Using of ultrasonic methods for determination of the elastic moduli on the Ti-Ni based alloys

The presented work is focused on the determination of elastic constants of selected alloys of the systems Ni-Ti and Ni-Ti-Cu with use of ultrasonic methods. Sample preparation was carried out using VIM in graphite crucible in combination with pouring into graphite mould. The prepared samples were appropriately heattreated, polished into the desired shape and subjected to measurement of density and then to ultrasonic measurements. In addition to conventional methods, such as mechanical tests, also less known methods are applied. Among the specific methods we can mention dynamic mechanical analysis, dynamic super microhardness measurement, electro acoustic resonance or ultrasonic test.The group of thus tested materials includes also Ti alloys

Predviđanje deformacije i temperature metodom konačnim elemenata (MKE) tijekom valjanja cijevi na pilger – stanu

3D - FEM simulation was used as an efficient tool for description of stress-deformation thermal field at rolling of tubes on a pilgrim mill. The monitored objectives comprised also behaviour of working tools at this rolling. This paper assumes rolling of already pierced thick-walled blank, which passes through the pilgrim stand at simultaneous reduction of thickness of inside and outside diameters at the expense of elongation of initial length. Main attention is focused on the mentioned parameters with respect to various conditions of rolling, such as different heat transfer, different friction or different distance of insertion of the rolled product into the gauge. The input data used at simulation were derived from real conditions of tubemaking.Za prikaz termičkog polja naprezanje – deformacija tijekom valjanja cijevi na pilger - stanu učinkovito je rabljena trodimenzijska metoda konačnih elemenata (3D – MKE). U radu je razmatrano i ponašanje alata tijekom izrade cijevi valjanjem. Pretpostavljeno je valjanje šuplje debelostjene cijevnice na pilger stanu uz istovremeno smanjenje vanjskog i unutrašnjeg promjera na uštrb produljenja početne duljine. Rad se fokusira na navedene parametre obzirom na promjenjive režime valjanja poput različitog prijenosa topline, različitog trenja ili različite udaljenosti uvođenja valjanog proizvoda u uređaj. Ulazni podaci rabljeni u simulaciji odgovaraju onima iz realnog procesa valjanja cijevi

Study of the process of equal channel angular pressing of aluminum alloy

This work is dedicated to the research of the influence of equal channel angular pressing to the microstructure and mechanical properties of the alloy based on aluminum. As a result of the carried out research it is found out that there are the properties improvement after ECAP. There by structure and mechanical properties depend on the ECAP route. The ECAP 4 cycles realization provides the formation on uniform ultra fine structure on the BC route as well as C route. The experiments showed that alloy based on aluminum allows to obtain ultra fine structure (0,8-1,2 μm) already after 2 passes of ECAPB

Finite elements method (FEM) simulation based prediction of deformation and temperature at rolling of tubes on a pilgrim mill

3D - FEM simulation was used as an efficient tool for description of stress-deformation thermal field at rolling of tubes on a pilgrim mill. The monitored objectives comprised also behaviour of working tools at this rolling. This paper assumes rolling of already pierced thick-walled blank, which passes through the pilgrim stand at simultaneous reduction of thickness of inside and outside diameters at the expense of elongation of initial length. Main attention is focused on the mentioned parameters with respect to various conditions of rolling, such as different heat transfer, different friction or different distance of insertion of the rolled product into the gauge. The input data used at simulation were derived from real conditions of tubemaking

In situ neutron diffraction investigation of texture-dependent Shape Memory Effect in a near equiatomic NiTi alloy

To explore the possibility of customising the functional behaviour of NiTi shape memory alloy via controlling texture, binary Ni55Ti45 (wt.%) alloys were manufactured in as cast and hot swaged conditions, presenting contrasting initial texture and macroscopic performance. In situ time-of-flight neutron diffraction technique was employed to study the texture effect on the microstructural evolution during Shape Memory Effect (SME), and a range of properties were evaluated. It was found that (i) hot swaging process leads to change in grain morphology and increase in microstrain; (ii) thermal expansion coefficients of martensite and austenite variants were weakly affected by the texture and phase transformation constraint; (iii) significant texture effect on the elastic properties at both macro- and micro-scale was quantified by Elasto-Plastic Self-Consistent (EPSC) modelling approach, while the anisotropic elastic moduli lie within the range for single crystal state and twinned structure; (iv) texture evolution during SME is weakly related to the initial microstructure; (v) grains reoriented so that the axis became aligned parallel to the loading direction, and retained this orientation upon unloading, revealing the underlying correlation between texture evolution and detwinning. Based on the experimental results, a multi-variant model was proposed to quantify the lattice strain evolution during SME. Validity of the conceptually simple and parametrically parsimonious model was confirmed by validation against experimental data

Grain structure engineering of NiTi shape memory alloys by intensive plastic deformation

To explore an effective route of customizing the superelasticity (SE) of NiTi shape memory alloys via modifying the grain structure, binary Ni55Ti45 (wt) alloys were fabricated in as-cast, hot swaged, and hot-rolled conditions, presenting contrasting grain sizes and grain boundary types. In situ synchrotron X-ray Laue microdiffraction and in situ synchrotron X-ray powder diffraction techniques were employed to unravel the underlying grain structure mechanisms that cause the diversity of SE performance among the three materials. The evolution of lattice rotation, strain field, and phase transformation has been revealed at the micro- and mesoscale, and the effect of grain structure on SE performance has been quantified. It was found that (i) the Ni4Ti3 and NiTi2 precipitates are similar among the three materials in terms of morphology, size, and orientation distribution; (ii) phase transformation happens preferentially near high-angle grain boundary (HAGB) yet randomly in low-angle grain boundary (LAGB) structures; (iii) the smaller the grain size, the higher the phase transformation nucleation kinetics, and the lower the propagation kinetics; (iv) stress concentration happens near HAGBs, while no obvious stress concentration can be observed in the LAGB grain structure during loading; (v) the statistical distribution of strain in the three materials becomes asymmetric during loading; (vi) three grain lattice rotation modes are identified and termed for the first time, namely, multi-extension rotation, rigid rotation, and nondispersive rotation; and (vii) the texture evolution of B2 austenite and B19′ martensite is not strongly dependent on the grain structure