Diagnostic tools for HVOF process optimization

Dissertation

Research output: ThesisDissertationCollection of Articles

Abstract

In the thermal spray process the coating is built up from lamellas formed by rapid solidification of the melted or semi-melted droplets attached to the substrate. A typical structure for the coating is a pancake-like lamellar structure, where the flattening stage and adhesion between the lamellas, together with the coating material itself, define the main properties of the coating. Thermal spray coatings are often applied for better corrosion and wear resistance. Therefore, low porosity and good adhesion are desired properties for the coating. High velocity processes - especially HVOF (High velocity oxy-fuel) spraying - are the most potential methods for producing a good adherent coating with low porosity. From a scientific point of view, particle velocity and particle temperature, together with substrate temperature, are the main parameters affecting the deposit formation. They determine the deposit build-up process and deposit properties. Particle velocity and temperature affect the deposit efficiency as well as the microstructure. The aim of this work was to show the workability of diagnostic tools in the HVOF process. The focus was on first order process mapping, including on-line diagnostics and single splat studies. Nanocrystalline alumina composites and quasicrystals were selected, two materials that are complex to spray. With both materials the melting state of the particles must be well optimized in order to produce dense, well-adhered coating without unwanted changes in coating phase structure. The main focus was on the HVOF spraying of alumina. The target was to obtain a systematic understanding of the influence of the process conditions on the microstructure development in HVOF alumina coatings. Conventional limits of gas ratios and flows were exceeded to obtain a wide velocity-temperature range. The study aimed to produce information for a first order process map, and was carried out at a much deeper level than previously reported. Propylene and hydrogen as fuel gases were compared, and other variables, such as total gas flow rate, fuel gas/oxygen ratio, and standoff distance were also varied. The obtained data was applied for nanostructured alumina composite coatings, and the effect of the process conditions was compared on the obtained coating microstructure and properties. On-line diagnostic measurements, in which particle temperatures and velocities in the flame can be measured, were performed. The main work was carried out for alumina by using a DPV-2000 system. Two clear regions of different temperature and velocity arise from the use of different fuel gases. Single splat studies correlated well with the obtained coating properties, and a first order process map for alumina was created showing the window for the spray parameters producing best coating quality plotted against coating hardness and abrasive wear resistance. It was shown that diagnostic results can be correlated with the coating microstructure and coating properties in HVOF spraying. It was also demonstrated that the coating properties and coating quality can be improved by optimizing and carefully selecting the spray parameters.
Original languageEnglish
Awarding Institution
  • Helsinki University of Technology
Supervisors/Advisors
  • Hannula, Simo-Pekka, Supervisor, External person
Award date16 Dec 2005
Place of PublicationEspoo
Publisher
Print ISBNs951-38-6677-7
Electronic ISBNs951-38-6678-5
Publication statusPublished - 2005
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

coatings
optimization
aluminum oxides
HVOF thermal spraying
sprayers
deposits
microstructure
lamella
wear resistance
gases
temperature
adhesion
porosity
rapid solidification
composite materials
abrasives
flattening
propylene
corrosion resistance
gas flow

Keywords

  • thermal spraying
  • HVOF
  • high velocity oxi-fuels
  • process optimizatic diagnostics
  • single splat studies
  • surface coatings
  • alumina
  • quasicrystals
  • nanofractions

Cite this

Turunen, E. (2005). Diagnostic tools for HVOF process optimization: Dissertation . Espoo: VTT Technical Research Centre of Finland.
Turunen, Erja. / Diagnostic tools for HVOF process optimization : Dissertation . Espoo : VTT Technical Research Centre of Finland, 2005. 66 p.
@phdthesis{12585eb4255346abba9d437ba3ceb640,
title = "Diagnostic tools for HVOF process optimization: Dissertation",
abstract = "In the thermal spray process the coating is built up from lamellas formed by rapid solidification of the melted or semi-melted droplets attached to the substrate. A typical structure for the coating is a pancake-like lamellar structure, where the flattening stage and adhesion between the lamellas, together with the coating material itself, define the main properties of the coating. Thermal spray coatings are often applied for better corrosion and wear resistance. Therefore, low porosity and good adhesion are desired properties for the coating. High velocity processes - especially HVOF (High velocity oxy-fuel) spraying - are the most potential methods for producing a good adherent coating with low porosity. From a scientific point of view, particle velocity and particle temperature, together with substrate temperature, are the main parameters affecting the deposit formation. They determine the deposit build-up process and deposit properties. Particle velocity and temperature affect the deposit efficiency as well as the microstructure. The aim of this work was to show the workability of diagnostic tools in the HVOF process. The focus was on first order process mapping, including on-line diagnostics and single splat studies. Nanocrystalline alumina composites and quasicrystals were selected, two materials that are complex to spray. With both materials the melting state of the particles must be well optimized in order to produce dense, well-adhered coating without unwanted changes in coating phase structure. The main focus was on the HVOF spraying of alumina. The target was to obtain a systematic understanding of the influence of the process conditions on the microstructure development in HVOF alumina coatings. Conventional limits of gas ratios and flows were exceeded to obtain a wide velocity-temperature range. The study aimed to produce information for a first order process map, and was carried out at a much deeper level than previously reported. Propylene and hydrogen as fuel gases were compared, and other variables, such as total gas flow rate, fuel gas/oxygen ratio, and standoff distance were also varied. The obtained data was applied for nanostructured alumina composite coatings, and the effect of the process conditions was compared on the obtained coating microstructure and properties. On-line diagnostic measurements, in which particle temperatures and velocities in the flame can be measured, were performed. The main work was carried out for alumina by using a DPV-2000 system. Two clear regions of different temperature and velocity arise from the use of different fuel gases. Single splat studies correlated well with the obtained coating properties, and a first order process map for alumina was created showing the window for the spray parameters producing best coating quality plotted against coating hardness and abrasive wear resistance. It was shown that diagnostic results can be correlated with the coating microstructure and coating properties in HVOF spraying. It was also demonstrated that the coating properties and coating quality can be improved by optimizing and carefully selecting the spray parameters.",
keywords = "thermal spraying, HVOF, high velocity oxi-fuels, process optimizatic diagnostics, single splat studies, surface coatings, alumina, quasicrystals, nanofractions",
author = "Erja Turunen",
year = "2005",
language = "English",
isbn = "951-38-6677-7",
series = "VTT Publications",
publisher = "VTT Technical Research Centre of Finland",
number = "583",
address = "Finland",
school = "Helsinki University of Technology",

}

Turunen, E 2005, 'Diagnostic tools for HVOF process optimization: Dissertation ', Helsinki University of Technology, Espoo.

Diagnostic tools for HVOF process optimization : Dissertation . / Turunen, Erja.

Espoo : VTT Technical Research Centre of Finland, 2005. 66 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - Diagnostic tools for HVOF process optimization

T2 - Dissertation

AU - Turunen, Erja

PY - 2005

Y1 - 2005

N2 - In the thermal spray process the coating is built up from lamellas formed by rapid solidification of the melted or semi-melted droplets attached to the substrate. A typical structure for the coating is a pancake-like lamellar structure, where the flattening stage and adhesion between the lamellas, together with the coating material itself, define the main properties of the coating. Thermal spray coatings are often applied for better corrosion and wear resistance. Therefore, low porosity and good adhesion are desired properties for the coating. High velocity processes - especially HVOF (High velocity oxy-fuel) spraying - are the most potential methods for producing a good adherent coating with low porosity. From a scientific point of view, particle velocity and particle temperature, together with substrate temperature, are the main parameters affecting the deposit formation. They determine the deposit build-up process and deposit properties. Particle velocity and temperature affect the deposit efficiency as well as the microstructure. The aim of this work was to show the workability of diagnostic tools in the HVOF process. The focus was on first order process mapping, including on-line diagnostics and single splat studies. Nanocrystalline alumina composites and quasicrystals were selected, two materials that are complex to spray. With both materials the melting state of the particles must be well optimized in order to produce dense, well-adhered coating without unwanted changes in coating phase structure. The main focus was on the HVOF spraying of alumina. The target was to obtain a systematic understanding of the influence of the process conditions on the microstructure development in HVOF alumina coatings. Conventional limits of gas ratios and flows were exceeded to obtain a wide velocity-temperature range. The study aimed to produce information for a first order process map, and was carried out at a much deeper level than previously reported. Propylene and hydrogen as fuel gases were compared, and other variables, such as total gas flow rate, fuel gas/oxygen ratio, and standoff distance were also varied. The obtained data was applied for nanostructured alumina composite coatings, and the effect of the process conditions was compared on the obtained coating microstructure and properties. On-line diagnostic measurements, in which particle temperatures and velocities in the flame can be measured, were performed. The main work was carried out for alumina by using a DPV-2000 system. Two clear regions of different temperature and velocity arise from the use of different fuel gases. Single splat studies correlated well with the obtained coating properties, and a first order process map for alumina was created showing the window for the spray parameters producing best coating quality plotted against coating hardness and abrasive wear resistance. It was shown that diagnostic results can be correlated with the coating microstructure and coating properties in HVOF spraying. It was also demonstrated that the coating properties and coating quality can be improved by optimizing and carefully selecting the spray parameters.

AB - In the thermal spray process the coating is built up from lamellas formed by rapid solidification of the melted or semi-melted droplets attached to the substrate. A typical structure for the coating is a pancake-like lamellar structure, where the flattening stage and adhesion between the lamellas, together with the coating material itself, define the main properties of the coating. Thermal spray coatings are often applied for better corrosion and wear resistance. Therefore, low porosity and good adhesion are desired properties for the coating. High velocity processes - especially HVOF (High velocity oxy-fuel) spraying - are the most potential methods for producing a good adherent coating with low porosity. From a scientific point of view, particle velocity and particle temperature, together with substrate temperature, are the main parameters affecting the deposit formation. They determine the deposit build-up process and deposit properties. Particle velocity and temperature affect the deposit efficiency as well as the microstructure. The aim of this work was to show the workability of diagnostic tools in the HVOF process. The focus was on first order process mapping, including on-line diagnostics and single splat studies. Nanocrystalline alumina composites and quasicrystals were selected, two materials that are complex to spray. With both materials the melting state of the particles must be well optimized in order to produce dense, well-adhered coating without unwanted changes in coating phase structure. The main focus was on the HVOF spraying of alumina. The target was to obtain a systematic understanding of the influence of the process conditions on the microstructure development in HVOF alumina coatings. Conventional limits of gas ratios and flows were exceeded to obtain a wide velocity-temperature range. The study aimed to produce information for a first order process map, and was carried out at a much deeper level than previously reported. Propylene and hydrogen as fuel gases were compared, and other variables, such as total gas flow rate, fuel gas/oxygen ratio, and standoff distance were also varied. The obtained data was applied for nanostructured alumina composite coatings, and the effect of the process conditions was compared on the obtained coating microstructure and properties. On-line diagnostic measurements, in which particle temperatures and velocities in the flame can be measured, were performed. The main work was carried out for alumina by using a DPV-2000 system. Two clear regions of different temperature and velocity arise from the use of different fuel gases. Single splat studies correlated well with the obtained coating properties, and a first order process map for alumina was created showing the window for the spray parameters producing best coating quality plotted against coating hardness and abrasive wear resistance. It was shown that diagnostic results can be correlated with the coating microstructure and coating properties in HVOF spraying. It was also demonstrated that the coating properties and coating quality can be improved by optimizing and carefully selecting the spray parameters.

KW - thermal spraying

KW - HVOF

KW - high velocity oxi-fuels

KW - process optimizatic diagnostics

KW - single splat studies

KW - surface coatings

KW - alumina

KW - quasicrystals

KW - nanofractions

M3 - Dissertation

SN - 951-38-6677-7

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Turunen E. Diagnostic tools for HVOF process optimization: Dissertation . Espoo: VTT Technical Research Centre of Finland, 2005. 66 p.