Search

The consequences of cold deformation phase transformation in chromium–nickel steel 12Kh18N10T have been studied. A metallographic study of samples has been performed with an increase of up to ×10 000 and an increase in the proportion of martensite in austenitic steel as a result of cold plastic deformation has been shown. A durometric study has been carried out, and the character of metal hardening with increasing degree of deformation has been confirmed, which shows the presence of at least two hardening mechanisms: deformation and phase. A magnetic study has been carried out, and the intensity of the growth of the magnetic phase with increasing deformation has been revealed. A comparison is made with the known data on the intensity of the martensitic transition for the same grade of chromium–nickel steel under cold deformation conditions. [ABSTRACT FROM AUTHOR]

The effect of hydrogen charging, ultrasonic treatment, and hydrogen charging after ultrasonic treatment on the fatigue life of VT6 alloy is investigated. Ultrasonic treatment causes the formation of a continuous nonetching α2(Ti3Al) layer within the surface layer, which reduces the fatigue life. Below this layer there are bands of the α2(Ti3Al) phase which, on the contrary, increase the fatigue life. These two effects together give a 1.3-fold increase in the fatigue life of the alloy. A catastrophic decrease in hydrogen charging after ultrasonic treatment is explained by the formation of regions of short-range displacements with a bcc lattice similar to the β phase. As a result of radial shear rolling, a martensitic phase with very high strength is formed in the alloy. Its formation is predicted by positron annihilation spectroscopy and is detected by transmission electron microscopy. The high stability of the martensitic phase contributes to the lower fracture toughness of the alloy processed by radial shear rolling. [ABSTRACT FROM AUTHOR]

In this study, CuAl13−xTax (% mass x = 1; 1.5; 2; 2.5) shape-memory alloys were produced through arc-melting method. Phase transformation temperatures were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis. Microstructures were examined with the aid of optical microscopy, scanning electron microscopy–energy-dispersive X-ray (SEM–EDX) and X-ray diffraction (XRD). The ratios of electron per atom (e/a) for CuAl13−xTa1, CuAl13−xTa1.5, CuAl13−xTa2 and CuAl13−xTa2.5 were calculated as 1.52, 1.51, 1.50 and 1.49, respectively. DSC results showed that CuAlTa alloys belong to high-temperature shape-memory alloys. Also, it was identified that these alloys demonstrate 2 H (γ 1 ′) → DO 3 (β 1) → 18 R (β 1 ′) phase transformation. It was observed that both phase transformation temperature and oxidation sensitivity of the samples decreased with the increase in the amount of Ta. In the XRD analysis of CuAlTa HTSMA alloys, some phases were observed, including γ ′ , β ′ Cu9Al4, CuAl and Ta2Al3. These phases were supported by SEM–EDX results. The micro-hardness values of the alloys were increased by increasing Ta content. [ABSTRACT FROM AUTHOR]

The microstructure of multiphase steels assisted by transformation-induced plasticity consists of grains of retained austenite embedded in a ferrite-based matrix. Upon mechanical loading, retained austenite may transform into martensite, as a result of which plastic deformations are induced in the surrounding phases, i.e., the ferrite-based matrix and the untransformed austenite. In the present work, a crystallographically based model is developed to describe the elastoplastic transformation process in the austenitic region. The model is formulated within a large-deformation framework where the transformation kinematics is connected to the crystallographic theory of martensitic transformations. The effective elastic stiffness accounts for anisotropy arising from crystallographic orientations as well as for dilation effects due to the transformation. The transformation model is coupled to a single-crystal plasticity model for a face-centered cubic lattice to quantify the plastic deformations in the untransformed austenite. The driving forces for transformation and plasticity are derived from thermodynamical principles and include lower-length-scale contributions from surface and defect energies associated to, respectively, habit planes and dislocations. In order to demonstrate the essential features of the model, simulations are carried out for austenitic single crystals subjected to basic loading modes. To describe the elastoplastic response of the ferritic matrix in a multiphase steel, a crystal plasticity model for a body-centered cubic lattice is adopted. This model includes the effect of nonglide stresses in order to reproduce the asymmetry of slips in the twinning and antitwinning directions that characterizes the behavior of this type of lattices. The models for austenite and ferrite are combined to simulate the microstructural behavior of a multiphase steel. The results of the simulations show the relevance of including plastic deformations in the austenite in order to predict a more realistic evolution of the transformation process. [ABSTRACT FROM AUTHOR]