Effect of Thermal Annealing on Tribological and Corrosion Properties of DLC Coatings

In this study, the mechanical, tribological, and corrosion properties of annealed diamond-like carbon (DLC) coatings on M2 steel with various annealing temperatures were investigated. The results indicated that DLC coating on M2 steel annealed at 500 °C had the worst performance. Both corrosion polarization resistance and wear resistance against ceramic alumina counterface of DLC coatings decreased with increasing annealing temperature, which can be due to the decline of the coating hardness after the thermal treatment. When sliding against aluminum counterface material, the DLC annealed at 600 °C had the lowest coefficient of friction (cof) and wear resistance due to its high graphitic structure and low hardness. Compared with the original coating, cofs increased for coatings treated at below 300 °C; however, further increasing the annealing temperature led to the decrease of the cofs. Little material attachment occurred between DLC coatings (original and annealed) and counterface materials (both alumina and aluminum balls) except for the DLC annealed at 600 °C, in which coating material transferred to the surface of counterface ball.     

Electrochemical evaluation of the corrosion protectiveness and porosity of vacuum annealed CrAlN and TiAlN cathodic arc physical vapor deposited coatings

The corrosion behavior of cathodic arc physical vapor deposited CrAlN and TiAlN coatings were examined in 1 M HCl solution before and after vacuum annealing at 700, 800, 900, and 1000 °C. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods were used to study the corrosion behavior and porosity of the coatings in comparison with the bare steel substrate (304SS). Structural and mechanical characterization of the coatings were also conducted. It is found that with increasing annealing temperature, the mechanical properties of TiAlN increased due to age hardening caused by spinodal decomposition while the hardness of CrAlN decreased as result of relaxation. Similarly, EIS and PDP results revealed that the as‐deposited and annealed coatings offer higher corrosion resistance as compared to the bare 304SS substrate. The coatings susceptibility to corrosion is reduced after annealing as indicated by the increasing nobility of E_corr. Both PDP and EIS tests revealed that CrAlN coating annealed at 1000°C exhibited superior corrosion resistance properties. It is found that the reduced current density for CrAlN coating annealed at 1000°C was due to the reduction in the porosity. Annealed TiAlN coating follows similar behavior until an optimum annealing temperature of 800°C. Beyond this temperature, porosity enlargement and an increase in the number of pores subsequent to structural changes deteriorated the corrosion resistance of TiAlN coating.     

Production of Annealed Cold-Sprayed 316L Stainless Steel Coatings for Biomedical Applications and Their in-vitro Corrosion Response

316L powders were successfully deposited onto Al5052 aluminium substrates by cold spray method. Annealing was treated on the coated samples at 250–1000°C temperatures under Ar atmosphere. The in vitro performances of the coatings have been compared with using electrochemical corrosion test technique in the simulated body fluid (SBF) at body temperature (37°C). A scanning electron microscope (SEM-EDS) and X-ray diffraction (XRD) have been used for microstructural characterization and phases identifications of the coatings, respectively. The results were shown that there are high adhesions at particle and substrate interfaces and between the particles deposited as well. Also, the increasing annealing temperature increases corrosion resistance of the cold sprayed 316L stainless steel coatings. The corrosion susceptibility of the coating annealed at 1000°C was similar that of standard 316L stainless steel implant material in Ringer’s solution. The microstructural observations revealed that corrosion starts between the inter-splat powders and continues throughout the surface not in-depth.     

Effect of Annealing Temperature on Tribological Properties and Material Transfer Phenomena of CrN and CrAlN Coatings

This study evaluates the effects of annealing temperature and of the oxides produced during annealing processes on the tribological properties and material transfer behavior between the PVD CrN and CrAlN coatings and various counterface materials, i.e., ceramic alumina, steel, and aluminum. CrAlN coating has better thermal stability than CrN coating in terms of hardness degradation and oxidation resistance. When sliding against ceramic Al₂O₃ counterface, both CrN and CrAlN coatings present excellent wear resistance, even after annealing at 800 °C. The Cr-O compounds on the coating surface could serve as a lubricious layer and decrease the coefficient of friction of annealed coatings. When sliding against steel balls, severe material transfer and adhesive wear occurred on the CrN and CrAlN coatings annealed at 500 and 700 °C. However, for the CrAlN coating annealed at 800 °C, much less material sticking and only small amount of adhesive wear occurred, which is possibly due to the formation of a continuous Al-O layer on the coating outer layer. The sliding tests against aluminum balls indicate that both coatings are not suitable as the tool coatings for dry machining of aluminum alloys.     

退火温度对IrO_2+ZrO_2涂层结构和电容性能的影响

采用热分解法在Ti基上被覆了IrO_2+ZrO_2氧化物涂层。通过XRD、SEM、EDX、XPS和循环伏安法等分析了退火温度对IrO_2-ZrO_2二元氧化物涂层的物相、表面形貌和电容性能的影响,引用非线性方程q~*(v)=A_1exp~(-v/t_1)+A_2exp~(-v/t_2)+y_0计算了涂层的内外活性点。结果表明:IrO_2-ZrO_2涂层的临界晶化温度为340~360℃,340℃退火的涂层物相为非晶结构,360℃退火,含有晶态和非晶态2种结构组织,其离子价态为Ir~(3+)、Ir~(4+)以及过饱和IrO_(2+x)(x0)。电容性能随着温度的升高呈先增大后减小变化,360℃退火的电极有最大的电容值,与其"非晶态/晶态"两相共存组织结构有关。涂层中质子迁移能力比电子导电能力对电容的影响要大,扫描速度对质子迁移的影响大于对电子导电的影响。     

Effects of annealing temperature and time on microstructure and magnetic properties of Pr-Co thin films

A series of Pr-Co thin films were deposited on the Si (100) substrates with Cr underlayer by magnetron sputtering. The effects of both the post-annealing temperature and the annealing time on the microstructure and magnetic properties for the Pr-Co films were studied systemati- cally. The as-deposited Pr-Co thin films are mostly amorphous and tend to crystallize after annealing at temperatures above 600 C. When the annealing time is increased, the films show a complicated structure with various phases coexisting. Accordingly, the as-deposited film and low temperature annealed films are soft magnets and films annealed at temperatures beyond 600 C tend to be hard magnets. When the annealing time is increased from 5 min to 2 h, the films transfer from hard magnets to soft again. The sample annealed at 600 C for 10 min shows the largest coercivity of 0.59 T.     

Correlation of crystallization behavior and mechanical properties of thermal sprayed PEEK coating

An amorphous PEEK coating was prepared on an Al substrate by a flame spraying process. The amorphous coating was subjected to an annealing treatment under an annealing temperature from 180 to 300 °C and a holding time from 1 to 30 min. The cold crystallization behavior of the as-sprayed coating differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) measurements. The hardness and tribological behavior of the coatings were investigated. Both DSC and WAXD analysis revealed that the annealed coatings exhibited a semi-crystalline structure. Coexistence of double crystal entities in annealed coatings was deduced. The annealed coatings exhibit higher hardness, lower friction coefficient and wear rate. Both the annealing temperature and holding time can benefit the coating hardness. The annealing condition in the studied range has little influence on the tribological behavior of the coatings. The variances of the coating mechanical properties were correlated with the modifications of the coating structures induced by the annealing treatments.     

Thermal Stability of Microstructure and Hardness of Cold-Sprayed cBN/NiCrAl Nanocomposite Coating

cBN/NiCrAl nanocomposite coatings were deposited by cold spraying using mechanically alloyed composite powders. To examine their thermal stability, the nanocomposite coatings were annealed at different temperatures up to 1000?°C. The microstructure of composite coatings was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the nanostructure can be retained when the annealing temperature is not higher than 825?°C, which is 0.7 times of the melting point of the NiCrAl matrix. The dislocation density was significantly reduced when the annealing temperature was higher than 750?°C. The reaction between cBN particles and the NiCrAl matrix became noticeable when the annealing temperature was higher than 825?°C. The effects of grain refinement and work-hardening strengthening mechanisms were quantitatively estimated as a function of annealing temperature. The influence of annealing temperature on the contribution of different strengthening mechanisms to coating hardness was discussed.     

化学沉积 Ni-Mo-P 和 Ni-P 镀层退火晶化组织及耐蚀性

目的研究化学沉积Ni-4.11%Mo-6.50%P和Ni-9.19%P合金镀层退火晶化转变特征,通过定量表征镀层的晶化程度、晶粒尺寸及结晶相的质量分数,建立显微组织与耐蚀性的关联。方法采用XRD衍射技术和Jade软件分析,定量表征镀层的晶化组织特征,由SEM/EDS测试确定镀层的成分及表面形貌,通过浸泡腐蚀实验及金相显微观察,对比两种镀层的耐蚀性。结果 Ni-Mo-P镀层在低于400℃退火时,只有Ni相结晶;在≥400℃退火时,发生Ni3P晶化反应,同时伴有Ni-Mo固溶体的形成,600℃时的晶化程度为88.13%。相比之下,Ni-P镀层中Ni3P相开始析出的温度降至300℃,600℃时的晶化程度达到91%。在相同温度进行热处理时,Ni-Mo-P镀层晶粒尺寸小于Ni-P镀层。在发生Ni3P晶化反应的温度下,两种镀层中Ni3P的晶粒尺寸总是大于Ni相。在0.5 mol/L的H2SO4中,对于Ni-Mo-P镀层,除300℃外,其他温度下的热处理均能显著改善其耐蚀性;而对于Ni-P镀层,镀态下具有最好的耐蚀性能。在10%的HCl溶液中,退火温度为600℃时,Ni-Mo-P镀层的耐点蚀性能更好;而Ni-P合金则相反,镀态及低温200℃退火后的耐点蚀性能最好。结论 Mo的共沉积提高了Ni-Mo-P镀层Ni3P的析出温度,降低了镀层的晶化程度及晶粒尺寸;与Ni-P镀层相比,高温退火的Ni-Mo-P镀层表现出了优异的耐点蚀性能,但耐硫酸均匀腐蚀的性能较差。     

Increased Lifetime for Biomass and Waste to Energy Power Plant Boilers with HVOF Coatings: High Temperature Corrosion Testing Under Chlorine-Containing Molten Salt

Heat exchanger surfaces of waste to energy and biomass power plant boilers experience often severe corrosion due to very aggressive components in the used fuels. High velocity oxy-fuel (HVOF) coatings offer excellent protection for boiler tubes against high temperature corrosion due to their high density and good adherence to the substrate material. Several thermal spray coatings with high chromium content were sprayed with HVOF technique. Their mechanical properties and high temperature corrosion resistance were tested and analyzed. The coating materials included NiCr, IN625, Ni-21Cr-10W-9Mo-4Cu, and iron-based partly amorphous alloy SHS9172 (Fe-25Cr-15W-12Nb-6Mo). High temperature corrosion testing was performed in NaCl-KCl-Na₂SO₄ salt with controlled H₂O atmosphere at 575 and 625 °C. The corrosion test results of the coatings were compared to corrosion resistance of tube materials (X20, Alloy 263 and Sanicro 25).     

Nanoscratching deformation and fracture toughness of electroless Ni-P coatings

In the present investigation electroless Ni-P coatings were prepared. Structural characterizations indicated that the as-deposited coating had an amorphous structure with a P content of 23 at.%. The deformation behavior of an electrolessly amorphous Ni-P coating was investigated by using the Vickers indentation and the Tribo-indenter instrumented nano-indentation technique. The hardness of the Ni-P coating is remarkably improved after proper heat-treatment and the hardness is as high as 12.7 GPa for the coating annealed at 400 °C for 1 h. However, the cracks were observed during the indentation of the Ni-P coatings annealed at 400 °C and 500 °C for 1 h. The corresponding fracture toughness was evaluated as 2.58 MPa m^0.5 and 1.33 MPa m^0.5, respectively. Nanoscratching tests indicated that the wear resistance of the Ni-P coatings was improved significantly with an increasing ratio of hardness (H) to elastic modulus (E). It was observed that the friction coefficient increased from 0.083 ± 0.006 for the Ni-P coating annealed at 300 °C up to 1.337 ± 0.009 for the IF steel substrate, while the H/E simultaneously decreased from 0.084 (10.7/128) to 0.009 (1.85/200). The study revealed that the electrolessly amorphous Ni-P coating had offered better corrosion resistance than the Ni-P coatings after heat-treatment. An annealing temperature of 300 °C is preferentially suggested for the trade-off between the wear resistance property and anti-corrosion property of the Ni-P coating.     

钼添加对CrN涂层抗氧化性能的影响

研究钼添加对CrN涂层微观结构和抗氧化性能的影响,采用反应磁控溅射法在硅片和高速钢片上制备不同Mo含量的Cr-Mo-N涂层,并在500~800 ℃的高温空气中退火1 h,用X射线衍射（XRD）、拉曼光谱和扫描电子显微镜（SEM）对涂层退火前后的微观形貌进行表征。沉积的CrN和Cr-Mo-N涂层均表现出基于CrN晶格的B1面心立方相（fcc）。Mo离子取代Cr-N晶格中的Cr离子,形成Cr-Mo-N固溶体。在600 ℃时,XRD和拉曼光谱表明,Mo含量较高的Cr-Mo-N涂层中形成MoO₃相,表面较粗糙,含氧量较高。在700 ℃时,CrN涂层由于内应力的作用,其横截面形貌为疏松的柱状晶,并有一定的多孔区,而Cr-Mo-N涂层则为致密的柱状晶结构。低Mo含量（<17at%）的Cr-Mo-N涂层比CrN涂层具有更好的抗氧化性。     

Oxidation Mechanisms of Copper and Nickel Coated Carbon Fibers

Differential-Thermal Analysis (DTA) and X-ray diffraction analysis were applied to determine the mechanisms of high-temperature oxidation of copper- and nickel-coated carbon fibers. Both kinds of coatings were deposited by electroless plating onto the fiber surface. The as-deposited copper film was crystalline, whereas the nickel coating consisted of an amorphous Ni–P alloy. Coated fibers were heated from room temperature to 900 °C in air at 10 °C min^?1. For the copper coating, the main oxidation product formed at low temperatures was Cu₂O, while at higher temperatures was CuO. The crystallization of Ni–P took place at 280–360 °C with the formation of Ni and Ni₃P. The final compounds were NiO, Ni₂P and Ni₃(PO₄)₂. After complete oxidation of the carbon fibers, copper and nickel-oxidized microtubes were obtained. Besides, while copper reduced the temperature of the fiber oxidation, nickel coatings increased the minimum temperature needed for this reaction.     

Characterization and Corrosion Behavior of Functional Gradient Hydroxyapatite Coating

The aim of the present work is to examine the characterization and corrosion behavior of functional gradient hydroxyapatite coating deposited on titanium-based alloy by plasma spray coating process. The functionally graded coating is designed to provide the crystalline hydroxyapatite at the interface with metallic substrate and the amorphous hydroxyapatite at the outer surface. It is considered that the top amorphous layer of hydroxyapatite has higher bioactivity, and its initial dissolution will lead to bone tissue growth enhancement and bonding, whereas the underneath crystalline hydroxyapatite coating after heat treatment is expected to enhance the long-term stability of coating at the interface with metal. The heat treatment of the underneath as-sprayed coating for crystallization was performed at 700 °C for 1 h. The characterization of the coatings was performed by various techniques such as scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction analysis, surface roughness, and microhardness. It was observed from potentiodynamic scan that heat-treated coating exhibited better dissolution resistance as compared to the as-sprayed coating. Heat treatment of the hydroxyapatite coating resulted in improved crystallinity of the coating which may provide long-term stability to the coating.     

Effect of Vacuum Annealing on the Characteristics of Plasma Sprayed Al2O3-13wt.%TiO2 Coatings

Adhesion strength is one of the critical properties for plasma-sprayed coating. In this study, the plasma-sprayed Al₂O₃-13wt.%TiO₂/NiCrAl coatings were annealed at 300-900?°C for 6?h in vacuum. The tensile bond strength and porosity of the coatings were investigated. The microstructure and the fracture were studied using optical microscopy, scanning electron spectroscopy, and x-ray diffraction. It was found that the tensile bond strength of coatings increased with the increase of annealing temperature until 500?°C, reaching the maximum value of 41.2?MPa, and then decreased as the annealing temperature continues to increase. All coatings presented a brittle fracture and the fracture occurred inside the ceramic coatings except for the coating annealed at 500?°C, which had a brittle-ductile mixed fracture and the fracture occurred at the interface of bond coating and the substrate.     

High-temperature tribological properties of Ni-P alloy coatings deposited by electro-brush plating

High-temperature tribological properties of Ni-P alloy coatings processed by electro-brush plating on 20CrMo steel have been investigated. A ball-on-disc configuration was employed and 4 mm diameter Si3N4 balls were used as static counterpart. All the wear tests were carried out at 450°C for 180 min without lubricants. The electro-brush plating Ni-P coating is amorphous in as-deposited condition, and it becomes polycrystalline with the formation of Ni and Ni3P after heat treatment at 450°C for 1 h. The friction coefficient of the Ni-P coating is just 50% of that of the 20CrMo steel at the friction temperature of 450°C. A mild adhesive wear mechanism was found for the electro-brush plating Ni-P coating tested at 450°C, whereas for the 20CrMo steel at the same temperature a mixed adhesive and abrasive wear mechanism was observed.     

High-Temperature Oxidation and Smelt Deposit Corrosion of Ni-Cr-Ti Arc-Sprayed Coatings

High Cr content Ni-Cr-Ti arc-sprayed coatings have been extensively applied to mitigate corrosion in black liquor recovery boilers in the pulp and paper industry. In a previous article, the effects of key spray parameters on the coating’s microstructure and its composition were investigated. Three coating microstructures were selected from that previous study to produce a dense, oxidized coating (coating A), a porous, low oxide content coating (coating B), and an optimized coating (coating C) for corrosion testing. Isothermal oxidation trials were performed in air at 550 and 900 °C for 30 days. Additional trials were performed under industrial smelt deposits at 400 and 800 °C for 30 days. The effect of the variation in coating microstructure on the oxidation and smelt’s corrosion response was investigated through the characterization of the surface corrosion products, and the internal coating microstructural developments with time at high temperature. The effect of long-term, high-temperature exposure on the interaction between the coating and substrate was characterized, and the mechanism of interdiffusion was discussed.     

Corrosion behavior of Cr3C2-NiCr vacuum plasma sprayed coatings

The objective of the present work is to determine the influence of the heat treatment on the corrosion resistance of a Cr₃C₂-NiCr coating of 450 μm thickness, deposited by a vacuum plasma spray process (VPS) on a steel substrate. The post-heat treatment of the as-deposited coating was carried out in Ar at 400 °C and 800 °C, respectively. The coatings were characterized by means of an electron probe micro analyzer (EPMA) with wavelength dispersive X-ray spectrometers (WDS). It was found that no significant changes were produced as a consequence of the heat treatment carried out at 400 °C. Therefore, the corrosion experiments were conducted for the substrate, the as-deposited coating and the post-heat treated coating at 800 °C. Potentiodynamic polarization showed that the annealed coating at 800 °C has a better corrosion resistance than the as-deposited coating. The corrosion current density (I_corr) of this coating was approximately 3 and 4 times smaller than that corresponding to the as-deposited coating and steel substrate, respectively. This significant improvement of the corrosion behavior of the post-heat treated coating is mainly due to both the microstructural changes that take place in the coating and the diffusion of Ni into Fe at the coating-substrate interface, which ensures the presence of a metallurgical bond.     

高速电弧喷涂FeNiCrBSiNbW非晶涂层组织结构与力学性能对热处理温度的响应∗

Fe 基非晶涂层因较高的性价比、良好的耐蚀性而广泛应用于众多工业领域,但其在高温环境下的使役性能会因微观结构的变化而发生改变。 为了探讨 Fe 基非晶涂层组织结构与力学性能对热处理温度的响应,利用高速电弧喷涂技术制备 FeNiCrBSiNbW 非晶涂层,随后对其进行不同温度热处理,获得三种具有不同组织结构的涂层。 采用 X 射线衍射仪、扫描电子显微镜、能谱仪、差示扫描量热仪、电子万能试验机、显微硬度计、纳米压痕仪对不同热处理温度下涂层的组织结构和力学性能进行表征。 结果表明:FeNiCrBSiNbW 涂层中非晶相的晶化过程包括初晶晶化与共晶晶化;随着热处理温度的升高,涂层的非晶相含量、孔隙率、结合强度与断裂韧性逐渐降低,而涂层的硬度与弹性模量不断增大。 研究成果对调控高速电弧喷涂 Fe 基非晶涂层的组织结构与力学性能有一定的指导意义。     

Influence of Lanthanum Coatings on a Model 330 Alloy (Fe–35Ni–18Cr–2Si) Oxidation at High Temperatures

The influence of a lanthanum sol–gel coating on chromia scale adherence has been studied on the 330 alloy (Fe–35Ni–18Cr–2Si) oxidized at 900 °C, in air. Argon annealing of lanthanum sol–gel coatings were performed at various temperatures. Kinetic results show that lanthanum sol–gel coatings lead to a lower oxidation rate compared to blank specimens. On blank 330 specimens scale spallation is observed after cooling to room temperature. On the non-annealed sol–gel coated specimen and the argon annealed specimens at 600, 800 or 1,000 °C, the oxide scale formed at 900 °C is adherent after 48 h isothermal oxidation. The adherent oxide scales are convoluted, resulting from a mixed anionic + cationic diffusion process in the chromia scale. Thermal cycling tests on lanthanum the sol–gel coated specimen show that the oxide scale remains adherent after 250 cycles. It is concluded that argon annealing of the lanthanum sol gel coating is not necessary to improve the scale adherence.