Dislocation network with pair-coupling structure in {111} γ/γ′ interface of Ni-based single crystal superalloy

Abstract

The γ/γ′ interface dislocation network is reported to improve the high temperature creep resistance of single crystal superalloys and is usually found to deposit in {001} interface. In this work, a new type of dislocation network was found in {111} γ/γ′ interface at a single crystal model superalloy crept at 1100 °C/100 MPa. The dislocations in the network are screw with Burgers vectors of 1/2 a<110> and most interestingly, they exhibit a pair-coupling structure. Further investigation indicates that the formation of {111} interface dislocation network occurs when the γ′ raft structure begins to degrade by the dislocations cutting into the rafted γ′ through the interface. In this condition, the pair-coupling structure is established by the dislocations gliding in a single {111} plane of γ′, in order to remove the anti-phase boundary in γ′; these dislocations also act as diffusion channels for dissolving of the γ′ particle that is unstable under the interfacial stress from lattice misfit, which leads to the formation of {111}-type zigzag interface. The formation of this network arises as a consequence of more negative misfit, low-alloying γ′ particle and proper test conditions of temperature and stress.

Direct observation of dislocation plasticity in high-Mn lightweight steel by in-situ TEM

“…But, when a succeeding dislocation shears the ordered phase again, the original symmetry of the ordered phase can be restored. Therefore, they suggested that the pairs of dislocations, called as superdislocations, should glide together at the slip band front to avoid the formation of the APB 31,43,44 .…”

Investigating the Dislocation-Driven Micro-mechanical Response Under Non-isothermal Creep Conditions in Single-Crystal Superalloys

“…dislocations have been observed by Ru et al [36] following isothermal creep at 1100°C and 100 MPa. However, the dislocation configuration observed by Ru et al [36] was identified as pure screw dislocations.…”

“…A higher misfit thus results in a denser interfacial dislocation network. In the case of Ru et al, [36] the paired dislocation network formed during isothermal creep in a 4th generation superalloy with a high misfit. Le Graverend et al showed that similarly high misfit magnitudes could be achieved during short high-temperature excursions.…”

Microstructure and dislocation structure evolution during creep life of Ni-based single crystal superalloys

“…Mughrabi ascribes this deterioration to a rapid increase in deformation induced by internal stresses, which cannot be released any longer by the interface dislocations once the ␥ phase is being split into discrete islands [38]. Other studies [33,39,40] have indicated that in the inversed microstructure the shape of ␥/␥' interfaces changes from smooth into zigzag, leading to the formation of new dislocation glide planes in ␥', which correspondingly promote the formation of dislocation pile-ups and consequently cutting of the ␥' phase.…”

“…Experimental results have shown that the {111}-type distorted interface forms as a consequence of the inversed microstructure [73,74,77]. The zigzag interface forms through dislocations which cut into the ␥'raft via {111} planes of interface [40]. The accelerated creep rate can then be attributed as the increased dislocation activity with the break-down of dislocation networks and the formation of new gliding planes.…”