In MPI, what is the purpose of using magnetic particle mediums?

In Magnetic Particle Inspection (MPI), one of the main purposes of using magnetic particle mediums is to create a magnetic field that attracts defects. When a magnetic field is applied to a ferromagnetic material, discontinuities such as cracks, laps, and inclusions can distort the field. The magnetic particle medium, often in the form of dry powder or a liquid suspension, responds to the magnetic flux leakage caused by these imperfections. This response is crucial as it allows the defects to become visually distinguishable.

The medium adheres to the areas where the magnetic field is disrupted, effectively highlighting the presence of defects for inspection. This principle is central to the effectiveness of MPI, allowing inspectors to identify flaws that might compromise the integrity of the material. The other options, while they may involve similar materials or processes in different contexts, do not specifically pertain to the fundamental purpose of magnetic particle mediums in the MPI process.