Papers by Keyword: Graded Coatings

Abstract: This paper reports some new progresses on layered and graded coatings for plasma facing materials in fusion devices in Laboratory of Special Ceramics and Powder Metallurgy (LSCPM), University of Science and Technology Beijing (USTB), China. They included tungsten coatings made be various particle sizes of initial feedstock and interlayers and boron carbide graded coatings. All the coatings were fabricated on the oxygen free copper by plasma spraying. The microstructures and properties were investigated for PFM. Water quenching and high heat loading experiments were also carried out to estimate the thermal performance of these coatings.

Abstract: Coating of austentic stainless steel substrates with Ti/O compositionally gradient film was examined using reactive DC sputtering technique, in order to improve not only the abrasion resistance of the stainless steel but also the adhesion between the deposited film and the substrate with preserving the high hardness of such a hard ceramic coating as titanium oxide coating. The deposition of Ti/O compositional gradient films were realized by varying continuously the oxygen content in Ar-O2 sputter-gas during the reactive sputtering. The obtained films were appeared to be uniform and adhesive, while Ti-O compositional constant (i.e. non-gradient) films which were deposited by reactive DC sputtering under the same sputtering conditions except for the Ar-O2 gas mixing condition, i.e., with the oxygen content in the gas mixture constant, peeled off partly. According to AES in-depth profiles, the oxygen (O) concentration in the obtained film gradually decreased in depth direction from the surface toward the substrate, confirming that Ti/O compositional films had formed on the stainless steel. On the basis of XRD, it was found that not only hcp alpha-titanium and titanium oxide (anatase) but also some types of suboxides had formed in the gradient films. Furthermore the gradient films approximately indicated Hv600 which was much higher than that of the stainless steel substrate. Therefore the abrasion resistance of the stainless steel and the adhesion at the interface were expected to be improved at the same time.

Abstract: In this study the three – dimensional surface cracking of a graded coating bonded to a homogeneous substrate is considered. The main objective is to model the subcritical crack growth process in the coated medium under a cyclic mechanical or thermal loading. Because of symmetry, along the crack front conditions of mode I fracture and plane strain deformations are assumed to be satisfied. Thus, at a given location on the crack front the crack propagation rate would be a function of the mode I stress intensity factor. A three – dimensional finite element technique for nonhomogeneous elastic solids is used to solve the problem and the displacement correlation technique is used to calculate the stress intensity factor.