Homogeneity Study of TiC and η Phases Via Electromagnetic Stirring in Arc-Melted Heat-Resistant A286 Superalloys Varied with Carbon and Titanium Contents

A286 is a precipitate-hardened heat-resistant superalloy for use above 700 °C temperature. Precipitation hardening is best reached in homogenized distribution of precipitates such as TiC and η-Ni3Ti phases. To investigate the effect of homogenized melting, A286 alloys with simultaneous variations of C and Ti contents, 0.02C–2.46Ti, 0.04C–2.54Ti, 0.05C–2.58Ti, and 0.06C–2.62Ti, were arc-melted with and without electromagnetic stirring. The stirred samples present round and spherical TiC particles after aging 720 °C/16 h, in contrast to plate- and needle-like TiC particles in the unstirred ones. They also show refined TiC particle mean sizes, about 1.2, 1.3, 1.1, and 1.0 µm, respectively, in the four alloys, compared with 1.3, 1.5, 1.7, 2.0 µm in unstirred samples, where more C and Ti contents induce a stronger stirring refining effect. η-Ni3Ti precipitate mean sizes, about 2.3, 4.9, 4.1 and 6.3 respectively in the four alloys, compared with 5.2, 6.3, 7.8, 6.5 µm in unstirred samples. Consequently strengthening is enhanced in high C–Ti alloys, with the largest yield and ultimate tensile strengths of 533 and 739 MPa in the stirred 0.06Cs–2.62Ti sample in comparison to 500 and 650 MPa. The elongation reaches 20% in this sample, which near doubles that of the unstirred sample. Fractography showed that the transgranular ductile fracture happened due to TiC phases and intergranular brittle fracture happened due to eta phases.