Non-destructive testing and material development

Experimental setup for neutron measurement of lithium ion batteries in the instrument STRESS-SPEC. (Photo: W. Schürmann / TUM)

Modern materials have a complex microstructure optimized for use and often consist of several phases. These microstructures are often exposed to extreme conditions such as high temperature or high load which they then have to withstand. Since neutrons are electrically neutral and very small, they can penetrate deep into most materials. They make it possible to look inside complex components and can be used for non-destructive material testing.

Neutrons are able to distinguish between different materials and even between the different isotopes of a chemical element. Under certain conditions, even small amounts of materials containing hydrogen, such as glue or lubricant in a metal component, are still visible. For example, the oil in a running engine or the distribution of sealant in a car door can be made visible non-destructively. In a high-resolution mode, structures smaller than 100 microns are recognizable in a fluoroscopy.

Neutrons are deflected or scattered by the atoms of an object under scrutiny. The method using this phaenomen is called neutron diffraction. It provides in addition, information on the distance between the individual atoms or the arrangement of atoms in a structure; the chemical compound and, if available, the distribution of residual stress within a component can be derived. Welds, crankshafts, cylinder heads or plastically deformed railroad tracks can in this way be precisely investigated. Even in-situ measurements under extreme conditions are possible to determine the composition and microstructure of materials. The texture analysis of materials is an important application of neutron beams and of considerable, not to mention economic, importance in industry.

Another economically important application is the development of new and functional materials. These consist of metallic alloys in addition to many other materials such as ceramics, polymers or composites, which are combined to suit the particular application. Critical to the development of new materials is the accurate analysis of the composition of the micro-structure and behavior under certain conditions. Even here, neutron beams are widely used.

In summary, it can be said that neutrons are always particularly useful when a non-destructive in-situ measuring method is required, which moreover entails measurements under certain conditions such as temperature, pressure, alternating electric, or magnetic, fields, etc.