Defect and Diffusion Forum Vol. 439

Abstract: Bond coats play a vital role in multi-layered thermal barrier coatings (TBCs), commonly made of B2 (Ni, Pt)Al. However, the presence of platinum (Pt) makes the bond coats costly. To reduce the overall cost and enhance the working temperature of TBCs, Pt can be partially or completely replaced by ruthenium (Ru). For the development of Ru-based bond coats, understanding the interdiffusion behavior of (Ni, Ru)Al is essential. In the present work, the interdiffusion behavior in the single B2 phase of the ternary (Ni, Ru)Al system was studied at 1100 °C using the diffusion couple technique. Experimental concentration profiles were obtained using an Electron Probe Micro-Analyzer, which was further fitted and analyzed for interdiffusion fluxes by utilizing the MultiDiflux software. Kirkaldy's approach was employed to determine the interdiffusion coefficients in the ternary B2 (Ni, Ru)Al system.

Abstract: This research synthesized a composite ceramic material base CaCO₃/Al₂O₃, CERMET, with possible biomedical applications. Eggshell was used as raw material to obtain CaCO_3, and it was reinforced with silver nanoparticles to improve the structural and mechanical properties of the ceramic system. The addition of silver nanoparticles promotes the formation of two phases. The first is a continuous phase called a matrix formed of CaAl₂O₄ (calcium aluminate). The second is a dispersed phase known as reinforcement made up of silver nanoparticles. The composite ceramics were synthesized using the solid-state synthesis technique from a chemical mixture of CaCO₃ and Al₂O₃ powders in the following chemical ratio: 49.5% CaCO₃ + 50.5% Al₂O₃, with silver nanoparticles added at different percentages (1%, 5%, 10%, 15%). The powder mixture was made in a high-energy mill for homogenization. After that, the mixture was compressed into cylindrical samples for their consolidation by sintering in a high-temperature muffle with a controlled atmosphere, using heating ramps. The sintered samples were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and microhardness, including fracture toughness studies. In addition, the Archimedes method determined the sintered samples' density. The results showed a clear relation between the mechanical properties of the CaAl₂O₄ ceramic base and the incorporated silver nanoparticles since these increased as the percentage of silver nanoparticles increased. In addition, it was observed that the porosity of the samples could be controlled, making the composite material suitable for biomedical applications.

Abstract: The objective of this study is to quantify the improvement of diffusion experiments in liquid alloys by using two measurement points of in situ X-ray fluorescence analysis (in situ XRF). The impurity diffusion coefficient of Bi in liquid Sn at 573 K was measured by monitoring the temporal change in the Bi concentration at two fixed points using in situ XRF. In the present study, two XRF measurement points were set in order to determine two unknown parameters that corresponded to the diffusion coefficient and the initial concentration at the measurement point just after complete melting. When only one measurement point is set for in situ XRF, the initial concentration is treated as a variable and the obtained impurity diffusion coefficients of Bi deviated by 20-30% from the reliable reference data. By using two measurement points for in situ XRF, the obtained impurity diffusion coefficient of Bi was (2.44±0.08)×10^-9 m²s^-1 and agreed with the reference data in the reported uncertainty of ±10%.

Abstract: The aim of the TULIP (Target ion soUrce for short-Lived Isotope Production) device is dedicated to the production of short-lived neutron deficient ions using ISOL (Isotope Separator On Line) method. The efficiency of such device depends on several parameters: diffusion, effusion and ionization processes, which must be optimized to maximize the efficiency. As short-lived, the elements must release from the stopping material in a short time, explaining our focus on the diffusion parameters and our effort to build a database gathering diffusion parameters concerning a large variety of target-element combinations. For this purpose, an important bibliographical work is underway in order to collect as much data as possible. An another offshoot of the TULIP ISOL project is to build a system (MELODICA device, MEsure en Ligne de cOefficients de DIffusion et de temps de Collage Atomique) to systematically measure the diffusion coefficients of atoms out of materials at high temperatures. Moreover, to get rid of constraints related to the use of radioactive elements, the MELODICA device uses stable atoms and embed a FEBIAD (Forced Electron Beam Induced Arc Discharge) source to ionize a large panel of elements. With this device, it will be possible to systematically extract several diffusion coefficients during the same experimental period, and to compare the relative release of different atoms out of materials currently used in the ISOL systems.

Abstract: Shot peening mechanical treatment surface, commonly used to improve material surface mechanical properties, as fatigue and wear resistance increase, induces deformations in the material crystal lattice, characterized by the presence of stress. Additionally, plasma nitriding, another surface treatment used to minimize failures in austenitic stainless steels, can produce resistant surface layers, composed of the interstitial nitrogen atoms accommodated in austenitic structure, increasing the layer hardness. Thus, the present work aims to study the residual stress and layer formation on austenitic stainless steel F138 surface, after different treatment conditions. Plasma nitriding treatment after shot peening differences were analyzed. Residual stress was investigated by X-ray diffraction, using sin²ψ method. Samples of surface morphology and formed layer were analyzed by scanning electron microscopy (SEM) and X-ray diffraction. Previous shot peening treatment to plasma nitriding promotes the formation of a less homogeneous layer, with microcracks and induced residual stress increase. It was observed the formation of iron nitrides and expanded austenite after plasma nitriding treatment. Surface residual stress induction after shot peening and plasma nitriding treatments can be efficient methods to improve material mechanical properties.

Abstract: Pseudoboehmite is a synthetic ceramic material obtained by the sol-gel process consisting of a network of inorganic oxides with high porosity and purity that can be used for drug delivery systems. This work studied the interaction between Metformin (Metformin Hydrochloride) and pseudoboehmite, which were treated with this ceramic material in the controlled drug release. The in vitro metformin release test was evaluated using UV-Vis spectrophotometry. X-ray diffraction data show that only the pseudoboehmite phase is present in the sample.

Abstract: The color of water atomized steel shots changes upon processing and heat treatments due to the compound formation on the steel shot surface. In this study, color change is studied at each step of the water atomized steel shots and for size variation using various microscopic techniques such as OM, SEM, TEM and spectroscopic techniques such as AES and XPS. The results show that the color of the shot balls changes due to the formation of FeOOH, Fe_xO_y, etc. depending on the heat treatment and natural oxidation upon exposure to the environment, whose thicknesses also depend on the severity of processing and heat treatment for the compound formation.

Abstract: Titanium and its alloys could have good biocompatibility, suitable levels of strength, fracture toughness, fatigue resistance and low elastic modulus, which are requirements for metallic materials used as biomaterials. Implants of commercially available Ti alloys show excessive levels of stiffness that cause stress shielding and often lead to bone resorption and failure. For better biomechanical performance, it is necessary to redesign biomaterials with lower elastic modulus. Alloying Ti with β-stabilizing elements (Ta, Mo, Nb) allows obtaining alloys with Young´s modulus closer to that of bone (10-30 GPa), minimizing the tendency for stress shielding and bone resorption. A combinatorial method, based on variable composition laser deposition, has been used for synthesizing alloys with a gradient of composition along a single clad track and scanning for the most interesting compositions. This study reports results on laser synthesis of alloys in the Ti-5Mo-xNb system, in search for compositions with microstructure and properties optimized for use as biomaterials. The alloys were then characterized in composition and microstructure by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The mechanical properties were assessed using depth-sensing ultramicroindentation tests. Their microstructures consist of the orthorhombic α’ phase with martensitic morphology, and untransformed β. The alloys indentation hardness increased with the Nb content from 2.79 ± 0.02 GPa to 3.7 ± 0.8 GPa, due to solid solution strengthening. The same trend was observed in the elastic moduli that increased from 38.8 ± 8.1 GPa to 76 ± 13 GPa, and in addition the H/E ratio was greater than 0.04 for all samples which indicates good wear resistance. Despite being dual phase (α’+β) all compositions present elastic modulus that are considerably lower than those of commercial Ti alloys currently used (above 100 GPa).

Abstract: Natural silicate melts (i.e., magmatic liquids) contain 5 to 10 major oxide components. Hence, diffusion in natural melts is always multi-component diffusion with manifestations such as uphill diffusion. However, complexities in rigorous treatment of multicomponent diffusion made geochemists shy away from treating such diffusion in the past. My group has been working on multicomponent diffusion in seven-and eight-component silicate melts for about 10 years. We started with multicomponent diffusion in a seven-component system (SiO₂-TiO₂-Al₂O₃-MgO-CaO-Na₂O-K₂O) and obtained the 66 diffusion matrix [1]. Then we focused on a synthetic mid-ocean ridge basalt with eight components (SiO₂-TiO₂-Al₂O₃-FeO-MgO-CaO-Na₂O-K₂O) [2,3] because basalt is the most abundant volcanic melt in the Earth. From experimental data, we obtained 77 diffusion matrix at three temperatures, and found that the eigenvector matrix is roughly invariant with temperature and each of the seven eigenvalues depends on temperature following the Arrhenius relation. This provides a formulation to calculate the diffusion matrix at any temperature within the experimental temperature range. Furthermore, we hypothesize that the diffusion eigenvectors are independent of melt compositions [4,5]. Therefore, we can examine diffusion in silicate melts in eigen-component space, and each eigenvalue is the diffusion coefficient for its corresponding eigen-component. Our preliminary examination of literature data shows that most data are consistent with the hypothesis. We are beginning to develop an online tool to model multicomponent diffusion in natural silicate melt using the eigen-component approach [5]. Here, I report these developments for the broader diffusion community and present future perspectives.

Abstract: Super304H is austenitic steel used predominantly for boiler and turbine components in thermal power plants due to the high strength, excellent creep and oxidation resistance in high-temperature steam environments. Microstructural degradation is inevitable upon long-term high-temperature exposure. Therefore, understanding the processes of degradation is critical for the determination of residual lifetime of the parts. In this study, the hardness, tensile strength and creep strength of a Super304H steel that was in service as a reheater for ~8 years at about 600°C was investigated with corresponding microstructural analysis. Grain growth is evident, but microhardness and tensile strength did not decrease, due to the precipitation of nanosized NbX and Cu-rich particles in grain interior. However, the creep rupture life of the aged S304H steel is ~90% lower at 650°C than that of the virgin S304H, due to the coarsening of σ phase and formation of M₂₃C₆ on the grain boundary. Our measurements and analysis of the specimens in this study indicates the remaining service life longer than those in the NIMS database.