Allotropic α→β transformation in diffusion-graded commercial-purity Ti–Zr multilayers: DSC overlapping peak deconvolution and kissinger kinetic analysis

Abstract

Multilayered Ti–Zr mesostructures were produced from commercially pure Ti and Zr by subsequent hot compression and heat treatment then annealed at 740 °C and 770 °C for 120 h to generate a near-continuous Ti-rich to Zr-rich concentration gradient. Differential scanning calorimetry (DSC) was used to examine the α→β transformation at heating rates of 10–25 K/min, supported by optical microscopy and SEM–EDS to assess the extent of diffusion. The first endothermic reaction starts near the ∼50–50 at% Ti-Zr region where the transformation temperature is lowest according to the published and Thermo-calc calculated phase diagrams, while subsequent reactions occur in adjacent Ti- and Zr-rich compositions, producing strongly overlapping peaks in a small temperature range. The low-temperature peak ranges occur at 549.9 °C −562.1 °C and 570.4 °C −576.6 °C after 740 °C annealing, and at 543.5 °C −589.3 °C and 584.6 °C −645.3 °C after 770 °C annealing, followed by a high-temperature β-completion peak at 838 °C −867.6 °C (740 °C) or 915 °C −926.8 °C (770 °C). A Savitzky–Golay filtering, derivative-based segmentation, and Avrami-type deconvolution were used to isolate the overlapping reactions, and Kissinger analysis of the deconvoluted peaks provided apparent activation energies for each step. For the 740 °C samples, the first two low-temperature (onset) steps show higher apparent activation energies (225.7 and 474.7 kJ·mol⁻¹) than the β-completion step (163.145 kJ·mol⁻¹), while for the 770 °C samples the trend reverses (74.5 and 60.1 kJ·mol⁻¹ vs. 676.3 kJ·mol⁻¹). This change in trend indicates that diffusion heat treatment changes the gradient geometry, which controls peak overlap and shifts the apparent kinetics from deconvolution.