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

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 hours 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. • SEM–EDS verified the diffusion state and linked peak evolution to gradient compactness. • Interdiffusion annealing (740–770 °C, 120 h) produced a continuous Ti–Zr composition gradient in a multilayer specimen. • Heat treatment shifted and compressed the α→β transformation temperature range across the gradient. • DSC at multiple heating rates captured sequential, strongly overlapping α→β endotherms initiating near the ~50/50 at% region. • Constrained Avrami-type deconvolution separated overlapping reactions and enabled Kissinger activation-energy estimates for each step. SEM–EDS line scans verified the diffusion state and linked peak overlap/evolution to gradient compactness.