Multilayer sintered ceramic body and method of making

6) A method of making a multilayer sintered ceramic body, the method comprising the steps of:

• a. combining yttria and alumina powders to make a first powder mixture;
• b. combining magnesium oxide, aluminum oxide and zirconium oxide powders to make a second powder mixture;
• c. calcining the first and second powder mixtures by applying heat to raise the temperature of the powder mixtures to a calcination temperature and maintaining the calcination temperature to perform calcination to form first and second calcined powder mixtures;
• d. separately disposing the first and second calcined powder mixtures inside a volume defined by a tool set of a sintering apparatus to form at least one layer of the first calcined powder mixture and at least one layer of the second calcined powder mixture and creating vacuum conditions inside the volume;
• e. applying pressure to the layers of the first and second calcined powder mixtures while heating to a sintering temperature and performing sintering to form the multilayer sintered ceramic body, wherein the at least one layer of the first calcined powder mixture upon sintering forms at least one first layer and the at least one layer of the second calcined powder mixture forms at least one second layer;
• and
• f. lowering the temperature of the multilayer sintered ceramic body,
• wherein the at least one first layer comprises polycrystalline YAG, wherein the at least one first layer has at least one surface;
• and at least one second layer comprising magnesium aluminate spinel, wherein the at least one surface of the at least one first layer comprises pores wherein the pores have a maximum size of from 0.1 to 5 μm as measured using SEM and image processing methods, and wherein each of the at least one first layer and the at least one second layer has a coefficient of thermal expansion (CTE), wherein the CTE of the at least one first layer and the CTE of the at least one second layer differ from Oto 0.6×10-6;0c as measured in accordance with ASTM E228-1 7 over a temperature range of 25 to 1400° C., whereby the CTE of the at least one first and second layers used for calculating each difference are each measured across the same temperature range. and the at least one second layer comprising from 0.1 to 1.0% by volume of zirconia.