NiAl Bond Coat Research Articles

Development and characterization of corrosion-resistant plasma-sprayed Ni-Al composite coatings via graphene oxide fillers

In this study, the authors propose a procedure to enhance pure Ni-Al powders through graphene oxide dispersion in water for plasma spraying. The enhanced powders were utilized to coat A36 steel via plasma spraying. Next, the powders and the coatings were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, micro-Raman spectroscopy, and field emission scanning electron microscopy. Given the capability of the generated X-ray to characterize near surfaces to a depth of a few micrometers, the performed X-ray microanalyses convey that the carbon species incorporated within the powders through the graphene oxide dispersion can act as nanofillers reducing the number of holes/pores in the plasma-sprayed coatings. Potentiodynamic polarization testing and electrochemical impedance spectroscopy were used to investigate the corrosion behavior of the samples at two intervals: after 1 h and after 30 days of exposure to a 3.5 % NaCl solution. According to the results of the corrosion testing, the enhanced coatings can display about 2.35 times lower corrosion current density compared to pure Ni-Al coatings, with the corrosion potentials of the enhanced coatings being higher than that of pure Ni-Al coatings (i.e., improved corrosion resistance). This improvement in corrosion resistance is also evident when the enhanced coatings are compared to the A36 substrate after 30 days of exposure to the solution. It appears that the incorporated carbon nanofillers, by reducing deep holes and pores that communicate with the surface of the substrate, ultimately determine the highest corrosion resistance. Thus, the outcome offers enhanced Ni-Al coatings possessing superior anticorrosion properties that typical plasma-sprayed Ni-Al bond coats may not exhibit.

Diffusion-controlled growth and microstructural evolution between Pt and Pd containing B2-NiAl bondcoats and Ni-based single crystal superalloy

Pt-modified NiAl bond coats are used to extend the lifetime of blades in gas turbine engine applications. However, they suffer from the growth of deleterious precipitates within the interdiffusion zone. Partial substitution of Pt by Pd is advantageous in reducing the interdiffusion zone thickness between the bond coat and the superalloy, providing comparable oxidation properties, and critically reducing the propensity to form brittle (Pt,Ni)Al2 precipitates. In this study, we utilize the pseudo-binary diffusion couple method to estimate the interdiffusion coefficients of Ni and Al in Pd, Pd-Pt and Pt-modified nickel aluminides. Additionally, the main and cross-interdiffusion coefficients are estimated in the ternary diffusion couples. The estimated diffusion coefficients in the β-NiAl phase reflect on the thickness of the β phase in the superalloy bond coat interdiffusion zone. Pd reduces the pseudo-binary interdiffusion coefficients of Ni–Al and also decreases the main and cross-ternary interdiffusion coefficients. This correlates with the reduction of the interdiffusion zone thickness by Pd. The diffusion process is strongly assisted by point defects in this phase. Ab initio-informed defect calculations are done to explain diffusion retardation in the presence of Pd (compared to Pt) with decreased defect concentrations. Furthermore, through in-depth microstructure characterization performed by electron probe micro analyser, transmission electron microscopy, and atom probe tomography, the presence of σ, R and μ phases as TCP precipitates in the interdiffusion zone are identified. The results give insights into the coatings’ diffusional properties that influence the service life of the product.

Enhanced reliability with bimodal microstructure and transformation-induced toughening in Al2O3-YSZ based thermal barrier coatings

Thermal barrier coatings (TBCs) are thermally insulating coatings used in hot sections of gas turbines with temperature > 1400 °C. Present work pursues controlled bimodal microstructure consisting of micrometre-sized Al2O3 and spray-dried nanometre-sized Al2O3, reinforced with 20 wt% 3 mol% yttria stabilized zirconia (3YSZ) and 4 wt% carbon nanotube (CNT) as a thermal barrier coating (TBC) deposited onto Inconel 718 substrate with NiAl bond coat via atmospheric plasma spraying. Bimodal microstructure depicts fully melted and partially melted (~32–34 vol%) regions eliciting denser microstructure with less defects than conventional deposited Al2O3 TBC. Reinforcement with nanostructures 3YSZ, Al2O3 and CNT resulted a reduction in average stiffness of coatings (using nano indentation) from 139.25 GPa (μ-Al2O3) to 125.9 GPa (with 3YSZ) and 135.2 GPa (with 3YSZ+ CNT). However, the elastic recoverability of composite coatings is superior (50–55 %) compared to that of μ-Al2O3 coatings (47 %), indicating an enhanced crack propagation resistance. A pop-out behavior in nanoindentation is attributed to stress induced phase transformation of ZrO2 from tetragonal to monoclinic phase. Further, statistical analysis of nanohardness, and Young's modulus of composite coatings reveals bimodal Weibull moduli corroborating bimodality of microstructure. An increased reliability of bimodal coatings in conjunction with transformation toughening validates the superiority of Al2O3-based composite coating as a prospective TBC.

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

Composition-dependent interdiffusivity matrices of ordered bcc_B2 phase in ternary Ni–Al–Ru system at 1273∼1473 K

Abstract In this paper, 5 Ni–Al–Ru ternary and 2 NiAl/RuAl binary equilibrium alloys were prepared, and their lattice parameters were evaluated by using the X-ray diffraction technique. The relation between the lattice parameters and Ru content satisfies Vegard’s law, confirming that a continuous single bcc_B2 phase exists between NiAl and RuAl in the ternary Ni–Al–Ru system. After that, three diffusion couples located in the bcc_B2 phase region were prepared at 1273, 1373 and 1473 K, respectively. With the presently measured concentration profiles, the composition-dependent interdiffusivity matrices along the entire diffusion paths were efficiently determined by using the High-throughput Determination of Interdiffusion Coefficients (HitDIC) software. The obtained interdiffusivities show a good agreement with the limited experimental data in the literature. Furthermore, the present results show that the addition of Ru to bcc_B2 NiAl alloys can significantly inhibit the interdiffusion rate of Ni, indicating that the bcc_B2 Ru-containing NiAl bond coats can serve as a potential diffusion barrier for Ni-based superalloy substrate.

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

Investigation of combustion and emission characteristics in a TBC diesel engine fuelled with CH4–CO2–H2 mixtures

In this study, an experimental investigation was performed to reveal combustion and emission characteristics of common-rail four-cylinder diesel engine run with CH4, CO2 and H2 mixtures. The engine pistons were thermally coated with zirconia and Ni–Al bond coat by plasma spray method. With a small amount of the pilot diesel, port fuelled methane (100% CH4), synthetic biogas (80% CH4 + 20% CO2), and hydrogen presented (80% CH4+10% CO2+10% H2) mixtures were used as main fuel at different loads (50 Nm, 75 Nm, and 100 Nm) at a constant speed of 1750 min−1. Comparative analysis of the combustion (cylinder pressure, PRR, HRR, CHR, ringing intensity, CA10, CA50, and CA90), BSFC, and emissions (CO2, HC, NOx, smoke, and oxygen) at the various engine loads with and without piston coating was made for all fuel combinations. It was found that coating the engine pistons enhanced the examining combustion characteristics, whereas it slightly changed BSFC and most of the emissions. As compared to the sole diesel fuel, the gaseous fuel operations showed higher in-cylinder pressure, PRR, and ringing intensity values, earlier combustion starting and CAs, and lower diesel injection pressure at the same engine operating conditions. Dramatic increase in the ringing intensity was particularly found by the hydrogen introduced mixture under the tests with coated piston. HC and CO2 emissions increased in operation with the synthetic biogas; however, hydrogen introduction reduced HC emissions by 4.97–30.92%, and CO2 emissions by 5.16–10%.

Correction to: Crack velocity measurements through continuous stiffness monitoring of cyclically loaded notched micro-beams of thin graded Pt–Ni-Al bond coats

Correction to: Crack velocity measurements through continuous stiffness monitoring of cyclically loaded notched micro-beams of thin graded Pt–Ni-Al bond coats

Processing, characterisation and oxidation resistance of βNiAl bond coat: Al and Zr effects

Platinum-modified-?NiAl is a bond coat (BC) material for thermal barrier coatings (TBCs) applications applied on aeroengine hardware to reduce their surface temperatures. However, it is desirable to minimize its production and material costs by the low-cost alternatives of similar performance. It has been acknowledged that the small concentration of the reactive elements (REs), such as Zr, Hf, and Y, could tremendously enhance the oxide adhesion even in some cases better than Pt modified counterparts. The aim of this study was to design and fabricate the Zr-modified-?NiAl bond coat on CMSX-4 superalloy using an aluminizing method. Moreover, the study focused on the development of a systematic understanding of underlying mechanisms behind the beneficial effects of REs. Initially, three sets of BCs were prepared: Zr-free ?NiAl (undoped), Al and Zr co-deposited in a single-step process (1SP), and Zr and Al, which were individually deposited in two processing steps (2SP): zirconizing and aluminizing. Such three sets of BCs helped to understand the processing, as well as Zr and Al effects on scale adhesion. In particular, 1SP/2SP BCs showed uniformity of Zr in the form of precipitates and networks that caused hardness enhancement. All BCs were isothermally oxidized at 1150?C for 100 hours wherein 2SP revealed the best spallation resistance, microstructural stability, and its Zr-oxide pegs were extended to substrates. In addition to the Zr effect, BC Al content was found to affect the oxide adhesion equally. Under identical Zr contents (of 1SP and 2SP = 1at %), the higher Al showed the better spallation resistance while lower Al caused the inverse effect of Zr owing to its reactive nature that was termed as over doping. Moreover, it was established that over-doping either local or into entire BC, accelerated the Al depletion that destabilized the ?NiAl into ??-Ni3Al phase. An extensive discussion is presented in the light of the observed results.

Impact of substrate temperature of yttrium doped NiAl bond coat fabricated by using EBPVD on inconel 625

The bond coat has been developed on Inconel 625 substrate by using Electron Beam Physical Vapour deposition (EBPVD) method at different substrate temperatures (ie. 873 K and 973 K). Intended for this persistence, the composition of Ni-49.8Al-0.2Y bond coat pellet was prepared. Structural information, Roughness, Morphology of coating have been characterized by using X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), and Field Emission Scanning Electron Microscopy (FESEM) respectively. Finally, the Coefficient of Thermal Expansion (CTE) is measured by using Dilatometer. Observed that the crystallinity was increased from 29.43 nm to 37.33 nm with increasing the substrate temperature. Also verified peak expansion is decreasing due to increase in substrate temperature. The average roughness increases to 17%. Columnar structure is observed at higher substrate temperature (973 K) of bond coat surface. The CTE of 973 K substrate temperature coating has 1.27 × 10 −5 K −1 at 1000 °C which is increases 8% with the substrate (1.16 × 10 −5 K −1 at 1000 °C). This is accomplished due to addition of Yttrium to bond coat material. These coatings used in thermal barrier applications such as in gas turbines, jet engines, and power aircraft etc. • Yttrium doped NiAl bond coat is deposited by EB PVD method on Inconel 625 substrate with different substrate temperatures. • Phase analysis, Average surface roughness and Surface morphology is measured by XRD, AFM and FESEM. • The thermal expansion coefficient is increased to 8% higher than the Inconel 625 substrate to bond coating (973 K).

Crack velocity measurements through continuous stiffness monitoring of cyclically loaded notched micro-beams of thin graded Pt–Ni-Al bond coats

The notched clamped beam geometry has proven to be a useful geometry in evaluating local mechanical properties like fracture and fatigue of thin graded platinum nickel aluminide bond coats. Cyclic fatigue tests performed on different zones of these coatings have shown that the structural stiffness of the beam is a useful parameter in estimating localized damage in front of the notch root, which can arise either due to cyclic softening from micro-crack nucleation and propagation in the crack wake or due to work hardening in the plastic zone surrounding the crack tip. This paper describes the use of finite element method-based analysis to quantify different geometrical factors that affect cyclic stiffness data in the micro-beam bending methodology employed in the present study. Variations in the stiffness values measured at the beginning of each loading cycle can occur due to factors such as the effect of loading line offsets (both lateral and angular) and the notch length to width ratio (a/W). Using this analysis, it was found out that lateral offsets affect the starting stiffness of the beam more profoundly compared to angular offsets. It has also been shown that for beams having lengths of $$\sim $$ $$80-90\,\upmu \mathrm{m}$$ and an a/W ratio of $$\sim $$ 0.3–0.4, the starting stiffness variations can be kept under 10%. The stiffness can also be used to estimate crack velocities (da/dN) in an approximate sense using the finite element method. Detailed finite element analysis has been performed to estimate through thickness crack lengths from cyclic stiffness drops. The applied stress intensity factor for real crack geometries observed during testing have been computed using the extended finite element methodology and da/dN vs $$\Delta $$ K plots have been generated for two cases. This paper highlights the importance of using computational analysis in optimizing and augmenting micro-scale fatigue testing data and thus providing for a richer dataset through such analysis.

Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy

Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary diffusion couple methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the conditions to solve the equations developed based on the Onsager formalism. The end-member compositions to produce ideal/near-ideal diffusion profiles are chosen based on thermodynamic details. The pseudo-binary interdiffusion coefficients of Ni and Al decrease in the presence of Co but increase in the presence of Pt. The pseudo-ternary interdiffusion coefficients indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. Marginal changes of the cross interdiffusion coefficients substantiate a minor change of the diffusional interactions between the components. The thermodynamic driving forces show opposite trends with respect to composition as compared to the changes of the interdiffusion coefficients advocating a dominating role of the Pt(Co)-induced modifications of point defect concentrations. DFT-based calculations revealed that Pt alloying increases the Ni vacancy concentration and decreases the activation energy for the triple defect diffusion mechanism. These findings explain the increase in the thickness of the interdiffusion zone between the B2-Ni(Pt)Al bond coat and the single crystal superalloy René N5 because of Pt addition. Furthermore, the EPMA and TEM analyses reveal the growth of refractory elements-enriched precipitates.

Assessment of non-uniform residual stress field of the thermal sprayed stainless steel coatings on aluminium substrates by the integral hole drilling method

Thermal spray is one of the most used techniques to produce coatings on structural materials. Such coatings are used as protection against high temperatures, corrosion, erosion and wear. The combined action of high pressures, temperatures and spraying conditions give rise to non-uniform residual stresses. The latter plays an important role in coating design and process parameters optimization. The present work highlights the influence of coatings thickness on the evolution of residual stresses in layered materials. Therefore, thick stainless steel coatings (ASTM 301) of different thicknesses are manufactured by wire arc spraying on aluminium alloy substrates (ASTM 2017A). For a better bond strength, a Ni–Al bond coat is first deposited. Furthermore, a numerically supported hole drilling strain gage method for residual stress field evaluation is proposed. Required calibration coefficients, for the strain–stress transformation formalism based on the integral method, are computed through finite element calculations using Abaqus software. The results indicate that the maximum residual stresses, for all thicknesses, are tensile and range from 140 to 275 MPa. The bond coat does not seem to affect the stress field. Also, it was found that the mean equivalent Von-Mises stress decreases with increasing coating thickness; hence reducing the interfacial adhesion energy of the sprayed materials.

Thermal Barrier Coating Development on Automobile Piston Material (Al-Si alloy), Numerical Analysis and Validation

Abstract This work is focused on the thermal barrier coating (TBC) development on aluminium - silicon (Al-Si) alloy casting materials, widely used as automobile components (cylinder blocks, pistons etc.). TBCs enable enhanced combustion within the chambers of diesel engines resulting in improved performance and components life. Uniform coating thickness development on complex contours of automobile pistons is a challenging task worldwide which results in varying thermal barrier characteristics across the non-uniform thickness. In consistent (in thickness) coatings are most likely to lead to uneven thermal barrier effects across the TBC thicknesses which directly affect the performance and the lubrication system of the engine. This warrants the development of stable and consistently thick coatings for ideal performance of the Low Heat rejection (LHR) engine. The present research work involved building different thicknesses (100, 125 and 150µm) of commercial 6-8%Yttria stabilized zirconia (YSZ) TBCs on 50µ to 75µ thick nickel aluminide (NiAl) bond coat. The influence of thickness on thermal barrier characteristics via experimentation and numerical analysis has been studied. Flat plates machined from automobile pistons were used as substrates. The coatings were characterized for thermal barrier effects for hot ceramic surface face temperatures up to 550°C (by using oxy-acetylene flame to heat up the TBC surface), structural phase analysis by X-ray Diffraction (XRD) and microstructure analysis in metallographic cross section by employing Scanning Electron Microscope (SEM). An analytical investigation also was carried out to determine the approximate temperature at each interface. A code was developed to calculate the temperature drops across the coated plate and the net heat available at the coated surface using MATLAB. This is important considering the effects, small changes in temperatures will bring on the creep life on the metal.

Investigation on the performance of air plasma sprayed thermal barrier coating with Lu/Hf-doped NiAl bond coat

The durability of air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiAl bond coats with/without Lu/Hf doping was investigated under thermal cycling at 1150 °C, and compared with the conventional NiCoCrAlY sample. The oxidation kinetics, microstructure evolution and surface roughness of the bond coats were characterized and the cycle lifetime measured. The TBC with the NiAl bond coat exhibited a lifetime of 456 h, which was comparable with the NiCoCrAlY sample (480 h). By contrast, the NiAl-Lu/Hf TBC showed a two or three fold enhanced lifetime, i.e., 840 h and 1248 h, respectively. It is proposed that the enhanced lifetime is a result of combination of decreasing of the oxidation rate and retention of the interfacial toughness. The APS NiAl bond coat with Lu/Hf doping has a great potential for TBCs designed for higher temperature applications.

The oxidation performance of plasma-sprayed NiAl bond coat: Effect of Hf addition in bond coat and substrate

NiAl bond coats with and without Hf addition (0.1 at.%) were deposited on two types of superalloy substrates (i.e., DZ125L, no Hf, and DZ125, 0.51 at.% Hf) using plasma spraying technique, and isothermally oxidized at 1150 °C. It demonstrates that Hf addition in the bond coat is more effective than in the superalloy substrate for improving the bond coat oxidation resistance. In addition, though the substrate chemistry could affect the bond coat oxidation performance, this effect was very sensitive to the chemistry of the bond coat - obvious for the RE (reactive element)-free NiAl bond coat, but less obvious for the RE-containing bond coats (NiAlHf and NiCoCrAlY). Moreover, compared with the NiCoCrAlY bond coat, the NiAlHf bond coat showed significantly improved oxidation resistance, regardless of the substrate chemistry, suggesting that NiAlHf bond coat prepared by plasma spraying is a promising candidate for the thermal barrier coating application.

Thermal cycling performance of La2Ce2O7/YSZ TBCs with Pt/Dy co-doped NiAl bond coat on single crystal superalloy

Thermal barrier coatings (TBCs) consisting of La2Ce2O7 (LCO) and Y2O3-stabilized-ZrO2 (YSZ) double-ceramic layer and Dy/Pt co-doped NiAl bond coat were produced by electron beam physical vapor deposition (EB-PVD). Thermal cyclic performance of the TBCs was evaluated by flame shock testing at 1300 °C. For comparison, the TBCs with a undoped NiAl bond coat were also studied. The microstructural evolution and failure mechanisms of the above TBCs during thermal cycling were investigated. Spallation failure of the TBCs with the undoped bond coat occurs after around 500 cycles by cracking at the interface between YSZ ceramic layer and thermally grown oxides (TGO) layer. The TBCs with Pt/Dy modified bond coat reveal improved interface bonding even after 1200 thermal cycles, whereas some delamination cracks are presented in the LCO layer. On the other hand, the Pt/Dy modified bond coat effectively suppresses the formation of the needle-like topologically closed packed phases (TCP) in the single crystal superalloy.

Phase Stability, Structure and Thermodynamics of Modified Ni- and Fe-Aluminides

The Ni-aluminides are integral constituents of thermal barrier coatings applied over Ni-based superalloys. These aluminides provide oxidation-resistance by forming a protective α–Al2O3surface layer. The Pt-modified β–NiAl bond coat has been developed with an impetus to increase the service-life of Ni-based superalloys. The Pt-modified β–NiAl bond coat significantly improves the oxidation-resistance of superalloys. An interdiffusion zone containing topologically closed packed phases develops at the bond coat/superalloy interface. This eventually leads to Al-lean γ′–Ni3Al transformation, whose oxidation resistance is inferior to that of β–NiAl. The Pt-group metals Ir and Ru delay this transformation and impart creep-resistance to the bond coat. Recent investigations demonstrate that alloying with transition metals such as Cr, Mo and Fe enhance the mechanical strength. The functional stability of bond coat-superalloy assembly counts on the interfacial reaction and associated local structural variations which is a function of bond coat composition. This chapter elucidates the effect of various alloying elements on phase constitutions, crystallographic structural stability and thermodynamics of Ni-and Fe-aluminides to engineer a prospective bond coat.

Investigation of NiAl intermetallic compound as bond coat for thermal barrier coatings on Mg alloy

Bond coats play a significant role in manipulating the stability of 8YSZ thermal barrier coatings (TBCs) deposited on Mg alloy. In this study, the metal of Ni-Al mixture was sprayed as bond coat via reaction plasma spraying (RPS). Besides, Intermetallic compound NiAl was prepared by self-propagating high-temperature synthesis (SHS). The pure intermetallic compound NiAl was sprayed as bond coat via atmospheric plasma spraying (APS). The microstructure, composition, bond stability and corrosion resistance of the produced bond coats were investigated to find the optimal bond coat for the TBCs on Mg alloy. Results indicate that the bond coats composed of NiAl show excellent bond stability. High toughness of the RPS Ni-Al bond coat results in high tensile bond strength. The APS NiAl bond coat leads to outstanding thermal shock resistance mainly attributing to its moderate thermal expansion match, good mechanical properties and excellent corrosion resistance.

Investigation of the effect of biogas on combustion and emissions of TBC diesel engine

In this study, the effect of biogas on the thermal barrier coated (TBC) dual-fuel engine was experimentally investigated. Experiments were carried out on a four cylinder, water cooled, turbocharged, common-rail coated and uncoated diesel engine under dual-fuel (biogas-diesel) mode and single fuel (neat diesel) mode. Combustion chambers of the pistons were coated with 400μm thickness 8% yttria stabilized zirconia main coat over a 100μm thickness NiAl bond coat using atmospheric plasma spray method. Combustion (cylinder gas pressure, rate of pressure rise), heat release (rate of heat release, cumulative heat release, duration and center of heat release) exhaust emission (HC, NOx and smoke emissions) parameters were investigated. Results showed that homogenous mixture of gaseous fuel and air caused high cylinder pressures. TBC can be used for decreasing smoke emissions under dual-fuel (biogas-diesel) mode. TBC had not a significant effect on NOx emission of single fuel mode.