Z. Ungarish, R. Padan, Y. Khoptiar, J. Flomenblit, I. Gutman, D. Gorni, Rafael Advanced Defense Systems Ltd., Haifa, Israel
In Ni-Rich super-elastic Nitinol, a "flag shaped" stress-strain curve and low residual strain, which are indications of good super-elasticity, are usually obtained following a one-step ageing process at temperatures in the vicinity of 773K. Nevertheless, some alloys have microstructures that are not affected by this thermal treatment as described above, and as a result poor super-elastic properties are obtained. In these cases, an alternative thermal treatment is necessary.
In this work we will present a Ni-rich Nitinol alloy that does not show good super-elasticity after the usual ageing treatment, due to the microstructure obtained in the final forming steps of its manufacturing process, which include hot forming. Such a process significantly improves the ductility of the alloy. In order to obtain good super-elasticity, a new two-step thermal process was developed. In this work, the effect of various one and two-step processes has been investigated. Optimal super-elasticity was obtained using a two-step thermal process, which includes solution (at temperatures around 873K) and ageing (at temperatures around 623K). Metallurgical explanations of these results will be proposed.
In Ni-Rich super-elastic Nitinol, a "flag shaped" stress-strain curve and low residual strain, which are indications of good super-elasticity, are usually obtained following a one-step ageing process at temperatures in the vicinity of 773K. Nevertheless, some alloys have microstructures that are not affected by this thermal treatment as described above, and as a result poor super-elastic properties are obtained. In these cases, an alternative thermal treatment is necessary.
In this work we will present a Ni-rich Nitinol alloy that does not show good super-elasticity after the usual ageing treatment, due to the microstructure obtained in the final forming steps of its manufacturing process, which include hot forming. Such a process significantly improves the ductility of the alloy. In order to obtain good super-elasticity, a new two-step thermal process was developed. In this work, the effect of various one and two-step processes has been investigated. Optimal super-elasticity was obtained using a two-step thermal process, which includes solution (at temperatures around 873K) and ageing (at temperatures around 623K). Metallurgical explanations of these results will be proposed.
