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Influence of Transient Liquid Phase Promoting Additives upon Reactive Plasma Spraying of AlN Coatings and Its Properties
Author(s) -
Shahien Mohammed,
Yamada Motohiro,
Fukumoto Masahiro
Publication year - 2018
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201700917
Subject(s) - materials science , wetting , phase (matter) , porosity , oxide , chemical engineering , crystallite , thermal conductivity , plasma , thermal spraying , raw material , aluminium oxide , sintering , aluminate , composite material , metallurgy , coating , cement , chemistry , physics , organic chemistry , quantum mechanics , engineering
The feasibility of using a transient liquid phase promoting agent upon reactive plasma spraying (RPS) of AlN coatings in atmospheric ambient is successfully investigated. Several sprayable fine AlN–Al 2 O 3 –Y 2 O 3 mixtures with different compositions are prepared by spray‐drying. Upon plasma spraying in N 2 /H 2 plasma, thick and homogeneous AlN based coatings ( h ‐AlN, c ‐AlN, γ ‐Al 2 O 3 , Al 5 O 6 N, α ‐Al 2 O 3 , and YAG) are fabricated. Fine Y 2 O 3 acts as transient liquid phase promoting additive, and reacts with Al 2 O 3 phase (from feedstock mixture and on AlN particles surface) to create wetting agent of yttrium aluminate Y–Al–O around solid AlN particles. However, due to rapid solidification rates of plasma, it is difficult to react with the interspersed oxygen in AlN grains. The Y 2 O 3 addition significantly reduces the coatings oxide content due to the consumption of starting Al 2 O 3 to form the YAG. Influence of Y 2 O 3 significantly observes with increasing AlN feedstock and high AlN content coatings with small oxides are fabricated by RPS of 80AlN–10Al 2 O 3 –10Y 2 O 3 mixture. Thermal conductivity is improved with using Y 2 O 3 and increasing AlN feedstock. However, the conductivity is not so high compared to the AlN compacts, due to increased porosity, incomplete sintering of the formed initial liquid phase state, remaining oxide content, and low density of the coatings.