Materials related to the HVAF technology:

• Thermal conductivity and thermal cyclic fatigue of multilayered Gd2Zr2O7/YSZ thermal barrier coatings processed by suspension pl…
  Satyapal Mahade, Nicholas Curry, Stefan Björklunda, Nicolaie Markocsan, Per Nylén
  Department of Engineering Science, UniversityWest, Sweden
  Treibacher Industrie AG, Austria
  ABSTRACT
  Rare earth zirconates have lower thermal conductivity, better phase stability, improved sintering resistance and CMAS (calcium magnesium alumino silicates) infiltration resistance than yttria stabilized zirconia (YSZ) at temperatures above 1200 °C. However, their lower fracture toughness and lower coefficient of thermal expansion (CTE) compared to YSZ lead to premature coating failure. In order to overcome these drawbacks at higher temperatures, a multilayered coating approach is attempted in this study and compared with the single layer YSZ. Suspension plasma spray of single layer YSZ, single layer gadolinium zirconate (GZ) and double layer GZ/YSZ was carried out. Additionally, a triple layer coating system, with denser gadolinium zirconate on top of the GZ/ YSZ system was sprayed to impart an added functionality of sealing the TBC from CMAS infiltration.Microstructural analysis was done using scanning electron microscopy and optical microscopy. Columnar microstructure with vertical cracks was observed. XRD analysis was used to identify phases formed in the as sprayed TBC samples. Porosity measurements were done using water impregnation method. Thermal diffusivity of single and multi-layered coatings was obtained by laser flash analysis and thermal conductivity of the coating systems was determined. It was found that the thermal conductivity of single layer gadolinium zirconate was lower than YSZ and that the thermal conductivity of multilayered systemswere between their respective single layers. The single (YSZ), double (GZ/YSZ) and triple (GZ dense/GZ/YSZ) layer TBCs were subjected to thermal cyclic fatigue (TCF) test at 1100 °C and 1200 °C. It was observed that the single layer YSZ had lowest TCF lifewhereas the triple layer TBC had highest TCF life irrespective of test temperature.
  
  
• Effect of spraying parameters on the microstructural and corrosion properties of HVAF-sprayed Fe–Cr–Ni–B–C coatings
  A. Milanti, V. Matikainen, H. Koivuluoto, G. Bolelli, L. Lusvarghi, P. Vuoristo
  Department of Materials Science, Tampere University of Technology, Korkeakoulunkatu 6, 33720 Tampere, Finland
  Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli, 10, 41125 Modena, Italy
  ABSTRACT
  Thermally sprayed Fe-based coatings have been extensively studied as future solution in order to replace more expensive, harmful and environmentally dangerous Ni- and WC-based coatings for several industrial applicationswhere high corrosion and wear resistance are required. The aimof the present study is to investigate the effect of spraying parameters on the microstructure and the corrosion resistance of Fe-based coatings manufacturedwith the High Velocity Air Fuel (HVAF) thermal spray process. Six sets of thermal spraying parameters have been chosen and their effect on the overall quality of coatings was investigated. All HVAF coatings showed comparably dense microstructure with near-zero oxidation, proving the high quality of the deposition process. However, higher anti-corrosion and mechanical properties were achieved by increasing the spraying air pressure and decreasing the particle feeding rate without altering the thickness and the overall deposition rate. Powder feeding rate was reported to have a remarkable effect on microstructure and corrosion properties. Coatings with beneficial compressive residual stresses were successfully obtained by increasing air pressure during spraying which resulted in improved microstructural and corrosion properties.
  
  
• Tribology of HVOF- and HVAF-sprayedWC–10Co4Cr hardmetal coatings: A comparative assessment
  G. Bolelli, L.-M. Berger, T. Börner, H. Koivuluoto, L. Lusvarghi, C. Lyphout, N.Markocsand, V. Matikainen, P. Nylénd, P. Sassatelli, R. Trache, P. Vuoristoc
  Dipartimento di Ingegneria “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10/1, I-41125 Modena (MO), Italy
  Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstr. 28, D-01277 Dresden, Germany
  Department of Materials Science, Tampere University of Technology, Korkeakoulunkatu 6, FI-33720 Tampere, Finland
  Department of Engineering Science, UniversityWest, Gustava Melins gata 2, SE-461 86 Trollhättan, Sweden
  ABSTRACT
  This paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC–10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes. Mild wear rates of b10-7 mm3/(Nm) and friction coefficients of ≈0.5 were obtained for all samples in ball-ondisk slidingwear tests at roomtemperature against Al2O3 counterparts.WC–10Co4Cr coatings definitely outperforma reference electrolytic hard chromiumcoating under these test conditions. Theirwearmechanisms include extrusion and removal of the binder matrix,with the formation of a wavy surfacemorphology, and brittle cracking. The balance of such phenomena is closely related to intra-lamellar features, and rather independent of those properties (e.g. indentation fracture toughness, elastic modulus) which mainly reflect large-scale inter-lamellar cohesion, as quantitatively confirmed by a principal component analysis. Intra-lamellar dissolution of WC into the matrix indeed increases the incidence of brittle cracking, resulting in slightly higher wear rates. At 400 °C, some of the hardmetal coatings fail because of the superposition between tensile residual stresses and thermal expansion mismatch stresses (due to the difference between the thermal expansion coefficients of the steel substrate and of the hardmetal coating). Those which do not fail, on account of lower residual stresses, exhibit higher wear rates than at room temperature, due to oxidation of theWC grains. The resistance of the coatings against abrasive wear, assessed by dry sand–rubber wheel testing, is related to inter-lamellar cohesion, as proven by a principal component analysis of the collected dataset. Therefore, coatings deposited fromcoarse feedstock powders suffer higherwear loss than those obtained from fine powders, as brittle inter-lamellar detachment is caused by theirweaker interparticle cohesion,witnessed by their systematically lower fracture toughness as well.
  
  
• Tribological Properties of Hard Metal Coatings Sprayed by High-Velocity Air Fuel Process
  C. Lyphout, K. Sato, S. Houdkova, E. Smazalova, L. Lusvarghi, G. Bolelli, and P. Sassatelli
  ABSTRACT
  Lowering the thermal energy and increasing the kinetic energy of hard metal particles sprayed by the newly developed HVAF systems can significantly reduce their decarburization, and increases the sliding wear and corrosion resistance of the resulting coatings, making the HVAF technique attractive, both economically and environmentally, over its HVOF predecessors. Two agglomerated and sintered feedstock powder chemistries, WC-Co (88/12) and WC-CoCr (86/10/4), respectively, with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Their dry sliding wear behaviors and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al2O3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with the formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviors were evaluated via standard Neutral Salt Spray, Acetic Acid Salt Spray, accelerated corrosion test, and electrochemical polarization test at room temperature. The optimization of the tribological properties of the coatings is discussed, focusing on the suitable selection of primary carbide size for different working load applications.
  
  
• Internal Diameter HVAF Spraying for Wear and Corrosion Applications
  C. Lyphout and S. Bjo¨rklund
  ABSTRACT
  Electrolytic hard chrome (EHC) methods are still widely utilized in the printing, automotive and offshore industries. Alternative methods to EHC have been widely developed in the past decade by conventional HVOF processes and more recently HVAF systems, which are processing at higher kinetic energy and more particularly at lower temperature, significantly increasing wear and corrosion resistance properties. A dedicated internal diameter HVAF system is here presented, and coatings characteristics are compared to the one obtained by standard HVAF coatings. Specially R&D designed fixtures with inside bore of 200 mm have been manufactured for this purpose, with a possibility to spray samples at increasing depth up to 400 mm while simulating closed bottom bore spraying. WC-based and Cr3C2- based powder feedstock materials have been deposited onto high-strength steel substrates. Respective coating microstructures, thermally induced stresses and corrosion resistance are discussed for further optimization of coating performances. The fact that the ID-HVAF system is utilized both for spraying and gritblasting procedures is also given a particular interest.
  
  
• Screening Design of Supersonic Air Fuel Processing for Hard Metal Coatings
  C. Lyphout, S. Bjo¨rklund, M. Karlsson, M. Runte, G. Reisel, and P. Boccaccio
  ABSTRACT
  Replacement of electrolytic hard chromium method by thermal spray technology has shown a growing interest in the past decades, mainly pioneered by depositing WC-based material by conventional HVOF processes. Lower thermal energy and higher kinetic energy of sprayed particles achieved by newly developed Supersonic Air Fuel system, so-called HVAF-M3, significantly reduces decarburization, and increases wear and corrosion resistance properties, making HVAF-sprayed coatings attractive both economically and environmentally. In the present work, full factorial designs of experiments have been extensively utilized to establish relationships between hardware configurations, process and engineering variables, and coatings properties. The relevance of those process factors is emphasized and their significance is discussed in the optimization of coatings for improved abrasion wear and corrosion performances.
  
  
• Screening design of hard metal feedstock powders for supersonic air fuel processing
  Christophe Lyphout, Katu Satob
  UniversityWest, Trollhättan, Sweden
  Fujimi Incorporated, Japan
  ABSTRACT
  Replacement of electrolytic hard chromium (EHC) method by Thermal Spray Technology has shown a growing interest the past decades, mainly pioneered by depositingWC-based material by conventional HVOF processes. Lower thermal energy and higher kinetic energy of sprayed particles achieved by newly-developed supersonic air fuel system, so-called HVAF-M3, significantly reduce decarburization, and increase wear and corrosion resistance properties, making HVAF-sprayed coatings attractive both economically and environmentally. In the present work, a first order process map has been intended via a full factorial design of experiments (DoE) to establish relationships between powder feedstock characteristics, such as primary carbides grain size, binder grain size and powder strength, and coating microstructure and mechanical properties. A second order process map was then established to study possible correlations between the deposit microstructural properties and their respective abrasion/erosion wear and corrosion performances.
  
  
• Optimization of Gritblasting Conditions by Supersonic Air Spraying
  C. Lyphout, S. Björklund, University West, Production Technology West, Trollhättan, SWEDEN
  P. Boccaccio, University of Modena and Reggio Emilia, Modena, Italy
  ABSTRACT
  Recent development of the HVAF-M3 system attracts a lot of interest in spraying Carbide-based and Iron-based materials as an economic, environmental and practical alternative to Electrolytic Hard Chrome (EHC) method, which is still widely utilized in the printing, automotive and off-shore industries. The use of compressed air instead of pure oxygen and the fact that gritblasting procedure can be operated with the HVAF gun itself offers economic advantages well perceived by the industry. A dedicated Design of Experiments on gritblasting parameters operated utilizing the HVAF-M3 system is proposed in the present work. Relationships between gritblasting media sizes – feed rate – offset – stand-off distance and substrate roughness profiles including grit residues level have been investigated. Additionally Carbide-based and Iron-based powder feedstock materials were HVAF-sprayed in order to study the influence of gritblasted conditions on their particular coating adhesion strength. Respective coating microstructure and adhesion strength are presented and discussed for further optimization of coating performances.
  
  
• Wear properties of CrC–37WC–18M coatings deposited by HVOF and HVAF spraying processes
  I. Hulka, V.A. Şerban, I. Secoşan, P. Vuoristo, K. Niemi
  Department of Materials and Welding Science “Politehnica” University of Timişoara, Blv. Mihai Viteazu, No 1, RO-300222, Romania
  Department of Materials Science, Tampere University of Technology, Korkeakoulunkatu 6, FI-33101 Finland
  ABSTRACT
  CrC–37WC–18M cermet coatings were deposited using new feedstock powders which seem to combine the properties of WC–CoCr and CrC–NiCr coatings. A conventional particle size CrC–37WC–18M powder was used as feedstock for the HVOF (high velocity oxygen fuel) thermal spraying process and a fine particle distribution was used as feedstock for the HVAF (high velocity air fuel) thermal spraying process. In order to characterize the morphology of the feedstock powders and deposited coatings SEM and X-ray diffraction were used. The microhardness of the coatings was also studied. The wear behavior of the coatings was evaluated by pin-on-disk and rubber wheel abrasion tests. The HVAF coating showed equal or even better wear resistance as compared to corresponding HVOF coatings.
  
  
• Tungsten Carbide Deposition Processes for Hard Chrome Alternative: Preliminary Study of HVAF vs. HVOF Thermal Spray Processes
  J. Kitamura, K. Sato, J. Yamada, Fujimi Incorporated, JAPAN
  S. Dizdar, Höganäs Sweden AB, SWEDEN
  ABSTRACT
  Electrolytic Hard Chrome (EHC) method, which is still widely utilized in the printing, automotive and off-shore industries, is coming to be subjected to strong restrictions in the next decade in the use of hexavalent Chromium, with the increasing strengthening of European normative. Alternative methods to EHC, such as High Kinetic Thermal Spray Technology, have shown a growing interest the past decades. Compared to conventional HVOF processes which pioneered the development of WC-based coated materials, newly developed HVAF systems are processing at higher kinetic energy and more particularly at lower temperature, which significantly reduces feedstock oxidation and decarburization, then increasing respective wear and corrosion resistance properties. A preliminary investigation of HVOF- and HVAF-sprayed coatings is here proposed on the evaluation basis of material decarburization, coating porosity and microhardness. Role of carbides size and morphology on coating adhesion strength, wear and corrosion resistance properties are preliminary discussed.
  
  
• Development of a Novel Erosion Resistant Coating System for Use on Rotorcraft Blades
  Matthew D. Trexler PhD, Victor K. Champagne Team Leader, Innovative Materials & Processing Team, US Army Research Laboratory (ARL), Army Research Laboratory, Materials and Manufacturing Technology Branch, RDRL-WMM-D BLDG 4600, Aberdeen Proving Ground, MD 21005-5069
  Jack Kopchik, Sikorsky Aircraft Corp
  ABSTRACT
  The costs associated with extended use of helicopters in erosive environments are well documented. Main and tail rotor blade erosion is among the leading drivers of a helicopter’s cost per flight hour. Improved polyurethane coatings provide a means to reduce these costs but require frequent touch up to prevent more severe damage. Furthermore, these coatings offer little protection from damage resulting from debris raised in the sand cloud generated during takeoffs and landings. An erosion resistant approach, developed in collaboration with AATD, ARL, United Technologies Research Center (UTRC) and Sikorsky utilizes a two part metal/cermet coating system on the leading edge of the blades to provide unmatched protection from sand, rain, and debris erosion. Tungsten carbide cobalt (WC-Co) is applied on the leading edge nose of the blade for direct impingement protection. Niobium is applied aft of the nose for indirect impingement protection. This paper will present techniques utilized to manage the process to meet the requirements of a fully functional coating without thermal damage to an expensive composite component.
  
  
• Potential of HVAF Spray Process
  Dr. Lutz-Michael Berger, Dipl.-Ing. Roberto Puschmann, Dipl.-Ing. Jörg Spatzier, Fraunhofer Institut für Werkstoff- und Strahltechnik (Fh-IWS), Dresden;
  Dr. Steven Matthews, Massey University, Auckland, New Zealand
  ABSTRACT
  The High Veloicty Air Fuel spray process abbreviated as HVAF is a high velocity flame spray process using air as the oxidizing gas. The concept behind this process is the use of particle temperatures below or around their melting point but high particle velocities such that plastic deformation at impact becomes possible and coating formation occurs. In this contribution a short historic survey is given and the typical structures and properties of HVAF coatings are compared with those of HVOF coatings. While coating quality was very high from the beginning of HVAF development, significant improvements in the deposition efficiency have occured with equipment developments over the last 10 years. Both HVAF and HVOF can produce dense coatings but their microstructural features and properties are different.