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This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (À60°C) in order to obtain a different volume fraction of strain-induced martensite (up to~70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (a¢ fi c). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted-strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov-Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

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A novel Zn-3Ag-0.5Mg alloy was plastically deformed using 3 processing paths: hot extrusion (HE), HE followed by cold rolling (CR) and high-pressure torsion (HPT). The processed samples consisted of the η-Zn phase, ε-Zn3Ag precipitates within the matrix, and nanometric Zn2Mg precipitates within the Zn11Mg2 phase located at the grain boundaries. Both the η-Zn phase and Mg-rich phases were enriched in Ag. Electron backscattered diffraction was used to examine the effects of grain size and texture on mechanical behavior with tensile tests performed at room temperature (RT) at different strain rates. The coarse-grained (~ 6 µm) samples after HE exhibited high strength with brittleness due to dislocation interaction with dispersed precipitates and, to some extent, with twinning activation. Significant grain refinement and processing at RT gave an increase in elongation to over 50 pct in CR and 120 pct in HPT. Ductile CR samples with an average grain size of ~ 2 µm and favorable rolling deformation texture gave a yield strength of ~ 254 MPa, a tensile strength of ~ 456 MPa, and a reasonable strain rate sensitivity. These values for the CR samples meet the mechanical requirements for biodegradable stents in cardiovascular applications.

The interest in using high vacuum-compatible timeof-flight secondary ion mass spectrometry (TOF-SIMS) detectors integrated within focused ion beam instruments (FIB) has increased due to the possibility of conducting correlative and/or complementary studies with other techniques such as scanning electron microscopy, energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy, electron backscatter diffraction, atomic force microscopy, and Raman spectroscopy without breaking vacuum conditions. This work discusses the practical aspects of FIB-TOF-SIMS analysis enhanced by fluorine gas. A series of systematic experiments with high-purity Al and Cu single crystals was conducted. We demonstrate that fluorine-assisted FIB-TOF-SIMS analysis yields up to several orders of magnitude higher SIMS signals due to chemically improved ionization probability of elements. The potential of fluorine gas-assisted FIB-TOF-SIMS analysis and the correlated benefits are demonstrated on a real-life sample based on comparing the results to EDS and TOF-SIMS experiments conducted without any gas. Our studies indicate that the presence of fluorine gas reduces the negative effect of preferential reoxidation of the sample surface. This enables high lateral resolution FIB-TOF-SIMS mapping because the secondary ion signals are not dominated by elements with strongly oxygen-enhanced ionization probability.