Mechanical spectroscopy and twin boundary properties in a Ni{sub 50.8}Ti{sub 49.2} alloy
- Univ. di Perugia (Italy). Dipt. di Fisica
- Consiglio Nazionale delle Ricerche, Lecco (Italy). Istituto per la Tecnologia dei Materiali e Processi Energetici
The internal friction (IF), Young`s modulus (E) and heat flow (DSC) have been measured in a Ni{sub 50.8}Ti{sub 49.2} alloy as a function of temperature after both ageing and solubilization followed by water quenching. The IF of aged material measured at kilohertz frequencies, besides hardly detectable peaks associated with the A {leftrightarrow} R and R {leftrightarrow} M transitions, displays two additional non-thermally activated peaks P{sub TWM} and P{sub TWR}, which appear to be due to stress-induced hysteretic motions of twin boundaries within the martensite and the R-phase, respectively. In the solubilized state a large peak corresponding to the A {leftrightarrow} M transition is observed together with a thermally activated relaxation P{sub d} occurring at around 100 K (for f = 1.2 kHz). The activation energy and limit time of this peak are 0.11 eV and 10{sup {minus}10} s, respectively. Peak P{sub TWM} was not observed in the solubilized state. Peak P{sub d}, which is found to increase with the number of thermal cycles through the transition region undergone by the sample, is attributed to stress-induced motions of dislocations around their equilibrium positions within the B19{prime} structure of the martensite. The absence of a twin boundary peak in the martensite formed from the solubilized austenite, as well as the large difference in the strength of the transformation relaxations in the aged and solubilized states of the material are accounted for in terms of the different nature of the predominant twin boundaries in the two different states of the material.
- OSTI ID:
- 353483
- Journal Information:
- Acta Materialia, Vol. 47, Issue 6; Other Information: PBD: 23 Apr 1999
- Country of Publication:
- United States
- Language:
- English
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