Study on the microstructure evolution and fracture mechanism of C7(Zr–1Nb-0.01Cu) cladding alloy with different hydrogen contents

The microstructural evolution, texture characteristics, and mechanical responses of the C7 (Zr-1Nb-0.01Cu) cladding alloy were systematically investigated as a function of hydrogen content (in weight parts per million, wppm). Specimens with hydrogen concentrations of 200, 400, 600, and 800 wppm were prepared through gas-state hydrogen absorption experiment charging. The distribution of hydride phases, the interfacial characteristics between hydrides and the matrix, and the corresponding changes in mechanical properties were examined using metallographic analysis, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and ring tensile testing. Pronounced microstructural alterations were observed with increasing hydrogen content, particularly in the precipitation behavior and spatial distribution of hydrides. Hydrides tested at 400 wppm, were predominantly distributed along grain boundaries and exhibited relatively low brittleness. Extensive hydride aggregation and the formation of a continuous network resulted in a significant increase in brittleness at 800 wppm. Ring tensile tests indicated that while the yield and tensile strengths remained largely unchanged, a marked reduction in ductility occurred, especially at higher hydrogen concentrations. The fracture mode transitioned from ductile dimple rupture to brittle cleavage. This study elucidates the effect of hydrogen content on the grain structure, hydride precipitation behavior, and mechanical properties of the C7 alloy.