The differences are in the degree of "mismatch". In the case of aerospace, normally a higher degree of "perfect" material is needed, so no segregations, equal grain size and the chemistry is often more limited to get a purer material. 

Hi Jasmin. Thank you for your answer. Would you mind to elaborate more on what do you mean by "perfect" or "purer" material? Do you mean that there would be less impurities or undesirable phase? And what would contribute to the degree of "mismatch", aren't they supposed to be prepared according to the standards/specifications, thus having same/similar microstructure?

Mismatch cool be impurities, lattice mismatch, different grain sizes or also some stringers in the microstructure.

I thought of "perfect" in the kind of the crystal lattice (excluding impurities in a first step). so the material should have a better quality for aerospace application than the standard material.

E.g. it is known, that for In718 the aerospace material is not that sentitive to hydrogen embrittlement than the "normal" commercial one. So the quality of this material is better.

The oil and gas alloy 718 has a single step heat treatment, compared to the two-step aging heat treatment applied when 718 alloy is used for aerospace applications, where property requirements are different. The heat treatment for oil and gas applications is designed to address higher fracture toughness with adequate strength and corrosion resistance to hydrogen embrittlement and stress corrosion cracking. On the other hand, d phase is intentionally utilised in the 718 aerospace heat treatment (AER HT) in order to control grain size for improved fatigue strength. The alloy is solution heat treated below δ solvus, followed by a two-step aging treatment to precipitation harden the material with γ' and γ''.

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