Diffusion Foundations Vol. 27

Abstract: Herein, solid-state diffusion-coupled joints (DCJs) were prepared in vacuum between stainless steel (SS) and Ti6Al4V by means of a pure niobium (Nb) interlayer (~200-μm thickness) using uni-axial compressive pressure of 4 MPa at 875 °C for 15 to 120 min. Interfacial characterization revealed the existence of successive layer wise Fe–Nb-based intermetallics like FeNb+(Nb) and Fe₂Nb at Nb|SS interfaces of DCJs processed from 60 to 120 min, but the DCJs processed for shorter duration (from 15 to 30 min) do not reveal any intermetallics; however, the DCJs processed for 45 min revealed a single reaction layer of FeNb whereas that of Ti6Al4V|Nb interfaces revealed solid solution behaviour for all bonding time intervals. Required chemical analysis (in at. pct) of the reaction products was found out using spectroscope and X-ray diffractometer. Mechanical characterization (at 32 °C) of the DCJs was carried out with a microhardness tester and tensile testing facility. Ti6Al4V|Nb interface experienced a hardness of ~298 HV (for all bonding time), whereas Nb|SS interface experienced ~200 HV for 15 and 30 min and ~650 HV for 45 min and longer. DCJs treated for 60 min have better strength properties. Manifestation of reaction layers: FeNb, FeNb+(Nb), and Fe₂Nb have significant effect on the strength. From the interfacial microhardness, path and surface of fracture surfaces characterizations, it was revealed that failure of the DCJs was transmitted seemingly along Nb|SS interfaces. The analytical finding of intrinsic diffusivity of Ti atoms in Nb along Ti6Al4V|Nb interface is higher by one order of magnitude than the diffusivity results of Fe atoms in Nb along the Nb|SS interface. Experimental evidences show that the growth of the reaction products along Ti6Al4V|Nb interface (adj. R-Square=0.982) and Nb|SS interface (adj. R-Square=0.999) follows a parabolic law. Recently, researchers considered diffusion coupling as the key technology to fabricate Ti|Al|Al-C_f biomimetic structure, graphite|Nb|Cu for fusion reactor devices, Ni|Ni₃Al for MEMS applications, hybrid heat exchangers for nuclear applications, etc.

Abstract: The positive effect of Sc,Zr-addition on mechanical properties in Al-based alloys preferred for automotive manufacture to produce lightweight vehicles is generally known. Microstructure, mechanical, electrical and thermal properties of the conventionally cast and homogenized (475 °C/60 min) Al-5.4wt.%Zn-3.1wt.%Mg-1.5wt.%Cu (7075) and Al-5.2wt.%Zn-3.0wt.%Mg-1.4wt.%Cu-0.2wt.%Sc-0.1wt.%Zr (7075-ScZr) alloys during isochronal annealing were characterized. Precipitation reactions were studied by microhardness, electrical resistivity and conductivity measurements, differential scanning calorimetry and positron annihilation spectroscopy. Microstructure observation by scanning and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries in the alloys. The melting of this eutectic phase was observed at ~ 481 °C for the both alloys. The distinct changes in microhardness and electrical resistivity isochronal curves as well as in heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and by formation of the metastable phase particles of the Al–Zn–Mg–Cu system. Clusters/GP zones were formed during the cooling and/or in the course of the storage at room temperature. These clusters/GP zones were formed predominantly by Mg and Zn alloying elements. Hardening effect after isochronal annealing at temperatures above ~ 300 °C reflects the Sc,Zr-addition in both states of the 7075-ScZr alloy. Probably precipitation of the T-phase (Al₂Zn₃Mg₃) and S-phase (Al₂CuMg) particles took place during the annealing. The Sc,Zr-addition does not significantly influence precipitation of the particles formed in the Al–Zn–Mg–Cu system.

Abstract: CoSb based compounds have gained much importance in the fields of thermoelectric devices. In this work, we have conducted the solid–state conventional bulk diffusion couple experiments. To study the phase evolutions, Co/Sb diffusion couples are annealed at 450–550 °C. The interdiffusion zone is analysed using field emission gun equipped scanning electron microscope and the composition measurements are done in electron probe micro−analyser to confirm the growth of various product phases. The marker experiment indicates that the CoSb₃ phase grows mainly by diffusion of Sb in the binary Co–Sb system. Growth of the CoSb₃ phase is discussed based on assessment correlating the difference in mobilities of species with the high homologous temperature, crystal structure of the phase, and the concept of sublattice diffusion mechanism in line compounds.

Abstract: In previous work, perturbed angular correlation spectroscopy (PAC) was used to determine jump rates of ¹¹¹Cd, the daughter of the ¹¹¹In radiotracer, in the series of phases RIn₃ (R = rare-earth element) through nuclear quadrupole relaxation. Greater relaxation, indicating faster Cd jump rates, was observed in heavy rare-earths for compositions more deficient in indium, as would be expected for diffusion mediated by vacancies on the In sublattice. On the other hand, greater relaxation was observed for light rare-earths (R = La, Ce, and Pr) for compositions with excess indium, suggesting Cd diffusion is mediated there by a different mechanism. In this work, computer simulations were carried out to better understand the nature of the relaxation observed for the light rare-earths and the origin of the change in behavior across the rare-earth series. As a first step, formation enthalpies of intrinsic defects were calculated using density functional theory (DFT) for series end-members LaIn₃ and LuIn₃. Both compounds were found to exhibit Schottky thermal disorder. Additional DFT simulations show that the binding enthalpy between In-and R-vacancies is larger in LaIn₃ than in LuIn₃, suggesting that diffusion in LaIn₃ might be mediated by divacancies. Site enthalpies of Cd also were calculated, and it was found more favorable energetically for Cd to occupy the In sublattice than the R sublattice in both end-member phases.

Abstract: Magnesium (Mg) alloys constitute an attractive structural material for transportation industries, due to their low density and high strength/weight ratio. However, high susceptibility to corrosion of Mg alloys limits their use. Therefore, there is a growing interest for development of new Mg alloys with good mechanical properties and superior corrosion resistance. Production of wrought Mg alloys results in enhancement of mechanical properties, whereas addition of alloying elements may result in improved corrosion behavior. In this study we distinguish the role of aluminum, zinc, tin and calcium additions on the corrosion performance of new wrought Mg alloys. Overall, addition of alloying elements resulted in precipitation of second phase particles with cathodic behavior (relatively to Mg matrix). This enhanced the micro-galvanic effects and the corrosion resistance in short periods of immersion was deteriorated. However, in longer periods of immersion the passive characteristics of the oxide layer played a significant role in improving the alloys' corrosion resistance. The contribution of each element to the oxide layer will be discussed in detail. In general, the quantities of alloying element should be sufficient to stabilize the corrosion products layer; yet as low as possible, in order to reduce the micro-galvanic effects.

Abstract: Polymeric plastic boxes (named Front Opening Unified Pods (FOUP)) were widely used in semiconductor manufacture to maintain the cleanliness of processed wafer substrates in a controlled mini-environment. Polymeric materials, however, are able to sorb airborne molecular contaminants (AMCs) and subsequently to outgas the sorbed AMCs backward to FOUP’s atmosphere, causing the transfer of AMCs to sensitive stored substrates, named cross-contamination. As a type of AMCs, the NH₃ cross-contamination could cause a severe yield loss to integrated circuits (crystals (haze), resist-development defects (T-topping) or metallic corrosion). Experiments were carried out to establish the NH₃ sorption and desorption kinetics in polyetherimide (PEI), Entegris Barrier Material (EBM)), and EBM/carbon nanotubes (EBMCNT) at NH₃ concentration of 800-ppbv, 21°C, and relative humidity of 40%. The transport coefficients i.e. solubility and diffusivity (D_NH3 and S_NH3) were then determined. The study on NH₃ provides an additional guideline to choose the best raw materials for FOUP formulation in taking into account the potential cross-contamination of AMCs. Numerical simulation model based on obtained solubility and diffusivity values was conducted to demonstrate NH₃ concentration profiles in FOUP walls during contamination and FOUP decontamination, which are inaccessible by conventional experiments.

Abstract: This work aims to numerically simulating the resin injection manufacturing process of a polymer composite,reinforced with ribbons of NiTishape memory alloy, using the software Ansys CFX^®. The multiphase flow mathematical modeling was used to describe the transient and isothermal resin-air flow during the process. Results of the pressure fields, velocity andvolume fractionsof the involved phases are presented. The fluid flow inside the mold was compared withthe flow between parallel flat plates and showed to be consistent. Process parameters, such as resin volumetric flow rate, resin inlet and air outlet positions have a large influence in the mold filling time, volume and position of voids fractions inside de mold and final product quality.

Abstract: The influence of LiSbO₃ on the structure, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K_0.5Na_0.5)NbO₃ ceramics has been studied. Changes in unit cell parameters correlated with ionic radii changes and high effective local d₃₃ piezoelectric coefficient values were observed depending on solid solutions compositions.

Abstract: The main purpose of this work is to evaluate the influence of the thickness and thermophysical properties of insulating materials on the maximum external surface temperature and energy gain provided for an intermittent ceramic kiln operating with natural gas as fuel. To evaluate the influence of independent variables on response variables, a factorial experimental design was developed. From the analysis of variance (ANOVA), it was possible to determine significant and well-adjusted mathematical models for both response variables. It was verified that the thickness and thermal conductivity of thermal insulation are the independent variables that have the greatest influence on the process efficiency.