Determination and distribution of stresses in the deformation zone can be obtained by advanced plasticity theory, especially by experimental-analytical method such as visioplasticity. The visioplasticity method is very useful in providing a detailed analysis of the distribution of stresses, strains or strain rates in deformed material. In this paper shear stress distribution in cold formed NiTi alloy is analyzed by using visioplasticity method. The specimens were cold forward extruded trough a conical die. Further, the influence of the coefficient of friction on shear stress distribution in deformed zone of the material is investigated. The results are presented in form of diagrams.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 18524182The shape memory alloys (SMA) nickel – titanium (NiTi) are very useful materials in medical use because of their good biocompatibility and functional properties. Especially, they are used in the field of orthodontics as for example for orthodontic wire, because of their lowest force delivery (small modulus of elasticity) and of their large recoverable strain for time continuous orthodontic treatment (superelasticity). This study presents the results of the microstructure observation of six different types of NiTi orthodontic wires in stress free conditions by means of Transmission Electron Microscopy (TEM, Jeol Jem-2100 HR). Within these analyses the chemical compositions of each wire were observed in different places by applying the Energy Dispersive X-Ray Spectroscopy (EDS) detector. Namely, the chemical composition in the orthodontic wires is very important because it shows the dependence between the phase temperatures and mechanical properties. Microstructure observations showed that orthodontic wires consist of nano-sized grains containing precipitates of Ti2Ni and/or TiC. The first precipitated Ti2Ni are rich in Ti, while the precipitated TiC is reach in C. Further investigation showed that there was a difference in average grain size in the NiTi matrix. The sizes of grains in orthodontic wires are in the range from approximately 50 nm to 160 nm, and the sizes of precipitates are in the range from 0.3 µm to 5 µm.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 1183402Continuous casting is a manufacturing process where molten metal is solidified into a semi-finished product. Metal is melted in the crucible and then cast through a mould. The casting travels downwards and its length increases with time. Continuous casting is characterized by high cooling rates which allow a very short time for the diffusion processes and may lead to an extremely fine microstructure that increases the material's toughness. This process is used most frequently to cast steels, aluminium and copper. On the other hand, continuous casting of nitinol is studied poorly. Nitinol is well known for its properties, like shape memory effect, superelasticity, high tensile strength, good fatigue and corrosion resistance and biocompatibility. The main problems with continuous casting of nitinol are the high reactivity and affinity for oxygen of titanium and great hardness and toughness of nitinol that makes it very hard to form a desired shape with this material. Nitinol was prepared with vertical continuous casting. Ni and Ti were melted in a graphite crucible with a vacuum induction furnace at a temperature above 1400°C. The nitinol was cooled and cast through a copper mould at a pre-defined casting rate. The final product was nitinol rods of different lengths with 1 cm diameter. The rods were further characterized for its microstructure using a scanning electron microscope (SEM) and composition using an X-ray fluorescence spectrometry (XRF).
B.03 Paper at an international scientific conference
COBISS.SI-ID: 19038486