On the interpretation of differential scanning calorimetry results for thermoelastic martensitic transformations: Athermal versus thermally activated kinetics

Journal Article · Wed May 01 00:00:00 EDT 1996 · Scripta Materialia

DOI:https://doi.org/10.1016/1359-6462(95)00674-5· OSTI ID:233884

Van Humbeeck, J ^[1]; Planes, A ^[2]

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1. K.U. Leuven (Belgium)
2. Univ. de Barcelona (Spain)

Experimentally, two distinct classes of martensitic transformations are considered: athermal and isothermal. In the former class, on cooling, at some well-defined start temperature (M{sub s}), isolated small regions of the martensitic product begin to appear in the parent phase. The transformation at any temperature appears to be instantaneous in practical time scales, and the amount of transformed material (x) does not depend on time, i.e., it increases at each step of lowering temperature. The transition is not completed until the temperature is lowered below M{sub f} (martensite finish temperature). The transformation temperatures are only determined by chemical (composition and degree of order) and microstructural factors. The external controlling parameter (T or applied stress) determines the free energy difference between the high and the low temperature phases, which provides the driving force for the transition. In the development of athermal martensite activation kinetics is secondary. Athermal martensite, as observed in the well known shape memory alloys Cu-Zn-Al, Cu-Al-Ni and Ni-Ti, cannot be attributed to a thermally activated mechanism for which kinetics are generally described by the Arrhenius rate equation. However, the latter has been applied by Lipe and Morris to results for the Martensitic Transformation of Cu-Al-Ni-B-Mn obtained by conventional Differential Scanning Calorimetry (DSC). It is the concern of the authors of this letter to point out the incongruences arising from the analysis of calorimetric results, corresponding to forward and reverse thermoelastic martensitic transformations, in terms of standard kinetic analysis based on the Arrhenius rate equation.

• OSTI ID: 233884
• Journal Information: Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 9 Vol. 34; ISSN 1359-6462; ISSN XZ503X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTIVATION ENERGY
ALUMINIUM ALLOYS
ARRHENIUS EQUATION
BORON ALLOYS
CALORIMETRY
COPPER BASE ALLOYS
CRYSTAL-PHASE TRANSFORMATIONS
FREE ENERGY
HYSTERESIS
IRON BASE ALLOYS
ISOTHERMAL PROCESSES
MANGANESE ALLOYS
NICKEL ALLOYS
STRESSES
TEMPERATURE DEPENDENCE
TITANIUM ALLOYS
TRANSITION TEMPERATURE
ZINC ALLOYS