Effect of beam angle on heat affected zone, recast and oxide layer in laser drilling of thermal barrier coated nickel alloys

2005 ◽  
Author(s):  
H. K. Sezer ◽  
Lin Li ◽  
B. Anderson ◽  
P. Williams ◽  
M. Schmidt
Keyword(s):  
Oxide Layer ◽  
Heat Affected Zone ◽  
Nickel Alloys ◽  
Laser Drilling ◽  
Thermal Barrier ◽  
Beam Angle

Effect of beam angle on HAZ, recast and oxide layer characteristics in laser drilling of TBC nickel superalloys

2006 ◽  
Vol 46 (15) ◽  
pp. 1972-1982 ◽  
Author(s):  
H.K. Sezer ◽  
L. Li ◽  
M. Schmidt ◽  
A.J. Pinkerton ◽  
B. Anderson ◽  
...  
Keyword(s):  
Oxide Layer ◽  
Laser Drilling ◽  
Nickel Superalloys ◽  
Beam Angle

On the Change in Stress State Associated with Bond Coat Oxidation during Heat Treatment of a Thermal Barrier Coating System

1997 ◽  
Author(s):  
Y.C. Tsui ◽  
T.W. Clyne ◽  
R.C. Reed
Keyword(s):  
Heat Treatment ◽  
Stress State ◽  
Oxide Layer ◽  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Driving Forces ◽  
Lateral Strain ◽  
Thermal Barrier ◽  
Residual Stress State ◽  
Barrier Coating

Abstract Thermal barrier coating systems have been heat treated in order to study the oxidation kinetics of the bond coat. All the surfaces of Ni superalloy substrates were sprayed with ~100 μm of a NiCrAlY bond coat, with or without ~250 μm of a ZrO2 top coat. Thermogravimetric analysis (TGA) was used to monitor continuously the mass change as a result of oxidation of the bond coat during heating at 1000°C for 100 hours in flowing air. In addition, some specimens were heated to 1000°C in static air, cooled to room temperature, weighed and re-heated cyclically. The total exposure time was 1000 hours. Rates of weight gain were found to be higher for the cycled specimens, despite the absence of air flow. This is attributed to damage to the oxide film, which was predominantly α-Al2O3, as a consequence of differential thermal contraction stresses. The changing residual stress state during heat treatment was predicted using a previously-developed numerical model. A thin (1 mm) substrate with ~100 μm bond coat and ~250 μm ZrO2 top coat was used in these simulations, which incorporated creep of the bond coat and the lateral strain associated with oxidation. It is concluded from these computations that, while high stresses develop in the oxide layer, the associated driving forces for interfacial debonding remain relatively low, as do specimen curvature changes. It seems likely that coating spallation after extensive oxide layer formation arises because the interface is strongly embrittled as the layer thickens.

Bond coating issues in thermal barrier coatings for industrial gas turbines

2005 ◽  
Vol 219 (2) ◽  
pp. 101-107 ◽  
Author(s):  
I. G. Wright ◽  
B. A. Pint
Keyword(s):  
High Temperature ◽  
Oxide Layer ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Metallic Surface ◽  
Thermal Barrier ◽  
Protective Oxide ◽  
Barrier Coatings ◽  
Bond Coating ◽  
Industrial Gas Turbines

Thermal barrier coatings are intended to work in conjunction with internal cooling schemes to reduce the metal temperature of critical hot gas path components in gas turbine engines. The thermal resistance is typically provided by a 100-250 μm thick layer of ceramic (most usually zirconia stabilized with an addition of 7–8 wt% of yttria), and this is deposited on to an approximately 50 μ thick, metallic bond coating that is intended to anchor the ceramic to the metallic surface, to provide some degree of mechanical compliance, and to act as a reservoir of protective scale-forming elements (Al) to protect the underlying superalloy from high-temperature corrosion. A feature of importance to the durability of thermal barrier coatings is the early establishment of a continuous, protective oxide layer (preferably α-alumina) at the bond coating—ceramic interface. Because zirconia is permeable to oxygen, this oxide layer continues to grow during service. Some superalloys are inherently resistant to high-temperature oxidation, so a separate bond coating may not be needed in those cases. Thermal barrier coatings have been in service in aeroengines for a number of years, and the use of this technology for increasing the durability and/or efficiency of industrial gas turbines is currently of significant interest. The data presented were taken from an investigation of routes to optimize bond coating performance, and the focus of the paper is on the influences of reactive elements and Pt on the oxidation behaviour of NiAl-based alloys determined in studies using cast versions of bond coating compositions.

Delamination-free millisecond laser drilling of thermal barrier coated aerospace alloys

2019 ◽  
Vol 31 (4) ◽  
pp. 042001 ◽  
Author(s):  
Sundar Marimuthu ◽  
Bethan Smith ◽  
Aislinn Kiely ◽  
Yijun Liu
Keyword(s):  
Laser Drilling ◽  
Thermal Barrier ◽  
Aerospace Alloys ◽  
Millisecond Laser

scholarly journals Enhanced Molten Salt Resistance by Sidewall Pores Repair during Fs Laser Drilling of a Thermal Barrier-Coated Superalloy

Materials ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 1905
Author(s):  
Zhengjie Fan ◽  
Xiaomao Sun ◽  
Xuesong Mei ◽  
Rujia Wang
Keyword(s):  
Molten Salt ◽  
Low Frequency ◽  
Salt Resistance ◽  
Laser Drilling ◽  
Thermal Barrier ◽  
Transient Pressure ◽  
Cooling Hole ◽  
Fs Laser ◽  
Transformation Stress ◽  
Plasma Sprayed

In this study, a novel laser-modified drilling method was used to manufacture cooling holes through thermal barrier coatings (TBCs). Due to the “cooling processing” properties during low-frequency femtosecond (LF-fs) laser drilling, the exposure of the sidewall pores, and the interlayer clearance, the inherent characteristics of plasma-sprayed coatings induced sidewall defects in the drilled holes. After drilling, a high-frequency fs (HF-fs) laser was used to repair the sidewall pores and interlayer clearance of the drilled ceramic holes. Then, the pores and microcracks were healed by local melting using the laser. Moreover, instead of obtaining laser-induced periodic surface structures (LIPSSs), refined and homogeneous grains were produced by the HF-fs laser repair treatment at high transient pressure and temperature. The results from a high-temperature corrosion test showed that healing of the open pores and microstructural improvement in the ceramic hole walls prevented the out-diffusion of Y2O3 stabilizers and the penetration of molten salt, resulting in less corrosive products and producing corresponding phase-transformation stress. Thus, reducing the stabilizer consumption can moderate corrosion fatigue and prolong the lifetime of a cooling hole and TBCs under service.

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