Characterization of interface irradiation damage in Ti-clad V-4Cr-4Ti composite material

Abstract

The development of electrically insulating coatings is extremely important for the lithium/vanadium (Li/V) blanket of the fusion reactor. However, Li/V cladding materials suffer many problems such as tritiumpermeation and material corrosion. Thus, it is very important to find suitable insulating, tritium-resistant and corrosion-resistant coatings. So, the " V-alloy/Ti/AlN” bilayer coating was proposed by our group in previous study for the first time. In this paper, the evolution of the hardness, irradiation defects and microstructure of the Ti-clad V-4Cr-4Ti composite material after Fe¹⁰⁺ implantation are studied by transmission electron microscopy (TEM) and nanoindentation. According to the characteristics of the composition and microstructure, V-4Cr-4Ti/Ti composite material can be divided into four zones: V-4Cr-4Ti matrix, interface I (the interface near V-4Cr-4Ti matrix), interface II (the interface near Ti matrix), and Ti matrix. The nanoindentation results show that radiation hardening occurs in all regions during irradiation. The radiation hardening in the interface is lower than in the V-4Cr-4Ti and Ti matrix. Thus, the interface of heterogeneous material exhibits fine resistance to radiation hardening. The experimental values of hardness are much higher than the values calculated by the dispersed barrier hardening model. One reason for the discrepancy is that the theoretical values are calculated under the hypothesis of the uniform loop distribution. Actually, a large number of dislocation loops accumulate and tangle with each other in the samples. In addition, the formation of the precipitates is also one of the key factors. The TEM results show that the irradiation defects in the interface are low in density, large in size, and uniform in distribution. As a contrast, high density, small size and twisted dislocation loops are observed in irradiated V-4Cr-4Ti and Ti matrix. These results indicate that the interface can play a critical role in the resistance to irradiation damage. Few tiny Ti-rich precipitates appear in the V-4Cr-4Ti matrix, while there are large quantities of Ti precipitates in the interface after irradiation. Moreover, the number and size of precipitates in the interface I are larger than those in the interface II due to the formation of a few V-rich precipitates in the interface I. The formation of precipitations changes the proportion of V/Ti, which leads to the transformation from <i>β</i>-Ti to <i>α</i>-Ti in the interface.