Bond Strength Of Coatings Research Articles

Degradation of bond coat strength under thermal cycling—technical note

Degradation in bond strength of plasma-sprayed thermal barrier coatings under thermal cycling was evaluated by tensile adhesion tests. The bond strength and failure mode for two types of bond coat materials were examined. Two bond coats having the same substrate and top ceramic coat behaved differently due to differences in the thermal mismatch stress at an interface between the metallic bond coat and the ceramic top coat.

Structure, solubility and bond strength of thin calcium phosphate coatings produced by ion beam sputter deposition

Ion beam sputter deposition was used to produce thin calcium phosphate coatings on titanium substrates. Structure, solubility and bond strength of the as-sputtered and heat treated coatings were evaluated. X-ray diffraction (XRD) analysis of the heat treated coatings revealed a hydroxyapatite-type structure. The heat treated coatings were found to have significantly lower solubility as compared to the amorphous as-sputtered coatings. Although the crystalline coatings exhibited the lowest solubility, in general, the bond strengths were lower for the heat treated coatings.

Laser surface sealing and strengthening of zirconia coatings

Abstract Plasma-sprayed zirconia coatings are of general interest as thermal barriers in diesel and gas turbine engines. However, their residual porosity and poor mechanical properties require surface sealing and strengthening. Moreover, dense zirconia is not impervious to oxygen at high temperatures (ionic conductivity). Surface densification was achieved by melting a thin layer, using a continuous wave CO 2 laser. The cracks induced by shrinkage and differential stresses were controlled by spraying alumina powder in the laser beam during surface melting. The formation of alumina-zirconia composites, or possibly eutectics, generates improved chemical resistance and mechanical properties. Both laser-sealed and as-sprayed coatings were tested for bond strength, wear, corrosion and thermal cycling up to 900 °C. The bond strength and thermal barrier efficiency of as-sprayed coatings were retained after laser treatment, whilst wear, corrosion and thermal shock resistances were clearly improved. Future works include thermal cycling up to 1200 °C and erosion tests. The main objective is to lower the operating and maintenance costs of gas turbine engines for electric power generation.

Surface‐Energy Determinations of Tin Oxide‐Coated Soda–Lime–Silica Glass

The dispersive and polar surface‐energy components, as well as the total surface energy, of tin oxide coatings on soda–lime–silica glass were determined by the Owens–Wendt method. The total surface energy of tin oxide is greater than soda–lime–silica glass and, more importantly, exhibits significantly more‐dispersive and less‐polar character. These results indicate that tin oxide is significantly more covalent than soda–lime–silica glass. It is postulated that the more‐covalent tin oxide coatings increase the bond strength of organic coatings to soda–lime–silica glass. These effects improve the friction‐damage resistance of glass surfaces coated with metal oxides and organics, compared with glass surfaces coated with organics only.

The variability in strength of thermally sprayed coatings

There is a large variability in the bond strengths of coatings which are determined by the tensile adhesion test method. The primary intention of this work is to establish a suitable parameter which measures the strength variability of thermally sprayed coatings, as well as a meaningful parameter to index that strength. The Weibull modulus for metal ( e.g. mild steel) and ceramic ( e.g. zirconia, alumina) coatings has been found and then related to the defect nature of the coating. This work has shown that the Weibull analysis method is a pertinent parameter to examine in the case of thermally sprayed coatings. The testing methods allow an “index of integrity” to be established for thermally sprayed coatings, involving both the Weibull modulus m and the characteristic value σ 0 so that interlaboratory tests or products from different manufacturers can be compared and contrasted.

Plasma sprayed coatings of hydroxylapatite.

The technique of plasma spraying has been applied to deposit a thin, dense layer of hydroxylapatite onto a titanium substrate. Bond strength of such apatite coatings with the substrate have been measured, as well as the (absence of) influence of the coating process on fatigue properties of the substrate. Animal studies showed similar histological reactions to apatite coatings as to (well documented) apatite bulk materials.

Performance of the TFTR moveable limiter tiles

The movable limiter for the Tokamak Fusion Test Reactor (TFTR) is composed of an Inconel X-750 backing plate covered with titanium carbide coated graphite tiles. It has been used for ohmic heating discharges at input powers up to about 2 MW for durations up to 3 s. Even though these levels were well within the design requirements, discharges showed high levels (up to 1%) of titanium contamination. It was observed that certain tiles were showing substantial coating removal which became progressively worse as more discharges were made. After about 800 discharges the tiles were removed. A few of the tiles were examined in the Sandia external beam facility. This analysis showed that the TiC coating was completely removed over large areas. There was also evidence of plasma deposited material on the tiles. The thickness of the remaining coating from this beam analysis agreed with the thickness determined from sectioning control coupons from the production runs. There was a weak correlation between damage and coating thickness. The correlation was such that there was a higher probability of coating failure as the coating thickness increased from 15 μm to 40 μm. Test were done using the ASTM-C-633 procedure for measuring coating bond strength. The adhesion strength agreed well with the behavior observed in TFTR. The coating has been removed, and the tiles reinstalled.

Bonding of detonation-sprayed coatings

Generally it has been presumed that the high bond strength of detonation-sprayed coatings is related to the high kinetic energy stored in each particle during acceleration and released as heat on impact with the substrate. An investigation was conducted to define the basic technological parameters of detonation spraying that determine the energy state of the particles and consequently the conditions of coating formation. Relationships between adhesion strength and the technological parameters of detonation spraying and some of the properties of the materials are obtained. The influence on adhesion strength of substrate surface plastic deformation by particle impact is demonstrated. The possibility of a mutual influence of the powder particles on coating formation is also discussed.

The influence of surface preparation on the bond strength of flame-sprayed aluminium coatings on mild steel

The bond strength of sprayed-aluminium coatings on grit blasted steel substrates was shown to be highly dependent on surface preparation. Type and condition of the grit and the angle of blasting markedly influenced bond strength but variations of blasting pressure, blasting speed, and nozzle–substrate distance had no effect. With chilled iron angular grit, failure occurred mainly at the sprayed metal–substrate interface. The level of bond strength was reduced when blunted grit or low blasting angles were used. With alumina grit the bond strength was increased and the failure location moved from the interface to within the spray coating. Examination of grit blasted surfaces with the scanning-electron microscope gave an indication of the cause of the above behavior in terms of surface roughness and surface debris. The work indicates that bonding between flame-sprayed aluminium and steel substrates is of a mechanical rather than metallurgical nature. From the technological viewpoint, the importance of grit condition and blasting angle can be seen and simple rules of surface preparation formulated.

Bond strength of coatings applied by the flame plating technique

1. A method is proposed for determining the bond strength of deposits prepared by the flame plating technique. The method makes it possible to establish, from the bond strength of a deposit 0.2–0.3 mm thick, the bond strength of deposits ranging in thickness from 0.2 to 1–1.5 mm, with an accuracy of +-20%. 2. An analysis is made of the existing bond-strength tests for flame-plated deposits, resulting in the choice of an optimum procedure.

1078 型わくはく離剤の性能に関する研究 : その2 モルタルの付着強さ試験(材料・施工)

1078 型わくはく離剤の性能に関する研究 : その2 モルタルの付着強さ試験(材料・施工)

1077 型わくはく離剤の性能に関する研究 : その1 引張りはく離試験(材料・施工)

1077 型わくはく離剤の性能に関する研究 : その1 引張りはく離試験(材料・施工)

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第1報の訂正