PLASMA SPRAYED ZrO2 THICK THERMAL BARRIER COATINGS

ZrO₂ thermal barrier coatings have been plasma sprayed onto steel substrates with a FeCrAlY bond layer. During spraying the conditions have been varied by cooling the back side of the substrate in ice-water or heating it on a hot plate, and simultaneously cooling the sprayed surface with air at various pressures. The residual strain distributions have been measured in the as-sprayed couples using the incremental blind-hole method. The measurements show that residual strains can be controlled through temperature manipulation, and the method can be used to determine the optimum spraying conditions. The microstructure has been observed in a transmission electron microscope, and the effect of microstructural features on the microstrains are briefly discussed.     

Effect of Differential Thermal Expansion Coefficient on Stresses Generated in Coating

Two different spraying powders [81FVNS and 80% (443)+20% (105)] were plasma sprayed on two types of substrates (AISI 316 and Ti) in order to verify the effect of differential thermal expansion coefficient (DTEC) between coating and substrate on the final residual stresses generated in the coating. Modulus of elasticity (E) was evaluated for the substrates and coatings (as a composite beam). Free-standing coatings were used to measure the thermal expansion coefficient, as a function of temperature, of the actual coatings with all defects, impurities and typical lamella structure. The results show that the residual stresses seems to be less dependent on the linear thermal expansion coefficients mismatching between substrate and coating, reflecting the importance of the other sources of stresses. i.e. quenching or deposition stresses induced during spraying. The suitable heat treatment condition of the coated samples may release some or most of the residual stresses. However in some cases the sign of the stress was completely changed as a result of neglecting the quenching stresses.     

Plasma Spraying of Al2O3 and ZrSiO4 to Form ZrO2- Mullite Composites

Zirconia is effective in improving fracture toughness of a number of ceramics when introduced as a reinforcement either in the form of participates, dispersed phase or whiskers because of its unique tetragonal-monoclinic (t → m) transformation. In this paper, the authors attempt to prepare ZrO₂, reinforced mullite by plasma spraying mixtures of zircon and alumina. Pre-mixed powders of zircon and alumina are injected onto a D.C. plasma jet. The plasma sprayed particles are collected in distilled water and analyzed. The results indicate that the plasma sprayed powders consist of zirconia, zircon, and alumina. It was found that fine grained, even amorphous and chemically homogeneous composite powders could be obtained by ball milling and plasma spraying. Recrystallization of amorphous phases and formation of mullite occurred at about 1OOO^°C in plasma sprayed powders. This value is more than 500^°C lower than the formation of mullite in asmilled powders. Uniform coatings with good structural integrity were obtained by plasma spraying. The relative quantity of mullite in coatings after heat treatment is about 4 times as much as that obtained in the spheroidized powders. Preheat treatment of the spheroidized powder promoted dissociation of zircon. Zirconia remained as tetragonal under 1000^°C in the sprayed coatings.     

等离子喷涂HA/Ti复合涂层研究 I.结构、组成和力学性能

采用等离子喷涂方法,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了ＨＡ／Ｔｉ复合涂层,并对复合涂层的微观结构、相组成和力学性能进行了研究．结果表明,ＨＡ和Ｔｉ两相均匀地分布于复合涂层中．ＨＡ／Ｔｉ复合涂层的结合强度明显高于纯 ＨＡ涂层,这主要是由于 ＨＡ／Ｔｉ的复合缓和了涂层与基体之间的热膨胀系数失配．ＨＡ／Ｔｉ复合涂层在模拟体液中浸泡一段时间后,结合强度没有明显降低．ＨＡ／Ｔｉ复合涂层的断裂韧性和硬度均高于 ＨＡ涂层．     

Characteristics of gas-tunnel plasma-sprayed coatings

The quality of Al₂O₃ coatings formed by gas-tunnel plasma-spraying apparatus has been evaluated with respect to hardness and porosity under various spraying conditions. The deposit characteristics of Al₂O₃ powder sprayed onto a substrate by this type of plasma spraying were also studied and the relation between the deposit characteristics and the spraying distance was investigated. Estimation of the deposit characteristics was found to be a very effective method for determining the proper spraying conditions under which a good quality coating can be obtained.     

Cr_2O_3-8%TiO_2等离子喷涂层结合强度、表面状态与喷涂层厚度的关系

以往,有关等离子喷涂CrO3-8%TiO2涂层厚度与涂层性能关系的报道较少,为此,通过优化工艺参数,在45钢表面等离子喷涂不同厚度(350,450,550μm)的Cr2O3-8%TiO2涂层,研究了涂层厚度与其结合强度、硬度和孔隙率之间的关系。涂层厚度为350,450,550μm时,结合强度分别为29.2,11.5,7.2MPa,显微硬度分别为2528,2190,1930HV;孔隙率分别为3.80%,3.95%,4.45%。结果表明,随Cr2O3-8%TiO2喷涂层厚度的增加,涂层的结合强度减小,孔隙率增加,造成显微硬度降低。     

等离子喷涂HA/Ti复合涂层研究 I.结构、组成和力学性能

采用等离子喷涂方法,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了ＨＡ／Ｔｉ复合涂层,并对复合涂层的微观结构,相组成和力学性能进行了研究。结果表明,ＨＡ和Ｔｉ两相均匀地分布于复合涂层中。ＨＡ／Ｔｉ复合涂层的结合强度明显高于纯ＨＡ涂层,这主要是由于ＨＡ／Ｔｉ的复合和了涂层与基体之间的热膨胀系数失配,ＨＡ／Ｔｉ复合涂层在模拟体液中浸泡一段时间后,结合强度没有明显降低,ＨＡ／Ｔｉ复合涂层的断裂韧性和硬度均高于Ｈ     

Study on corrosion resistance of aluminium coating deposited on magnesium-zinc-yttrium-calcium alloy by cold spray

Pure aluminium coatings were prepared on magnesium-zinc-yttrium-calcium alloy substrate via cold spraying technology with different scanning speeds and working gas temperature. The correlation between the corrosion resistance of the coatings and the different spraying process was studied. While the working gas temperature is 600 °C and the scanning speed is 1 mm/s, aluminium coating has less porosity and the coating was well combined with the substrate. Higher temperature of working gas increases the plastic deformation of particles, which lead to a dense aluminium coating. The relationship of corrosion resistance on working gas temperature and scanning speed of aluminium coatings has also been investigated by immersion corrosion test and electrochemical impedance spectroscopic techniques. The results show that the cold sprayed aluminium coatings revealed a lower porosity and higher corrosion resistance with the decreasing scanning speed and the increasing temperature of working gas. The porosity and corrosion current densities were 0.938 vol.% and 2.427 ⋅ 10⁻⁶ A/cm². The experimental results show that the aluminium coating prepared by cold spraying has a good protective effect on magnesium alloy.     

涂布刮刀表面等离子喷涂纳米AI203—13％Ti02涂层的特性

为了深入研究纳米A1203-13％TiO：（ATl3）涂层的组织、性能与喷涂工艺参数之间的关系,采用正交试验法对等离子喷涂工艺的电流、电压、送粉率和喷涂距离等参数进行了优化,在涂布刮刀表面制备了纳米ATl3涂层。采用金相显微镜,SEM,EPMA和XRD等对纳米ATl3涂层的组织、磨粒磨损性能和结合强度进行了分析。结果表...     

Application of reaction synthesis principles to thermal spray coatings

Reaction synthesis principles have been extended to plasma spraying to obtain coatings consisting of mixed oxide phases and iron aluminides. Elemental powders of iron and aluminium were fed through a d.c. plasma torch to deposit intermetallic coatings on carbon steel substrates. Carbon steel substrates were also pre-heated with a plasma flame to create an iron oxide surface on the substrate such that an exothermic thermite reaction takes place when molten splats of aluminium impinge the pre-heated substrate at sub- or supersonic velocities. A thermite reaction between iron oxide and aluminium allowed the formation of alumina, FeAl2O4, iron, and iron aluminide phases. The presence of FeAl2O4 and Al2O3 increased the surface hardnesses of the coating, and the hardnesses of the coatings are significantly higher than the hardnesses of steel substrate, and aluminium particles. X-ray analysis of the coatings, microstructural observations, and microhardness measurements suggest that plasma spraying conditions can be tailored to obtain coatings with high hardness values with in situ synthesized reinforcements (spinel and alumina) or iron aluminide phases. Aluminium-rich phases were observed in the as-deposited coatings when a mixture of aluminium and iron or aluminium and nickel were fed through the plasma gun in ratios equivalent to Fe3Al, FeAl, Ni3Al, and NiAl. In some cases, annealing allowed the formation of iron-rich or nickel-rich aluminide phases. High solidification rates of molten splats allowed very limited diffusional reactions between the splats of aluminium and iron, or aluminium and nickel because the available diffusional time for exothermic interfacial reactions is limited to a fraction of a second at best. Oxidation of part of the aluminium led to the formation of alumina in the as-deposited coatings, and therefore, a vacuum plasma spraying technique is desirable to obtain intermetallic phases. The results suggest that reactive spraying will allow deposition of coatings by utilizing the heats of reaction between the constituents, and reactive spraying will broaden the engineering applications of reaction synthesis techniques.     

超音速电弧喷涂Ti-Al涂层抗滑动磨损性能研究

采用二次正交回归试验设计原理和钛铝双丝超音速电弧喷涂Ti-Al合金复合涂层方法，对LY12铝合金进行了表面强化研究，并采用金相、XRD、SEM、硬度和磨损试验方法，对涂层的组织结构及力学性能进行了表征，考察了喷涂工艺参数对涂层孔隙率、显微硬度和耐滑动磨损性能的影响，研究结果表明：在本文的实验条件下，涂层的体积磨损量、孔隙率、显微硬度与喷涂电压和喷涂距离之间的变化规律，可用回归模型进行描述；随喷涂电压的增大，涂层磨损量逐渐下降；喷涂距离小于220mm时，随喷涂距离的增大涂层磨损量逐渐增大；喷涂距离为220mm时，磨损量达到最大，继续增加喷涂距离，涂层的磨损量逐渐下降；在干摩擦条件下，Ti-Al合金涂层的磨损机制主要以化合物相剥落引起的磨粒磨损和氧化磨损为主。     

Structural characterisation of apatite coatings

The current, most frequently employed, commercial route to produce hydroxyapatite prosthetic coatings is plasma spraying. However, this has several important limitations especially for textured surfaces. Low temperature methods of coating fabrication such as cathodic electrodeposition are attractive alternatives. However, quantitative characterisation of the phase composition of thin electrodeposited coatings can be problematic. An X-ray diffraction method, which provides quantitative compositional information without reference to external or internal standards, is introduced and validated. The method can also be applied when Bragg peaks from the supporting substrate are apparent within the data and preferred orientation can be tolerated. This method has been used to examine in detail the microstructure of electrodeposited coatings which are compared directly with those formed by a commercial plasma spraying process.We show that, unlike the plasma sprayed coatings, the electrodeposited material consists of a single crystalline phase (hydroxyapatite) and a significantly reduced amorphous phase. The electrodeposited coatings also possess significantly more microstrain and a smaller crystallite size than the corresponding plasma sprayed material.     

High performance surface engineering from plasma spraying

The continuing trends in engineering are to increase component productility, reliability and lifetime. For example, the emphasis in turbine engine technology is to raise engine ratings, reduce fuel consumption and generally higher efficiency levels. In addition to advances in mechanical engineering and materials technologies, these increases are being gained by the use of a coating technology based on the concept that the substrate provides the mechanical strength and the coating sufficient protection to inhibit the environment. Plasma spraying is a coating technology producing surface layers from materials in powder form. Machine tooling for the production of plasma sprayed coatings onto engineering components in an economic and consistent manner requires proper equipment selection in connection with both the surface preparation (grit blast) and the subsequent deposition process of coating.

This paper reports on the status of plasma spraying for a variety of industries and in particular on the types of machine tooling required together with the level of sophistication for the preparation and deposition of plasma sprayed coatings.     

Grenzflächenphänomene und Haftung bei thermisch gespritzten Verbundwerkstoffen

In this paper. results from investigations on the bonding mechanism between thermally sprayed metal and ceramic coatings and different substrates are presented. The materials were sprayed by atmospheric arc (Ni, Mo und Cu) and plasma spraying techniques (NiCr-Al, Al₂O₃, ZrO₂-7Y₂O₃) on iron (Armco-Fe) and steel (St37) substrates. The morphology, microstructure and impact behaviour of sprayed particles on the polished substrates have been analysed as a function of particle properties (temperature, heat content, size and velocity, surface tension, viscosity) and substrate properties (composition, temperature, surface structure). The results of the influence of investigated properties on the adherence mechanism of sprayed particles can be also directly correlated to the experimentally measured bond strength of are sprayed nickel coatings.     

微束等离子喷涂羟基磷灰石涂层

采用微束等离子喷涂(MPS) 在Ti6Al4V基体上制备了羟基磷灰石(HA)涂层, 并以大气等离子喷涂(APS)为对照. 利用光学显微镜、SEM和XRD分析技术对MPS涂层形貌、相组成和结晶度进行了研究. 结果表明: 在微束等离子喷涂过程中, HA 的分解程度比大气等离子喷涂有显著降低, 除了HA相, 仅形成β-TCP相和非晶相. MPS涂层的结晶度主要受喷涂距离的影响. 喷涂距离较短(<80mm)时, 涂层结晶度高于APS方法制备的涂层. 喷涂距离在130mm时, 涂层结晶度低. 大气等离子喷涂层含有β-TCP、α-TCP、TTCP、CaO和非晶. MPS涂层分解较APS少的主要原因是喷涂过程中HA粒子过热不严重.     

Numerical simulation of coating growth and pore formation in rapid plasma spray tooling

Rapid plasma spray tooling (RPST) is a process that can quickly make molds from rapid prototyping or nature patterns without limitation of pattern's size or material. In this paper, the process of coating growth and pore formation in RPST has been analyzed by numerical simulation. The objective of this work was to determine the porosity in plasma sprayed coatings and verify the developed computer model, which might serve for future thermal residual stress studies of plasma sprayed coatings. The analysis was divided into two steps: particle flattening and coating growth. In the analysis, a ballistic model was used for modeling the in-flight powder particles. The method allows for the calculation of off-normal spray angle, which is common in plasma spraying of engineering components. Also, a set of rules for coating growth as well as pore formation in the coating has been proposed. Based on these works, a computer program was developed to calculate the effects of process parameters, such as gun scanning velocity, spray angle, etc., on the porosity of the coating. Finally, an experiment was carried out to verify the effects of spray parameters on the porosity. The results agree with the prediction of the model.     

Thermal Shock Endurance of Porous Steel with Plasma Sprayed ZrO2 Coating

A new thermal shock resistant material has been developed by plasma spraying ZrO₃ (stabilized with 7 wt% CaO) on porous steel. When the porosity of the substrate steel is more than 25% and a Ni-Cr undercoating is applied, the ZrO₂ coating cracks but does not spall off by water quenching from 1125°C to 25°C. Because the cracks are produced regularly, the water quenching test is considered as a new heat treatment method for high thermal shock endurance of the ZrO₂ coatings. This material has gas penetrating capability, and may be used as a permanent casting mold.     

Characterizations of the pore-crack network architecture of thermal-sprayed coatings

This study aims at developing three techniques permitting to complementary characterize the architecture of the pore-crack network architecture of thermal-sprayed coatings:

(i) image analysis quantifies the coating porous morphology, that is to say the overall porosity level and the crack network orientation;

(ii) electrochemical analysis qualitatively characterizes the ratio of connected pores;

(iii) Archimedean porosimetry quantifies the non-connected porosity level.

These techniques were applied to characterize the pore structure of yttria-partially stabilized zirconia (Y-PSZ) thermal barrier coatings (TBCs) manufactured implementing air plasma spraying and hybrid plasma spraying, which combines plasma spraying and laser remelting. Thermal and mechanical properties of Y-PSZ TBCs are especially dependant from their pore network architecture.     

等离子喷涂工艺参数对FeCrBSi合金涂层结合强度的影响

采用等离子喷涂工艺在Q235钢基体上直接制备了FeCrBSi合金涂层,使用正交试验法研究了喷涂工艺参数对涂层结合强度的影响,并对喷涂工艺参数进行了优化,同时在优化参数的基础上进一步研究了涂层厚度对结合强度的影响。结果表明：等离子喷涂制备FeCrBSi合金涂层的最佳工艺参数为喷涂电流900A,主气流量44．8L·min-1,辅气流量27．8L·min-1,喷涂距离110mm;采用最佳工艺制备的涂层与基体的结合强度为18．2MPa,内聚强度为33．5MPa;随着涂层厚度的增加,涂层与基体的结合强度明显下降,而涂层的内聚强度先上升后下降,较佳的涂层厚度为347．2μm。     

Tribological Evaluation of Plasma Sprayed Coatings for High Temperature Sliding Surface Against Cordierite

A study has been carried out to develop a high temperature sliding seal for the ceramic gas turbine engine's (CGT) regenerator. The solid-lubricant coatings, which consisted of the following combinations: NiO, Ni/Cr, Cr₃ Cr₂,/NiCr, ZrO₂,/ CaO, CaF₂, BaF₂, Ag₂O and graphite, were synthesized by low pressure plasma spraying. Friction and wear characteristics were evaluated at temperatures from 50 to 1000^°C by rubbing the coatings against a cordierite disk. After the sliding tests, the worn surfaces were analyzed by SEM-EDX and XRD. The analytical results showed that the tribological properties of coatings were significantly related to the surface layers. Formation of a CaF₂/BaF rich layer led to a low friction and a low wear property. On the other hand, formation of solid-state reaction product (Mg_0.4Ni_0.6O) between the coating and the cordierite increased the friction coefficients, and the transfer of the cordierite debris caused a seizure and/or a severe wear. Among the sprayed coatings, the Cr₃Cr₂/NiCr based coating containing CaF₂/BaF₂ and Ag₂O showed excellent tribological properties, which should satisfy the specifications for the basic design of a CGT engine.