Bucureºti) ♦ 61♦ Nr

A new Materials used as permanent implants must possess corrosion resistance, biocompatibility, vitality and elasticity. Titanium base materials partly realize these conditions. Titanium and its Ti-6Al-4V alloy were frequently used in orthopaedic applications. But, it was proved that vanadium is a toxic material both as element and as oxide V 2 O 5 [1]. Now, new titanium base alloys without vanadium are developed Several metallic elements can be used as β stabilizer for titanium alloys: Fe, V, Ta, Nb, Mo, Ni, Cr, etc.; α stabilizer can be: Al, O and Zr Protective oxides on the alloy surface are in contact with human cells and fluids and by friction, wear and corrosion can release their component ions in surrounding tissues. Therefore, is very important to analyse the biocompatibility of the individual elements There is a number of alloys used for biomedical applications such as: Ti-15Mo-5Zr-3Al [13][14] In recent times it was proved that the following titanium base alloys may be used as implants: Ti-15Zr-4Nb-4Ta A new Romanian, cheaper alloy that contains only nontoxic elements Ti-10Zr-5Ta-5Nb was obtained. Anticorrosive resistance of this new alloy was studied in simulated physiological fluids, Ringer solution, in extreme functional conditions, namely acidic, neutral and alkaline pH. Acidic pH appears after surgery (because the hydrogen ions concentration increases in the traumatic tissues) and by the hydrolysis in time of the protective oxides [30, * email: [email protected] Experimental part Ti-10Zr-5Ta-5Nb alloy was obtained by vacuum melting. An electron beam furnace type EMO 80, with an installed power of 80 kW was used. The alloy synthesis was performed in two steps under vacuum, consisting in melting and re-melting both with cooling stages inside furnace. The chemical composition, in weight % was: Zr -9.12; Nb -4.09; Ta -4.16; Fe -0.036; O 2 -0.195; N 2 -0.004; H 2 -0.0016; Ti -up to the balance. The electrodes were grinded with emery paper and aluminium paste to mirror surface, fixed in a SternMakrides mount system, rinsed with distilled water, degreased in boiling benzene and dried. All measurements were carried out in Ringer solution of pH = 2.33 (obtained by HCl addition), pH = 7.1 (normal pH) and pH = 9.12 (obtained by KOH addition). Solution composition as (g/L) is: NaCl -6.8; KCl -0.4; CaCl 2 -0.2; MgSO 4 .7H 2 O -0.2048; NaH 2 PO 4 .H 2 O -0.1438; NaHCO 3 -1.1; glucose -1. Temperature was 37 0 ± 1 0 C and was constantly maintained by a thermostated bath for shortterm experiments and by a drying oven for long-term experiments. An electrochemical glass cell with three electrodes provided with a central inlet for the electrode assembly, a cylindrical platinum grid counter electrode, a Luggin probe connected with a saturated calomel electrode (SCE) was used. The electrochemical techniques of potentiodynamic and linear polarization were used. Cyclic potentiodynamic measurements were applied starting from -0.5 V to +4.0 V (versus SCE) using a scan rate of 10 mV/s. Voltalab 80 equipment with a VoltaMaster 4 software was used for data processing. From the voltammograms, the main electrochemical parameters were determined: E corrcorrosion potential, like the zero current potential; E ppassivation potential; E cp -complete passivation potential; ΔE p -passive potential range; i p -passive current density. If the reverse curve of cyclic voltammogram presents lower current densities than the current densities from the direct curve it results that the studied material has a passive, stable behaviour. If the reverse curve shows the highe

{332}<113> and {112}<111> Twin Variant Activation during Cold-Rolling of a Ti-Nb-Zr-Ta-Sn-Fe Alloy

Deformation twinning is a phenomenon that causes local shear strain concentrations, with the material either experiencing elongation (and thus a tensile stress) or contraction (compressive stress) along the stress directions. Thus, in order to gauge the performance of the alloy better, it is imperative to predict the activation of twinning systems successfully. The present study investigates the effects of deformation by cold-rolling on the {332} and {112} twin variant activation in a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) (TNZTSF) alloy. The Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) alloy was synthesized in a cold crucible induction levitation furnace, under an argon-controlled atmosphere, using high-purity elemental components. The TNZTSF alloy was cold-deformed by rolling, in one single step, with a total deformation degree (thickness reduction) of ε ≈ 1% (CR 1), ε ≈ 3% (CR 3), and ε ≈ 15% (CR 15). The microstructural investigations were carried out with the SEM-EBSD technique in order to determine the grain morphology, grain-size distribution, crystallographic orientation, accumulated strain-stress fields and Schmid Factor (SF) analysis, all necessary to identify the active twin variants. The EBSD data were processed using an MTEX Toolbox ver. 5.7.0 software package. The results indicated that the TNZTSF alloy’s initial microstructure consists of a homogeneous β-Ti single phase that exhibits equiaxed polyhedral grains and an average grain-size close to 71 μm. It was shown that even starting with a 1% total deformation degree, the microstructure shows the presence of the {332} twinning ((233)[3¯11] active twin variant; Schmit factor SF = −0.487); at a 3% total deformation degree, one can notice the presence of primary and secondary twin variants within the same grain belonging to the same {332} twinning system ((323¯)[13¯1¯] primary twin variant—SF = −0.460; (233¯)[3¯11¯] secondary twin variant—SF = −0.451), while, at a 15% total deformation degree, besides the {332} twinning system, one can notice the activation of the {112} twinning system ((11¯2)[1¯11] active twin variant—SF = −0.440). This study shows the {332} and {112} twinning variant activation during cold-deformation by rolling in the case of a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) (TNZTSF) alloy

Influence of Aging Treatment on Microstructure and Tensile Properties of a Hot Deformed UNS S32750 Super Duplex Stainless Steel (SDSS) Alloy

In this present study, the influence of isothermal aging temperature and duration on microstructural and mechanical properties of a hot-deformed UNS S32750 super duplex stainless steel (SDSS) alloy was investigated by SEM-EBSD (scanning electron microscopy-electron backscatter diffraction) and tensile testing techniques. An isothermal aging treatment, at temperatures between 400 and 600 &deg;C and treatment duration between 3 and 120 h, was applied to a commercial UNS S32750 SDSS alloy. Microstructural characteristics of all thermomechanical (TM) processed states, such as distribution and morphology of constituent phases, grain&rsquo;s modal orientation (MO), and obtained mechanical properties were analysed correlated with the TM processing conditions. The obtained experimental results show that the constituent phases, in all TM processed states, are represented by elongated &gamma;-phase grains within the &delta;-phase matrix. The R-phase was observed in the case of aging treatment performed at 600 &deg;C for 120 h. Within the &delta;-phase matrix, dynamically recrystallized grains were identified as a result of applying hot deformation and isothermal aging treatments. Also, it was observed that aging treatment parameters can significantly influence the mechanical behaviour exhibited by the UNS S32750 SDSS alloy, in terms of elongation to fracture and absorbed energy during impact testing

Microstructure Evolution during Hot Deformation of UNS S32750 Super-Duplex Stainless Steel Alloy

The present paper analyzes UNS S32750 Super-Duplex Stainless Steel hot deformation behavior during processing by upsetting. The objective of this paper is to determine the optimum range of deformation temperatures, considering that both austenite and ferrite have different deformation behaviors due to their different morphology, physical, and mechanical properties. Because the capability of plastic deformation accommodation of ferrite is reduced when compared to austenite, side cracks and fissures can form during the hot deformation process. Consequently, it is important to find the optimum conditions of deformation of this type of stainless steel to establish the best processing parameters without deteriorating the material. The experimental program involved the application of hot deformation by the upsetting method on a series of samples between 1000 °C and 1275 °C, with a total degree of deformation of 30%. The resultant samples were examined by SEM-EBSD to establish and analyze the evolution of the phases present in the structure from several points of view: nature, distribution, morphology (size and shape), and their structural homogeneity. The GROD (Grain Reference Orientation Deviation) distribution map was also determined while taking into account the possible precipitation of the secondary austenite phase (γ2-phase) and the analysis of the dynamic recrystallization process according to the applied deformation temperature. The main conclusion was that UNS S32750 SDSS steel can be safely deformed by upsetting between 1050–1275 °C, with an experimented total degree of deformation of 30%

Optimizing Structural and Mechanical Properties of an Industrial Ti-6246 Alloy below β-Transus Transition Temperature through Thermomechanical Processing

This study aims to investigate the effect of hot deformation on commercially available Ti-6246 alloy below its β-transus transition temperature at 900 °C, knowing that the α → β transition temperature of Ti-6246 alloy is about 935 °C. The study systematically applies a thermomechanical processing cycle, including hot rolling at 900 °C and solution and ageing treatments at various temperatures, to investigate microstructural and mechanical alterations. The solution treatments are performed at temperatures of 800 °C, 900 °C and 1000 °C, i.e., below and above the β-transus transition temperature, for 9 min, followed by oil quenching. The ageing treatment is performed at 600 °C for 6 h, followed by air quenching. Employing various techniques, such as X-ray diffraction, scanning electron microscopy, optical microscopy, tensile strength and microhardness testing, the research identifies crucial changes in the alloy’s constituent phases and morphology during thermomechanical processing. In solution treatment conditions, it was found that at temperatures of 800 °C and 900 °C, the α′-Ti martensite phase was generated in the primary α-Ti phase according to Burger’s relation, but the recrystallization process was preferred at a temperature of 900 °C, while at a temperature of 1000 °C, the α″-Ti martensite phase was generated in the primary β-Ti phase according to Burger’s relation. The ageing treatment conditions cause the α′-Ti/α″-Ti martensite phases to revert to their α-Ti/β-Ti primary phases. The mechanical properties, in terms of strength and ductility, underwent an important beneficial evolution when applying solution treatment, followed by ageing treatment, which provided an optimal mixture of strength and ductility. This paper provides engineers with the opportunity to understand the mechanical performance of Ti-6246 alloy under applied stresses and to improve its applications by designing highly efficient components, particularly military engine components, ultimately contributing to advances in technology and materials science

Design and Optimization of a Curved-Crease-Folding Process Applied to a Light Metallic Structure

Presently, the realization of complex, unconventional designs using efficient modalities is possible due to an increasing interest in interdisciplinary approaches: materials science, mathematics, IT, architecture, etc. Computerized techniques, among which the algorithmic/generative design is the most advanced one, that are associated with the individualized production methods are used for finding solutions for modern spatial forms with an unconventional spatial geometric shape, which are generically called “free-forms”. This work presents the design, realization and testing of a thin-walled metallic structure proposed as a light structural unit. An integrated research approach was proposed that utilized an algorithmic/digital design applied to the curved-crease-folding method with the study (at different length scales) of the metallic material behaviour after folding. An original method was proposed for the digital design and simulations. The specific mechanical behaviour of the metallic material in the elastic–plastic regime was used in this case to improve the structural performances; mechanical and structural tests were realized to analyse the behaviour of the entire structure. The results are useful for enhancing the accuracy of the digital design, the structural simulation programs and the fabrication methods