Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Effect of Grain Boundary Precipitates on High Temperature Creep Properties of Ni-2OCr-Nb-W Alloys
Masao TAKEYAMAKaoru KAWASAKITakashi MATSUORyohei TANAKA
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1986 Volume 72 Issue 10 Pages 1605-1612

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Abstract

Creep properties and microstructure of Ni-20Cr-Nb-W alloys containing variable amounts of niobium and tungsten were investigated at 900 and 1 000°C, focusing on a role of grain boundary precipitates. The alloys with higher niobium content, in which the Widmanstätten type β-Ni3Nb phase precipitates after its precipitation at grain boundaries, showed a relatively small minimum creep rate at 900°C accompanied by the degradation of rupture elongation. The effect of the time lag between the in-grain and grain boundary precipitations of the β-phase on the creep resistance of the alloys was evaluated by observing their creep rate-time curves. When the tungsten content of a Ni-20Cr-3Nb-13W alloy increased up to 17 wt%, marked improvement of creep properties was found under lower stress levels and it is strongly correlated to the grain boundary precipitation of the α2W-phase which occurs after that of the β-phase. It is concluded that the grain boundary precipitation strengthening effect due to such dual phases as β and α2 is one of most effective methods for improving the creep strength.

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© The Iron and Steel Institute of Japan
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