Thermal Diffusion Treatment Research Articles

Spontaneous growth of Sn whisker on the hot-dipping Al[sbnd]Sn alloy coating on Fe-Cr-B cast steel

Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.

On the effect of thermal diffusion treatment on the hot-dipped Al-Si alloy coating on Fe-Cr-B cast steel

The periodic layered structures (PLSs) consisting of alternatively arranged Cr-Al-B MAB phase and FeAl3 were formed in-situ at the (Cr, Fe)2B/pure Al melt interface during hot dip aluminizing (HDA) of Fe-Cr-B cast steel. In the present investigation, HDA of a novel Fe-Cr-B cast steel was carried out in an Al-5.7 wt% Si alloy melt at 750 ℃ for 30 min. The HDA samples were given thermal diffusion treatment (TDT) at 750 ℃. The microstructural evolution of the Al-Si coating during HDA and TDT were analyzed in details. Results showed that Si in Al melt had a great influence on the compositions of PLSs. During HDA, Si atoms in the melt partially replaced Al atoms in the Cr-Al-B MAB phase, and Si-rich phase were rich at the boundary of Cr-Al-B MAB phase. While, during TDT, the Si-rich phase dissolved into the adjacent FeAl3. The formation process of PLSs during TDT experienced the both transformation from the laminar structure formed in the initial stage to the graininess structure at last and from disordered to ordered arrangement.

Effects of Zn and Si on the microstructure evolution of the Cr-Al-B MAB phase contained in the periodic layered structure formed in-situ

The MAB phases gain large attention in today's world because of their combination of metallic and ceramic. In our previous work, the periodic layered structures (PLSs) containing Cr-Al-B MAB phase were formed at the Fe-Cr-B cast steel/molten Al interface. This work reports the preparation method of the new A-site alloyed Cr-Al-B MAB phase through hot-dip aluminizing (HDA) in different Al melts and subsequent thermal diffusion treatment (TDT) of Fe-Cr-B cast steel. It was found that the Zn and Si in the Al melts had great effects on the formation and microstructure evolution of the Cr-Al-B MAB phase formed during HDA and TDT. Both Zn and Si could partially replace the Al atoms in Cr-Al-B MAB phase, leading to forming a solid solution with double A atoms. The Cr-(Al, Zn)-B and Cr-(Al, Si)-B MAB phases were achieved by A-site replacement in Cr-Al-B MAB phase. Meanwhile, Zn thickened the thickness of this MAB phase, while, Si decreased that of the MAB phase. However, when they were dopped simultaneously, Zn atom preferentially replaced Al atom in Cr-Al-B MAB phase with that of the substitution of Si not happening.

Orthogonal Experimental Optimization of Preparation and Microstructural Properties of a Diffusion Barrier for Tantalum-Based Silicide Coatings.

To solve the problem of silicide coatings on tantalum substrates failing due to elemental diffusion under high-temperature oxidation environments and to find diffusion barrier materials with excellent effects of impeding Si elemental spreading, TaB2 and TaC coatings were prepared on tantalum substrates by the encapsulation and infiltration methods, respectively. Through orthogonal experimental analysis of the raw material powder ratio and pack cementation temperature, the best experimental parameters for the preparation of TaB2 coatings were selected: powder ratio (NaF:B:Al2O3 = 2.5:1:96.5 (wt.%)) and pack cementation temperature (1050 °C). After diffusion treatment at 1200 °C for 2 h, the thickness change rate of the Si diffusion layer prepared using this process was 30.48%, which is lower than that of non-diffusion coating (36.39%). In addition, the physical and tissue morphological changes of TaC and TaB2 coatings after siliconizing treatment and thermal diffusion treatment were compared. The results prove that TaB2 is a more suitable candidate material for the diffusion barrier layer of silicide coatings on tantalum substrates.

Influence of thermal diffusion treatment on microstructure evolution and corrosion behavior of hot-dipped Al coated Fe-Cr-Si-B cast steel

The influence of thermal diffusion treatment on the microstructure and corrosion behavior of hot-dipped Al coated Fe−Cr−Si−B cast steel in a 5 wt.% NaCl solution was studied. The results showed that the product obtained from the interfacial reaction between the Fe matrix in Fe−Cr−Si−B cast steel and molten Al was FeAl3 with a columnar crystal structure. Periodic layered structures at the (Cr, Fe)2B/Al interface were formed during the subsequent thermal diffusion treatment but not hot dip aluminizing. The corrosion behavior of the residual Al layer predominated that of the hot dip aluminizing and thermal diffusion treatment coatings over a short duration till the Al topcoat was consumed completely. Localized corrosion caused by Cl− preferentially began from the block-like B−Al−Cr phase/FeAl3 interface and propagated along periodic layered structures. The Si particles acted as a cathode and promoted the corrosion of the coating. The steel substrate retained its cathodic protection until the Fe−Al intermetallic compounds layer was corroded completely. Additionally, the corrosion in the NaCl solution at an elevated temperature was greatly accelerated.

Formation mechanism of periodic layered structure between Fe–Cr–Si–B cast steel with high B content and molten Al

The periodic layered structures (PLSs) have been confirmed to be formed as the Fe–Cr–B cast steels containing about 3.0 wt% B were dipped into Al melt. However, there was no PLSs formed, in terms of a novel Fe–Cr–Si–B cast steel with B content much higher. The interfacial reaction between borides contained in this novel Fe–Cr–Si–B cast steel with 8.5 wt% B content and Al at 750 °C was studied using hot dip aluminizing, thermal diffusion treatment, and subsequent SEM, TEM, and 3DAP of the obtained specimens. The PLSs were formed in situ after a long period of incubation because of the high chemical stability induced by the overstoichiometric (Cr, Fe)2B. The formation of PLSs proceeded through an intermediate state which involved transformation from disordered particles to ordered Cr–Al–B intermetallic compound. Owing to the formation of the localized melt of FeAl3–Al eutectics, the understoichiometric Cr–Al–B intermetallic compound gradually drifted to agglomerate and grew under the effects of the driving force of the lamellar growth of MAB phase and the thermal flux, along with the drag of the overstoichiometric Cr–Al–B intermetallic compound due to the interlaced structure.

High-Efficiency Carbon-based CsPbI2 Br Perovskite Solar Cells from Dual Direction Thermal Diffusion Treatment with Cadmium Halides.

In recent years, carbon-based CsPbI2 Br perovskite solar cells (PSCs) have attracted more attention due to their low cost and good stability. However, the power conversion efficiency (PCE) of carbon-based CsPbI2 Br PSCs is still no more than 16%, because of the defects in CsPbI2 Br or at the interface with the electron transport layer (ETL), as well as the energy level mismatch, which lead to the loss of energy, thus limiting PCE values. Herein, a series of cadmium halides are introduced, including CdCl2 , CdBr2 and CdI2 for dual direction thermal diffusion treatment. Some Cd2+ ions thermally diffuse downward to passivate the defects inside or on the surface of SnO2 ETL. Meanwhile, the energy level structure of SnO2 ETL is adjusted, which is in favor of the transfer of electron carriers and blocking holes. On the other hand, part of Cd2+ and Cl- ions thermally diffuse upward into the CsPbI2 Br lattice to passivate crystal defects. Through dual direction thermal diffusion treatment by CdCl2 , CdI2 and CdBr2 , the performance of devices has been significantly improved, and their PCE has been increased from 13.01% of the original device to 14.47%, 14.31%, and 13.46%, respectively. According to existing reports, 14.47% is one of the highest PCE of carbon-based CsPbI2 Br PSCs with SnO2 ETLs.

An in-situ transient photo-induced voltage method to understand the PEC efficiency of C, N co-doped TiO2 photoanode

Photoelectrocatalysis (PEC) is one of the most important green energy conversion technologies. During the development of PEC, the Jabs, ηsep and ηinj are challenges that hinder the performance enhancement of different kinds of photoanodes in PEC systems. As a stable, cheap and non-toxic PEC material, TiO2 is also limited by the above challenges. Here, a series of C, N co-doped TiO2 photoanodes were synthesized by hydrothermal method combined with a simple one-step thermal diffusion treatment. Under AM 1.5 G light intensity, the PEC performance of TCN-1.5 is 4.06 mA cm−2 at 1.23 V vs RHE in 1.0 M NaOH, which is ca. 2.08 times as high as the photocurrent density of the pristine TiO2. Especially, an in-situ transient photoinduced voltage (TPV) method was developed to measure the changes on efficiencies mentioned above: Jabs, ηsep and ηinj are improved by about 9.8 %, 24.9 % and 48.3 %, respectively, and their product is equal to the increase of photocurrent density. This work analyzes the improvement of efficiencies in the PEC process through in-situ characterization and opens up a new way for PEC material design and fabrication.

Dy evolution and coercivity improvement mechanism of sintered NdFeB magnets in thermal diffusion process

Heavy rare earth (such as Dy) thermal diffusion process is a promising method to increase the coercivity of sintered NdFeB magnets and optimizes their thermal performance. However, the Dy evolution process and the mechanism of coercivity improvement still require further clarification. In this work, commercial 30 M magnets were employed as the initial magnet, and a homemade DyF3 coating was prepared for thermal diffusion treatment. The optimal Dy diffusion process was obtained at 900 ℃ for 8 h. The coercivity of the magnet was increased from 14.16 kOe to 20.43 kOe with a negligible decrease in remanence. The Dy evolution process was systematically analyzed for understanding the mechanism of coercivity improvement. The diffusion coefficient was calculated based on Fick's second law. The diffusivity of Dy along the grain boundaries (5.16 × 10−8 cm2·s−1) is much higher than that in the grains (2.33 × 10−11 cm2·s−1). Therefore, the Dy diffused into the magnet along the grain boundaries with a faster diffusivity, forming uniform and continuous grain boundaries of the Dy-rich phases around the grains, which plays a decoupling effect and significantly increases the coercivity of the magnet. Simultaneously, the Dy in the grain boundaries diffused into the main phase with a slower diffusivity to form a (Nd, Dy)2Fe14B thin layer with higher magnetocrystalline anisotropic, which can inhibit the nucleation of reversed magnetic domains and further improve intrinsic coercivity. However, over diffusion process led to the excess Dy diffused into the grain, which will decrease the performance of the magnet. This work provides an insight of Dy evolution process during the diffusing period, and is significant to understand the improvement mechanism of coercivity for preparing NdFeB magnets with high-performance and low cost.

Фреттинг-изнашивание наводороженного циркониевого сплава Э125, упрочненного диффузионными покрытиями

Protective coatings that improve the corrosion resistance of the E125 zirconium alloy under conditions of the combined effect of a hydrogen-containing medium and friction wear have been investigated. The formation of coatings on the surface of the samples was carried out by thermal diffusion treatment in powder saturating media with halogen activation at temperatures from 400°C to 950°C. The resulting coatings were formed as a result of the processes of oxidation, siliconization, and nitrocarburizing. Wear tests were carried out on a SRV Testsystem multifunctional testing system according to the disk-ball scheme without lubrication. Cathodic hydrogenation of the samples was carried out in an electrolyte solution containing a single normal sulfuric acid solution at room temperature. The cathodic current density was from 20 to 500 mA / cm2. The hydrogen concentration in the samples was determined on a highly sensitive G8 Galileo H gas analyzer by melting the samples in a carrier gas flow. As a result of the study, it was shown that the wear of the coated specimens after siliconizing and nitrocarburizing is three times lower than that of the original uncoated specimen. Oxidation leads to a significant, more than fivefold, increase in the amount of wear, in comparison with the same initial sample. Hydrogenation of the surface of the samples allows not only to reduce the coefficient of friction, but also to reduce the amount of wear in the process of testing samples for fretting wear. This study makes it possible to obtain modified surfaces of zirconium samples that significantly improve the mechanical properties, as well as reduce the level of hydrogenation, and increase the performance of components made of zirconium alloys under conditions of increased friction.

Enhanced output performance of ZnO thin film triboelectric nanogenerators by leveraging surface limited ga doping and insulting bulk

Although triboelectric nanogenerator (TENG) has been developed as a new green energy source, the dominant charge transfer mechanism regarding surface chemistry has not been fully uncovered yet, especially in semiconductor materials. Semiconductor materials are technically important not only capable of tuning total carrier concentrations available for charge transfer in TENG, but corresponding optoelectronic properties for applications into tribo-tronics. However, doping renders one serious drawback as tribo-charges tend to leak and cannot be held in place for energy output. In order to prevent carriers from leaking while maintain the characteristics of tunable carrier concentrations in semiconductors, a two-layer structure of Ga-doped ZnO/undoped-ZnO is proposed by a two-step growth methodology. A ZnO thin film was first grown by magnetron sputter followed by Ga doping restricted to a shallow surface region by thermal diffusion treatment in the second step. The results support that surface work function difference between two materials in electrification under the well preservation of tribo-charges retention governs the charge transfer capability responsible for output performance of TENGs, where the output voltage and current of the ZnO film doped with 0.93 at% Ga can be drastically enhanced by 16 and 13 times, respectively. However, β-Ga2O3 forms on the surface when Ga concentration is higher than 0.93 at%. Nevertheless, the even larger work function of β-Ga2O3 than Ga-doped ZnO does not lead to larger output performance, implying that work function difference is not the prime factor but carrier concentration in the conduction band needs to be considered for the performance of TENGs. This work demonstrated a viable method to modify the work function of ZnO only confined to the surface through doping without disturbing the bulk, optimizing the device structure for TENGs based on semiconductor.

THERMODIFFUSION SATURATION OF THE SURFACE LAYERS OF α-TITANIUM BY OXYGEN, NITROGEN, CARBON

The purpose of the study is to analytically assess the depth of the gas-saturated zone in the case of a single-component diffusion saturation of alpha-titanium with nitrogen, oxygen and carbon from a rarefied controlled gas environment. Results. Based on the analysis of the literature data, the work schematically shows the interaction of alpha titanium with the elements of implementation and presents the processes with the corresponding parameters that characterize. It is shown that the surface impurity concentration is equal to the equilibrium concentration and is established instantly and does not depend on time. Consequently, with the proposed generalized nonstationary boundary condition in the absence of diffusion of impurities into the volume of the metal, the time dependence of its surface concentration is given, determined by the intensity of surface processes. The dependence of the relative change in the microhardness in the diffusion zone of titanium due to dissolved nitrogen (without taking into account the contribution of nitride inclusions) is presented. Analytically calculated concentration profiles of nitrogen generally correlate well with the distribution of the corresponding relative changes in microhardness in the surface layer. Analytical calculations of the concentration profiles of oxygen, nitrogen and carbon in titanium at a saturation temperature of 700 °C are presented. Practical value. The results obtained will make it possible to preliminarily estimate the size of the fortified near-surface layer depending on the parameters of chemical-thermal treatment and select the optimal parameters of thermal diffusion treatment to ensure the formation of reinforced layers on products made of alpha-titanium based on elements of interstitial in order to increase the functional properties.

Microstructure, phase evolution and magnetocaloric properties of LaFe11.6Si1.4/La70Co30 composite

LaFe11.6Si1.4/16 wt%La70Co30 composites were fabricated by hot-pressing (HP) followed by thermal diffusion treatment in the temperature range of 923–1273 K. Significant microstructural and phase evolution occurred during diffusion heat treatment. Thermal decomposition (TD) occurred between 1023 and 1223 K, which increased the Curie temperature (TC) but smeared out the magnetic transition, decreasing magnetic entropy change (–ΔSM). Co atoms first diffused into the α-Fe(Si) and LaFeSi (1:1:1) phases. And then, the α-Fe(Co,Si) and La(Fe,Co)Si phases, attached to large LaFe11.6Si1.4 particles, transformed to a NaZn13-type La(Fe,Co,Si)13 (1:13) phase at 1273 K. Hence, a core-shell La(Fe,Co,Si)13 phase formed, resulting in a table-like magnetic entropy change over a wide temperature range (∼202–292 K). Greater Co diffusion and more homogeneity of the composition of the 1:13 phase could be achieved by increasing the annealing time. The maximum magnetic entropy change (–ΔSM)max of the composites at 0–2 T could be increased from 5.62 J/(kg·K) at ∼196 K to 8.81 J/(kg·K) at ∼244 K.

Improvement of corrosion resistance of twinning-induced plasticity steel by hot-dipping aluminum with subsequent thermal diffusion treatment

Fe–Al intermetallic layers were formed on the surface of twinning induced plasticity (TWIP) steel by hot-dipping aluminum (HDA) and subsequent thermal diffusion treatment (TDT). It was shown that the coating layer was composed of Al, FeAl3 and Fe2Al5 phases in the hot-dip state while only Fe3Al phase retained after subsequent TDT. It was found that, the corrosion resistance of TWIP steel had been significantly improved with a shift of 224 mV in the Ecorr towards anodic direction and the jcorr reduced from 26.1 μA/cm2 to 2.70 μA/cm2. Fe-Al intermetallics could lower the corrosion rate because the Al2O3 film formed during stable soak stage was slightly stable due to the higher aluminum content than matrix steel.

Structure of Al-based composite coatings prepared by thermal diffusion of the arc-ion plating Al coatings

In order to improve the high-temperature oxidation resistance of the hydrogen-resistant steel, Al coatings were firstly deposited on the hydrogen-resistant steel by arc-ion plating and then the thermal diffusion treatment was used to produce the Al-based composite coatings on the hydrogen-resistant steel. The effect of thermal diffusion parameters on the structure of Al-based composite coatings was studied. The crystal structure, composition and morphology of Al-based composite coatings were analyzed by using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The results showed that the double inner diffusion layer was formed on Al coatings treated at 700[Formula: see text]C. And the single inner diffusion layer with uniform composition distribution could be formed on Al coatings treated at 950[Formula: see text]C. The Al-based composite coating prepared by thermal diffusion treatment at 950[Formula: see text]C had a dense and thick [Formula: see text]-Al2O3 surface layer, and it exhibited good high-temperature oxidation resistance.

Manufacturing a Long-Period Grating with Periodic Thermal Diffusion Technology on High-NA Fiber and Its Application as a High-Temperature Sensor.

We demonstrated a kind of long-period fiber grating (LPFG), which is manufactured with a thermal diffusion treatment. The LPFG was inscribed on an ultrahigh-numerical-aperture (UHNA) fiber, highly doped with Ge and P, which was able to easily diffuse at high temperatures within a few seconds. We analyzed how the elements diffused at a high temperature over 1300 °C in the UHNA fiber. Then we developed a periodically heated technology with a CO2 laser, which was able to cause the diffusion of the elements to constitute the modulations of an LPFG. With this technology, there is little damage to the outer structure of the fiber, which is different from the traditional LPFG, as it is periodically tapered. Since the LPFG itself was manufactured under high temperature, it can withstand higher temperatures than traditional LPFGs. Furthermore, the LPFG presents a higher sensitivity to high temperature due to the large amount of Ge doping, which is approximately 100 pm/°C. In addition, the LPFG shows insensitivity to the changing of the environment’s refractive index and strain.

Effects of diffusing DyZn film on magnetic properties and thermal stability of sintered NdFeB magnets

The DyZn film on sintered NdFeB magnet surface was prepared through DC magnetron sputtering. The magnetic properties, thermal stability and microstructure of annealed and DyZn diffused magnets were compared. The coercivity enhances significantly from 1174.10 kA/m to 1711.40 kA/m by a striking increment of 45.7% with only a slight reduction in remanence from 1.20 T to 1.19 T after DyZn thermal diffusion treatment. The thermal stability of NdFeB magnets can be improved by grain boundary diffusion. The temperature coefficient of coercivity (β) and remanence (α) are improved from −0.506%/°C, −0.120%/°C to −0.481%/°C, −0.105%/°C in the range of 20 °C–180 °C, respectively. The irreversible magnetic flux losses of DyZn diffused magnet are reduced to 37.5% at 180 °C for 2 h and 29.8% in HAST for 288 h, respectively. Dy elements diffusing along the grain boundary phase mainly aggregate between the grain boundary phase and the main grain epitaxial layer via SEM and EPMA observations. The optimization of microstructure and composition of grain boundary phases and the formed (Nd,Dy)2Fe14B transition layer are the main reasons for the significant enhancement of intrinsic coercivity.

Research of improvement and hydraulic model test for the treatment of thermal diffusion around the intake and outlet structure of Linkou power plant in Taiwan coastal zone

Research of improvement and hydraulic model test for the treatment of thermal diffusion around the intake and outlet structure of Linkou power plant in Taiwan coastal zone

TEMPERATURE FLUCTUATIONS DRIVEN BY MAGNETOROTATIONAL INSTABILITY IN PROTOPLANETARY DISKS

The magnetorotational instability (MRI) drives magnetized turbulence in sufficiently ionized regions of protoplanetary disks, leading to mass accretion. The dissipation of the potential energy associated with this accretion determines the thermal structure of accreting regions. Until recently, the heating from the turbulence has only been treated in an azimuthally averaged sense, neglecting local fluctuations. However, magnetized turbulence dissipates its energy intermittently in current sheet structures. We study this intermittent energy dissipation using high resolution numerical models including a treatment of radiative thermal diffusion in an optically thick regime. Our models predict that these turbulent current sheets drive order unity temperature variations even where the MRI is damped strongly by Ohmic resistivity. This implies that the current sheet structures where energy dissipation occurs must be well resolved to correctly capture the flow structure in numerical models. Higher resolutions are required to resolve energy dissipation than to resolve the magnetic field strength or accretion stresses. The temperature variations are large enough to have major consequences for mineral formation in disks, including melting chondrules, remelting calcium-aluminum rich inclusions, and annealing silicates; and may drive hysteresis: current sheets in MRI active regions could be significantly more conductive than the remainder of the disk.

Effects of Mo Contents in Matrix on Microstructure and Properties of Vanadium Carbide Coating Formed by Thermal Diffusion Treatment

Thermal diffusion salt-bath vanadizing was finished for Cr12MoV die steel, in order to investigate the properties of vanadium carbide coatings related with the Mo contents in Crl2MoV die steel. Scanning electron microscopic observation reveals that Mo can decrease the growth rate of coating as a carbide forming element. Besides, Mo element can promote grain refinement of the coating. X-ray diffraction analysis shows that the different Mo contents have no influence on the phase structure of the coatings. Energy dispersive spectrum analysis and mechanical properties test show that Mo can diffuse into the coating and make a strengthening effect on the coating.