Three-dimensional macroscopic defects are called bulk defects. They generally occur on a much larger scale than the microscopic defects. These macroscopic defects generally are introduced into a material during refinement from its raw state or during fabrication processes. These include cracks, pores, foreign inclusions, and other phases. The working and forging of metals can cause cracks that act as stress concentrators and weaken the material. Any welding or joining defects may also be classified as bulk defects.
- Three-dimensional macroscopic or bulk defects, such as pores, cracks, or inclusions.
- Voids — small regions where there are no atoms, and which can be thought of as clusters of vacancies.
- Impurities can cluster together to form small regions of a different phase. These are often called precipitates.