Ly. Chao et al., ROLLING-CONTACT FATIGUE AND WEAR OF CVD-SIC WITH RESIDUAL SURFACE COMPRESSION, Journal of the American Ceramic Society, 78(9), 1995, pp. 2307-2313
The rolling-contact fatigue life and wear of CVD-SiC coatings with sur
face compression were studied using a three-ball-on-rod rolling-contac
t fatigue (RCF) tester. Two levels of surface compression in the coati
ngs, approximately 190 mu m thick, were introduced by using substrates
of a liquid-phase sintered SiC and a SiC-30 vol% TiC to obtain desire
d thermal-expansion mismatches with the CVD-SiC. Residual surface comp
ressions of 250 and 680 MPa were measured in the CVD-SiC coatings on S
iC and SiC-30 vol% TiC substrates, respectively, by a strain-gage tech
nique, In the RCF test, the fatigue life of the CVD-SiC coating with t
he moderate surface compression was limited by severe wear by a brittl
e fracture mechanism at a Hertzian contact stress of 5.5 GPa. The CVD-
SiC coating on the SiC-30 vol% TiC composite, on the other hand, did n
ot show measurable wear. A majority of the tests (11 out of 16) were s
uspended at 100 h or stopped due to failure of the steel balls, Five t
ests stopped due to spalling of the CVD-SiC coating at weak interfaces
10 to 15 mu m below the contact surface, Examination of the microstru
cture of the CVD-SiC coating in cross sections revealed that the weak
interfaces that led to the spalling were related to discontinuous grow
th of the CVD-SiC in the form of nodules or growth regions. Eliminatio
n of these defective structures is likely to enhance the tribological
performance of surface-toughened CVD-SiC.