RESUMO
Nanosized precipitates play a critical role in increasing the strength of metallic alloys. There are many reports that the initial precipitates are metastable phases holding a different composition and crystal structure from the equilibrium precipitate. The metastable precipitate transforms to its stable phase during heat treatment. A transmission electron microscope enables researchers to study the phase transition of metastable precipitates to stable phases due to its fine resolution in identifying crystal structures and chemical compositions. This review introduces the various phase transformation mechanisms of metastable precipitates to stable phases obtained from the analysis using a transmission electron microscope. The role of dislocation movement in the phase transition is further discussed.
RESUMO
An electron probe X-ray microanalyzer (EPMA) is an essential tool for studying chemical composition distribution in the microstructure. Quantifying chemical composition using standard specimens is commonly used to determine the composition of individual phases. However, the local difference in chemical composition in the standard specimens brings the deviation of the quantified composition from the actual one. This study introduces how to overcome the error of quantification in EPMA in the practical aspect. The obtained results are applied to evaluate the chemical composition of retained austenite in multi-phase steel. Film-type austenite shows higher carbon content than blocky-type one. The measured carbon contents of the retained austenite show good coherency with the calculated value from the X-ray diffraction.
RESUMO
High strength steels are becoming more important than ever before for automotive applications to reduce the weight of automobiles and to ensure the safety of passengers. Since increased strength usually results in degraded formability, however, cold forming of high strength steels into final shapes remains a challenge to both automotive manufacturers and suppliers. Here we report novel alloy and processing design concepts that can impart high strength to cold-formable steels, which deviates from the traditional approach of improving the formability of high strength steels. Such designed steel subjected to a designed processing route shows an excellent combination of formability and strength as well as crashworthiness, which is crucial for the safety of passengers in the automobiles. The alloy and processing design concepts used in the present study are based on the utilization of thermally induced austenite to martensite transformation, which imparts high strength to cold-formable austenite by cryogenic treatment.
RESUMO
Although magnesium alloys, as the lightest structural alloys, offer significant potential for automotive applications, their applications remain limited due to their poor formability at room temperature. Since the strategies used for improving formability usually result in a degradation of strength, there are no high strength magnesium alloys showing good formability. Here we report an alloy design concept that can simultaneously provide high strength and good formability. Such designed alloy when subjected to an appropriate processing technique shows a combination of strength and formability that surpasses those of the existing magnesium alloys reported so far. The alloy design concept used in the present study is based on the utilization of alloying elements that can induce precipitation, as well as maximize the segregation of other texture-controlling alloying elements. Such developed alloy is expected to broaden the application of Mg alloy sheets, which are now starting to gain acceptance by automotive industries.
RESUMO
The concentrations of some important endocrine disrupting chemicals and pharmaceuticals after various stages of wastewater treatment were investigated. The endocrine disrupting chemicals included natural and synthetic estrogenic and androgenic steroids. The pharmaceuticals included a series of sulfonamide antibiotics and trimethoprim. The removal efficiency of a membrane bioreactor (MBR) was investigated and compared with a conventional activated sludge (CAS) system. Samples were analysed by liquid chromatography tandem mass spectrometry. Results showed that the MBR and CAS systems effectively removed steroidal estrogens and androgens, but only partially eliminated the target antibiotics from wastewater. The MBR was shown to be more effective than the CAS system which was possibly attributed to the high solid retention time and concentration of biosolids in the MBR. The results highlight the potential wider application of MBRs for the removal of trace chemical contaminants in wastewater and their potential for use as decentralised wastewater treatment systems.
