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Fracture toughness of martensitic NiTiHf high-temperature shape memory alloy

Fracture behavior of a martensitic Ni50.3Ti29.7Hf20 (at.%) high-temperature shape memory alloy (SMA) under mode-I nominally isothermal loading was examined. The material was characterized using differential scanning calorimetry to identify the transformation temperatures and uniaxial tensile testing to portray the stress–strain behavior. Pre-cracked disk-shaped compact specimen was tested at room temperature and unstable crack growth was observed. Fracture toughness was measured using the associated load versus crack-mouth opening displacement record. Digital image correlation was implemented to obtain the strain field on the surface and near the crack-tip. Moreover, fracture surface was examined using scanning electron microscopy. The results provide key insights into the fracture properties of NiTiHf high-temperature SMAs.