Effect of size-dependent thermal conductivity on heat transfer and fluid flow in TiC-reinforced nanocomposites during moving annular laser melting

Abstract

Laser surface processing of metal matrix nanocomposites (MMNCs) has attracted extensive attention due to its potential for high-precision fabrication and microstructural tailoring. However, the thermal transport mechanisms influenced by the size-dependent thermal conductivity of nanoparticles remain insufficiently understood, especially in molten pools where strong thermal gradients and fluid flow coexist. To address this challenge, this study investigates the heat transfer and melt pool dynamics of TiC-reinforced Ti6Al4V MMNCs using the double distribution lattice Boltzmann method (LBM), supported by theoretical modeling, numerical simulation, and experimental validation. A size-dependent thermal conductivity model for TiC nanoparticles is established, incorporating both phonon and electron contributions as well as interfacial scattering effects. Comparative simulations at a particle diameter of 50 nm reveal notable differences in thermal and flow fields between the size-dependent and conventional models. Additionally, varying the nanoparticle diameter (30 nm, 50 nm, 100 nm) demonstrates that reduced particle size significantly lowers thermal conductivity, intensifies thermal accumulation, and elevates the melt pool temperature. Increased viscosity further suppresses Marangoni convection and reduces convective heat loss. These effects ultimately lead to an enlarged molten pool area with smaller particles. The results highlight the critical influence of nanoparticle-scale thermal conductivity on heat-fluid coupling and melt morphology, offering theoretical insight for tailoring nanoparticle properties and enhancing process control in nanocomposite laser processing. This study provides practical guidance for selecting appropriate particle sizes to improve melt pool stability, thermal efficiency, and geometric accuracy in laser surface processing of MMNCs.