The influence of Nb atoms on the crystallization process of Fe-B-Nb amorphous alloys

The ferromagnetic Fe-based amorphous alloys have been studied due to the attractive properties for soft magnetic applications. Depending on di erent Nb concentration, we studied the formation of crystalline phases in annealed samples of amorphous metallic alloys for Fe80xB20Nbx (x = 0, 4, 10). The nature of the crystallization products as well as the phase structure were determined by using the Mössbauer spectrometry combined with X-ray di raction and di erential scanning calorimetry results. Substitution of Fe atoms by Nb lead to signi cant changes in hyper ne magnetic eld (Bhf ) distributions in as-quenched amorphous alloys Fe80xB20Nbx, for x = 10 the minimal value of Bhf is observed. Addition of this element causes shift of crystallization process towards higher temperatures and induces formation of phase complex including the -Fe, Fe2B and Fe3B. Combination of X-ray di raction and Mössbauer spectroscopy is very useful method in studying the structural environment of Fe atoms on a nearest-neighbor length scale

Corrosion study of resorbable Ca60Mg15Zn25 bulk metallic glasses in physiological fluids

The corrosion activity of amorphous plates of Ca60Mg15Zn25 alloy was investigated. The biocompatible elements were selected for the alloy composition. The electrochemical corrosion and immersion tests were carried out in a multi-electrolyte fluid and Ringer's solution. Better corrosion behavior was observed for the samples tested in a multi-electrolyte fluid despite the active dissolution of Ca and Mg in Ringer's solution. The experimental results indicated that reducing concentration of NaCl from 8.6 g/dm3 for Ringer's solution to 5.75 g/dm3 caused the decrease of the corrosion rate. The volume of the hydrogen evolved after 480 min in Ringer's solution (40.1 ml/ cm2) was higher in comparison with that obtained in a multi-electrolyte fluid (24.4 ml/cm2). The values of opencircuit potential (EOCP) for the Ca60Mg15Zn25 glass after 1 h incubation in Ringer's solution and a multielectrolyte fluid were determined to be −1553 and −1536 mV vs. a saturated calomel electrode (SCE). The electrochemical measurements indicated a shift of the corrosion current density (jcorr) from 1062 μA/cm2 for the sample tested in Ringer's solution to 788 μA/cm2 for the specimen immersed in a multi-electrolyte fluid. The corrosion products analysis was conducted by using the X-ray photoelectron spectroscopy (XPS). The corrosion products were identified to be CaCO3, Mg(OH)2, CaO, MgO and ZnO. The mechanism of corrosion process was proposed and described based on the microscopic observations. The X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) also indicated that Ca(OH)2, CaCO3, Zn(OH)2 and Ca(Zn(OH)3)2·2H2O mainly formed on the surface of the studied alloy.The work was supported by National Science Centre under research project no.: 2013/09/B/ST8/02129

Structure, properties, and crystallization of Mg-Cu-Y-Zn bulk metallic glasses

The Mg60Cu30Y10 and Mg65Cu 20Y10Zn5 bulk metallic glasses in the form of a rod 2 mm in diameter were successfully prepared by the conventional Cu-mold casting method. The addition of Zn caused the decrease in the crystallization and melting temperatures in comparison with the Mg60Cu 30Y10 alloy. The crystallization and melting temperatures are crucial factors that influence the casting process. An increase in annealing temperature leads to structural changes by the formation of the crystalline phases and lowers the compressive strength. These results obtained for the Mg-based bulk metallic glasses (Mg-BMGs) are important for some practical reasons, in particular, for developing the fabrication process. It has been shown that minor addition of an alloying element can change glass-forming ability and strength of the Mg- BMGs

New resorbable Ca-Mg-Zn-Yb-B-Au alloys : structural and corrosion resistance characterization

New resorbable Ca32Mg12Zn38Yb18-2xBxAux (x = 1,2) alloys were designed and prepared in order to verify their use for medical applications as potential short-term implants. Their amorphous structure containing some crystalline phases (CaZn, CaZn2 and MgZn) was determined by X-ray and neutron diffraction and electron microscopy methods. The biocorrosion behavior of the plates was tested by hydrogen evolution measurements, immersion, electrochemical polarization tests, and electrochemical impedance spectroscopy in Ringer’s solution at 37 C. The corrosion analysis was also supplemented by X-ray diffraction, photoelectron, and ICP-AES spectroscopy. The corrosion resistivity measurements revealed that the alloys manifest enhanced corrosion resistance. The corrosion current density for Ca32Mg12Zn38Yb18- 2xBxAux (x = 1, 2) alloys were 18.46 and 8.79 lA/cm2, which is lower than for pure Mg (47.85 lA/cm2) and Zn (33.96 lA/cm2). A decreasing tendency for hydrogen to evolve as a function of time was noted. The hydrogen evolution did not exceed 1 ml/cm2 over 1 h and average corrosion rate is calculated as 0.32 g/m2 . h for Ca32Mg12Zn38Yb14B2Au2 alloy after 312 h. The corrosion mechanism of the alloys includes an anodic dissolution, a hydroxide precipitation, corrosion product layer formation and corrosion propagation stage

Amorphous and Crystalline Magnesium Alloys for Biomedical Applications

Amorphous and crystalline magnesium alloys, developed for medical applications – especially implantology – present the characteristics of biocompatible magnesium alloys (Mg-Zn, Mg-Zn-Ca, Mg-Ca etc.). This chapter provides a brief description of the role of magnesium in the human body and the use of Mg in medicine. It presents the concept of using magnesium alloys in medicine (advantages and limitations) and the scope of their potential applications (orthopedic implantology, cardiac surgery etc.). The chapter shows classification of magnesium alloys as potential biomaterials, due to their structure (amorphous, crystalline) and alloying elements (rare earth elements, noble metals etc.). The mechanism and in vitro degradation behavior of magnesium alloys with amorphous and crystalline structures are described. The chapter also discusses the influence of alloying elements (rare earth elements, noble metals) on the in vitro degradation process. It also presents the methods of reducing the degradation rate of magnesium alloys by modifying their surface (application of protective layers)

Structure and corrosion resistance of Al–Cu–Fe alloys

The microstructure and electrochemical properties of Al–Cu–Fe alloys with the atomic compositions of Al65Cu20Fe15, Al78Cu7Fe15 and Al80Cu5Fe14Si1 have been studied. The alloys were produced by induction melting of pure elements with copper mold casting. The microstructure of the alloys was analyzed by X-ray diffraction and high-resolution transmission electron microscopy. The formation of quasicrystalline phases in the Al–Cu–Fe alloys was confirmed. The presence of intermetallic phases was observed in the alloys after crystallization in a form of ingots and plates. The electrochemical measurements were conducted in 3.5% NaCl solution. The electronic structure of the alloys was determined by X-ray photoelectron spectroscopy. The post corrosion surface of the samples was checked using a scanning electron microscope equipped with the energydispersive X-ray detector. It was observed that the Al65Cu20Fe15 alloy had the highest corrosion resistance. The improved corrosion resistance parameters were noted for the plate samples rather than those in the as-cast state. And the hardness of the Al65Cu20Fe15 alloy was significantly higher than the other alloy samples

Surface modification of biomedical MgCa4.5 and MgCa4.5Gd0.5 alloys by micro-arc oxidation

The aim of this work was to characterize the structure and corrosion properties of the MgCa4.5(Gd0.5) alloys surface treated by the micro-arc oxidation (MAO) process. The MgCa4.5 and MgCa4.5Gd0.5 alloy samples were processed by MAO in an electrolyte composed of NaOH (10 g/dm3), NaF (10 g/dm3), NaH2PO4 (5 g/dm3), Na2SiO2·5H2O (10 g/dm3) and water. Two different voltages (120 V and 140 V) were used in the MAO process. The alloys protected by an oxide layer formed in the MAO were then the subject of corrosion resistance tests in an environment simulating the human body (Ringer’s solution). After the experiments, the resulting samples were investigated with using SEM, XPS and EDS techniques. The addition of Gd affected the fragmentation of the coating structure, thereby increasing the specific surface; higher voltages during the MAO process increased the number and size of surface pores. Corrosion tests showed that the MgCa4.5Gd0.5 alloys were characterized by low polarization resistances and high corrosion current densities. The studies indicated the disadvantageous influence of gadolinium on the corrosion resistance of MgCa4.5 alloys. The immersion tests confirmed lower corrosion resistance of MgCa4.5Gd0.5 alloys compared to the referenced MgCa4.5 ones. The MgCa4.5 alloy with the MAO coating established at voltage 140 V demonstrated the best anticorrosion properties

Structure and Magnetic Properties of Fe-B-La-Al Alloy

Nanocrystalline magnetic materials are of great interest in order to meet the needs of electronics and electrical engineering. There are many possibilities to modify the synthesis parameters and chemical composition in order to obtain the most desirable magnetic properties and microstructure. The paper discusses an iron-based alloy with the addition of boron lanthanum and aluminium. The alloy was obtained by induction melting and casting with a melt-spinner. The main purpose of the work was to analyze the structure and properties of both the starting alloys in the form of ingots and the obtained tapes. X-ray diffraction (XRD), scanning electron microscopy (SEM), vibration magnetometry (VSM) and microhardness measurements using the Vickers method were carried out

Glass-forming ability and corrosion resistance of Al88Y8-xFe4+x (x = 0, 1, 2 at.%) alloys

The effect of iron and yttrium additions on glass forming ability and corrosion resistance of Al88Y8-xFe4+x (x = 0, 1, 2 at.%) alloys in the form of ingots and melt-spun ribbons was investigated. The crystalline multiphase structure of ingots and amorphous-crystalline structure of ribbons were examined by a number of analytical techniques including X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy. It was confirmed that the higher Fe additions contributed to formation of amorphous structures. The impact of chemical composition and structure of alloys on their corrosion resistance was characterized by electrochemical tests in 3.5% NaCl solution at 25 ◦C. The identification of the mechanism of chemical reactions taking place during polarization test along with the morphology and internal structure of the surface oxide films generated was performed. It was revealed that the best corrosion resistance was achieved for the Al88Y7Fe5 alloy in the form of ribbon, which exhibited the lowest corrosion current density (jcorr = 0.09 µA/cm2) and the highest polarization resistance (Rp = 96.7 kΩ·cm2)

Influence of copper addition and heat treatment parameters on nanocrystallization process of Fe-Co-Mo-B-Si amorphous ribbons with high saturation magnetization about 1.6 T

In this paper the influence of copper addition on the formation of the amorphous phase and the nanocrystallization process of Fe79.8−xCo2CuxMo0.2Si4B14 (x=0, 0.25, 0.5, 0.75, 1, 1.5, 2) ribbons was described. The formation of crystalline phases was described using differential scanning calorimetry, X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy. It was confirmed that the addition of copper decreases the glass forming ability, while facilitating the process of nanocrystallization. The analysis of the Avrami exponent allowed to state, that for fully amorphous alloys the crystallization of the α-Fe phase is associated with diffusion-controlled growth with decreasing nucleation rate and the Fe2B phase with interface controlled growth with increasing nucleation rate. Additionally, with increasing copper addition onset temperature of crystallization of α-Fe phase shifts to lower values, whereas for second, Fe2B phase, these changes are not so visible. Optimization of the annealing process of toroidal cores made from amorphous ribbons with different copper content allowed to obtain nanocrystalline, soft magnetic materials characterized by low coercivity ~9 A/m and high saturation induction of about 1.6 T. Analysis of transmission electron microscope images and electron diffraction confirmed that high magnetic parameters are related to the coexistence of the amorphous and nanocrystalline phases, which was confirmed also by Mössbauer spectroscopy