Investigation of spark plasma sintered aluminum nitride ceramics for MIR windows applications

Abstract This study reports the development of translucent‐grade aluminum nitride (AlN) ceramics using a spark plasma sintering (SPS) technique for MIR applications. To enhance densification and translucency, a low‐melting‐point additive, CaF 2 , was introduced at varying concentrations. The optimized composition of 97 wt% AlN with 3 wt% CaF 2 yielded translucent‐grade ceramics with a relative density of 99% and a hardness of 1289 HV 1 . At a sintering temperature of 1800°C, near monolithic AlN ceramics were produced, exhibiting an average grain size of 2.30 µm, a thermal conductivity of 95.2 W/m·K, and a negligible presence of secondary phases and pores. Consequently, the in‐line transmission efficiency improved, remaining stable across the 2.5–6.0 µm wavelength range, attributed to well‐defined grain boundaries that minimized scattering losses. Moreover, intergranular fracture was predominant in the AlN sintered sample with CaF 2 , whereas AlN without the additive underwent oxidation at higher temperatures, which resulted in increased bulk density and predominantly transgranular fracture. In addition, surface machining using the micro laser‐assisted machining technique achieved a surface finish of 0.1855 µm. Overall, the developed AlN ceramics, with their obtained optical, thermal, and mechanical properties, demonstrate potential for use as MIR window materials.