Dense cu-sialon materials were produced by hot isostatic pressing (HIP) and post-hot isostatic pressing (post-HIP) using compositions with the formula Yx(Si 12-1.5i,A14.5x)-(Ol,5x,NL6-,.5x) with 0.1 5 x 5 0.9 and with the same compositions with extra additions of yttria and aluminum nitride. X-ray diffraction analyses show how the phase content changes from large amounts of p-sialon (x = 0.1) to large amounts of a-sialon (x = 0.4) and increasing amounts of mellilite and sialon polytypoids (x = 0.8). Samples HIPed at 1600°C for 2 h contained unreacted a-silicon nitride, while those HIPed at 1750°C for 1 h did not. This could be due lo the fact that the time is too short to achieve equilibrium or that the high pressure (200 MPa) prohibits cY-sialon formation. Sintering at atmospheric pressure leads to open porosity for all compositions except those with excess yttria. Therefore, only samples with excess yttria were post-HIPed. Microstructural analyses showed that the post-HIPed samples had the highest wsialon content. A higher amount of crsialon and subsequently a lower amount of intergranular phase were detected at x = 0.3 and x = 0.4 in the postHIPed samples in comparison to the HIPed. The hardness (HVIO) and fracture toughness (Krc) did not differ significantly between HIPed and post-HIPed materials but vary with differentx values due to different phase contents. Measurements of cell parameters for all compositions show a continuous increase with increasing x value which is enhanced by high pressure at high x values. [
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