Friction stir welding (FSW) for the joining of metals is becoming an increasingly mature technology with numerous NASA and non-NASA applications. There remains an opportunity to further develop the process by extending the longevity of the FSW tools that are prone to wear and improving the economics of the processing. In Phase I, higher wear resistant tools will be designed for FSW of aluminum alloys in the 2xxx series, but these FSW tools could also be applicable to harder metals such as titanium and metal matrix composites. Tungsten carbide (WC) and particularly WC cermets with a cobalt (Co) binder are the materials of choice for FSW of many metals. However, it is desirable to develop higher performance WC cermets/composites without Co, a costly strategic metal which is also a known carcinogen and health hazard. In this program, WC-based materials using an iron-based binder with and without carbon nanotube (CNT) reinforcements will be fabricated, using a recently developed consolidation approach which should result in residual porosity levels ≤1% and thus the optimum mechanical properties. Traditional metallurgical methods for enhancing fracture toughness, such as grain size refinement, Co content optimization, and strengthening agents, have been substantially exhausted with respect to conventional WC cermets, and this program represents an innovative means to improve performance via 3 separate or combined approaches: (1) use of higher hardness iron-based binder, (2) use of CNT reinforcements to increase toughness, and (3) use of novel consolidation approach to minimize porosity and optimize performance. Improved performance FSW tools should result in higher wear resistance and longer lifetime tools. The materials will be characterized for microstructure, hardness, fracture toughness, and strength, and preferred compositions assessed through the FSW of Al 2xxx plates over a length of 1200” and depth of 0.625”.
This proposal addresses the need for longer lifetime, wear resistant FSW tools with the development of improved quality WC cermet/composite tools which would be utilized for NASA applications involving the FSW of propulsion and propulsion-related components and hardware. Decreasing costs and shortening the time for manufacturing crew modules and large-scale aerospace hardware like fuel and oxidizer tanks, and particularly the use of lightweight aluminum tanks, would be highly beneficial to NASA.
The largest application is cutting tools for machining steels and hard metals. Others are armor-piercing projectile cores for military weapon systems, knives/hammers, road scarfing inserts for patching and replacement of roadways, bearing/sealing applications, and inserts for roller cone bits and those used in mining and drilling of earthen material in the coal, oil, and gas industries.