Effect of annealing process on IR transmission and mechanical properties of spark plasma sintered Yttria

In this study, fully dense Yttria ceramics were successfully fabricated by spark plasma sintering (SPS) at temperatures of 1300 and 1350 degrees C. The effects of post-annealing on IR transmission were investigated by Fourier transform infrared spectroscopy (FTIR) at various temperatures ranging from 1050 to 1250 degrees C. It was found that the optimum annealing temperature depends strongly on the sintering temperature. Annealed samples showed white opaqueness mainly due to the increase and coalescence of pores after annealing and showed an absorption band around 6.6 mu m which limits usage of yttria in IR applications. Sintering at 1350 degrees C and annealing at 1250 degrees C led to the maximum IR transmittance above 80% at wavelength of 5 mu m for a 3.5-mm-thick sample. The hardness and the fracture toughness of the samples were analyzed in detail and hardness of 9.2 GPa and fracture toughness of 1.65 MPa m(1/2) were obtained for the above sample.