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)

Use of DMT and CPTU tests in the evaluation of shear modulus G 0 for soils of different origin

The subject of this article is the analysis of the relationship between G 0/ M DMT and K D, where G 0 is the small strain shear modulus, while M DMT and K D are respectively the constrained modulus and the horizontal stress index determined from DMT tests. This relationship allows to determine a profile with depth of G 0 from standard DMT test results, useful when data from nonseismic DMT investigations are available. The analysis was based on a large amount of data for a wide range of soils of different origins in Poland. The dataset included OC and NC loams, silts, medium sands, silty sands and fine sands. The overconsolidation ratio (OCR) was estimated using data from CPTU and DMT tests. The obtained empirical G 0/ M DMT vs. K D relationships were compared with the correlations established by Marchetti et al. [1] for different soil types. To account for the significant influence of overconsolidation, an original empirical relationship between G 0/�� p and K D, where �� p is the preconsolidation stress, was defined based on data from all investigated fine-grained soils

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

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)

The effect of cooling rate on the structure and selected properties of AlCoCrFeNiSix (x = 0; 0.25; 0.5; 0.75) high entropy alloys

High entropy alloys with variable silicon content were prepared by two different methods to determine the influence of the cooling rate and chemical composition on the structure and properties of the alloys. First, the structure of the alloys was investigated using X-ray diffractometry and electron microscopy and compared with Mössbauer spectra to obtain a comprehensive description of the atom arrangement. The formation ability of the BCC and B2 phases was confirmed. The magnetic properties were examined using a vibrating sample magnetometer and Mössbauer spectroscopy. The corrosion resistance behavior was stu died by electrochemical testing. Our results show that the saturation magnetization tends to decrease with increasing silicon content and that the lowest coercive force was noted for rapidly cooled plates. The highest corrosion resistance in a 3.5% NaCl solution characterizes the AlCoCrFeNiSi0.75 alloy in the form of plates. For which Ecorr and jcorr was equal to − 0.155 V and 0.17 μA/cm2. The addition of Si led to an increase in the hardness of the ingots and plates. For example, AlCoCrFeNiSi0.75 shows 859 HV for the ingot and 727 HV for the plate

Structural Characterization of Rapidly Solidified Al71Ni24Fe5 Alloy

The influence of rapid solidification from the liquid state on the structure of Al71Ni24Fe5 alloy was studied. The samples were prepared by induction melting (ingots) and high pressure die casting into a copper mold (plates). The structure was examined by X-ray diffraction (XRD), light microscopy and high resolution transmission electron microscopy (HRTEM). The mechanism of crystallization was described on the basis of differential scanning calorimetry (DSC) heating and cooling curves, XRD patterns, isothermal section of Al-Ni-Fe alloys at 850°C and binary phase diagram of Al-Ni alloys. The fragmentation of the structure was observed for rapidly solidified alloy in a form of plates. Additionally, the presence of decagonal quasicrystalline phase D-Al70.83Fe9.83Ni19.34 was confirmed by phase analysis of XRD patterns, Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) of transmission electron microscopy images. The metastable character of D-Al70.83Fe9.83Ni19.34 phase was observed because of the lack of thermal effects on the DSC curves. The article indicates the differences with other research works and bring up to date the knowledge about Al71Ni24Fe5 alloys produced by two different cooling rates

The Influence of Rapid Solidification on Corrosion Behavior of Mg60Zn20Yb15.7Ca2.6Sr1.7 Alloy for Medical Applications

Biodegradable magnesium alloys with Zn, Yb, Ca and Sr additions are potential materials with increased corrosion resistance in physiological fluids that ensure a controlled resorption process in the human body. This article presents the influence of the use of a high cooling rate on the corrosion behavior of Mg60Zn20Yb15.7Ca2.6Sr1.7 alloy proposed for medical applications. The microstructure of the alloy in a form of high-pressure die-casted plates was presented using scanning electron microscopy in the backscattered electrons (BSEs) mode with energy-dispersive X-ray spectrometer (EDX) qualitative analysis of chemical composition. The crystallization mechanism and thermal properties were described on the basis of differential scanning calorimetry (DSC) results. The corrosion behavior of Mg60Zn20Yb15.7Ca2.6Sr1.7 alloy was analyzed by electrochemical studies with open circuit potential (EOCP) measurements and polarization tests. Moreover, light microscopy and X-ray photoelectron spectroscopy were used to characterize the corrosion products formed on the surface of studied samples. On the basis of the results, the influence of the cooling rate on the improvement in the corrosion resistance was proved. The presented studies are novel and important from the point of view of the impact of the technology of biodegradable materials on corrosion products that come into direct contact with the tissue environment

Structural characterization of Al65Cu20Fe15 melt-spun alloy by X-ray, neutron diffraction, high-resolution electron microscopy and Mössbauer spectroscopy

The aim of the work was to characterize the structure of Al65Cu20Fe15 alloy obtained with the use of conventional casting and rapid solidification-melt-spinning technology. Based on the literature data, the possibility of an icosahedral quasicrystalline phase forming in the Al-Cu-Fe was verified. Structure analysis was performed based on the results of X-ray diffraction, neutron diffraction, 57Fe Mössbauer and transmission electron microscopy. Studies using differential scanning calorimetry were carried out to describe the crystallization mechanism. Additionally, electrochemical tests were performed in order to characterize the influence of the structure and cooling rate on the corrosion resistance. On the basis of the structural studies, the formation of a metastable icosahedral phase and partial amorphous state of ribbon structure were demonstrated. The possibility of the formation of icosahedral quasicrystalline phase I-AlCuFe together with the crystalline phases was indicated by X-ray diffraction (XRD), neutron diffraction (ND) patterns, Mössbauer spectroscopy, high-resolution transmission electron microscopy (HRTEM) observations and differential scanning calorimetry (DSC) curves. The beneficial effect of the application of rapid solidification on the corrosive properties was also confirmed

Electrochemical behavior and morphology of selected sintered samples of Mg65Zn30Ca4Pr1 alloy

In order to investigate the effect of the milling time on the corrosion resistance of the Mg65Zn30Ca4Pr1 alloy, powders of the alloy were prepared and milled for 13, 20, and 70 hours, respectively. The samples were sintered using spark plasma sintering (SPS) technology at 350◦C and pressure of 50 MPa. The samples were subjected to potentiodynamic immersion tests in Ringer’s solution at 37◦C. The obtained values of Ecorr were –1.36, –1.35, and –1.39 V, with polarization resistance Rp = 144, 189, and 101 Ω for samples milled for 13, 20 and 70 h, respectively. The samples morphology showed cracks and pits, thus signaling pitting corrosion