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Shock‐Induced Transformations in Hexagonal Boron Nitride by High‐Velocity Thermal Spray
Author(s) -
Goswami Ramasis,
Herman Herbert,
Sampath Sanjay,
Parise John,
Zhu Yimei,
Welch David
Publication year - 2002
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.1151-2916.2002.tb00477.x
Subject(s) - materials science , boron nitride , nucleation , shearing (physics) , shock wave , transmission electron microscopy , thermal shock , amorphous solid , composite material , hexagonal boron nitride , shock (circulatory) , crystallography , nanotechnology , chemistry , mechanics , medicine , physics , graphene , organic chemistry
Shock synthesis of cubic BN ( c ‐BN) was accomplished using high‐velocity thermal spray. Al‐8Si‐20BN (hexagonal BN, h ‐BN) composite powders were injected into a high‐energy flame where the particles partially melted and accelerated to impact on steel substrates. The shock wave generated by the sudden impact of the droplets propagated through the underlying deposit, which experienced a polymorphic transition to high‐pressure forms. Transmission electron microscopy revealed that the deposits contained platelike c ‐BN embedded in h ‐BN. The c ‐BN formed with a specific orientation relation, with (0001) h ‐BN parallel to (111) c ‐BN and [11–20] h ‐BN nearly parallel to [2–20] c ‐BN. As a result of shock propagation, a number of half‐Frank loops with Burgers vector ½[0001] were introduced and thin (∼3 nm) layers of amorphous BN ( a ‐BN), parallel to the (0002) plane, were formed. Significant shearing of the (10–10) plane with respect to the c ‐axis, delamination, and kink bands were also observed in most of the h ‐BN grains. The Hugoniot pressure calculation suggested that the impact pressure was sufficient to trigger the nucleation of c ‐BN.