The Effect of Thermal Annealing on Structural-phase Changes in the Ni-Ti Alloy Implanted with Krypton Ions

The influence of thermal annealing within the temperature range 100-300A degrees C on the structural-phase state of a Ni-Ti alloy with shape memory effect (SME) implanted with Kr-84 ions at the energies E = 280 keV and 1.75 MeV/nucl and the fluences within 5 center dot 10(12)-1 center dot 10(20) ion/m(2) is investigated. For the samples modified by Kr-84 ions at E = 1.75 MeV/nucl up to the fluences 1 center dot 10(20) and 5 center dot 10(12) ion/m(2), the formation of a martensitic NiTi phase with the B19 (') structure, responsible for the SME, is revealed at the annealing temperatures 100 and 300A degrees C, respectively, in the near-surface region corresponding to the outrange area. This is accompanied by the formation of nanosized NiTi particles in the R-phase. As the implantation fluence increases, the probability of their formation decreases. It is shown that annealing of the implanted structures can increase the strength of the Ni-Ti alloy. The degree of hardening is determined by the value of annealing temperature, and an increase in strength is primarily due to ordering of the radiation-induced defect structures (phases). A correlation between the onset temperature of a forward martensitic transition and the structural-phase state of the thermally annealed Ni-Ti alloy is established.