STUDY OF THE SURFACE STRENGTH AND CRACK RESISTANCE
OF VERY HARD CERAMIC MATERIALS
BY THE MICROINDENTATION METHOD
O. I. Pushkarev
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 18 – 21, October, 2002.
The relationship between elastoplastic strain and brittle fracture in very hard brittle materials is studied by the
microindentation method. Forcing and energy conditions for the nucleation, incipient subcritical growth, and
subsequent propagation of cracks initiated by a local stress concentrator (a diamond-tipped indenter) are ex
amined for various materials.
In recent years, much attention has been given to stu-
dying the surface strength and crack resistance of very hard
ceramic materials, using, among others, the microindentation
method. This method provides a means of studying the pro-
cesses of nucleation and growth of cracks that finally result
in the brittle fracture of materials [1 – 3].
Microindentation of very hard and brittle materials is a
process of elastoplastic deformation that can be character-
ized in terms of two parameters — the size (diagonal diame-
ter) d of the impression formed and the size (diameter) D of
the brittle-fracture zone exhibiting features attesting to a
breakdown of the structural integrity of the material: crack
ing, spalling, etc. (Fig. 1). The size D of this zone is deter
mined by the mechanical properties of the material (such as
strength and brittleness) and by the testing conditions (in
denter load P, indentation angle a, and indenter geometry).
Formally, microindentation of hard and brittle materials
can be described using the familiar law P = f (d ), conven
tionally applied to plastic materials ignoring brittle fracture
of the material in the zone of impression. To make the picture
complete, one will want to follow the process of crack
growth with increasing indenter load P = f (d ).
With a view to establishing a microindentation law for
hard and brittle materials, tests were conducted over a wide
range of indenter loads using diamond pyramid-tipped in
denters of tetrahedral and trihedral shape, which made it pos
sible to examine objects of rather small size (less than
0.5 – 1 mm), including thin coatings and films made of mate
rials of any hardness. A wide range of materials (abrasives,
rocks, hard alloys, glasses, ceramics and piezoceramics,
semiconductors, ferrites), including superhard materials (dia-
mond, cubic boron nitride), were studied [3 – 9].
For all materials, microindentation relationships charac-
terizing elastoplastic deformation and brittle fracture (with
correlation coefficients of 0.95) were established.
Refractories and Industrial Ceramics Vol. 43, Nos. 9 – 10, 2002
1083-4877/02/0910-0295$27.00 © 2002 Plenum Publishing Corporation
Volzhskii Construction Engineering Institute, Russia.
Fig. 1. Schematic diagram illustrating the performance of a pyra
mid-tipped indenter in the surface testing of very hard materials
[d ) impression diagonal; D ) crack length; a) indentation angle].