Thermal stability in microstructure as well as static and creep rupture strengths of directionally solidified Ni-Al-Ti eutectic alloys for high temperature use were investigated; the dislocation substructure in ruptured specimens was observed by means of transmission electron microscopy. Results obtained are as follows:
(1) The oriented structure of γ and γ′ phases, so-called “DS” structure was fairly stable in the temperature range below 1273 K, but it was disintegrated at higher temperatures. The more the γ content was, the more stable the DS structure was.
(2) DS structure was disintegrated rapidly by thermal cycling.
(3) Static tensile strength showed a maximum value at temperatures ranging between 973 K and 1173 K, and decreased rapidly at higher temperatures. γ fibres were broken by tension at temperatures below 1173 K, but they were elongated with matrix at 1373 K.
(4) DS structure was disintergrated during creep at higher temperatures than 1273 K.
(5) It was considered from the above-mentioned results that the temperature range for use of these alloys was limited below 1273 K, but the rupture strength of the present alloy (L: 80.5 at%Ni-11.0 at%Al-8.5 at%Ti) was superior to that of a Jackson’s alloy.
(6) Characteristic dislocation substructures in specimens subjected to creep were observed.