Formation Of Diffusion Zone Research Articles

Features of formation of diffusion zone obtained on steel 20 by boriding in induction furnace

The article presents data on studies of iron borides synthesis during induction heating to 1000 °C for 5 min of steel 20 samples with a coating from a charge containing Fe – H3BO3. Content of boric acid in the charge varied from 25 to 75 % wt. Charge in the experiments could be diluted with a solution of liquid glass in water with addition of small amount of ammonium hydroxide and coal. Study of the surface layer microhardness showed that during saturation of the surface layer of carbon steel 20 with boron, a macroscopically extensive diffusion zone 900 – 1000 μm in size is formed, in which the boride content gradually decreases when moving deeper into the matrix. Such a size of the diffusion zone indicates an anomalously high mass transfer during boriding of steel 20. Indeed, the calculated diffusion coefficient during boriding under induction conditions (about 1.35·10–9 m2/s) is two orders of magnitude higher than the diffusion coefficient in the classical boriding. X-ray studies showed that, under the considered conditions, Fe2B and FeB borides are synthesized, and a solid solution of boron in α­iron is also formed. An analysis of phase composition of the diffusion zone structural components indicates that, from the surface to the matrix, formation of boride phases occurs in the following sequence: FeB → Fe2B → (α­phase + B) → base metal. Microstructure of the diffusion zone consists of more or less pronounced layers consisting of FeB and Fe2B boride phases. On the whole, especially deep-ying regions of the diffusion zone are a composite material consisting of plastic α-phase and iron boride crystals. Crystals in FeB and Fe2B in the layer are oriented mainly perpendicular to the diffusion front. Perhaps, this is due to the rapid predominant growth of the boride phase under conditions of high diffusion mobility of boron atoms in one direction and hindered in others.

Investigation of the Diffusion Zone Formation Mechanisms during the Production of Functional Steel-Aluminium Compositions by Arc Processes

Interaction at the interface during the production of functional steel-aluminum compositions by arc processes has been investigated. Regularities and mechanisms of the diffusion zone formation have been proposed upon contact of a melt based on aluminum, alloyed with 11-13 wt% Si, with the steel substrate or Al-Fe system intermetallic compounds. It was found that the presence of Si in the composition of filler material leads to diffusion mobility of Al and Fe decreasing due to the replacement of Al, as well as the occupation of structural vacancies in double FexAly intermetallics and ternary intermetallic phases with different stoichiometric composition FexAlySiz formation. It was determined that during the arc cladding process using as substrate the steel with intermediate zinc coating, a diffusion zone with an average thickness of 7 μm is formed, while in the presence of an intermediate coating from aluminum deposited by the “cold metal transfer” process, its average thickness is 18 μm.

Microstructure and Mechanical Properties of Diffusion-Bonded CoCrNi-Based Medium-Entropy Alloy to DD5 Single-Crystal Superalloy Joint

This study focuses on the diffusion bonding of a CoCrNi-based medium-entropy alloy (MEA) to a DD5 single-crystal superalloy. The microstructure and mechanical properties of the joint diffusion-bonded at variable bonding temperatures were investigated. The formation of diffusion zone, mainly composed of the Ni3(Al, Ti)-type γ′ precipitates and Ni-rich MEA matrix, effectively guaranteed the reliable joining of MEA and DD5 substrates. As the bonding temperature increased, so did the width of the diffusion zone, and the interfacial microvoids significantly closed, representing the enhancement of interface bonding. Both tensile strength and elongation of the joint diffusion-bonded at 1110 °C were superior to those of the joints diffusion-bonded at low temperatures (1020, 1050, and 1080 °C), and the maximum tensile strength and elongation of 1045 MPa and 22.7% were obtained. However, elevated temperature produced an adverse effect that appeared as grain coarsening of the MEA substrate. The ductile fracture of the joint occurred in the MEA substrate (1110 °C), whereas the tensile strength was lower than that of the MEA before diffusion bonding (approximately 1.3 GPa).

Fatigue behavior and life predictions of thermally oxidized Ti6Al4V alloy according to oxidation parameters

Thermal oxidation is a surface treatment thought to improve the wear behavior of Ti alloys. However, oxidation can impact adversely the fatigue behavior of the alloys. Thermal oxidation of the Ti-6Al-4V alloy was performed under uncontrolled furnace atmosphere, at 600 °C, for 5 h and 10 h, and at 700 °C, for 15 h. Microstructure analysis was performed and no significant changes were observed in the microstructure of the oxidized alloys, except for the diffusion zone formation. XRD analysis denoted rutile peaks (TiO2) in the oxidized alloys. Roughness increased due to oxidation time and temperature, whereas layer thickness was influenced mainly by temperature. The influence of oxidation parameters on fatigue behavior was tested and fracture micromechanisms were analyzed. Fatigue endurance limit after oxidation at 600 °C, for 5 and 10 h; and at 700 °C, for 15 h decreased by 27%, 29% and 68%, respectively, in comparison to the untreated alloy. Premature cracks in the oxide layer encouraged fatigue nucleation, and the premature crack formation explains the diminished fatigue performance of the oxidized alloys. Fatigue endurance limit was assessed through the Murakami’s model, and a fatigue life model was established, which agree with the experimental results.

Structure and Mechanical Properties of a Layered Composite Based on Fe–Cr–V Alloy and High-Nitrogen High-Chromium Steel After Hot Pressing and Annealing

A hot pressing method was used to obtain a layered composite consisting of alternating layers of AISI 439 type steel with a high nitrogen content (0.8%) and Fe-20% Cr-5%V alloy with a low nitrogen content (less than 0.02%). Annealing of the composite at T = 700–850 °C after hot pressing leads to diffusion of nitrogen from the nitrided AISI 439 layers into the Fe–Cr–V layers, the formation of diffusion zones containing dispersed vanadium nitrides in the Fe–Cr–V layers and the formation of diffusion zones with a low nitrogen content in the AISI 439 layers. A tendency towards a decrease in the sizes of the vanadium nitride particles with decreasing annealing temperature was revealed. Annealing at T = 750 °C increases the plastic characteristics and reduces the strength characteristics of the composite compared to the state after hot pressing. The presence of dispersed vanadium nitrides precipitated in the composite structure during annealing increases the strength of the composite by 15%.

The Theory of Diffusion Zone Formation during Surface Modification of Materials with Allowance for the Thermodiffusion Effects

Using asymptotic methods in the theory of differential equations, an analytical approximate solution to the problem of diffusion of interstitial atoms in a restricted medium under the condition of a constant temperature gradient is obtained. As follows from the analysis, this solution is applicable to plate samples undergoing thermal and ionic modification of one of the surfaces, whose thickness does not exceed the diffusion penetration depth of impurities, provided that a stationary temperature distribution over the thickness is established. For the certification of the proposed method, a comparison of the approximate solution with the numerical solution of the thermal diffusion problem is carried out. Conditions are obtained under which the contribution of thermal diffusion effects to the total diffusion mass transfer of the impurity is significant.

Research of the intermetallics formation mechanism during the synthesis of functionally graded layered steel-aluminum compositions

The features of the formation and growth of intermetallic compounds in the production of functionally graded layered steel-aluminum compositions by the arc surfacing process have been revealed. The influence of the intermediate aluminum layer formed by the arc surfacing process on the diffusion zone formation mechanism has been shown.

The mechanisms of scale and subsurface diffusion zone formation of heat-resistant HP40NbTi alloy at long-term high-temperature exposure

Surface multilayer scale and the subsurface diffusion zone of heat-resistant HP40NbTi alloy were characterized by SEM and X-ray mapping after high-temperature exposure for different durations. After long-term exposure, conditional equilibrium is established in the alloy subsurface area: scale formation and internal oxidation deplete the diffusion zone of Cr and Si, which is compensated for by their diffusion along with Ni and Fe diffusion from the bulk of the metal to the surface. The process slows over time owing to the increase in the diffusion zone depth and the formation of a silicon oxide “barrier” layer.

Orbital Welding of Heterogeneous Joints

The paper summarizes the conclusions of the study prepared in cooperation with Janka engineering s.r.o. in production of pipe-tube joints. The parent materials (PM) were unalloyed steel P265GH and high-alloy steel X10CrNiTi 18-9. The GTAW method with filler material (FM) OK Autrod 309LSi was used. Welding parameters were optimized and their influence on the change of structure and mechanical properties of the weld joint was determined. The influence of diffusion transition zones with a marked increase of hardness was found. It was confirmed that when using low heat input, despite the formation of diffusion zones, the quality of welded joints is satisfactory.

Inhibiting effect of Ni-Re interlayer between Ni-Al coating and steel substrate on interdiffusion and carburization

A Ni-Re film was electroplated as a diffusion barrier between the Ni-Al coating and the iron alloy substrate. The interdiffusion between the coating and the substrate was investigated by micro-structure analysis, and the interdiffusion coefficient was calculated using Boltzmann-Matano method. The results indicated that the Ni-Re interlayer played a superior barrier effect, almost fully blocking interdiffusion and retarding the formation of diffusion zone (DZ). The Ni-Al coating without a diffusion barrier showed severe carburization corrosion in the diffusion zone during carburization process, while the Ni-Al coating with the Ni-Re diffusion barrier effectively protected the steel substrate from carbon attack.

Formation of diffusion zone in welded joints of porous aluminium alloy with monolithic magnesium alloy at chemical activation by gallium

Formation of diffusion zone in welded joints of porous aluminium alloy with monolithic magnesium alloy at chemical activation by gallium

Формирование диффузионной зоны сварных соединений пористого сплава алюминия с монолитным сплавом магния при химической активации галлием

Формирование диффузионной зоны сварных соединений пористого сплава алюминия с монолитным сплавом магния при химической активации галлием

Formation of diffusion zones around growing clusters during electrocrystallization of metals

The problem of the radius of depleted-by-diffusion zones around the growing individual clusters during the electrocrystallization in the mode of diffusion kinetics is solved. It is shown that a decrease in the probability of nucleation in every prescribed instant of time depends on the diffusion coefficient, overpotential, and individual characteristics of deposited metal: a specific surface energy and molar volume.

Effect of thermal tempering on microstructure and mechanical properties of Mg-AZ31/Al-6061 diffusion bonding

The objective of this study is to investigate the effect of the types thermal tempering of aluminum alloy on microstructure and mechanical properties of AZ31-O Mg and Al 6061-T6 diffusion bonding. Using Optical Microscope (OM) and Scanning Electron Microscopes (SEM) equipped with EDS analysis and line scan the interfaces of joints were evaluated. The XRD analysis was carried out to characterize phase constitution near the interface zone. The mechanical properties of joints were measured using Vickers micro-hardness and shear strength. According to the results in bonding of AZ31-Mg/Al-6061-O, in less plastic deformation in magnesium alloy, diffusion rate of most magnesium atoms occurred to aluminum alloy and formation of diffusion zone with minimum micro-hardness (140 HV) and maximum shear strength (32MPa) compared to Al 6061-T6/Mg-AZ31 bonding. Evaluation of fracture surfaces indicates an occurrence of failure from the brittle intermetallic phases.

Influence of boron contents on oxidation behavior and the diffusion mechanism of Fe–B based alloys at 1073 K in air

The microstructure and oxidation behavior of Fe–B alloys have been investigated. Oxide scale cross-sectional microstructures oxidized at 1073K for 100h have been studied. EPMA investigations show that B2O3–SiO2 oxides accumulates in the inner oxide layer which improves the oxidation behavior and oxide layer adhesion considerably. Cyclic oxidation kinetics data indicates that Fe–B 3.08wt.% alloy presents the best oxidation resistance. The formation of diffusion zone in the Fe–B alloys indicate that the oxidation of the Fe2B boride is controlled by boron diffusion. The diffusion zone increases with time and reaches a maximum width of 60–65μm.

Diffusion and Mechanical Stresses in a Material with Two-Component Coating at External Heating

Multilayer materials and materials with coatings are widely used in various applications. In studies of properties of new materials are run into poorly explored occurrences quite often. In such occurrences are among thermal diffusion (Soret effect) in solid materials. At this paper presented the model of formation of diffusion zone between two-component coating and base at the condition of heat flux action. Model completed of mechanical equilibrium problem. It was formulated the analytical solution of problem, which are applicable for concentration redistribution calculations and also for stresses and deformations in diffusion zone.

Contact melting and the structure of binary eutectic near the eutectic point

Computer simulations of contact melting and associated interfacial phenomena in binary eutectic systems were performed on the basis of the standard phase-field model with miscibility gap in solid state. It is shown that the model predicts the existence of equilibrium three-phase (solid–liquid–solid) states above the eutectic temperature, which suggest the explanation of the phenomenon of phase separation in liquid eutectic observed in experiments. The results of simulations provide the interpretation for the phenomena of contact melting and formation of diffusion zone observed in the experiments with binary metal–silicon systems.

Integration of PZT-Ceramic Modules using Hybrid Structures in High Pressure Die Casting

High pressure die casting (HPDC) is one of the most suitable fabrication processes for complex shaped and thin walled castings. Applied in transport vehicles vibrations can occur due to weight-optimized component designs. Potential noise exposure can be avoided by the integration of smart materials. Contrary to an application on the component surface, the functional module is protected against external influences and force/form-fitted in the casting. Using HPDC is a challenging approach due to high thermal and mechanical loads during the fabrication cycle. In addition, the module has to be firmly connected to the aluminum matrix. Subsequent to the casting process, active Zn-coatings are applied. Results are presented, which exhibit a damage free integration of the smart components and the formation of diffusion zones between casting matrix and hybrid support structure.

Diffusion zone formation in aluminized MAR-247 from Bi-velocity Phase Field Method

The Bi-velocity Phase Field Method (BPFM), which allows a quantitative description of diffusion mass transport in multi-phase materials, is presented and applied to simulate formation of a diffusion zone in aluminized MAR-247. The method links the bi-velocity Darken approach with the phase-field model in which the diffusion zone is quantitatively characterized by phase volume fractions. Accordingly, composition dependent diffusivities in a two-phase region are defined. The present method allows calculation of element-distribution profiles and volume fractions of the phases across a diffusion couple. Hence, a diffusion path can be determined for three component systems and, besides, the average stress field and entropy production during diffusion can be calculated.An example of the application of BPFM in the modeling of high-temperature reactive diffusion in an AlCrNi ternary system is presented. The simulated results are compared with experimental data obtained in aluminization of MAR-247 by the chemical vapor deposition process.

Surface Oxygen Diffusion Hardened Titanium Material TC4

In this study, surface oxygen diffusion-hardened treatment for TC4 titanium alloy was carried out to enhance the wear and corrosion resistance. The surface oxygen diffusion-hardened treatment was performed in an electrical resistance furnace under atmosphere. Characterization of modified surface layers was made by means of microscopic examinations, microhardness measurements and X-ray diffraction (XRD) analysis. The wear resistance of both treated and untreated samples was evaluated. The accelerated corrosion tests in HCl solution was used to determine the corrosion resistance. The corrosion and wear resistant surface layers were obtained after treatment. The surface layers mainly consisted of rutile TiO2. A significant increment in surface hardness was achieved due to the formation of an oxygen diffusion zone. Corrosion and wear resistant surface on TC4 were obtained after the formation of diffusion zone.