Volume 51, Issue 11

This work presents a comparison of crystallographic properties of twin bands formed in bcc iron and those formed in iron meteorites (Neumann bands) during high speed deformation identified by means of electron backscatter diffraction (EBSD). Deformation twins were produced in Armco iron and in steel S235 by firing with an AK74 gun and by impact pressure in the drop impact tester. The twin bands of a few micrometers thickness are embedded in the surrounding crystallographically uniformly oriented grain matrix with a misorientation angle of approx. 59° and the Σ3 incidence. The twin system {112}<111> is preferentially activated. The temperature during loading and the grain size have an impact on the extent of twin formation. However, they do not influence the twin system. The findings provide relevant information on the twin formation mechanism in ferrous bcc materials.

During hot rolling, coiling and subsequent cooling of low-alloy steel sheets, internal oxides are formed at the grain boundaries (intergranular) and within the grains (intragranular) as a consequence of oxygen diffusion into the steel and segregating alloy elements. The assembly/microstructure and composition of the oxides found were investigated via transmission electron microscopy (TEM) and electron energy loss (EELS)- or energy-dispersive X-ray (EDX) spectroscopy therein. Our spectroscopic data reveal various simple oxide species, located separately or side by side. Those findings apply to grain boundary oxides and intragranular oxides, for all the steel compositions investigated (Fe-Mn-Cr, Fe-Mn-Al-Si, Fe-Si-Al-P). For example, within the Mn-Cr-alloyed steel we find Mn oxide at all oxide locations (inter- and intragranular), but Cr oxide is not present always. We also discuss the sequences of oxide formation, which follow the thermodynamic rules of oxide formation.

A particular heavy-duty gas turbine burner, used in a burner rig test, featured a Y-shaped fuel gas feed pipe. The Y-pipe was made by non-conventional production, in an attempt to test the component and its specialty manufacturing process in an environment that simulates service conditions without causing collateral damage to other engine components in case of failure. The Y-pipe was produced by additive manufacturing (AM), using a process that is known as selective laser melting (SLM). This process is well suited for complex parts due to its advantageous geometrical freedom. It is known to have been used for intricate piping systems before. However, the Y-shaped pipe failed by thermal-mechanical fatigue cracking (TMF).