Aging Influence on the Shape Memory Effects and Superelasticity in Titanium-Nickel Single Crystals
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387 Mat. Res. Soc. Symp. Proc. Vol. 459 © 1997 Materials Research Society
EXPERIMENTAL RESULTS AND DISCUSSION It was experimentally found that in the homogeneous state the orientation dependence and asymmetry of the a,, depend on the Ni concentration in crystals. Such the orientation dependence and asymmetry in Ti-50.45at.%Ni crystals are significantly stronger than in the Ti-50.Sat.% Ni (I), Ti-51 at.%Ni (II) and Ti-51.3at.%Ni (I1I) (fig. 1) ones.
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T,. Fig. I The dependence of the ao.j on the test temperature of the TiNi single crystals: 1-Ti-50.45 at.%Ni; 2-Ti-5lat.%Ni-quench; 3-Ti-51at. %Ni aged at 573 Kfor Whr.; 4-Ti-5lat.%Ni aged at 773K for lhr,, 5-Ti-51.3at,% Ni aged 773 K for lhr. Figure 2 shows the temperature dependence of the electrical resistance p(T) in the Ti-51at.% Ni crystals aged at 573 K for 1 hr. This heat treatment leads to the increase of the deforming stresses ac. as compared with the quenched state. For the specimens aged at 773 K for I hr., the decrease in deforming stress is observed which is particularly appreciable in the stress-induced MT interval (fig. 1). L shifts to the high temperature range as compared with the quenched crystals. In the temperature range of the stress-induced martensite formation the increase of the angle cv-da/dT on the dependence ca(T) is observed. In this temperature interval at T
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