Gradient materials

A gradient material is a material whose properties vary in a spatially defined manner. This may be due to changes in chemical composition, microstructure or porosity. A typical feature is a continuous or stepwise transition between different functional zones. For example, hard, wear-resistant edge zones can be combined with a tougher, fracture-resistant core.

In powder metallurgy, gradient materials are frequently produced by the targeted arrangement of different powder zones. To achieve this, metal powders with different compositions, grain sizes or densities are layered in a controlled manner, compacted and then sintered. During sintering, the particles form local bonds. This results in a component with spatially varying microstructural properties without the sharp interfaces found in conventional composite materials.

An important field of application is tools and wear-resistant components. Here, for example, very hard surfaces are combined with a more ductile substrate to minimise abrasion on the one hand and prevent fracture or spalling on the other. The same applies to components subjected to high thermal loads. Here, gradients in thermal conductivity or thermal expansion can be utilised to reduce stresses and increase service life. The production of these gradient materials places high demands on powder mixing and shaping. The local compositions must be achieved in a reproducible manner. The mixing quality, particle size distribution and flow properties of the powders are crucial in this regard. Precision powder mixers help to provide defined powder combinations for individual zones. In a second step, these zones must be filled and compacted in such a way that the desired gradient is created within the component.

Gradient materials form an interface between powder metallurgy, ceramics technology and composite materials. Similar concepts are used in hard metals, cermets and high-performance ceramics to combine different property profiles within a single component.