The gradual disappearance of yield plateau in Zr–Sn–Nb–Fe–Mo alloy by the trace addition of Cr and V

Abstract

Trace chromium (Cr, 0.1 wt. %) and vanadium (V, 0.05 wt. %) were doped to the Zr–Sn–Nb–Fe–Mo alloy (denoted as Zir) to investigate the tensile properties at room temperature. A clear yield plateau was observed in Zir alloy, while the yield plateau was gradually disappeared by the addition of Cr to Zir alloy (denoted as Zir-0.1Cr) and by the combined addition of Cr and V to Zir alloy (denoted as Zir-0.1Cr-0.05 V). Microscopic characterization results revealed that doping of Cr and V retarded the re-crystallization process in Zir alloy. Firstly, the mean grain size of matrix was reduced from 1.9 μm to 1.7 μm and 1.5 μm by addition of 0.1% Cr and 0.1% Cr + 0.05% V to Zir alloy, respectively. The fraction of low angle grain boundaries (LAGBs) increased from 50.2% to 53.9% and 60.8% in Zir-0.1Cr and Zir-0.1Cr-0.05 V, respectively. Secondly, the volume fraction of second phase particles (SPPs) increased from 7.2% to 11.1% and 11.8% in Cr-containing and Cr + V-containing alloys, respectively. The mechanism of yield plateau in our alloy was explained by the impurity-dislocation interaction and dislocation multiplication mechanism, and the gradual disappearance of yield plateau behavior at the early stage of yielding could be attributed to the gradual increment of mobile dislocation density in Zir-0.1Cr and Zir-0.1Cr-0.05 V alloys. The tensile tests with different pre-strains proved that the gradual disappearance of yield plateau was caused by the increase of mobile dislocations with increasing pre-strain.