Effect of Cold Work and Heat Treatment on the 4°K Tensile, Fatigue and Fracture Toughness Properties of Incoloy 908
The influence of prior cold work on tensile properties, fatigue crack growth rates and fracture toughness of Incoloy 908 was examined at 293°K and 4.2°K. Fatigue crack growth rates were measured using a constant AK technique. Crack length was determined using compliance. Fracture toughness was determined by the J-integral technique. Properties following heat treatment were compared for two starting conditions: (1) solution annealed at 980°C for 1, hour and (2) solution annealed followed by 20% cold work. Three heat treatments were studied: (1) aging at 650°C for 200 hours, (2) aging at 700°C for 100 hours, and (3) aging at 750°C for 50 hours.
The results of this investigation show that the fracture toughness of Incoloy 908 is greater than 230MPa.fifi at 4.2°K for all heat treatments. The fatigue response at 4.2°K is almost independent of heat treatment and is comparable to stainless steel. The yield strength of the solution annealed and aged material ranged from 823 to 961 MPa at 293°K and from 980 to 1070 MPa at 4.2°K depending on heat treatment. The cold worked and aged material exhibited significantly higher yield strength, ranging from 1240 to 1280MPa and 1320 to 1490MPa at 293°K and 4.2°K, respectively. Ductility is only slightly reduced (3–6% as measured by total elongation (25mm gage)) by cold working.
The results of this investigation show that Incoloy has excellent mechanical properties. These properties, coupled with a low thermal expansion coefficient, make Incoloy 908 an attractive alternative for superconducting magnet structural applications.
KeywordsFracture Toughness Crack Growth Rate Crack Opening Displacement Fatigue Crack Growth Rate Crack Opening Displacement
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