TOUGHENING OF CAST Ni_3 Al-BASE ALLOYS

Investigation was made of the ductility and microstructure of a series of cast Ni_3Al-base al-loys,with 19—23 at.-% Al and other alloying elements.An obvious improvement onmorphology,distribution,amount and size of primary Ni_3Al(γ')intermetallic compound wasapproached by such alloying elements such as Hf,Ti and Zr,but no more by Nb,W and Ta.The formation of ductile γ'-γ-γ' boundaries in the alloys with refined primary γ'-phase caneliminate the weakened nature of brittle γ'-γ' boundaries,and reduce the size of primaryγ'-phase to tens of μm.Thus,the ductility of the alloys,especially at intermediate tempera-tures may be markedly improved.In addition,an alloy free from Cr is still significantlyductile,and only its structure is refined.The availability of Cr to improve the intermediatetemperature ductility seems to be due to the change of amount and distribution of γ-phase.

TOUGHENING OF CAST Ni_3 Al-BASE ALLOYS

Investigation was made of the ductility and microstructure of a series of cast Ni_3Al-base al- loys,with 19—23 at.-% Al and other alloying elements.An obvious improvement on morphology,distribution,amount and size of primary Ni_3Al(γ')intermetallic compound was approached by such alloying elements such as Hf,Ti and Zr,but no more by Nb,W and Ta. The formation of ductile γ'-γ-γ' boundaries in the alloys with refined primary γ'-phase can eliminate the weakened nature of brittle γ'-γ' boundaries,and reduce the size of primary γ'-phase to tens of μm.Thus,the ductility of the alloys,especially at intermediate tempera- tures may be markedly improved.In addition,an alloy free from Cr is still significantly ductile,and only its structure is refined.The availability of Cr to improve the intermediate temperature ductility seems to be due to the change of amount and distribution of γ-phase.