Study of precipitation and dislocations in nitrogen implanted Zircaloy-4

The purpose of this investigation is to develop the relationship between implantation conditions and material properties for nitrogen implanted Zircaloy-4. The distribution of precipitation in annealed Zircaloy-4 is homogeneous. The size of most precipitate particles is in the range 10–200 nm and the dislocation density is very low. Microanalysis of the precipitation of the substrate shows that these particles are Zr(Fe,Cr) 2 ternary intermetallics, which have both hexagonal Laves-phase Zr(Fe,Cr) 2 structure and cubic Zr(Fe,Cr) 2 structure with a higher Fe:Cr ratio (from 1.53 to 2.47). The average value of microhardness of the substrate was measured to be Hv 221. After implanting nitrogen in Zircaloy-4, the dislocation density was significantly increased and a dislocation substructure was formed in the implanted layer. The original precipitate did not change obviously. The ZrN phase was discovered in the implanted layer. The dislocation substructure and the amount of ZrN were varied with increasing implantation temperature and dose. As the implantation temperature varied from 310 °C to 640 °C, the average value of microhardness was increased to Hv 580 and Hv 740 respectively. The effect of implantation temperature and dose on the microstructure, phase structure and composition, and surface hardness is presented in this paper.