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 4 iTSSe TSS iTSSe TSS JTST HIGHLIGHTS 10 T he Journal of Thermal Spray Technology (JTST), the official journal of the ASM Thermal Spray Society, publishes contributions on all aspects—fundamentalandprac- tical—of thermal spray science, including processes, feedstock manufacture, testing, and char- acterization. As the primary vehicle for thermal spray infor- mation transfer, its mission is to synergize the rapidly advanc- ing thermal spray industryand related industriesbypresenting research and development efforts leading to advancements in implementable engineering applications of the technology. Articles from the January and February issues, as selected by JTST Editor-in-Chief Armelle Vardelle, are highlighted here. The January issue features papers based on presentations at ITSC 2017. The first four articles highlighted below are from this special issue. In addition to the print publication, JTST is avail- able online through springerlink.com . For more information, visit asminternational.org/tss. Fig. 1 − Optical micrograph showing cross sections of the Sn coatings cold sprayed at 200°C and 1.4 MPa on ABS. METALLIZATION OF VARIOUS POLYMERS BY COLD SPRAY Hanqing Che, Xin Chu, Phuong Vo, and Stephen Yue Previous results have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fiber reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a benchmark substrate. The CFRP used in this work has a ther- mosetting matrix, and the ABS, PEEK, and PEI are all thermo- plastic polymers with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders—tin, copper, and iron—were cold sprayedwith both a low-pressure systemand a high-pressure systemat var- ious conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermoset- ting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI. Based on the results, a method is proposed to determine the feasibility and deposition window of cold spraying specific metal powder/polymeric substrate combinations (Fig. 1). IN SITU ACOUSTIC MONITORING OF THERMAL SPRAY PROCESS USING HIGH- FREQUENCY IMPULSE MEASUREMENTS Wolfgang Tillmann, Frank Walther, Weifeng Luo, Matthias Haack, Jens Nellesen, and Marina Knyazeva In order to guarantee their protective function, thermal spray coatings must be free of cracks, which expose the sub- strate surface to, e.g., corrosivemedia. Cracks in thermal spray coatings are usually formed due to tensile residual stresses. Most commonly, the crack occurrence is determined after the thermal spraying process by examination of metallographic cross sections of the coating. Recent efforts focus on in situ monitoring of crack formation by means of acoustic emission analysis. However, the acoustic signals related to crack prop- agation can be absorbed by the noise of the thermal spraying process. In this work, a high-frequency impulse measurement technique was applied to separate different acoustic sources by visualizing the characteristic signal of crack formation via quasi-real-time Fourier analysis. The investigations were car- ried out on a twin wire arc spraying process, utilizing FeCrBSi as a coatingmaterial. The impact of the process parameters on the acoustic emission spectrum was studied. Acoustic emis- sion analysis enables obtaining global and integral informa- tion on the formed cracks. Coating morphology and coating defects were inspected using light microscopy on metallo- graphic cross sections. Additionally, the resulting crack pat- terns were imaged in 3D using x-ray microtomography (Fig. 2). Fig. 2 − Metal plate with a rectangular bezel in front of the specimen.