Diffusion Annealing Research Articles

Oxygen-18 tracer diffusion in a crystallised lithium-aluminosilicate glass

In this work we present first 18O tracer diffusion data in a crystallized LAS4 glass. The glass of LAS4 composition (close to Li2O⋅Al2O3⋅4SiO2) is free of nucleating agents and has a very low tendency to nucleate crystals in the volume. A thin ZrTiO4 layer (∼70 nm thick) was deposited by argon ion beam sputtering and served to preferentially nucleate high-quartz solid solution crystallites from the surface. All samples crystallised at the very early stage of the respective diffusion annealing time, i.e. virtually before the onset of the 18O tracer diffusion. The microstructure of the crystallised LAS glass is composed of crystalline domains (high-quartz solid solutions and keatite solid solutions) and a glassy phase of low viscosity in the domain boundaries. The oxygen transport occurs predominantly in the glassy phase of the domain boundaries and is faster than the transport of network forming cations or larger configurations in the glassy phase.

Solute Profile during Diffusion Annealing of Thinly Coated Semi-Infinite Metallic Substrate

Solute Profile during Diffusion Annealing of Thinly Coated Semi-Infinite Metallic Substrate

High-performance gradient Fe-Si alloy thin sheets fabricated by solid powder siliconizing and diffusion annealing

High-performance gradient Fe-Si alloy thin sheets fabricated by solid powder siliconizing and diffusion annealing

Synthesis and properties of La-Fe-Si/La-Co magnetocaloric composites

LaFe11.8Si1.2/16wt%La65Co35 samples were prepared by spark plasma sintering (SPS) and subsequent annealing. The La65Co35 binder increased the desired 1:13 phase content in these samples during annealing at 1323 K. Interestingly, the α-Fe phase formed between the LaFe11.8Si1.2 particles and the La65Co35 binder and then disappeared as the annealing time extended. The sample annealed for 0.5 h had a distinct core-shell structure with Co in the shell, a desirable table-like (−∆SM)−T curve was obtained and its RC (153 J·kg−1) was 107% higher compared to the sample before annealing. The diffusion of Co from La3Co to the 1:13 phase was hampered by the growth of La5Si3 phase. Relatively large (−∆SM)max of 8.51 J·kg−1·K−1 (Δμ0H=2 T) and (σbc)max of 374 MPa for the sample annealed for 24 h were obtained. These results indicated that the method combining SPS and diffusion annealing is promising to prepare La-Fe-Si based magnetocaloric composites with good properties.

Improvement in deformation degree of Zr surface-layered Bi-2223 ceramics by diffusion annealing temperature

This study investigated the effects of different annealing temperatures (650 °C ≤ T ≤ 840 °C) on the surface morphological and mechanical performance properties of Zr surface-layered Bi-2223 materials with scanning electron microscopy (SEM) images, Vickers microhardness (Hv) measurements, and semi-empirical mechanical approaches. It was observed that the ceramic compound exposed to 650 °C annealing temperature exhibited the superior performance features due to the enhancement in the deformation degree. This is because the Zr ions behaved as the nucleation centers to prevent the propagations of cracks and dislocations throughout the main matrix depending on the decrease in the degree of granularity and distributions of crystal structure problems over a wider area. Similarly, the SEM pictures indicated that the diffusion mechanism increased the random distributions of the thinner plate-like granular structures (serving as nucleation centers), leading the decrease in the coupling problems between the grains. Among the materials, the highest surface densification was observed for the compound exposed to 650 °C. Namely, surface morphological analysis showed a strong correlation between microstructure and mechanical performances. Further, the zirconium ions were found to decrease in the non-recoverable stress concentration sites, crack-initiating defects, and dislocations in the ceramic system. Accordingly, the sensitivity to the applied test load was noted to decrease dramatically. Shortly, crack growth size and velocity were observed to be more easily under control. Correspondingly, the Zr ions delayed considerably the beginning points of saturation limit (load-independent) regions for the bulk Bi-2223 superconducting materials. Additionally, the Zr ions led to the change in the mechanical characteristic behavior from typical indentation size effect to reverse indentation size effect. Lastly, the microindentation hardness measurements were semi-empirically analyzed by the different models. According to the comparison, Hays-Kendall mechanical model was noted to provide the closest parameters to the load-independent microhardness results.

Effect of diffusion annealing on wear and cohesion behaviours of boronized AISI 1040 steel

AISI 1040 grade steel is a commonly used steel in industry. In this study, pack boriding of AISI 1040 steel was carried out in Ekabor-II powder at different temperatures (900 °C and 950 °C) for 4 h holding time, which was followed by Diffusion annealing process (DAP) for 4 h at different temperatures (950 °C and 1000 °C). The morphology of the boride layers generated on the steel surfaces was investigated using optical and SEM microscopes following boriding experiments. The micro-hardness tester was used to assess the hardness values, and the XRD method was used to determine the phases generated on the layer. In XRD analysis, a boride layer consisting of the Fe2B phase was shown to form as a single-phase structure following the DAP at 1000 ℃ for 4 h. While the original hardness of AISI 1040 steel was 233 HV0.05, the hardness increased up to 1950 HV0.05 using the Boriding process and DAP. Wear tests were carried out using the ball-on-disc method at a sliding speed of 0.3 m/s, under a load of 10 N, at a sliding distance of 500 m in a dry environment. The Daimler-Benz Rockwell-C indentation test was used to study the adhesion capabilities of the boride layer. Wear resistance increased with boriding process and diffusion annealing temperatures. It was discovered that high Diffusion annealing temperatures resulted in the best adhesion and wear resistance.

Interdiffusion in Refractory Metal System with a BCC Lattice: Ti/TiZrHfNbTaMo

Interdiffusion of the elements in a diffusion pair consisting of Ti and an equiatomic high-entropy alloy (HEA) TiZrHfNbTaMo in the temperature range of 1473-1673 K has been studied. A calculated results phase diagram of the alloy by Thermo-Calc 2021-B software as used to determine the temperature stability range of the β-phase in the alloy. Ti-HEA diffusion pairs were obtained by low = temperature welding and then diffusion annealing was carried out at temperatures of 1473, 1573, and 1673 K during 12, 9, and 6 h, respectively. The interdiffusion zone was profiled using electron probe microanalysis (EPMA). The diffusion parameters of the HEA's elements were obtained using Hall's method. An experimental results discussion is given.

Effect of the diffusion annealing process and cooling rate on the microstructure of Zr/Ti layered materials

Effect of the diffusion annealing process and cooling rate on the microstructure of Zr/Ti layered materials

Interdiffusion in refractory metal systems with a BCC lattice: titanium–tantalum and titanium–multicomponent (high-entropy) alloy

In this work, the interdiffusion features in multicomponent (high-entropy) alloys of refractory metals were studied. The following pairs were chosen as the diffusion study objects: titanium–equiatomic alloy (Hf–Nb–Ta–Ti–Zr–Mo) and titanium–tantalum for the sake of comparison. The article covers the issues of sample preparation, microstructure study, sample preparation methodology for diffusion research, and experimental results. Diffusion annealing was carried out for 12 h in a vacuum at a residual argon pressure of 6.65·10–3 Pa and a temperature of 1200 °С. Particular attention was paid to the method of combining diffusion pairs (titanium with tantalum, titanium with alloy) by thermal cycling near the polymorphic transformation temperature in titanium (882 °C) within ± 50 °C. The behaviour of the most characteristic elements (Ta, Zr, Ti) in the weld area after the titanium and alloy diffusion pair joining was demonstrated. This is the first time that data on the dependence of the intensity of the corresponding spectral line for titanium and elements of a multicomponent alloy on the penetration depth were obtained. A change in the signal intensity for system elements was observed at a depth of 150–200 μm, whereas a sharp drop in the signal intensity was seen to occur at depths of about 50 μm. The effective value of the coefficient of diffusion of elements into titanium averaged over all elements of the alloying system (except for titanium) at a temperature of 1200 °C was calculated. The obtained value was compared to reference data: the self-diffusion coefficient in β-titanium and diffusion coefficients in titanium pairs with alloy doping elements.

Влияние термической обработки и содержания вольфрама на структуру, фазовый состав и коррозионную стойкость высокоэнтропийных сплавов системы Fe – Cr – Ni – Mo – W

The effect of heat treatment (diffusion annealing, quenching, low-temperature and high-temperature tempering) on the structure, phase composition and corrosion resistance of high-entropy 35 Fe – 30 Cr – 20 Ni – 10 Mo – 5 W and 30 Fe – 30 Cr – 20 Ni – 10 Mo – 10 W alloys has been studied. High-entropy alloys of the Fe – Cr – Ni – Mo – W system with different concentrations of tungsten were obtained by sintering mechanically alloyed powders in a vacuum furnace. It was revealed that the total and pitting resistance of the obtained high-entropy alloys to aqueous solutions of NaCl is higher than that of industrially produced austenitic corrosion-resistant steel 316 L used in the oil and gas industry.

Primary Carbide Formation in Tool Steels: Potential of Selected Laboratory Methods and Potential of Partial Premelting for the Generation of Thermodynamic Data

To predict the solidification and product properties of tool steels with complex chemical compositions, an understanding of the transformation behavior is crucial. Therefore, the quaternary Fe–C system with 10 wt% Cr and 3 wt% W (a subsystem of cold work steels, with M7C3 and M23C6 carbides) and the Fe–C system with 6 wt% W and 5 wt% Mo (simplified high‐speed steel, with M6C and MC carbides) are selected. The motivation for this study is to develop a methodology for the safe and fast production of model alloys and the close to equilibrium performance of differential scanning calorimetry (DSC) measurements. Regular diffusion annealing of as‐cast carbidic steels is time‐consuming, but with an additional heat treatment during the DSC measurement in the semisolid zone (30–50% liquid phase fraction), a status close to equilibrium can be achieved within minutes due to the high diffusion. To prove the potential of the equilibration by partial premelting in the DSC, additional equilibration and quenching experiments are performed in a Tammann furnace and investigated using a scanning electron microscope and X‐ray diffraction analysis. By combining these methods, carbide types and the transformation temperatures can be verified to evaluate and construct complete phase diagrams.

“Non-equilibrium” grain boundaries in additively manufactured CoCrFeMnNi high-entropy alloy: Enhanced diffusion and strong segregation

Grain boundary diffusion in an additively manufactured equiatomic CoCrFeMnNi high-entropy alloy is systematically investigated at 500 K under the so-called C-type kinetic conditions when bulk diffusion is completely frozen. In the as-manufactured state, general (random) grain boundaries are found to be characterized by orders-of-magnitude enhanced diffusivities and a non-equilibrium segregation of (dominantly) Mn atoms. These features are explained in terms of a non-equilibrium state of grain boundaries after rapid solidification. The grain boundary diffusion rates are found to be almost independent on the scanning/building strategy used for the specimen’s manufacturing, despite pronounced microstructure differences. Grain boundary migration during diffusion annealing turned out to preserve the non-equilibrium state of the interfaces due to continuous consumption of the processing-induced defects by moving boundaries. Whereas the kinetic “non-equilibrium” state of the interfaces relaxes after annealing at 773 K, the non-equilibrium segregation is retained, being further accompanied by a nano-scale phase decomposition at the grain boundaries. The generality of the findings for additively manufactured materials is discussed.

Superior properties of LaFe11.8Si1.2/La65Co35 magnetocaloric composites processed by spark plasma sintering

A series of LaFe11.8Si1.2/La65Co35 bulk composites were fabricated by spark plasma sintering (SPS) followed by diffusion annealing. The effect of sintering temperature (1073–1223 K) on the magnetocaloric and other properties of LaFe11.8Si1.2/La65Co35 bulk composites were investigated. The 1:13 phase content in all the annealed samples was ∼90 wt%. The mechanical and magnetocaloric properties of these annealed bulk composites could be improved by tuning the sintering temperature. The Curie temperature (TC) and maximum magnetic entropy change (−ΔSM)max of the annealed samples varied in the range of 211–228 K and 5.56–9.33 J kg−1 K−1, respectively. Selected samples exhibited excellent mechanical and magnetocaloric properties. The (−ΔSM)max value was 9.33 J kg−1 K−1 at TC of 217.8 K. Its maximum compressive strength (σbc)max value was 540 MPa at a strain of 3.48%, which exceeded the mechanical properties of most La–Fe–Si based bulk composites prepared by hot-pressing sintering (HPS). Thus, La–Fe–Si based bulk composites with good comprehensive properties could be obtained by combining SPS and diffusion annealing.

Hydrogen Diffusion in Clinopyroxene at Low Temperatures (195°C–400°C) and Consequences for Subsurface Processes

AbstractStudying diffusion of hydrogen in nominally anhydrous minerals, like clinopyroxene, at low temperatures is a challenging task due to experimental and analytical difficulties. In this study, to overcome these problems we have produced H concentration gradients in single crystals of natural diopsidic clinopyroxene by ion implantation and measured the nanoscale profiles before and after diffusion anneals using Nuclear Resonance Reaction Analysis. These steps allowed us to conduct experiments at temperatures between 195°C and 400°C. Obtained diffusion rates show a consistent Arrhenius relation DH= 5.47(±13.98) · 10−8 · exp (−115.64(±11.5) kJ mol−1/RT) m2s−1. Notably, our results lie well within the range of extrapolations from high temperature experiments (≥600°C) of previous studies. This implies that fast diffusion of hydrogen (compared to other elements) extends to low temperatures. We used these results in a non‐isothermal diffusion model that simulates the ascent of crystals (0.5, 1.0, and 2.0 mm) along two representative P‐T‐paths from 600°C to 100°C, to assess potential re‐equilibration of H contents in clinopyroxene at low temperatures. Our model highlights the need to carefully consider boundary conditions, which are a function of P‐T‐fO2, that control the concentration gradient at the crystal's rim. The results from this model help to assess, as a function of crystal size and cooling rate, when re‐equilibration must be considered.

Variation of fundamental features of cobalt surface-layered Bi-2212 superconductor materials with diffusion annealing temperature

The present study appears extensively on the role of diffusion annealing temperature intervals 650–850 °C on electrical conductivity, flux pinning ability, superconducting and crystallinity quality of Cobalt (Co) surface-layered Bi-2212 compounds with experimental tests including dc resistivity, bulk density, X-ray diffraction, critical current density measurements, and theoretical calculations. Experimental findings display that the Co ions may be replaced mostly by bismuth sites in the crystal lattice as a consequence of appropriate cation-vacancy, electron configurations of the outer shell, chemical valence states, and electronegativity of chemical contents in the main composition. The fundamental characteristic features refine considerably with 650 °C annealing temperature due to enhancement of antiferromagnetic spin fluctuations in the clusters of microdomains, re-ordering of Cu–O bonds, stabilization of system, pairing mechanism, modulation of insulating Bi–O double layers, and orbital hybridization mechanisms. Accordingly, bulk Bi-2212 ceramic obtained at optimum annealing temperature exhibits the best conductivity because of a decrease in systematic crystallinity problems and potential grain boundary interaction problems expected in the system. Likewise, the optimum annealing temperature triggers the artificial nucleation regions for 2D discrete pancakelike Abrikosov vortices to decelerate thermal fluxon movements. Moreover, the X-ray diffraction results indicate that optimum Co ions in crystal lattice significantly improve crystal structure quality, grain alignment distributions in c-axis orientation, the extension of high-Tc Bi-2223 superconducting phase, and average crystallite size parameters. Additionally, the nucleation activation energy is noticed to reduce with optimum Co ions due to enhancement in the nucleation stability and crystallization temperature values to higher temperature zones. Namely, optimum Co ions easily diffusing into the lattice points support the formation of surface nucleation. In contrast, after a critical value of 650 °C, the characteristic properties mentioned suppress remarkably. In conclusion, the main characteristic features are extensively improved by the optimum diffusion annealing temperature for usage in novel and feasible market areas.

Chemical composition of brass coating for steel cord

The objective of the research was to identify transitional diffusion layers in the steel wire – brass coating system. Brass wire is used in the production of steel cord. Such wire made from steel 80 by dry drawing, two-stage deposition of brass coating (Cu + Zn) and subsequent diffusion annealing was used for this research. The chemical composition was studied using a TESCAN Vega3 SBH scanning electron microscope with an Oxford Instruments attachment for X-ray microanalysis (MRSA). To obtain maps of the elements distribution, the overlay of the received frames was used. The authors studied chemical composition of the brass coating of steel wire for steel cord by spectra; the copper concentration gradient was determined; iron content in the coating and copper content in the steel core were revealed. The presence of a transitional diffusion layer from a brass coating to a steel core on a wire for wet drawing with a diameter of 1.67 mm and 1.85 mm was determined in two parts with different thicknesses of a brass coating in opposite sections (maximum and minimum). A map of the elemental distribution of Fe, Cu and Zn is shown, as well as a general map of overlay of Fe, Cu and Zn content; graphs of the elements’ content for two studied cross-sections are presented. It was established that the transition diffusion layer has gradient transition in concentrations of Fe, Cu and Zn, which characterizes good connection of the brass coating with steel. Diffusion layer of a brass coating of a steel wire with a diameter of 0.30 mm, produced by wet drawing of a steel wire with a diameter of 1.67 mm, was studied. An image of the coating was obtained by overlaying frames. Thickness of the coating together with the diffusion layer was determined, the average value of which is 1.4 µm with an apparent coating thickness of 0.5 µm.

Refinement of some basic features of Zr surface-layered Bi-2223 superconductor with diffusion annealing temperature

Refinement of some basic features of Zr surface-layered Bi-2223 superconductor with diffusion annealing temperature

Industrial metallization of fired passivating contacts for n-type tunnel oxide passivated contact (n-TOPCon) solar cells

Poly-Si/SiO x passivating contacts enable the manufacturing of highly-efficient Si solar cells, but their fabrication commonly relies on an extra high-temperature process such as dopant diffusion or thermal annealing for achieving excellent passivation and contacting properties. This extra process is eliminated in the fired passivating contact (FPC) approach used for simplified fabrication of poly-Si/SiO x passivating contacts. Instead, FPCs rely on the thermal budget of the fast/short and high-temperature firing process used for metallization of solar cells to achieve similar final properties. Despite this, compatibility of FPCs with industrially viable metallization techniques has not been demonstrated yet, which is studied in this work for fire-through Ag screen-printing and Ni/Ag plating. With screen-printing, low recombination current density ( J 0 ) down to 4.9 fA/cm 2 , low contact resistivity between the Ag contacts and the FPC ( ρ c,m ) down to 7.2 mΩ⋅cm 2 , and Ohmic transport through the FPC including the SiO x film were achieved using wet-chemically grown SiO x . Nevertheless, J 0 of metallized regions ( J 0,m ) exceeded 1000 fA/cm 2 . Reducing J 0,m was attempted by mitigating the blistering observed in FPCs, but J 0,m remained high. With Ni/Ag plating, excellent surface passivation with J 0 down to 2.7 fA/cm 2 and very low J 0,m < 50 fA/cm 2 were achieved, but no Ohmic contacts could be obtained. Integration of screen-printed FPCs in large-area n-TOPCon solar cells was also demonstrated, yielding average efficiencies of 18.4%, limited mainly by the high J 0,m and series resistance of the FPCs. The results presented reveal the challenges for the industrialization of FPCs and provide valuable insights for tackling these. • Fired passivating contacts (FPCs) developed relying only on the thermal budget of firing and not on conventional annealing. • Compatibility of FPCs with fire-through Ag screen-printing and Ni/Ag plating tested. • Screen-printing: J 0,pass ≈ 5 fA/cm 2 & ρ c < 10 mΩ∙cm 2 achieved, but J 0,metal was high. • Plating: J 0,pass < 3 fA/cm 2 & J 0,metal < 50 fA/cm 2 achieved, but contacts were non-Ohmic. • Integration of FPCs in screen-printed large-area n-TOPCon cells led to 18.4% efficiency.

Degradation of the electrical conductivity of the charged domain wall in reduced lithium niobate

In the present work, we investigated the effect of prolonged exposure on the electrical conductivity of crystals with a charged domain wall (CDW) in congruent lithium niobate crystals (LiNbO3, LN) of a nonpolar x-cut. Bidomain ferroelectric structures containing charged head-to-head domain boundaries were formed in the samples using methods of diffusion annealing in the air near the Curie temperature and infrared annealing in an oxygen-free environment. Reduction annealing of crystals in a nitrogen atmosphere was carried out to form color centers and concomitant increase in conductivity. Using an atomic force microscope (AFM) we observed the effect of degradation of the current value recorded when measuring the I-V curve. The influence of storage conditions on the electrical conductivity of CDW was studied. It was found that this effect was not related to the influence of the surrounding atmosphere on the surface but was presumably related to the redistribution of charge carriers shielding the bound charge of the CDW.

Degradation of the electrical conductivity of charged domain walls in reduced lithium niobate crystals

In this work, the effect of long-term room temperature exposure on the electrical conductivity of the charged domain wall (CDWs) in nonpolar x-cut congruent lithium niobate (LiNbO3, LN) crystals has been studied. Bidomain ferroelectric structures containing head-to-head charged domain boundaries have been produced by diffusion annealing in air near the Curie temperature and by infrared annealing. The crystals have been reduction annealed in a nitrogen atmosphere for the formation of color centers and growth of the electrical conductivity. The current measured during the recording of the I-V curves of the specimens using scanning probe microscope after room temperature exposure for 91 days has been found to decrease. The effect of storage conditions on the electrical conductivity of the CDWs has been studied. Degradation of the electrical conductivity does not originate from the effect of environment on the crystal surface. It has been hypothesized that the degradation is caused by distribution of charge carriers shielding the bound charge of the CDWs.