Volume 54, Issue 11

Apart from temperature and time, the deformation introduced in the material is another important parameter that affects the recryristallization process in metallic materials. The present study aims at examining the impact of the introduced deformation on recystallization and grain growth in Al 6061 alloy sheet. The deformation was introduced by hardness indentations in accordance with the Brinell test method applying two different loads. The samples with the hardness indentations were cut in half along the line on which the indentations were performed. One half served as sample providing a reference condition, while the other half was recrystallized. The grain size and the degree of misorientation (Kernel Average Misorientation, KAM) of the two neighboring measurement points were evaluated in both halves of the samples. Using the FE method, the hardness measurement procedure could be numerically simulated and the deformations which occurred beneath the hardness indentations could be evaluated and associated with experimental findings related to the grain size and the misorientation.

Microstructures of copper materials for slide bearings are often complex and may exhibit a carrier crystal structure characterized by a coexistence of hard and soft structural constituents. Relief polishing is an interesting option for the sample preparation of such materials, as it allows for statements regarding the resistance of the microstructure to abrasive wear. Differential interference contrast microscopy as well as confocal microscopy are particularly suited in order to study the relief polished sections. In addition to that, simple metallographic procedures may be applied to assess the mechanical properties of the structural constituents. Different examination methods combined give an idea of how carrier crystal structures behave in slide bearing applications.

The nut of a horizontal joint fastener cracked upon tightening during assembly in an industrial steam turbine factory. It was previously used in an over-pressure test, but was otherwise not yet used in service. Nut and bolt were made of the nickel-based superalloy Nimonic 80A, a precipitation-hardenable wrought high-strength alloy with excellent creep and corrosion properties. Such alloys usually get a complex heat treatment after hot-rolling, comprising homogenizing and multiple ageing cycles. The subject nut failed due to an extreme case of mixed grain size which detrimentally affected mechanical properties and was attributed to an insufficient degree of deformation during hot rolling.