Abstract The highest temperature of turbine entrance of the latest large-sized and highly efficient jet engine rises to more than 1773K. The TBC coating receives heat stress, mechanical stress, and according to combustion gas the coating is suffered corrosion damage etc during the operation. Therefore, TBC coating becomes indispensable and longer service life and higher heat resistant coating systems are strongly required. This paper employs a ternary coating system. The bond coating was vacuum plasmas sprayed NiCrAlY, and PSZ top coating was sprayed by an APS process. The molybdenum disilicide-metal composite coating was applied as middle coating. It is expected that the middle molybdenum disilicide layer can interrupt oxidation of NiCrAlY bond coating, therefore, extension of service life of TBC coating can be expected. Paper includes a German-language abstract.

Abstract The present investigation compares blast erosion characteristics of coatings that are prepared with abrasion resistant surface treatment materials and various consolidation processes. Furthermore, it elucidates operating mechanisms in blast erosion of various sprayed coatings. The investigation presents the blast erosion test conditions and assessment of test results and discusses the effects of coating materials on abrasion loss and impingement angle on abrasion loss. It includes illustrations on SEM observation and cross-sectional observation of damaged areas. In addition, information on blast erosion resistant characteristics of materials tested and wear mechanism in blast erosion is also provided.

Abstract Trends of turbine blades of advanced aircraft gas turbine engines are to increase output power of the engines, to increase engine efficiency, and to reduce environmental emission, and thus, higher operating temperatures of the engines are required. One of the technologies for increasing the operating temperature is a thermal barrier splayed coating. A research paper claims that molybdenum silicide in a splayed coating has a self-healing capability for cracks formed in the coating by embedding the cracks with silicon dioxide formed from molybdenum silicide at high temperatures. This article discusses the methods for the extension of life of thermal barrier sprayed coatings by incorporating molybdenum silicide. It discusses monitoring method for detecting cracking conditions in heating and cooling cycles by signals of acoustic emission. A possibility of estimating fatigue life by utilizing an X-ray method for measuring residual stress is also considered.

Abstract This paper focuses on the mechanism responsible for crack expansion and contraction: the behavior of cracks in the ceramic bed of zirconium dioxide membranes formed by plasma spraying, and the thermal stresses caused by differences in thermal expansion factors between the base material and sprayed bed, under a thermally cyclic environment. The test sample was prepared by spraying NiCrAlY on a stainless-steel base material to form a substrate membrane, then covering it with sprayed 8YSZ (zirconium dioxide-type ceramic). To clarify the self-recoverability of fatigue cracks caused during the thermal cycle, membrane cracking and crack expansion/contraction is studied. Paper includes a German-language abstract.

Abstract In this paper, the influence of the plasma spray parameters on the mechanical properties of Ni-50% Cr coatings is systematically studied using the method of orthogonal regression test planning. The target properties include adhesive strength, micro-hardness, grinding wear, and erosion wear. The three spray parameters used as variables are plasma arc current, Ar flow rate, and spray distance. From the regression formulas, it is concluded that the effects of the spray parameters on the properties largely depend on the individual properties. Paper includes a German-language abstract.

Abstract The effects of powder types and HVOF spray systems used to produce Cr 3 C 2 -NiCr coating on the relationships between spray parameters and wear performance were investigated based on the effect of fuel gas conditions on abrasive wear and erosion wear. The relationships between spray parameters and wear properties were obtained by orthogonal regression experimental design method. Four types of powders and two HVOF spray systems were used. It is found that with the increase in fuel gas flow or pressure the abrasive wear and erosion of Cr 3 C 2 -NiCr coatings change following a concave curve. The Cr 3 C 2 -NiCr coating with the best wear performance will be deposited under intermediate fuel gas condition. It is experimentally confirmed that by different types of powders and HVOF systems applicable to HVOF spraying of Cr 3 C 2 -NiCr coating, although the optimized fuel gas conditions to deposit coating with the best wear performance will be influenced by types of starting powders.

Abstract Low cycle fatigue tests were performed at room temperature (RT) and at 673 K for l%Cr-0.5%Mo steel comparing the specimens coated with chromium carbide by gas spraying and the ordinary uncoated specimens, and the mechanism of fatigue crack formation was investigated. Following observations and conclusions were made: (1) When sprayed with ceramic, the fatigue life suffers reduction at either temperature, but at 673 K, the degradation was so much smaller than that at RT that the fatigue life was actually, though slightly, longer than that at RT. (2) The cracks are initiated in the ceramic layer very early in the whole fatigue life, the crack initiation lifetime becoming the longer, the smaller the strain range. (3) The fatigue failure process can be viewed as comprising following steps: first, early initiation of fatigue crack at the surface of the ceramic coating, rapid propagation through it to the substrate metal, and initiation of crack in the metal, the initial rate of propagation of such a crack being a number of times (perhaps as much as one full order of magnitude) faster than that in uncoated steel.