Effect of dual elements (Ca, Mg) and (Ca, La) on cell dimensions of multi-cation α-sialons

The lattice parameters of multi-cation α-sialons containing Ca and Mg have been studied for the compositions MxSi12–3nAl3–nOnN16–n (M=0.5Ca+0.5Mg) with x ranging from 0.3 to 1.4 by using a Guinier–Hägg camera film data. The results indicated that the cell dimensions of Ca, Mg-α-sialon were obviously smaller than that of Ca-α-sialon with the same compositions. The EDAX analysis showed that the contents of Ca in the grains were much higher than Mg and the average value of Ca contents could be close to the one in nominal composition, implying that Ca was easily “pushed” towards α-sialon structure in multi-cation α-sialons case. Based on these results, α-sialon ceramics using 70%Ca+30%La as additives were prepared. The lattice parameters of the α-sialons, in which 30%Ca were replaced by La as additives, were close to the single-cation Ca-α-sialon under the same compositions, indicating that most of Ca were incorporated in α-sialon because La cannot be absorbed to α-sialon structure. The advantage of using additives Ca combined with La to form α-sialon was discussed in the paper. Consequently, one composition of α-sialon with Ca and La as additives possessing hardness Hv10 and fracture toughness K1c to be 18.5 GPa and 5.5 MPa m1/2, respectively, was obtained.