Fatigue Crack Growth Mechanisms and Interface Stability in Cold-Spray 6061 Aluminum Alloys

Cold-spray materials exhibit several advantages associated with the solid-state character of the deposition process, very fine microstructures, and appealing tensile properties.  Although the effects of processing parameters on particle bonding and static properties of cold-spray materials and coatings have been studied, very little is known about the influence of the materials microstructure and processing on fatigue and fatigue crack growth and the coating-substrate interfacial mechanisms.  In this innovative work, systematic fatigue crack growth studies were conducted on bulk cold-spray processed 6061 alloys and 6061 cold-spray coatings for various processing conditions (as cold-sprayed, annealed, T6).  Tests were performed in room temperature air at three stress ratios (R=0.1,0.5,0.7).  Long and small fatigue crack growth mechanisms at the microstructure scale of cold-spray materials were identified, and a microstructure-based Paris-type law was successfully developed to predict crack growth rates in Regions II and III.  Finally, the interfacial behavior between the cold-spray coating and the wrought 6061 substrate was uniquely examined, and crack-interface stability maps were created.  These developments will be presented and discussed.