DSC calibration in the study of shape memory alloys

Airoldi, G.; Riva, G.; Rivolta, B.; Vanelli, M.

doi:10.1007/bf02546750

Cited by 18 publications

(6 citation statements)

References 6 publications

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“…Despite the traditional thermodynamic description of martensitic transformations as first-order, (4)(5)(6)(7) this material exhibits a continuous transition that is similar in shape to that of the order-disorder transition in β-brass. (13) The heat capacity shown in inset (a) of figure 4 tends to infinity at T M with a characteristic lamda shape.…”

Section: Discussionmentioning

confidence: 93%

“…(4)(5)(6)(7) However, the limited resolution and accuracy of differential scanning techniques has motivated us to do a more careful study of the martensitic transformation in a single crystal of AuZn using a low-temperature heat capacity apparatus designed for high-accuracy and high-precision measurements. Because the single-crystal sample used in these measurements only constitutes a small fraction of the total measured heat capacity, we also present heat capacity results on a high-purity single crystal of copper to demonstrate the accuracy and resolution of our apparatus.…”

Section: -9614/02mentioning

confidence: 99%

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The heat capacity of single-crystal AuZn near the martensitic transition

Lashley

Lang

Boerio‐Goates

et al. 2002

The Journal of Chemical Thermodynamics

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Section: Discussionmentioning

confidence: 93%

Section: -9614/02mentioning

confidence: 99%

The heat capacity of single-crystal AuZn near the martensitic transition

Lashley

Lang

Boerio‐Goates

et al. 2002

The Journal of Chemical Thermodynamics

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“…The calorimeter was calibrated using an ad hoc calibration method developed for shape memory alloys [6]. A 0.083 "Clsec rate was adopted.…”

Section: Methodsmentioning

confidence: 99%

The Reversion Force of NiTi Orthodontic Wires in the Temperature Domain 5 ÷ 55 °C

1997

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Abstract. The interest in using the pseudoelastic properties of NiTi wires in orthodontic practice arises chiefly from the expectation that they can afford low continuous forces at constant temperature. The reversion force developed by NiTi archwires depends, however, upon temperature since the superelastic force follows a Clausius-Clapeyron like equation. Actually the oral environment temperature is modified as a consequence of hotJcold liquid/solid intake in the temperature range 5"-5S°C, as previously evaluated. In the above-mentioned temperature range first results have already been obtained on the reversion force variation. Attention is focused here on the reversion force as a function of temperature under different fixed constraints. Tensile and 3-point bending tests have been performed on NiTi orthodontic wires, adopted in orthodontic practice, starting at body temperature: loading and partial unloading have been performed in order to fix different constraint conditions corresponding to different states in orthodontic therapy. The variation of the reversion force has been studied as a function of temperature. Evidence has been obtained of the hysteretic behaviour of the reversion force as a function of temperature. The results show that after a temperature loop to high temperature the reversion force is generally changed: the overall shape of the hysteresis cycle appears dominated by the presence of the R-phase at T<37OC and by the stress-induced martensite at P37OC.

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“…Following [23], k can be calculated by using the high temperature B2 structure. In fact, it is well known that in cubic systems the error A(28) in the determination of the Bragg peaks positions is related to the error in the determination of the lattice parameter a , through the relation:…”

Section: The Calibration Methodsmentioning

confidence: 99%

X-Ray Powder Diffraction Study of the R-Phase in a Ti50Ni48Fe2 Alloy by a New Calibration Method

Airoldi

Carcano²,

Riva

et al. 1995

J. Phys. IV France

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the R-phase in a polycrystalline 50Ti48Ni2Fe shape memory alloy has been here investigated by X-Ray Powder counter Diffractometry (XRPD). With the aim to determine the R-phase lattice parameters accurately, a n original XRPD calibration method, specifically apt for shape memory alloys, has been developed. The intrinsic aberrations that affect the XRPD have been takeninto account by evaluating theXRPD spectrum of the high temperature b.c.c. phase. The correction function A(28) has been calculated and applied to the R-phase diffraction peaks. A full indexing of the X-ray spectrum of the R-phase, not achievable by raw experimental data, has thus been obtained and the lattice parameters calculated on a set of reflections in un-aberrated angular positions with a n accuracy of = 1 part in 10000. The calibration method here developed can be used also in the XRPD study of crystalline materials that undergo a first solid-solid phase transition. l. INTRODUCTIONThe shape memory alloys (SMA) rely their unusual mechanical properties (shape memory and pseudoelasticity) on the thermoelastic martensitic transformation (TMT), a first-order solidsolid, diffusionless, athermal transformation. In NiTi alloys, critically depending upon composition andlor thermo-mechanical treatment, a rhombohedral phase (R-phase) can appear stable between the high temperature b.c.c phase (B2-phase) and the low temperature lnonoclinic phase (M-phase). Since the first detection of electric transport anomalies in the premartensitic region [l], the R-phase in NiTi alloys has been widely investigated. Initially considered a "pre-martensitic" effect and later assessed as an independent phase from the martensitic one, the R-phase does exhibit precursory effects during the B2+R phase transformation: the softening of some elastic constants [2], the appearance of diffuse "extraspots" not in the exact 113 positions in the electronic diffraction patterns [3,4], and the very large minimum in the electrical resistance, have been extensively studied. The break-through was given by [5] investigating a 50Ti47Ni3Fe where the B2+R transformation is well separated from the R+M one, on the temperature scale. Theoretical models to explain the origin of the R-phase transformation and the related precursory effects, have been proposed [6-81. The thermoelastic nature of the B2-R transformation and the process of R-phase variants self-accomodation have been assessed . Moreover, the shape memory effect and the pseudoelasticity related to the B2++Rhas beenillvestigated [9,11-121 as well. Concerning tothe R-phase crystal structure itself, many investigations were also accomplished [10,13-141, Article published online by EDP Sciences and available at http://dx

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DSC calibration in the study of shape memory alloys

Cited by 18 publications

References 6 publications

The heat capacity of single-crystal AuZn near the martensitic transition

The heat capacity of single-crystal AuZn near the martensitic transition

The Reversion Force of NiTi Orthodontic Wires in the Temperature Domain 5 ÷ 55 °C

X-Ray Powder Diffraction Study of the R-Phase in a Ti50Ni48Fe2 Alloy by a New Calibration Method

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