Processing and Characterization of Multiphase Ceramic Composites Part II: Triplex Composites with a Wide Sintering Temperature Range

Abstract

Three‐phase (triplex) ceramic composites with improved thermal stabilities resulting from minimized grain growth due to extended grain separations are introduced. Al2O3, yttrium aluminum garnet (YAG, Y3Al5O12), and ZrO2 were chemically compatible to make a stable triplex composite. Another stable composite could be made due to chemical compatibility among Al2O3, NiAl2O4, and 3 mol% yttria‐tetragonal zirconia polycrystals (3Y‐TZP). The composites of 33 vol% Al2O3–33 vol% YAG–33 vol% ZrO2, 33 vol% Al2O3–33 vol% NiAl2O4–33 vol% 3Y‐TZP, and 50 vol% Al2O3–25 vol% NiAl2O4–25 vol% 3Y‐TZP were fabricated using either sintering or hot pressing procedures. The sintered 33 vol% Al2O3–33 vol% YAG–33 vol% ZrO2 and 33 vol% Al2O3–33 vol% NiAl2O4–33 vol% 3Y‐TZP composites demonstrated a “self accommodating sintering effect” having a wide sintering range without any extensive change in properties. Annealing of the 33 vol% Al2O3–33 vol% NiAl2O4–33 vol% 3Y‐TZP composite at 1600°C for 50 h resulted in higher strength retention after heat treatment compared with that expected from the sum of the strengths of constituent phases. This was attributed to a mutual, grain growth retardation effect. Chemical compatibilities, mechanical properties, microstructures, and thermal stabilities of the composites were studied.

Al2O3/ZrO2/Y3Al5O12 Composites: A High-Temperature Mechanical Characterization

“…Concerning the triphasic AZY system, Oelgardt et al [16] investigated a 45 vol% alumina–17 mol% ZrO 2 –38 mol% YAG composite and determined a flexural strength of about 280 MPa. Kim et al [17] determined values in the range of 200–350 MPa for the 33 vol% alumina–33 vol% ZrO 2 –33 vol% YAG composite. Although limited, these previous data are in a good agreement with the current results.…”

“…All of these drawbacks can be easily overcome by the manufacturing of sintered polycrystalline materials. Once again, the binary Al 2 O 3 /YAG [14,15] and the ternary Al 2 O 3 /ZrO 2 /YAG [16,17] sintered composites seem promising for high-temperature structural applications [14,15,16]. …”

Issues in Nanocomposite Ceramic Engineering: Focus on Processing and Properties of Alumina-based Composites

“…This approach allows the generation of interconnected structures, so that the growth of each phase during sintering is hindered by the others, as the long-order interdiffusion is strongly limited (28, 29). Equivolumetric Al 2 O 3 –YAG–ZrO 2 composites were produced by Kim and Kriven (30) as well as by Oelgardt et al (31), with the aim of yielding materials with high strength retention even after prolonged high-temperature annealing. For the same purpose, Kim and Kriven produced alumina-based quadruplex and quintuplex composites (32), to achieve an increased microstructural stability during prolonged high-temperature service, due to longer interdiffusion distances between grains of the same phase.…”

Processing and Characterization of Multiphase Ceramic Composites Part III: Strong, Hard and Tough, High Temperature‐Stable Quadruplex and Quintuplex Composites

“…For an ideal, close‐packed single‐phase system, the average grain separation distance ( S avg ), with respect to the center grain, from the nearest six grains of the same phase, is 2 R ( R is the average radius of the grains). The S avg values of two‐, three‐, four‐, and five‐phase composites are 3.15 R , 3.46 R , 4.25 R , and 4.68 R , respectively 44 . This means that S avg in the four‐ and five‐phase composites increase by 2.13 and 2.34 times, respectively, as compared with that of the single‐phase material.…”