The shear test developed within a European research project has important advantages compared to the coating strength test mainly in use today, the adhesion strength test according to DIN EN 582 or ASTM C 633. One of the main advantages is that no glue is used avoiding any possible influences of the glue. Furthermore the test is a rapid process compared to the adhesion strength test as there is no gluing procedure. However a number of very important directions have to be obeyed in order to make sure that the shear test is correct and comparable results can be reached. This is very important as in many cases it is not possible to control after the test if the directions had not been correctly obeyed. A number of further rules need to be followed to make sure the test results are correct. Within this presentation these direction will be summarized and essential hints will be given to make sure the test is carried out in the correct way. Finally a comparison will be given between the tensile adhesive test and the shear test from the practical and economical point of view of obz innovation gmbh, a thermal and cold spray job shop.

Biomedical Ti-coatings were deposited on Ti-substrates by the microplasma wire spraying method. The influence of different factors of the wire spraying process on sizes of the particles produced as a result of atomisation of the wire melt by the microplasma jet, as well as the deposition efficiency were determined by using multifactorial experimental design. Linear regression models were developed, showing the effect of the most significant process parameters (current, plasma gas flow rate, wire feed speed) on formation of a jet of the spraying Ti-particles, structure and properties of the Ti-coatings. Establishing the possibility of controlling macroporosity of the Ti-coatings in microplasma wire spraying and correspondence of the Ti-coatings bond strength in tensile and shear tests to the ISO 13779-2 and ASTM C633 requirements, as well as data of the Ti-coatings “in-vivo” tests proved the efficiency of using them for manufacture of various-purpose endoprostheses (hip joint, dental, etc.).

The shear test in accordance with DIN EN 15.340 is a method to test the bond between substrate and coating in thermal spraying. It has been developed in order to avoid the disadvantages of the test mainly in use, the adhesion test (DIN EN 582). In quality management in a thermal spraying job shop often results of coating analyses are necessary within a very limited time frame; very important is a low number of necessary specimens and a fast and reliable test method. It is described how the shear test can be implemented into the practice of a job shop and the experiences of the OBZ innovation GMBH, which has used the shear test for more than four years, are explained.

The shear test in accordance with EN 15340 is a new test method for testing the bond between substrate and thermally sprayed coatings. It has been developed in order to enable a test method without the disadvantages of the method currently in use, the adhesion test. In the adhesion test the adhesives influence the test results; therefore in the shear test no adhesives are used. The adhesives are among others the reason for a large deviation of the test results using the pull-off test. Using the shear test the mode of the test results depend on the ratio between adhesion and cohesion; this ratio causes three different fracture modes. In order to investigate the deviation depending on the fracture mode samples have been coated by wire flame spraying, arc, plasma and HVOF spraying. Different ceramics, carbides and metals have been used as thermal spraying materials. For each material-process combination between 30 and 120 samples have been coated. This report describes the interpretation of the results of the shear test depending on the fracture mode and the coating materials applied by different thermal spraying processes. The deviation of the results depending on the fracture mode has been investigated using a shear test device by which the shear force is recorded over the displacement of the coating. The knowledge of the deviation and the distribution of the results is necessary to decide on the required number of samples to reach a result with a defined reliability.

Instabilities of plasma spray jets have been a source of inconsistencies in coating properties. These instabilities can be minimized through the use of central injection torches or torches with fixed anode attachment. However, any low density ( < ~0.7) jet is globally unstable to small disturbances. Globally unstable jets are characterized by a short potential core, rapid spreading, and high entrainment, all of which are present in a plasma jet. Plasma jets have ratios of jet density to density of the surrounding gas on the order of 0.01, as well as rather low Reynolds numbers and thick boundary layers. In the present work, the instabilities are investigated through analysis of the disturbance growth in the shear layer between the plasma and the cold surrounding gas. These investigations are using two types of experiments, one consisting of a SG 100 spray torch with several optical diagnostic methods being applied to the shear layer analysis. The other experiment simulates the plasma jet at low temperatures by using a helium core jet exhausting into a sulfur hexafluoride (SF6) environment. The simulated plasma jet (SPJ) has a density ratio of 0.03. The simulated plasma jet (SPJ) allows controlled variation of the boundary layer through different fluid dynamic arrangements. It further allows use of diagnostics such as hot wire anemometry and PIV to clearly characterize the shear layer. Some of the characteristics of the shear layer are presented and comparisons between the plasma jet and the simulated plasma jet, and initial results on controlling the jet instability, are discussed. Abstract only; no full-text paper available.

The characterization of the adhesive and cohesive strength of thermally sprayed coatings is often evaluated according to given standardized testing procedures. These tests require the preparation of normally large coupons which have to be fixed together using an appropriate adhesive. Additionally they need time for preparation (e.g. annealing/curing of the adhesive) and require test equipments normally not available at job shops for coating development. One of the largest limitations of these tests is the applicability only for non-porous coatings, and in some cases the limited strength of the adhesive. Within a European CRAFT research project on “standards, measurements and testing”, a new shear test method was developed to characterize the mode and value of failure of thermally sprayed layers in a more reliable and less limited manner. This new shear test does not need any adhesive and yields more intrinsic information on coating quality than conventional tensile tests.