Controlled grain size modulation in metals via spatial thermal gradient sintering

Grain size engineering offers a powerful pathway to enhance the mechanical performance of metallic materials, yet conventional methods for creating gradient microstructures suffer from limited penetration depth, slow processing, and complex fabrication routes. Here, we present a spatial thermal gradient sintering (STGS) approach that addresses these limitations by using independently powered carbon heaters to impose programmable spatial temperature gradients with millisecond-level temporal resolution, enabling ultrafast (<2 min) processing of bulk samples. STGS provides a scalable platform for one-step fabrication of grain-size gradients in bulk metals through spatially differentiated grain growth. As a proof-of-concept demonstration, STGS of titanium was carried out at heater temperatures of 1300 K and 2500 K, producing distinct low- and high-temperature regions. Spatially resolved electron backscatter diffraction reveals a systematic decrease in average grain size from 17.57 ± 8.21 µm to 11.94 ± 4.21 µm across four ordered regions from the high-temperature side toward the low-temperature side. The corresponding average hardness increases from 238.63 ± 8.85 HV to 282.71 ± 21.31 HV and exhibits a clear Hall-Petch-type dependence on representative grain size. This work establishes STGS as a scalable and versatile platform for fabricating bulk grain-size gradients metals, enabling spatially programmable property distributions for applications ranging from aerospace structures to biomedical implants and other advanced engineering systems.