Microstructure and high temperature oxidation resistance of Si-Y co-deposition coatings prepared on TiAl alloy by pack cementation process

In order to improve the high temperature oxidation resistance of TiAl alloy, Y modified silicide coatings were prepared by pack cementation process at 1030, 1080 and 1130 °C, respectively, for 5 h. The microstructures, phase constitutions and oxidation behavior of these coatings were studied. The results show that the coating prepared by co-depositing Si?Y at 1080 °C for 5 h has a multiple layer structure: a superficial zone consisting of Al-rich (Ti,Nb)5Si4 and (Ti,Nb)5Si3, an out layer consisting of (Ti,Nb)Si2, a middle layer consisting of (Ti,Nb)5Si4 and (Ti,Nb)5Si3, and aγ-TiAl inner layer. Co-deposition temperature imposes strong influences on the coating structure. The coating prepared by Si?Y co-depositing at 1080 °C for 5 h shows relatively good oxidation resistance at 1000 °C in air, and the oxidation rate constant of the coating is about two orders of magnitude lower than that of the bare TiAl alloy.

Effect of Rare Earth Doping on the Tensile Properties of High Temperature Oxidation Coating

The failure process was characterized by complex diffusion of elements in the bonding layer,TGO growth and growth stress inside the coating.We studied the aluminum migration phenomenon of NiCoCrAlY and NiCoCrAlYHf coatings under high temperature oxidation,TGO growth characteristics,the microstructure and composition of the bonding layer,and integrates them into the description of the surface strain under coating tension.The experimental results show that the TGO growth rate of NiCoCrAIYHf coating is lower than that of NiCoCrAIY coating,and the formed TGO is thinner.After high temperature oxidation,the cracking time of NiCoCrAIY coating is advanced,while the cracking time of rare earth doped coating is delayed.The addition of rare earth elements can effectively inhibit the generation of spinel phase,improve the fracture toughness of TGO,refine the grains in the bonding layer,and increase the grain boundary strengthening by 29.1 MPa which is consistent with the experimental value.Therefore,the yield strength of the doped coating is improved and the crack time of the coating is delayed.

Microstructure, mechanical and oxidation characteristics of detonation gun and HVOF sprayed MCrAlYX coatings

Microstructure, mechanical property and oxidation resistance of MCrAlYX coatings prepared by detonation gun (D-gun) and HVOF spraying were investigated. Lamellar microstructure and uniform microstructure formed in D-gun sprayed MCrAlYX coating and HVOF sprayed coating, respectively. Element redistribution and formation of new phase took place during the detonation process. Besides, the porosity of D-gun sprayed coating was much lower than that of HVOF sprayed coating. On the mechanical property, the micro-hardnesses of the two coatings were in the same level (~HV 910). However, D-gun sprayed MCrAlYX coating exhibited larger standard deviation of microhardness due to its lamellar microstructure, and exhibited better bend bonding strength owing to the existence of residual compressive stress between the layers and particles. Meanwhile, due to the much more compact microstructure, D-gun sprayed MCrAlYX coating showed superior oxidation resistance to the HVOF sprayed coating. The continuous dense protective layer can form earlier in D-gun sprayed coating and thus suppress further oxidation and control the oxide thickness at a relatively low level.

Studies on High Temperature Oxidation of Electrodeposited RE-Ni-W-P-SiC Composite Materials

The oxidation of the Electrodeposited RE-Ni-W-P-SiC Composite materials at high temperature is investigated. The results show that during high temperature oxidation the relationship between the mass change of pure Ni, Ni-W-P, Ni-W-P-SiC or RE-Ni-W-P-SiC coatings and the oxidation time follows a mixed curve, i.e. it is approximately a linear relationship when the oxidation time is less than 60 mins while it is a power function relationship when the oxidation time is over 60 mins. The order for the oxidation rate of the four coatings is Ni> Ni-W-P> Ni-W-P-SiC>RE-Ni-W-P-SiC. The mass change of Ni-W-P, Ni-W-P-SiC or RE-Ni-W-P-SiC coatings increases exponentially with a rise of oxidation temperature. The high temperature-oxidation resistance of RE-Ni-W-P-SiC composite material is 3-4 times than that of Ni-W-P alloy coating. The cross section morphologies and X-ray diffraction patterns indicate that the high temperature-oxidation resistance of RE-Ni-W-P-SiC composite coating is better than any other coatings.

煤油流量对HVOF喷涂FeCrMoSi-Ti_(3)SiC_(2)涂层高温摩擦磨损性能的影响

目的提高燃煤锅炉四管的耐磨性能。方法使用喷雾造粒技术制备FeCrMoSi/Ti_(3)SiC_(2)复合粉末,并利用超音速火焰喷涂技术(HVOF)在12CrMoV基体上制备煤油流量分别为26、28、30、32 L/h的复合涂层。使用X射线衍射仪(XRD)、扫描电镜(SEM)及其自带的能谱仪(EDS)、Raman、维氏显微硬度计和摩擦磨损试验机研究FeCrMoSi/Ti_(3)SiC_(2)粉末及其涂层相组成、组织结构,检测涂层的力学性能,并对涂层在800℃下的摩擦学性能和磨损机理进行系统分析。结果粉末物相主要由Ti_(3)SiC_(2)、Fe-Cr和TiC组成,涂层的物相与粉末类似,但是新产生了SiC相,且随着煤油流量的升高,Ti_(3)SiC_(2)物相逐渐分解。当煤油流量为30、32 L/h时,涂层内Ti_(3)SiC_(2)物相大量分解。涂层的硬度和断裂韧性随着煤油流量的升高表现出先升高、后降低的趋势,孔隙率和磨损率呈现先减小、后增大的趋势。当煤油流量为28 L/h时,涂层磨损率最低,约为5.44×10^(-15)m^(3)/(N·m)。结论煤油流量为28 L/h时,涂层表面生成的SiO_(2)、TiO_(2)和Fe_(2)O_(3)等氧化物均匀分布在磨痕和对偶球表面,有效阻挡了对偶球和涂层的直接接触,使得涂层显示出最优异的摩擦学性能。涂层的主要磨损机制为氧化磨损和黏着磨损。

AC-HVAF和HVOF制备MCrAlY粘结层的组织结构及高温氧化性能

热障涂层金属粘结层的制备工艺影响涂层的微观组织结构及性能。采用活性燃烧-超音速火焰喷涂(AC-HVAF)和传统超音速火焰喷涂(HVOF)2种工艺喷涂制备NiCoCrAlTaY粘结层,并对2种粘结层的组织结构及高温氧化性能进行对比。结果表明:AC-HVAF喷涂层表面半熔颗粒的尺寸为(13.242±1.392)μm,孔隙率为(1.34±0.18)%,氧含量为0.630%,表面粗糙度为(10.12±0.36)μm;HVOF喷涂层表面半熔颗粒的尺寸为(19.438±2.413)μm,孔隙率为(5.96±2.11)%,氧含量为2.300%,表面粗糙度为(11.35±0.43)μm;AC-HVAF制备的NiCoCrAlTaY金属粘结层高温氧化后表面生成了以α-Al2O3为主的热生长氧化物(TGO),而HVOF制备的NiCoCrAlTaY金属粘结层高温氧化后表面生成了以Cr-Ni复合氧化物为主的TGO,AC-HVAF制备的金属粘结层具有更优异的抗氧化性能。

煤油流量对HVOF喷涂WC-12Co/NiCrBSi复合涂层显微组织与性能的影响

在CrZrCu基体上电镀Ni粘结层,通过超音速火焰喷涂(HVOF)技术,采用不同煤油流量在电镀Ni粘结层上制备了WC-12Co/NiCrBSi复合涂层。利用XRD、SEM、Raman、维氏显微硬度计、电子拉伸试验机和球盘式摩擦磨损试验机考察了不同煤油流量下涂层相组成、组织结构、力学性能和高温摩擦磨损性能。结果表明:不同涂层的物相组成基本相同,喷涂过程中发生了一定程度的分解脱碳生成了W2C,以及少量的Cr7C3和Co3W3C相;随着煤油流量升高,涂层硬度提高,涂层孔隙率和耐磨性表现出先降低后升高趋势,致密的结构与较高的硬度有利于提高涂层的耐磨性;煤油流量为26 L/h的工艺下制备的涂层孔隙率最低,为0.11%,硬度较高达到927.0 HV0.3,摩擦因数最低约为0.46,磨损率最低为2.83×10-15m3/(N·m),抗粘着磨损性能最好。

Evaluation of Oxidation of Ti-Al and Ti-Al-Cr Coatings Arc-ion Plated on Ti-60 High-temperature Titanium Alloy

High-temperature titanium alloy for aeroengine compressor applications suffers from high-temperature oxidation and environmental corrosion, which prohibits long-term service of this kind alloy at temperatures above 600℃. In an attempt to tackle this problem, Ti-48Al （at. pct） and Ti-48Al-12Cr （at. pct） protective coatings were plated on the substrate of alloy Ti-60 by arc ion plating （ALP） method. Isothermal and cyclic oxidation tests were performed in static air at elevated temperatures. Phase composition, morphology of the coatings and distribution of elements were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy dispersive X-ray analysis （EDX）. The results showed that the Ti-48Al coating exhibited good isothermal oxidation resistance during exposure at 800℃, but poorer resistance against oxidation at 900℃. By contrast Ti-48Al-12Cr coating demonstrated excellent isothermal oxidation resistance at both temperatures. Cyclic oxidation tests performed at 800℃ indicated that resistance and no spallation of coatings was observed. But both coatings demonstrated good cyclic oxidation at 900℃ only Ti-48Al-12Cr coating demonstrated excellent cyclic oxidation resistance.

High-temperature Oxidation Resistant Coatings Composed of YSZ Particles Packaged by Nano-Al_2O_3 Film

The alloy performance to resist high-temperature oxidation is mainly determined either by the formation of oxide scales or by the deposition of oxide coatings on the surface of alloys.In the former case,a protective oxide scale,such as Al_2O_3,Cr_2O_3 and SiO_2,can be selectively formed by adjusting the composition of alloys.Even if the oxide scale on the surface of alloys is spalled,new oxide can grow continuously,so the oxidation of alloys can be inhibited effectively.In the latter case,theoretically, depositing oxygen diffusion barrier oxide coatings,such as Al_2O_3,Cr_2O_3 and SiO_2,can prevent alloys from oxidation as well.However,the integrity of these oxide coatings can not maintain for a long time,owing to the thermal stress produced by the difference of the expansion coefficients between the oxide coatings and alloy substrates.Consequently,the ability to resist high-temperature oxidation by depositing such oxide coatings should be disappeared.Therefore,an oxide coating possessed both properties to act as an excellent oxygen diffusion barrier and match a suitable expansion coefficient with alloy substrate,is the basic conditions for the coating to maintain the ability to resist high-temperature oxidation of alloys. Based on above-mentioned idea,a novel composite oxide coating has been developed to obtain two kinds of functions,to act as an oxygen diffusion barrier and to adjust the expansion coefficient of coating as required.Figure 1 shows the schematic diagram of such novel oxide coating.This coating is composed of ZrO_2-8%Y_2O_3(YSZ) particles packaged by nano-Al_2O_3 film.The nano-Al_2O_3 film has a bubble-like structure,each YSZ particle is packaged in an Al_2O_3 bubble.Owing to YSZ is a good conductor for oxygen ions,so oxygen diffusion in this composite coating is determined by the walls of Al_2O_3 bubbles or the nano-Al_2O_3 film.If the thickness of all walls of Al_2O_3 bubbles in the direction perpendicular to the surface of alloy is over a critical value,the Al_2O_3 bubbles can act as an excellent oxygen diffusion barrier. Owing to YSZ has a high thermal expansion coefficient,so the thermal expansion coefficient of coatings can be easily increased by enhancing the ratio of YSZ to Al_2O_3 in these coatings. These composite coatings have been prepared by an improved sol-gel method.Firstly, YSZ particles packaged Al_2O_3 gel film were painted or deposited by electrophoresis on the alloy surface. Then,the specimens were treated by thermal pressure filtration to get primary coatings without cracks.Finally,the primary coatings were sintered in microwave furnace to obtain compact coatings. It is demonstrated from the result of cycling oxidation experiment that both of the hightemperature oxidation resistance and oxide spallation resistance are increased obviously with the ratio of YSZ to Al_2O_3 in the coatings,which are much superior to that of MCrAlY coatings.Therefore, these novel coatings can be used to protect various kinds of alloys from high-temperature oxidation,and can be also served as the interlayer in the thermal barrier coating system.

High temperature oxidation resistance and microstructure change of aluminized coating on copper substrate

The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the coating oxidized in ambient air at 1000 °C for 25-250 h were investigated using SEM, X-ray diffraction and optical microscope methods. The results show that the copper with single phase Ni2Al3 coating possesses the best high temperature oxidation resistance, and the mass gain of the coating is 1/15 that of pure copper and 1/2 that of nickel coating, respectively. The specimen surface after being oxidized for 25 h still comprises Ni2Al3 phase. However, when the time of oxidizing treatment increases to 50 h, the Ni Al phase is formed. It is also found that the Ni2Al3 phase completely turns into Ni Al phase after oxidizing treatment for 100 h and above. The Ni Al coating shows excellent high temperature oxidation resistance when oxidation time is 250 h.

High temperature oxidation behavior of Ti(Al,Si)_3 diffusion coating on γ-TiAl by cold spray

A Ti(Al,Si)3 diffusion coating was prepared on γ-TiAl alloy by cold sprayed Al?20Si alloy coating, followed by a heat-treatment. The isothermal and cyclic oxidation tests were conducted at 900 °C for 1000 h and 120 cycles to check the oxidation resistance of the coating. The microstructure and phase transformation of the coating before and after the oxidation were studied by SEM, XRD and EPMA. The results indicate that the diffusion coating shows good oxidation resistance. The mass gain of the diffusion coating is only a quarter of that of bare alloy. After oxidation, the diffusion coating is degraded into three layers: an inner TiAl2 layer, a two-phase intermediate layer composed of a Ti(Al,Si)3 matrix and Si-rich precipitates, and a porous layer because of the inter-diffusion between the coating and substrate.

Protective Effect of the Sputtered TiAlCrAg Coating on the High-Temperature Oxidation and Hot Corrosion Resistance of Ti-Al-Nb Alloy

The effect of a sputtered Ti-48AI-8Cr-2Ag (at. pct) coating on the oxidation resistance of the cast Ti-46.5AI-5Nb (at. pct) alloy was investigated in air at 1000-1100℃. Hot corrosion in molten 75 wt pct Na2SO4+25 wt pct K2SO4 was investigated at 900℃. The scale on the cast TiAINb tends to spall in air, while the scale on coating is very adherent. The sputtered Ti-48AI-8Cr-2Ag coating remarkably improved high temperature oxidation resistance of the cast Ti-46.5AI-5Nb alloy because of the formation of an adherent Al2O3 scale. Due to the inward diffusion of Cr, Kirkendall voids were found at the coating/substrate interface. TiAICrAg coating provided excellent hot corrosion resistance for TiAINb alloy in molten 75 wt pct Na2SO4+25 wt pct K2S04 at 900℃ due to the formation of a continuous Al_2O_3 scale.

High temperature induced“glaze”layer formed in HVOF-sprayed NiCrWMoCuCBFe coating and its wear reduction mechanism

The in-situ formation of oxides on alloy surface induced by high temperature can effectively reduce wear and resist oxidation.In consideration of the solid solution strengthening effect and great oxidation resistance of additional elements at elevated temperature,the NiCrWMoCuCBFe coating was prepared by high velocity oxygen flame(HVOF)spraying technology,and its tribological behavior was scrutinized from 25 to 800°C.By means of high temperature Vickers hardness tester and high temperature X-ray diffractometer,the mechanical properties and microstructures of NiCrWMoCuCBFe coating were measured.And the effect of the mechanical properties and microstructures of the coating on tribological performance was discussed in detail.The results showed both its friction coefficient(0.37)and wear rate(5.067×10^(−6)mm^(3)·N^(−1)·m^(−1))at 800℃ were the lowest,which was mainly related to the formation of“glaze”layer on the coating surface at high temperature.The glaze layer consisted of two parts,which were NiCr_(2)O_(4)oxide film with the ability of interlaminar slip formed in the outer layer and nano-grains existed in the inner layer.Worth mentioning,these nano-grains provided bearing capability while the oxide film was vital to reduce wear rate and friction coefficient.As the ambient temperature increased,many hard oxides were produced on the wear scars,including NiO,Cr_(2)O_(3),MoO_(3),and Mo_(2)C.They can improve tribological and mechanical properties of NiCrWMoCuCBFe coating at a wide temperature range.

Oxidation Behavior of Pd-Modified Aluminide Coating at High Temperature

(Ni,Pd)AI coating, prepared by low pressure pack cementation on the Ni-base superalloy M38 where Pd-20 wt pct Ni alloy was predeposited, consists of a single β-(Ni,Pd)AI phase. The initial isothermal oxidation behavior of (Ni,Pd)AI coating was investigated by TGA, XRD, SEM/EDS at 800-1100℃. Results show that oxidation kinetics accord preferably with parabolic law at 800, 900 and 1100℃, but not at 1000℃. θ-AI203 was observed at 800-1100℃. It is found that Pd plays an important role in accelerating the diffusion of Ti from the substrate to the coating surface in the aluminide coating.

High temperature performance of arc-sprayed aluminum bronze coatings for steel

The high-temperature oxidation behavior of arc-sprayed aluminum bronze coatings on steel substrate was studied during isothermal exposures in air at 900 ℃. The surface morphologies and interface of the coatings after isothermal oxidation at 900 ℃ for different times were observed. The experiments showed that the coatings on steel substrate were not deteriorated and the substrate was protected well, being exposed to high temperatures up to 900 ℃ . The coatings withstood more than ten times thermal shock tests without any coating separation. The thermal expansion coefficient of the coatings was measured, revealing not much difference between it and that of steel substrate. After exposure at high temperature, the coatings were still adhered to steel substrate well. Isothermal mass gain of the coatings at elevated temperature in dry air was measured by means of a thermal balance and the oxidation behavior was evaluated by oxidation kinetic curves, exhibiting the oxidation kinetics curve accorded with a parabolic law. The parabolic rate constant of the oxidation kinetic curve is 1.02×10?9 g2·cm?4·s?1 for the first 60 min and from 150 min to 2 880 min the constant is 5.1×10?12 g2·cm?4·s?1.

Oxidation performance of Fe-Al/WC composite coatings produced by high velocity arc sprayed at 800 ℃

Fe-Al/WC intermetallic composite coatings were prepared by high velocity arc spraying (HVAS) technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings was studied. The results demonstrate that the kinetics curve of oxidation approximately follows the logarithmic law and the oxidation velocity of Fe-Al/WC composite coatings is less than that of 20G steel after 5 h. The composition of oxidized coating is mainly composed of Al2O3, Fe2O3, Fe3O4 and FeO. These phases distribute unevenly. The protective Al2O3 film firstly forms and preserves the coatings from further oxidation.

Surface Microstructure and High Temperature Oxidation Resistance of Thermal Sprayed NiCoCrAlY Bond-Coat Modified by Cathode Plasma Electrolysis

The surface properties of the air-plasma sprayed bond-coat have been modified by cathode plasma electrolysis（CPE）. After modification, a re-melted layer without obvious pores and oxide stringers is formed,the gain size of re-melted layer is approximately 80–120 nm. It is shown, from cyclic oxidation at 1100℃,that a thin oxide scale mainly composed of α-Al;O;has been formed on the modified bond-coat and the oxidation resistance of the modified bond-coat has been significantly improved. Such beneficial result can be attributed to following effects: during CPE process, the plasma discharges with high temperature take place on the bond-coat surface. With plasma discharge treatment, the surface is melted and quickly re-solidified, the grain size decreases, and the pores and oxide stringers disappear. During cyclic oxidation, owing to the above modification of surface properties, the critical content of Al for selective oxidation is significantly decreased. Therefore, a continuous Al;O;scale is formed.

High-temperature protective coatings on superalloys

Protective coatings are essential for superalloys to serve as blades of gas turbines at high temperatures, and they primarily include aluminide coating, MCrAlY overlay coating, thermal barrier coating and microcrystalline coating. In this paper, all these high temperature coatings are reviewed as well as their preparing techniques. Based on the most application and the main failure way, the importance is then presented for further deepgoing study on the high temperature oxidation law of aluminide coatings.

Oxidation Performance of Fe-Al/WC Composite Coatings Produced by High Velocity Arc Sprayed at 650 ℃

The Fe-Al/WC intermetallic composite coatings have been prepared by high velocity arc spraying(HVAS) technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings has been studied by means of thermogrativmetic analyzer. The results demonstrate that the kinetics curve of oxidation approximately follows the logarithmic law. The composition of the oxidized coating surface mainly is composed of A12O3, Fe2O3, Fe3O4 and FeO which distribute unevenly. The protective A12O3 film firstly forms and preserves the coatings from further oxidation.

High temperature oxidation resistance of plasma sprayed NiCrAl+(ZrO_2+Y_2O_3) gradated coating on stainless steel surface

The plasma sprayed gradated coating with the bottom layer of NiCrAl and the top layer of(ZrO2+Y2O3) was prepared by the plasma spraying technique. The phase structure and morphology of the gradated coating were analyzed by means of X-ray diffractometry(XRD) and scanning electron microscopy(SEM). The high temperature oxidation resistance of the plasma sprayed samples at 800 ℃ was investigated. The oxidation kinetics curve was obtained. The results show that the thickness of gradated coating is about 410 μm. The plasma sprayed gradated coating on stainless steel surface can improve the high temperature oxidation resistance of stainless steel. The oxidation rate of stainless steel is less than that of plasma sprayed gradated coating. The oxidation film of plasma sprayed sample is very dense and is not easily exfoliated. The dense oxidation film prevents the stainless steel from more oxidation.