Formation of Ni_3Nb and Influence of Y_2O_3 on Mechanical Properties of Nano-grained Ni20Cr20Fe5Nb1 Y_2O_3 Alloy

摘要

The effects of adding Y_2O_3, and the precipitation of Ni_3Nb by heat treatment, on the mechanical properties of mechanically alloyed Ni20Cr20Fe5Nb alloy were studied. The addition of Y_2O_3 caused an increase in the tensile strength at room temperature, 400℃ and 600℃. The difference in the tensile strength between the Ni20Cr20Fe5Nb and Ni20Cr20Fe5NblY_2O_3 alloys decreased gradually with increasing test temperature. The tensile strength of the Ni20Cr20Fe5Nb1 Y_2O_3 alloy at relatively low temperature was increased by the addition of Y_2O_3, but decreased abruptly at temperature above 600℃. This seems to result from a change in the deformation mechanism due to the ultra-fine grain size, that is, grain boundary sliding is predominant at temperatures above 600℃ while internal dislocation movement is predominant at temperatures below 600℃. Following the conventional heat treatment of the solution and subsequent aging, only a small amount of δ(Ni_3Nb) phase was formed in the Ni20Cr20Fe5Nb alloy, whereas in a previous report it was indicated that a large amount of γ″(Ni_3Nb) was formed in IN 718 alloy. The small amount of δ(Ni_3Nb) phase formed in the present case is due to the exhaustion of the Nb content resulting from the formation of NbC during consolidation.