In situ observation of texture evolution during α → β and β → α phase transformations in titanium alloys investigated by neutron diffraction

Texture changes during recrystallization and the α–β–α phase transformation in two titanium alloys were investigated in situ by time-of-flight neutron diffraction by heating in a vacuum furnace to 950 °C. In commercially pure titanium, a strong texture memory effect is observed. This effect is a direct consequence of an orientation-selective α → β transformation, favoring new orientations produced during nucleation and grain growth. The β–α transformation favors β orientations with minimal misorientations, resulting in a strong final α texture that emphasizes the grain growth component. In Ti–6Al–4V, the texture memory effect is less pronounced. The high-temperature β texture is obtained by growth of pre-existing β nuclei. In a similar way, during cooling, the growth of α domains is controlled by high-temperature α orientations inherited from the β grains with Burgers orientation relation.     

Synthesis and compressive behavior of Cr2GeC up to 48 GPa

M_n+1AX_n compounds have gathered huge momentum because of its exciting properties. In this paper we report the synthesis of ternary layered ceramic Cr₂GeC, a 211 M_n+1AX_n compound by hot-pressing. Scanning electron microscopy and X-ray diffraction have been employed to characterize the new synthesized phase. High-pressure compressibility of Cr₂GeC were measured using diamond anvil cell and synchrotron radiation at room temperature up to 48 GPa. No phase transformation was observed in the experimental pressure range. The bulk modulus of Cr₂GeC calculated using the Birch–Murnaghan equation of state is 169 ± 3 GPa, with K′ = 3.05 ± 0.15.     

In situ high-energy X-ray diffraction studies of deformation-induced phase transformation in Ti-based amorphous alloy composites containing ductile dendrites

The deformed-induced microstructure evolution and phase transformation behavior of Ti-based amorphous alloy composites (AACs) containing ductile dendrites in situ formed during solidification were investigated using ex situ transmission electron microscopy (TEM) and in situ high-energy X-ray diffraction (HE-XRD). In situ synchrotron-based HE-XRD experiments provide clear evidence on the deformation-induced phase transformation from β to α″ martensite initiated already in the linear elastic stage of the macroscopic stress–strain curve. Detailed analyses from the diffraction experiments show that the grains that were aligned with [0 0 1]_β along the loading direction (LD) were then easily transformed into α″ martensite, whereas the martensitic variants oriented with [1 0 0]_α″ along LD were preferentially formed under compression. The current study provides quantitative information about changes in various microstresses between the crystal phase and the amorphous matrix during deformation. Enhancement of the macroscopic plasticity of the AACs was mainly attributed to the strain relaxation in the β phase and to the formation of multiple shear bands in the amorphous matrix triggered by the deformation-induced phase transformation inside β, knowledge of which greatly deepens understanding of the complex micromechanical behaviors in advanced AACs.     

In situ synchrotron X-ray diffraction study of scale formation during CO2 corrosion of carbon steel in sodium and magnesium chloride solutions

In situ synchrotron X-ray diffraction was used to follow the formation of corrosion products on carbon steel in CO₂ saturated NaCl solution and mixed NaCl/magnesium chloride (MgCl₂) at 80 °C. Siderite (FeCO₃) was the only phase formed in NaCl solution, while Fe(OH)₂CO₃ was also detected when MgCl₂ was present. The proposed model is that siderite precipitation, occurring once the critical supersaturation was exceeded within a defined boundary layer, caused local acidification which accelerated the anodic dissolution of iron. The current fell once a complete surface scale was formed. It is suggested that MgCl₂ addition decreased the required critical supersaturation for precipitation.     

In situ neutron diffraction study of the microstructure and tensile deformation behavior in Al-added high manganese austenitic steels

In situ neutron diffraction experiments were performed to measure the tensile deformation behavior of high manganese austenitic steels with different Al contents (0, 1.5, 2.0, 3.0 wt.%). Significant variations of peak shift, broadening and asymmetry of the diffraction peaks were observed in the plastic region with the measurement. Diffraction peak profile analysis was applied to determine microstructural parameters such as stacking/twinning fault probabilities, dislocation density and stacking fault energy (SFE). These parameters are quantitatively correlated to the yield strength, serrated flow and strain hardening rate during tensile deformation. The main results showed that the twin/stacking fault probability considerably decreases from 0.05 to 0.01 and dislocation density from 10¹⁶ to 4 × 10¹⁵ m⁻² as a function of Al addition, while SFE (γ) increases from 20 to 45 mJ m⁻² with the relationship of γ = 8.84 wt.% Al + 19.0 mJ m⁻². Such microstructural parameters are also in good agreement with the results of the misorientation and pattern quality map obtained by the electron backscatter method.     

Subsolidus phase relations of the SrO–MO2–CuO systems (M = Ti, Zr and Hf) at 900 °C in air

The subsolidus phase relations of the SrO–MO₂–CuO (M = Ti, Zr and Hf) systems were investigated in air. The samples were equilibrated at 900 °C. The SrTi₄Cu₃O₁₂ compound is the only ternary oxide phase stable under these conditions in the investigated systems. This phase is non-stoichiometric, its actual composition being Sr_0.95Ti_4.05Cu_2.95O_x. The SrO–ZrO₂–CuO and SrO–HfO₂–CuO systems have a similar structure. No Zr or Hf equivalents of the SrTi₄Cu₃O₁₂ phase were formed under the present conditions.     

In situ synchrotron X-ray diffraction study of surface scale formation during CO2 corrosion of carbon steel at temperatures up to 90 °C

In situ synchrotron X-ray diffraction was used to follow the formation of corrosion product scales on carbon steel in CO₂ saturated brine at temperatures from 40 to 90 °C. The corrosion process was accelerated by applying a small anodic current, and in selected tests a scale inhibitor, amino trimethylene phosphonic acid (ATMPA), was added. Siderite was identified as the major phase in the scale formed in all conditions. With increasing temperature, the scale formation rate increased, while the scale thickness and crystallite size decreased. Above 60 °C, the scale became increasingly protective. The scale thickness and crystallite size decreased with increasing ATMPA concentration.