Question

what happens to shape memory alloys when they are fatigued? their ability to change between phases decreases. they become more resistant to corrosion. they become more flexible. their color changes.

Explanation:

Shape - memory alloys rely on phase - change mechanisms for their shape - memory properties. Fatigue refers to the material undergoing repeated stress or strain cycles. When a shape - memory alloy is fatigued, the micro - structural changes (such as the formation of defects, dislocations, and the degradation of the ordered martensitic or austenitic phases) occur. These changes disrupt the reversible phase - transformation process.
Corrosion resistance is a property related to the alloy's chemical composition and its ability to form protective oxide layers, not directly related to fatigue in the context of shape - memory functionality. Flexibility is a mechanical property related to the alloy's ability to bend or deform without breaking, but fatigue in shape - memory alloys is more about the degradation of the phase - change mechanism rather than an increase in flexibility. Color change is not a typical consequence of fatigue in shape - memory alloys; their color is more related to surface treatment or composition rather than the fatigue - induced micro - structural changes relevant to shape - memory.

Answer:

Their ability to change between phases decreases.