The long-term durability of ceramics coated glass with high performance should be appropriately evaluated prior to their applications. Fatigue properties of such materials should be clarified to ensure the long-term durability. In this work, a borosilicate glass was coated with single-and two-layered ceramic thin films by a sputtering method. Fatigue tests of coated glass were conducted under bending mode, and fatigue properties of coated glass were investigated. It was revealed that the fatigue life of glass coated with two-layered film became longer compared with those of glass substrate and glass coated single-layered film. Hardness as surface characteristics of coated films, and bending strength as bulk property of coated glass were correlated with the average fatigue life, though no good correlation was found between them. Fatigue resistance strength was proposed as another strength parameter. It was found that the average fatigue life was adequately expressed by a power function of fatigue resistance strength.static strength and fatigue tests were conducted under bending mode, instead of axial loading tests. Fatigue life distributions for various thicknesses of coated ceramic film were statistically discussed. It is convenient that fatigue characteristics obtained by long-time tests can be evaluated by using static strength properties given in short-time tests. In this work, the average fatigue life was correlated with some static strength parameters, and resultant correlations were discussed. Finally, a new strength parameter, "fatigue resistance strength," was proposed to get a better correlation with the average fatigue life.
Experimental Procedures
Material processingA commercial borosilicate glass was used as a substrate material. The geometry of glass substrate was a disk type with a diameter of 100mm and a thickness of 2mm. An oxide ceramics Al2O3 of 99.99% purity and a carbide ceramics SiC of 99.8% purity were selected as target materials. In the present work, Al2O3 or SiC film of single-layer was coated by sputtering procedure as mentioned below. Glass coated with single-layered ceramic film for tests to get static strength properties was prepared so that the film thickness tf of single-layered ceramics should be 1µm, 3µm or 5µm. In addition, glass coated with two-layered ceramic film was also produced for static and fatigue tests. In coating two-layered films, Al2O3 film was first coated on the substrate glass, and afterward SiC film was coated on Al2O3-coated glass. This layer order of coating films has an advantage in tribological aspect because SiC is harder than Al2O3. In two-layer coated glass, the thickness tf of Al2O3 film as the first layer was set to be 3µm, and SiC film in the second layer was coated to be 1µm, 3µm or 5µm in its thickness.An RF magnetron sputtering apparatus of upper deposit type was used in the coating process. The distance between substrate and target material was fixed to be 40mm in this apparatus. Substrate and target materials were being water-cooled during the proc...
