The transformation of unstable austenite to ferrite or α′ martensite as a result of exposure to Xe+ or Ga+ ions at room temperature was studied in a 304 stainless steel casting alloy. Controlled Xe+ and Ga+ ion beam exposures of the 304 were carried out at a variety of beam/sample geometries. It was found that both Ga+ and Xe+ ion irradiation resulted in the transformation of the austenite to either ferrite or α′ martensite. In this paper, we will refer to the transformation product as a BCC phase. The crystallographic orientation of the transformed area was controlled by the orientation of the austenite grain and was consistent with either the Nishiyama–Wasserman or the Kurdjumov–Sachs orientation relationships. On the basis of the Xe+ and Ga+ ion beam exposures, the transformation is not controlled by the chemical stabilization of the BCC phase by the ion species, but is a result of the disorder caused by the ion-induced recoil motion and subsequent return of the disordered region to a more energetically favorable phase.

The shape memory properties of Ni–Al alloy are investigated using molecular dynamics simulation. The phase transformation behaviors for various Ni composition ratios are studied under quasistatic cooling and heating process. Various loadings, i.e., uniaxial, shear, and biaxial, are applied on a 68% Ni–Al alloy till plasticity takes place. The atomic configurations are inspected and analyzed using a common neighbor parameter. The shape recovery capability of the plastically deformed alloy is examined after heating above the phase transformation temperature. It is found that there would be shape recovery if the twinning plane reorientation or moving was the major yielding mechanism. For those loadings in which stacking faults or dislocations nucleate, the deformed model would not restore to its original shape after heating and the corresponding maximum shear stress is noticeably higher. There is no direct dependence between the yield strain and the shape recovery capability. Our findings could provide a possible explanation for the functional fatigue of the polycrystalline shape memory alloy.

The mineral conichalcite from the western part of Bagdad mine, Bagdad, Eureka District, Yavapai County, Arizona, USA has been characterized by electronic, near-infrared (NIR), Raman and infrared (IR) spectroscopy. Scanning electron microscopy (SEM) images show that the mineral consists of bundles of fibres. Calculations based on the results of the energy dispersive X-ray analyses on a stoichiometric basis show the substitution of arsenate by 12 wt.% of phosphate in the mineral. Raman and IR bands are assigned in terms of the fundamental modes of AsO43− and PO43− molecules and are related to the mineral structure. Near-IR reflectance spectroscopy shows the presence of adsorbed water and hydroxyl units in the mineral. The Cu(II) coordination polyhedron in conichalcite can have at best pseudo-tetragonal geometry. The crystal field and tetragonal field parameters of the Cu(II) complex were calculated and found to agree well with the values reported for known tetragonal distortion octahedral complexes.

The X-ray micro-diffraction laboratory technique was applied to study the quantitative changes of austenite content in TRIP steels after deformation and to reveal the phase composition of precipitates in an inner part of a hearth of a blast furnace. The usefulness of this technique was shown by calculating the austenite content after tensile test in three different parts of a small tensile test sample and after a clinching test in two areas of a clinching joint. The calculations showed the decrease in austenite content in deformed parts in comparison to not deformed areas. The presence of various kinds of chlorides, including the iron oxide chloride hydroxide in a sample taken from a graphite refractory lining of blast furnace, was confirmed by micro-diffraction patterns.

Using a combination of high-resolution dilatometric measurements and microstructural analysis, this study investigated the bainitic transformation behavior in ultra-high strength 30CrNi3MoV steel after experiencing small deformation at 850 °C (in the nonrecrystallization austenite region). Under the influence of the small deformation in the nonrecrystallization austenite region, the bainite starting temperature (Bs) raised, the bainite finishing temperature (Bf) decreased, granular bainite was promoted to form, and intersections of differently oriented bainite laths became more common in the microstructure. The increase of Bs is owing to the stored energy in distorted austenite grain boundaries, which can serve as an extra mechanical driving force for bainitic transformation during continual cooling. The decrease of Bf can attributed to the more universal intersections of bainite laths with different orientations, which can decelerate the overall growth rate of bainite. The promoted formation of granular bainite is closely related to the increase of Bs because granular bainite usually forms at relatively high temperatures in the bainite range, above upper bainite and lower bainite.

The martensitic transformation behavior of the meta-stable austenite phase in low alloyed TRIP steels has been studied in situ using high-energy X-ray diffraction during deformation. The stability of austenite has been studied at different length scales during tensile tests and at variable temperatures down to 153 K. A powder diffraction analysis has been performed to correlate the macroscopic behavior of the material to the observed changes in the volume fraction of the phases. Our results show that at lower temperatures the deformation induced austenite transformation is significantly enhanced and extends over a wider deformation range, resulting in a higher elongation at fracture. To monitor the austenite behavior at the level of an individual grain a high-resolution far-field detector was used. Sub-grains have been observed in austenite prior to transformation.

A model has been developed to describe the rheology of austenite at high temperatures, characteristic from hot strip rolling of low-alloyed steels. It is based on the evolution of a single dislocation density through storage and strain rate-dependent dynamic recovery. The model gives good predictions of the stress-strain curves in a wide range of temperatures, strain rates and chemical compositions. It is now applied on industrial hot strip mills to predict the rolling loads of a wide range of industrial steels.

This paper describes a method to determine the equilibrium transformation temperatures in low C steels using the in situ high-temperature X-ray diffraction technique. The samples were heated and then cooled from 1000 to 720 °C in a stepwise manner decreasing to −10 °C. Austenite and ferrite fractions were determined by a quantitative method using the integrated intensities of austenite (111)γ and ferrite (110)α peaks from X-ray diffraction patterns. The effect of the temperature on interplanar d spacings of (111) and (110) crystallographic planes was determined using 2θ maximum positions of the austenite (111)γ and ferrite (110)α peaks. The equilibrium transformation temperatures were determined to be Ae1=720 °C and Ae3=950 °C. The results are in excellent agreement with those obtained by dilatometric analysis and Thermo-Calc phase diagram simulation software. In addition, the results were supported by microstructural observations: the formation of thin ferrite films (5–10 μm) was observed at temperatures near to experimental Ae3.

Electron backscatter diffraction (EBSD) techniques were used to characterize “hot-rolled” quenched and partitioned microstructures produced via Gleeble thermal simulations representing a hot-strip cooling practice for steel. In particular, EBSD was utilized to positively identify the morphology and location of retained austenite, to qualitatively distinguish martensite from ferrite, and in an attempt to identify transition carbides. Large pools of retained austenite and some thin films were accurately indexed; however, there was some disparity between austenite volume fractions measured by EBSD and those measured by X-ray diffraction. Due to similarities between the crystal structures of martensite and ferrite (body centered tetragonal versus body centered cubic, respectively), martensite could not be distinguished from ferrite by indexing of diffraction patterns; however, martensite could qualitatively be distinguished from ferrite by regions of low image quality based on the very high dislocation density of martensite.

This work concerns the use of parallel electron energy loss spectroscopy (PEELS) to investigate the detection, distribution, and quantification of carbon in various steel microstructures generated by rapid cooling rates or by isothermal transformation. The feasibility of detecting C in steels containing very small amounts of carbon was first examined by calculating the minimum detectable mass fraction for a variety of binary Fe-C alloy specimen thicknesses and microscope conditions. These theoretical studies indicated that the detection of carbon in steel microconstituents containing about 0.01 wt.% (or even less) was easily possible with an analytical transmission electron microscope equipped with a LaB6 emitter and a PEEL spectrometer. These theoretical calculations seemed to be reasonable, as it proved possible to make a quantitative PEELS study of the partitioning between the microconstituents ferrite, retained austenite, and martensite found in an ultralow carbon (0.03 wt.%) steel weld metal provided care was taken to avoid hydrocarbon contamination. Studies of both carbon and molybdenum segregation to ferrite/martensite interfaces in an isothermally transformed Fe-C-Mo alloy were also carried out in order to investigate the nature of the “solute drag” effect in this alloy system.