Ni-Cr계 고용강화형 합금에서 조성에 따른 기계적 및 고온부식 특성 평가
Effects of alloying elements on the mechanical and high temperature corrosion properties of solid-solution hardening nickel-base alloy
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Alloy 617 is considered as a candidate Ni-based superalloy for the intermediate heat exchanger (IHX) ofa very high-temperature gas reactor (VHTR) because of its good creep strength and corrosion resistanceat high temperatures. Helium is used as a coolant in a VHTR owing to its high thermal conductivity, inertness,and low neutron absorption. However, helium inevitably includes impurities that create an imbalance inthe surface reactivity at the interface of the coolant and the exposed materials. As the Alloy 617 has beenexposed to high temperatures at 950°C in the impure helium environment of a VHTR, the degradationof material is accelerated and mechanical properties decreased. The high-temperature strength, creep, andcorrosion properties of the structural material for an IHX are highly important to maintain the integrityin a harsh environment for a 60 year period. Therefore, an alloy superior to alloy 617 should be developed. In this study, the mechanical and high-temperature corrosion properties for Ni-Cr alloys fabricated in thelaboratory were evaluated as a function of the grain boundary strengthening and alloying elements. Theductility increased and decreased by increasing the amount of Mo and Cr, respectively. Surface oxide wasdetached during the corrosion test, when Al was not added to alloy. However the alloy with Al showedimproved oxide adhesive property without significant degradation and mechanical property. Aluminum seemsto act as an anti-corrosive role in the Ni-based alloy.
Abstract
Alloy 617 is considered as a candidate Ni-based superalloy for the intermediate heat exchanger (IHX) ofa very high-temperature gas reactor (VHTR) because of its good creep strength and corrosion resistanceat high temperatures. Helium is used as a coolant in a VHTR owing to its high thermal conductivity, inertness,and low neutron absorption. However, helium inevitably includes impurities that create an imbalance inthe surface reactivity at the interface of the coolant and the exposed materials. As the Alloy 617 has beenexposed to high temperatures at 950°C in the impure helium environment of a VHTR, the degradationof material is accelerated and mechanical properties decreased. The high-temperature strength, creep, andcorrosion properties of the structural material for an IHX are highly important to maintain the integrityin a harsh environment for a 60 year period. Therefore, an alloy superior to alloy 617 should be developed. In this study, the mechanical and high-temperature corrosion properties for Ni-Cr alloys fabricated in thelaboratory were evaluated as a function of the grain boundary strengthening and alloying elements. Theductility increased and decreased by increasing the amount of Mo and Cr, respectively. Surface oxide wasdetached during the corrosion test, when Al was not added to alloy. However the alloy with Al showedimproved oxide adhesive property without significant degradation and mechanical property. Aluminum seemsto act as an anti-corrosive role in the Ni-based alloy.
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