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2866 |
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Thursday, September 29, 2011, Saal B2.2 2:25 PM Characterization & Testing 4 |
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Testing and characterization methods to describe the mechanical properties of an HVOF coating sprayed with ultrafine powder materials |
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Rafael Kassimi / Thermico GmbH & Co. KG, Germany Goetz Matthäus* / Thermico GmbH & Co. KG, Germany MIchael Molnar/ hermic US, Inc, USA |
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HVOF spraying with ultrafine (+2 -10 µm) and spherodized powder materials dramatically improves coating quality concerning spraying accuracy, surface roughness, density, constant hardness and a homogeneous phase distribution of the applied material. These performance characteristics are forming the baseline of high quality coatings. Furthermore a close control of coating thickness with a accuracy of +/- 10 µm and a very low, as-sprayed surface roughness of Ra < 1.2 µm dramatically reduces grinding and finishing costs of the coated part. But developing a High-Performance-Coating for Applications in Aerospace, Landing Gear, Oil & Gas and other demanding Industries means achieving high residual compressive stresses, bond-strength and ductility enhancement. To develop coatings with such high performance characteristics it is essential to have different characterization and testing methods. The Almen-Test is well known to characterize the amount of residual compressive stresses in a coating. A modified Bend-Test provides the necessary feedback to develop coatings which do not spall-off in case of resulting tensile stresses. To characterize the bond-strength of this coating in a reproducible and reliable way, a modified Shear-Test has been developed. Furthermore this test allows analyzing the behavior of the coating, when it is exposed to massive shear-forces. It is possible to show an interrelationship between the crack formation in the coating structure and the chosen spray and powder-spherodization parameters. The information enables a systematic procedure to increase the ductility, by interpreting the crack behavior of the coating. It is shown that the test results are measurable and reproducible facts which deliver the necessary feedback to develop High-Performance-Coatings, with enhanced residual compressive stresses and substantial improved bond-strength and overall ductility in comparison to conventional HVOF coatings. |