Oxidation and its effects on the mechanical properties of Nb–1Zr

The alloy Nb–1Zr is a high temperature material that is often considered for applications where strength and resistance to alkali metals are required. However, these favorable properties can be compromised because it lacks oxidation resistance in many environments. After reviewing the oxidation behavior of Nb–1Zr, additional studies were conducted in high temperature, low pressure gaseous oxygen environments to determine the effects of oxidation on the tensile properties and hardness of Nb–1Zr for a specific space system application. Strengthening and loss of ductility were found to occur from room temperature to 900°C following low pressure oxidation in vacuum or argon at 750°C and 900°C, respectively. In general, oxygen that is associated with zirconium as extremely fine zirconium–oxygen zones is responsible for the strengthening/embrittlement that is observed. Heat treatments that result in non-coherent ZrO2 precipitates can neutralize the effects of oxygen on mechanical properties provided the total oxygen content is below that required to convert all of the Zr to oxide.