Thermal spray coatings are subjected to mechanical loadings in many applications, and there is a need to evaluate the mechanical properties of these coatings. Mechanical properties of interest in the performance of thermal spray coatings include fatigue life, wear resistance, bond strength. Young's modulus, Poisson's ratio, and residual stresses. One property that has a large effect on the performance of thermal spray coated parts is the residual stress distribution in the thermal spray coating and in the substrate. Thus, it is important to have (1) a fundamentally sound method for evaluating residual stresses and (2) a written recommended procedure for applying the method. ASM International is not a standard writing organization. Yet, the increased use of thermal spray coatings and the need for documentation on methods for evaluating mechanical properties of thermal spray coatings have generated a need to prepare Recommended Practices. To meet this need, the ASM International Thermal Spray Society has formed three subcommittees to prepare Recommended Practices for thermal spray coatings. This paper describes a draft form of a Recommended Practice for evaluating residual stresses in thermal spray coatings. This Recommended Practice is being developed by the Subcommittee on "Evaluating of Mechanical Properties of Thermal Spray Coatings". The method, called the Modified Layer Removal Method, has been presented in several papers and has been used for a variety of different coatings. The paper describes the dimensions of the test specimen, the equipment needed, the procedure for removing layers, and the methods for collecting and interpreting the data to evaluate through thickness residual stresses. The Recommended Practice (RP) is in Draft form, but is presented to let the thermal spray community know about the RP effort and invite comments and volunteers to write other RP's.

Tungsten Carbide (WC) thermal spray coatings have had increased acceptance in commercial aircraft applications driven by the desire to replace chromium electroplate due to environmental and economic considerations [1]. In order to confidently replace chromium electroplate by WC thermal spray coatings, evaluation of wear and fatigue characteristics of the WC thermal spray coatings is necessary. For WC thermal spray coatings to replace chromium electroplate in aircraft applications, the coatings must demonstrate wear and fatigue characteristics as good as or better than those of chrome plating. Previous research in this area has shown that the fatigue life of the WC thermal spray coatings can be improved by inducing compressive stresses in the coating. This paper compares the wear characteristics of several types of WC thermal spray coatings with those of chromium electroplate in sliding wear tests following the "block-on-ring" procedures described in ASTM G77 standard. Wear results are interpreted in terms of coating residual stresses and in terms of X-ray diffraction and Scanning Electron Microscope (SEM) analysis.

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.