A combined grain scale elastic–plastic criterion for identification of fatigue crack initiation sites in a twin containing polycrystalline nickel-base superalloy

In the present work, theoretical approaches, based on grain orientation dependent Young’s modulus and Schmid factor are used to describe the influence of local grain orientation on crack initiation behaviour of the coarse grained nickel base superalloy René80. Especially for strongly anisotropic crystal structures with large grain size, such as the investigated material, the local elastic properties must be taken into account for assessment of fatigue crack initiation. With an extension of Schmid’s law, the resulting shear stress amplitude, which triggers local cyclic plastic deformation, can be calculated depending on local Young`s modulus and Schmid factor. A Monte Carlo simulation with 100,000 samples shows how random grain orientation affects these parameters. Furthermore, the product of Young`s modulus and Schmid factor (called E·m) is used as a parameter to determine how grain orientation influences resulting shear stress amplitude for given total strain amplitude. In addition to the theoretical work using that approach, this model is also validated using isothermal LCF experiments by determining local grain orientation influence on the crack initiation site using SEM-EBSD analyses.

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Correlation Between Local Chemical Composition and Formation of Different Types of Ordered Phases in the Polycrystalline Nickel‐Base Superalloy A718Plus

Advanced Engineering Materials ◽

10.1002/adem.202100558 ◽

2021 ◽

pp. 2100558

Author(s):

Daniel Hausmann ◽

Andreas Förner ◽

Martin Pröbstle ◽

Daniela Hünert ◽

Peter Felfer ◽

...

Keyword(s):

Chemical Composition ◽

Nickel Base Superalloy ◽

Polycrystalline Nickel ◽

Ordered Phases ◽

Different Types ◽

Nickel Base ◽

Base Superalloy

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Fatigue crack growth behaviour of an alternative single crystal nickel base superalloy

International Journal of Fatigue ◽

10.1016/j.ijfatigue.2017.12.003 ◽

2018 ◽

Vol 109 ◽

pp. 166-181 ◽

Cited By ~ 13

Author(s):

Frans Palmert ◽

Johan Moverare ◽

David Gustafsson ◽

Christian Busse

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Single Crystal ◽

Crack Growth ◽

Nickel Base Superalloy ◽

Growth Behaviour ◽

Crack Growth Behaviour ◽

Nickel Base ◽

Base Superalloy

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Grain Refinement of a Powder Nickel-Base Superalloy Using Hot Deformation and Slow-Cooling

Materials ◽

10.3390/ma11101978 ◽

2018 ◽

Vol 11 (10) ◽

pp. 1978 ◽

Cited By ~ 2

Author(s):

Xianqiang Fan ◽

Zhipeng Guo ◽

Xiaofeng Wang ◽

Jie Yang ◽

Jinwen Zou

Keyword(s):

Grain Size ◽

Grain Refinement ◽

Hot Deformation ◽

Nickel Base Superalloy ◽

Polycrystalline Nickel ◽

Slow Cooling ◽

Homogeneous Microstructure ◽

Average Grain Size ◽

Nickel Base ◽

Base Superalloy

A pre-hot-deformation process was applied for a polycrystalline nickel-base superalloy to active deformation twins and dislocations, and subsequent slow cooling treatment was used to achieve grain refinement and microstructure homogenization. The microstructural evolution of the alloy was investigated, and the corresponding underlying mechanism was discussed. It was found that twinning mainly occurred in large grains during pre-hot-deformation owing to the stress concentration surrounding the large grains. High density dislocations were found in large grains, and the dislocation density increased approaching the grain boundary. The average grain size was refined from 30 μm to 13 μm after slow cooling with a standard deviation of grain size decreasing from 10.8 to 2.8, indicating a homogeneous microstructure. The grain refinement and microstructure homogenization during cooling process could be achieved via (i) static recrystallization (SRX), (ii) interaction of twin tips and γ’ precipitates, and (iii) grain coarsening hindered by γ’ precipitates in grain boundaries.

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