On the thermodynamics of thermoelastic martensitic transformations

INTRODUCTIONThe characteristic behavior of the acoustic emission during thermoelastic phase transformations in Au-Cd alloys has previously been reported (1-3). The estimated energy of the acoustic energy was found to be approximately one order of magnitude larger during the phase transformation on heating than on cooling. No attention has been paid, so far, as to the source of the acoustic activity during martensitic phase transformations. However, it is generally accepted that the rapid release of energy within a material generates transient elastic waves of a certain amplitude and frequency content. This acoustic emission is related to the intrinsic mechanism of the martensitic transformation.Martensite formation occurs by a diffusionless shear mechanism involving the cooperative movement of a large number of atoms accompanied by a release of elastic strain energy. The thermoelastic martensite is typically athermal, where the amount of martensite depends on the formation temperature during cooling. Upon heating, the reverse transformation occurs by the backward movement of the martensitic interfaces, thus annihilating the elastic shape strains introduced during the forward transformation on cooling. The almost perfectly reversible mechanism, characterizing the thermoelastic martensitic transformation (4,5) is paradoxically accompanied by a high asymmetric acoustic energy balance (1-3).The objective of this paper is to present experimental evidence concerning the acoustic energy evolved during the heating and cooling phase changes in Au-47.5 at.% Cd polycrystals. The results are examined from the point of view of the stored elastic strain energy during the martensite formation, and the frictional work that is dissipated by the movement of martensite interfaces in either direction, upon heating and cooling (6-8). EXPERIMENTAL PROCEDURE AND RESULTSPolycrystalline specimens of Au-47.5 at.% Cd alloy were heated and cooled through the transformation temperature range, from 10°C up to 120°C and back, at controlled heating and cooling rates. A quartz rod was used as a waveguide, and coupled to a PZT transducer with a resonant frequency in the 150-300 kHz range. The experimental procedure was described elsewhere (3). Filtered signals, preamplified at a constant gain of 40 dB, were fed into an amplitude detector that characterizes the acoustic emission signals according to their peak-amplitude. Amplitude *on leave from the Materials Engineering Department, Ben Gurion University, Beer Sheva, Israel distribution, with 1 dB resolution, was then performed by a Distribution Analyzer gLV1ng a definite voltage for each channel. The amplitude distribution was chart~recorded.The correlation between the peak amplitude of the signals and the energy release at the transducer face was established by letting hardened steel balls of different mass m fall onto the quartz rod and the transducer face from different heights h. The square of the recorded peak voltage and the potential energy (E = mgh) were found to be linearly related aswh...

show abstract

“…This frictional work has been shown to be dependent on the grain size (6), and is not evolved in single crystal (single interface) samples (9).…”

Section: Discussionmentioning

confidence: 99%

Release of elastic strain energy as acoustic emission during the reverse thermoelastic phase transformation in Au-47.5 at .% Cd alloy

Baram

Avissar

Gefen

et al. 1980

Scripta Metallurgica

View full text Add to dashboard Cite

show abstract

“…The austenite finish temperature, A f , can be approximated as T 0 for superelastic polycrystals [16] and modeled as a function of B2 composition using a Redlich-Kister polynomial for a 2-sublattice system. This model is analogous to the substitutional regular solution model used in solution thermodynamics with a Redlich-Kister power series model for higher-order excess free energy contributions [17].…”

Section: A F Modelmentioning

confidence: 99%

“…Jiang conducted a solution treatment study in which a 950°C 20 h homogenization was followed by 100 h solution treatments at 900, 950, 1000, and 1050°C [20]. [12], Pd (30)(31)(32)(33)(34)(35)(36) Ni (14)(15)(16)(17)(18)(19)(20) Ti (45-46) Al (4)(5) [12] The value of A corresponds to the equilibrium solubility of each component in the phase [20], (e, f) Pd 42.2 Fe 7.8 Ti 44 Al 6 at 600°C [21], and (g, h) Pd 30 Ni 20 Ti 38 Zr 8 Al 4 at 600°C. The x-axis is scaled such that x max = 1/r * , i.e., corresponding to the critical radius for nucleation Solution treatments led to spheroidization and a slight reduction in phase fraction of the Ti-rich secondary phase, but full dissolution of the phase was not observed.…”

Section: Pdti-base Systemsmentioning

confidence: 99%

Design of Heusler Precipitation Strengthened NiTi- and PdTi-Base SMAs for Cyclic Performance

Frankel

Olson

2015

Shap. Mem. Superelasticity

View full text Add to dashboard Cite

For a wide range of actuation applications, the performance of NiTi-based shape memory alloys is limited by cyclic instability associated with accommodation slip. For medical applications, low-Ni compositions are also desirable. Increasing yield strength via precipitation of a coherent nanoscale Ni 2 TiAl-type Heusler phase from a supersaturated B2 matrix is an effective approach for eliminating slip in order to improve the stability of the functional response and increase the structural fatigue life. Quaternary additions that partition into the L2 1 Heusler phase, such as Zr or Pd, are favorable for reducing interphase misfit and maintaining coherency during aging. Phase relations and precipitation kinetics in quaternary Ni(TiZrAl), low-Ni (PdNi)(TiAl), and Ni-free (PdFe)(TiAl) systems are summarized from TEM and atom probe tomography data in the literature. Strengthening behavior during isothermal aging is compared in the NiTiZrAl and PdNiTiAl systems, and recent work characterizing a high-strength, low-Ni ''Hybrid'' (PdNi)(TiZrAl) alloy is presented. A systems design approach is taken in which an optimal microstructure for peak strengthening is identified while other property objectives such as transformation temperature, misfit, radiopacity, and biocompatibility are satisfied.

show abstract

“…Pr8-123 Accordingly, replacing T 0 by (12) in (8) as well as (9) the quantities (13) can be calculated as the function of pressure, where AH c (0)=T o (0)AS c is the chemical enthalpy difference between the two phases at T o (0). The curves according to (13) are shown on Fig.4a-b.…”

Section: Esomat2000mentioning

confidence: 99%

Effect of hydrostatic pressures on thermoelastic martensitic transformations

et al. 2001

View full text Add to dashboard Cite

Abstract. Supposing that -according to the Clausius-Clapeyron equation -the volume change of the transformation is responsible for the pressure dependence of the equilibrium temperature T 0 , and that the elastic energy term, e 0 , corresponding to the martensite start, M s , (and austenite finish, Af;) temperatures, differs from zero as well, the pressure dependence of the elastic and dissipative energy terms of the martensitic and reverse transformations can be separated. It is illustrated by the example of our experimental results for the pressure effect on the transformations in Cu-22at%Zn-12at%Al-lat%Mn [1] as well as in near equiatomic NiTi shape memory alloys [2]. The elastic energy term, e", showed different behaviour in the low-pressure range for samples of different pre-history, while at high pressures the pressure dependence of the elastic and dissipative terms showed a more general trend.

show abstract

On the thermodynamics of thermoelastic martensitic transformations

Cited by 362 publications

References 11 publications

Release of elastic strain energy as acoustic emission during the reverse thermoelastic phase transformation in Au-47.5 at .% Cd alloy

Release of elastic strain energy as acoustic emission during the reverse thermoelastic phase transformation in Au-47.5 at .% Cd alloy

Design of Heusler Precipitation Strengthened NiTi- and PdTi-Base SMAs for Cyclic Performance

Effect of hydrostatic pressures on thermoelastic martensitic transformations

Contact Info

Product

Resources

About