Abstract
The damaged K465 nickel-based superalloy parts were repaired by laser forming repair technology. The cracking characteristics and grain boundary liquation in heat affected zones were investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the cracks originated from the heat-affected zone and extended to the repaired zone. The calculation by Thermol-Cale software showed that the larger γ′ particles at grain boundaries partly dissolved in the γ phase, which made the solutes’ concentration at the γ′/γ interface meet the eutectic-type liquation reaction condition of γ + γ′ → L. Then, grain boundaries liquation occurred and liquid films appeared with the temperature increasing in a rapid heating process. However, the intragranular γ′ phase completely dissolved into the γ phase with no devotion to the liquid film. The dissolution of M5B3 borides at grain boundaries could promote grain boundary liquation.
Highlights
K465 superalloy is a kind of cast nickel-based superalloy strengthened primarily by precipitation of ordered L12 intermetallic Ni3 (Al, Ti) γ1 phase, which possesses excellent elevated temperature strength and superior hot corrosion resistance [1,2]
2016, 6, 64 blocky MC carbides appear in different sizes and some slight borides exist as white filamentous discontinuities
The damage accumulation and micro-crack nucleation in heat affected zone (HAZ) of the LFRed K465 specimens result from the grain boundary liquation
Summary
K465 superalloy is a kind of cast nickel-based superalloy strengthened primarily by precipitation of ordered L12 intermetallic Ni3 (Al, Ti) γ1 phase, which possesses excellent elevated temperature strength and superior hot corrosion resistance [1,2]. This superalloy is, usually made into turbine blades and turning vanes of aircraft engines due to its excellent properties. Laser forming repairing (LFR), as a kind of metal additive manufacturing technology, can be utilized to recover complex shaped damaged parts up to certain depth, without affecting the inherent mechanical properties of the body [4,5,6,7].
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