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Journal of Thermal Spray Technology
Journal Prestige (SJR): 0.688  Citation Impact (citeScore): 2 Number of Followers: 5  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1544-1016 - ISSN (Online) 1059-9630 Published by Springer-Verlag  [2468 journals]
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- Study on High-Temperature Properties of (La0.5Eu0.25Y0.25)2Zr2O7 Ceramic
Coating-
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Abstract: Abstract In this work, rare-earth elements Eu and Y were added to La2Zr2O7 (LZ) as doping elements, and the ceramic coating of (La0.5Eu0.25Y0.25)2Zr2O7 (LEYZ) was prepared. The evolution of the sintering resistance, thermal shock resistance, and thermal insulation properties of the multi-element rare-earth co-doped modified coatings under long-term and high-temperature conditions was studied. The results showed that the sintering resistance of the doped coating was significantly improved, and the coating still does not fall off after 200 h at 1100 °C. The thermal shock life of the coating at 1000 °C is increased by 47% compared with that of the undoped modified LZ coating. The length of the vertical cracks in LEYZ ceramic layer is obviously shorter than that in LZ coating, which will be more beneficial to preventing the coating from peeling off. Compared with LZ coating, the insulation temperature of the LEYZ ceramic coating is increased by 24, 26 and 34% in the range of 900 ~ 1100 °C, respectively. The coating has the best thermal insulation effect, which is consistent with theoretical calculation results. The results demonstrate that the modified lanthanum zirconate coatings doped with Europium and Yttrium has great potential in high-temperature performance.
PubDate: 2023-12-07
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- Modeling the Formation of Thermal Spray Coatings on Substrates with
Arbitrary Shapes-
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Abstract: Abstract The main focus of this study is on simulation of coating formation on substrates with arbitrary shapes. For this purpose, several substrate geometries shaped as inclined step, cylinder and sphere are considered. The stress analysis for these complex coating geometries is also performed. The formation of Nickel coatings on various shapes of stainless-steel substrates and Yttria-Stabilized Zirconia (YSZ) on NiCrAlY in the atmospheric plasma spray (APS) process is investigated. The topography of the coatings, as well as their microstructure, e.g., porosity, average thickness and average roughness, are evaluated. An algorithm, which is based on the Monte-Carlo stochastic model, is employed in this work. The parameters of the droplets impacting the surface, including their velocity, temperature and size, are predicted through the use of this stochastic model. Simulation results show that on the inclined part of the step or peripheral parts of the cylinder/sphere, the coating porosity is considerably lower than the flat parts, while the roughness is remarkably higher. A significant difference between the coating temperature and that of the substrate leads to the formation of residual thermal stresses. These stresses are analyzed using the object oriented finite-element (OOF) software, which utilizes an adaptive meshing technique and finite-element method to calculate residual thermal stresses. The maximum stress in the coatings occurs at the interface between the coating and the substrate. The coatings' topography and microstructure are compared with those of the experiments.
PubDate: 2023-12-04
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- Microstructure, Mechanical Property and Corrosion Behavior of Cold-Sprayed
Zn Coatings on Mg Alloy Substrate-
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Abstract: Abstract Zn coatings on Mg alloy substrate were prepared by in-situ micro-forging-assisted cold spraying with different stainless steel shot additions. Phase, microstructure, mechanical properties and corrosion resistance of Zn coatings were investigated. The results show that the shot addition enhanced the ZnO formation and increased the full width at half maximum of the Zn phase in the Zn coatings. Plastic deformation of Zn particles was enhanced with the coating densities. Microhardness of Zn coatings was increased due to work hardening, grain refinement and densification by the hammering effect of shots. Bond strength was increased and fracture surfaces showed both metallurgical bonding and mechanical interparticle interlocking in Zn coatings. Zn coatings effectively improved the corrosion resistance of the Mg alloy substrate, and the shot addition made a small contribution to the corrosion resistance. The corrosion behavior of Zn coatings was discussed in terms of corrosion products and microstructures after immersion.
PubDate: 2023-12-01
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- Tungsten Heavy Alloys from Mixed Feedstock by RF Plasma
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Abstract: Abstract Tungsten heavy alloys (WHA) are particulate composites of spherical W particles embedded in a ductile Ni-rich matrix. In our study, pre-treated W and Ni feedstock powders were used to prepare three different compositions (all wt.%) for spraying: W-10Ni, W-20Ni for two different WHA, and W-65Ni for a matrix-only material without the reinforcing W particles. Using radio frequency inductively coupled plasma spraying (RF-ICP) method, low porosity deposits were obtained with ductility exceeding 5%. By a detailed study of the microstructure and the particle-matrix interfaces, the mechanism of the composite formation was identified: a rapid dissolution of W in the liquid Ni and a subsequent W particle solidification followed by the solidification of the matrix. The mechanical properties of the composites are defined by the Ni-rich matrix (tough and significantly stronger than pure Ni) with well bonded stiff W particles. The elastic behavior was related to the W content following the Reuss model, describing a layered composite modulus in a serial configuration. Contrary to this, in the plastic regime, all WHA exhibited nearly identical behavior regardless of the W content. In this regime, the deformation of the W particles reached several percent, indicating an extremely strong particle-matrix bonding. Last, the failure mechanisms of the materials were investigated, with the matrix behavior governing the fatigue failure, and particle-matrix decohesion dominating in the static loading at higher loads.
PubDate: 2023-12-01
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- Effect of Impact Angles and Temperatures on the Solid Particle Erosion
Behavior of HVOF Sprayed WC-Co/NiCr/Mo and Cr3C2-CoNiCrAlY Coatings-
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Abstract: Abstract Extreme erosion wear from elevated temperature caused by the impact of entrained solid particles in the fluid stream primarily affects aerospace components and marine parts. This work focuses on increasing the base material erosion resistance by applying thermally sprayed carbide-based coatings. A high-temperature Solid particle erosion behavior of WC-Co/NiCr/Mo and Cr3C2-CoNiCrAlY coatings deposited by the HVOF process on a titanium-31 was evaluated using an air-jet erosion tester. The erosion test was conducted utilizing alumina erodent of grit size 35-50 µm. The effects of impact angles (30°, 60°, and 90°) and temperatures (200-800 °C) on the erosion performance of two coatings are compared. The feedstock powder and as-sprayed coatings were characterized for micro-structure phase composition, porosity, density, micro-hardness, and adhesion strength. SEM/EDS and a 3D optical profilometer were used to examine eroded samples further to determine the erosion mode. The Cr3C2-CoNiCrAlY coating shows a brittle mode behavior of erosion at 200-400 °C and ductile mode behavior of erosion at 600-800 °C. In contrast, the WC-Co/NiCr/Mo coating shows brittle mode behavior of erosion at 200-400 °C and 600-800 °C, a mixed mode behavior of erosion. The erosion loss in volume of Cr3C2-CoNiCrAlY is lower than WC-Co/NiCr/Mo for all temperatures and impact angles. The development of carbide and oxide phases on the eroded surfaces demonstrates increasing erosion resistance at high temperatures. The optical profilometer measures the volumetric erosion loss, compares it with the weight loss method, and finds consistency between them.
PubDate: 2023-12-01
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- Effect of Laser-Textured Edge Splashing on Adhesion and Fracture Mechanism
of Plasma-Sprayed Coatings-
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Abstract: Abstract The material surface was sinusoidally textured using nanosecond laser processing technology, and Ni-based MoS2 coatings were applied to the resultant surfaces via plasma spray. The adhesion of the coating was investigated through separate adhesion tests to assess the impact of retaining the fusion-sputtered splash bulges and subsequently grinding them off. The coating's cross-sectional microstructure and fracture morphology were characterized to investigate its deposition and fracture mechanisms. The comparison of textured surfaces with and without bulges has shown that the exposed plain areas diminish the coating's adhesion. Furthermore, the splash bulge also significantly affects the adhesion. Fracture analysis has demonstrated that the mixed failure mode is dominated by no uplift, and adhesive failure occurs in practically all plain areas. By analyzing specimen cross-sectional morphologies and extracting coating morphological features in and around the splash bulge, several aspects, such as filling and spreading mode, the state of sprayed droplets, porosity comparison, and crack formation mechanism and distribution, were investigated. Finally, it was concluded that the excessive or large splash bulges detrimentally impact the bonding properties of the coating.
PubDate: 2023-12-01
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- Effect of In Situ Generated TiNx on Structure and Tribological Behavior of
Al2O3-13wt.% TiO2 Composite Coatings Produced via Reactive Plasma Spraying
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Abstract: Abstract Microstructure, mechanical properties, and tribological behavior of Al2O3-13wt.% TiO2 (AT13)-based coatings with different TiNx (x = 0.3 or 1) contents were investigated. Herein, TiNx complexes were generated from Ti powder via reactive plasma spraying. The morphology and microstructure of AT13-TiNx multiphase ceramic coatings were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. The presence of TiNx complexes improved microhardness of coatings. At the same time, excessive TiNx content led to uneven microhardness distribution in coatings. Moreover, with the increase in TiNx concentration, wear mechanisms of coatings changed from adhesive and abrasive wear (coating A) or abrasive wear with lubricating phase (coating D) to severe brittle fracture and abrasive wear (coating E). Besides, the coefficient of friction (COF) of coating D reached its lowest value. This was because TiO2 and TiN0.3 with the smallest hardness were predominant in the coating, playing the role of lubricating phases in friction process. As a result, the pinning effect of hard TiN particles prevented plastic deformation of the coating, thus reducing COF and wear quality loss of coating D. In turn, excessive TiNx particles led to the formation of uneven coating (coating F), in which stress concentration during friction testing increased and abrasive wear was aggravated, causing an increase in COF. At low friction speed (100 rpm), wear mechanism of AT13-TiNx composite coating remained unchanged, and COF reached its maximum. At high friction speed (300 rpm), wear mechanism was transformed into adhesive wear and oxidation wear, and COF achieved its lowest value. At last, under the condition of low load (5 N), the wear mass loss of AT13-TiNx composite coating was the minimum, but COF increased.
PubDate: 2023-12-01
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- Enhancing Mechanical and Tribological Properties of Cold-Sprayed Aluminum
Through Graphene Nanoplatelet and Boron Carbide Reinforcement-
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Abstract: Abstract This study explores the effects of adding graphene nanoplatelets (GNP) and micro-boron carbide (μB4C) on the mechanical and tribological behaviors of cold-sprayed aluminum matrix composites (MMC) coatings. The coatings were synthesized through high energy ball milling (HEBM) and cold sprayed with nitrogen, resulting in 4 distinct Al-MMC compositions: pure Al, 2 vol.% µB4C, 2 vol.% GNP, and 1 vol.% µB4C with 1 vol.% GNP. The as-sprayed coatings underwent heat treatment at 400 °C to enhance their density and strength. Compared to the pure Al coating, the Al-GNP/µB4C and Al-µB4C compositions exhibited an improvement of 27.5 and 39.6%, respectively, in hardness and adhesive strength values. Moreover, the Al-GNP/µB4C coating demonstrated a significant reduction of 42.5 and 45.3% in specific wear rate and depth of the wear track, respectively.
PubDate: 2023-12-01
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- Influence of Crystallographic Orientation on the Deformation of Ag
Nanoparticles During High-Speed Impact-
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Abstract: Abstract Several related aerosol processes utilize a supersonic gas jet to impact solid nanoparticles to produce nanograined films. Although the influence of important control variables such as particle size and particle impact velocity on particle deformation and film formation for these processes have been previously studied, other variables have not been systematically explored. One parameter that cannot be controlled in experiments is the particle impact orientation. Because particles impact with a full range of crystallographic orientations, an understanding of the effect of particle orientation is required to predict film microstructures. In this study, molecular dynamics simulations were conducted with Ag to determine the influence of particle crystallographic orientation on the deformation experienced by the particle upon impact and the resulting microstructure of the deposit. It is shown that the orientations that produce the largest overall particle deformation are not correlated to orientations where the initiation of plastic deformation is easiest, as one might expect. Rather, the deformation experienced by the particle is heterogeneous and depends on the mechanisms responsible for deformation. Two deformation mechanisms are identified: (1) dislocation plasticity and (2) disordering followed by viscous flow. The fraction of the atoms in the impacting particle that experience deformation by each mechanism is quantified as a function of particle orientation. The implications of the effects of particle crystallographic orientation on film microstructures are also discussed.
PubDate: 2023-12-01
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- Microstructural Nano-Scale Evolution at Inter-Particles Bonding Interface
of Cold-Sprayed Ti6Al4V Deposits During Heat Treatment-
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Abstract: Abstract The inter-particle bonding (IPB) mechanism of cold-sprayed titanium alloy during heat treatment (HT) is not clear. The interfacial microstructure and bonding characteristics at the interface of cold-sprayed Ti6Al4V after HT were studied at the micro- and nano-scale. As a result, the nanocrystallization at IPB during cold spray (CS) cannot cause obvious metallurgical bonding between Ti6Al4V particles. The average Young’s modulus of CS Ti6Al4V is 57% higher than that of powder, but the average Young’s modulus of HT sample decreases by 16%. The internal stress and dislocation distribution of interfacial microstructure can lead to various microstructure features and non-uniform rates of microstructure growth at deformed transition layer and IPB during HT. The nanograins at the IPB grow into micron-equiaxed grains. On the contrary, the micron martensitic laths at deformed transition layer adjacent to IPB show the characteristics of equiaxed nanograins transformation under the action of grain boundary bulges induced by dislocation entanglement.
PubDate: 2023-12-01
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- Wear Mechanisms of Cold-Sprayed Stellite-6 During Reciprocated Dry Sliding
Under Different Sliding Speeds-
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Abstract: Abstract Cobalt–chromium alloys are often employed in those environments that require reliable wear and friction properties. Cold Gas Dynamic Spray offers the opportunity to obtain good quality deposits of Stellite-6, that can be successfully used in harsh environments, where good surface performance, in terms of wear resistance, is required. It is also well-known that Stellite-6 is subjected to several physical changes at the interface during dry sliding, that are often related to the loading conditions. As a consequence, wear behavior of this alloy can undergo some variations that linear models are not able to capture, since micro-structural modifications occur during operation. To better understand the wear mechanisms of cold-sprayed Stellite-6 coatings together with the occurring physical phenomena, a systematic experimental study was performed, in fact, to date, no such in-depth tribological studies have been performed. Tests were conducted under combinations of two sliding speeds (0.1 and 0.5 m/s) and four contact pressure in the range of 2-5 MPa. In low-speed tests, abrasive wear is evident, where detachment and pull-out phenomena mainly affect the worn surface of coatings. On the other hand, subsurface cracking was observed in high-speed tests, as well as evidence of plastic deformation on the wear surface. These results suggest that observed wear mechanisms are more likely a consequence of adhesive wear. Unique to this study, the cross-sectional nano-indentation tests showed how the stiffness of the coating, near to wear interface, increases significantly in the case of the lowest value of sliding speed (i.e., v = 0.1 m/s), whereas tends to decrease at high speeds, i.e., v = 0.5 m/s, as a consequence of the formation of subsurface cracks into the coating.
PubDate: 2023-12-01
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- Characterization and Corrosion Behavior to Molten Zinc of TiAl-Nb/NiCrAl
Gradient Coatings-
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Abstract: Abstract In the present work, TiAl-Nb/TiAl-Nb + 50%NiCrAl/NiCrAl triple-layer coating (TC) and TiAl-Nb/NiCrAl gradient coating (GC) were fabricated by high-velocity oxygen fuel (HVOF) spraying, with TiAl-Nb/NiCrAl duplex-layer coating (DC) as reference. The porosities of GC (0.87 ± 0.06%) and TC (1.02 ± 0.06%) were significantly lower than that of DC (1.22 ± 0.11%). The gradient change in composition and microstructure could alleviate the stress concentration and retard the formation and propagation of void and microcrack. The tensile testing results showed that the adhesive strengths of GC and TC were 69.5% and 43.3% higher than that of DC (43.6 MPa), respectively. The thermal shock test showed that the thermal shock lifetimes of GC and TC were 142.9% and 62.6% higher than that of DC (91 cycles), respectively. The lifetimes of GC and TC in molten zinc were significantly longer than that of DC. Both corrosion processes of DC, TC and GC could be divided into incubation period and rapid corrosion period. The lifetime of coating primarily depends on the incubation period. The prolongation of the incubation period for gradient coating can be attributed to the existence of the gradient structure, which alleviates the stress concentration on the coating surface and reduces its defects.
PubDate: 2023-12-01
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- Characterization and Early-Stage Oxidation Behavior of
CoNiCrAlY/Nano-Al2O3 Composite Coatings Using Satellited Powders Deposited
by HVOF and LPPS Processes-
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Abstract: Abstract In this study, satellited CoNiCrAlY/nano-Al2O3 feedstocks with 2 wt.% of oxide nanoparticles and pure CoNiCrAlY powder were deposited by the HVOF and LPPS processes on Inconel738 superalloy substrates. Microstructure and phase composition of powders and coatings were characterized by FESEM and XRD, respectively. The early-stage oxidation test was done at 1050 °C for 10 min. The results showed that the satelliting seems to be a promising method to produce nano-particles dispersed composite powders suitable for thermal spraying. Adding α-Al2O3 nanoparticles increased the porosity of the HVOF and LPPS coatings from 0.6 to 1 and from 2 to 2.45 vol.%, respectively. In the HVOF-sprayed CoNiCrAlY/nano-Al2O3, coating including γ-Co,Ni,Cr, β-(Co,Ni)Al, and α-Al2O3, the growth of non-protective NiO and spinel oxides was significantly limited and a dense α-Al2O3 oxide layer was promoted after the early-stage of oxidation. However, for the LPPS-deposited CoNiCrAlY/nano-Al2O3 coating consisting of γ-Co,Ni,Cr and γ-Al2O3, after oxidation, the presence of Al-rich oxides like θ-Al2O3 whiskers and porous transformed α-Al2O3 were observed on the coating. The correlation between microstructure, phase composition, and early-stage oxidation was discussed in detail.
PubDate: 2023-12-01
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- Evolution of Microstructures and Mechanical Properties of Cold Sprayed
Copper in Hot Rolling-
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Abstract: Abstract Hot rolling is an emerging post-processing method for improving mechanical properties of cold sprayed materials. However, the effects of hot rolling on cold sprayed materials are not well clarified. Accordingly, hot rolling assisted with heat treatment was conducted to investigate the effects of hot rolling on plastic deformation of cold sprayed copper bulks. The porosity, crystal grains and dislocation density of copper bulks were characterized through scanning electron microscope, electron back-scatter diffraction and transmission electron microscope. The evolution of pores during hot rolling was simulated using finite element analysis. The microhardness, tensile strength and breaking elongation of the bulks were measured to further explore the effects of hot rolling. The results show that the apparent porosity of the copper bulks sharply decreased due to the dynamic generation and healing processes of the pores in hot rolling. The tensile strength of the copper bulks increased significantly due to the evolution of bonding mechanisms and grain sizes of the copper bulks in hot rolling.
PubDate: 2023-12-01
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- Effect of Laser-Glazed Treatment on Thermal Cyclic Behavior of
Plasma-Sprayed Lanthanum Zirconate/Yttria-Stabilized Zirconia Double
Ceramic Layered on NiCoCrAlYTa-coated Inconel-
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Abstract: Abstract This paper investigates the thermal barrier coating (TBC) performance of La2Zr2O7/ZrO (2-8 wt.%) Y2O3 coatings (LZ/YSZ TBCs) deposited using atmospheric plasma spray (APS) over high velocity oxy-fuel (HVOF) NiCoCrAlYTa coated on Inconel 625. On the outermost surface of the double-layered coating, a laser glazing method was used to treat the TBC systems. Specifically, a Nd:YAG pulsed laser was used to change the surface layer of plasma-sprayed La2Zr2O7 top coatings. The study found that the laser glazing treatment resulted in a higher number of temperature cycles needed to generate 5-20% spallation of the top surface of coatings, with 100 cycles compared to 30 cycles in the as-sprayed coatings. This improvement in performance was attributed to the dense surface of the laser-glazed LZ topcoat, which led to a lower thermally grown oxide (TGO) layer growth rate and improved TBC lifetime. Furthermore, the strain adaptation through segmented cracks that were created by laser glazing may have contributed to the enhanced TBC performance.
PubDate: 2023-12-01
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- Mario Guagliano, Vincent Rat, and Katy Voisey Join JTST Editorial Team
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PubDate: 2023-11-17
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- On the Heat-Transfer Effect of Spraying Speed During the Plasma Spraying
on Turbine Blade-
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Abstract: Abstract To investigate the changes in the substrate temperature field during the thermal spraying of turbine blades, this study first uses finite element technology to map the surface of the spraying workpiece and generate different spraying paths by ordering the index of the mesh node. Second, an analysis is conducted on the robot kinematics for different types of paths, and the results reveal that adopting a vertical path has better robot kinematics. Then, a heat source model is established for the thermal spray process on free-form surfaces. The spray path, direction of the plasma jet axis, and surface morphology of the blade are combined with heat simulation to study the thermal behavior of the substrate. The comparison and discussion of the substrate’s temperature change are based on two different methods of heat source calculation during the spraying process. Finally, by changing the scanning speed of the gun during the spraying process, simulations are conducted to analyze and compare the transient temperature fields for the substrate sampling points corresponding to the thermal spray trajectories at different scanning speeds. The comparative results of thermal simulation indicate that the maximum and minimum temperatures during the spraying process decrease evidently with an increase in scanning speed. After the spraying process, the maximum temperature of the substrate reduces from 574.64 to 493.43 K, while the minimum temperature reduces from 354.78 to 331.04 K, and the average temperature of the substrate reduces from 385.13 to 353.42 K. This study has important guidance and theoretical references for the optimization of the scanning speed parameters for the plasma spraying of turbine blades.
PubDate: 2023-10-23
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- Structure and Deposition Characteristics of Cold-Sprayed AA5083 and Al-Mg
Binary Alloys Using Gas-Atomized Al-Mg Powders-
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Abstract: Abstract This paper investigates customized AA5083 and Al-Mg binary powders produced by gas atomization and assesses cold spray (CS) deposition of these materials with the evaluation of interface quality, deposition efficiency, porosity, and microhardness. While there has been extensive research progress on CS deposition of AA2024, AA6061, and AA7075, less attention has been given to CS 5xxx-series (Al-Mg) aluminum alloys. For the development and investigation of CS Al-Mg series alloys, AA5083 and customized Al-Mg binary powders were fabricated using a close-coupled inert gas atomizer, and those powders were sprayed using a high-pressure cold spray system to produce CS Al-Mg deposits. The microstructural characteristics of the powders, such as lattice constant and the formation of intermetallic networks, were affected by the Mg content of as-atomized powders. Selected CS parameters were able to produce highly dense CS deposits over a range of 1.7-5 wt.% Mg. The Mg content of as-atomized powders also influenced the hardness of the deposits and the DE while having no effect on porosity. The influence of Mg content on powder properties, CS process, and CS Al-Mg deposits has been discussed.
PubDate: 2023-10-23
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- An Investigation of the Effect of Post Heat Treatment on the Wear and
Corrosion Behavior of HVOF-sprayed WC-10Co4Cr Coatings-
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Abstract: Abstract The impact of heat treatment on the wear and corrosion behavior of WC-10Co4Cr coating was investigated in this study. Firstly, the prepared samples were subjected to argon protection heat treatments at 550, 750 and 950 °C. The samples were characterized using SEM, XRD and microhardness testing. The results showed that the change in temperature affected the phase transformation and mechanical properties. The coating did not undergo a phase change after the heat treatment at 550 °C, while the transformation of the η-phase occurred in the coating after heat treatment at 750 and 950 °C. However, heat treatment of the coating led to adhesive failure, resulting in partial separation between the coating and substrate. Due to the formation of hard phases, the wear resistance of the coating was improved after heat treatment, with the main wear mechanisms being micro-cutting and delamination. According to the corrosion test results, the corrosion resistance of the coating was significantly improved after heat treatment at 950 °C, with a reduction of 78.1% in its corrosion rate in 3.5 wt.% NaCl compared to the original coating. This was attributed to the precipitation of η-phase and recrystallization of the bonding phase in the coating which reduced the micro-cell effect within the coating.
PubDate: 2023-10-12
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- Effect of Thermal Spraying Method, Time and Temperature on the Thickness
of Thermally Grown Oxide and Lifetime of Thermal Barrier Coatings-
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Abstract: Abstract This paper investigates various parameters affecting the thickness of the thermally grown oxide (TGO) layer affecting the lifetime of conventional thermal barrier coatings (TBCs) with two new coatings. The thickness of the TGO layer directly influences the generation of interfacial stresses and delamination of the coating layers. This study examines the effects of the thermal spraying method, time, temperature, and the TC absence on the TGO thickness. In the first new coating, two bond coats are utilized, applied using the high-velocity oxygen fuel (HVOF) and air plasma spraying (APS) methods. The second new coating involves an aluminide diffusion coating applied between the bond coat and substrate. Scanning electron microscope (SEM) analysis of the test samples reveals that the HVOF-applied coating forms a TGO with lower thickness compared to the APS coating. The most extended lifetime of 336 h is achieved by the new coating with a two-layer bond coat, followed by the HVOF coating with 288 h, the diffusion coating with 238 h, and the APS coating with 192 h, respectively. Despite the lower TGO thickness in the HVOF coating compared to the two-layer bond coat, its lifetime is reduced due to severe spinel growth at the interface of TBCs with the HVOF bond coat caused by the faster depletion of aluminum (Al). The diffusion coating increases the concentration of Al in the upper part of the substrate, thereby reducing the depletion of Al from the bond coat through interdiffusion. By retaining the Al in the bond coat for a longer duration, the diffusion coating enhances the lifetime of TBCs.
PubDate: 2023-10-11
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