Microstructure
The term texture or microstructure can regardless of the material ( metal, ceramic or polymer ) to Shatt / Worchester be defined as follows: " The term structure characterizes the nature of the whole body of the sub-volumes, each of which in terms of its composition and in terms of the spatial arrangement of its components is homogeneous in the first approximation with respect to a laid into the material stationary coordinate system. [ ... ]. the structure is characterized by the type, shape, size, distribution and orientation of the structural components. "
The structural components ( crystallites or grains, fillers and amorphous regions ) are usually microscopic in size and can be described for example by means of a light microscope qualitatively and quantitatively. The relevant areas are called metallic materials: Metallography, with ceramic materials: Ceramography and polymers: Plastographie.
In the field of metallic materials and alloys distinction is made between the primary structure and the secondary structure, even though colloquially the term structure is usually the secondary structure is meant.
Monocrystals and amorphous materials have no resolvable light microscope structure.
Primary structure
The primary structure is produced when the melt of a crystalline substance is cooled. On reaching the setting temperature, it is in many places within the melt, starting from incidental crystallization nuclei for crystal formation. These crystals grow in the course of cooling until they finally collide. Depending on whether it is a single or multiphase solidification material in the melt, the partial crystallization layer of melt at the dendrites can still segregation phenomena occurring in the course. These separations are due to different melting points of the two substances and their solubilities. The individual crystals, the chance of the formation and its location in the melt accordingly, have different orientations and can not grow together at the interfaces.
If the primary structure made visible by the methods of metallography, we obtain a qualitative impression of the inhomogeneity of the material. For cast materials can thus usually also show dendritic structures.
Secondary structure
In many cases, it comes in the wake of the solidification of the melt due to the presence of residual heat to a quasi " involuntary " heat treatment. This process is referred to as self- annealing. A self- starting, as well as a technical heat treatment, leading to conversion, excretory and Rekristallisierungsvorgängen that have the secondary structure result. However, these are always solid-state reactions.
Attempt to structure formation
A visible with the naked eye structure can be generated using a simple experiment: " Klempnerlot " ( lead tin alloy with about 35 % tin ) is heated with an alcohol or Bunsen burner in a steel trowel and melted. ( Pushed aside the resulting slags ) The addition of rosin makes the surface oxide-free. If we let now the melt to cool slowly, the crystallization and structure formation can be observed directly.
Microstructure micrographs and their use
The microstructure of metals are worked out by the means of metallography on samples and are visible under the light microscope microstructure micrographs subsequently analyzed. Through assessment of size, shape and arrangement of the crystallites with their grain boundaries and impurities to extensive statements on the heat treatment condition and the expected mechanical properties can make.
Conversely, the structure of metals ( and the resulting technological properties ) by specific heat treatment very precisely. Thus, for example, the case of austenitic stainless steels set a certain particle size in order to achieve a defined elongation and strength.
For evidence, especially in the analysis of claims, the microstructure are usually documented photographically.
Selection schematic structure Micrographs
This is a selection of illustrated schematically microstructure micrographs:
Generally
Eutektikumsnahe alloy with " primary -A" crystals
Eutectic
Eutektikumsnahe alloy with " primary B" crystals
Iron alloy
Perlite
Perlite secondary cementite