bluuebunny/crossref_metadata_2025 huggingface dataset:
A Concept of Aerospike Nozzle for Cold Spray Additive Manufacturing—Towards a Potential Solution for Preventing the Issue of Clogging
Authors: Raoelison Rija Nrina , Msolli Sabeur , Deng Sihao , Vashishtha Ashish , Sharma Amit , Callaghan Dean , Zaim-Mounajed Wassim , Zhang Teng , Padayodi Essolé , Sagot Jean-Claude , Raghavendra Ramesh
Published: May 2023

The clogging, a frequent gas passage deformation phenomenon because of powder accumulation on inner nozzle wall, is a major issue in long duration Cold Spray (CS) operations and a major challenge for Cold spray technology to be adopted for additive manufacturing. This study aims to design and integrate new nozzle design in Cold Spray operations for addressing the clogging issues in traditional circular convergent-divergent (CD) nozzles. The concept of the Aerospike nozzle is proposed for that purpose and is investigated using numerical simulation methods in this paper. An aerospike nozzle allows gases to accelerate externally bounded by environment on one-side and contoured spike wall on other side. After accelerating along the spike wall, aerospike nozzle can generate a longer supersonic gas stream. The spike region can be truncated near the tip to provide a flat face for powder injection. This proposed strategy will allow powder particles to accelerate through a longer supersonic core region, without interacting with nozzle wall. With appropriate operating parameters, an aerospike nozzle can reduce or eliminate the clogging issue completely. The efficiency and operation of aerospike nozzle is compared with same Mach number C-D nozzle using numerical simulations at stagnation pressure of 30 bar and temperature of 623K, where the aluminium powder particles are injected at 30 g/min in the centerline of both nozzles and are accelerated to similar velocities. The powder particles are accelerated in supersonic core region of aerospike nozzle without interacting with nozzle wall, it is concluded that the aerospike nozzle can be a promising nozzle design to provide clogging free long duration CS operations.
Investigation of a Modified Circular Nozzle for Cold Spray Applications
Authors: Sharma Amit Kumar , Vashishtha Ashish , Callaghan Dean , Bakshi Srinivasan Rao , Kamaraj M. , Raghavendra Ramesh
Published: May 2023

The current work numerically evaluates the efficacy of a coflowing nozzle for cold spray applications with the aim to mitigate nozzle clogging by reducing the length of its divergent section. The high-pressure nitrogen flow through convergentdivergent axis-symmetric nozzles was simulated and the particle acceleration is modelled using a 2-way Lagrangian technique which is validated using experimental results. An annular co-flow nozzle with a circular central nozzle has been modelled for nitrogen gas. Reduction of nozzle divergent length from 189 mm to 99 mm showed an approximate 2.2% drop in particle velocity at high pressure operation while no variation at lower pressure operation was observed. Co-flow was introduced to the reduced nozzle length to compensate for particle velocity loss at higher operating conditions and it was found that co-flow facilitates momentum preservation for primary flow resulting in increased particle speed for a longer axial distance after the nozzle exit. The reduced divergent section nozzle, when combined with co-flow, is comparable to the original length nozzle.
Erosion Behaviour of Cold Sprayed Coatings Made of CrMnFeCoNi High-Entropy Alloy or Composite Powders Containing WC Hard Particles in a Pure Nickel Matrix
Authors: Cappelli Giacomo , Yin Shuo , Lupoi Rocco
Published: May 2023

The performance of two distinct coating materials under alumina particle impingement was tested in this study. CrMnFeCoNi and WC-Ni coatings were applied to 2205 duplex stainless steel substrates using cold spray method with nitrogen as the process gas. In between the substrate and the high entropy alloy coating, an interlayer coating of 316 stainless steel was used. The presence of WC particles in the WC-Ni composite coatings was confirmed by SEM cross sectional inspection. Following deposition, the coatings were heat treated in an air furnace. The influence of heat treatment holding time on the WC-Ni coatings was studied using chemical analysis by X-ray diffraction. Heat treatments peak temperatures for the WC/Ni- Ni and high entropy alloy coatings were 600°C and 550°C, respectively. Coatings microhardness and porosity volume fraction were measured for all the samples. The HEA coating outperformed the WC/Ni-Ni hardness but exhibited a higher level of porosity. The coatings were then subjected to erosion experiments using alumina particles with variable impact angles (30°, 60°, and 90°). To compare the different materials, an average erosion value was calculated for each target specimen. The WC/Ni-Ni as-sprayed coating was the most effective against a 60° impingement angle. The HEA coating, on the other hand, demonstrated greater resistance to impact angles of 30° and 90°. SEM was utilized to examine the eroded areas and determine the main mechanisms of erosion.
Forming Behaviour of Additively Manufactured Al/Ti Material Compounds Produced by Cold Spraying
Authors: Drehmann Rico , Graf Marcel , Lampke Thomas , Colditz Pascal , Awiszus Birgit , List Alexander , Gärtner Frank
Published: May 2023

Cold spraying has great potential for additive manufacturing, especially of oxidation-sensitive metals, because the material is not melted and significantly higher deposition rates can be achieved than with conventional additive manufacturing processes such as selective laser melting or direct metal deposition. Titanium is regarded as a high-performance engineering material due to its unique combination of properties, including good corrosion resistance, biocompatibility and high strength at comparatively low density. However, due to its high price, it appears reasonable for many applications to use material compounds in which titanium is only used on the surface of the workpiece, while less expensive materials such as aluminum are used for the remaining volume. In the present work, cold sprayed pure titanium coatings were deposited on Al substrates and then formed to defined 3-dimensional final contours by die forging and rotary swaging. Different porosities were selectively set in order to evaluate their influence on the coating adhesion and cohesion in the forming process. Pre-consolidation of the coatings and the use of Al/Ti interlayers proved to be promising strategies.
Multi-Purpose Additives Towards a Better Polymer Cold Spray Process
Authors: Bacha Tristan W. , Haas Francis M. , Stanzione III Joseph F.
Published: May 2023

Polymers have proven to be challenging to cold spray, particularly with high efficiency and quality when using inexpensive nitrogen (N2) and air propellants. Helium (He) when used as a process propellant can improve spray deposit properties but is often undesirable due to its limited availability and high cost. In this study, additives of multiple particle sizes and materials were mixed with polymer powder in an effort to improve the performance of polymer sprays using mainly N2 as a process propellant. The effects of additives on deposit microstructure were investigated by precise ion-beam polishing of deposit cross sections and subsequent electron microscope imaging. Additional metrics including the density and post - spray composition of deposits were investigated to quantify the peening effect and the amount of embedded additive. Additives, regardless of size, were observed to embed in the spray deposits. Additionally, hard-phase additives demonstrated nozzle-cleaning properties that continually remove polymer fouling on the nozzle walls. Inversely, sprays with polymer powder and no additives tended to clog the nozzle throat and diverging section as a result of continual fouling.
Effect of Carbon Fiber Orientation when Cold Spraying Metallic Powders onto Carbon Fiber Reinforced Polymers
Authors: Liberati Andre C. , Patel Payank , Roy Amit , Vo Phuong , Pan Chunzhou , Moreau Christian , Chromik Richard R. , Yue Stephen , Stoyanov Pantcho
Published: May 2023

A previous study on the pull-off testing of metallized carbon fiber reinforced polymers (CFRPs) via cold spray showed that better adhesion strengths could be obtained when features such as carbon fibers or surfacing elements were present, by providing potential mechanical interlocking features. In this work, the effect of the fiber orientation on the deposition and bonding of the metallic coating to the thermoplastic composite substrate is explored. Pure Sn powder was cold sprayed onto two thermoplastic Polyether-Ether- Ketone (PEEK) CFRP substrates, containing carbon fibers with different orientations: one had fibers in the plane of the substrate (uni-directional tape), while the other had fibers mostly perpendicular to the substrate (ZRT film). Characterization of the coatings was performed via scanning electron microscopy (SEM) and confocal microscopy, and some aspects of mechanical testing (namely wear and scratch testing) were carried out to assess the effect of the substrate on the properties of the coatings.
Improvement of the Cold Sprayability of Hard Steel Alloy Powders
Authors: Guerreiro B. , Poirier D. , Thomas Y.
Published: May 2023

Successful cold spray of tool steels and other hard steels would unlock several opportunities, including the repair of molds as well as ships and heavy industry components. However, the high hardness of typical atomized steel powders strongly limits their cold sprayability. It has been recently demonstrated that heat treatment in a rotating furnace can significantly improve H13 cold sprayability via softening and agglomeration. In this work, this powder modification method is extended to a range of transformation hardenable steels: 4340, SS420, A588, 1040 and P20. The results show that powder heat treatment improves the powder deposition efficiency and the quality of the final cold sprayed coating, probably as the result of the decreased powder micro-hardness. The effects of the powder heat treatment atmosphere, a key parameter, will also be presented and discussed.
Thermal Oxidation of Heavily Deformed Zn Coatings Produced by Cold Spray and Formation of ZnO Nanowires
Authors: Razavipour Maryam , Criado Denise , Zúñiga Alejandro , Jodoin Bertrand
Published: May 2023

Zinc oxide (ZnO) is known for its rich diversity of microstructures and has been attracting attention for its unique combination of mechanical and physical properties. It has been a material of interest in different areas such as optoelectronics, sensors and the general ceramic industry. It also has been a material of interest in biomedicine due to its antimicrobial characteristics and biocompatibility properties. A simple processing route to produce ZnO micro/nanostructures is the thermal oxidation of zinc, which results in a wide range of ZnO nanostructures depending on the oxidation conditions. The main objective of this study was to investigate the influence of a severe plastically deformed zinc microstructure on the formation of ZnO nanostructures produced by oxidation, with a special attention to the zinc oxide growth mechanism and nanostructures characteristics. For this purpose, the cold spray process was used to produce Zn coatings using different feedstock powders that required different process parameters in order to obtain Zn coatings with severely deformed particles. A non-catalytic thermal oxidation method was then used to successfully produce ZnO nanostructures at the surface of the heavily deformed cold sprayed Zn coatings. The as-grown ZnO nanostructures were investigated in detail using scanning electron microscopy and X-ray photoelectron spectroscopy. These investigations revealed that the chemical fingerprint of the oxides grown in the cold sprayed samples was different from that of conventional ZnO. It was also observed that in the oxidized cold sprayed Zn coatings, the formation of ZnO nanowires was hindered due to the formation of blisters generated during the high temperature exposure, revealing nonoptimized process parameters.
Process Innovation for the Internal Coating of Carbon Fiber Reinforced Plastic (CFRP) Tubes via Thermal Spraying
Authors: Semmler Christian , Killinger Andreas
Published: May 2023

The application of thermally sprayed coatings on CFRPs has gained great interest to enhance thermal and tribological properties and several processes have been optimized. However, for the coating of internal surfaces of tubes there is no sufficient technical solution. This paper introduces a novel and unique process technique for coating the internal surfaces of CFRP tubes using the transplantation of thermally sprayed coatings. A negative shape tube with defined surface and material properties was used as a mandrel and coated using atmospheric plasma spraying (APS). The CFRP was then produced using filament winding onto the coating, and after curing, the specimen was separated from the mandrel. With this process innovation, CFRP tubes with internal ceramic or metallic coatings can be produced without any thermal degradation of the polymeric matrix or damage to the carbon fibers. Compared to conventional coating methods, this novel process technique has several advantages. It allows for the production of internal coatings with low roughness of Rz = 10 μm as sprayed without post-processing. The specimens also have a significantly lower tendency to corrode compared to conventional coated CFRPs. A high adhesion strength of the coatings of 15.9 MPa was achieved and the hardness of the internal ceramic coating is 918 HV0.1
The Steady-State Composition and Microstructure of 42%WC-42%Cr3C2-16%Ni HVOF and Shrouded Plasma Sprayed Coatings at 900°C
Authors: Matthews Steven , O’Neil Francesca
Published: May 2023

Conventionally, bulk WC and Cr3C2-based carbide compositions have been used independently of each other. However, recent investigations have begun to explore combining these carbides together within the same composite/hardmetal coating system. This research builds on earlier work characterising 42%wt% WC-42%wt% Cr3C2- 16%wt% Ni coatings sprayed under “low”, “medium” and “high” thermal input conditions, to assess their compositions and microstructures after heat treatment in air at 900°C for up to 30 days. Coatings were deposited by HVOF, Ar-He and Ar- H2 shrouded plasmas respectively, onto Alloy 625 substrates with Ni20Cr bond-coats and top-coats. The coating compositions and lattice parameters were quantified by Rietveld peak fitting of XRD patterns. The microstructures were analysed from cross sectional backscatter electron micrographs. Rapid phase development occurred within the first five days, beyond which the compositions and microstructures remained stable. The microstructures retained extremely fine, sub-micron grain sizes, while the carbide phases exhibited high degrees of metastable alloying, even after 30 days at 900°C. The coating compositions are discussed, and a mechanism proposed to account for the rate of development and overall metastable microstructure.
Characterization of Thermally Protective Al2O3-TiO2 Coating Fabricated by Atmospheric Plasma Spraying
Authors: Kwon Hansol , Yoo Yeonwoo , Park Youngjin , Nam Uk Hee , Byon Eungsun
Published: May 2023

In this study, Al2O3-based coatings with varying TiO2 contents (0, 3, 13, and 40%) were fabricated using atmospheric plasma spraying technique. To compare the superiority of the samples, their thermal properties (thermal conductivity and thermal shock resistance) were characterized. As observed, Al2O3- 40%TiO2 (A-40T) coating exhibited relatively superior thermal insulation and thermal shock resistance at 600°C. According to the microstructure and phase analysis, this finding can be attributed to the special phase, Al2TiO5, and the pre-existing microcracks inside the coating. Thus, A-40T manifested excellent characteristics for thermal insulation application compared with pure Al2O3 and low-TiO2 content coatings.
Investigating the Effect of Solid Lubricants Addition on Friction and Wear Behaviour of Thermally Sprayed Coatings
Authors: Patrikalos J. , Ioannou P. , Andreouli D. , Georgiopoulos I. , Skaltsas D. , Papadopoulos C. I. , Sarafoglou Ch. I.
Published: May 2023

Composite coatings using mixed alloy matrices reinforced with carbon-based solid lubricants as feedstock materials were prepared by atmospheric plasma spraying. The aim of the present study was to investigate the tribological characteristics of such coatings exploring potential benefits of CNTs as nano-additive to reduce friction and wear, improving lubrication conditions during operation in tribosystems, such as piston ring – cylinder liner systems. The chemical composition of feedstock materials and the thermal spray parameters during coatings deposition are correlated to friction coefficient and wear rate using pin-on-disk measurements. The developed coatings hybrid behaviour is studied. Co-based cermet as well as metal alloy anti-wear performance along with the promoted lubrication conditions during operation is revealed. The dependence of the developed coatings quality and performance on the characteristics of the feedstock powder is thoroughly discussed.
Effect of Heat-Treatment on the Microstructure and Mechanical Properties of CoCrFeNiMn High Entropy Alloy Additively Manufactured via Cold Spray
Authors: Akisin Cletus J. , Bennett Chris J. , Venturi Federico , Hussain Tanvir
Published: May 2023

The application of cold spray (CS) for additive manufacturing (CSAM) of structural components using metallic materials has recently attracted much attention. However, there are limited reports on developing thick deposits or components with high entropy alloys (HEAs) via CSAM and investigating the microstructural evolution and mechanical properties after deposition and subsequent annealing heat-treatment. This work investigated the microstructure and mechanical properties of asdeposited and heat-treated thick CoCrFeNiMn HEA deposit fabricated via CSAM. The microstructure of the HEA deposit and after heat-treatment were characterised using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and x-ray diffraction (XRD). The microstructural analysis reveals heterogeneous grain size distribution with ultrafine grains at the particle-particle interfacial regions and coarse grains at the particle interiors in the as-deposited sample. The as-deposited sample, characterised by moderate porosity, was consolidated following the heat treatment at different temperatures. Additionally, increasing the temperature increases grain sizes resulting from static recovery and recrystallisation, with annealing twin formed at higher temperatures. Most notably, phase decomposition of the deposit microstructure occurs at 600 ºC, with Cr-rich phase particles formed at regions of high dislocations and grain boundaries. Nano-and micro-hardness and tensile testing of micro-flat dogbones samples were performed on the as-deposited and heattreated samples. The effect of heat-treatment on the microstructure and mechanical properties of the cold-sprayed HEA deposit were analysed and discussed.
Laser Texturing as Interfacial Treatment for Enhancing the Material Behaviors—The Real Influence of the Laser Treatment
Authors: Costil Sophie , Convert Laura , Bourillot Eric , Pocholle Nicolas , François Manuel
Published: May 2023

Surface texturing is one of the most technologically appropriate laser surface treatment applications. Over the past few decades, texturing has emerged as an attractive surface engineering option and has been used by researchers to generate micro/nanopatterns on operating surfaces. This technique can create simple or complex patterns on component surfaces depending on their aesthetic or functional goals and without altering the overall properties. In addition, this non-contact process can be applied to hard-to-reach areas. Recently, laser surface texturing has been applied to improve the adhesion of contact surfaces. Several authors have demonstrated the impact and benefits of textured surfaces to achieve optimal adhesion of coatings and increase in-service behavior. Nevertheless, based on the laser-matter interaction phenomena, chemical and mechanical transformations of the surfaces can be noticed but are difficult to characterize. Indeed, the affected layers are of the order of a few hundred nanometers. Then, analyses must be performed with variable levels of resolution in order to analyze the structural, chemical and mechanical characteristics of the matter. To develop new applications of unconventional assemblies and improved adhesion of new materials, a control of these local modifications is required.
Automated Path and Trajectory Planning for Automated Repair of Damaged Components by Cold Spray
Authors: Lewke Marcel , Wu Hongjian , List Alexander , Gärtner Frank , Klassen Thomas , Fay Alexander
Published: May 2023

Cold spraying has emerged as a promising technique for the repair of metallic components. For controlled material deposition, manipulation of the cold spray gun is performed by industrial robots. Such robot-guided cold spraying provides flexible control and automation of the entire process. To enable effective and material-efficient material deposition at specified repair locations, this work proposes a method for automated planning of cold spray paths and trajectories. The method begins with the extraction of the volume to be filled by comparing the nominal and actual component. To produce the extracted volume, it is divided into suitable adaptively curved layers and converted into point clouds for path planning. The cold spray path is then converted into a trajectory by adding a suitable velocity distribution for the spray velocity to produce the required locally varying layer thickness. To validate the suitability of the path and trajectory, a simulation of the material deposition is performed. In addition, the implementation of the entire method is demonstrated by exemplary use cases. The results demonstrate that the proposed method enables successful automated path and trajectory planning, both contributing to the overall goal of automated repair of damaged components by cold spray.
Anisotropy of Mechanical Properties of DMD Build Inconel 738
Authors: Kovarik Ondrej , Cech Jaroslav , Kiziklioglu Egehan , Cizek Jan , Stittgen Tobias
Published: May 2023

Anisotropy of stress-strain behavior, fracture toughness, and fatigue crack growth rate was studied for Inconel 738LC alloy built by the Dynamic Metal Deposition technique (3DMD, a high-speed Directed Energy Deposition technique). The measured quasi-static properties, i.e. stress-strain and fracture toughness showed only subtle anisotropy, with no more than 10% differences found for different orientations. The fatigue crack growth rate was influenced by the specimen orientation more significantly (30% for fatigue crack growth threshold, up to 90% for Paris exponent and coefficient). This pilot study attributes the anisotropy of fatigue crack growth properties to material texture and the columnar grain geometry resulting from directional solidification. The obtained testing results indicate that 3DMD technology can produce materials with good mechanical and fracture properties even from materials considered as non-weldable such as In 738LC. The study provides a solid experimental base for further investigation of the fatigue crack growth mechanism relation to the material texture in 3DMD In 738LC.
Cost-Effective UHVOF-Sprayed Coatings for the Wear Protection of Valves
Authors: Bobzin Kirsten , Heinemann Hendrik , Burbaum Elisa , Schulz Marvin
Published: May 2023

Thermally sprayed WC/CoCr coatings are the most established coatings in the valve industry. However, due to the high wear resistance and as-sprayed surface roughness, the surface post processing costs are very high. Near-net-shaped fine powder coatings have the possibility to reduce the costs effectively. Due to the high specific surface to volume ratio of the powders, undesired phase transformations can occur during the spraying process. To avoid such phase transformations, the novel thermal spraying process Ultra-HVOF (UHVOF) is used in this study. An extensive parameter study is carried out on the influences of the process parameters on microhardness, porosity, as-sprayed surface roughness, phase composition and wear resistance. With suitable process parameters, near-netshaped and almost pore-free coatings can be applied. Compared to a conventional HVOF sprayed WC/CoCr coating, a wear reduction by a factor of three can be achieved in a pin-on-disktest against Al2O3 at a load of F = 15 N. Due to the pore-free and highly wear-resistant coatings, significantly thinner coatings can be used for the protection against corrosion and wear in valves. In addition, the required surface quality of the near-net-shape coatings can be achieved by polishing only. Thus, the novel UHVOF coatings represent a cost-effective alternative to conventionally used valve coatings.
Comparative Corrosion Behaviour of Cold Sprayed Titanium/Hydroxyapatite and Titanium/Baghdadite Composite Coatings in Simulated Body Fluid Environment
Authors: Kumar Avneesh , Chand Teekam , Kant Ravi , Singh Harpreet
Published: May 2023

Bioceramics deposition on medical devices is a widespread area of research for biomedical industries since such deposits can induce excellent chemical and biological properties to the devices. Thermal spraying has been a popular choice for developing coatings to enhance the mechanical, chemical, and biological responses of medical devices. However, the high heat involved during the thermal spraying of bioceramics limits their functionality. In this context, low processing temperature in cold spraying is believed to protect the bioceramics from degradation. However, depositing bioceramics using cold spray and achieving good mechanical properties are still challenging tasks because of their poor ductility. Therefore, bio metal matrix composites with reinforced bioceramics produced using cold spray are expected to give good mechanical, chemical, and biological properties. The present work presents deposition and microstructural characterization of titanium/hydroxyapatite (Ti/HA) and titanium/baghdadite (Ti/BAG) composite coatings by cold spraying. Furthermore, the comparative corrosion response of these coatings under a simulated body fluid environment is reported. The effect of laser remelting on microstructure and corrosion behavior is also discussed.
Cold Spray Nickel-Coated Aluminum Composite Powder Part I—Study on Microstructure of Coatings
Authors: Lu Xiaoliang , Zheng Zhaoran , Yuan Kang , Du Kaiping
Published: May 2023

NiAl coating can be used as bond coats for thermal barrier coatings (TBCs) with good ductility and excellent resistance against high temperature oxidation. In this study, nickel-coated aluminum composite powders were used to prepare NiAl intermetallic compound coatings on nickel-based superalloys using an air plasma spray (APS), high-velocity oxygen-fuel (HVOF) and cold spray (CS) processes. Different spraying parameters in the HVOF and CS processes were used to make different coating microstructures, and the coating prepared by the APS technique served as a control for the HVOF and CS processes. The microstructure and phase constitution of the coatings were studied using XRD, SEM and EDS. The results indicate that the deformation behavior of the NiAl powder was different under the different spraying parameters. Less defects of oxides and inclusions were observed in the CS coatings compared with the HVOF coatings.
Effect of Laser Power on Forming Quality and Crystallization of Amorphous Alloy Prepared by SLM
Authors: Chen Xing , Du Kaiping , Pi Ziqiang , Zheng Zhaoran
Published: May 2023

Amorphous alloys have attracted extensive attention due to their unique atomic arrangement and excellent properties. However, the application in practical engineering is seriously limited due to the size, crystallization and other problems. Laser additive manufacturing technology has the characteristics of high heating, cooling rate and point by point melting deposition, which provides a new idea for the preparation of amorphous alloys. Zr50Ti5Cu27Ni10Al8 amorphous alloy was prepared on the surface of pure zirconium substrate by selective laser melting technology. The composition and structure of the samples were characterized. The results show that the samples are mainly composed of amorphous phase, and the crystallization mainly occurs in the superimposed zone of heat affected zone. With the decrease of laser power, the area of crystallization zone and the number of crystallization particles decrease. However, if the laser power is too low, there will be non-fusion defects and cracks, which will seriously affect the forming quality and amorphous rate of amorphous alloy.
Investigation of Corrosion Behavior and Surface Characteristics of CoCr Alloy using Plasma-Sprayed HA/ZnO Reinforced Coatings for Biomedical Implants
Authors: Bansal Puneet , Singh Gurpreet , Sidhu Hazoor Singh
Published: May 2023

The enhancement of the surface characteristics and corrosion resistance of cobalt alloys is under continuous examination for its biomedical applications. In this work, the investigation of corrosion performance of cobalt alloy coated with HA and HA/ZnO reinforced powders using plasma spray technique revealed that on the continuous increase of ZnO reinforcement the corrosion resistance improved progressively. The increment in surface hardness and drop in surface roughness was examined with the rise in ZnO content. Each coated sample exhibits a hydrophilic property. According to SEM and EDX investigations, homogeneous distribution of HA/ZnO coatings and intact reinforcement of ZnO in pure HA powder was noticed. All of the coated specimens maintain their morphological integrity, ensuring excellent protection of the prepared samples. The obtained outcomes denote HA/ZnO reinforced coatings on CoCr alloy as a suitable combination of enhanced surface properties and excellent corrosion resistance for future bone implant practices.
Effects of Zr and Si Addition on Mechanical Properties of Al0.5CoCrFeNi High-Entropy Alloys
Authors: Bobzin Kirsten , Heinemann Hendrik , Erck Marvin , Schacht Andreas , Korte Benedikt , König Paul
Published: May 2023

Thermally sprayed heating coatings are a recent approach for temperature control in moulding tools. While there are material options in the lower temperature range up to T = 300 °C, new alloys have to be developed to improve the range of application. The Al0.5CoCrFeNi high-entropy alloy (HEA) with further addition of Zr and Si shows favourable electrical properties due to severe lattice distortion. The alloy development was carried out with Al0.5CoCrFeNiZrxSiy by arc melting. Thereby, the molar Zr content x was varied from 0 to 0.5 and the Si content y from 0 to 0.2. In order to evaluate the alloy’s prospective performance, the phase composition was studied by SEM with EDX and the fracture toughness was determined to estimate fracture properties, which are found to be a typical failure mechanism of heating coatings. The different HEA exhibit a typical dendritic microstructure with fcc dendrites and a bcc interdentritic phase. The hardness of the alloys increases with increasing bcc content, while the ductility decreases. With knowledge about the effects of Zr and Si on the electrical and mechanical properties, which are justified by the microstructure, Al0.5CoCrFeNiZrxSiy HEA can be tailored specifically towards the needs of individual heating applications.
Cold Spray Deposition of Aluminium 6061 Decorated with Al2O3 Nanoparticles
Authors: Marzbanrad Bahareh , Marzbanrad Ehsan , Jahed Hamid
Published: May 2023

This research presents a novel approach for producing metal matrix composite powders using a nanoparticle decoration technique. A 1wt% stable suspension of 30nm Al2O3 particles was decorated onto primary AA6061using a redispersion method. The resulting AA6061-1wt% Al2O3 composite powder was mixed in a rotary mixer for one hour and subsequently dried at 45°C. Scanning electron microscopy of the composite powder confirmed the successful material composition. The composite powders were then deposited onto an AA6061 substrate using a low-pressure cold spray system, with the coating quality, deposition efficiency, surface roughness, and hardness of the deposited materials analyzed. After heat treatment at 430oC, the role of the nanoparticles in hindering recrystallization was studied, with Orowan strengthening shown to be the main mechanism for preventing recrystallization and grain growth. This technique provides a promising alternative method for producing metal matrix composites and offers potential for further exploration of their properties and applications.
Composite Capsule Embedded Coatings Deposition using Thermal Spraying
Authors: Skaltsas D. , Papadopoulos C. I. , Sarafoglou Ch. I. , Ioannou P. , Andreouli D. , Georgiopoulos I. , Zotiadis C. , Korres D. M. , Vouyiouka S.
Published: May 2023

The study of self-lubricant coatings is a rapidly developing research field that is expected to address major issues arising from operation under high loads and thermal stresses of machine parts. It is of utmost importance that various critical tribological pairs such as crankshaft bearings, piston rings, etc. maintain their integrity, thus contributing to the engines efficient and reliable operation for long periods of time. Therefore, a choice of high-strength metals is required, with special treatments and/or coatings in combination with sufficient lubrication. In the present study, liquid lubricants encapsulated in poly(urea-formaldehyde) were incorporated in ceramic-metal matrices for the production of composite coatings by Atmospheric Plasma Spraying. Aspects concerning the survival of the capsules during their flight through the high temperature plasma flame, the maintenance of their integrity at impact with the substrate with high kinetic energy, their homogeneous dispersion within the coating mass, thermal spray deposition parameters adjustment and optimization are thoroughly discussed. Coating properties such as roughness, friction, adhesion strength, and wear behaviour were also investigated. Microstructural characteristics and friction-wear behaviour were found to be critical to the durability of coating.
Tab-to-Busbar Interconnects Formed by Dual Flow Cold Spraying
Authors: Maev Roman Gr. , Leshchynsky Volf , Strumban Emil , Pantea Mircea , Robert Brian J. , Brackett Thomas P.
Published: May 2023

Battery manufacturing involves a large number of individual cells arranged in modules configured within a battery pack and connected either in series and/or parallel to deliver the required power and driving range. Cells within a module are linked using a tab-to-busbar connection as the electrical interconnect. Therefore, a battery pack contains a plurality of tab-to-busbar joints, and each must provide low electrical resistivity connection to minimize losses that may reduce the effective performance of the battery. In this work, the Dual Flow Cold Spray (DFCS) process, a modification of low-pressure cold spraying, was used to form low resistivity Cu+10%Zn and Al+10% Zn tab-to-busbar interconnects. As test coupons, 0.8 mm thick copper (Cu) was used to represent the busbar while 0.3 mm thick aluminum and nickel coated copper foils represented the respective electrode tabs. Low resistivity joint interconnects (≈100 μΩ) with high adhesion strength (≈120 MPa) have been formed. The influence of busbar surface preprocessing on the resistivity of the tab-to-busbar joints has been studied.
Oxidation of In-flight Particles During HVAF—A Numerical Study
Authors: Diop Sokhna Awa Bousso , Moreau Christian , Nasti Aleksandra , Dolatabad Ali
Published: May 2023

Oxygen present in the High Velocity Air-Fuel (HVAF) process can react with the in-flight metallic particles and cause their oxidation. A grown brittle oxide shell on metallic microsize particles can reduce their deposition efficiency and impair the coating final deposited properties/microstructure. In the current study, the oxide growth of MCrAlY particles, where M stands for Ni and Co, during their flight in the HVAF process has been modeled using the particle tracking scheme. A comprehensive theoretical oxide layer growth background is presented and used to track the particle oxidation process. The oxidation development includes the Mott-Cabrera theory for very thin films, which is function of the particle surrounding temperature and oxygen partial pressure. The very thin film regime, applicable under a limiting thickness, is defined based on the electric field present across the growing oxide layer. As the electric field decreases with oxide thickness, the oxidation rate is determined by thermal diffusion. The obtained results provide a correlation between HVAF system design and surface oxidation phenomena while offering a clear description of different oxidation stages.
Influence of HVAF Process Parameters on In-Flight NiCoCrAlY Particle Oxidation and Corresponding Splat Characteristics
Authors: Thoutam A.K. , Lamana M.S. , Mahdavi A. , Liberati A.C. , Ben Ettouil F. , Moreau C. , Dolatabadi A.
Published: May 2023

The deposition of MCrAlX coatings (where M is Ni, Co, Fe, or a combination of these, and X is Y, Si, Ta, Hf, or a combination of these) via thermal spraying has acquired significant importance in industries such as aerospace, power plants, oil, and gas, etc. Among various thermal spray deposition techniques, high-velocity air fuel (HVAF) has shown a growing potential for the deposition of metallic powders which are sensitive to high-temperature oxidation during spraying. Thus, it is essential to understand the in-flight behavior of these metallic particles in the high-velocity, low-temperature HVAF flame. In this work, a NiCoCrAlY powder was sprayed using two sets of HVAF deposition parameters onto stainless steel substrates. In-flight particle diagnostic tools such as AccuraSpray were employed to understand the behavior of these spray particles. The deposited particles were comprised of partially molten particles and fully deformed splats. Samples with higher powder feed rates showed a primary coating buildup on the substrate surface. EDS plots revealed no traces of inflight particle oxidation but contained carbon residue due to the presence of unburnt hydrocarbons from the fuel-rich HVAF-M3 torch. This study provides a preliminary understanding towards the significance of deposition parameters on the in-flight particle oxidation behavior and splat deformation characteristics by HVAF spraying.
Study on the Attack of Molten Silicates to Thermal Barrier Coatings at Varying Service Temperatures
Authors: Martins Roberto Fernando , Couto Antonio Augusto , Camello Lima Carlos Roberto
Published: May 2023

Thermal barrier coatings have provided a revolution in the industry as they allow a higher operating temperature of equipment, improving the efficiency of gas turbines. However, one of the biggest challenges in terms of increasing the lifespan of TBC systems is the attack of fused silicates or simply CMAS (Calcium-Magnesium-Alumina-Silicate). CMAS are particles from the environment that can penetrate the TBC structure and cause delamination of the coating when exposed to high temperatures during thermal cycling. In this study, a plasma sprayed YSZ coating in the as coated and surface treated condition were given CMAS depositions from various preparation methods, and then subjected to thermal cycles at different evaluation temperatures and exposure times. The permeability of the ceramic layer and the penetration path of CMAS at different temperature levels were evaluated, as well as the penetration characteristics in relation to the microstructure of the ceramic layer. X-Ray diffraction and Scanning Electron Microscopy were used to characterize the applied CMAS and the penetration kinetics and conditions. Samples with longer exposure time had a considerable volume increase. The conditions to guarantee the formation of the silicate and its consequent wettability are also discussed.
High Entropy Alloy (HEA) Bond Coats for Thermal Barrier Coatings (TBCs)—A Review
Authors: Shahbazi H. , Vakilifard H. , Nair R.B. , Liberati A.C. , Moreau C. , Lima R S.
Published: May 2023

Due to the aggressive operation conditions of turbine hot sections, protective coatings are required to provide oxidation and hot corrosion resistance for superalloy components. Thermal barrier coatings (TBCs) are comprised of a ceramic top coat and a metallic bond coat (BC) and are typically used as thermal protection systems against these aggressive environments. Conventional BC materials are MCrAlX, with M being metals or alloys (e.g., Ni, Co or NiCo) and X being reactive elements such as Y, Hf, Ta, Si. Due to their strength, thermal stability, and oxidation resistance, high-entropy alloys (HEAs) have presented promise for use as BC materials in hightemperature applications. Owing to its cocktail effect, optimally chosen HEAs could help to enhance the hot corrosion resistance of BCs by forming a more continuous, dense, and uniform thermally grown oxide (TGO). Furthermore, HEAs could help to control the diffusion between the bonding layer and substrate in elevated temperature environments. This paper will discuss the thermodynamic, mechanical, and microstructural behaviour of HEAs. Furthermore, the selection and usage of HEAs as BCs will be explored and compared to conventional BCs in TBC systems.
High Entropy Oxides as Promising Materials for Thermal Barrier Topcoats—A Review
Authors: Vakilifard H. , Shahbazi H. , Liberati A.C. , Nair R.B. , Moreau C. , Lima R. S.
Published: May 2023

Multi-layered thermal barrier coatings (TBCs) are deposited on gas-turbine metallic components to protect them against high temperatures, oxidation, and corrosion. However, TBCs have limited working temperatures and lifetimes due to their material properties. Several approaches are being tested to increase TBC topcoats' phase stability and properties. Increasing entropy to stabilize phases is a concept introduced in 2004 and required decreasing the Gibbs free energy. Many high-entropy ceramics are being developed for structural and functional applications, and high-entropy oxides (HEOs) are promising TBC ceramics due to their unique characteristics. HEOs are single-phase solid solutions that contain five or more cations, usually a mixture of transition metals and rare earths. Due to the cocktail effect, the final material has a different behavior from its constituents, making it a viable method to improve the properties of traditional materials. Generally, high entropy materials are characterized by three additional phenomena: sluggish diffusion, severe lattice distortion, and high entropy. A review of possible improvements in the lifetime of TBC topcoats using different HEOs in terms of their composition, properties, and stability are presented here. Different HEOs are then examined and various thermophysical properties, high-temperature stability, and sintering resistance are discussed.
Advanced Techniques for Evaluation of Thermal Shock Durability of Thermal Barrier Coating
Authors: Takeno Kazuma , Okajima Yoshifumi , Torigoe Taiji , Kuroda Seiji , Ito Kaita
Published: May 2023

Although increasing the thickness of thermal barrier coating (TBC) enhances its thermal protection capability, it generally decreases its thermal shock durability. This is caused by an increase of thermal stress due to the increase of the temperature differential between the TBC surface and the metal surface. In order to realize the optimum TBC thickness, the thermal shock durability of TBC should be evaluated precisely and quantitatively. This study focused on two advanced techniques to evaluate the durability of TBC that were developed through joint research with the National Institute for Materials Science (NIMS). The first technique utilizes a new acoustic emission (AE) measurement system called continuous wave memory (CWM), which can analyze AE events more precisely than conventional AE systems. The second technique is a noncontact strain measurement method using laser speckles, which can measure the strain on the TBC surface at high temperature. These techniques were combined with a laser thermal cycle test to establish the “𝜖H-N diagram”, which shows the relationships between the hot shock strain 𝜖H in the laser thermal cycle test and the cycle number N to failure for different TBC thicknesses. In these experiments, CWM was used to determine the TBC failure more precisely, while the laser speckle method was used to measure the thermal shock strain 𝜖H. The obtained 𝜖H-N diagram revealed the durability of TBC for various thicknesses and was transformed to an evaluation map to predict the TBC thickness limitation. For real parts, this evaluation map is useful to estimate if a thicker TBC will fail or not by comparing the maximum strain it is predicted to undergo by numerical analysis.
Comparative Study of Mo and W Bonding Layers on Graphite during Plasma Spraying
Authors: Kwon Sik-Chol , Kang Neo , Hyun S-K , Kim J-K , Kim I-S , Park T-H , Bong H-M
Published: May 2023

Graphite is useful in high-temperature applications in many engineering fields, such as heat-treating, brazing, and sintering industries. As the operation becomes severe, carbon experiences degradation leading to failure. In this study, a protective coating of W and Mo as the intermediate layer by air plasma spraying on graphite substrate was investigated to find a better intermediate layer. Their performance was explored as a bonding layer in a protective alumina-YSZ ceramic topcoat. X-ray diffraction and scanning electron microscope were used to observe the cross-section of coatings and the difference in the bonding characteristics between W and Mo, respectively. W was found inferior to Mo as a bonding performance over 1450 °C in view of carbide formation against the thermodynamic data. It seems to be related to the formation of a barrier layer as oxide during air plasma spraying.
Electrochemical Investigations and Corrosion Behavior of HVOF WC-12Co Coatings Obtained from Powder and Aqueous Suspension
Authors: Langklotz Ulrike , Toma Filofteia-Laura , Meyer Anja , Stallmann Milena
Published: May 2023

In our previous work, the potential of the suspension-HVOF spraying (S-HVOF) to produce dense-structured WC-12Co coatings has been shown. This contribution proposes a comparative study of the corrosion properties of the S-HVOF WC-12Co coatings and conventional sprayed HVOF coatings. The corrosion properties were evaluated at room temperature in NaCl electrolytes with different pH values and in a pH neutral 0.5 M Na2SO4 solution. By varying the pH value, the corrosion mechanism of the cemented carbide coatings should be assessed more precisely, since the two components, WC and Co, show strongly different pH dependencies. The electrochemical properties of the sprayed coatings were investigated using open circuit potential measurements, linear sweep voltammetry and potentiodynamic polarization methods. Before and after corrosion tests, microstructural evaluations of the coatings were performed. Moreover, element analyses of the eluates have been performed to determine soluble corrosion products. The S-HVOF coatings show a similarly good corrosion resistance as the conventional HVOF WC-Co coatings. Generally, the coating properties, i.e. microstructure and phase compositions, as well as the electrolyte significantly influence the corrosion performance of the sprayed coatings.