Metal Spalling – Definition, Causes and Treatments
Metal spalling describes the process of surface failure of metals such as steel or iron. Small particles break away as flakes from the surface. Spalling is one of the many challenges materials have to resist in industrial environments. There are many ways to prevent metal sparring from occurring, most of which include a type of surface treatment such as BoroCoat®.
About Metal Spalling
Metal spalling is a common problem in industries using steel or iron appliances. Particles of the surface often chip away when the component is impacted by another. However, the component has been likely weakened beforehand by corrosion, cavitations or weathering. Metal spalls are concentrated on the highest point of pressure or in crevices, where corrosion damage often forms the easiest. Spalling is also referred to as “flaking,” “peeling,” or “pitting.”
Causes for Metal Spalling
Metal spalling is one of the most common failures in many areas of application because it can be induced by different causes.
- Corrosion: Corrosion is a process in which metals oxide. While corrosion can be desired in passivation surface layers, it can lead to surface failure in the form of spalling. Small metal oxide flake away from the surface, causing the underlying layer to be exposed to the environment.
- Weathering: The surface of a material can be damaged by chemical and/or mechanical weathering. Mechanical weathering includes thermal stress, stress by rain and water and microorganisms. Chemical weathering is caused by materials such as salt and acids, which weaken the wear resistance of metal surfaces. If the tolerance against these materials is not high enough, corrosion is quick to appear.
- Cavitation: Cavitations are, in essence, small cavities in metals that are caused by rapid movement in liquids. If these cavities collapse, due to high pressure or impact, metal spalling occurs.
- Rolling wear: If two materials are in rolling contact with each other, rolling wear can occur. Too much pressure or stress can cause the flakes of the surface layers to break away.
- Impact damage: One of the most common causes to metal spalling is impact damage. When a component collides with another, metal spalling can occur, provided that corrosion damage has preceded the collision.
Metal Spalling Treatments
Spalling occurswhenfatigueaffectseither surface or subsurface, resultingin fractures in running surfaces. When the rolling elements travel over these cracks, pieces, or flakes, of material break away.
Spalls can only form when the component corrodes or is damaged beforehand. So in order to prevent metal spalling, corrosion resistance, surface hardness and wear resistance is to be improved.
