Laser infrared photothermal radiometry (PTR) can be used to determine the thermophysical properties (thermal diffusivity and conductivity) and interfacial defects (i.e. disbonding) of various thermal sprayed coatings on carbon steel substrates. PTR experimental results are compared with a one-dimensional photothermal model that can take into account roughness affects and interfacial defects by considering a roughness equivalent-layer and an equivalent-thermal resistance, respectively. The foregoing thermophysical parameters of the thermal sprayed coatings are obtained when a multi-parameter optimization algorithm is used to fit the PTR experimental results. The potential of the PTR technique for in-situ monitoring of the coating process and the characterization of the thermal sprayed coatings will be discussed in this paper.

In situ values of Young's modulus and Poisson's ratio for thermal spray coatings are needed to evaluate properties and characteristics of thermal spray coatings such as residual stresses, in-service stresses, bond strength, fracture toughness, and fatigue crack growth rates. It is important to have methods documented in detail so that people can follow the document and use the methods. Such a document requires more pages than are allowed in conference proceeding and journal papers. Thus, Recommended Practices and Standards describing these methods are needed. Currently, there is not a recommended practice or standard for evaluating Young's modulus and Poisson's ratio for thermal spray coatings. The ASM International Thermal Spray Society has recognized this need and formed a committee on Recommended Practices for Thermal Spray Coatings. This paper describes one of the recommended practices being written by the Mechanical Properties Evaluation Subcommittee of the Recommended Practices Committee. The specimen is a coated substrate in the form of a cantilever beam. The method is easy to use and inexpensive. The equipment needed is a vise or clamping fixture, strain gages, a strain indicator, a micrometer, a ruler, a hanger, and a set of weights. The specimen is easy to machine and spray. The loading is easy to apply and remains constant during readings. The method can be used to evaluate Young's modulus and Poisson's ratio in tension or compression. A description of the method, a verification, and a sensitivity analysis was done and published in Reference [1]. Some of the details of implementing the method and the data sheet are presented here.

The effect of high frequency pulse detonation (HFPD) and HVOF thermally sprayed WC-Co coatings on the high cycle fatigue (HCF) behavior of 2024-T4 aluminum was investigated. The fatigue life distributions of specimens in the polished and coated conditions are presented as a function of the probability of failure. The monotonic and cyclic deformation behaviors of the as-received and as-coated specimens were investigated. The conclusions show that, (i) the HFPD sprayed specimens exhibited slightly higher fatigue lives compared to the uncoated specimens, (ii) the HVOF sprayed specimens exhibited significantly higher fatigue lives compared to the uncoated specimens, and (iii) the as-coated specimen was cyclically stable.

Wear resistant thermal spray coatings are hard but brittle, making them useless for applications sensitive to metal fatigue. New coatings have been developed, however, that resist crack formation under load as well corrosion and wear. This study compares the properties and behaviors of many of these coatings along with chrome plating using standard test methods.

MIL-STD-1687 (SH) has been in use for many years as one of the specifications that the United States Military performs thermal spray operations at overhaul facilities. The U.S. NAVY has asked AWS (American Welding Society) to develop an ANSI/AWS national standard to replace it and then provide long range maintenance of the new specification when necessary. This paper discusses both the procedure used to develop this standard and the content of the specification. Particular attention will be paid to the quality controls, training of operators and use of other specifications to accomplish compliance with this specification. The approval process for this document will be discussed with a probable time line including a plan to publicize and smoothly replace the MIL-STD-1687 (SH) specification. The further integration and use of it globally will be discussed and recommendations presented. The new standard will be in harmony with the ISO thermal spray standards program.

Thermal-spray standards in the United States are developed by several professional societies that include American Society for Testing and Measurement (ASTM) for test & measurements methods and composition specifications; American Welding Society (AWS) for feedstock, equipment acceptance, application process, training & certification; American Water Works Association (AWWA) for thermal-sprayed zinc as potable water tank lining; International Association of Corrosion Engineers (NACE) for corrosion protection processes and inspection; and Society of Protective Coatings (SSPC) for test & measurement methods, application specification & inspection in regards to protective coatings for the protection of steel. This paper provides information on various standards set by these bodies.

An innovative methodology to deposit, by plasma spraying, ceramic thermal barrier coatings on gas turbine blades and vanes was developed. Such a methodology produces a pattern of microcracks in the coating, thus improving its thermal shock resistance. After a laboratory campaign of process optimization and coating characterization, real components were coated with a 150µm thick layer of NiCoCrAlY as a bond coat and a 300µm thick layer of ZrO2, partially stabilised with 8%of Y2O3, as a top coat. In particular, four vanes, taken from the first stage of a land based gas turbine (V64.3, produced by Ansaldo), were coated on the whole airfoil. The four vanes were submitted to a cyclic oxidation test in a burner rig simulating the operative conditions of a gas turbine. In particular, they were exposed to a gas flow with the same composition, temperature and speed of the inlet gas of a real gas turbine; moreover, they were cooled by an internal stream of compressed air for obtaining the same temperature profile of a vane in operation. The surface temperature of the vanes was monitored during the test by an optical pyrometer and the internal temperature by a thermocouple. After 550 hours of test, corresponding to 550 cycles, the four vanes did not show any sign of damage.

Air plasma sprayed thermal barrier coatings have been widely used to reduce metal wall temperatures of industrial gas turbine combustor liners. Thermal barrier coatings provide thermal gradients, with the goal of reducing the liner wall temperature to acceptable levels as a result of their low thermal conductivity. A typical thermal barrier coating consists of a 0.1-0.2 mm MCrAlY bond coating and a 0.25-0.35 mm thick 8 wt.% yttria stabilized zirconia ceramic top coating. A method to increase thermal barrier coating effectiveness is the application of thicker ceramic coatings. Development and performance testing of 0.5-0.8 mm thick ceramic coatings are discussed in this paper. Cyclic oxidation tests that simulate industrial gas turbine environments were conducted. Thermal barrier coating degradation-mechanisms were determined from microstructural evaluation of thermally exposed samples.

Lock-in thermography is a nondestructive inspection method based on modulated heat transport in combination with infrared imaging. Measurement times are relatively short, about 3 or 4 minutes, and the method is amenable to inspecting a wide range of large and small parts. This paper describes the basic principle behind the method and its application to different thermal sprayed coatings (e.g., Cr-steel, Al2O3). It explains how the test samples were prepared with artificial defects simulating delaminations, inclusions, and other types of imperfections and how the method performed in each case.

The aim of this work is to study the adhesion of WC-Co coatings using acoustic emission testing. The coatings were produced by HVOF spraying then subjected to four-point bending while in situ acoustic emission measurements were made. The test specimens were then examined under a microscope, revealing regularly spaced transverse cracks on the coating surface as well as interfacial cracking. An analysis of the acoustic emission data revealed two types of acoustic events based on absolute energy and amplitude. This appears to be linked to the cracks that were observed forming the basis for an interfacial cracking model.

FeAl iron-aluminide based materials with the ordered B2 structure are excellent candidates for use in high temperature applications because of the combination of good mechanical properties, low density, low cost and availability of raw materials, and improved oxidation resistance. The aim of this article is to produce an ultra-fine grained FeAl coating by HVOF thermal spraying of milled powders and characterize the fine scale features of its microstructure. Comparison is made with a more conventional coating obtained by projection of powders obtained by atomization. Starting powders and coatings were investigated using X-ray diffraction and transmission electron microscopy. It was observed that the coating obtained from milled powders had a microstructure essentially characterised by a nanometer grain size and the presence of a disordered FeAl phase.

Frequent reporting of microhardness data for thermal spray coatings testifies to the widespread use of this technique for coatings characterization. However, inadequate reporting of microhardness procedures makes comparisons between published coatings hardness statistics difficult and it appears that both microhardness in general and its significance to characterizing thermal spray coatings in particular, are poorly understood. This paper demonstrates that though microindentation technique is a useful laboratory procedure that can be used for coatings optimization, research and quality control purposes, poor understanding often leads to worthless data and thus to erroneous conclusions. A high quality WC-12%Co coating supplied by Sulzer Metco was hardness tested on both the polished cross-section and plane surface of the coating. Contributions to the variance in results obtained and sources of significant errors are discussed and conclusions are drawn regarding the methodology and suitability of hardness testing for characterizing thermal spray coatings. The limits in repeatability and reproducibility of Vickers microhardness data for hard metal thermal spray coatings are discussed. The necessity for rigorous statistical procedures of data analysis is demonstrated. It is suggested that the technique is inherently unsuitable for characterizing hard thermal spray coatings due to poor intrinsic reproducibility.

The high technical level of thermal spraying is based on four segments: available know-how, equipment and installations, spray materials, and industrial gases. This article discusses the application of industrial gases used in thermal spraying. It describes the processes involved in the production, provision, and storage of industrial gases as well as their properties. In addition, the article also discusses the influence of quality on the individual fuel gases used in thermal spraying.

Thermal Barriers Coatings (TBC) are mass-produced in several industrial fields: aeronautic, automotive or energetic industries. All production requires the same constant level of fest and reproducible quality control at the lowest cost. The metallographic process is the primary way to evaluate thermally sprayed coatings but it must be both highly very repeatable and fast, especially when metallography is used to keep the production at a constant level. Therefore the management and the organization of a metallographic laboratory is of prime importance in order to reduce the cost and to provide a quality structure. The present approach to the whole chain of characterization is based on the user's point of view. Generally speaking, metallographic control of widely used parts often seems to be considered to be an uninteresting and obtuse subject, since it has been in practice for so long. Despite the lack of the prestige associated with the subject, optimization of an appraisal post can provide very concrete and more importantly profitable, results.