Influence of heat treatment on structure and oxidation behavior of Zr-2 5Nb

Abstract

This paper presents the influence of different heat treatments on the microstrueture and isothermal oxidation behavior of Zr- 2.5Nb in oxygen. The quenched structure consisted of martensitic c~'. Upon tempering the quenched alloy at 500°C for up to 100 h, /3Nb precipitated in the matrix, at twin and c¢' needle boundaries. At higher tempering temperatures and after longer periods, Nb-rich/3Zr also precipitated. Specimens slowly cooled from the/3-phase showed the least resistance to oxidation. The oxidation behavior also varied with the tempering time and temperature. The increased oxidation rate of specimens tempered at 500°C for 1000 h or at 600°C, as compared to those tempered at 500°C for shorter times, has been attributed to formation of Nb containing oxides on the coalesced Nb-rich precipitates and to cracking.