FGM of YAG-MgO composites with enhanced thermal conductivity using spark plasma sintering

YAG-based materials, widely used as lasing media, offer only moderate thermal conductivity (~ 10 W/mK), posing challenges for thermal management in solid-state lasers where pump-induced heat leads to thermal gradients that impair performance. To address this issue, MgO with high thermal conductivity (40–60 W/mK) is proposed as a heat sink material. Direct bonding of MgO to YAG is challenging due to their different thermal expansion coefficients. This study introduces a novel approach using a functionally graded material (FGM) to bond heat conductive MgO/YAG composite to YAG disc via spark plasma sintering (SPS). It was found that a YAG/MGO composite with 50 wt% MgO led to an improvement of over 100% in thermal conductivity between room temperature and 200 °C. The influence of FGM architecture, layer composition and thickness, and sintering parameters on sample integrity and microstructure was systematically investigated. Through optimization, a dense FGM structure with step-gradient concentrations, and robust interfacial bonding was obtained. The final sample consisted of a 13-layer FGM bonded to a YAG disc, fabricated under optimal sintering conditions of 1350 °C and 100 MPa, with a 15 min dwell time and a cooling rate of 30 °C min^− 1. SEM/EDS analysis confirms a gradual distribution of phases and seamless bonding at the interfaces. These findings indicate that the proposed FGM approach offers an effective means for fabricating smart structures tailored to advanced technological applications.