DISLOCATION RELAXATION IN THE MARTENSITIC PHASE OF THE THERMOELASTIC NiTi AND NiTiCu ALLOYS

Abstract

The internal f r i c t i o n has been measured i n the martensitic phase of NiTi(Cu) alloys a t 1 Hz and 4 kHz. The d e t a i l e d study of the s t r a i n amplitude dependence of the internal f r i c t i o n and the whole spectrum as a function of the temperature i n the martensitic phase have a1 lowed t o a t t r i b u t e t o dislocations t h e main source of internal f r i c t i o n .

On the Effect of Hydrogen on the Low-Temperature Elastic and Anelastic Properties of Ni-Ti-Based Alloys

“…The strong dependence of the temperature position of the low-temperature IF maximum on the hydrogen content leads us to the suggestion that many of the “different” low-temperature IF peaks (Tirbonod-Koshimizu peak, P d , P TWM , P 150K , P 200K’ , P 50K ), reported earlier for differently treated Ni-Ti-based alloys [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ], may actually be the same IF maximum. The assumption of Reference [ 12 ] that P TWM and P 150K represent the same phenomenon was the first step in this direction.…”

“…The anelasticity of the martensitic phases of Ni-Ti-based alloys is usually attributed to the motion of twin boundaries (see, for example, References [ 1 , 13 ]), though dislocation mechanisms (involving twin [ 5 , 23 ] or bulk [ 6 ] dislocations) are also occasionally invoked. The data presented here do not permit further refinement; therefore, twin boundaries will be considered hereafter as sources of the IF of the martensitic phase, unless otherwise stated.…”

“…Now we can add the Tirbonod-Koshimizu and P d peaks to this unification. They were claimed as relaxational, but the effective modulus exhibited a pinning stage rather than relaxation (see Figure 1 in Reference [ 5 ] and Figure 10 in Reference [ 6 ]). The activation parameters in both cases were evaluated from only two experimental curves, of which only one exhibited a maximum.…”

“…It has been attributed to an interaction of twin boundaries with hydrogen [ 3 , 4 ]. Another IF peak around 100 K was reported and ascribed to a dislocation relaxation by Tirbonod and Koshimizu [ 5 ]. Numerous peaks were found by Mazzolai et al at temperatures between 40 and 240 K: P TWM [ 6 , 7 , 8 , 9 , 10 ], P d [ 6 , 7 ], P 150K [ 11 , 12 , 13 ], P 200K’ [ 13 ], P 50K [ 13 ], and also several peaks for hydrogen-doped samples [ 13 ].…”

STACKING FAULT FORMATION IN A FAULTED Cu-Zn-Al - MARTENSITE

“…The mechanical properties of the martensitic phase are quite different from those of the parent phase. For instance the internal friction (Q-l) or damping capacity is always higher in the martensite and its dependence on the amplitude of vibration is not simple (5,6). It was shown that the higher damping in the martensite phase compared to the matrix phase can be explained qualitatively by the movement of a large number of parallel dislocations (7).…”