Mechanical behavior of NiTi shape memory alloy fiber reinforced Sn matrix "smart" composites

The detrimental effects of Pb on the environment and human health have provided the driving force for replacement of Pb-Sn solders with Pb-free alternatives. Sn-rich Pb-free solder alloys with silver and copper alloying additions have higher strength but lower elongation-to-failure than Pb-Sn solders. Thus, these alloys are more susceptible to failure under mechanical shock, drop, and thermal fatigue conditions. In this article, mechanical tensile testing of NiTi-Sn3.5Ag single fiber composites demonstrates superelastic behavior of the composite with 85% strain recovery. Fatigue experiments show an evolution in damage over cycles, and an S-N curve shows sharp transition between a nearly vertical low-cycle fatigue behavior and the high-cycle fatigue regime. The solder composite exhibits constant fatigue strength over the superelastic range of the NiTi fiber.