Abstract
Thermal spray WC based powders are now frequently used as chrome replacement alternatives for a wide range of industrial and aeronautical applications. In numerous cases, the carbide materials outperform the hard chrome in many property evaluations. However, their usage on highly stressed parts, especially in fatigue loading, can be limited by spalling resistance of the coating. While HVOF is being used on many flight critical parts, stringent applications like the landing gear components of carrier-based aircraft are still under investigation. This work, on WC-17%Co, relates coating bend test performance and fatigue/cyclic step loading behavior to the processing history using different HVOF systems. Initially, twelve (12) different coatings were monitored using a DPV- 2000 for temperature/velocity profiles. The mechanical properties were then assessed using an instrumented four-point bend test as well as uniaxial cyclic loading. After mechanical testing, the coating microstructures were characterized using X-Ray diffraction and electron microscopy in order to investigate the phase content and nature. In particular, the cracks generated during the bend test were measured using SEM on sample cross sections to understand characteristics such as spacing and crack penetration to the substrate. The interactions of processing parameters with the cracking/spalling resistance of the various coating deposits will be discussed and a potential criteria for the control of cracking phenomena will be presented.
