Volume 17, Issue 3 (May 1989)
Influence of Heat Treatment on Structure and Oxidation Behavior of Zr-2.5Nb
This paper presents the influence of different heat treatments on the microstructure and isothermal oxidation behavior of Zr-2.5Nb in oxygen. The quenched structure consisted of martensitic α′. Upon tempering the quenched alloy at 500°C for up to 100 h, βNb precipitated in the matrix, at twin and α′ needle boundaries. At higher tempering temperatures and after longer periods, Nb-rich βZr also precipitated. Specimens slowly cooled from the β-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.