Time-resolved three-dimensional X-ray tomography study on the barrier mechanism of SiC during hot-press sintering of titanium matrix composites

Achieving full densification in titanium matrix composites via sintering is critically hindered by the presence of ceramic reinforcements, yet the underlying three-dimensional mechanisms remain insufficiently characterized. This study addresses this gap by developing an integrated platform for in situ X-ray computed tomography under simulated hot-press sintering conditions at 950 °C and 20 MPa. This novel apparatus enables time-resolved three-dimensional visualization of the densification behavior of SiC-reinforced TC4 composites, compared directly with unreinforced counterparts. The results reveal the dual role of SiC particles: while their size gradation elevates the initial relative density from 67.7% (pure TC4) to 71.2%, they ultimately act as a potent kinetic barrier. SiC spatially hinders particle contact network formation, increases interparticle distances in rich domains to 20∼50 μm, and significantly limits final densification to 94.7%, markedly below the 98.0% achieved in pure TC4. Through quantitative pore evolution analysis, we establish two distinct kinetic models: "contact-diffusion-densification" for the monolithic system and "delay-hindrance-stagnation" for the composite. These findings provide convincing three-dimensional evidence that reinforcement-induced packing heterogeneity and interfacial diffusion barriers are the fundamental causes for densification stagnation, offering crucial guidance for processing high-performance titanium matrix composites.