Calculation Of Interdiffusion Coefficients Of Ni And Alatoms In Β--Nial Phase As Aluminide Coatings

通过纯Ni和K465合金表面渗Al涂层中Al原子浓度分布曲线的分析，考虑到K465合金复杂的化学成分和显微组织，基于一定的假设，推导出Wagner修正式，并分别计算了850，950和1050℃纯Ni和K465合金表面渗Al涂层中β-NiAl相Ni，Al互扩散系数。计算结果表明：K465合金表面渗Al层中β-NiAl相Ni，Al互扩散系数明显小于纯Ni表面渗Al涂层中β-NiAl相Ni，Al互扩散系数；与化学计量比β-NiAl相相似，K465合金表面渗Al中β-NiAl相Ni，Al互扩散系数与Al原子浓度有很大的相关性。简要分析了合金元素和析出相对渗Al涂层中β-NiAl相Al，Ni互扩散系数的影响。     

模拟高温海洋环境中铝化物/搪瓷复合涂层腐蚀行为研究

对镍基高温合金GH4169基体先采用包埋渗铝工艺制备铝化物涂层,随后在渗铝涂层表面喷烧搪瓷涂层,得到了渗铝+搪瓷复合涂层.该涂层外层由搪瓷涂层组成,厚度约为40 μm;中间层为渗铝涂层,厚度约20μm,主要为Ni2Al3相,搪瓷涂层和渗铝涂层结合良好;内层为互扩散区,厚度约为3μm.分别考察了搪瓷+渗铝复合涂层、渗铝涂...     

硅改性铝化物涂层的CVD制备工艺

研究了CVD法制备硅改性铝化物涂层工艺。结果表明,采用先渗硅后渗铝的两步法工艺可在Inconel 718表面获得铝-硅涂层。铝-硅涂层分为明显的两层结构,内层富硅,外层富铝。硅的加入阻碍高温条件下Al原子的内扩散,并促进了试样表面Al2O3膜的生成。铝-硅涂层具有比单一的铝化物涂层更为优秀的耐高温氧化性能。     

一种可内生Al_2O_3扩散障的δ-Ni_2Al_3-Cr_2O_3/Ni-Cr_2O_3涂层体系

通过对Ni-Cr2O3复合镀层620℃部分渗铝制备了δ-Ni2Al3-Cr2O3/Ni-Cr2O3涂层体系。Cr2O3颗粒在渗铝的过程中和Al反应生成更为稳定的Al2O3。1000℃恒温氧化20 h后发现,铝化物涂层和复合镀层内掺杂的Cr2O3颗粒完全转化为Al2O3,并在铝化物涂层/Ni镀层界面自发形成了一层Al2O3富集层,该富集层起扩散障作用,阻碍铝化物涂层因互扩散所致的退化。     

浆料包渗温度对Cu基体Ni镀层表面渗铝组织和性能的影响

采用浆料包渗法在Cu基体Ni镀层表面渗铝，制备出了Ni2Al3金属间化合物渗层，研究了包渗温度对渗层组织、厚度、扩散系数和显微硬度的影响。结果表明：在600-900℃渗铝12h，均形成了单相Ni2Al3金属间化合物渗层。随着温度升高，Ni2Al3晶粒尺寸增大，渗层厚度和扩散系数增加，显微硬度降低。     

稀土对低碳钢热浸渗铝扩散系数的影响

研究了热浸渗铝液中添加微量稀土元素对低碳钢热浸渗铝时铝的扩散系数的影响，结果表明，稀土元素能增大铝原子的扩散激活能，降低铝原子的扩散系数。     

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.     

(Ni,Pd)Al涂层的抗高温氧化性能

采用低压固体粉末包埋渗铝方法在M38镍基高温合金上制备钯改性铝化物涂层，利用热重分析(TGA)、扫描电镜(SEM)、X射线衍射(XRD)等方法，研究其l100℃的高温氧化行为．结果表明，(Ni，Pd)Al涂层的恒温氧化动力学近似符合抛物线氧化规律．与NiAl涂层相比，(Ni，Pd)Al涂层具有更优良的抗高温氧化性能，退化过程与NiAl涂层类似．添加改性元素Pd有利于稳定β相，延缓涂层的退化，有益于提高铝化物涂层的抗高温氧化性能．     

低碳钢表面抛丸加速制备纳米铝化物涂层的研究

将粉末包埋渗铝与抛丸过程相结合,在440-600℃相对较低的温度范围内,在低碳钢表面制备纳米结构的铝化物涂层.涂层为单层结构,均匀致密,呈现纳米结构特征,晶粒尺寸20nm左右.涂层由富铝相Fe-Al化合物组成,主要有η-Fe2Al5相和少量的θ-FeAl3相和β-FeAl相.合金球的冲击作用导致表面纳米化,加速表面原子扩散过程,使铝化物涂层可以在相对较低的温度下形成.     

CeO2颗粒含量和尺寸对铝化物涂层和基体互扩散行为的影响

研究发现,在铝化物涂层中添加活性元素（Reactive Element,简称RE）,例如钇,铪,锆,铈及其氧化物,可以显著提高涂层的抗氧化性能。本文通过在Ni基体电沉积纳米CeO2颗粒（15-30 nm）含量~0,~1,~2,~3 wt. %和微米CeO2颗粒（5 μm）含量~1 wt. %的Ni-CeO2复合镀层并对其进行部分渗铝,制备了不同CeO2颗粒含量和尺寸掺杂的δ-Ni2Al3/Ni涂层体系。将以上CeO2掺杂的铝化物涂层在1000 °C真空退火不同时间,研究CeO2颗粒含量和尺寸对铝化物涂层和基体互扩散行为的影响。退火结果表明,纳米CeO2颗粒的添加可有效减轻δ-Ni2Al3/Ni涂层体系的退化,而且随着CeO2颗粒含量的增加,其对互扩散的抑制作用明显增强;但微米CeO2颗粒的添加对涂层和基体的互扩散几乎没有影响。这是因为CeO2颗粒含量和尺寸会影响高温过程中铝化物/Ni镀层界面处CeO2富集层的形成,该富集层可作为扩散障,阻碍铝化物涂层和基体的互扩散。     

钯改性铝化物涂层的工艺及组织

研究了用二氯二氨基钯为主盐电镀Ｐｄ及Ｐｄ－Ｎｉ合金的配合及工艺条件,再通过传统固渗铝方法制备高温合金Ｍ３８的防护涂层。研究了镀层状态、渗铝方式、渗铝活化剂、预扩散处理等工艺条件对钯改性铝化物涂层组织的影响,经ＸＲＤ,ＥＰＭＡ及金相观察,发现该涂层为固溶Ｎｉ的β－ＰｄＡｌ或固溶Ｐｄ的β－ＮｉＡｌ单相结构,随工艺改变,涂层中Ｐｄ,Ｎｉ含量不同。     

OXIDATION RESISTANCE OF NANOCRYSTAL ODS ALUMINIDE COATINGS PRODUCED BY PACK ALUMINIZING PROCESS ASSISTED BY BALL PEENING

Nanocrystal ODS （oxide dispersion strengthening） aluminide coatings were produced on a stainless steel and nickel-based superalloy by the pock aluminizing process assisted by ball peening, Pure Al powders and 1% of ultra-fine Y2O3 powders were mixed by ball milling. The ultra-fine Y2O3 powders were dispersed in Al particles. Ball peening welded the Al particles onto the substrate and accelerated the formation of aluminide coating. Nanocrystal ODS aluminide coatings were produced by the outward growth at a much low temperature （below 600℃） in a short treatment time. The effects of the operation temperature and treatment time on the formation of the coatings were analyzed. SEM （scanning electron microscope）, AFM （atomic force microscope）, EDS （energy dispersive X-ray spectroscopy）, XRF （X-ray fluorescence spectrometer） and XRD （X-ray diffraction） methods were applied to investigate the microstructure of the coatings. High-temperature oxidation tests were carried out to evaluate the oxidation resistance of the ODS aluminide coatings.     

High-Throughput Determination of Interdiffusion Coefficients for Co-Cr-Fe-Mn-Ni High-Entropy Alloys

In this report, a combination of the diffusion multiple technique and the recently developed pragmatic numerical inverse method was employed for a high-throughput determination of interdiffusivity matrices in Co-Cr-FeMn-Ni high-entropy alloys (HEAs). Firstly, one face-centered cubic (fcc) quinary Co-Cr-Fe-Mn-Ni diffusion multiple at 1373 K was carefully prepared by means of the hot-pressing technique. Based on the composition profiles measured by the field emission electron probe micro analysis (FE-EPMA), the composition-dependent interdiffusivity matrices in quinary Co-Cr-Fe-Mn-Ni system at 1373 K were then efficiently determined using the pragmatic numerical inverse method. The determined interdiffusivities show good agreement with the limited results available in the literature. Moreover, the further comparison with the interdiffusivities in the lower-order systems indicates the sluggish diffusion effect in Co-Cr-Fe-Mn-Ni HEAs, which is however not observed in tracer diffusivities. In order for the convenience in further analysis, a generalized transformation relation among interdiffusivities with different dependent components in multicomponent systems was finally derived.     

Formation and Characterization of Titanium Modified Aluminide Coatings on IN738LC

Up to now, the aluminide coatings used to protect industrial components at high temperature and corrosive environments have been modified by Pt, Cr, Si and Ni. In this investigation, aluminide coatings were modified by titanium and the microstructural feature and formation mechanism were evaluated. The coatings were formed on a Ni-based superalloy(IN738LC) by a two stage process including titanizing at first and aluminizing thereafter. Pack cementation titanizing performed at temperatures 950℃ and 1050℃ in several mixtures of Ti, Al2O3 and NH4Cl. At the second stage,aluminum diffused into surface of the specimens by an industrial aluminizing process known as Elcoatl01(4 hrs at 1050℃C). The modified coatings were characterized by means of standard optical microscopy, scanning electron microscopy,energy dispersive spectroscopy and X-Ray diffraction methods. The results show that Ti in the coatings is mainly present in the form of TiNi and Al67CrsTi25. Titanium modified coatings grew with a mechanism similar to simple aluminizing; this includes inward diffusion of Al from the pack to the substrate and then outward diffusion of Ni from the substrate to the coating. The advantages and characteristics of this two-stage modified coating is discussed and the process parameters are proposed to obtain a coating of optimum microstructure.     

Factors affecting the microstructure of platinum-modified aluminide coatings during a vapor phase aluminizing process

Platinum (Pt)-modified aluminide coatings were developed by electroplating a thin layer of Pt followed by an industrial vapor phase aluminizing process. The goal of this work was to systematically investigate the effect of critical coating process parameters (such as the electroplated Pt thicknesses, Al contents in Cr-Al nuggets, diffusion heat treatments) and substrates on the final Pt-modified aluminide coatings. Surface morphology and cross-section microstructure of the developed coatings were inspected and compared by using Optical Microscope, Scanning Electron Microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Experimental results showed that the Al and/or Pt increase shall favor the formation of ξ-PtAl₂ phase; transformation of ξ-PtAl₂ into β-(Ni,Pt)Al phase can be obtained via a heat treatment process; Cr, Co elements in the studied Ni-base superalloy substrates did not show significant influence on coating outer layer microstructure; while substrate elements affect the microstructure of the coating interdiffusion layer.     

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.     

IN738合金上铂铝涂层的高温氧化

研究了IN738镍基高温合金的铂改性渗铝涂层在1100℃空气中的氧化行为,铂的存在,通过阻止合金元素穿过Al2O3膜向外扩散,改善Al2O3膜与基体的结合力,抑制γ′-NiAl相的形成,推迟涂层的高温退化,同时讨论铂的作用机制。     

Microstructural investigation of PGM‐based alloy coatings for oxidation protection

It is well known that Pt addition significantly improves the resistance of aluminide coatings to high‐temperature oxidation and hot corrosion, which has led to the widespread application of Pt modified aluminide coatings on the superalloy components of advanced gas turbine engines. Other platinum group metals (PGMs) such as Ir and Ru attract researchers for high temperature applications. In this study, oxidation properties of Pt‐Ir and Pt‐Ru based alloy coatings were investigated. Pt, Ru, and Ir were electroplated on a directionally solidified Ni‐base superalloy DZ125. The cyclic oxidation test revealed that both Pt‐Ir and Pt‐Ru alloys exhibited good oxidation performance. The effect of substrate alloy and coating compositions on microstructural changes during cyclic oxidation tests were discussed.     

Oxidation and Microstructure Evolution of CoAl Coating on Directionally Solidified Ni-Based Superalloys DZ466EI北大核心CSCD

Alumimde coatings are widely employed to protect internal cooling channels of high grades blades and buckets in gas turbines have always been in severe conditions including high temperature oxidation and hot corrosion. There is a major concern for the application of aluminide coatings that refer to the inter-diffusion between alumimde coating and superalloy substrate at high temperatures. Diffusion of Al from the coating to the underlying substrate usually leads to depletion of Al in the coating, resulting in inferior oxidation resistance of the coating. Accordingly, Ni declines to diffuse counter currently from the substrate into the coating, as well as other refractory elements, such as Cr, Mo and W etc.. The inter-diffusion between alumimde coating and superalloy substrate results in degradation or various evolution behaviors of alumimde coatings, in other words, substrate composition significantly affects the properties of aluminide coatings. CoAl coating was prepared on directionally solidified superalloy DZ466 by low pressure chemical vapour deposition (LP-CVD). Oxidation behavior and microstructure evolution of CoAl coating was investigated during long term (about 5000 h) exposure at 900 degrees C. Results suggested that, high concentration of aluminum did help to form Al2O3 on the surface of coating, improving oxidation resistance of DZ466 at 900 degrees C. Evolution of matrix phase and precipitates in the CoAl coating during exposure was displayed, beta-NiAl/CoAl phase in the coating transformed gradually to gamma'-Ni3Al phase, higher transformation rate for the gamma phase closed to the substrate due to the diffusion between the coating and the sub strate superalloy. During exposure, alpha-Cr phase precipitated in the middle layer, which inclined to form close to carbides and grow by consuming them. Needle like TCP phase (mu phase) grew in the inner layer that arranged in order, which was due to the cubic microstructure of gamma/gamma'. Heredity-effect was in company with the precipitates evolution.     

Preparation and Enhanced Hot Corrosion Resistance of a Zr-Doped PtAl2+(Ni,Pt)Al Dual-Phase CoatingEI北大核心CSCD

Prior to practical service, hot-section components (e.g. airfoils and vanes) of a gas turbine engine are necessarily coated by a protective metallic coating (such as aluminidi diffusion coating, modified aluminide coating and MCrAlY overlay etc.) to resist high temperature oxidation and hot corrosion. Among the modified aluminide coatings, the coating with Pt-modification has attracted great attention and is widely used in applications requiring high reliability and extended service life since it possesses superior oxidation/corrosion resistance at high temperature. The presence of Pt in aluminide coating is favorable for increasing bonding strength of oxide scale, enlarging phase region of beta 3-NiAI and confining detrimental effect of sulphur etc. Although Pt-modification has exhibited visible benefits for acquiring better high-temperature performance, it is far from satisfaction to develop an ideal aluminide diffusion coating. Reactive elements such as Y, Hf, Zr or their oxides have been employed to modify the nickel aluminide coating system, with an aim to further improve scale adhesion and promote exclusive formation of alpha-Al2O3 simultaneously. In this work, a Zr-doped PtAl2+(Ni, Pt)Al dual-phase aluminide coating was prepared on a Ni-based single crystal superalloy by co-deposition of Pt-Zr through electroplating and sub-sequent aluminization treatments The coating was mainly composed of three layers: the outmost layer consisted of double phases with PtAl2 particles dispersed in beta-(Ni, Pt)Al domain, while the interlayer comprised beta-(Ni, Pt)Al with small amount of Cr-precipitates, and the bottom layer was an inter-diffusion zone (IDZ). Zirconium was mainly distributed inside beta-(Ni, Pt)Al solid solution in both the outmost layer and the interlayer. Compared with normal PtAl2+(Ni, Pt)Al dual-phase coating, the hot corrosion behavior of the Zr-doped PtAl2 + (Ni, Pt)Al coating was assessed in a salt mixture of Na2SO4/NaCI (75:25, mass ratio) at 850 degrees C in static air. The results indicated that the Zr-doped PtAl2+(Ni, Pt)Al dual-phase coating exhibited superior hot corrosion resistance since Zr was confirmed able to capture and fix S and CI to diminish their detrimental effects. Meanwhile, a pre-oxidation treatment did not effectively improve the overall hot corrosion resistance of normal PtAl2+(Ni, Pt)Al coating because the thin alumina scale formed during pre-oxidation was unable to prohibit the sustained inward-invasion of the mixed salt.