Microstructure change under hot deformation in zirconium alloys synthesized by powder metallurgy

Highlights: • Microstructure peculiarities in zirconium alloys made by powder metallurgy. • Hot compression better heals the porosity and solves the bismuth than hot forging. • Beta nanoparticles are formed at hot forging in alpha phase of alloy with tin. • Microstresses have appeared at hot forging in beta phase of alloy with bismuth. • Bismuth more effectively enhances the creep resistance of zirconium alloy than tin. -- Abstract: The microstructure evolution upon high temperature synthesis and hot deformation of Zr-based alloys (Zr-1.2Sn-1Nb-0.4Fe and Zr-1.2Bi-1Nb-0.4Fe, in wt. %) produced by powder metallurgy (PM, namely pressing and sintering) has been investigated. Bismuth has unique features but is poorly soluble in zirconium. Therefore, it was introduced in alloy with using PM. In spite of high bulk porosity (about 4–7%), the forging and hot compression led to almost complete healing the porosity and essentially decreasing the different inhomogeneities. In alloy with bismuth the microstresses caused by undissolved bismuth microparticles have arisen in the beta-phase during hot-forging. In alloy with tin the beta-phase breaks down into nanocrystallites. Under hot-forging dislocations have more accumulated in the beta-phase. Structure analysis lead to suggestion that under hot compression at the specified conditions the strain rate is controlled by viscous glide of dislocations. Wherein bismuth turns out to be a more effective strengthening element than tin.