Feb_March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 8 4 6 iTSSe TSS iTSSe TSS JTST HIGHLIGHTS 12 IMPROVING EROSION RESISTANCE OF PLASMA-SPRAYED CERAMIC COATINGS BY ELEVATING THE DEPOSITION TEMPERATURE BASED ON THE CRITICAL BONDING TEMPERATURE Shu-Wei Yao, Guan-Jun Yang, Cheng-Xin Li, and Chang-Jiu Li Interlamellar bonding within plasma-sprayed coatings is one of the most important factors dominating the properties and performance of coatings. The interface bonding between lamellae significantly influences the erosion behavior of plas- ma-sprayed ceramic coatings. In this study, TiO 2 and Al 2 O 3 coatings with different microstructures were deposited at dif- ferent deposition temperatures based on the critical bonding temperature concept. The erosion behavior of ceramic coat- ings was investigated. It was revealed that the coatings pre- pared at room temperature exhibit a typical lamellar structure with numerous unbonded interfaces, whereas the coatings deposited at the temperature above the critical bonding tem- perature present a dense structure with well-bonded interfac- es. The erosion rate decreases sharply with the improvement of interlamellar bonding when the deposition temperature increases to the critical bonding temperature. In addition, the erosion mechanisms of ceramic coatings were examined. Unbonded interfaces in the conventional coatings act as pre- cracks accelerating the erosion of coatings. Thus, controlling interlamellar bonding formation based on the critical bonding temperature is an effective approach to improve the erosion resistance of plasma-sprayed ceramic coatings (Fig. 3). HEAT TREATMENT OF COLD-SPRAYED C355 AL FOR REPAIR: MICROSTRUCTURE AND MECHANICAL PROPERTIES J.W. Murray, M.V. Zuccoli, and T. Hussain Cold gas dynamic spraying of commercially pure alumi- num is widely used for dimensional repair in the aerospace sector as it is capable of producing oxide-free deposits of hundreds of micrometer thickness with strong bonding to the substrate, based on adhesive pull-off tests, and often with enhanced hardness compared to the powder prior to spray- ing. There is significant interest in extending this application to structural, load-bearing repairs. Particularly, in the case of high-strength aluminum alloys, cold spray deposits can ex- hibit high levels of porosity and microcracks, leading to me- chanical properties that are inadequate for most load-bearing applications. Here, heat treatment was investigated as a po- tential means of improving the properties of cold-sprayed coatings from Al alloy C355. Coatings produced with process conditions of 500°C and 60 bar were heat-treated at 175°, 200°, 225°, and 250°C for 4 hours in air, and the evolution of the microstructure and microhardness was analyzed. Heat treatment at 225° and 250°C revealed a decreased porosity (~ 0.14% and 0.02%, respectively) with the former yielding slightly reduced hardness (105 versus 130 HV 0.05 as-sprayed). Compressive residual stress levels were approximately halved at all depths into the coating after heat treatment, and tensile testing showed an improvement in ductility (Fig. 4). Fig. 3 − Surface morphology of eroded Al 2 O 3 coatings at the center of erosion crater. Coating deposition temperature was 300°C. Fig. 4 − EPMA analysis showing distribution of Cu before 225°C HT.