Ceramic Composite Coatings Research Articles

Microwave processing of sprayed alumina composite for enhanced performance

Abstract To meet the challenging in-service requirements, surfaces of many mechanical components need to be modified. This can be achieved by altering the surface properties through deposition technique followed by suitable post processing. Apart from the conventional methods, laser treatment is the most popular post processing technique. Of late, microwave heating is emerging as one of the potential post processing sources. Microwave processing of materials is fundamentally different from traditional techniques. In microwave processing, energy is directly transferred to the material through interaction of electromagnetic waves with molecules leading to volumetric heating. However, for processing of transparent (to microwaves) materials, a technique known as microwave hybrid heating (MHH) can be used. In this study, MHH is used for post processing of plasma deposited alumina–titania ceramic composite coatings on steel substrate; resulting properties of the post processed coatings are evaluated. Results show reduction in porosity, enhancement in microhardness, and wear resistance of the irradiated coatings owing to microstructural changes and densification. Results are discussed with suitable illustrations.

235 Response Characterisation of Microwave Glazed Plasma Spray Deposited Ceramic Composite Coatings

Microwave (MW) processing of materials has been an area of active research in the last two decades and use of microwaves of processing of ceramics/ceramic composites is reported increasing a faster rate. The present study is concerned with post processing of plasma sprayed ceramic composites and hence characterisation of response of the post processed composites while subjected to sliding environment at high speed (5m/s). Spray deposits were irradiated (glazed) at 2.45GHz microwave frequency at 1kW power. During glazing modification of the characteristic layered structure of the plasma sprayed composites takes place resulting in densification of the porous structure. Spray deposits were characrterized through monitoring of wear, and also examining the worn surfaces under scanning electron microscope (SEM). Glazed spray deposits exhibit higher wear resistance and higher sliding stability in terms of less elemental depletion and meterial spalling. Enhanced sliding stability of the glazed deposits was also demonstrated by p-v-t analysis of the monitored wear data.

Fabrication of ceramic composite coatings using electrophoretic deposition, reaction bonding and low temperature sintering

We have developed a novel combination of electrophoretic deposition (EPD), reaction bonding and low temperature sintering techniques for the fabrication of yttria stablised zirconia (YSZ)/alumina composite coatings on Fecralloys. A mixture of ethanol and acetylacetone solvent was found to be an effective medium for YSZ and aluminium particle suspension. With the particle size of YSZ and aluminium being significantly reduced during ball milling. By using the EPD process, uniform green form coatings containing YSZ and aluminium particles were produced on Fecralloys. After oxidation of aluminium at 500°C and sintering at 1200°C, a dense and adherent YSZ/Al2O3 coating was produced. The presence of aluminium in the green form coatings not only contribute to the bonding between the coating and the metal substrate, but also compensate for the volume shrinkage of the coatings during sintering by the volume expansion arising from oxidation of aluminium to alumina.

Tribological properties of ceramic and metallic composite coatings

Tribological properties of ceramic and metallic composite coatings

Microwave glazing of alumina–titania ceramic composite coatings

The application envelop of atmospheric plasma sprayed ceramic composites can be widened considerably by reducing/eliminating inherent surface defects by treating them through techniques like microwave irradiation. In microwave processing, microwave energy is directly applied to the material. High-frequency microwaves (>1 GHz usually) penetrate into the bulk of the material and the volumetric interaction of the electromagnetic fields with the material results in dielectric (volumetric) heating. This leads to higher heating efficiency with faster processing. Ceramics are transparent to microwaves at low temperatures, however, start absorbing microwaves at higher temperatures resulting change in microstructure and material characteristics. This paper presents microwave processing of atmospheric plasma sprayed alumina–titania ceramic composite coatings in conventional microwave heating system and evaluation of the processed materials through XRD, SEM, microhardness survey and surface finish with illustrations. Results indicate microwave irradiation induces densification of the material and possible flow of dominant gamma-alumina phase that leads to glazing of coated surface. Glazed surfaces exhibit enhanced microhardness as well as surface finish.

An investigation of the corrosion behavior of Al 2O 3-based ceramic composite coatings in dilute HCl solution

In this paper, the corrosion behavior of Al 2O 3–SiO 2, Al 2O 3–TiO 2 and Al 2O 3–SiO 2–TiO 2 ceramic composite coatings in boiling 1 N HCl solution is investigated. It is shown that the addition of 3% SiO 2 to the base spraying powder of Al 2O 3 increases porosity in the coatings and causes deterioration in their corrosion resistance. Adding 13% TiO 2 to Al 2O 3 improves the anti-corrosion property of the ceramic coating due to a reduction in porosity. The connected porosity in the Al 2O 3-based ceramic composite coatings rises with the open porosity and is independent of the density of the coating.

A Consistent Rationale for the Superior Strength and Ultra-Hardness of Ceramic Nano-Composite Coatings

AbstractNano-structured composite ceramic coatings such as TiN with Si3N4 orT iSi2 prepared by variousforms of plasma assisted CVD, composed of crystalline components of equiaxed TiN of several nm diameter, surrounded by amorphous Si3N4 intercrystalline layers of roughly 0.2 volume fraction have exhibited hardnesses in the range of 70-100 GPa-quite commensurate with polycrystalline diamond layers, and thermal stability up to 1000C. Preliminary considerations indicate that such ultra-hardness, uninfluenced by the usual artifacts of nano-indentations are not governed by processes of crystal plasticity in the crystalline component but by the characteristic flow mechanisms of the often topologically continuous amorphous component exhibiting “liquid-like” behavior in the constrained spaces between the crystalline components.

Scuffing and wear behavior of aluminum piston skirt coatings against aluminum cylinder bore

Various coatings, especially nickel based ceramic composite (NCC) coatings, have been considered as an alternative to the use of iron plating on aluminum pistons in aluminum cylinder bore engines. Laboratory simulation tests were conducted to determine the scuffing and wear behavior of piston coatings against 390 Al engine cylinder bore. The tested piston coatings included nickel–tungsten (Ni–W) plating, electroless Ni plating, Ni–P coatings with ceramic particles such as boron nitride (BN), SiC, or Si 3N 4, as well as titanium nitride physical vapor deposition (PVD) coating, diamond-like carbon (DLC) coating, and hard anodizing. The scuffing and wear resistances of these coatings were evaluated and compared with tin plating and iron plating. Wear tests were performed in lubricated sliding at 400 K, using a modified Cameron Plint High Frequency test machine with a special fixture to hold the piston samples. Scuffing tests were conducted under the conditions in which lubricant starvation occurred. Metallographical work and chemical analysis of the interactive surface layers were performed on the tested samples. The simulation test results ranked the relative performance of the coatings against 390 Al bore, and revealed their tribological characteristics. Ni–P–BN coating, iron plating and Ni–W plating showed very good scuffing resistance when sliding against 390 Al bore samples. DLC, electroless Ni plating and Ni–P–SiC coating had moderate scuffing resistance against 390 Al. Ni–P–Si 3N 4 and TiN coatings had marginal scuffing resistance against 390 Al. TiN PVD coating had the most severe wear on 390 Al bore samples. Hard anodizing, DLC, Ni–P–SiC and Ni–Si 3N 4 coatings had less severe wear on 390 Al than TiN coating. With very good wear resistance themselves, Ni–W plating, electroless Ni plating, iron plating and Ni–P–BN coating produced the least wear on 390 Al. Engine dynamometer tests were conducted to confirm the simulation test results. This work indicates that the scuffing and wear bench simulation tests can be used as a rapid, low-cost and repeatable means of screening and studying the tribological behavior of the potential material combinations of piston coatings and cylinder bores.

Composite Sol-Gel Ceramic Coatings

Apart from microelectronics where sub-micron coatings are sufficient, the conventional sol get coating method has never fully reached its potential. One of the reasons is that the conventional sol-gel films tend to crack when a certain thickness is reached. This is primarily because sol get films shrink significantly during firing and this problem is reduced in thinner layers. The large strain of the conventional sol-gel films upon heat treatment and densification can be prevented by dispersing in the sol get matrix particulates of calcined ceramics. The composite sol-gel coatings (CSG) are produced by dispersing calcined ceramics in the sol and hydrolising the mixture into a composite gel. The resulting slurry can be applied onto a substrate and heat treated to full density by methods similar to the conventional sol gel. The preliminary results indicate, that high density composite coatings can be obtained for variety of matrix/filler combinations, at relatively low heat treatment temperature of 500 - 1000C. For the first time therefore the possibility opened up for deposition of protective ceramic coating in a relatively fast and economic non-line-of-sight process. The CSG technique offers the primary advantages of the classical sol get, i.e. ease of application, low - temperature sinterablity and good adhesion due to formation of chemical bonds with the substrate. Simultaneously, CSG avoids the biggest disadvantage of the classical sol - gel: large strains upon densification , leading to large stresses and cracking of layers thicker than few microns.

A novel gas sensor for binder burnout : R. Raman et al. (MATSYS, Inc., USA.)

The work presents results of the experimental investigation of vacuum sprayed yttria stabilized zirconia, nickel oxide, nickel (YSZ–NiO–Ni) ceramic composite coatings deposited on Al2O3 ceramic and stainless steel substrates produced at different Ar and H2 gas flow rates. The Ar and H2 gas flow was varied according to the factorial plan design. It is shown that for the used vacuum plasma spray YSZ and NiO powder mixture the produced coatings were composed of three phases mainly: cubic YSZ (c-YSZ), cubic NiO (c-NiO), and cubic Ni (c-Ni). The quantitative X-ray diffraction (XRD) analysis was used to evaluate each phase amount in the coatings. It was found that the vacuum spray technique enables formation of composite layers with a variable composition and that phase content in the coatings can be controlled choosing the Ar and H2 gas flow rates. The electrical conductivity measurements revealed that a variation of the phase content in the YSZ–NiO–Ni composites is responsible for the existence of different electrical conduction mechanism and rapid change in the conductivity of coatings with the used powder content. The surface morphology and the cross-section analysis by scanning electron microscope (SEM) have shown porous structures of the deposited coatings.

Three-dimensional granular modelling for simulation of powder compaction behaviour: S. Tamura et al (University of Tokyo, Tokyo, Japan)

Duplex-treated composite ceramic coatings with and without compound layer were produced by the combination of plasma nitrocarburizing and follow-up multi-arc ion plating. The microstructures and mechanical properties of the ceramic coatings were investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy, in association with property characterization. The results show that the composite ceramic coatings are composed of an inner nitrocarburized layer, a CrN interlayer and an outmost AlCrTiSiN layer. The AlCrTiSiN layer consists mainly of alternately nanoscaled (Cr,Al)N sublayer and amorphous sublayer with a few (Ti,Al)N phases embedded in a matrix of amorphous Si3N4 and Si. The compound layer has transformed to the γ′-phase sublayer, which enhances considerably the adhesion strength of the CrN interlayer to compound layer. The improved adhesion strength is attributed to the γ′-phase acting as nucleation sites of epitaxial growth for the CrN phase. The composite ceramic coating with compound layer reveals much higher hardness, bearing capacity and wear resistance when compared with the composite ceramic coating without compound layer. The improvement of mechanical and tribological properties is associated with presence of the γ′-phase sublayer, which provides a smooth transition, gradient in hardness and stress between the substrate and the CrN/AlCrTiSiN coating. In addition, the hard γ′-phase sublayer provides a strong supporting effect for CrN/AlCrTiSiN layer under loading.

MA粉末のプラズマ溶射によるTi炭化物粒子分散強化皮膜の作製

Composite powder materials possess a potential to fabricate the high performance structural coatings instead of the conventional mechanically mixing powders. In the many composite powder making processes, machanical alloying (MA) process enables to obtain the homogeneous microtructure of metal/ceramic materials system. In the DC plasma spraying of metal/ceramic MA composite powders, separation phenomena of ceramic phase from metal phase has been recognized.In this study, metal/ceramic MA composite powders were made by using the ceramic making original elements as the starting material and these MA powders were plasma sprayed. Possibility of fabrication of ceramic particles dispersed composite coatings, by the inter-diffusion of these starting elements, was investigated.The main results obtained in this work are summarized as follows:(1) Separation was recognized even in the Cu/TiC MA powder material system, which had good wettability between metal and ceramic materials.(2) Separation is basically caused in MA composite powder materials under the spraying conditions of high power level, on which both materials can be fully melted.(3) TiC dispersed homogeneous coating was made by DC plasma spraying of Cu/Ti/C MA powder.(4) Coating made from MA powders showed slightly higher hardness with less scattering compared with that made from the conventional powders, because of the homogeneously dispersed structures.

Preparation of Dispersed Phase Ceramic Boron Nitride and Aluminum Nitride Composite Coatings by Chemical Vapor Deposition

Dispersed phase ceramic composite coatings containing BN and AIN were prepared by chemical vapor deposition. The BN + AIN coatings were deposited on Al2O3 from the BCI3–AICI3‐NH3 reagent system in the temperature range of 700° to 1200°C. Also, single‐phase BN and AIN coatings were prepared for comparison purposes. The composite coatings consisted of very small BN and AIN regions which were either crystalline or amorphous, depending on deposition temperature and reagent concentrations. For example, a composite containing AlN whiskers of less than 100‐nm diameter in a matrix of turbostratic BN of 2‐nm grain size was deposited at 1100°C and 20 kPa.

Electrolytic ZrO2 Coatings: II. Microstructural Aspects

Zirconia coatings were formed on graphite and titanium substrates by electrodeposition. The as‐deposited coatings were amorphous and cracked during the drying stage. Sintering of the coatings on the graphite substrates caused crystallization, with formation of a variety of mixtures of the tetragonal and monoclinic polymorphs having nanosize crystallites. Oxidation of the Ti substrate and reaction with zirconia during the heat‐treatment resulted in addition to a microstructure resembling ceramic composite coatings.

Microstructural study of dispersed phase ceramic Bn-AlN composite coatings by chemical vapor deposition

Dispersed phase ceramic composites have recently received much attention because of their superior mechanical properties including fracture toughness, strength, hardness, resistance to wear and erosion. Chemical vapor deposition (CVD) offers one avenue of preparing ceramic composites by simultaneous deposition of multiple phases, i.e. codeposition. The major advantage of preparing dispersed phase ceramic composites by CVD is that mechanical as well as chemical, electrical, optical, and thermal properties of the composites can be favorably tailored by controlling the composites’ composition and microstructure via variation and optimization of CVD process variables such as temperature, pressure, reagent concentration, substrate type, reactor geometry, etc.In this study, the codeposition of boron nitride (BN) and aluminum nitride (AlN) was explored because the BN+AlN composite system (as a deposited coating) offers the promise of tailoring properties such as friction coefficient, hardness, and resistance to wear and erosion for possible radome, electromagnetic window and tribological applications.

Does corrosion matter?

Does corrosion matter?