Materials Science Forum Vol. 802

Abstract: Arthroplasty is a surgery that aims to replace the defective joint surfaces, aiming to restore their functions. Is employed in this type of surgery that metallic materials play a key role in the constitution of orthopedic prostheses. In this context, we studied the chemical composition, mechanical and structural behavior of stainless steel developed for applications as biomaterials used in the manufacture of orthopedic implants. In this paper, two prostheses were analyzed established brands in the market. Proceeded through the chemical Spectroscopy Energy Dispersive X-ray (EDX) analysis. Characterized the crystal structures of these materials by diffraction of X-ray and mechanical behavior using tensile test. We compared the results of chemical composition and strength of the samples according to ASTM F-138 (2008). The results of EDX showed the presence of chloride in stainless steel alloys as an impurity that can compromise the durability of the prosthesis. The XRD patterns showed the presence in austenitic stainless steel alloys. As the tensile strength of the alloys analyzed, values that are consistent with those presented in the standards were recorded. In a general analysis, it became apparent incompatibility of assessed as biomaterials for use in prosthetic alloys, although meets the structural and mechanical requirements.

Abstract: Titanium is the most adequate metallic material for orthopedic or dental implants fabrication, due to a very favorable combination of properties, when compared with other metals, such as good corrosion resistance, good mechanical properties, relatively low density, elasticity modulus close to that of bone and good biocompatibility, which assures good adhesion/integration to bone. Powder metallurgy has been used for titanium based implants fabrication due to advantages such as the production of more complex shapes and reduction of machining operation. In this work, compacted pure titanium powders, consolidated by rolling at different temperatures, were characterized by means of optical microscopy, Field Emission Scanning Electron Microscopy (FESEM) with Electron Back Scattering Diffraction (EBSD) analysis, automatic image analysis and hardness tests. The hardness of rolled samples increased from 200 to 400oC , which indicated that 300 to 400°C is the most adequate temperature range for this processing route, since it allowed obtaining low porosity with satisfactory and relatively high hardness.

Abstract: A commercial magnet following the N 48 specification was submitted to a detailed microstructural characterization. The magnet presents 10 kOe of coercivity and good 2^nd quadrant squareness. The grain size is around 10 micrometers. Scanning electron microscope (SEM) EDAX analysis shows that it is a high copper NdPrFeB alloy following the 3Nd:1Pr proportion, with some aluminum. The magnet was covered by a 15 micrometers layer, with nickel and copper. The microstructural data allow a better understanding of the effect of the alloying elements.

Abstract: Fe50Ni alloys are used when very high magnetic permeabilities are necessary. Parts of these alloys can be produce by different mechanical processes. Metallurgical processes as investment casting and powder metallurgy can also be used. Sintered Fe50Ni parts have two disadvantages, in terms of magnetic properties: the presence of porosity and the limited grain size. This paper investigates the effects of compactation pressure on the final microstructure and density. Mixtures of atomized iron and carbonyl nickel powder were uniaxially pressed. Cylindrical samples with around 6.5g/cm³ of green density were vacuum sintered at 1220 °C. After sintering samples were cold deformed and then heat treated.

Abstract: Deposits of the Fe-6.5wt%Si alloy rapidly quenched by spray forming were investigated. The order phase can be either B2 or DO3 depending on annealing treatment conditions. The observation of pairs dislocations indicates the presence of super dislocations and B2 antiphase boundaries (APBs) which affects significantly the soft magnetic properties. The dislocations bound the APBS which yield δ fringes when image 200 superlattice reflections. Samples treated at 700oC for 1 h were oil quenched, this has induced a decreasing of power loss and the TEM micrographs have showed developed 1⁄4 <111> antiphase domain structure in the B2 phase. The magnetic properties were: power loss of 1.59 W/kg and coercive force of 76 A/m, at B=1 T, f=60 Hz. The samples annealed at 1250°C for 1h showed the same interaction between the APBs but better power losses on their magnetic properties. The magnetic properties were: 1.30 W/kg power loss and 40 A/m coercive force, at same conditions described above. This suggests a strong interaction between magnetic properties and antiphase domain structure in the B2 ordered phase. Optical microscopy observations corroborate the magnetic measurement conclusions.

Abstract: Nowadays, superparamagnetic iron oxide nanoparticles are an important tool for cancer treatment, such as magnetic hyperthermia. The goal is heating diseased tissue and then tumor cells are destroyed. Magnetic nanoparticles are promising mainly because they have specific ability to reduce side effects. However, for in vivo applications, nanoparticles need to be coated by a biocompatible material. In this work, nanoparticles are coated by PEG (biocompatible polymer). Samples were produced by coprecipitation process. Information about particle size, magnetic properties and crystallinity were obtained.

Abstract: Two different effects need to be considered in the sintering: (i) The densification should be maximum, to optimize the energy product BHmax and the remanence, however, (ii) the .grain size should be small, in order to maximize the coercivity. Grain growth takes place during the sintering step of the magnets, usually performed at the range 1000-1100°C. In this study, the grain growth kinetics is investigated. Samples of NdPrFeB magnets (proportion 3 Nd : 1 Pr) were heat treated at the temperature of 1050 °C, for times between 1 to 12 hours. The knowledge of the grain growth and coarsening kinetics allows extrapolation to other temperatures, and this information is helpful to maximize coercivity and remanence at the same time.

Abstract: The dysprosium-diffused Nd₂Fe₁₄B magnets are a feasible way to increase coercivity and saving dysprosium at the same time. In the practice, a dysprosium source layer is placed over a NdFeB magnet substrate, and Dy diffusion takes place from the surface to the center of the substrate. This practical situation is modeled in the present study. The main microstructural variables are the grain size of the magnets and the volume fraction of the intergranular phase (Nd-rich), the modeling temperature of 900°C. It is found that this process may have increased kinetics if the grain is reduced or if the volume fraction of the intergranular phase is increased.

Abstract: Ferrite beads are ferromagnetic materials that exhibit a small inductance at low frequencies, becoming resistive at high frequencies. These devices are used as low pass filters for reducing electromagnetic interference (EMI) in communications and power electronics because the resistive losses attenuate the undesired frequencies. As ferrite beads have a nonlinear behavior with current and frequency they have been used in nonlinear transmission lines (NLTLs) for high power microwave generation in space and defense applications. In this work, high frequency ferrite beads are characterized in the frequency range up to 1 GHz by measuring S₁₁ reflection parameter in order to calculate their complex permeability and losses, key parameters in the design of NLTLs. In addition, X-ray diffraction (XRD) is used to identify their chemical element composition. Finally, the motivation for this work is basically due to the limited information on ferrite materials provided by the manufacturers.

Abstract: The volume fraction of the single domain size particles can be directly estimated from the initial magnetization of thermally demagnetized magnets. Multi-domain grains present initial magnetization curve with high initial susceptibility, whereas single-domain grains present low susceptibility initial magnetization curve. In the case of single domain size particles, the coercivity mechanism is coherent rotation and the Stoner-Wohlfarth (SW) model can be applied. From the initial magnetization curve of magnets, the volume fraction of grains with diameter less than 0.3 micrometers can be estimated in NdFeB magnets. This is possible because the Nd₂Fe₁₄B phase is single domain below 0.3 micrometers.