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

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 (tan δ ) shows a slight increase when approaching M s (=225 K), suggesting the formation of movable interfaces even above M s . The value of tan δ is nearly proportional to (1 − c/a ) 2 below M s , meaning that highly mobile twinned interfaces are essential for internal friction below M s . The so-called transitory term of tan δ is negligibly small for the MT of this alloy.