Crystallinity and grain distributions of fiber-formed nanostructure on tungsten surface with helium plasma exposure

Abstract

Growth mechanisms of complex tungsten (W) fuzzy nanostructure on helium-plasma-irradiated W surface have been extensively studied since the discovery of the phenomenon in 2006. However, the growth process of complicated W nano-fibers from the atomistic and crystal structure standpoints is not well understood. In this study, the X-ray diffraction (XRD) and transmission electron microscopy (TEM) were performed to investigate complexity of nano-fibers as well as their crystallinity. Small-angle-incident XRD on the substrate with fuzz and He-defected bulk surface was used to determine grain distribution among contributions of different crystal orientation families, showing the difference in grain distribution of surface fuzz layer and the basing W bulk surface with helium defects compared with the distribution of pristine powder metallurgy W (PM-W). Peak shifts and broadenings of X-ray diffracted spectra with respect to pristine PM-W substrate and TEM observations were discussed in terms of crystallinity and He-bubbles induced strain. It is speculated that the grain distribution of the He-defected W with nano-fibers would be very similar to that of bulk α-phase W globally. Moreover, the scraped-off fuzz aggregate without basing plate makes it possible to conduct XRD using a thin glass capillary tube. The grain distribution of pure fuzz aggregate was found to be very similar to natural α-phase W with intensification of high grain orientation modes. The process of such high modes may bring morphological complexity to nano-fibers because grain boundaries play a role of turning surfaces along nano-fibers.