far beyond 1 urn and capture deuterium in the form of D atoms. Additionally, D atoms can be trapped by vacancies and adsorbed on bubble walls. In fine-grain CVD tungsten carbides irradiated with 10 keV D ions at 300 K the deuterium has been accumulated in the form of only D atoms far beyond the implantation zone. At 650 K the D atoms have been captured within the implantation zone.