H. Tamura et al., SPRAYING OF THE BRITTLE CERAMIC ZIRCONIUM DIBORIDE BY A WIRE EXPLOSION TECHNIQUE, Journal of applied physics, 75(3), 1994, pp. 1789-1797
A wire explosion technique was employed for the spraying of zirconium
diboride, a high-melting-point, brittle ceramic. To study its spraying
mechanism and the feasibility of high-density coating, the explosion
of a ZrB2 ceramic wire was examined with time-resolved measurements of
the apparent resistance of an exploding wire, expansion of a discharg
e channel, wire fragmentation, and gas flow around the wire. The explo
sion under argon gas of 0.1 MPa in base pressure was started with heat
ing up to the melting point of ZrB2, and with sequential gas breakdown
around the wire. The breakdown was followed by the formation of a cyl
indrical shock wave and an electrical discharge channel, and by their
expansion. Wire breaks were found at a later period of the electrical
discharge, and resulted in the fragmentation of the wire of less than
1 mm in size, and in the transformation of almost the whole wire into
fine-molten particles. On the other hand, at the explosion under air o
f 13.3 Pa in base pressure no shock wave was found, but larger fragmen
ts of the wire and the transformation of about 50% of the wire volume
into fine particles were observed. ZrB2 coated substrates were analyze
d with x-ray diffraction and scanning electron microscopy. The sprayin
g under the high-base-pressure condition provided a much denser coatin
g than that under the low base pressure. However, a small number of cr
acks was found on the sprayed film surface, and it was assumed that th
eir formation was induced due to the brittleness of ZrB2. These measur
ements have revealed the close relation of the wire explosion to the b
ase pressure of surrounding gas, and, in particular, the result that t
he high-base-pressure explosion associated with a cylindrical shock wa
ve could provide a high-density coating. In consideration of the exist
ence of high-base-pressure gas and the structure of a shock wave and a
n associated discharge channel, it is suggested that adequate heating
and high-temperature holding of the wire plays an important role in th
e spraying. The spraying of ZrB2 wires presented here has revealed the
feasibility of high-density coating of refractory, brittle ceramics w
ith the wire explosion technique.