Modified Aluminide Coatings Research Articles

(Invited) Pt-Modified Aluminide Coatings for Ni-Base Single Crystal Superalloy

Single phase (Ni,Pt)Al coating has been widely employed as state-of-the-art bondcoat for protecting hot-sectional components in commercial aero engines, especially for the parts made of Ni-base single crystal (SX) superalloys. For high temperature protective coating serving on SX superalloy, two interfaces are vitally essential for acquiring reliably long service life: the interface growing thermally-grown oxide (TGO) and the interface connecting coating and substrate alloy. Normally, the excellent performance of PtAl coating derives from high Al content and the incorporation of Pt, which ensures formation of exclusively adherent oxide scale, α-Al2O3. To further improve the performance of Pt-modified aluminide coating, in present study reactive elements are introduced using co-electroplating method. Compared with singular doping, co-doping of Hf-Y demonstrated superior oxidation resistance. The oxide scale growth rate and spallation tendency of Hf-Y co-doped (Ni,Pt)Al coating were much smaller, as well as the surface rumpling extent. Besides, the grain size of Hf-Y co-doped (Ni,Pt)Al coating was finer than that of Hf- or Y- doped coatings in as-received state, indicating the capability of grain refinement. With the benefits of RE co-doping, the desirably thin/smooth TGO is thus accessible for Pt-modified aluminide coatings. The other issue is the element interdiffusion at high temperature, which would affect the mechanical property of SX superalloy. According to Fick′s law of diffusion, J Al = - D Al · δμ Al / δ x ,to reduce diffusion coefficient ( D Al ) or chemical potential ( δμ Al / δ x ) would both decrease the diffusion extent ( J Al ). Therefore, two strategies are employed: adding a diffusion barrier between coating and substrate, or designing a γʹ-PtAl coating. The performance of these modified aluminide coatings are evaluated in high temperature oxidation test. At last, doping behavior of some elements were explained by First-Principle Calculations.

Preparation and oxidation behavior of novel CeO2/Y2O3-modified aluminide coatings on Ni using sol–gel derived/pack cementation process

CeO2/Y2O3-modified aluminide coatings were prepared on Ni substrate using a sol–gel derived/pack cementation process. For comparison, simple aluminide coatings were also produced on Ni substrate using the same pack cementation process. The microstructure and high temperature oxidation behavior of three aluminide coatings at 900 °C for 50 h in air were comparably analyzed using SEM/EDS and XRD. The results indicated that both CeO2/Y2O3-modified aluminide coatings exhibited better oxidation resistance than the CeO2/Y2O3-free one, because of various effects of CeO2/Y2O3 on the oxidation including the grain refinement effect of the aluminide, the “reactive element effect”(REE) and the epitaxial template effect of Y2O3 to promote the growth of α-Al2O3.

Hot corrosion behavior of reactive-element modified aluminide coatings: The importance of the substrate carbides

Aluminide coatings were developed on a nickel alloy with the addition of RE (Ce, Y, La, and Zr) oxides to the coating powder mixture. The specimens were aluminized at 760 °C for 2 h and diffusion annealed at 1050 °C for 4 h. The characterization of the specimens confirmed the formation of NiAl phase on all the specimens. The hot corrosion test at 900 °C using a 2 mg/cm2 loading of the Na2SO4 -NaCl-V2 O5 mixture showed a similar general protective behavior along with different degrees of local penetration at the surface carbide locations.

The Si influence on the microstructure and oxidation resistance of Ti-Al slurry coatings on Ti-48Al-2Cr-2Nb alloy

In the presented study, different Ti-Al-Si coatings were deposited on Ti-48Al-2Cr-2Nb (at. %) alloy via the slurry method. Al and Si's nominal content in coatings was varied (100 at. % Al, Al-5Si, Al-12.5 Si, Al-20Si, Al-40Si, Al-60Si, Al80Si, 100 at. % Si) to find an optimal coating resistant to high-temperature oxidation. The deposited materials were analyzed because of the microstructure and phase composition. Afterwards, the obtained modified aluminide coatings were subjected to the isothermal oxidation at 900 °C for 500 h. After the oxidation experiment, the oxidized coatings were evaluated, taking into account the microstructure, chemical and phase composition of the oxidation products. The most favourable oxidation behaviour was noticed for the aluminide coatings with Si's small content (respectively 5 and 12.5 at.% Si). In these cases, on the surfaces, the protective α-alumina scale was formed. Moreover, the Ti5Si3 phase was detected for the oxidized Al-12.5Si (at. %) coating. In the case of other coatings, the formation of TiO2 oxide on the surface was observed.

Structure of Pd-Zr and Pt-Zr modified aluminide coatings deposited by a CVD method on nickel superalloys

Structure of Pd-Zr and Pt-Zr modified aluminide coatings deposited by a CVD method on nickel superalloys

Rhodium influence on the microstructure and oxidation behaviour of aluminide coatings deposited on pure nickel and nickel based superalloy

Abstract The rhodium 0,5 μm thick layer was deposited on pure nickel and CMSX 4 Ni-based superalloy using the electroplating method. The rhodium coated substrates were aluminized by the CVD method. Oxidation resistance of nonmodified and rhodium modified coatings deposited both on nickel and CMSX 4 superalloy was compared. The triple-layer structure of rhodium modified coatings deposited on pure nickel was found. The β-(Ni,Rh)Al, rhodium doped γ'-Ni3Al and rhodium doped γ-Ni(Al) phases were the main components of the coatings on pure nickel. Two layers – additive and interdiffusion ones were identified in coatings deposited on CMSX 4 superalloy. TEM, SEM and XRD analysis revealed that β-(Ni,Rh)Al phase was the main component of the additive layer. Moreover Topologically Closed-Pack σ phases containing refractory elements in the β-(Ni,Rh)Al matrix of the interdiffusion layer were found. The rhodium modified aluminide coatings have better oxidation resistance than the nonmodified ones both on the pure nickel and CMSX 4 superalloy.

Oxidation Resistance of Modified Aluminide Coatings

The application of protective aluminide coatings is an effective way to increase the oxidation resistance of the treated parts and prolongs their lifetime. The addition of small amount of noble metals (platinum or palladium) or reactive elements such as: hafnium, zirconium, yttrium and cerium has a beneficial effect on oxidation behavior. This beneficial effect includes an improvement of adhesion of alumina scales and reduction of oxide scale growth rate. Platinum and hafnium or zirconium modified aluminide coating were deposited on pure nickel using the electroplating and CVD methods. The coatings consisted of two layers: an outer, β-NiAl phase and the interdiffusion γ’-Ni3Al phase. Palladium dissolved in the whole coating, whereas hafnium and zirconium formed inclusions on the border of the layers. Samples were subjected to cyclic oxidation test at 1100 °C for 200h. Oxidation resistance of the palladium, Hf+Pd and Zr+Pd modified coatings deposited on pure nickel does not differ significantly, but is better than the oxidation resistance of the non-modified one.

High Temperature Oxidation Behavior of Co-Cr-Y2O3 Modified Aluminide Coatings on Ni-based Superalloy by Pack Cementation Process

The microstructure and high temperature oxidation behavior of Co-Cr-Y2O3 modified pack aluminide coatings on Ni-based superalloy GH586 were investigated. The results show that the specific Co-Cr-Y2O3 modified aluminide coating has a mass gain of only 0.36 mg/cm2 after oxidation at 1000 °C for 100 h, which is much less than that of the substrate at 1000 °C. From X-ray diffraction, the phase of the coatings is mainly AlNi, and after oxidation at 1000 °C for 100 h the denser oxidation scale is composed of Al2O3, Cr2O3, and CoCr2O4. Surface and cross sectional morphologies were characterized by scanning electron microscope (SEM). The coating exhibits a better resistance to high temperature oxidation, compared to the oxidation film of GH586 without coating. Moreover, the growing Cr (W) rich phase is gradually gathered at the grain boundaries during the oxidation, and it is beneficial to providing more Cr element for the dense oxidation film, which is mainly attributed to the excellent high temperature oxidation resistance.

Microstructure and Oxidation Resistance of a Si Doped Platinum Modified Aluminide Coating Deposited on a Single Crystal Superalloy

A Si doped Pt modified aluminide coating was prepared by electroplating and the chemical vapour deposition method. The microstructure and oxidation resistance of the coating were studied, with a single Pt modified aluminide coating as a reference. The results showed that the Si doped Pt modified aluminide coating consisted of singular β-(Ni, Pt)Al phase, and no PtAl2 phase was detected, which might be due to the fact that the addition of Si retarded the formation of PtAl2 phase in the outer layer. Si was dissolved in the β-(Ni, Pt)Al phase in the outer layer and might form silicide with refractory elements in the inter-diffusion zone. The Si doped Pt modified aluminide coating possesses a better oxidation resistance than the Pt modified aluminide coating since Si could promote the formation of α-Al2O3 and inhibit the diffusion of the refractory elements, reducing the formation of detrimental volatile phase.

Effect of Pd and Hf co-doping of aluminide coatings on pure nickel and CMSX-4 nickel superalloy

Microstructure of palladium and hafnium co-doped aluminide coatings deposited on pure nickel and CMSX4 nickel super alloy by the CVD method was examined by the SEM and TEM methods. Both coatings have a double layer structure: additive and interdiffusion zones. The additive zone is formed by the hafnium doped β-(Ni,Pd)Al phase. The interdiffusion zone on pure nickel contains the palladium and hafnium doped γ′-Ni3Al phase, whereas that on CMSX-4 superalloy the hafnium doped β-(Ni,Pd)Al phase with precipitations of Topologically Closed-Pack phases (μ and σ) and Al2O3 at adhesive/interdifusion zones interfaces. Palladium is distributed uniformly in whole coatings. Hafnium forms precipitates that are situated in a Hf-rich belt. In both coatings this belt is in the additive layer, near the line of porosity and Al2O3 precipitates. Palladium and hafnium modified aluminide coatings show better oxidation resistance than those modified only with palladium.

Microstructural evolution of silicon-platinum modified aluminide coatings on superalloy GTD-111

The microstructure evolution of (Si,Pt)-modified aluminide coatings has been investigated. Coatings were prepared by slurry silico-aluminizing of different thicknesses of platinum-electroplated GTD-111 Ni-based superalloy. Microstructure and phase characterizations were conducted by means of SEM, EDX, XRD and EPMA. The composition of the coating's outer layer altered from single β-(Ni,Pt)Al phase to two phase β-NiAl+PtAl2 by increasing the initial Pt thickness. Silicon diffusion into the coating is shown to be less in the presence of the PtAl2 phase. Furthermore, refractory metal-containing precipitates in the outer two phase layer of the platinum modified coating were replaced by silicides in the corresponding (Si,Pt)-modified aluminide coating.

Fabrication and Cyclic Oxidation of Y 2 O 3 /CeO 2 -Modified Low Temperature Aluminide Coatings

With Y 2 O 3 /CeO 2 powder, instead of part of Al 2 O 3 , acting as filler, Y 2 O 3 /CeO 2 -modified aluminide coatings were produced on Ni based using a conventional pack-cementation method at 600 °C for 10 h. For comparison, a normal aluminide coating was also produced using pure Al 2 O 3 acting as filler. Effect of Y 2 O 3 /CeO 2 in the pack on the alumina phase transformation and cyclic oxidation resistance in air at 1000 °C was investigated. The results indicate that Y 2 O 3 and CeO 2 have different effects on θ-α phase transformation: Y 2 O 3 suppresses the growth of the θ-alumina but CeO 2 promotes the q-a phase transformation. However, compared to the normal aluminide coating, the addition of Y 2 O 3 /CeO 2 significantly improves the cyclic oxidation resistance due to the formation of adherent alumina scale, especially the later. The effects of Y 2 O 3 /CeO 2 on alumina phase transformation and cyclic oxidation resistance were discussed.

The Microstructure of Hafnium Modified Aluminide Coatings Deposited by CVD Method

The paper presents results of microstructural analysis of Hf-modified aluminide coatings. The coating was obtained using chemical vapour deposition (CVD) method at 1040°C using BPX-Pro 325 S equipment (Iond Bond). The deposition process time was 960 mintutes. The IN-718, IN-100 as well as CMSX-4 single-crystal nickel superalloys were the substrate material. The observation of coating was carried out using scanning electron microscopy. Chemical composition was analyzed using EDS method. The results showed that hafnium accumulates mainly on diffusion/additive layer interface and forms a „chain” of small precipitations. Hafnium was found in the additive NiAl layer of aluminide coating deposited on IN-100 superalloy. Its amount did not exceed 0.3 at %.

Thermal fatigue behaviour of Al–Si coated Inconel 713 LC

The effect of single and two-stage Si modified aluminide coatings on thermal fatigue behaviour of nickel based superalloy Inconel 713LC was examined. Specimens were loaded under test condition of heating to 1100°C followed by cooling to25°C. The experimental results showed that the coatings increased thermal fatigue resistance in both crack initiation and propagation stages. The comparison of the crack growth rates indicated that both coatings imparted resistance to the crack lengthening. However, the effect of single stage coating on the fatigue resistance was superior compared with that of two-stage coating. Through scanning electron microscopy observation, it was found that the width of γ′ denuded zone was the main reason in the control of crack growth in all specimens.

The Influence of Surface Preparation Method on Microstructure of HF-Modified Aluminide Coatings Deposited by CVD Method on Rene 80 and MAR M-247 Nickel Superalloys

In the article the hafnium modified aluminide coatings deposited using chemical vapour deposition (CVD) method were analyzed. The influence of surface treatment (grinding, sandblasting with different pressures) on microstructure of coatings were described. The Re 80 and M-247 nickel superalloys were used as substrate. Thickness of the obtained aluminide coating was in the range 32-45 mm on Re 80 and 40-45 mm on M-247 respectively. The average amount of Al in the additive layer was 22-24 wt% on Re 80 and about 21 wt % on M-247 base alloy. The total amount of hafnium in coatings did not exceed 2.5 wt % - usuallly below 0.5 wt %. The conducted research has shown that there is no strong influence of surface preparation methodology on microstructure of aluminide coatings obtained by CVD method.

Microstructure and oxidation resistance of Si modified aluminide coating on TiAl based alloys

Two γ-TiAl based alloys of Ti–48Al–2Nb–2Cr (at-%) and Ti–45Al–2Nb–2Mn–1B (at-%) were used as substrate materials. The coatings’ deposition process was prepared using the slurry method. After the deposition of water based slurry containing Al and Si powders on the substrates, diffusion treatment has been carried out at 1000°C for 6 h in Ar atmosphere. The structure of the silicon modified aluminide coatings is as follows: (a) an outer layer consisting of a TiAl3 matrix and Ti7Al5Si12 grains dispersed within this matrix, (b) a middle layer composed of a TiAl3 matrix and columnar grains of Ti5Si3 and (c) an inner layer as TiAl2 phase. According to the energy dispersive spectroscopy analysis results, it can be concluded that Cr had a high tendency to move towards the Si enriched compounds. The results of isothermal oxidation test of 1000°C/200 h showed that the formation of Si modified aluminide coatings on γ-TiAl alloys by slurry method can greatly improve their high temperature oxidation resistance.

Hot Corrosion Behavior of Four Modified Aluminide Coatings on DZ38G Alloy

Hot Corrosion Behavior of Four Modified Aluminide Coatings on DZ38G Alloy

Corrosion Resistance of Novel Coatings on Ferritic Steels for Oxycombustion–Supercritical Steam Boilers: Preliminary Results

Increasing the efficiency of coal fired steam power plants is an important contribution towards clean coal power. In fact, new ferritic steels are expected to withstand 325 bar and 650 °C. Moreover, in order to facilitate CO2 capture oxygen can be used instead of air for combustion (oxycombustion) so that no NOX emissions are produced. Boiler components, such as superheater tubes, are exposed to both steam and fireside corrosion and at higher temperatures, ferritic steels corrode at very fast rates under both atmospheres. A solution can be found in the use of protective coatings, a number of which, applied by techniques capable of depositing said coatings both on the inner and outer surfaces of tubes, are being studied within nationally and European funded projects. In particular, two new Ni and Cr modified aluminide coatings deposited on P92 by non-line-of-sight hybrid processes have been produced and the preliminary results of on-going laboratory testing, both under oxycombustion model atmospheres as well as under pure steam at 650 °C are promising, in particular those exhibited by the Cr enriched aluminide coating. Moreover, results obtained in a pilot oxycombustion boiler operated by CIUDEN in Leon, Spain are also shown.

Thermal cycling behavior of EB-PVD TBCs on CVD platinum modified aluminide coatings

Thermal barrier coating systems (TBCs) including of chemical vapor deposited (Ni, Pt)Al bond coat with grit blasting process and electron beam physical vapor deposited Y2O3-stabilized-ZrO2 (YSZ) ceramic coating were investigated. The phase structures, surface and cross-sectional morphologies, cyclic oxidation behaviors and residual stresses of the TBCs were studied in detail. It was found that the fracture path traverses through the ceramic coating to TGO interface, as well as at the TGO to bond coat interface is obviously detected. The change in fracture plane occurs at grain boundaries. The ridge top spallation leads to separate of sufficient size to result in unstable fracture driven by the strain energy stored in the TGO. The bond coat can undergo a volume increase upon oxidation, so that a cavity, enlarged strictly by oxidation would be full to overflowing with TGO layer. The spalled location of the TBCs probably occurs either at the interface of TGO layer and bond coat or inside of TGO layer. The lower strain energy release rate within TGO layer during thermal cycling is beneficial to prolong of TBCs life. The lower is the compressive stress within TGO layer, the longer is the lifetime of TBCs.

Cyclic oxidation resistance of Ce/Co modified aluminide coatings on nickel base superalloys

Ce/Co modified aluminide coatings with different CeO2 content were prepared on nickel base superalloys by pack cementation method. The microstructure and cyclic oxidation behavior of the coatings were investigated. The results show that the Ce addition is beneficial to improving adhesion of oxide scales by forming the “oxide pegs” structure and reducing voids at the scale/coating interfaces. When the content of CeO2 addition in the pack mixture is 2wt.%, the Ce/Co modified aluminide coating has the highest content of Ce in the outer layer and exhibits the best cyclic oxidation resistance at 1323K.