Excellent combination of strength and elongation of TZM alloys achieved by c-ZrO2 and single cross rolling

Abstract

In this study, new TZM-xZrO2 (x = 0, 0.5, 1, 1.5) (wt%) alloys were designed by powder metallurgy solid-solid mixing method combined with single cross rolling. The results show that c-ZrO2 in TZM alloys was mainly spherical, and the average size of c-ZrO2 particle increases gradually from 1.28 μm to 1.71 μm with the increase of its content. c-ZrO2 can effectively refine the molybdenum grain and adsorb the free brittle element O in grain boundaries in the form of TiO2 layer. The interface was composed of three phase: c-ZrO2, Y2O3 and TiO2, with the presence of [0−11] c-ZrO2 ǁ [−11−2] Y2O3 ǁ [−10−3] TiO2 crystal relationship. The rolled plates mainly exist 〈100〉//ND and 〈111〉//ND two kinds of grain orientation, the addition of c-ZrO2 particles promote <100>//ND orientation ratio, thus weakening the texture strength (maximum pole density value from 8.34 to 5.39), conducive to the improvement of plasticity. When the c-ZrO2 content was 0.5 wt%, the best performance was achieved, with good strength and elongation (ultimate tensile strength: 958 MPa; Elongation: 17.3%), showing excellent strength and elongation product (16.6 GPa·%), 31% higher than TZM alloy, better than most reported molybdenum alloys. With the further increase of c-ZrO2 content, the particles gradually coarsened, the hindering effect on dislocations was weakened, and it was easy to become the nucleation site of main cracks, resulting in the decrease of strength and plasticity. Fine grain strengthening and dislocation strengthening were important factors to improve the strength. The excellent ductility was mainly due to the deflection mechanism of microcracks and the blocking effect of grain boundary enrichment on crack propagation.