NiAl Phase Research Articles

Effect of Mn on eutectic phase equilibria in Al-rich Al-Ce-Ni alloys

Microstructural analysis of additively manufactured (AM) Al-Ce-Ni-Mn alloys has identified phases not predicted from existing ternary liquidus projections in the Al-Ce-Ni system. Because the rapid cooling rate of AM is orders of magnitude above that of traditional casting, it is unclear if these additional phases arose from the non-equilibrium processing conditions of AM, a drastic shift in phase stability in the system due to the addition of 1 wt% Mn, or some combination of these two influences. The phases and microstructure of cast samples of Al-Ce-Ni and Al-Ce-Ni-Mn alloys were characterized for several annealing conditions which revealed the equilibrium phases at different temperatures. Phase analysis confirmed that minute levels of Mn substituted for Ni in the system drastically shifts the liquidus projection in the Al-rich corner of the ternary phase diagram such that the eutectic Al3Ni phase is suppressed in favor of the Al23Ni6(Ce,Mn)4 phase. Further addition of Mn promotes the formation of Al20Mn2Ce and Al10Mn2Ce phases. The phase analysis data was then used to improve the CALPHAD modeling of the liquidus projection and isothermal sections for the Al-rich Al-Ce-Ni-Mn quaternary system. Thermodynamic modeling and experimental analysis on phases in the AM sample of Al-Ce-Ni with Mn confirmed that the phases present are consistent with Mn-containing Al-Ce-Ni cast samples. This investigation demonstrates the potential for using secondary alloying elements to drastically alter phase stability and microstructure in alloy systems.

Post-deposition annealing effects on microstructure, mechanical and tribological properties of AlCrN films

The post-deposition annealing of AlCrN films was conducted in an atmospheric environment for 2 h, with annealing temperatures ranging from 25 to 1000 °C. The microstructure, mechanical, and tribological properties were systematically investigated as a function of the annealing temperature. The results show that the AlN phase in the film began to oxidize at 600 °C, resulting in deterioration of the film's toughness and resistance to plastic deformation. Subsequently, the wear resistance also deteriorated, with the wear rate being nearly 16 times that of the as-deposited film. At 800 °C, the AlN obviously underwent oxidization to form Al2O3. The high temperature annealing promoted the coalescence of Cr on the film surface and caused a reaction with the Al2O3 to form a replacement solid solution of Cr–O–Al, thereby improving the mechanical properties of the annealed films. At the same time, the tribological properties of the films were not significantly deteriorated by annealing at temperatures other than 600 °C, similar to those of the films without any annealing treatment.

Hydrogen-enhanced decohesion mechanism of the Ni-Ni3X interfaces in precipitation-hardened Ni-based alloys

Ni and its alloys are susceptible to hydrogen embrittlement. In this study, we investigate the phenomenon of hydrogen-enhanced decohesion at inter-phase interfaces in precipitation-hardened Ni-based alloys using a systematic first-principles approach. We demonstrate that hydrogen atoms primarily prefer to localize at the Ni3Al phase in the Ni/Ni3Al interface, while they tend to be trapped by Ni in the Ni/Ni3Nb interface. Our findings reveal that hydrogen induces inter-phase embrittlement in both the Ni/Ni3Al and Ni/Ni3Nb interfaces. Moreover, we show that the hydrogen-enhanced decohesion at these interfaces is influenced by various factors such as hydrogen pressure, hydrogen content, temperature, and strain. Finally, we discuss in detail the hydrogen-enhanced decohesion mechanisms at the Ni/Ni3Al and Ni/Ni3Nb interfaces, including their electronic structures, energy landscape of hydrogen at trapping sites, and schematics of crack propagation.

Influence of Ni Contents on Microstructure and Mechanical Performance of AlSi10Mg Alloy by Selective Laser Melting.

To improve the tensile strength and wear resistance of AlSi10Mg alloys, a novel in situ synthesis method of selective laser melting (SLM) was used to fabricate the Ni-reinforced AlSi10Mg samples. The eutectic Si networks formed around the α-Al crystals by diffusion and transportation via Marangoni convection in the SLM process. Moreover, the XRD and TEM results verified that the Al3Ni nanoparticles were created by the in situ reaction of the Ni and aluminum matrix in the Ni/AlSi10Mg samples. Therefore, the microstructure of the Ni-containing alloys was constituted by the α-Al + Si network + Al3Ni phases. The dislocations accumulated at the continuous Si network boundaries and cannot transmit across the dislocation walls inside the Si network. SEM results revealed that the continuity and size of eutectic Si networks can be tailored by adjusting the Ni contents. Furthermore, the Al matrix also benefited from the Al3Ni nanoparticles against the dislocation movement due to their excellent interfacial bonding. The 3Ni-AlSi10Mg sample exhibited high mechanical properties due to the continuous Si networks and Al3Ni nanoparticles. The tensile strength, elongation, Vickers hardness, friction coefficient, and wear volumes of the 3Ni-AlSi10Mg samples were 401.15 ± 7.97 MPa, 6.23 ± 0.252%, 144.06 ± 0.81 HV, 0.608, 0.11 mm3, respectively, which outperformed the pure AlSi10Mg samples (372.05 ± 1.64 MPa, 5.84 ± 0.269%, 123.22 ± 1.18 HV, 0.66, and 0.135 mm3).

Microstructure reconfiguration of duplex high entropy alloy/BCC ferrite bimetallic interface under electropulsing

Additive manufacturing of multi-materials is one of the effective pathways to enrich the performance diversity of metallic materials, and it is generally acknowledged that the bimetallic interface is the weakest position because of stress concentration and compositional mutation. Here it was found that the stress concentration along the BCC + FCC duplex Al-Co-Cr-Fe-Ni high entropy alloy/BCC ferrite bimetallic interface can be significantly released by electropulsing, and the compositional mutation region was also reasonably widened from 2 μm to 10 μm. Meanwhile, the neighboring grains rotated to form High Angle Grain Boundaries, which can reduce the Gibbs free energy of the system. Additionally, the nano-scale second phase including spherical BCC NiAlFe and rod-like B2 NiAl particles was generated at the interface. The BCC NiAlFe phase is coherent with the matrix and has numerous crystal defects inside the precipitates, whereas the B2 NiAl phase has a stable structure without stress fluctuation because of its greater maturation degree.

Study on the relationship between TCP phase and AlN phase in a fourth-generation single-crystal superalloy

Study on the relationship between TCP phase and AlN phase in a fourth-generation single-crystal superalloy

Thermal-induced decomposition and mechanical properties of AlN/CrN superlattice coating

Here, the thermal-induced decomposition and mechanical properties of AlN/CrN superlattice coating with modulation period of ∼8 nm are investigated in detail. Introduction of CrN template layers stabilizes the cubic growth of AlN layers, where the coherent AlN/CrN coating exhibits the higher hardness value of ∼24.1 GPa than CrN (∼16.9 GPa) and AlN (∼18.5 GPa) monolithic coatings. After thermal exposure, the AlN/CrN coating decomposes into stable body-centered cubic Cr and wurtzite AlN via intermediate phases of hexagonal Cr2N and cubic AlN. Especially, the formation of metastable cubic AlN is observed due to the destruction of coherent interfaces. Meanwhile, the thermal load leads to the grain deformation, which causes the change of AlN and CrN sublayers from the crossover to pinch-off to finally dissociation. The driving force of grain deformation mainly arises from the N-loss of CrN sublayers and the high-density stacking faults formation of AlN sublayers. Furthermore, the occurrence of stacking faults and h-Cr2N phase offset the softening effect caused by the thermal decomposition. Correspondingly, the hardness almost remains unchanged between 900 and 1100 °C.

Optimizing the electrochemical corrosion performance of laser cladded Ni-based single crystal superalloy via manipulation of γ′(Ni3Al) phase

The morphology of γ′(Ni3Al) phase is essential for the performance of laser additive manufacturing repaired Ni-based single crystal superalloy, thereby, it is of crucial significance to manipulate γ′ phase in order to optimize the corrosion performance of laser cladded component. In this research, the morphology of γ′ phase is tuned via different heat treatments. The microstructure and corrosion behaviors of laser repaired superalloy are analyzed by electron microscopy and electrochemical measurements. It is found that the electrochemical corrosion resistance of as-deposited part is superior than that of the substrate, and the dominant morphology of γ′ phase changes from spherical shape to cuboidal shape and to rafted morphology with increasing heat treatment temperature. The corrosion resistance peaks at 1050 °C, attributing to the combined effects of decreased volume fraction of γ′ phase and favored distribution of Cr, W, and Al. Our results offer a practical means for the post-repair heat treatment of single crystal turbine blades.

Al-Al3Ni In Situ Composite Formation by Wire-Feed Electron-Beam Additive Manufacturing.

The regularities of microstructure formation in samples of multiphase composites obtained by additive electron beam manufacturing on the basis of aluminum alloy ER4043 and nickel superalloy Udimet-500 have been studied. The results of the structure study show that a multicomponent structure is formed in the samples with the presence of Cr23C6 carbides, solid solutions based on aluminum -Al or silicon -Si, eutectics along the boundaries of dendrites, intermetallic phases Al3Ni, AlNi3, Al75Co22Ni3, and Al5Co, as well as carbides of complex composition AlCCr, Al8SiC7, of a different morphology. The formation of a number of intermetallic phases present in local areas of the samples was also distinguished. A large amount of solid phases leads to the formation of a material with high hardness and low ductility. The fracture of composite specimens under tension and compression is brittle, without revealing the stage of plastic flow. Tensile strength values are significantly reduced from the initial 142-164 MPa to 55-123 MPa. In compression, the tensile strength values increase to 490-570 MPa and 905-1200 MPa with the introduction of 5% and 10% nickel superalloy, respectively. An increase in the hardness and compressive strength of the surface layers results in an increase in the wear resistance of the specimens and a decrease in the coefficient of friction.

Corrosion Behavior of Alumina-Forming Austenitic Steel in Supercritical Carbon Dioxide Conditions: Effects of Nb Content and Temperature.

The corrosion behavior of alumina-forming austenitic (AFA) stainless steels with different Nb additions in a supercritical carbon dioxide environment at 500 °C, 600 °C, and 20 MPa was investigated. The steels with low Nb content were found to have a novel structure with a double oxide as an outer Cr2O3 oxide film and an inner Al2O3 oxide layer with discontinuous Fe-rich spinels on the outer surface and a transition layer consisting of Cr spinels and γ'-Ni3Al phases randomly distributed under the oxide layer. Oxidation resistance was improved by accelerating diffusion through refined grain boundaries after the addition of 0.6 wt.% Nb. However, the corrosion resistance decreased significantly at higher Nb content due to the formation of continuous thick outer Fe-rich nodules on the surface and an internal oxide zone, and Fe2(Mo, Nb) laves phases were also detected, which prevented the outward diffusion of Al ions and promoted the formation of cracks within the oxide layer, resulting in unfavorable effects on oxidation. After exposure at 500 °C, fewer spinels and thinner oxide scales were found. The specific mechanism was discussed.

Low-Lattice Thermal Conductivity in Zr-Doped Ti2NiCoSnSb Thermoelectric Double Half-Heusler Alloys

The effect of doping on the thermoelectric properties of Half-Heusler (HH) high-entropy alloy (HEA) Ti2NiCoSnSb was studied. Lower thermal conductivity was observed with increased Sb doping. Mass scattering by heavy (Ta, Zr) and light (Al) dopants was studied to further lower the thermal conductivity. Dopants at the level of up to 50% at the Ti site were studied. A high HH phase content was obtained in the Zr-doped samples, and a low-lattice thermal conductivity of 1.9 W/(m·K) was observed. This value is one of the lowest reported lattice thermal conductivities in HH alloys. The poor solubility of Ta led to undissolved Ta in the samples, which enhanced the electrical properties. In the case of Al doping, the NiAl phase raised the power factor value of Ti1.8Al0.2NiCoSn0.5Sb1.5 to 2.2 × 10–3 W/(m·K2), which is almost twice the corresponding value reported for Ti2NiCoSnSb. Interestingly, a maximum ZT of 0.29 was found in all of the doped systems, although the transport mechanism and microstructure varied widely with the type of dopant. An optimum dopant level of 25% of Zr, 7.5% of Ta, and 10% of Al is necessary to obtain the maximum ZT in these alloys. Compared to HH systems, the HH high-entropy alloy (HEA) systems provide a larger composition field for tuning the transport properties by simultaneous doping of multiple elements to lower the thermal conductivity.

Kinetics analysis and enhancement mechanism of aluminum-enhanced plasma nitriding for 42CrMo steel

Aluminum-enhanced plasma nitriding (Al-PN) was developed by a complex treatment of electrolyzing aluminum nitrate and plasma nitriding (PN) for 42CrMo steel; the kinetics and enhancement mechanism was analyzed. Optical microscope and X-ray diffractometer were used to determine the microstructure and phases constituents of the samples. The results show that much thicker case depth is obtained, with hard phases of AlN and FexAl formed in the surface layer by Al-PN treatment, which brings about much harder surface layer and excellent wear resistance. The kinetics analysis shows that the diffusion coefficient is enhanced by Al-PN, and the diffusion activation energy is reduced from 100.531 kJ/mol by PN to 45.177 kJ/mol by Al-PN. The relationship between case depth, temperature T (K) and holding time t (s) is obtained as: dAl-PN = 1.17 × 10−5exp(−5434T)t. (753 K ≤ T ≤ 793 K). Finally, the verification tests confirmed that the developed kinetics agrees quite well with the measured values; therefore, it can be used to predict the case depth for a designed process parameters in practical applications.

NaCl-induced hot corrosion behaviors of NiSiAlY coatings

In the marine environments, NiCrAlY coatings with high content of Cr would suffer much severer corrosion due to the effect of NaCl. Thus, NiSiAlY coatings with different Si content were proposed and deposited on Ni-based superalloys by multi-arc ion plating. The as-deposited coating was mainly composed of γ’-Ni3Al phase with a small amount of β-NiAl phase. NaCl-induced hot corrosion tests were performed on the coatings at 500°C, 600°C, and 700°C, respectively. Compared with Ni-based alloy substrates, the NiSiAlY coatings exhibited a good corrosion resistance to NaCl at elevated temperatures. However, with an excessive amount of Si, the NiSiAlY coating showed a degradation in the hot corrosion resistance. In this work, the corrosion mechanisms of the tested coatings were discussed. Moreover, the role of Si was also investigated.

Accurate prediction of the solid-state region of the Ni-Al phase diagram including configurational and vibrational entropy and magnetic effects

The solid-state region of the Ni-Al phase diagram is predicted from first-principles calculations and Monte Carlo simulations through the cluster expansion formalism. In addition to the formation enthalpy and to the configurational entropy, the vibrational entropy and the magnetic enthalpy are included to calculate the Gibbs free energy of each phase. The computed phase diagram is in excellent agreement with the experimentally accepted phase diagram and provides information about the phase boundary between AlNi3 and Ni below 300 K. These results demonstrate the potential of this methodology to determine accurately the phase diagram of alloys of technological interest. Finally, the contributions of vibrational entropy and magnetic effects to the overall stability and solubility of the different phases are analyzed independently.

The effect of Al and Ti on the microstructure, mechanical properties and oxidation resistance of γ′-Ni3(Al, Ti) strengthened austenitic stainless steels

Both Al and Ti are the key elements for the formation of γ′-Ni3(Al, Ti) phase and protective oxide scale in the γ′-Ni3(Al, Ti) precipitation strengthened austenitic stainless (AS) steels. To obtain good mechanical properties, especially at elevated temperatures, high volume fraction of γ′ phase is required, which is strongly dependent on the total amounts of Al and Ti. For a given concentration of (Al + Ti), changing Al or Ti addition also has significant effects on the microstructure, mechanical properties and oxidation resistance of alloys. In this study, three alloys are designed by moderately adjusting Al and Ti addition while keeping (Al + Ti) concentration constant (8.7 at.%). It is found that increasing Ti and decreasing Al addition lead to fine Laves precipitates and close spacing between them, which in turn refine grain size and enhance strength at temperature lower than 750 °C. But at about 800 °C, the strength of there alloys is almost the same. Increasing Al and decreasing Ti addition have no apparent influence on the γ′ phase but promote the formation of B2–NiAl phase, resulting in reduced ductility at elevated temperature. Besides, high Al addition facilitates the formation of continuous protective oxide layer (mainly alumina) and is beneficial for oxidation resistance at 750 °C for 500 h. As Ti replaces Al, the integrity of protective alumina layer is destroyed and the discontinuous Al-rich oxides are interlaced with Cr-rich and Ti-rich oxides.

First-principles study on effects of X (Ta, Ti, and W) on the nitriding behavior of γ′-Ni3Al in Ni-based superalloys: From the surface adsorption and diffusion of nitrogen

The role of X (Ta, Ti, and W) doping in affecting the adsorption and diffusion behavior of nitrogen at Ni3Al(110) and Ni3Al(111) surfaces was studied based on first-principles calculations to understand the nitriding mechanism of γ′-Ni3Al in Ni-based superalloys. The calculated results show that the substituting of X atom on the 1st-layer (top layer) Al site could enhance the adsorption ability of N on Ni3Al surface, especially on Ni3Al(111), owing to the stronger bonding strength between N and X atoms. For comparison, the effect of the X atom on the adsorption behavior of nitrogen is not significant when it is doped in the 2nd-layer or 3rd-layer. Nitrogen diffusion into the Ni3Al surfaces as the rate-determining step of nitriding is calculated based on the climbing image nudged elastic band (CI-NEB) method. The doping of Ti could significantly decrease the energy barriers of N penetration into γ′-Ni3Al surface, regardless of surface orientation, which contributes to promoting the nitriding process of γ′ phase. The strongest strengthening effect of Ti explains the experimental results that γ′-Ni3Al contains Ti element having a great nitriding behavior in Ni-based superalloys. Our results can provide an in-depth insight into the diffusion mechanism of nitriding γ′-Ni3Al phase in Ni-based superalloys.

Effect of Different Si Target Currents on Performance of Magnetron Sputtering Wear Resistant Coatings

In order to ameliorate the properties of the coating material on the surface of the key moving parts of artillery, the influence of different Si target currents on microstructure and mechanical performances of magnetron sputtering TiAlMoSiN coating was studied. The phase structure of the coating, microstructure, coating adhesion, friction and wear properties were characterized, respectively. The deposited TiAlMoSiN coatings were mainly composed of TiN phase, Mo2N phase, amorphous Si3N4 phase and amorphous AlN phase. A typical columnar nano-multilayer structure was formed on the TiAlMoSiN coating after magnetron sputtering process. When the Si target current reached 1.0A, the coating hardness was supreme, valued 32.6 GPa. Along with the addition of the Si target current, the hardness and the bonding strength between the coatings and 45 steel substrates declined. As the Si target current was 1.5 A, TiAlMoSiN coating has the lowest friction coefficient and wear rate. Moreover, it was found out the coating with Si target current at 1.0A had shown the optimal surface properties.

Microstructural characteristics and mechanical response of diffusion bonding Inconel 617 superalloy

This study focuses on the microstructural characteristics and mechanical response of the diffusion-bonded joints of Inconel 617 superalloy. The joints exhibited two types of interfacial microstructure involving the straight interface (i.e., bond line) and the interface with partial migration of grain boundaries (GB). The straight interface was composed of the GB of γ-Ni, M23C6 carbide and α-Al2O3 oxide. The M23C6 carbide was precipitated with a semi-coherence of 33̅3M23C6//111̅γ−Ni, and an amorphous interface was detected between the α-Al2O3 and γ-Ni phase. The migration of GB across the interface was mainly caused by dynamic recrystallization and strain-induced GB migration. In addition, the α-Al2O3 oxide was remained inside the migrated grain. The formation of the M23C6 and α-Al2O3 was governed by diffusion mechanism, and the γ′-Ni3Al phase was formed surrounding the α-Al2O3 due to the abundant diffusion of Al. The straight interface, particularly embedded with the hard particles (i.e., the M23C6 carbide and α-Al2O3 oxide), restricted GND slipping, resulting in concentration of stresses and initiation of cracks. The migrated interface, in contrast, effectively prevented crack propagation and induced crack deflection, supporting more continuous and uniform plastic deformation. The elongation of 51.2 % was obtained for the joint with partial migrated interface, reaching 71 % of the base metal. Nevertheless, the optimum impact toughness of the joints (20.38 J/cm2) was merely 24 % of the base metal, mainly affected by the remained straight interface.

Crystallization sequence of an (Al86Ni9La5)98Si2 amorphous alloy under continuous heating

Based on isochronal phase transformation kinetics, the crystallization sequence of (Al86Ni9La5)98Si2 amorphous alloy was fcc-Al→fcc-Al→Al3Ni+La3Al11+unidentified phases at a heating rate > 5 K/min; while the crystallization sequence changed to fcc-Al→Al3Ni+La3Al11+unidentified phases→fcc-Al at a heating rate < 5 K/min. However, the last two crystallization events were kinked rather than reversed in sequence even if the heating rate decreased from 160 to 1 K/min in experiments. This inconsistency illustrated that the crystallization sequence associated with the two crystallization events can hardly be profiled sophisticatedly by their individual thermal analyzed kinetics, and here was attributed to two bifurcate originations: the prerequisite conditions for the formation of Al3Ni, La3Al11, and unidentified phases was actually the precipitation of the second stage fcc-Al, and the monotonous Al can hardly be existed independently in the amorphous state.

Microstructure and Mechanical Properties of Cast Al-Si-Cu-Mg-Ni-Cr Alloys: Effects of Time and Temperature on Two-Stage Solution Treatment and Ageing

Ameliorating the high-temperature performance of cast Al-Si alloys used as engine components is essential. The effects of different T6 heat-treatment processes on the microstructure and mechanical properties of cast Al-Si-Cu-Mg-Ni-Cr alloys were investigated in the present study. The results demonstrate that, under the optimal solution treatment conditions of 500 °C for 2 h and 540 °C for 4 h, the T-Al9FeNi phase was present in the alloy, and the roundness of primary Si and the aspect ratio of eutectic Si in the alloy reached valley values of 1.46 and 2.56, respectively. With increasing ageing time at 180 °C, the tensile strength significantly improved, while the microhardness first increased and then decreased. When the ageing time was 4 h, microhardness reached a peak value of 155.82 HV. The fracture characteristics changed from quasi-cleavage to the coexistence of quasi-cleavage and dimples. After heat treatment, the high-temperature tensile properties of the alloy improved, which is a significant advantage compared to the as-cast alloy. The stable Al3Ni and Al9FeNi phases inhibited the cracking of the alloy at 350 °C.