Ni-based Solid Solution Research Articles

Study on the Wear Resistance of Micro-Nanostructured WC Composite Coating Sintered by Induced Heating

Micro-nanostructured WC composite coatings were successfully fabricated by induced heating sintering method on the surface of Q235 steel .The microstructure, micro-hardness and the wear resistance of the composite coatings were studied .The results show that the microstructure of induced heat layer is mainly composed of Ni-based solid solutions and WC particles. And there exists excellent metallurgical bonding between coating and substrate. The wear resistance of micro-nanostructured WC Composite Coatings is increased by 1.5 times on an average as compared with that of micron.

Room-temperature dry sliding wear behavior of γ-Ni/Mo 2Ni 3Si metal silicide “in situ” composites

Ni-base solid solution (γ) toughened Mo 2Ni 3Si metal silicide “in situ” composites were fabricated with different volume fraction of Mo 2Ni 3Si primary dendrite uniformly distributed in irregular Mo 2Ni 3Si/γ eutectic matrix. Results of room-temperature dry sliding wear tests indicated that the composite with a medium volume fraction of primary Mo 2Ni 3Si phase possessed the best wear resistance by optimum combination of the unique mechanical property of Laves phase Mo 2Ni 3Si and toughening effect of ductile γ phase. The primary wear mechanism is microplowing and soft-abrasion of the interdendritic Mo 2Ni 3Si/γ and subsequent brittle fracture of the hard Mo 2Ni 3Si primary dendrites. Ductile γ phase provided good toughening effect to Mo 2Ni 3Si Laves phase during dry sliding wear process.

Experimental studies and thermodynamic optimization of the Ni-Bi system

Experimental studies by electron microprobe analyses, optical microscopy, and differential scanning calorimetry were performed. New data about the liquidus in the central and the Bi-rich regions were obtained. A narrow homogeneity region (about 50–52 at.% Bi) was found for the compound NiBi while the second intermediate phase in this system (NiBi3) was stoichiometric. Thermodynamic optimization of the Ni-Bi phase diagram was achieved by the CALPHAD method by combining phase diagram and thermodynamic data. Thus, NiBi was modeled with two sublattices, allowing mixing of Bi and Ni on one of them only. The intermetallic phase NiBi3 was modeled as a stoichiometric compound. Redlich-Kister polynomials were used to describe the excess Gibbs energies of the solution phases (liquid, pure bismuth, and Ni-based solid solutions).

Atomistic Modeling of Crystal-to-Amorphous Transition and Associated Kinetics in the Ni−Nb System by Molecular Dynamics Simulations

With the aid of ab initio calculations, an n-body potential of the Ni-Nb system is constructed under the Finnis-Sinclair formalism and the constructed potential is capable of not only reproducing some static physical properties but also revealing the atomistic mechanism of crystal-to-amorphous transition and associated kinetics. With application of the constructed potential, molecular dynamics simulations using the solid solution models reveal that the physical origin of crystal-to-amorphous transition is the crystalline lattice collapsing while the solute atoms are exceeding the critical solid solubilities, which are determined to be 19 atom % Ni and 13 atom % Nb for the Nb- and Ni-based solid solutions, respectively. It follows that an intrinsic glass-forming ability of the Ni-Nb system is within 19-87 atom % Ni, which matches well with that observed in ion beam mixing/solid-state reaction experiments. Simulations using the Nb/Ni/Nb (Ni/Nb/Ni) sandwich models indicate that the amorphous layer at the interfaces grows in a layer-by-layer mode and that, upon dissolving solute atoms, the Ni lattice approaches and exceeds its critical solid solubility faster than the Nb lattice, revealing an asymmetric behavior in growth kinetics. Moreover, an energy diagram is obtained by computing the energetic sequence of the Ni(x)Nb(100)(-)(x) alloy in fcc, bcc, and amorphous structures, respectively, over the entire composition range, and the diagram could serve as a guide for predicting the metastable alloy formation in the Ni-Nb system.

High temperature tribology behaviors of brush plated Ni–W–Co/SiC composite coating

The high temperature wear behavior of Ni–W–Co/SiC composite brush plated coatings deposited on a hot work die steel has been investigated using a plate-on-ring test rig. The microstructure and wear characteristics of coating have been analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that typical microstructure of Ni–W–Co/SiC composite coating consists of Ni-based solid solution and SiC particles. The TEM observation of Ni–W–Co/SiC composite coating has revealed the fine SiC particles of nano-size in the brush plated coatings and the matrix of Ni–W–Co plated coating is composed of a mixed crystalline and amorphous structure. The worn surface morphology of the plated coating is observed by SEM and laser profile analysis. In the temperature range 400–600 °C, wear rate and average friction coefficient of the Ni–W–Co/SiC brush plated composite coatings are lower than that of the 3Cr2W8V (ASTM H21) hot work die steel. Abrasive and adhesive wears are the major wear mechanisms of brush plated composite coating at high temperature.

Structural transition and glass-forming ability of the Ni–Hf system studied by molecular dynamics simulation

A tight-binding Ni–Hf potential is constructed by fitting some of the ground-state properties, such as the cohesive energy, lattice constants, and the elastic constants of some Ni–Hf alloys. The constructed potential is verified to be realistic by reproducing some static and dynamic properties of the system, such as the melting points and thermal expansion coefficients for the pure Ni and Hf as well as some of the equilibrium compounds, through molecular dynamics simulation. Applying the constructed potential, molecular dynamics simulations are performed to compare the relative stability of the face-centered-cubic (fcc)/hexagonal close-packed (hcp) solid solutions to their disordered counterparts as a function of solute concentration. It is found that the solid solutions become unstable and transform into the disordered states spontaneously, when the solute concentrations exceed the two critical solid solubilities, i.e., 25 at.% Ni for hcp Hf-rich solid solution and 18 at.% Hf for fcc Ni-based solid solution, respectively. This allows us to determine that the glass-forming ability/range of the Ni–Hf system is within 25–82 at.% Ni. Interestingly, simulations also reveal for the first time, that two mixed regions exist in which an amorphous phase coexists with a crystalline phase, and at about 18 at.% Ni, the hcp lattice turns into a new metastable phase identified to be face-centered orthorhombic structure.

Thermodynamic assessment of the Ni-Ga system

Phase diagram and thermodynamic properties of the Ni-Ga system are assessed based on the CALPHAD approach, using all available experimental data and applying appropriate thermodynamic models. The liquid phase and the Ni-based solid solution (Ni) are treated as disordered solutions. The thermodynamic behavior of the ordered intermetallic compounds with appreciable ranges of homogeneity, Ni3Ga and NiGa, are described by a two-sublattice model, and the order-disorder transformation between Ni3Ga and fcc-(Ni) is also explicitly considered in this work. The other five intermetallic compounds are treated as stoichiometric line compounds. The phase diagram and the thermodynamic properties calculated from the optimized model parameters are in good agreement with most of the experimental data.

The structure and properties of a Cr3C2-Ni coating deposited by a high-velocity plasma jet onto a copper substrate

Chromium carbide-nickel coatings were deposited onto a technical grade copper substrate by means of a high-velocity plasma jet of a plasmatron operating in specially selected regimes. An analysis of the coatings showed evidence of the formation of a Ni-based solid solution, a complex chromium carbide (Cr7C3), and an fcc crystal phase with a lattice parameter of 3.614 A. The surface of the coatings exhibits a characteristic relief resulting from a dynamic interaction between melted and fused particles of the initial powder. The local hardness on some areas of the surface and in depth of the coating reaches 66±4.5 HRC, while the coating adhesion strength varies from 25 to 300 MPa.

Thermally sprayed Ni(Cr)–TiB 2 coatings using powder produced by self-propagating high temperature synthesis: microstructure and abrasive wear behaviour

High velocity oxy-fuel (HVOF) thermal spraying was used to deposit Ni(Cr)–TiB 2 cermet coatings onto steel substrates from a feedstock powder produced by a self-propagating high-temperature synthesis (SHS) reaction. The powder and coating microstructures were investigated by scanning electron microscopy and X-ray diffraction (XRD), whilst dry sand rubber wheel abrasive wear and microhardness tests were performed on the coatings. The SHS reacted powder was found to comprise principally 1–5 μm sized TiB 2 in a crystalline, Ni-based solid solution matrix, with approximately 60 vol.% TiB 2 and 40 vol.% metallic binder. XRD revealed the presence of only around 2% of the following phases: TiB, Ni 2B, NiTi, TiO. The reacted compact was crushed, ground and classified into a powder of size range (+8 to −38) μm for thermal spraying. The HVOF sprayed deposits had layered, splat-like morphologies typical of thermally sprayed cermets. The coating microstructure consisted primarily of TiB 2 in the Ni-rich binder phase but the boride fraction was reduced compared to that of the feedstock powder as a result of TiB 2 dissolution in the molten alloy during spraying. XRD analysis of the coating indicated that the binder solidified to, in part, an amorphous/nanocrystalline structure with ∼2% of Ti-containing oxide phases also present. The TiB, Ni 2B and NiTi phases were not detected in the coating. Under the wear conditions employed, angular alumina generated significantly higher wear rates than the rounded silica abradent, and the wear mechanism changed from microcutting with alumina to pull-out with silica. The wear coefficients obtained with the coating were significantly reduced compared with those of mild steel, in the case of alumina abrasive a factor of four reduction. Additionally, a significant improvement in wear resistance was also found when compared to HVOF-sprayed chromium carbide–nickel/chromium cermet coatings produced from commercially available powders.

Correlation of lattice constant versus tungsten concentration of the Ni-based solid solution examined by molecular dynamics simulation

In order to investigate the Ni-enriched Ni–W solid solution at an atomic level, an n-body Ni–W potential was firstly derived based on the cohesion energies, lattice constants and bulk moduli of four Ni–W non-equilibrium solid phases obtained by ion mixing experiment or ab initio calculation. Based on the derived potential, molecular dynamics simulation was then performed to examine the correlation of the lattice constant of the Ni–W solid solution vs. the W concentration and the results were in good agreement with the experimental data.

Lubrication behavior of Ni–Cr-based alloys containing MoS 2 at high temperature

Ni–Cr-based alloys with excellent self-lubricating property in a wide temperature range were prepared by powder metallurgical hot pressing of alloyed Ni–Cr powder, Mo, Al, Ti, B and various proportions of MoS 2 powder. The effects of MoS 2 on some mechanical and tribological properties of the alloys when rubbing with W18Cr4V high-speed steel were investigated in the temperature range of 20–600°C. The results show that the anti-bending strength of the alloy decreases with addition of MoS 2, and the tribological properties of the alloy were improved by adding MoS 2. The best comprehensive properties of mechanics and tribology were obtained when the amount of MoS 2 in the alloy is up to 10 wt.%. XRD analysis shows that the alloy was mainly composed of Ni-based solid solution, Ni 3Al, Cr x S y , MoS 2 and Mo 2S 3. The selective transfer of oxides between rubbing pairs occurs in the friction process at 600°C. The glaze layer is formed on the oxide film at worn surface of the alloy during high temperature friction process. The hardness of the glaze and oxide film is higher than that of the matrix alloy, which accounts for the wear resistance of the alloy at high temperature. The synergistic action of oxides and residual sulfides in the wear surface and wear debris at high temperature is responsible for reduction of friction.

Microstructure and mechanical properties of a directionally solidified and aged intermetallic Ni–Al–Cr–Ti alloy with β-γ′-γ-α structure

Microstructure and mechanical properties were investigated in a directionally solidified (DS) Ni–21.7Al–7.5Cr–6.5Ti (at.%) alloy. The dendrites of the as-grown alloy were composed of β(B2)-matrix (NiAl), coarse γ′( L1 2)-particles (Ni 3Al), fine γ′-needles and spherical α(A2)-precipitates (Cr-based solid solution). The majority of fine γ′-precipitates was found to be twinned. The interdendritic region contained γ(A1)-matrix (Ni-based solid solution) separating ordered domains of γ′-phase and fine lath-shaped α-precipitates. Ageing in the temperature range 973–1373 K decreased the volume fraction of dendrites from about 50 vol.% measured in the as-grown material to about 38 vol.% in the material aged at 1373 K for 300 h. During ageing in the temperature range 973–1273 K the γ-phase transformed to the γ′-phase in the interdendritic region. This transformation was connected with precipitation of lath-shaped α-precipitates. Ageing at higher temperatures of 1373 and 1473 K resulted in stabilisation of the γ-phase and precipitation of spherical γ′-particles in the interdendritic region. Ageing at 973 K significantly increased the microhardness, hardness and decreased room-temperature tensile ductility. Neither ageing nor finer dendritic microstructure were found to be effective in increasing the ductility of the alloy. The measured tensile ductility up to 1.1% can be attributed to the effect of extrinsic toughening mechanisms operating in the β-phase such as blunting and bridging of cracks by the α- and γ′-precipitates.

Structural evolution and metastable phase formation in Ni-W multilayers upon ion irradiation

A crystal-to-amorphous structural transition was induced in the Ni25W75 and Ni35W65 multilayers by ion irradiation at room temperature. More interestingly, prior to complete amorphization, a sequential disordering of first Ni and then W crystalline lattices was observed in the Ni25W75 sample with increasing ion dose. Such sequence in disordering is attributed to the difference in melting points between the two constituent metals. In another two multilayered samples with overall compositions of Ni60W40 and Ni78Nb22, ion irradiation under similar conditions resulted in the formation of two Ni-based fcc solid solutions, respectively. In comparison, the same Ni-based fcc solid solution was formed in the Ni35W65 multilayered sample upon solid-state reaction at 500 °C. Solid-state reaction at 550 °C resulted in the formation of a new W-rich metastable hcp phase in the Ni25W75 multilayered sample and the bcc–hcp transition was thought to be realized through a shearing mechanism. A Gibbs free-energy diagram, including the free-energy curves of the newly formed metastable crystalline phases, of the Ni-W system was calculated based on Miedema’s model and it can give a reasonable explanation of the observed sequential disordering. The calculated results also showed that the free-energy difference between the amorphous and metastable crystalline phases was quite small, leading to a situation that the phase selection, namely which phase was more favored to be formed eventually than its competitors, was influenced or even determined by the kinetics involved in the respective processes. Besides, the growth kinetics of the MX phases was also discussed.

Mikrostruktur und Ausscheidungsverhalten von Superlegierungen mit Wärmedämmschichtsystemen / The Microstructure and Precipitation Behaviour of Superalloys with Thermally Insulating Coating Systems

The Ni-base solid solution- and carbide hardening alloy NiCr22Co12Mo9 is used preferentially for cladding the combustion chambers of stationary gas- and aircraft turbines. In order to increase combustion temperatures, the combustion chamber is protected against excessive temperatures by the application of a multi-layered coating consisting of a thermally insulating ceramic layer and a corrosion resistant layer. By considering the mechanical behaviour separately from the corrosion behaviour, it becomes clear that this type of coating detrimentally affects the creep properties of the substrate metal. The purpose of the investigation was to determine the microstructural cause of this behaviour. The deterioration in the creep properties of the alloy NiCr22Co12Mo9 after coating was found to be caused by the degradation of the M 23 C 6 -carbide precipitate in the substrate material and by a weakening in the mechanisms of solid solution hardening and precipitation hardening taking place at the interface, on which the creep strength of the material relies.

Effect of ageing on the microstructure and mechanical behaviour of a directionally solidified Ni3Al-based alloy

Abstract The effect of ageing in the temperature range from 1023 to 1373 K on the micro-structure and mechanical behaviour of a directionally solidified (DS) Ni3Al-based alloy modified with additions of chromium and iron was investigated. The microstructure of the as-grown alloy consisted of well-aligned and equally spaced lamellas composed of β(B2) intermetallic compound NiAl (Cr, Fe), some β′(L10) martensite and spherical α-Cr precipitates. The matrix consisted of γ′(L12) intermetallic compound Ni3Al (Cr, Fe), γ-phase (Ni-based solid solution) and lath-shaped α-Cr precipitates. Ageing at 1123 and at 1173 K was found to be the most effective in transforming the unstable lamellae to γ′-phase and α-Cr precipitates. The change of microstructural characteristics such as volume fraction of lamellae, size, morphology and distribution of γ′-phase, γ-phase and α-Cr precipitates significantly influenced the room-temperature yield strength and elongation of DS alloy after ageing. The strain-hardening exponent varied with the ageing temperature between 0.30 and 0.46 and the quasi-steady work-hardening rate between 2710 and 5340 MPa. In the specimens with the lowest amount of disordered regions, the strain-hardening exponent was found to be 0.46 and the quasisteady work hardening rate was determined to be 3340 MPa.

Mechanical alloying synthesis and structural characterization of ternary Ni-Al-Fe alloys

Ternary Ni-Al-Fe alloys with different Fe additions have been synthesized by mechanical alloying of elemental powder mixtures. The effects of Fe-substitution for Al in an equi-atomic NiAl alloy on the mechanical alloying process and on the final Ni-Al-Fe alloys were investigated experimentally. Lower Fe additions have been found to prolong the milling time prior to explosive formation of the NiAl(Fe) compound, while ≥ 15 at % Fe addition has been found not only to eliminate the explosive reaction during milling but also to produce a Ni-based supersaturated solid solution (the 15 at % Fe addition results in the formation of an amorphous-like phase). The addition of Fe improves the plastic deformation ability of the alloys and hinders the tendency of fracture during milling, resulting in the formation of larger alloy particles. Upon heating, the as-milled samples with lower Fe addition remain as NiAl(Fe) compound, whereas the Ni-based supersaturated solid solutions decompose into a mixture of compounds of β-(Ni, Fe) (Al, Fe) + γ′-(Ni, Fe)3Al. It is suggested that the ternary addition into the binary intermetallic compound might be a possible route to improve ductility by forming the dual phase of β + γ′.

Fabrication and microstructure of ZrO 2/NiCrCoAlY graded coating by plasma spraying

An 8 wt% Y 2O 3-ZrO 2/NiCrCoAlY graded coating was fabricated on a TC4 (Ti-6Al-4V) surface by air plasma spraying. Microscopic analysis showed that the ZrO 2/NiCrCoAlY graded coating exhibits a stepwise distribution in composition from metallic bond layer to ceramic top layer, consisting of t′-ZrO 2 phase and supersaturated Ni-based solid solution phase, and displays tight coherence with the TC4 substrate. In addition to mechanical combination, chemicometallurgical reaction combination occurs at some locations and small amounts of NiTi 2 and TiAl 3 phases at the coating-substrate interface develop during spraying.

Laser cladding of ZrO 2-(Ni alloy) composite coating

The microstructure of laser-clad 60 vol.% ZrO 2 (partially stabilized with 2 mol% Y 2O 3) plus 40 vol.% Ni alloy composite coating on steel 1045 was investigated by scanning electron microscopy, electron probe microanalysis, X-ray diffraction, energy-dispersive X-ray analysis and microhardness tests. The composite coating consists of a pure ZrO 2 clad layer in the outer region and a bonding zone of Ni alloy adjacent to the substrate. The pure ceramic layer exhibits fine equiaxed ZrO 2 grains in the outer zone and columnar ZrO 2 dendrites in the inner zone, growing from the ceramic layer-bonding zone interface. This ceramic layer is composed of metastable t′-ZrO 2 phase and a very small amount of m-ZrO 2 phase and displays a microhardness of 1700 HV 0.2. The high heating and cooling rate caused by laser cladding restrains the t → m phase transformation in the ZrO 2 ceramic layer. Interdiffusion of alloy elements takes place in the bonding zone, in which the coexistence of ZrO 2 particles, Ni-based solid solution and (Fe,Cr) 23C 6 particles in the interdendritic regions was found.

High-Temperature Applications of Intermetallic Compounds

One of the greatest challenges currently facing the materials community is the need to develop a new generation of materials to replace Ni-based superalloys in the hot sections of gas-turbine engines for aircraft-propulsion systems. The present alloys, which have a Ni-based solid-solution matrix surrounding Ni3Al-based precipitates, are currently used at temperatures exceeding 1100°C, which is over 80% of the absolute melting temperature. Since Ni3Al melts at 1395°C and Ni at 1453°C, it is clear that significantly higher operating temperatures, with the attendant improvements in efficiency and thrust-to-weight ratio, can only be attained by the development of an entirely new materials system. This problem is a primary reason for the current high level of interest in high-temperature intermetallic compounds.The development of such a material system has important implications for national defense and for spin-offs to civilian technology, as well as for the economy and balance of payments. Obviously it would be a boon to any economy to have these new materials developed domestically, as was the case in the United States for the currently used single-crystal technology applied to Ni-based superalloys. As an example, the aerospace industry is one area where the United States is still the undisputed world leader, with net exports of $29 billion in 1989, twice that of any other U.S. industry.

High-temperature nitridation of Ni-Cr alloys

The nitriding behavior of nickel-chromium alloys was investigated at 1398 K over the range 1 to 6000 bar of external nitrogen pressure. The morphology of the nitrided zone depends on the concentration of chromium in the initial alloy and the N2 pressure (fugacity) applied upon the system. The transition from CrN to Cr2N precipitation was observed within the reaction zone after nitriding at 100 to 6000 bar of N2 when the chromium content in the initial alloys was 28.0 at. pct or higher. It is shown that the ternary phase π (Cr10Ni7N3) is formed in this system at 1273 K. through a peritectoid reaction between Cr2N and nickel solid solution and becomes unstable above 1373 K. The thermodynamic evaluation of the Ni-Cr-N system was performed and phase equilibria calculated. Evidence for “up hill” diffusion of nitrogen near the reaction front during the internal nitridation of Ni-Cr alloys at 1398 K was found. It was attributed to the relative instability of chromium nitrides and strong Cr-N interaction in the matrix of the Ni-based solid solution within the nitrided zone.