November AMP_Digital

iTSSe TSS 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 | N O V E M B E R / D E C E M B E R 2 0 1 9 4 5 iTSSe TSS JTST HIGHLIGHTS 11 RESIDUAL STRESS IN HVOF THERMALLY SPRAYED WC 10Co-4Cr COATING IN LANDING GEAR APPLICATION M. Gui, R. Eybel, S. Radhakrishnan, F. Monerie-Moulin, R. Raininger, and P. Taylor Type “N” Almen strips were HVOF thermally sprayed WC- 10%Co-4Cr coating with spraying parameters used for landing gear coating production. The Almen strips were coated at vari- able passes and different cooling conditions. Deflections of Al- men strip specimens were measured, and the coating residual stresses were calculated. With the same facility and spraying parameters, an in situ coating property sensor was also used to continuously monitor the curvature of beam specimens being coated during and after coating deposition to evaluate coating deposition stress and final residual stress. The experiments, together with amicrohardness test, reveal that peening action occurring in the current HVOF spraying is limited, and the re- sidual stress in the coating is dominated by quenching stress and cooling stress. In this study, the substrate temperature of specimens was adjusted by cooling air flow and torch recess time in between spraying passes. The coating residual stress apparently impacts the substrate temperature because it sig- nificantly affects the cooling stress. Since the spraying param- eters are frozen in industrial coating production, the cooling condition is a feasible approach for tailoring the coating resid- ual stress (Fig. 3). Fig. 3 — SEMmicrographs showing morphology of WC-10Co-4Cr powder (a) at lowmagnification and (b) at high magnification. Fig. 4 — Cross-sectional image of CP Al deposited on ABS with four passes. DEPOSITING Al-BASED METALLIC COATINGS ONTO POLYMER SUBSTRATES BY COLD SPRAY M.R. Rokni, P. Feng, C.A. Widener, and S.R. Nutt The feasibility of depositing aluminum onto thermoplas- tic substrates via cold spray (CS) was investigated. Dense coat- ings of 7075 Al and CP Al (commercial purity) were achieved on three substrates—polyetheretherketone (PEEK), polyether- imide (PEI), and acrylonitrile butadiene styrene (ABS) using an iterative optimization process. 7075 Al deposition yielded low deposition efficiencies (DEs) and low thicknesses but high ad- hesive strengths, while CP Al deposition led to high DEs and thicknesses but relatively low adhesive strengths. PEEK and PEI were more suitable substrates for cold spray than ABS, which suffered from surface erosion and substrate distortion. Two key factors were identified that influenced the DE and adhesive strength of the coating. The first factor was the bond layer, the initial fewparticle layers that fusedwith the substrate to allow subsequent buildup. The bond layer was influenced by the substrate hardness, yield strength, glass transition temperature, and impact strength, as well as the differences in thermal expansion coefficients of Al and the polymer sub- strates. The second factor was the CS process parameters se- lected, as the bond layer and the build-up layers may require different process conditions in order to optimize both bonding strength and coating strength, respectively (Fig. 4). (a) (b)