Ni-based Alloys Research Articles

Effect of SO2 on corrosion behaviour of Ni-base alloys in a simulated combustion environment

Alloys of Ni-25Cr-(2Mn-1Si) under deposits of sulphate or ash + sulphate were exposed to a wet CO2 gas with or without 0.5 vol% SO2 at 650 °C for 300 h. Without SO2, multi-layered reaction products formed. Under sulphate, they were external NiO, inner NiCr spinel + Cr2O3 band, internal oxidation zone and internal CrxS precipitates. Under ash + sulphate, they were external NiO + Ni above the internal oxidation zone. Introducing SO2 in the gas promoted alloy passivation, forming thin chromia scales under both deposits. Alloying with Mn and Si produced only minor improvements. These effects are examined in light of gas-deposit-alloy interactions.

Machine learning-enabled prediction of high-temperature oxidation resistance for Ni-based alloys

A machine learning (ML) model was developed to predict the oxidation resistance, with the natural logarithm of the parabolic rate constant (lnkp) as the output. Five algorithms were used to training the model, revealing that backpropagation neural network and gradient boosting exhibited superior performance with an R2 of 0.908 and 0.907. The trained models were employed to predict lnkp for changes in temperature, time, and elemental compositions. At last, promising areas with slower oxidation kinetics in typical commercial alloys were predicted under the guidance of the present ML methods.

Effect of Hydrogen Charging on the Mechanical Properties of High-Strength Copper-Base Alloys, Austenitic Stainless Steel AISI 321, Inconel 625 and Ferritic Steel 1.4511

Hydrogen embrittlement (HE) poses the risk of premature failure for many metals, especially high-strength steels. Due to the utilization of hydrogen as an environmentally friendly energy source, efforts are made to improve the resistance to HE at elevated pressures and temperatures. In addition, applications in hydrogen environments might require specific material properties in terms of thermal and electrical conductivity, magnetic properties as well as corrosion resistance. In the present study, three high-strength Cu-base alloys (Alloy 25, PerforMet® and ToughMet® 3) as well as austenitic stainless AISI 321, Ni-base alloy IN 625 and ferritic steel 1.4511 are charged in pressurized hydrogen and subsequently tested by means of Slow Strain Rate Testing (SSRT). The results show that high-strength Cu-base alloys exhibit a great resistance to HE and could prove to be suitable for materials for a variety of hydrogen applications with rough conditions such as high pressure, elevated temperature and corrosive environments.

Role of Cr addition in Ni-based interlayer on strengthening titanium and steel dissimilar bimetallic structures enabled by directed energy deposition with laser beam

For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam (DED-LB), pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work. Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically. The distribution of intermetallic compounds (IMCs) such as β-Ti, Ti2Ni, TiNiFe0.2, Ti2Ni3Si and TiB2 in joints was revealed. The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely. Notably, additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus, leading to fewer IMCs in joints. As a result, both bonding strength and toughness of joints were remarkably improved. The findings emphasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.

Research on the Effect Mechanism of Re on Interface Dislocation Networks of Ni-Based Single Crystal Alloys.

The effect of interface dislocation networks on the mechanical properties of new Ni-based single crystal alloys containing Rhenium (Re) is very large. Because the interface dislocations are microscopic in the nano-scale range, this has not been investigated, and it is very difficult to prepare new Ni-based single crystal alloys containing Re. Therefore, six kinds of new Ni-based single crystal alloys containing Re were prepared, and the hardness tests and nonlinear ultrasonic lamb wave tests were performed on the samples. It was found that the density of interface dislocation networks increases with the increase in the content of Re, which improves the blocking ability of matrix phase dislocation cutting into precipitated phase and enhances the inhibition of dislocation movement. The nonlinear ultrasonic lamb wave tests showed that the materials exhibit better mechanical properties when the density of the interface dislocation networks increases. Meanwhile, a new molecular dynamics model which is closer to the real state of an Ni-based single crystal alloy was constructed to reveal the evolution mechanism of interface dislocation networks. The results showed that the potential energy of Re atoms at the interface is the lowest, which affects the reduction of the potential energy of other atoms at the interface, and thus the stability of the model is improved. In addition, according to the change in the total length of dislocation loops in the model system, with the increase in the content of Re atoms, the inhibition of dislocation movement by dislocation networks at the interface is strengthened.

Characterization of the interfacial structure and fracture behavior of in situ synthesized ceramics to reinforce Ni-based composite coatings

This work used the in-situ synthesis of molten-state nitride ceramic phase-reinforced Ni-based alloy coatings, aiming to improve the phase-interface bonding through the interdependent co-solidification between molten droplets. The XRD was used to analyze the physical phases of the composite coatings. The microstructure and phase-interface structure were characterized in detail by combining SEM, TEM, HRTEM, FFT, and SAED techniques. Microhardness tester and microforce microhardness tester were employed to measure the surface hardness and elastic modulus of the composite coatings. The fracture behavior of the composite coatings was characterized by observing the fracture morphology of the coatings using SEM combined with the EDS technique. It was found that the formation mechanisms of interfacial misfit dislocation assistance, lattice distortion, aggregation of stacking faults, and specific growth orientation between the γ-Ni matrix phase and each ceramic phase in NiCrBSi-TiCrN composite coatings improved the lattice matching between the two-phase interface, which resulted in the formation of atomically corresponding coherent lattice relations and stepped interfacial semi-coherent lattice relations, and enhanced the degree of phase-interface bonding. On this basis, the composite coatings with high Cr content further inhibited the expansion of interphase penetration cracks due to the existence of Cr-rich zones at the phase interface, thus exhibiting high fracture toughness. This work provides new opinions on the improvement of phase-interface bonding and composition design of Ni-based composite coatings.

Design of Ni-based amorphous alloy corrosion-resistant to high temperature hydrochloric acid

A corrosion-resistant Ni-based amorphous alloy was developed by combining the Inoue’s three principles and the dissolution-ionization-diffusion-deposition (DIDD) model. The calculations showed that a rapid localized increase of pH value at the metal-solution (M-S) interface is due to the dissolution of both Ta and Nb in the Ni-Nb-Ta-Fe-P alloy system and is beneficial to the formation of two-layered structure of corrosion inhibition in the passivation film, in which the dense Ta/Nb mixed oxides formed initially in the passivation film while the extra mixed-phosphates appeared in the inner layer neighboring the substrate. The 140 d immersion experiment in the 80 ℃/32 wt% hydrochloric acid and the electrochemical testing showed that the (Ni57.5Nb19.5P8Fe14.9)87Ta13 amorphous alloy had the lowest corrosion rate together with the best resistance to the metastable pitting. The structure of passivation film was mainly composed of dense Ta-Nb mixed oxides with an inner phosphate layer, which was consistent with the theoretical calculations. The work indicated that the DIDD model could be useful in designing Ni-based amorphous alloys for extremely corrosive service environments.

Effect of Alloying Elements on the High-Temperature Yielding Behavior of Multicomponent γ'-L12 Alloys.

The exceptional mechanical properties of Ni-based high entropy alloys are due to the presence of ordered L12 (γ') precipitates embedded within a disordered matrix phase. While the strengthening contribution of the γ' phase is generally accepted, there is no consensus on the precise contribution of the individual strengthening mechanisms to the overall strength. In addition, changes in alloy composition influence several different mechanisms, making the assessment of alloying conditions complex. Multicomponent L12-ordered single-phase alloys were systematically developed with the aid of CALPHAD thermodynamic calculations. The alloying elements Co, Cr, Ti, and Nb were chosen to complexify the Ni3Al structure. The existence of the γ' single phase was validated by microstructure characterization and phase identification. A high-temperature compression test from 500 °C to 1000 °C revealed a positive temperature dependence of strength before reaching the peak strength in the studied alloys NiCoCrAl, NiCoCrAlTi, and NiCoCrAlNb. Ti and Nb alloying addition significantly enhanced the high-temperature yield strengths before the peak temperature. The yield strength was modeled by summing the individual effects of solid solution strengthening, grain boundary strengthening, order strengthening, and cross-slip-induced strengthening. Cross-slip-induced strengthening was shown to be the key contributor to the high-temperature strength enhancement.

The effect of hot isostatic pressing pressure level and solution annealing cooling rate on CM247 LC nickel-based superalloy processed by laser-based powder bed fusion

AbstractIn the present work, CM247 LC samples produced by laser-based powder bed fusion (PBF-LB) were heat treated inside a hot isostatic pressing (HIP) furnace (HIP quench treatment) at 1260 °C for 3 h to combine the solution annealing with the elimination of defects of the additively manufactured parts. In particular, the effects of different applied pressures (50–170 MPa) and cooling rates (from 162 to 2450 °C/min) on the final densification, grain coarsening, and γ’ precipitation were studied. The results were also compared to a sample heat treated in a low-pressure furnace and gas-quenched at 195 °C/min. The study revealed that the applied pressure has a negligible effect on densification, grain coarsening, and the size and shape of γ’, which is always irregular after solution annealing, independently from the cooling rate. For this reason, first aging was subsequently applied at 1080 °C for 4 h to HIP-quenched samples, revealing that this step of treatment is effectively responsible for the final cubic shape of γ’, even if a starting irregular morphology is considered. Finally, additional samples were heat treated in an air furnace and air cooled to room temperature prior to the HIP quench; this procedure allowed assessing the solutioning effectiveness of the HIP quench with coarse precipitates typical of conventional processing (e.g., investment casting). Overall, this study underscores the efficacy of the HIP quench in enhancing microstructural attributes and mitigating defects, providing valuable insights for enhancing the properties of challenging Ni-based alloys fabricated through additive manufacturing techniques.

The influence of microstructural heterogeneities on high-temperature mechanical properties of additively manufactured γ'-forming Ni-based alloys

AbstractAdditive manufacturing (AM) of metallic materials yields distinctive hierarchical and heterogeneous microstructures owing to the complex thermal conditions during the build-up process. Consequently, the knowledge gained from creep properties of conventionally manufactured (CM) Ni-based alloys cannot be directly applied to AM-processed alloys. Furthermore, insufficient creep life has posed a significant challenge in the development of Ni-based superalloys fabricated by laser powder bed fusion (LPBF), one of the most important AM techniques. Nevertheless, limited research has been conducted to understand their creep behavior due to the time-consuming nature of creep testing and extended research cycles. This study delves into investigating the creep behavior of an additively manufactured, precipitation-strengthened Ni-based alloy (NiCrAl) in comparison to its CM counterpart, focusing on the structure-property relationships. Constant-load creep tests were conducted at temperatures of 750 °C and 950 °C up to a maximum duration of nearly 1500 h. Although both the AM and CM states demonstrated high creep activation energy and creep exponents, indicative of a dislocation climb mechanism, the AM state demonstrated inferior creep life and ductility compared to the CM state for creep times below 500 h. To gain deeper insights into the underlying mechanisms, multi-scale microstructural characterization was performed to understand the effect of the AM-inherent microstructure. Overall, this study provides a comprehensive understanding of the creep behavior of Alloy 699XA after AM and CM processes, emphasizing the significance of AM-specific microstructural heterogeneities.

Understanding the high-temperature deformation behavior of additively manufactured γ'-forming Ni-based alloys by microstructure heterogeneities-integrated creep modelling

Additively manufactured (AM) alloys present unique and heterogeneous microstructures due to the complex, highly dynamic laser-material interactions. These AM-inherent heterogeneities impede the widespread adoption of AM components, necessitating a profound comprehension of their impact on mechanical properties. Despite extensive research on AM of Ni-based alloys, limited attention has been paid to their creep behavior due to the time-intensive nature of creep tests and the long research cycles. Moreover, experiments and conventional alloy-centric approaches to creep modelling are deemed insufficient in quantifying the effects of AM-specific heterogeneities on creep cavity acceleration and in incorporating the microstructural evolution during creep. To address this critical knowledge gap, a novel computational framework was developed within the structure-property paradigm to unravel the intricate mechanisms governing creep properties. A mechanistic creep model was formulated based on fundamental dislocation creep mechanisms, encompassing dislocation climb-glide motion controlled by γ' precipitates, grain-boundary-sliding (GBS) resistance resulting from M23C6 carbides, and the kinetics of cavity formation. The framework integrates the in situ nucleation, precipitation, and coarsening of γ' precipitates during creep by a precipitation model. The results revealed an excellent agreement in terms of γ' precipitate evolution, creep strain, and strain-rate evolution, the predicted creep life, and times to 1 % strain. By elucidating the intricate interplay between microstructural heterogeneities and creep behavior on the cavity nucleation and GBS mechanisms, the developed computational framework provided valuable insights for enhancing the performance of Ni-based alloys manufactured through AM.

A review of the microstructure and properties of superalloys regulated by magnetic field

Superalloys play a critical role in aerospace applications due to their exceptional mechanical properties at high temperatures. The application of magnetic fields to regulate superalloys presents novel avenues for optimizing microstructures, controlling solidification defects, and enhancing their high-temperature properties. This paper provides a comprehensive review of research findings on the influence of magnetic fields on the microstructure and properties of superalloys. It systematically elucidates the effects of different types and intensities of magnetic fields on alloy solidification. Moreover, this paper extensively explores the effects of various types of magnetic fields on the phase composition, microstructure, and properties of superalloys, including Ni-based and Co-based alloys, as well as high-entropy alloys. The underlying mechanisms behind the impact of magnetic fields on these alloy types are thoroughly analyzed. Finally, the last section offers a brief summary of the current development status and prospects of magnetic field-regulated superalloys.

Observation and Numerical Prediction of Concentration Distribution at Cast Coating Interface of Solid Pt, Ir, Re Using Liquid Ni-Based Alloys

Observation and Numerical Prediction of Concentration Distribution at Cast Coating Interface of Solid Pt, Ir, Re Using Liquid Ni-Based Alloys

Oxidation behaviour of NiSi–NiCr thin film thermocouples and antioxidation effect of SiNxOy film

NiSi–NiCr thin film thermocouples (TFTCs) have significant application value as contact temperature sensors in cutting temperature measurements owing to their fast response and negligible volume. However, due to the relatively high chemical activity of Ni-based alloys, high-temperature oxidation strongly affects the operational reliability of NiSi–NiCr TFTCs. In this respect, depositing an anti-oxidation coating onto the surface of NiSi–NiCr TFTCs is considered an effective way to protect them in high-temperature environments. In this study, NiSi and NiCr films were deposited on cemented carbides and annealed at 200 °C–600 °C in air. Scanning electron microscope, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, and four-probe resistivity tests were used to characterize the microstructure and resistivity of NiSi and NiCr film. Then SiNxOy films were deposited onto the NiSi and NiCr films and compared with uncoated samples after annealing at 600 °C. The effect of SiNxOy films on the thermal stability and thermoelectric output of NiSi–NiCr TFTCs was investigated. The results show that the NiSi film was partially oxidized at 200 °C and entirely oxidized when the temperature exceeded 400 °C. The completely oxidized NiSi films had evident defects and cracks, and the resistivity increased by a factor of over 1000. The NiCr film could not be completely oxidized at 600 °C, which is attributed to the formation of Cr2O3 as an external oxide barrier layer. Below 600 °C, SiNxOy films could effectively protect NiSi and NiCr films from oxidation. Thus, the addition of SiNxOy film increases the maximum temperature at which NiSi–NiCr TFTCs can be used.

Outstanding shape memory effect and thermal stability of Cu–Al–Ni-based high temperature shape memory alloys achieved by Gd and Mn doping

In this paper, the effects of Mn element and rare earth element Gd on the microstructure, thermal stability, mechanical properties and shape memory effect of polycrystalline Cu-12.0Al-4.0Ni and Cu-12.0Al-4.0Ni-1.5Mn-xGd high-temperature shape memory alloy were investigated. The results show that the Cu-12.0Al-4.0Ni alloy exhibits millimeter-sized grain, dual-phase structure with coexistence of 18R and 2H martensite and poor thermal stability. When the Mn and Gd element was added to Cu-12.0Al-4.0Ni alloys, the grain size can be refined by an order of magnitude, and the 2H martensite disappeared completely, accompanied by the formation of the AlCu4Gd phase, meanwhile, thermal stability is significantly improved. The grain refinement improves the mechanical properties and shape memory effect of Cu-12.0Al-4.0Ni-1.5Mn-xGd alloys. When x = 0.3, the compressive fracture stress, compressive fracture strain and recoverable strain can reach 969 MPa, 15 % and 8 %, respectively.

Microstructure and mechanical properties of in-situ nano TiC reinforced Ni-based alloy composites prepared by spark plasma sintering

Carbide dispersion reinforcing has been demonstrated to be an effective way of strengthening metal matrix composites. However, plagued by the nerve-wracking fact that the carbide particles tend to aggregate at the grain boundary of the metal matrix, grow up, and form an incoherent interface with it, their improvement in mechanical strength tends to be limited. In this study, spark plasma sintering (SPS) was used to prepare the bulk alloy Ni20Cr and its composites with different carbides including TiC, SiC, and Ti3SiC2. Plasma leads to discharge and elevates temperature at the interface to melt the Ni20Cr alloy particles locally. When cooled down, the alloy is heterogeneously solidified on the surface of the carbide and builds up a coherent interface with it. Owing to the decomposition of Ti3SiC2 during sintering, it completely transformed into nanosized TiC particles, which are engulfed by the outer melted layer of Ni20Cr and well dispersed within the alloy grains. In comparison to the Ni20Cr alloy, the composite with merely 4 wt% Ti3SiC2 gains over three times enhancement in yield strength to 879 MPa, while keeping a moderate high elongation of 17.8 %. Finite element analysis demonstrated that the combination of SPS and precursor MAX phase of Ti3SiC2, which results in the in-situ precipitation of coherent ultrafine TiC particles in alloy grains, plays the key role in getting a good balance between mechanical strength and ductility for the Ni20Cr matrix composites.

Effects of lattice misfit of γ/γ′ phases on hydrogen embrittlement behavior in Ni-based single crystal superalloy

The effect of γ/γ′ phase lattice misfit on hydrogen embrittlement (HE) behavior was fundamentally investigated by utilizing a Ni-based single crystal CMSX-4 superalloy with a simple microstructure that can exclude the H-trapping effects of grain boundary, c-vacancy, and misfit dislocation. Increasing isothermal aging time increased γ′ precipitate size while maintaining its volume fraction and a fully coherent interface. The magnitude of negative lattice misfit between the γ and γ′ phases increased from −0.08 to −0.22% according to γ′ precipitate coarsening, resulting in a well-developed tensile-strain field within the γ′ precipitate. The increased tensile-strain field enhanced activation energy for H-desorption in the γ′ precipitate from 31.9 to 35.1 kJ/mol. Therefore, H is preferentially distributed along the γ/γ′ interface within the γ′ precipitate even before deformation. H basically promotes the slip planarity through the H-enhanced localized plasticity (HELP) mechanism in Ni-based single crystal alloys, in which slip is the dominant deformation behavior. As the superalloy possesses a larger negative lattice misfit, H becomes trapped as diffusible-state at the tensile-strain field of the γ/γ′ interface, resulting in cuboidal brittle fracture along the {001} planes. In this process, the HELP mechanism facilitated H localization at the γ/γ′ interface. Thus, the HE behavior distinctly transitioned from HELP to an interaction between HELP and H-enhanced decohesion mechanisms (HEDE) with an increase in the magnitude of the lattice misfit. The HE behavior was investigated by correlating microstructural characterization, H-trapping behavior, and crystallographic fracture mechanism analysis.

Corrosion of Ni-based alloy coatings prepared by laser cladding in high-temperature chloride environment

Due to the complex incineration environment of waste incineration power generation boilers generates large amounts of acidic gases (such as Cl2 and HCl) and alkali metal chlorides (such as NaCl and KCl), leading to boiler corrosion failure. Herein, a new type of NiCrAlTi alloy coatings was deposited on 304 stainless steel surfaces by laser cladding technology. High-temperature corrosion experiments were then carried out at 650 °C for 64 h and the results were compared with those of traditional Inconel625 alloy coating. The high-temperature chloride corrosion mechanism and the corrosion resistance of alloy coatings were examined. The results revealed the decomposition of chlorides, such as HCl, NaCl, and KCl into Cl2 at high temperatures as the source of corrosion of high-temperature chlorides. The released C12 reacted with the metals present in the coating to form nonprotective metal chlorides. The low melting point and high vapor pressure of metal chlorides allowed their transition into a gaseous state to diffuse outward and oxidize into Cl2. In turn, the released Cl2 reacted with the metal to induce corrosion. During the corrosion process of NiCrAlTi alloy coating, a Cr depletion zone was induced, and a continuous Al2O3/TiO2/Cr2O3 three-layer protective film was formed on the coating surface, conducive to better alleviating the corrosion caused by the reaction between Cl2 passing through the film and the metal substrate. Under the conditions of this experiment, the corrosion resistance of NiCrAlTi alloy coating is 1.8 times that of the common material 304 stainless steel, and about 1.2 times that of Incon625 alloy coating. With the extension of the experiment, its corrosion resistance will be better. Overall, rich experimental data and theoretical guidance were provided for further research and development on high-temperature chloride corrosion-resistant alloys or coating materials for high-efficiency cost-effectiveness boilers.

Designing an ultrahigh-strength and ductile Ni-based alloy with a partially recrystallized structure

Designing an ultrahigh-strength and ductile Ni-based alloy with a partially recrystallized structure

The bifunctional low mismatch nano strengthening phase leads to a high strength-ductility W-Ta-Ni-Fe-Cu alloy

As a typical tungsten-based composite consisting of tungsten (W) particles and matrix phase, tungsten heavy alloys (WHAs) are extensively utilized in the military due to their exceptional strength and high density. However, the large grain size (>30 µm) of powder metallurgy liquid phase sintered (LPS) WHAs and the low strength of the matrix phase limit the further improvement of the alloy. In this work, high-density ultrafine WHAs were fabricated by two-step low-temperature sintering, and the density of the alloy reached 17 g/cm3 with an average W particle size of 7.81 µm. Additionally, the eutectic reaction between Ni and Ta was controlled to generate dispersed nano-Ni3Ta phases in situ in the matrix phase, further improving the strength of the alloy. Under the synergistic strengthening effect of fine-grain strengthening, dispersion strengthening, and solid solution strengthening, the average ultimate tensile strength of the alloy reached 1190.39 MPa. At the same time, the alloy maintained good elongation with a total elongation of 20.8 % due to the good co-grid interface orientation between the Ni3Ta phase and the matrix phase. This study provides a new idea for developing high-strength WHAs and has a guiding significance for developing Ni-based alloys.