Dynamic mechanical analysis of weak first-order martensitic transformation in an iron–palladium alloy

• Martensitic transformation behavior of an Fe–Pd alloy was studied by DMA.
• Storage modulus show a minimum at the transformation start temperature (Ms).
• Loss tangent starts to increase slightly above Ms, and shows a high value below Ms.
• The transitory term of loss tangent is negligibly for the transformation.

A disordered Fe-31.2Pd (at.%) alloy exhibits a weak first-order martensitic transformation (MT) from a face-centered cubic structure to a face-centered tetragonal structure. We employed a Dynamic Mechanical Analysis (DMA) to understand the transformation behavior. As the temperature decreases, the storage modulus E′ decreases in the parent phase and increases in the martensite phase. The loss tangent (tanδ) shows a slight increase when approaching Ms (=225 K), suggesting the formation of movable interfaces even above Ms. The value of tanδ is nearly proportional to (1 − c/a)2 below Ms, meaning that highly mobile twinned interfaces are essential for internal friction below Ms. The so-called transitory term of tanδ is negligibly small for the MT of this alloy.

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