Is Glass Infiltration Beneficial to Improve Fretting Wear Properties for Alumina?

Abstract

In this article, we report the tribological properties of the glassinfiltrated (GI) alumina with a major aim to understand scientifically the influence of glass infiltration on the underlying mechanisms of material removal (when fretted against steel). For this purpose, the test samples were fabricated by infiltrating molten borosilicate glass on a sintered alumina. Thermal expansion coefficient mismatch of two phases (3.5 Â 10 À6 1C À1 for glass and 9 Â 10 À6 1C À1 for alumina) causes residual compressive stresses, which assists in the enhancement of mechanical properties. Systematic fretting wear experiments were performed on as-sintered Al 2 O 3 and GI alumina surface against bearing steel under dry-unlubricated conditions at varying load (2 N, 5 N, and 10 N) with different fretting durations (10 000, 50 000, and 100 000 cycles). Relatively less variation in steady state COF (0.5-0.6) was measured for both the as-sintered Al 2 O 3 and GI Al 2 O 3 under the varying operating conditions. Laser surface profilometer analysis indicates that better wear resistance could be obtained for GI alumina at lower load (2 N) after 100 000 fretting cycles (7.5 Â 10 À6 mm 3 /N . m), in comparison with the bare or virgin alumina surface (1.1 Â 10 À5 mm 3 /N . m). Also, the wear rate decreases with an increase in load to 5 N and 10 N, with the lowest value of 1.5 Â 10 À6 mm 3 / N . m measured after fretting at 10 N load. Importantly, no noticeable difference in wear rate between as-sintered and GI alumina could be measured at a higher load (5 N, 10 N). Atomic force microscopy and X-ray diffraction analysis of wear debris illustrate that an amorphous tribolayer and finer debris particles, with composition of Fe(OH) 3 and/or Fe 2 SiO 4 , adhere to the worn surface. The formation of triboreaction products has been explained using thermodynamically feasible reactions. The major wear mechanisms depend on the applied load and are being identified as fatigue wear, three-body abrasion, and formation of a tribochemical layer.

Load dependence of oxidative wear in metal/ceramic tribocouples in fretting environment

“…The proposed model results have been compared with the experimental wear data obtained with Al 2 O 3 /steel [18], WC-TiCCo/steel [19] and TiB 2 -MoSi 2 /steel [20], Ti6Al4V/alumina [33] and ASP23 steel/alumina [34] tribocouples, where oxidative wear has been reported during fretting wear experiments in earlier studies. In first three tribocouples, the flat ceramic discs were fretted against steel balls, while for the last two tribocouples the metallic flat was fretted against a ceramic ball.…”

“…In the cases where tribochemical reaction happens to be the oxidation of one of the counter bodies, tribochemical wear is also referred to as oxidative wear. The oxidation reactions have been observed to play an important role in determining the wear behaviour of various metal reinforced ceramics as well as non-oxide ceramics under both dry [18][19][20] and oil lubricated conditions [21][22][23]. Under these conditions, reaction products are formed and they may increase or decrease the wear resistance of the material depending on the stability and the wear resistance of the reaction products.…”

“…The value of pre-exponential constant (k 0 ) for the oxidation of carbon steel [36] and Ti6Al4V [37] (Table 2) was extracted from the parabolic rate constants measured in the temperature range of 773-973 K and 1050-1340 K respectively. Fe 2 O 3 and TiO 2 have been reported to be the major oxidation products [18,33] of steel and Ti6Al4V respectively; hence their theoretical densities were taken for the calculations. Since the exact value of critical oxide layer thickness for various metal oxides of the present case was not available, a minimum critical oxide layer thickness of 1 nm was assumed as suggested by Fisher [24].…”

“…To calculate the pre-oxidation tribomechanical wear of Ti6Al4V/ alumina tribocouple, the mechanical properties of commercially pure (99.5%) alumina were taken from Ref. [18].…”

“…The case of the formation of a stable oxide layer at the interface is analysed, which has been frequently observed for many tribocouples fretted in ambient environment and at very low sliding velocities ( $ 10 À 3 m/s) [18][19][20]. The dependence of wear volume on operating parameters (load/velocity) has been formulated and a very basic model has been proposed for stable oxide layer formation during the fretting wear.…”