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Phase Relations and Microstructural Development of Aluminum Nitride–Aluminum Nitride Polytypoid Composites in the Aluminum Nitride–Alumina–Yttria System
Author(s) -
Tangen IngerLise,
Yu Yingda,
Grande Tor,
Høier Ragnvald,
Einarsrud MariAnn
Publication year - 2004
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2004.01734.x
Subject(s) - materials science , nitride , sintering , nucleation , equiaxed crystals , high resolution transmission electron microscopy , composite material , aluminium nitride , phase (matter) , aluminium , fracture toughness , composite number , ternary operation , microstructure , nanotechnology , transmission electron microscopy , chemistry , organic chemistry , layer (electronics) , computer science , programming language
AlN–AlN polytypoid composite materials were prepared in situ using pressureless sintering of AlN–Al 2 O 3 mixtures (3.7–16.6 mol% Al 2 O 3 ) using Y 2 O 3 (1.4–1.5 wt%) as a sintering additive. Materials fired at 1950°C consisted of elongated grains of AlN polytypoids embedded in equiaxed AlN grains. The Al 2 O 3 content in the polytypoids varied systematically with the overall Al 2 O 3 content, but equilibrium phase composition was not established because of slow nucleation rate and rapid grain growth of the polytypoid grains. The polytypoids, 24 H and 39 R , previously not reported, were identified using HRTEM. Solid solution of Y 2 O 3 in the polytypoids was demonstrated, and Y 2 O 3 was shown to influence the stability of the AlN polytypoids. The present phase observations were summarized in a phase diagram for a binary section in the ternary system AlN–Al 2 O 3 –Y 2 O 3 parallel to the AlN–Al 2 O 3 join. Fracture toughness estimated from indentation measurements gave no evidence for a strengthening mechanism due to the elongated polytypoids.