KINETICS OF COMPACTION OF HOT-PRESSED COMPOSITE MATERIALS
IN THE TiN – AlN SYSTEM
T. V. Mosina
Translated from Novye Ogneupory, No. 8, pp. 57 – 60, August, 2004.
Original article submitted February 2, 2004.
The kinetics of compaction of hot-pressed materials in the TiN – AlN system has been studied. The shrinkage
of TiN – AlN composites (for an AlN concentration varying within 10 – 90 vol.%) occurs within 10 – 15 min
in the temperature range 1750 – 1850°C at a pressure of 65 MPa. The calculated activation energy for
hot-pressed ceramic [50% TiN + 50% AlN] was found to be 5.0 eV, intermediate between the activation ener
gies for neat TiN and AlN species. This implies that the sintering of hot-pressed heterophase mixtures charac
terized by a decrease of temperature under isothermal conditions is an activated process.
Techniques commonly employed in the manufacture of
engineering components from powders are molding followed
by sintering in high-temperature furnaces or sintering of
powders under pressure (hot pressing). In the hot pressing
(HP) method, the compaction is effected by the combined ac-
tion of capillary forces and pressure applied. This method
makes it possible to save compaction time and to prepare
specimens with a density close to theoretical.
Materials and methodology. Powdered materials tested
for compaction were: (i) 100% TiN; (ii) 10% TiN + 90%
AlN; (iii) 25% TiN + 75% AlN; (iv) 35% TiN + 65% AlN;
(v) 50% TiN + 50% AlN; (vi) 65% TiN + 35% AlN;
(vii) 75% TiN + 25% AlN; (viii) 90% TiN + 10% AlN, and
(ix) 100% AlN.
Commercial powders TiN (TU 09-112–75 Specifica
tions) and AlN (TU 6-09-110–75 Specifications) (available
from a Donetsk manufacturer of chemicals) were used. The
as-received powders were ground to a finer grain size. The
average particle size for separately ground materials was
8.3 mm for TiN and 2.7 mm for AlN; the average particle size
for the two materials ground in the mixture was2–5mm.
The HP parameters were: temperature, 1750 – 1850°C;
isothermal holding time, 15 – 30 min, and molding pressure,
25 – 30 MPa.
Hot pressing was done on an inductively heated
SPD-120 unit using graphite press-molds. A press-mold was
heated to a specified temperature (controlled by a Promin’-
type optical pyrometer) and a molding pressure was applied.
Press-molds made from MPG-7 graphite were used. To mini-
mize external friction, the die walls were machined to a high
degree of surface finish; additionally, a solid lubricant, boron
nitride, was used. Boron nitride prevented the interaction of
AlN and TiN with graphite during hot pressing.
In the final HP stage, the process of material compaction
tends to decelerate because of the “entrapment” of the gas in
pores. The compaction process may stop as soon as a state of
equilibrium is reached between the external pressure and
Laplace pressure, on the one hand, and the pore gas pressure
on the other hand. A strong gas effect on the density of
hot-pressed components has been observed with finely dis
persed powders where the powder particles, owing to their
well-developed surface, are capable of uptaking a large
amount of gas. The gas desorption is another factor that in
terferes with obtaining a high density in powders treated by
hot pressing. It was shown experimentally that the surface of
preforms subjected to rapid heating under pressure becomes
hardened and impervious to the gas escape, which results in a
low density and degraded physicomechanical characteristics.
The shrinkage of hot-pressed specimens was continu
ously recorded by means of an indicator card drum mechani
cally linked to the plunger lever of the press. The relative ac
tual density r was determined by the formula
r = g
is the theoretical density of the specimen, h
the actual height, and h
is the final height of the specimen.
Refractories and Industrial Ceramics Vol. 45, No. 6, 2004
1083-4877/04/4506-0424 © 2004 Springer Science+Business Media, Inc.
I. N. Frantsevich Institute for Problems of Materials Science, Na
tional Academy of Sciences of Ukraine, Kiev, Ukraine.