Abstract:
Bonding strength
of hard coatings suggested to be evaluated by cyclic loading. On
the basis of contact stress calculation the proper testing
parameters were selected in order to determine the initiation of
factigue crack in the interface region. A predict area of
debonding patch was defined as the initiation point for contact
factigue failure and symbolized as σc. Different surface
treatments and different coating thicknesses have been processed
on the substrates for PVD and PCVD TiN coatings to strengthen or
to weaken the bonding strengths between the films and the
substrates to as to testify the significance of cyclic bonding
strength and compare σc with Lc
by scratch tests. The
experimental data show that the cyclic bonding strengths tested
under normal press with sliding agree well with the experience
in the manufacturing. However, the critical coating values by
scratch tests Lc do not reflect the results of different states
perfectly. In this paper, a new fatigue crack initiation
criterion is suggested when residual stress is involdved. It is
theoritically found that the optimised residual stress is
compressive with the magnitude of 0.2 Gpa and at the present
experimental parameters, this confirms with the experimental
results that the decrease of residual stress can improve the
cyclic bonding strength for PVD TiN which holds originally 4～7
Gpa compressive stress.
Key words:
Coating Bonding strength Cyclic
loading Vapor deposition Residual stress
*
This project
is supported by National Natural Science Foundation of China, and
Lanzhou Solid Lubrication Laboratory and Doctorate Foundation of
Education Committee of China. Manuscript received on June 12, 1992
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