SURFACE STRENGTH AND CRACK RESISTANCE OF VERY HARD
CERAMIC MATERIALS TESTED BY MICROINDENTATION
O. I. Pushkarev
and E. D. Kuznetsova
Translated from Novye Ogneupory, No. 4, pp. 38 – 41, April, 2002.
Load and energy conditions for nucleation and crack growth in the vicinity of a local stress concentrator — the
impression of a diamond indenter — are formulated. Crack resistance characteristics are given for a wide
range of carbide and boride ceramic materials, and their correlation with the wear resistance of friction surface
determined under laboratory and industrial conditions is discussed.
In recent years, much attention has been given to the
study of surface strength and crack resistance of very hard
refractory materials, using, among other techniques, the
microindentation method owing to its ability to provide a
high localization of the external load applied. This method
makes it possible to explore the nucleation and propagation
of cracks that finally results in the brittle failure of materials
tested [1 – 3].
Microindentation of very hard and brittle materials initi-
ates interrelated processes of strain of the material — the for-
mation of an impression of size d (diagonal) and brittle fail-
ure of its individual microscopic components and the occur
rence in the vicinity of the impression of a brittle damage
zone D including all types of impaired structural integrity,
for example cracks and spallings (Fig. 1). The size of this af
fected zone varies with the brittle and strength properties of
the material tested and testing conditions (indenter load P,
angle of indentation a, and indenter geometry).
The familiar indentation law P = f (d ), commonly ap
plied to plastic materials, fails to provide a sufficient descrip
tion of the process of indentation in very hard and brittle ma
terials because it ignores the brittle fracture in the indentation
zone. A deeper insight can be provided by a parallel study of
the crack growth with increasing indenter load P = f (D ).
To establish an indentation law for very hard and brittle
materials, tests were carried out over a wide load range using
square-based diamond pyramid indenters or trihedral dia
mond indenters which proved to be convenient tools for
studying small-sized specimens (0.5 – 1 mm) and thin coat
ings and films of practically any hardness. The materials
tested were abrasives, rocks, hard tool alloys, glass, ceramics
and piezoceramics, semiconductors, ferrites and ultrahard
materials diamond and cubic boron nitride [3 – 9].
In all of these materials, the elastoplastic strain and brit-
tle fracture parameters as determined by microindentation
were found to be in good correlation (with a correlation coef-
Refractories and Industrial Ceramics Vol. 44, No. 6, 2003
1083-4877/03/4406-0379$25.00 © 2003 Plenum Publishing Corporation
Volzhskii Construction Engineering Institute, Russia; Volgograd
Architechture and Construction Engineering Academy, Volgo
Fig. 1. Schematic illustration of a cube-corner indenter penetrated
in a very hard material.