Oxidation Behavior of Pt–Ir Modified Aluminized Coatings on Ni-base Single Crystal Superalloy TMS-82+

The oxidation resistance of Pt–Ir modified aluminized coatings, prepared by magnetron sputtering, was investigated. Cyclic oxidation tests revealed that Pt–30 at%Ir and Pt–50 at%Ir modified aluminide coatings demonstrated a smaller mass change compared with Pt, Pt–80 at%Ir and Ir modified aluminide coatings. Cross-sectional analyses following cyclic oxidation tests showed that the TGO layer formed on the Pt modified aluminide coating surface is almost twice as thick as those on the Pt–30 at%Ir and Pt–50 at%Ir coatings. In addition, the Pt–30 at%Ir and Pt–50 at%Ir samples had a much smoother surface than the Pt modified coatings after cyclic oxidation, and the latter suffered from severe surface rumpling. However, when the Ir content exceeded 80 at% in Pt–Ir modified coatings, internal voids formed during cyclic oxidation. These results show that the addition of 30–50 at%Ir to Pt-modified aluminized coatings is most effective in enhancing oxidation resistance.     

Effect of superalloy substrate and bond coating on TBC lifetime

Several different single-crystal superalloys were coated with different bond coatings to study the effect of composition on the cyclic oxidation lifetime of an yttria-stabilized zirconia (YSZ) top coating deposited by electron beam physical vapor deposition from a commercial source. Three different superalloys were coated with a 7 μm Pt layer that was diffused into the surface prior to YSZ deposition. One of the superalloys, N5, was coated with a low activity, Pt-modified aluminide coating and Pt-diffusion coatings with 3 and 7 μm of Pt. Three coatings of each type were furnace cycled to failure in 1 h cycles at 1150 °C to assess average coating lifetime. The 7 μm Pt diffusion coating on N5 had an average YSZ coating lifetime > 50% higher than a Pt-modified aluminide coating on N5. Without a YSZ coating, the Pt-modified aluminide coating on N5 showed the typical surface deformation during cycling, however, the deformation was greatly reduced when constrained by the YSZ coating. The 3 μm Pt diffusion coating had a similar average lifetime as the Pt-modified aluminide coating but a much wider scatter. The Pt diffusion bond coating on superalloy X4 containing Ti exhibited the shortest YSZ coating lifetime, this alloy-coating combination also showed the worst alumina scale adhesion without a YSZ coating. The third generation superalloy N6 exhibited the longest coating lifetime with a 7 μm Pt diffusion coating.     

Hybrid intermetallic Ru/Pt-modified bond coatings for thermal barrier systems

NiAl-based bond coatings for thermal barrier coating (TBC) systems containing varying amounts of Ru and Pt have been investigated. The addition of Ru to bulk NiAl has shown substantial increases in the creep strength of these aluminide materials, while Pt-modifications are known to improve the oxidation resistance of NiAl. The oxidation and interdiffusion behavior of these hybrid Ru/Pt bond coat systems are compared to conventional Pt-modified aluminide bond coats. The Ru/Pt-modified aluminide bond coats demonstrate cyclic oxidation lives comparable to those of Pt-modified aluminide bond coatings. These hybrid Ru/Pt-modified bond coats exhibit better creep properties than traditional Pt-modified coatings and suppress the rumpling mechanism typically responsible for the spallation of TBC from Ni(Pt)Al bond coatings. The evolution of coating microstructures at various stages of cyclic life was studied, and phase equilibria issues relevant to the fabrication and oxidation behavior of these multilayer systems are discussed.     

Structure and cyclic oxidation resistance of Pt, Pt/Pd-modified and simple aluminide coatings on CMSX-4 superalloy

The coatings were prepared by the means of Pt and Pt/Pd galvanizing, followed by vapor phase aluminizing at 1050 °C. Microstructural and phase analysis revealed that all the investigated coatings consisted mainly of β-NiAl phase, however the Pt-modified aluminide coating also contained PtAl₂ phase and pure platinum precipitates. The cross-sectional microstructure of the coatings was zonal and composed of β-NiAl phase zone and the diffusion zone. The Pt modified aluminide coating's cross-section also incorporated an outermost zone consisting of β-NiAl and PtAl₂ phases. The concentration profiles proved that both Pt and Pd contents decrease gradually inwards the modified coatings. Cyclic oxidation tests at 1100 °C proved that Pt/Pd-modified aluminide coatings exhibit the best performance under cyclic conditions. The analysis of oxidation kinetics curves showed that the course of simple aluminide coating's oxidation is slightly different from that of Pt- and Pt/Pd-modified aluminide coatings.     

The effects of ultrasonic nanocrystal surface modification (UNSM) on pack aluminizing for the fabrication of Pt-modified aluminide coatings at low temperatures

An 8–9 μm thick Pt layer was coated on a superalloy and transformed to a Ni–Pt alloy layer by the interdiffusion of Ni and Pt at 1050 °C for 3 h. The surface of the Ni–Pt alloy layer was pack aluminized to form a Pt-modified aluminide coating. Ultrasonic nanocrystal surface modification (UNSM) was applied to the alloy layer prior to pack aluminizing. The effects of UNSM on Pt-modified aluminide coatings fabricated at 750, 850, 950, and 1050 °C were studied. The treated Ni–Pt alloy layers had finer grain sizes than the untreated specimens. In addition, UNSM made the grain size of the Ni–Pt alloy finer and reduced the surface roughness. During pack aluminizing, the Pt-modified aluminide coatings fabricated following UNSM uptook more Al and were thicker than the untreated Pt-modified aluminide coatings at the various temperatures (750, 850, 950, and 1050 °C). The untreated Pt-modified aluminide coatings with pack aluminizing performed at 750 and 850 °C were composed of only a two-phase (NiAl + PtAl₂) layer, due to insufficient diffusion of Pt at the lower temperatures. However, two-phase and one-phase (NiAl) layers were obtained in the treated Pt-modified aluminide coatings which were pack-aluminized at 750, 850, 950, and 1050 °C, due to the diffusion of Pt through the greater amount of grain boundaries and increased volume generated by UNSM before the pack aluminizing. Additionally, the treated coatings had smoother surfaces even after the pack aluminizing. During cyclic oxidation at 1150 °C for 1000 h, the treated Pt-modified aluminide coatings aluminized at relatively low temperatures (750 and 850 °C) showed better cyclic oxidation resistance than the untreated Pt-modified aluminide coating aluminized at 1050 °C.     

Evaluation of aluminide diffusion coatings for thermal cyclic oxidation protection of a nickel‐base superalloy

Active element modified aluminide diffusion coatings on IN738 substrates were produced by a new route using continuously cast, aluminum alloy wires consisting of Al‐Y, Al‐Ce, Al‐La and Al‐Si‐Y. The cast wires were used as evaporation sources for ion‐vapour deposition followed by diffusion heat treatments to form nickel aluminide coatings. In order to examine the oxidation resistance of these coatings at elevated temperatures, thermal cyclic oxidation experiments were carried out in air at 1050°C. While all coatings were found to provide significant protection, the Al‐La modified coatings provided the greatest resistance to cyclic oxidation. On the other hand, with coatings based on Al‐Si‐Y alloys, while silicon has a strong ability to reduce the outward diffusion of aluminum, the adverse effect of silicon on mechanical properties of the coating, together with the formation of volatile silicon monoxide, led to catastrophic localized oxidation of the protective coatings.     

Microstructural aspects of plain aluminide and Pt-aluminide coatings on Ti-base alloy IMI-834

One of the major limitations of the near-α titanium alloys such as IMI-834 and IMI-829 that is currently restricting their use at high temperatures is their poor oxidation resistance. Several protective coatings including diffusion aluminide coatings are currently being examined to enhance the oxidation performance of these alloys in the temperature range of 600–750 °C. In the present study, various microstructural aspects of plain aluminide and Pt-aluminide coatings on Ti-base alloy IMI-834 have been studied. Plain aluminide coating shows a single layer consisting of only Al₃Ti phase in the as-aluminized state. Pt-aluminide coating consists of three layers, namely an outer platinum-rich layer, an intermediate Al₃Ti layer, and the inner interdiffusion layer. The above structure of Pt-aluminide coating on IMI-834 alloy is very similar to that reported on Ni-base superalloys. It has further been found in the present study that the structure of Pt-aluminide coating depends on its Pt and Al contents. The nature of such dependence is similar to that reported for Pt-aluminide coatings on Ni-base superalloy substrates.     

Cyclic Oxidation and Hot Corrosion Behavior of Y/Cr-Modified Aluminide Coatings Prepared by a Hybrid Slurry/Pack Cementation Process

Y/Cr-modified aluminide coatings were prepared on a Ni-base superalloy K417G using a hybrid slurry/pack cementation process. The coatings consisted of a NiAl layer with dissolved Cr and Y. The microstructures and high temperature corrosion behavior of the coatings were characterized using SEM/EDS, XRD, EPMA and SIMS. Cyclic oxidation tests at 1000 °C for 200 h were carried out in air. The results indicated that specimens coated by either the Y/Cr-modified aluminide coatings or the simple aluminide coatings exhibited better oxidation resistances than the cast alloy. The Y/Cr-modified aluminide coatings possessed lower oxidation rates and better degradation resistance than the simple aluminide coatings during the oxidation tests. Furthermore, the alumina scales formed on the Y/Cr-modified aluminide coatings were considerably more adherent than those on the simple aluminide coatings during the thermal cycling. The hot corrosion tests consisted of applying a 25 wt% K₂SO₄ +75 wt% Na₂SO₄ salt mixture to the specimens and exposing at 900 °C. The Y/Cr-modified aluminide coatings showed the longest service life compared with the cast alloy and aluminide coatings, which suffered significant sulfur attack. After 200 h, the Y/Cr-modified aluminide coatings were still protective.     

Novel processing in inert atmosphere and in air to manufacture high‐activity slurry aluminide coatings modified by Pt and Pt/Ir

Slurry‐derived coatings are an interesting alternative method to pack aluminization of nickel‐base superalloys, which provide similar properties and protection at high temperatures. For highest performance, these aluminide coatings are modified by the addition of Pt or, as recent research suggests, with Pt/Ir. While the combination of Pt and Pt/Ir with an out‐of‐pack process is state of the art, slurry coatings are of special interest as a repair method for turbine blades. In this study, the microstructural evolution of slurry‐derived coatings manufactured on CM 247 in inert atmosphere as well as in air was investigated. Layers of Ni, Pt, and Pt/Ir mixtures were electrodeposited. After annealing, a diffusion heat‐treatment with a slurry containing aluminum or aluminum–silicon powder was applied on the samples. The addition of silicon is well known to be beneficial for hot corrosion environments. The reaction and interdiffusion behavior of aluminum/aluminum–silicon determines the microstructural evolution of the coatings. Depending on the initial electroplated layer on the surface, different microstructures can be obtained, such as the Pt/Ir‐modified beta phase (Ni,Pt)Al or two‐phase layers of PtAl₂ and NiAl. Additionally, the reactivity between the elements at the surface and those from the slurry was shown to determine homogeneity and surface roughness of the diffusion coating, also depending on the atmosphere used during slurry aluminization. Finally, it was demonstrated that iridium has a high influence on the diffusion behavior and especially the distribution of platinum in the coatings. Such new coatings have the potential to overcome some disadvantages of conventionally manufactured high‐activity aluminide coatings, as the combination of Pt/Ir‐electroplating with the slurry process results in less detrimental substrate elements like molybdenum or tungsten close to the surface.     

Effect of increased water vapor levels on TBC lifetime with Pt-containing bond coatings

To investigate the effect of increased water vapor levels on thermal barrier coating (TBC) lifetime, furnace cycle tests were performed at 1150 °C in air with 10 vol.% water vapor (similar to natural gas combustion) and 90 vol.%. Either Pt diffusion or Pt-modified aluminide bond coatings were applied to specimens from the same batch of a commercial second-generation single-crystal superalloy and commercial vapor-deposited yttria-stabilized zirconia (YSZ) top coats were applied. Three coatings of each type were furnace cycled to failure to compare the average lifetimes obtained in dry O₂, using the same superalloy batch and coating types. Average lifetimes with Pt diffusion coatings were unaffected by the addition of water vapor. In contrast, the average lifetime of Pt-modified aluminide coatings was reduced by more than 50% with 10% water vapor but only slightly reduced by 90% water vapor. Based on roughness measurements from similar specimens without a YSZ coating, the addition of 10% water vapor increased the rate of coating roughening more than 90% water vapor. Qualitatively, the amount of β-phase depletion in the coatings exposed in 10% water vapor did not appear to be accelerated.     

Cyclic oxidation of Pt/Pd-modified aluminide coating on a nickel-based superalloy at 1150 °C

Pt-, Pd-, and Pt/Pd-modified aluminide coatings were prepared on Inconel 738LC by pack aluminizing at 1034 °C. During pack aluminizing, Pt-modified aluminide coating formed a two-phase β-NiAl + PtAl₂ layer and a β-NiAl layer on an interdiffusion zone, whereas Pd- and Pt/Pd-modified aluminide coatings formed only the thicker β-NiAl layer. However, Pd-modified aluminide coating had many pores. During cyclic oxidation, Pt/Pd-modified aluminide coating had a surface that was less rumpled than that of Pt-modified aluminide coating due to its thicker thickness. Pt/Pd-modified aluminide coating had a 22% greater Al-uptake than Pt-modified aluminide coating. Cyclic oxidation tests at 1150 °C showed that Pt/Pd-modified aluminide coating had the best cyclic oxidation resistance. After the cyclic oxidation, an additional γ-Ni phase was seen beneath the outermost alumina scale on the the γ′-Ni₃Al phase in Pt/Pd-modified aluminide coating. The γ-Ni phase, which had a higher Cr content, increased the adhesion and stability of the alumina.     

Influences of Iridium and Palladium on Oxidation Resistance of PtAl Coating

The overarching goal of present study is to investigate the effects of Ir and Pd additions on the oxidation behaviour of PtAl coatings. Prior to depositing standard PtAl coating, Ir layer was electroplated by IrBr 3 aqueous solution while Pd layer was prepared using electroless deposition. Comparing with normal PtAl coating, cyclic oxidation tests were carried out on both the Ir-and Pd-modified aluminide coatings. The results showed that Ir-modified PtAl coating exhibited better oxidation resistance than both Pd-modified and normal PtAl coatings because Ir partly served as diffusion barrier to reserve Al while Pd did not.     

Oxidation and alkali sulfate‐induced corrosion of aluminide diffusion coating with and without platinum

A platinum‐free (MDC210) and a platinum‐rich (MDC150L) aluminide diffusion coating applied to a CMSX4 single crystal Ni‐based superalloy were investigated after exposure to sulfate‐induced corrosion and oxidation at 900 °C for a total of 100 h. Weight changes, microstructural, and microchemical analyses of the products were performed by the means of gravimetry, scanning electron microscopy (SEM), energy dispersive X‐ray (EDX), and X‐ray diffraction (XRD). Platinum was found to have a beneficial effect on both the oxidation and corrosion resistance of the coating. In both cases the scale was thicker on the platinum‐free coating. However, the difference in the extent of oxidation of the two coatings was small.     

The Main Degradation Modes of an Aluminide Coating on a Co-Base Superalloy During High-Temperature Oxidation in Air

Degradation of aluminide coatings occurs by two ways, one by coating oxidation, and the other by interdiffusion of Al. In this paper, the structure variation and phase transformation are analyzed for the aluminide coating on a newly developed Co-base superalloy (DZ40M alloy) after oxidation at 900 and 1000°C in air. The results show that degradation of this coating was mainly by oxidation at 900°C, but principally by interdiffusion at 1000°C. The main degradation mode of the coating is primarily dependent on the oxidation temperature and the specific structure of the coating itself.     

The isothermal and cyclic oxidation behaviour of two Co modified aluminide coatings at high temperature

The isothermal and cyclic oxidation behaviour of two Co modified aluminide coatings together with the simple aluminide coating were performed at 1000 °C and 1100 °C. All the three coatings show a much lower oxidation rate compared with the bare alloy. Results also indicate the addition of Co to the aluminide coating decreases the oxidation resistance slightly. It can be ascribed to that Co is easier to be oxidized than Ni at high temperature, and the Cr(W) rich phases which could act as a diffusion barrier are less in the coating with higher Co content.     

An evaluation study of aluminide and chromoaluminide coatings on IN-100

Aluminide diffusion coatings are commonly used to protect aircraft gas turbine blades and vanes from oxidation and hot-corrosion attack. These coatings are based on NiAl intermetallic compound with other alloying elements like Cr and Ti either diffused from the superalloy substrate or incorporated in a separate coating step. The present investigation is mainly concerned with the development of both aluminide and chromoaluminide coatings on IN-100, a cast Ni-base superalloy. The coating structure and composition have been characterized and the cyclic oxidation and hot corrosion properties have been evaluated for the different types of coatings. The difference in the hot-corrosion properties between the aluminide and the chromoaluminide coatings has been rationalized in terms of the coating chemistry. The mode of coating degradation under hot-corrosion conditions has also been analyzed.     

DZ40M钴基合金铝化物涂层的循环氧化

以新型定向凝固钴基高温合金ＤＺ４０Ｍ为基体,研究其低压化学气相沉积铝化物涂层的循环氧化行为,发现该涂层具有较高的抗循环氧化性能,涂层与基体结合良好。涂层退化主要是由外表面氧化膜的愈合消耗Ａｌ源所造成,沉积渗剂中加入Ｔｉ可加速涂层的退化。     

Performance of Bond Coats Modified by Platinum Group Metals for Applications in Thermal Barrier Coatings

We have investigated the partial replacement of Pt with other less expensive Pt group metals on the properties of γ′ + γ bond coats used in thermal barrier coatings (TBCs) deposited on a nickel-base superalloy. The microstructure, thermal stability, oxidation behavior and performance in TBC systems of bond coats synthesized with Pt + Ru, Pt + Ir and Pt + Rh are compared with those of a reference bond coat synthesized with Pt. Yttria-stabilized zirconia has been employed as top coat in all coating systems. It is shown that at high temperatures all bond coats are degraded by interdiffusion and oxidation, however, with different kinetics. The lifetime of each TBC system is found to be limited by the cohesion between the thermally grown oxide and underlying bond coat. Differences in the behavior of various bond coats are correlated with their properties. Among the three Pt group metals investigated, the properties of the Pt + Ru bond coat are shown to closely approach those of the Pt bond coat. It is concluded that Ru with much lower cost presents a potential candidate for reducing the consumption of Pt.     

简单/改性铝化物涂层的研究现状

航空发动机各部件高温结构材料在苛刻环境下服役时,会遭受严重的高温氧化和热腐蚀.在合金表面施加铝化物涂层后,高温下表面能够生成一层致密且生长缓慢的Al2O3氧化膜,从而隔绝腐蚀介质,以防止合金被快速氧化腐蚀.概述了铝化物涂层的优点,包括制备简单、成本低廉.重点综述了以Ni、Fe、Ti/TiAl为合金基体的铝化物涂层微观结构.涂层的微观结构主要由渗铝工艺、基材成分及后处理工艺等因素决定,渗铝工艺包括渗剂成分、渗铝温度和渗铝时间.在高温下渗铝,Al的活度较低,涂层主要以基体元素向外扩散形成外扩散型涂层为主;在低温下渗铝,Al的活度较高,涂层主要以Al向内扩散形成内扩散型涂层为主.还归纳了不同渗铝涂层在干燥空气和水蒸气环境中的高温氧化行为,阐述了水蒸气对铝化物涂层高温氧化行为的影响,比较了Ni-Al系和Fe-Al系涂层的抗高温氧化性能.同时介绍了Cr-Al、Si-Al和Pt-Al 3种改性铝化物涂层的研究进展,包括制备方法、微观结构及抗高温氧化和腐蚀性能.最后,展望并总结了高温防护涂层的发展趋势.     

铂铝涂层高温氧化的影响因素研究

研究比较沉积热障涂层和无热障涂层的镍基高温合金铂改性铝化物涂层在900,1000和1100℃空气中高温氧化生成的氧化铝层表面形态和断面结构。发现低铂含量涂层氧化初期热生长层(TGO)表面有放射状裂纹形成和长大,造成氧化铝的局部脱落,并在TGO与铂铝涂层界面形成空洞。涂层900℃循环氧化300h后TGO内部均形成空洞。而在1100℃氧化时,TBC陶瓷层的存在改变了两种铂铝涂层TGO的内应力变化趋势,升高温度使TGO厚度迅速增大,涂层寿命迅速下降。