Effect of cold rolling on the magnetic susceptibility of Zr-14Nb alloy

The magnetic susceptibility of cold-rolled Zr-14Nb was evaluated to apply a new metallic medical device used for magnetic resonance imaging (MRI). The magnetic susceptibility of cold-rolled Zr-14Nb decreased up to the reduction ratio of 30%, then gradually decreased up to the ratio of 90%. Transmission electron microscopic observation revealed the strain-induced formation of ω phase after cold rolling at the reduction ratio of 5%, indicating that the initial decrease in magnetic susceptibility was caused by the formation of the ω phase. The ω phase was saturated at the reduction ratio of 30%. The formation of the ω phase could be explained on the basis of the increase in the Young's modulus and Vickers hardness of cold-rolled Zr-14Nb. The effect of texture formation on these properties was not obvious in the cold-rolled Zr-14Nb. Because of the strain-induced formation of the ω phase, the magnetic susceptibility of Zr-14Nb can be reduced by cold rolling to as low as that of as-cast Zr-9Nb, which is one-third that of Ti and Ti alloys. Therefore, cold-workable Zr-14Nb with low magnetic susceptibility could be a promising alloy for medical devices under MRI.