Once the potential directions for developing self-healing
metal castings were identifi ed, computational simulation was performed to aid in predicting the types of cracks that could be healed using the third system being explored. While the precise microstructure of self-healing metal castings has not been determined, the examination of the systems at UWM was intended to help drive the development of casting methods in the future. The techniques and concepts developed for solder and Mg-
based castings can be extended to aluminum castings. In the case of SMA-reinforced systems, a metalcaster or designer would need to identify a suitable aluminum alloy matrix and an interfacing material that will liquefy and become sealed under the clamp- ing force needed to heal the crack. For systems involving a low melting point-encapsulated healing agent, the healing agent must be selected based on its fl ow and solidifi cation characteristics. Other off-eutectic systems also can be identifi ed based on the thermodynamic phase diagrams of aluminum alloys, leading to self-healing in the selected system. Self-repairing metal castings would be ideal for use in applications such as high temperature turbine blades, au- tomotive engines, fatigue and failure prone structures and aircraft castings. The success of self-healing concepts when used with polymers, ceramics, solders and magnesium-based alloys could pave the way for the success of production castings in the future.
The Three Methods
Following is an exploration of the three self-healing sys- tems under consideration at UWM.
SMA Inserts When a casting with embedded SMA wires or particles
is cracked, the reinforcements deform. Upon heating the
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One method of healing cracks in metal castings would involve infusing the cast metal matrix with microcapsules containing a healing agent and a catalyst capable of polymerizing the agent. When a crack breeches a microcapsule, the agent fl ows out into the crack and is solidifi ed by the catalyst, sealing the crack.
METAL CASTING DESIGN AND PURCHASING 25
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