Assessment OF HVOF Coatings for Wet Corrosion Protection

1998 ◽  
Author(s):  
M. Dvorak ◽  
P. Heimgartner
Keyword(s):  
Corrosion Protection ◽  
Corrosion Behaviour ◽  
Metallic Coatings ◽  
Hvof Spraying ◽  
Special Cases ◽  
Recent Developments ◽  
High Investment ◽  
New Generation ◽  
Thermally Sprayed ◽  
Sprayed Coatings

Abstract Until now the use of thermal sprayed metallic coatings for wet corrosion protection is limited to applications where the coating (Al-alloys, Zn-alloys and their mixtures) acts as an anode to protect the substrate or special cases, where thick cold sprayed metallic layers give good results. Other atmospheric cold sprayed layers made of corrosion resistant Ni, Co, Cu or Fe base alloys have their limitations due to the process related discontinuities like pores and oxide films. In more aggressive environments thermal sprayed and fused layers made of so called self-fluxing Ni and Co based alloys are commonly applied. Also in some applications the use of specially designed gas shrouds or of spraying techniques running in inert gas atmospheres or vacuum can yield protective coating solutions. However, these techniques have high investment or service costs or the size of the parts to be coated is restricted. Recent developments in HVOF-spraying open new possibilities in applying cold sprayed coatings on site with good corrosion resistance. The aim of this paper is on one hand to give a comparative overview about the wet corrosion behaviour of thermally sprayed metallic coatings using different spraying techniques related to the performance of the corresponding bulk materials and on the other hand to demonstrate the potential of a new generation of coatings to protect or repair structures exposed to aggressive environments.

The Development of Corrosion Resistant Coatings by HVOF Spraying

2000 ◽  
Author(s):  
D. Harvey ◽  
O. Lunder ◽  
R. Henriksen
Keyword(s):  
Corrosion Resistance ◽  
Flow Rate ◽  
Corrosion Behaviour ◽  
Deposition Efficiency ◽  
Spray Angle ◽  
Powder Size ◽  
Hvof Spraying ◽  
Coating Materials ◽  
Efficient Manner ◽  
Sprayed Coatings

Abstract Coatings have been prepared using the Diamond Jet hybrid and JP5000 high velocity oxyfuel (HVOF) systems with the objectives of improving corrosion resistance and reducing costs through increasing deposition efficiency. Models relating deposition efficiency, coating oxygen content and corrosion resistance to process parameters including fuel flow rate, oxygen flow rate and stand-off distance have been developed. A corrosion test cell has been designed and a procedure determined for studying the corrosion behaviour of large numbers of thermally sprayed coatings in an efficient manner. A significant improvement to the corrosion resistance of HVOF sprayed coatings has been achieved by spraying parameter optimisation and investigation of powder size and distribution. The project has also investigated the influence of spray angle on coating performance with a view to future onsite application. Coating materials tested and compared include nickel alloys Hastelloy C276 and 59, cobalt alloy Ultimet, duplex stainless steel S32750 and an experimental iron-based spray-fuse composition.

High Energy Beam Surface and Interface Modification of Thermally Sprayed Coatings

1997 ◽  
Author(s):  
J. Wilden ◽  
M. Brune ◽  
Y. Kruzhanov ◽  
H.-D. Steffens
Keyword(s):  
Corrosion Behaviour ◽  
Power Level ◽  
High Energy ◽  
Energy Beam ◽  
Surface And Interface ◽  
Thermally Sprayed Coatings ◽  
Beam Surface ◽  
Thermally Sprayed ◽  
Sprayed Coatings ◽  
High Energy Beam

Abstract The application of thermally sprayed coatings is often limited by their porosity as well as their low adhesion. A new approach for high energy beam surface treatment of thermally sprayed coatings is presented using simultanously a lower power level for continuous remelting and pulses of higher power in order to get coatings with good corrosion behaviour and improved adhesion. This technology is applied to titanium as well as to NiCr-coatings on steel substrates. The investigations prove that remelted thermally sprayed coatings with a smooth and dense surface layer, followed by a heat treated section of the coating and a reaction zone at the substrate/coating interface can be obtained. Therefore, a change in chemical composition of the coating is avoided, while at the same time the bond strength of the remelted coatings can be influenced by metallurgical reactions at the interface zone.

Tribology of Thermally Sprayed Coatings in the Al2O3-Cr2O3-TiO2 System

2015 ◽  
pp. 227-267 ◽  
Author(s):  
Lutz-Michael Berger
Keyword(s):  
Atmospheric Plasma ◽  
Hvof Spraying ◽  
Properties Of Coatings ◽  
Wear Protection ◽  
Recent Developments ◽  
Lower Porosity ◽  
Detonation Gun ◽  
The Individual ◽  
Sprayed Coating ◽  
Thermally Sprayed

With the exception of ZrO2, the individual oxides and binary compositions in the system Al2O3-Cr2O3-TiO2 are the most important oxide materials for thermally sprayed coating solutions. Traditionally, these coatings are prepared by Atmospheric Plasma Spraying (APS), but processes such as Detonation Gun Spraying (DGS) and High Velocity Oxy-Fuel (HVOF) spraying can produce coatings with lower porosity and higher wear resistance. Traditionally, feedstock powders have been used for coating preparation. Recent developments have seen the emergence of suspensions as a new feedstock, but tribological properties of coatings prepared using suspensions have not yet been studied in detail. This chapter summarizes some important issues regarding wear protection applications of coatings in the Al2O3-Cr2O3-TiO2 system, the advantage of alloying the individual oxides, and the influence of different feedstocks and spray processes.

Corrosion Behaviour of HVOF Sprayed Coatings on ASME SA213 T22 Boiler Steel in an Actual Boiler Environment

2017 ◽  
Vol 20 ◽  
pp. 1-9 ◽  
Author(s):  
Varinder Pal Singh Sidhu ◽  
Khushdeep Goyal ◽  
Rakesh Goyal
Keyword(s):  
Corrosion Behaviour ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Hvof Spraying ◽  
Boiler Steel ◽  
Nickel Chromium ◽  
Boiler Environment ◽  
Sprayed Coatings ◽  
Spraying Process ◽  
Thin Band

In present study HVOF spraying process had been employed for depositing 93(WC-Cr3C2)-7Ni, 75Cr3C2-25NiCr, 83WC-17CO and 86WC-10CO-4Cr coatings on ASME SA213 T22. All the coatings were found dense and uniform having thickness between 200-250µm. All the coatings on ASME SA213 T22 used in present studies have provided resistance to corrosion in coal fired boiler environment in superheater zone when exposed for 10 cycles at 900°C. Each cycle consists of 100 hours heating followed by 1 hour cooling at ambient conditions. X-ray diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) techniques were used to analyse corrosion products. The results showed that among coated specimens 93(WC-Cr3C2)-7Ni and 75Cr3C2-25NiCr coatings has shown maximum and minimum resistance to corrosion respectively. The better corrosion resistance of 93(WC-Cr3C2)-7Ni coated steel alloys may be attributed to the formation of thin band of oxides of nickel, chromium; and carbides of tungsten.

Recent developments in low-voltage SEM of polymers

1993 ◽  
Vol 51 ◽  
pp. 866-867
Author(s):  
S.J. Krause ◽  
W.W. Adams
Keyword(s):  
Low Voltage ◽  
Chromatic Aberration ◽  
Thermal Electron ◽  
Analytical Technique ◽  
Recent Developments ◽  
Beam Currents ◽  
New Generation ◽  
First Time ◽  
Voltage Scanning ◽  
Beam Damage

Over the past decade low voltage scanning electron microscopy (LVSEM) of polymers has evolved from an interesting curiosity to a powerful analytical technique. This development has been driven by improved instrumentation and in particular, reliable field emission gun (FEG) SEMs. The usefulness of LVSEM has also grown because of an improved theoretical and experimental understanding of sample-beam interactions and by advances in sample preparation and operating techniques. This paper will review progress in polymer LVSEM and present recent results and developments in the field.In the early 1980s a new generation of SEMs produced beam currents that were sufficient to allow imaging at low voltages from 5keV to 0.5 keV. Thus, for the first time, it became possible to routinely image uncoated polymers at voltages below their negative charging threshold, the "second crossover", E2 (Fig. 1). LVSEM also improved contrast and reduced beam damage in sputter metal coated polymers. Unfortunately, resolution was limited to a few tenths of a micron due to the low brightness and chromatic aberration of thermal electron emission sources.

Sign in / Sign up

Export Citation Format

Share Document