2Cr13钢表面激光熔覆Co基合金组织及其性能

采用横流连续波2kW CO2激光在2Cr13不锈钢表面进行激光熔覆处理,对熔履层的组织结构、磨损及高温和PbSO4盐热腐蚀性能进行了系统研究。试验结果表明,表面激光熔覆Co基合金后,其耐磨粒磨损性能、高温PbSO4盐热腐蚀性能均提高了2.5倍以上,熔覆层的热腐蚀机制是沿晶腐蚀及硫化-氧化循环进行造成的剥落型腐蚀破坏。     

热腐蚀和盐雾腐蚀影响氮化物涂层冲蚀行为的机制

金属氮化物涂层是目前重点关注的航空发动机压气机抗冲蚀涂层体系。为了兼顾热物理化学环境和应力环境的影响,进行涂层的腐蚀-冲蚀耦合行为研究十分重要。本研究对比了TiN/Ti涂层与TiN/ZrN涂层的原始状态、热腐蚀后和盐雾腐蚀后的冲蚀行为。结果表明,对于TiN/Ti涂层,在涂层的缺陷处盐雾腐蚀时形成点蚀坑,这是发生冲蚀的薄弱环节,盐雾腐蚀后TiN/Ti涂层的抗冲蚀能力及结合力低于原始涂层和热腐蚀后的涂层。对于TiN/ZrN涂层,热腐蚀过程中液滴表面形成疏松的腐蚀产物和氧化物,使其在冲蚀时更容易脱落,热腐蚀过程中产生的层间热应力削弱了涂层的结合力。热腐蚀涂层冲蚀后呈现严重的螺旋状剥落,热腐蚀后TiN/ZrN涂层的抗冲蚀能力及结合力低于原始涂层和盐雾腐蚀后涂层。     

不同Mn含量Cu-Mn合金熔覆层的腐蚀特性（英文）

为研究不同Mn含量Cu-Mn合金熔覆层的腐蚀特性和防污性能，利用激光熔覆技术制备了成分均匀、稀释率低的Cu-Mn合金熔覆层。采用电化学测试、盐雾腐蚀实验、腐蚀形貌观察及铜离子释放试验对3种不同Mn含量的Cu-Mn合金熔覆层在3.5%（质量分数）NaCl溶液中的腐蚀特性进行研究，重点研究了Mn对腐蚀产物和铜离子释放率的影响。结果表明：在电化学测试中，随着Mn含量增多，熔覆层的耐腐蚀性降低。盐雾腐蚀实验中，随着Mn含量的增多，Cu-Mn合金熔覆层腐蚀程度加深，平均质量损失增大。对电解腐蚀后的熔覆层样品进行腐蚀形貌观察，Mn含量高的Cu-Mn合金样品生成的腐蚀产物较低Mn含量的样品更疏松，裂纹孔洞数量多，腐蚀产物更易剥落。铜离子释放试验中，3种Mn含量合金熔覆层样品都可以抑制海洋生物生长，且Mn含量越高，铜离子渗出率越大，在防污材料方面有良好的应用前景。     

β—CEZ钛合金的加工性能和应用

研究了不同显微组织Ｔｉ８１１合金的热盐应力腐蚀性能。结果表明，经不同热处理，Ｔｉ８１１合金可获得板条组织、等轴组织、双态组织和针状组织。热盐优先浸蚀其原始β晶界α相，并且裂纹优先沿原始β晶界扩展。针状组织和板条组织由于在热盐应力腐蚀过程中原始β晶界α相的腐蚀通道作用、Ｔｉ３Ａｌ相的析出以及所产生的氢的作用，所以受热盐的浸蚀严重，强度和塑性显著降低。等轴组织的抗热盐应力腐蚀性能最佳。     

感应熔覆Ni60涂层显微组织及耐蚀性

利用两步法,感应熔覆制备了内、外壁Ni60合金涂层钢管.研究了熔覆涂层腐蚀前、后截面显微组织以及腐蚀产物膜的微观形貌特征,利用失重法测量了涂层盐雾、CO2腐蚀速率,定量评价了熔覆涂层的耐腐蚀性能.结果表明:熔覆Ni60涂层全致密,内部均匀分布大量碳化物、硼化物硬质点,涂层与基体之间冶金结合,界面处互扩散区宽度约为8 μm.熔覆Ni60涂层对基体有较好的防腐保护作用,盐雾腐蚀环境下出现锈斑的时间大于150 h,平均腐蚀速率为0.75 g/(m2· h),涂层动态CO2腐蚀相对静态CO2腐蚀更加剧烈,实验温度348 K时,静态腐蚀速率为0.78 g/(m2·h),动态腐蚀速率为1.02 g/(m2·h).     

热暴露和热盐暴露的交互作用对Ti811合金热盐应力腐蚀性能的影响

Ｔｉ８Ａｌ１Ｍｏ１Ｖ（Ｔｉ８１１）合金对热盐应力腐蚀（ＨＳＳＣ）较敏感,单个因素对合金ＨＳＳＣ行为影响已有研究,而复合因素的影响研究很少。采用工业生产的Ｔｉ８１１合金棒材,经双重退火后,研究了热暴露和热盐暴露的交互作用对合金ＨＳＳＣ性能的影响。结果表明：４２５℃实验条件下,热暴露和热盐暴露交互作用与单热盐应力腐蚀相比使合金的ＨＳＳＣ性能明显降低。延伸率由１８％降至６％;合金中存在位错在晶界处塞积诱发的沿晶裂纹,腐蚀产物易于在裂纹尖端积聚。导致沿晶断裂,加速腐蚀。此外,在交互作用过程中,合金中α２（Ｔｉ３Ａｌ）脆性相的析出以及晶间β相发生转变,使合金的ＨＳＳＣ敏感性增大,并加速热盐应力腐蚀。     

Na_2SO_4沉积引起的Fe─10Cr合金在700℃的热腐蚀

研究了涂有Na2SO4盐膜的Fe-10Cr合金在700℃,O2-0.5%(SO2+SO3)气氛中的热腐蚀行为。结果表明,该合金在实验条件下发生了“低温”热腐蚀。腐蚀产物分两层,即在熔盐中沉积出的疏松氧化物层和在合金表面直接成长的相对致密的氧化物层。腐蚀形貌观察说明,热腐蚀的发展主要伴随着致密氧化层的增厚。腐蚀动力学和腐蚀形貌特点支持热腐蚀的电化学机理模型。     

BT20钛合金热盐应力腐蚀开裂

研究了BT20钛合金的热盐应力腐蚀(HSSC).结果表明,在一定温度范围内(300-400℃),BT20钛合金对热盐应力腐蚀敏感.用气相色谱法测得试样平均氢含量表明,氢是引起热盐应力腐蚀的重要因素.盐在高温应力条件下与试样发生反应产生氢,氢定向扩展到裂纹处,使试样断裂,发生脆化.     

Na_2SO_4沉积引起的Fe─10Cr合金在700℃的热腐蚀

研究了涂有Ｎａ２ＳＯ４盐膜的Ｆｅ－１０Ｃｒ合金在７００℃，Ｏ２－０．５％（ＳＯ２＋ＳＯ３）气氛中的热腐蚀行为。结果表明，该合金在实验条件下发生了“低温”热腐蚀。腐蚀产物分两层，即在熔盐中沉积出的疏松氧化物层和在合金表面直接成长的相对致密的氧化物层。腐蚀形貌观察说明，热腐蚀的发展主要伴随着致密氧化层的增厚。腐蚀动力学和腐蚀形貌特点支持热腐蚀的电化学机理模型。     

TA15钛合金高温持久腐蚀行为研究

为深入分析热盐应力腐蚀对TA15钛合金高温性能的影响,对大规格TA15钛合金棒材进行不同的表面腐蚀处理,测试了500℃/470 MPa条件下的持久性能,并对试样表面、断口处的组织特征进行观察,分析TA15钛合金的热盐应力腐蚀机制。结果表明：在500℃/470 MPa下,TA15钛合金对热盐应力腐蚀非常敏感,导致持久寿命显著降低;在腐蚀过程中,沿着α相界(β基体)发生复杂的化学反应,形成腐蚀氧化物并向内扩散;应力作用加速了腐蚀裂纹扩展,形成沿晶断裂特征,降低了试样的持久寿命。     

热腐蚀的盐溶机理及其局限性

本文综述了有关热腐蚀机理的研究成果,着重叙述目前仍被公认的盐溶机理模型的研究进展,包括Rapp-Goto准则和金属氧化物在熔融Na_2SO_4中溶解度的实验测试。并以实验事实为依据阐述了盐溶机理模型的局限性,提出热腐蚀是依电化学机制发展的观点,依此举例说明金属和合金的热腐蚀历程。     

Hot corrosion of materials: a fluxing mechanism?

Hot corrosion is the accelerated oxidation of a material at elevated temperature induced by a thin film of fused salt deposit. Fused Na₂SO₄, which is the dominant salt involved in hot corrosion, is an ionic conductor, so that the corrosion mechanism is certainly electrochemical in nature. Further, the acid/base nature of this oxyanion salt offers the possibility for the dissolution (fluxing) of the normally protective oxide scale. Non-protective precipitated oxide particles are often observed in the corrosion products. In this paper, the status of knowledge for the solubilities of oxides in fused Na₂SO₄ is reviewed, and the effects of various influences on a fluxing mechanism are discussed. An evaluation of a “negative solubility gradient” as a criterion for continuing hot corrosion is made.     

Hot corrosion of materials: Fundamental studies

Hot corrosion is the accelerated oxidation of materials at elevated temperatures induced by a thin film of fused salt deposit. Because of its high thermodynamic stability in the mutual presence of sodium and sulfur impurities in an oxidizing gas, Na₂SO₄ is often found to be the dominant salt in the deposit. The corrosive oxyanion-fused salts are usually ionically conducting electrolytes that exhibit an acid/base chemistry, so that hot corrosion must occur by an electrochemical mechanism that may involve fluxing of the protective oxides. With the aid of high-temperature reference electrodes to quantify an acid/base scale, the solubilities for various metal oxides in fused Na₂SO₄ have been measured, and these show remarkable agreement with the theoretical expectations from the thermodynamic phase stability diagrams for the relevant Na-Metal-S-O systems. The solubilities of several oxides infused Na₂SO₄-NaVO₃ salt solutions have also been measured and modeled. Such information is important both in evaluating the corrosion resistance of materials and in interpreting any oxide fluxing/reprecipitation mechanisms. Various electrochemical measurements have identified the S₂O₇ ^2? anion (dissolved SO₃) as the oxidant that is reduced in the hot corrosion process. Electrochemical polarization studies have elucidated the corrosion reactions and clarified the corrosion kinetics of alloys. Mechanistic models for Type I and Type II hot corrosion are discussed briefly.     

铸造镍基合金K-3的热腐蚀及防护研究

用光学显微镜、X 光衍射、扫描电镜、能谱分析和化学分析等多种手段,对经热腐蚀后的K-3合金试样及渗铝的 K-3合金涡轮叶片进行了分折研究。结果表明叶片失效的原因是硫化及熔盐引起的热腐蚀;低铬、富难熔金属的 K-3合金的热腐蚀机制是硫化、碱性熔解和酸性熔解的综合作用。用 RFL 燃气腐蚀装置对不同的保护涂层进行抗热腐蚀性能的对比试验表明:渗铝的防护效果并不理想,而富硅的扩散型和融烧型料浆铝硅涂层则具有良好的抗热腐蚀性能。     

α-Fe_2O_3、Fe_3O_4和Cr_2O_3在熔融Na_2SO_4中的溶解度

作者于1200K在1大气压氧和几个低氧压下测定了α-Fe_2O_3及Fe_3O_4及Cr_2O_3在熔融Na_2SO_4中的溶解度与Na_2SO_4熔盐碱度的关系,结果与热力学预示是一致的。在测量溶解度的基础上,确定了这几种金属氧化物在熔融Na_2SO_4中碱性和酸性溶解的溶质形式,计算了它们在该熔盐中的活度系数。金属氧化物溶解行为的研究将有助于了解热腐蚀的盐溶机理和电化学机理。     

Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-Deposit-Induced Corrosion of Mo-Containing Alloys

Disk alloys used in advanced gas turbine engines often contain significant amounts of Mo (2 wt% or greater), which is known to cause corrosion under Type I hot corrosion conditions (at temperatures around 900 °C) due to alloy-induced acidic fluxing. The corrosion resistance of several model and commercial Ni-based disk alloys with different amounts of Mo with and without Na₂SO₄ deposit was examined at 700 °C in air and in SO₂-containing atmospheres. When coated with Na₂SO₄ those alloys with 2 wt% or more Mo showed degradation products similar to those observed previously in Mo-containing alloys, which undergo alloy-induced acidic fluxing Type I hot corrosion even though the temperatures used in the present study were in the Type II hot corrosion range. Extensive degradation was observed even after exposure in air. The reason for the observed degradation is the formation of sodium molybdate. Transient molybdenum oxide reacts with the sodium sulfate deposit to form sodium molybdate which is molten at the temperature of study, i.e., 700 °C, and results in a highly acidic melt at the salt alloy interface. This provides a negative solubility gradient for the oxides of the alloying elements, which results in continuous fluxing of otherwise protective oxides.     

Hot corrosion in a temperature gradient

Hot corrosion is the accelerated attack of materials at elevated temperatures that is induced by a thin film of fused salt. Many materials that experience hot corrosion are exposed to high heat fluxes and temperature gradients. The hot corrosion of metals can be described by the dissolution of a protective metal oxide into the fused salt and the subsequent precipitation of the metal oxide in a nonprotective form. Rapp and Goto have established a criterion for the sustained hot corrosion of a pure metal that the solubility gradient of the protective oxide in the salt film must be negative at the oxide/salt interface. The influence of a temperature gradient on the metal oxide solubility gradient (and the predicted hot corrosion susceptibility) is discussed. Solubility data for NiO in Na₂SO₄ are used to illustrate the effects of a temperature gradient. The effects of a temperature gradient were determined by examining various combinations of dissolution reactions, oxidants, and transport kinetics. Based on these results, and the thinness of the molten salt films, temperature gradients are not expected to be of importance to hot corrosion fluxing mechanisms.     

Hot Corrosion Behavior of a Ni3Al-Based IC21 Alloy in a Molten Salt Environment

Ni₃Al-based alloys have become important candidates for hot components in turbine engines, owing to their low densities and outstanding mechanical properties in service environments. The hot corrosion behavior of a Ni₃Al-based IC21 alloy in a molten salt environment of 75 wt% Na₂SO₄ and 25 wt% NaCl at 900 °C was studied, via oxidation kinetics analyses, scanning electron microscope observations and energy dispersive as well as diffraction analyses by X-ray. A multilayer corrosion oxide scale and dendritic morphology internal corrosion zone formed after hot corrosion, and inter-phase selective corrosion phenomena were also observed. Salt fluxing and oxidation-sulfidation processes were inferred to be the essential hot corrosion mechanisms of the alloy. Moreover, additions of Cr and Y proved to be beneficial to the hot corrosion resistance of the IC21 alloy, while the Mo content should be strictly controlled.     

Corrosion of Ni–Al high velocity oxyfuel (HVOF) thermal spray coating by fly ash and synthetic biomass ash deposits

Abstract

Corrosion of a thermal spray (HVOF) Ni–Al coating has been investigated at 600°C under both biomass generated fly ash and synthetic biomass ashes and has been monitored as a function of reaction time for up to 1000 h. Detailed microstructral and compositional analyses have been carried out to investigate the hot corrosion mechanism. Various microstructural defects and compositional inhomogeneities are found to play an important role in the initiation of hot corrosion. Deposition of molten reactants from the ashes creates the aggressive environment. Molten salts cause initial rapid hot corrosion via fluxing reactions between planar interlamellar porosity resulting in debonding of the surface lenticular splats followed by subsequent slow dissolution. Comparison between the performance of the coating in the fly ash and the synthetic ashes provides information for improved laboratory corrosion tests.     

801铁基合金熔盐热腐蚀的交流阻抗谱特征

采用交流阻抗技术研究了801铁基合金在熔融(Na,Li,K)_2SO_4中的腐蚀行为。结果表明,合金阻抗谱呈明显的扩散特征,合金腐蚀反应始终受扩散控制。提出了相应的等效电路,并采用有关拟合程序对阻抗谱进行了拟合,求取了相关电化学参数。