Volume 59, Issue 4

CoSm permanent magnets are characterized by high coercivity, which is due to the formation of a cellular nanostructure. For the understanding and optimization of these magnets, the evolution and morphology of the cellular structure need to be analyzed, most commonly by transmission electron microscopy (TEM). Meanwhile, high-resolution scanning electron microscopy (SEM) is enabling the visualization and large-scale imaging of the nanostructure while requiring relatively little preparation effort, combined with easy sample handling. Different preparation techniques will be used to visualize different microstructural constituents, enabling the analysis of their morphologies and fractions.

Martensitic stainless steels are commonly prefered in industries requiring high mechanical strength, corrosion resistance, and hardness. The dry sliding wear behavior of 15-5 precipitation-hardenable (PH) martensitic stainless steel was investigated in a heat chamber with ball-on-disc tribometer under room temperature (RT), 100 °C, 200 °C, and 300 °C. The wear tracks were characterized using SEM, EDS, WCM and XRD. The results showed that wear resistance improved proportionally with increasing temperature and increased surface hardness enabled coefficient of friction to decrease. Corrosion rate decreased with increasing temperature owing to natural passivation film on stainless steel specimens. In comparison with RT and 300 °C tests, hardness increased from 341 HV 0.1 to 401 HV 0.1 and wear rate lowered by 94 %. It was shown that application and operation of 15-5 PH stainless steels is eligible in aircraft and aerospace industry.

Metallic heat shields, used in combustion chambers of heavy-duty gas turbine engines and made of nickel-based superalloys, were accidentally heat treated during fabrication, using wrong parameters. There were concerns about embrittlement. Nondestructive metallurgical material characterization using the replica technique verified embrittlement by secondary phases. In spite of this, it was recommended to the client to use the affected parts as is, this on the grounds that no grain growth was observed and hardness was not elevated. While the case study presented in this contribution may appear trivial at first sight, it interestingly shows how metallographic examinations may sometimes be performed non-destructively, without sacrificing any engine components. The inclined reader should also note the superb quality of the photomicrographs presented in this contribution. They were taken from replica foils, not actual metallographic sections.