Diffusion Of Aluminum Research Articles

Current Transport Mechanisms and Electrophysical Characteristics of the 4H-SiC p-n Junctions Formed by Aluminum Diffusion

In this paper, the electrophysical characteristics of the 4H-SiC p-n junction created by low-temperature diffusion of aluminum were studied. Current-voltage (I-V) characteristics are analysed, and the current transport mechanisms in 4H-SiC p-n junctions are discussed. It is shown that at low forward bias voltages, the generation–recombination mechanism dominates, and the I-V characteristics at voltages U > 3.0 V obey the linear law. At reverse biases, the dominant mechanism of current transfer is limited by the space charge.

High-temperature oxidation behaviour of additively manufactured and wrought HAYNES 282

Direct Metal Laser Sintered Haynes 282 specimens as well as wrought ones were subjected to high-temperature exposure at 1000 °C for 100h in air to compare their oxidation behaviour. The specimens were removed from the furnace after 1h, 5h, 25h, 50h and 100h to reveal and study oxidation mechanisms through morphological and cross-sectional examination by using scanning electron microscopy with energy dispersive spectroscopy attachment and X-ray diffraction. Microstructural studies revealed that the oxidation kinetics, determined by changes in thickness scale and depth of aluminium diffusion zone, were mainly driven by the formation of Cr2O3 for the wrought material, and TiO2 for DMLS one. The wrought material was characterized by the oxidation rate equal to 0.96 and followed the logarithmic law. On the other hand, DMLS-manufactured Haynes 282 exhibited oxidation rate of 0.90 and follows the linear law for the thickness scale considerations. However, when the depth of aluminium diffusion was investigated, it had an oxidation rate of 0.87 and followed cubic law.

The oxide films formed under the low oxygen pressure in a particular system containing competing chromium and aluminium

AbstractIn this paper, pre‐oxidation treatment was carried out at 950 °C under oxygen pressure of 10−16 atm for nickel‐10 % chromium‐x % aluminium‐1 % silicon‐0.5 % yttrium(x=0 wt.–%, 1 wt.–%, 3 wt.–%, 5 wt.–%) alloys. Morphology and structure of oxide layers on the alloys after pre‐oxidation were analyzed by scanning electron microscopy and electron discharge spectroscopy. The results showed that a chromium oxide film was formed on the surface of the alloy without aluminium addition, while the oxide layer on the surface of the alloy with aluminium addition gradually transformed into M2O3 (M=aluminium and chromium) oxide film. The oxidation behavior was analyzed by means of chemical thermodynamics, and it was seen that because the interaction coefficient,εijof aluminium and chromium is a positive value, the increase of aluminium addition will strengthen the interaction and increase the diffusion coefficient,Diof aluminium and chromium. The diffusion of chromium and aluminium in each other therefore promotes their interaction, which is beneficial to the formation of the outer oxide film. Thus, with the increase of aluminium addition, the thickness of the outer oxide film gradually increased, and the aluminium content in M2O3 (M=aluminium and chromium) increased significantly, and with 5 % aluminium added, the aluminium oxide of the outer oxide film became the main body.

High Temperature Intergranular Oxidation of Nickel Based Superalloy Inconel 718

AbstractIntergranular oxidation (IGO) of the Ni-based superalloy Inconel 718 was studied at 650 °C, 700 °C and 900 °C. The oxidized samples were characterized by X-ray diffraction and scanning electron microscopy. For all the studied temperatures, the external scale was mainly composed of Cr2O3, while the oxides along the grain boundaries were rich in Al and, to a minor extent, Ti. This was consistent with thermodynamic computations. The time evolution of the maximum depth of IGO was found to be parabolic with an apparent activation energy of 164 kJ/mol. The results of this study confirm with three temperatures that IGO kinetics can be described using an extension of the Wagner’s theory of internal oxidation, as recently suggested in the literature at 850 °C. According to this description, the mechanisms controlling the IGO kinetics of Inconel 718 are the aluminum diffusion in the alloy matrix and the oxygen diffusion along the interface between the alloy matrix and the oxidized grain boundary.

Recent Progress in Creep-Resistant Aluminum Alloys for Diesel Engine Applications: A Review.

Diesel engines in heavy-duty vehicles are predicted to maintain a stable presence in the future due to the difficulty of electrifying heavy trucks, mine equipment, and railway cars. This trend encourages the effort to develop new aluminum alloy systems with improved performance at diesel engine conditions of elevated temperature and stress combinations to reduce vehicle weight and, consequently, CO2 emissions. Aluminum alloys need to provide adequate creep resistance at ~300 °C and room-temperature tensile properties better than the current commercial aluminum alloys used for powertrain applications. The studies for improving creep resistance for aluminum casting alloys indicate that their high-temperature stability depends on the formation of high-density uniform dispersoids with low solid solubility and low diffusivity in aluminum. This review summarizes three generations of diesel engine aluminum alloys and focuses on recent work on the third-generation dispersoid-strengthened alloys. Additionally, new trends in developing creep resistance through the development of alloy systems other than Al-Si-based alloys, the optimization of manufacturing processes, and the use of thermal barrier coatings and composites are discussed. New progress on concepts regarding the thermal stability of rapidly solidified and nano-structured alloys and on creep-resistant alloy design via machine learning-based algorithms is also presented.

Effect of preheating before rolling on the microstructural and mechanical properties of lamellar Al/Ti/Al composite produced by roll bonding

This study explores the effect of preheating before rolling on the microstructural and mechanical properties of an AA5052/Ti/AA5052 lamellar composite fabricated by roll bonding. The roll bonding was done in two ways: conventional rolling and preheating before rolling. Preheating was done before rolling for 7 min at 350 °C. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness, and tensile tests were used for microstructural and mechanical investigations. By performing preheating, the strength increased from 468 MPa to 511 MPa, elongation changes were insignificant, and hardness decreased in aluminum and titanium layers from 108 to 100 HV and 234 to 212 HV, respectively. By preheating, aluminum diffusion in titanium and metallurgical connection occurred. Therefore, SEM showed better bonding in preheated specimens.

Structural characteristics and mechanical properties of partially reacted and non-reacted Al–Fe66Cr10Nb5B19 metallic glass composites

The microstructure and mechanical properties of partially reacted and non-reacted Al–Fe66Cr10Nb5B19 metallic glass composites obtained by spark plasma sintering were comparatively analyzed. For the first time, the compositional features of core-shell particles formed upon the partial reaction of the Fe66Cr10Nb5B19 metallic glass with aluminum were examined using transmission electron microscopy combined with elemental mapping. The key finding is that iron of the alloy selectively dissolved in aluminum. The inner layer of the shell formed via diffusion of aluminum into the metallic glass. The introduction of the glassy reinforcement did not lead to such a dramatic ductility reduction as the formation of a complex “metallic glass core-thick intermetallic shell” reinforcement. In the non-reacted composite, the glassy reinforcement did not reveal its full potential in terms of the strengthening effect.

High-temperature oxidation and diffusion studies on selected Al–Cr–Fe–Ni high-entropy alloys for potential application in thermal barrier coatings

In this work, the properties of two high-entropy alloys (HEAs) Al25Cr20Fe20Ni35 and Al20Cr20Fe20Ni40 (at.%) were compared for potential application as bond coats in thermal barrier coatings (TBCs). For this reason, both their oxidation resistance under isothermal and thermal shock conditions, as well as diffusion phenomena occurring at the substrate-HEA diffusion couple interface, were investigated. It was determined that both alloys demonstrate good phase stability and oxidation resistance during prolonged exposure to air atmosphere at 1000°C. In the initial 100 h period, selective aluminum oxidation is responsible for the protective scale growth on both materials under both isothermal and thermal shock conditions. However, only the Al20Cr20Fe20Ni40 high entropy alloy maintains a single Al2O3 layer for over 1000 h of oxidation with cyclic temperature changes. On the other hand, diffusion studies indicate that mainly iron and chromium travel between the ferritic steel substrate and the HEAs. Aluminum diffusion is seemingly limited by the unexpected formation of a thin aluminum nitride layer at the interface between the materials. From all these results it can be concluded that the Al20Cr20Fe20Ni40 alloy shows more promise for application in TBCs based on high entropy materials than Al25Cr20Fe20Ni35.

Aluminide diffusion coatings for improving the pesting behavior of refractory metals

Refractory metal based alloys show great potential as structural materials for high-temperature applications due to their high melting points, but they are prone to catastrophic oxidation at around ▪. The effectiveness of aluminium diffusion coatings on the oxidation resistance of pure molybdenum, niobium, tantalum, and tungsten was investigated. Homogeneous diffusion layers of Al-rich intermetallic phases were formed on all four refractory metals after pack cementation. Thermodynamic calculations and experimental assessments (e.g., of the activator) determined the most suitable conditions for the pack cementations. Subsequent thermogravimetric analysis of the uncoated and coated samples at ▪ and ▪ for up to ▪ in dry synthetic air was used to determine the protective effect of the coatings and investigate the underlying oxidation mechanisms. Optical and electron microscopy, EPMA, XRD and Raman spectroscopy were used to investigate the diffusion layers and the oxide scales. For two refractory metals (Mo and Ta) the aluminization resulted in an improved oxidation behavior and a substantially decreased oxide growth rate compared to uncoated substrates.

Study on properties and soil solidification mechanism of alkali - activated cementitious materials

Due to the low strength and poor durability of soil, it is limited in engineering application. To improve its strength and durability, the alkali-activated (AA) cementitious materials were prepared using industrial wastes, and experiments were performed on AA cementitious materials and solidified soil, including mechanical properties tests, water stability tests, and microscopic properties tests. The results indicate that the content ratio of fly ash and slag can significantly affect the properties of AA cementitious materials, and the maximum 28d compressive strength reaches 36.1 MPa. With increasing AA cementitious materials content (up to 50%) and age, both the compressive strength and tensile strength of AA solidified soil enhance. The microstructure evolution process of soil after solidification includes four stages, including mineral material dissolution, silicon aluminum diffusion, polymerization of low polymer silicon aluminum salts, and polymer soil particle cementation and hardening. The mineral raw material particles and soil particles are effectively bonded due to the adhesion between the reaction products and the mineral material, which improves the performance of the AA solidified soil. The maximum 28d compressive strength of AA solidified soil was 3.6 MPa, the maximum tensile strength was 1.05 MPa, and the maximum water stability coefficient was 0.89.

Activation of Al2O3 surface passivation of silicon: Separating bulk and surface effects

Understanding surface passivation arising from aluminium oxide (Al2O3) films is of significant relevance for silicon-based solar cells and devices that require negligible surface recombination. This study aims to understand the competing bulk and surface lifetime effects which occur during the activation of atomic layer deposited Al2O3. We demonstrate that maximum passivation is achieved on n- and p-type silicon with activation at ∼ 450 °C, irrespective of annealing ambient. Upon stripping the Al2O3 films and re-passivating the surface using a superacid-based technique, we find the bulk lifetime of float-zone and Czochralski silicon wafers degrade at annealing temperatures > 450 °C. By accounting for this bulk lifetime degradation, we demonstrate that the chemical passivation component associated with Al2O3 remains stable at activation temperatures of 450─500 °C, achieving an SRV of < 1 cm/s on n- and p-type silicon. In conjunction with the thermal stability, we show that films in the range of 3–30 nm maintain an SRV of < 1 cm/s when annealed at 450 °C. From atomic-level energy dispersive X-ray analysis, we demonstrate that, post deposition, the interface has a structure of Si/SiO2/Al2O3. After activation at > 300 °C, the interface becomes Si/SixAlyO2/Al2O3 due to diffusion of aluminium into the thin silicon oxide layer.

Interfacial evolution and coordinated deformation mechanism of Ti/Al laminated metal composites prepared by diffusion bonding

Laminated metal composites (LMCs) of titanium and aluminum (Ti/Al), combining the high strength and thermal stability of titanium with the low density and corrosion resistance of aluminum, hold substantial promise for industrial applications. Utilizing diffusion bonding under optimal processing conditions—specifically a bonding temperature of 550 °C and a holding time of 120 min—an average interfacial shear strength of 68.7 MPa was achieved. Transmission electron microscopy (TEM) revealed a metallurgically bonded interface facilitated by the mutual atomic diffusion of titanium and aluminum; this diffusion layer predominantly comprises the TiAl3 phase. Detailed insights into the microstructural evolution at the interface, including dislocation configurations, were also obtained in this study. The Burgers vectors of these dislocations were determined using the two-beam electron diffraction contrast imaging method. Based on these results, it can be elucidated that the deformation mechanism of Ti layer was dominated by the dislocation slip (mainly prismatic and the basal slip), while the coordinated deformation of TiAl3/Al interface benefitted by the dislocations gliding across the interface.

Phase formation and morphological characteristics of aluminum bronze and nickel alloy composites produced by the additive manufacturing process

This study discusses the effect of increasing the volume concentration of nickel alloy (Inconel 625) on the structure and properties of an aluminum bronze/nickel alloy composite. The addition of Inconel 625 to aluminum bronze was found to produce chromium carbide followed by a NiAl phase. As the nickel alloy concentration increases, the NiAl phase is depleted by aluminum diffusion into the matrix, resulting in the formation of a cuboidal Ni3Al phase. As a result of complex diffusion, the volume fraction of the Cr23C6 phase increases, resulting in a loss of strength as the Inconel 625 concentration increases up to 50% by volume.

Determination of the alumina diffusivity and dissolution rate for alumina samples immersed in a cryolitic bath

The alumina dissolution is one of the main concerns for the stability and efficiency of the electrolysis cells in the Hall-Héroult process. Therefore, to correctly describe this phenomenon, it is necessary to know the diffusivity of alumina in the electrolyte to use mass transfer relations and approximate Fick’s law of diffusion. In this work, a formulation for the molecular diffusivity is proposed to take into account the influence of the different chemistry of each condition on the mobility of dissolved alumina. Then, data obtained by a gravimetric method are correlated to obtain a general formulation of the Sherwood number of alumina discs immersed in a cryolitic bath. Conditions similar to the industrial range were used to produce these data with and without bubbling. Consequently, the different conditions slightly modified the flow around the sample, which needs an accurate description to obtain an optimal relationship. Finally, a discussion explains how this research is relevant for industrial use.

In-situ generated particle synchronous enhancement of strength and toughness in pressureless sintered Ti3AlC2 layered ceramics

Ti3AlC2 as a typical MAX phase has attracted extensive attention due to its advantages of both metals and ceramics. However, the decomposition of Ti3AlC2 during pressureless sintering leads to a low density, which restricts its application in complex-shaped components. To address this challenge, MgO, CeO2, Y2O3, and La2O3 were employed as additives to fabricate Ti3AlC2 ceramics with minimal decomposition via pressureless sintering. It was observed that these oxide additives reacted with aluminum and oxygen, forming MgAl2O4, CeAlO3, YAlO3, and LaAlO3, respectively. These in-situ generated aluminate particles effectively impeded the outward diffusion of aluminum and the inward diffusion of oxygen, thereby inhibiting the decomposition of Ti3AlC2. Furthermore, the thermal expansion mismatch between the in-situ generated particles and the matrix induced beneficial residual stresses. These combined effects contributed to the synchronized enhancement of both strength and toughness. Among the four additives, CeO2 displayed the best efficiency. Ti3AlC2-1.0 wt%CeO2 reached a flexural strength of 680.74 MPa and fracture toughness of 7.82 MPa m1/2, equivalent to those by pressure assisted sintering. The calculated toughness considering the residual stress was approximately 7.71 MPa m1/2, in good agreement with the measured value.

Synergetic Effect of Aluminum Oxide and Organic Halide Salts on Two‐Dimensional Perovskite Layer Formation and Stability Enhancement of Perovskite Solar Cells

AbstractLong‐chain organic halide salts are widely used in perovskite‐based optoelectronic devices for surface passivation owing to their capability to interact with the surface defects of perovskites. Here, aluminum oxide (AlOx) is introduced via atomic layer deposition onto octylammonium iodide (OAI) to exploit the benefits of organic halide salts without generating undesired defects. The devices incorporating AlOx on OAI‐treated perovskite (OAI/AlOx) show enhancement in both device performance and photo‐stability compared to those with only treatment. A diffusion of aluminum from AlOx into the perovskite through surface characterization contributes to a uniform photo‐generated carrier transport in both the surface and the bulk of the perovskite absorber. In addition, it is revealed that light‐induced two‐dimensional perovskite formation on OAI/AlOx. This may be ascribed to preventing the loss of OA cations due to the presence of AlOx, leading to a decrease in the number of iodine anions which suppresses the light‐induced degradation of corresponding devices. Consequently, the devices show over 24% efficiency and retain their efficiency over 1000 hours under continuous light illumination.

RF loss reduction by a carbon-regulated Si substrate engineering in GaN-based HEMT buffer stacks

A carbon-regulated Si substrate engineering has been adopted to reduce the RF loss of GaN-based HEMT buffer stacks. By implanting the substrate with high-dose carbon, undersaturation of Si self-interstitials is formed, and the self-interstitial-assisted aluminum diffusion into the Si substrate during the growth can be significantly suppressed. Consequently, the formation of parasitic conductive channel is suppressed, and the RF loss of the buffer stacks can be reduced. By combining the substrate engineering with low-temperature growth, the RF loss of the buffer stacks is reduced to as low as 0.13 dB/mm at 10 GHz. In addition, the crystal quality of the buffer stacks grown on the regulated substrates does not degrade. This work shows a great potential for fabrication of high-quality and low-loss GaN-on-Si RF devices.

Formation mechanism of TiC/Al2O3 composite from porous Ti3AlC2 ceramics in 35 vol.% CO‐N2 atmosphere

AbstractThermal reaction and microstructure evolution of porous Ti3AlC2 ceramics in a graphite bed (65% N2 and 35% CO) between 1100 and 1500°C were investigated in this work. The main products of Ti3AlC2 in a graphite bed were titanium carbide and alumina. At 1100°C, a thin alumina layer formed on the Ti3AlC2 particles due to the outward diffusion of slight aluminum. As the temperature increased to 1300°C, more aluminum diffused outward from the Ti3AlC2 particles, and a partial of Ti3AlC2 transformed into titanium carbide. Consequently, the alumina layer formed on the surface of particles got thicker, and defects occurred inside the particles due to the Kirkendall effect. When the temperature was 1500°C, Ti3AlC2 was transformed entirely into alumina and titanium carbide, and visible pores were left inside the particles. The formation mechanism of TiC/Al2O3 composite from porous Ti3AlC2 ceramics in a graphite bed was proposed in detail.

Real-time temperature monitoring of weld interface using a digital twin approach

A new friction processing technique is developed for lap welding of Al–Cu sheets using inter diffusion of copper and aluminium at their interface. The metals selectively melt at the interface at a temperature near their eutectic point. This paper proposes a digital twin approach for real-time temperature monitoring at the joint interface using the machine’s real-time current data. The real time temperature data is used to predict exact instance of interface melting and to control the resulting weld microstructure. The digital twin model is calibrated using a finite element model which is in turn calibrated using experiments. Moving average of machine current and temperature history are used to predict real time interface temperature using a linear regression based recursive machine learning model with high precision. The model predictions have an R2 value of 99.5%. The digital twin approach resulted in significant increase in joint strength and fracture energy.

A comparative study on the surface degradation mechanisms of arc melted and laser remelted CoCrFeNiAl0.5Nb0.5 HEA

In the current study, a CoCrFeNiAl0.5Nb0.5 high entropy alloy was manufactured via arc melting and exposed to laser surface remelting. The presence of Nb and Al was limited to the formation of single simple cubic phase formations. Both alloys are composed of four phases. Laser remelting did not change current phases, but it affected the microstructure. Hardness increased from 475 HV to 785 HV thanks to the change in phase ratios and grain refinement resulting from laser remelting. Wear resistance improved due to the increase in hardness, and volume losses decreased by 28 %. In short-term high-temperature oxidation, laser remelting enabled better oxidation resistance in alloy since it provided more paths for the diffusion of aluminum, which forms an alumina oxide scale. Interestingly, such a trend was not observed in the increased oxidation period. In the final oxidation stage, the depletion of B2 phases and the formation of inner oxides significantly worsened the oxidation resistance of LR alloy. Although Icorr, which expresses the corrosion resistance of the laser-melted alloy, was higher than before the laser-remelting process, the changes in the alloy's microstructure with rapid cooling caused a decrease in the passivation resistance of laser-remelted CoCrFeNiAl0.5Nb0.5 HEA.