Interdiffusion Zone Research Articles

Preparation and oxidation performance of a low-diffusion (Ni,Pt)Al coating with an in-situ formed α-W based diffusion barrier

A quasi-continuous α-W-based diffusion barrier (DB) forms in-situ between the (Ni,Pt)Al and the inter-diffusion zone by adding a Ni-W plating layer before the coating preparation. The oxidation behavior of the DB-contained coatings is compared with the normal (Ni,Pt)Al coating at 1100 ℃. The results indicate that the (Ni,Pt)Al with DB exhibits lower oxidation rate, slighter inter-diffusion and flatter surface. Additionally, martensite was observed in (Ni,Pt)Al-DB coatings, which contributed to lower surface rumpling for its higher stiffness and better resistance to creep. The mechanism of the DB and its effects on the oxidation performance of the (Ni,Pt)Al coating were discussed.

Effect of coatings on microstructure and oxidation behavior of the Ni-based single crystal superalloys containing different Ru contents

The element Ru in single crystal superalloy usually plays an important role in inhibiting the mutual diffusion between coating and substate. The MCrAlY coating and PtAl coating were prepared on the fourth and third generation single crystal superalloy, and the isothermal oxidation behaviors of the two superalloys and the two coatings were investigated in static laboratary air at 1200 °C. The oxidation kinetic curves showed that the mass gain of the coated samples was less than the alloys without coatings, which meant the coatings showed more excellent oxidation resistance at high temperature, and the oxidation resistance of the two coatings was slightly enhanced by the addition of Ru during the oxidation tests. Meanwhile, the interdiffusion of elements, such as Al in coating and refractory elements in substrate, was hindered by the addition of ruthenium. The size of γ' phase was also inhibited. As a result, the formation of interdiffusion zone and the precipitation of topological-close packed phase were suppressed, resulting that the DD91 showed more stable microstructure at elevated temperature than the DD90 during the oxidation process. The advantage of Ru in the alloys with coatings will be discussed in detail as well as the protective performance of coatings.

A scanning electron microscope-based comparative evaluation of resin tag formation at the resin dentin inter-diffusion zone

Aim of study was evaluate and compare the formation of the resin dentin interdiffusion zone (RDIZ) at the radicular dentin and resin interface after etching with phosphoric acid (PA) and glycolic acid (GA), using either light-cure and self-cured adhesives. Twenty extracted teeth were root canal treated. Post space preparation was done, and the samples were randomly divided into two main groups depending upon the etchant. Each group was further divided into two subgroups depending on the type of adhesive used. One group was etched with 37% PA (Prime® Dental Products PVT LTD, India) and the other with 35% GA (Glycolic 35 Peel, Rejsol, India). Etching was followed by the application of light-cured adhesive (3M ESPE Adper Single Bond, USA) or self-etch (3M ESPE Single Bond Universal, Germany). Fibre posts were then placed and after a coronal build-up, the teeth were sectioned longitudinally and observed under SEM. Statistical analysis: Data was analyzed by descriptive statistics as a percentage of resin tag density for all the groups. The Kruskall-Wallis test was applied for overall comparison and a Mann-Whitney U test for inter-group analysis. Resin tag density was found to be the highest in the coronal third followed by the middle third of radicular dentin and was the least in apical thirds for both groups. Resin tag density was similar for light cure and self-etch adhesives in the coronal, middle, and apical thirds of both groups. In conclusion this study concluded that GA could be thought of as a potential etchant for the radicular dentin.

WC–Co/316L stainless steel bonding enhancement by laser surface texturing and pressure-assisted sintering

WC–Co cutting tools are widely used in harsh conditions, but the brittleness of this material can limit their use. Joining steels to WC–Co can provide an alternative, by combining the toughness of steel with the high hardness and wear resistance of WC–Co. The creation of textures at the bonding interface is known to increase the adhesion between materials, through a mechanical interlocking effect and an increase in the contact area. In this sense, this work proposes the laser surface texturing of WC–Co green compacts with cross-hatched and circular micropatterns and subsequent pressure-assisted sintering of the textured and sintered WC–Co with 316L SS powder to improve the bonding between materials. Results showed that the bonding of the textured multi-material was successfully processed and an interdiffusion zone was formed at the bonding interface without the presence of detrimental compounds. The addition of textures showed a tendency to increase the shear bond strength, with the cross-hatched micropatterns generally showing a higher bonding strength than the circular micropatterns. This approach showed to have the potential to improve the bonding between materials, thus contributing to the development of novel multi-material WC–Co/316L stainless steel cutting tools with enhanced properties and performance.

Evolution of the F82H/Cr interface after solid-state diffusion bonding below Ac1 temperature: examination of microstructures and hardness

F82H steel and pure Cr metal were joined by solid-state diffusion bonding under high vacuum at various temperatures below Ac1 in the range 964 to 1072 K for 240 min. Bonding was successful at all temperatures and the diffusion behaviour, chemical composition and microstructure at the F82H/Cr interface and interdiffusion zone were characterised using SEM-EDS and TEM analysis. A hard, M23C6-rich interface layer formed on the Cr side of the joint due to diffusion of C from the F82H steel. The thickness of the M23C6-rich interface layer reduced with reducing temperature, from ∼1.1 µm when bonded at 1072 K, to ∼0.2 µm at 964 K. Cr diffusion into F82H was only observed at the highest temperature of 1072 K, with minor Cr enrichment detected at a depth of <1 µm into the F82H. The slow diffusion behaviour below Ac1 meant a lath martensite microstructure appears to have been retained throughout the F82H after bonding below the typical tempering temperature, and hardness testing of the F82H suggests no post-bonding heat treatment would be required. Simple models for the interface evolution of the F82H/Cr joint both above and below Ac1 are proposed, which can act as reference points for the further development of Cr-coated F82H and its likely behaviour in a range of fusion power plant operational scenarios.

Diffusion and Interdiffusion Study at Al- and O-Terminated Al2O3/AlSi12 Interface Using Molecular Dynamics Simulations.

The equivalent characteristics of the materials' interfaces are known to impact the overall mechanical properties of ceramic-metal composites significantly. One technological method that has been suggested is raising the temperature of the liquid metal to improve the weak wettability of ceramic particles with liquid metals. Therefore, as the first step, it is necessary to produce the diffusion zone at the interface by heating the system and maintaining it at a preset temperature to develop the cohesive zone model of the interface using mode I and mode II fracture tests. This study uses the molecular dynamics method to study the interdiffusion at the interface of α-Al2O3/AlSi12. The hexagonal crystal structure of aluminum oxide with the Al- and O-terminated interfaces with AlSi12 are considered. A single diffusion couple is used for each system to determine the average main and cross ternary interdiffusion coefficients. In addition, the effect of temperature and the termination type on the interdiffusion coefficients is examined. The results demonstrate that the thickness of the interdiffusion zone is proportional to the annealing temperature and time, and Al- and O-terminated interfaces exhibit similar interdiffusion properties.

Effect of NaCl and Na2SO4 on Low Temperature Corrosion of Vapour- and Pack-Aluminide Coated Single Crystal Turbine Blade Alloys CMSX-4 and RR3010

The current work presents a systematic study of two alloy compositions (RR3010 and CMSX-4) and two types of coatings: inward grown (pack) and outward grown (vapour) deposited aluminides, exposed to 98Na2SO4–2NaCl mixture. Grit blasting was used on some of the samples, prior to coating, to mimic in-service procedures and remove oxides from the surface prior to coating. Two-point bend tests were then performed on the coated samples, with and without applied salt at 550 °C for 100 hours. Samples were pre-strained at 0.6 pct strain to deliberately pre-crack the coating and then strained at 0.3 pct for the heat treatment. Exposure to 98Na2SO4–2NaCl under applied stress of vapour-aluminide coated samples of both alloys, revealed significant coating damage in the form of secondary cracks in the intermetallic-rich inter-diffusion zone, although only CMSX-4 exhibited cracks propagating further into the bulk alloy while RR3010 proved more resistant. The pack-aluminide coating proved more protective for both alloys, with cracks propagating only into the coating and never into the underlying alloy. In addition, grit blasting proved beneficial in reducing spallation and cracking for both types of coating. The findings were used to propose a mechanism based on thermodynamic reactions, to explain the crack width changes through the formation of volatile AlCl3 in the cracks.

Inhibiting effect of Ni/Re diffusion barrier on the interdiffusion between Ni-based coating and titanium alloys

A Ni/Re layer was electroplated as a diffusion barrier between the Ni coating and TC4 substrate. Isothermal diffusion treatments for the specimens with or without diffusion barriers were conducted at 600 ℃ at different times. Besides, the interdiffusion behaviors and the growth of the intermetallic layers were investigated. Results showed that the Ni/Re layer played a superior barrier effect, which inhibited the interdiffusion and retarded the formation of the interdiffusion zone. Moreover, the relationship between the thickness of the interdiffusion zone and the annealing time conformed to the parabolic law, and the square of the thickness of the intermetallic layer was proportional to the annealing time. Besides, the inhibiting mechanism of the Ni/Re diffusion barrier was discussed in detail.

Metallurgical aspect of a joint made of Inconel 718 and CuCrZr brazed with Ag-Cu eutectic filler

The realization of bimetallic structures is one of the major challenges of manufacturing industry, to this aim different technologies are employed, among these vacuum brazing presents some advantages: this technology, in fact, is relatively easy to use and the relative low temperature and low process time employed, avoid the formation of brittle intermetallics and thermally affected zones. An application of vacuum brazing technology is the realization of regenerative thrust chamber for rocket engines where cooling channels of CuCrZr are joined to Inconel 718 combustion chamber. In this work the critical metallurgical aspects occurring during brazing of Inconel 718 and CuCrZr using eutectic Ag-Cu filler are described in detail. These aspects include the formation of two distinct metallurgical zones inside the filler and an interdiffusion zone with Kirkendall porosity at the interface Inconel 718-Brazing Alloy. The analysis of fracture surface after tensile tests indicates that the interdiffusion zone is the weak point of the joint.

Effect of independent alloying of zirconium with bronze and niobium on superconducting properties of Nb3Sn in a Cu(Sn)/Nb system

The present work focuses on the effect of internal (niobium) and external (bronze) alloying of Zr on the superconducting properties of Nb3Sn in a Cu(Sn)/Nb system through the diffusion couple method. Alloying of Zr with either Cu(5.5 at.% Sn) or Nb enhances the critical current density (Jc) of the Nb3Sn superconductor phase developed at the interdiffusion zone of Cu(5.5 at.% Sn, 2 at.% Zr)/Nb and Cu(5.5 at.% Sn)/Nb(2 at.% Zr). Enhancement of Jc of Zr-alloyed Nb3Sn has been attributed to an increment in grain boundary fraction for Nb3Sn. Dew Hughes model provided an insight into the pinning mechanisms responsible for enhancement of Jc. Strengthening of pinning forces of Nb3Sn with internal alloying of Zr might have originated because of the nanometer-sized β-(Nb, Zr) second-phase developed within the Nb3Sn phase matrix. No change in critical temperature for Zr-alloyed Nb3Sn makes Zr a suitable alloying element for applications.

Cyclic oxidation behavior of Pt modified NiCoCrAlYHfZr + AlNiY coating on a Ni-based single crystal superalloy

In this study, the NiCoCrAlY + AlNiY, NiCoCrAlYHfZr + AlNiY and Pt modified NiCoCrAlYHfZr + AlNiY coatings are prepared by combining arc ion plating (AIP), electroplating Pt and annealing treatment. All the coatings are composed of three different zones including an outer layer and an inner layer as well as an interdiffusion zone (IDZ), therein, the outer layer consists of β-NiAl phase with dispersed α-Cr phase and the inner layer is composed of NiCoCr-rich phase with dispersed β-NiAl phase. In addition, an Y-rich belt is formed between the outer layer and the inner layer. The cyclic oxidation behaviors of the three coatings at 1100 °C are investigated. Results indicate that Pt and Y-rich belt exhibit synergistic effect on preventing the interdiffusion between coating and substrate, thus a thinner secondary reaction zone (SRZ) forms in Pt modified NiCoCrAlYHfZr + AlNiY coating. The evolution processes of Y-rich belts in the three coatings are also discussed. Besides, a lower oxidation rate and enhanced oxide scale adherence are achieved in Pt modified NiCoCrAlYHfZr + AlNiY coating, the enhanced oxidation performance is mainly attributed to the co-segregation of Pt-Hf-Zr-Y at oxide scale grain boundaries and the synergistic effect of Pt-Hf-Zr-Y on suppressing interfacial voids growth.

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.

Tuning the secondary reaction zone between PtAl coating and nickel based single crystal superalloy during high-temperature oxidation through regulating aluminizing time

Microstructure degradation caused by interdiffusion between coating and superalloy is an important factor affecting the performance of thermal barrier coatings. Tuning the interdiffusion microstructure of PtAl Coatings/Superalloys interface is the key to preparing high performance thermal barrier coatings. In this paper, two β-(Ni, Pt)Al coatings with different compositions and thicknesses were first deposited on the same nickel-based single-crystal superalloy by regulating the aluminizing time. After the isothermal oxidation at 1100 °C, a typical two-layer structure forms in the two different coating/superalloy specimens but with different interdiffusion microstructures. It was found that a noticeable secondary reaction zone (SRZ) with topologically close-packed (TCP) precipitates develop in the specimen with 6 h aluminizing after oxidation for 36 h and its thickness continuously increase. By contrast, no SRZ forms in the specimen with 4.5 h aluminizing after oxidation for even 100 h, but only the microstructure transformation of the interdiffusion zone (IDZ) occurred. That is mainly due to the existence of an incomplete transformed sublayer in the as-prepared specimen with a short aluminizing time, which may affect the subsequent interdiffusion of Al, Ni, and refractory elements. It is highly expected that regulating the aluminizing time is an effective strategy to tune the interdiffusion structure between coating and substrate, which should be helpful for designing the coating/substrate system with better performance.

Preliminary investigation of Cr-coated F82H: Evolution of microstructure and mechanical properties at the F82H/Cr interface during solid-state diffusion bonding above Ac1 temperature

Solid-state diffusion bonding was employed to join F82H steel and pure Cr metal under high vacuum at various temperatures above Ac1 in the range 1114 to 1323 K for 60 min, and at 1323 K for 120 min. After successful bonding at all temperatures, the F82H/Cr interface and interdiffusion zone were characterised using SEM-EDS, TEM and EBSD analysis, with respect to diffusion behaviour, chemical composition and microstructure. A thin interface layer formed on the Cr side of the joint, which decreased in thickness with decreasing bonding temperature, and was rich in M23C6 with mixed columnar and particulate nature. The depth of Cr diffusion into F82H decreased with decreasing bonding temperature. At temperatures ≥1231 K a layer of ferrite grains formed in the F82H region adjacent to the interface, due to the combined stabilising effect of enhanced Cr concentration and depleted C. At the lowest bonding temperature of 1114 K, a lath martensite microstructure was retained throughout the F82H due to a significantly lower extent of Cr and C diffusion. The diffusion coefficient of Cr in F82H was determined at all temperatures examined, and the activation energy of Cr diffusion in F82H >Ac1 was approximated as 225 KJ mol−1. Finally, hardness testing of the interface and interdiffusion zone suggests the F82H properties were retained after bonding at the lowest temperature of 1114 K, however at higher temperatures the newly formed ferrite region was softer. Further research is required to understand the impact of the hard M23C6-rich interface layer on mechanical properties of the joint, and whether microstructural change can be minimised, or even eliminated, below the Ac1 temperature.

Effect of coating degradation on the hot corrosion behaviour of directionally solidified superalloy

The effect of coating degradation on the hot corrosion performance of coated alloys was investigated in Na2SO4/NaCl (75:25, wt./wt.) salt at 900 °C. Degraded coatings were obtained by thermal exposure before the hot corrosion test. The results indicate that when the β-NiAl phases within the coating were completely depleted, the hot corrosion process was delayed due to the Al-rich interdiffusion zone (IDZ) formed after the 900 °C thermal exposure to provide Al for the healing of the Al2O3 layer. Nevertheless, the Cr-rich IDZ formed after 1000 °C thermal exposure failed to repair the Al2O3 layer, causing the alloy to corrode aggressively even though Cr has been substituted for Al to participate in the corrosion process.

Failure mechanism and interfacial diffusion behavior of Ru-doped NiAlHf coatings at 1200 °C

Ru-doped NiAlHf coatings were deposited on Ni-based single crystal substrate by arc ion plating technology. The failure mechanism and interfacial diffusion behavior were comparatively investigated with NiAlHf coating using scanning electron microscopy, electron probe micro-analyzer, and transmission electron microscopy. The results indicated that microstructure evolution of oxide scale induced by element diffusion process significantly affected oxidation resistance of NiAlHf/Ru coatings, resulting in formation of cracks and voids, thereby accelerating failure process. The precipitates in interdiffusion zone and secondary reaction zone of the substrate initiated by interfacial element diffusion were P phase and σ phase, respectively. And the discrepancy in content was elucidated from the perspective of thermodynamics and kinetics. Besides, microstructural evolution between NiAlHf/Ru coatings and substrate was also deliberated. The research could not only provide profound understanding of NiAlHf/Ru coatings failure mechanism, but also had significant guidance for suppressing precipitation of topological close-packed phases and facilitating development of single crystal Ni-based superalloys.

Synergistic effect of Pd+Rh on the microstructure and oxidation resistance of aluminide coatings

The Pd+Rh modified aluminide coatings were deposited on nickel and CMSX-4 nickel superalloy. The Pd layer (2.5 ?m thick) and the subsequent Rh layer (0.5 ?m thick) were electroplated on both nickel and CMSX-4. The aluminization of the substrates with Pd+Rh layers was carried out using the CVD method. Two zones (outer and interdiffusing) were observed on both coatings. The ?-NiAl phase doped in palladium was formed in the outer zones and ?-NiAl phase doped with palladium and rhodium was formed at the boundary between the outer and interdiffusion zones of both coatings. The ??- Ni3Al phase and ?-Co7Mo6 precipitates in the ?-NiAl matrix were found in the interdiffusion zone on nickel and CMSX-4 superalloy respectively. The simultaneous use of Pd and Rh in the aluminide coating slowed down their oxidation rate. Moreover, Pd+Rh co-doping is more efficient than Pd+Hf in reducing the oxidation rate of aluminide coating on CMSX-4 superalloy.

Effect of Pt on diffusion-controlled growth characteristics of interdiffusion zone between CM247LC superalloy and Ni(Pt)Al bond coat

Effect of Pt on diffusion-controlled growth characteristics of interdiffusion zone between CM247LC superalloy and Ni(Pt)Al bond coat

The Oxidation Properties of a NiCrAlY Coating Fabricated by Arc Ion Plating

The microstructures, phase compositions, and high-temperature oxidation behavior of a NiCrAlY coating fabricated by arc ion plating were investigated by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), atomic force microscope (AFM), and X-ray diffractometer (XRD). The results indicate that the NiCrAlY coating was covered by a protective Al2O3 scale with excellent oxidation resistance after oxidation at 1050 °C for 100 h; the β phase rich in Al in the as-deposited coating was transformed into a γ/γ’ phase; the interdiffusion zone (IDZ), secondary reaction zone (SRZ), and needle-like TCP phases were detected in the superalloy substrate beneath the coating.

Effects of interdiffusion in nickel coated AISI 441 steel

Ferritic steel AISI 441, electroplated with nickel, is explored for the use as interconnects in solid oxide cell stacks. High-temperature oxidation tests are performed in air, and samples are investigated using scanning electron microscopy, energy-dispersive x-ray spectroscopy, and electron backscatter diffraction. Results revealed in-depth diffusion of nickel that promotes austenite formation during typical solid oxide cell operating temperatures accompanied by chromium depletion, grain refinement, and an enhanced depletion of Laves phase in the surface-near region of the steel. Effects of a formed interdiffusion zone on the protective oxide scale are discussed, considering the role of diffusion along grain boundaries and across the scale/alloy interface. The interdiffusion zone alters the morphology and continuity of Si-rich oxide that forms in this steel, and an underlying mechanism is suggested. Associated implications on the expected performance of nickel coated AISI 441 as interconnects for solid oxide cell stacks are postulated: Although no corrosion or scale spallation is observed and a good contact to the simulated oxygen electrode is maintained, there are signs of limited oxidation resistance and scale adhesion, which potentially affect lifetime and robustness of solid oxide cell stacks during (cyclic) oxidation of longer exposure than tested here.