Elevated temperature deformation behaviour of multi-phase Ni-20 at % Al-30 at % Fe and its constituent phases
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The mechanical behaviour of the multi-phase (β′ + γ/γ′) alloy Ni-20 at % Al-30 at % Fe and alloys similar to its constituent β′ and γ/γ′ phases, Ni-30 at % Al-20 at % Fe and Ni-12 at % Al-40 at % Fe, respectively, were investigated. When tested in tension at 300 K, the alloys exhibited ≈ 20%, 2% and 28% elongation, respectively. At elevated test temperatures (700, 900 and 1100 K), the multi-phase alloy exhibited increased ductility, reaching an elongation in excess of 70% at 1100 K without necking or fracture. Similarly, the β′ alloy demonstrated increased ductility with increasing test temperatures. In contrast, the γ/γ′ alloy showed greatly reduced ductility with increasing temperature and was quite brittle both at 900 and 1100 K. Thus, whilst at room temperature the γ/γ′ phase improved the ductility of the β′ + γ/γ′ aggregate, at elevated temperatures the β′ phase alleviated the brittleness of the γ/γ′ phase, thereby preventing any embrittlement of the multi-phase alloy over the temperature range 300–1100 K. Also, whilst the β′ phase improved the room-temperature strength of the multi-phase alloy, at elevated temperatures where the β′ phase is known to be weak, the γ/γ′ phase improved the strength of the multi-phase alloy up to 900 K, beyond which the strength deteriorated due to disordering and lack of anomalous strengthening in the γ/γ′ component.
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