Microstructures and wear resistance of Zr-4 and N36 alloys subjected to pulsed laser surface remelting

Two typical Zr alloys (Zr-4 and N36) for nuclear applications were surface-treated by laser surface remelt-ing (LSR). Electron channeling contrast imaging and electron backscatter diffraction were used to char-acterize their main microstructure characteristics before and after the LSR, which were also correlated with their hardness and wear resistance. The results show that two surface modification zones with dis-tinct microstructure characteristics appear in both the LSRed Zr alloys: ( i ) remelting zone (RZ) composed of fine alpha laths with dense internal nano-twins, and ( ii ) heat affected zone (HAZ) consisting of blocky alpha, lath alpha and second phase particles. The average hardness values of the RZs of Zr-4 and N36 alloys are 254.9 +/- 8.5 HV and 269.5 +/- 7.9 HV, respectively, similar to 30% higher than their substrates. The wear rates of the LSRed Zr-4 and N36 alloys are found to be about 30% and 18% lower than their substrates, re-spectively, indicating significantly improved wear resistance. Comprehensive analyses reveal that refined grains, solid solution and internal nano-twins generated by ultrafast heating and cooling during the laser treatment have jointly led to the enhanced surface hardness of the LSRed Zr alloys, accounting for their improved wear resistance as well. Compared to the Zr-4 alloy, the refinement of the surface microstruc-ture of the N36 alloy after the LSR treatment is more remarkable, contributing to higher hardness and wear resistance, which is mainly related to the addition of 1 wt.% Nb.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Two typical Zr alloys (Zr-4 and N36) used for nuclear applications were modified using laser surface remelting (LSR). The LSR led to the formation of two distinct zones in the alloys: a remelting zone (RZ) and a heat affected zone (HAZ). The RZ showed enhanced surface hardness and improved wear resistance compared to the substrates. Analysis revealed that refined grains, solid solution, and internal nano-twins contributed to the improved properties in the LSRed Zr alloys.