otherwise copper is ultra stabil electrically and mechanically. cryo for fe based elements is a totally different reason.
taken from Cu atomic info
What is Metallography?
Metallography is the study of the structure of metals. It includes the techniques used to prepare specimens for examination, examining the specimen and interpreting the structures. Specimen preparation is an important part of metallography. A specimen must be appropriately prepared to ensure correct observation and interpretation of the microstructure. Specimen preparation consists of sample selection, sectioning, grinding, polishing, and etching. Adequate sample selection provides a statistically reliable description of the material quality. The number, location and orientation of the samples examined are important parameters in sample selection. Sectioning, grinding and polishing are used to prepare a flat specimen with a mirror like finish. Care must be taken during sample preparation not to introduce artifacts which lead to invalid microstructure interpretations. Sometimes it is beneficial to examine the specimen in the as polished condition. The as polished condition is useful for examining the microstructures of materials whose constituents exhibit large differences in light reflectivity after polishing. Porosity and inclusions are examples of features that are easily observed in the as polished condition. But most materials are etched to reveal the microstructure. Etching is a controlled corrosion process resulting form electrolytic action between surface areas of different potential. Etching reveals the microstructure of a material by selective dissolution of the structure. Specimens are then examined using optical and electron microscopes. There are also many other techniques used to characterize the structure of metals, but this article will concentrate on microstructural characterization.
Please see the proof belowhttps://www.copper.org/resources/properties/microstructure/coppers.html