Adhesion scratch testing

A common mode of coating failure is delamination at the coating-substrate interface. The strength of this interface is measured using adhesion tests that range from the simple adhesion scratch test to the more sophisticated tests based on fracture and/or contact mechanics. Many of the qualitative tests, such as the Adhesion Tape Test, are covered in the ASTM standards (e.g. [43-45]). These should be used only for comparative purposes, where a quick evaluation of adhesion is required. 

Burnett and Rickerby [78] and Bull and Rickerby [79] analyzed the scratch test of a coated sample and derived a relation between the critical normal load Wcr and the work of adhesion... 

Kim etal. (1998) deposited about 0.5 pm thick homogeneous and dense hydroxyapatite coatings by IBAD on a-alumina substrates. The ACP layer crystallised to dense HAp after annealing at 500 °C for 2 h and immersion in deionised water for 72 h at room temperature. The adhesive strength between HAp and the a-alumina substrate was measured by a scratch test and the critical load was found to be around 43 N (4300 gf). The ion-beam sputtered coatings were used as control samples. The adhesion was found to be worse for IBSD than for IBAD. Indeed, using IBSD the critical load of HAp on alumina was measured to be only about 39 N (3900 gf). 

The scratch test is a standard method to provide a measure of the coating-to-substrate adhesion and was found to be a useful method to test thin HAp coatings deposited on implant surfaces. Forsgren et al. (2007) estimated the critical load of a biomimetically deposited hydroxyapatite layer on a cp-Ti substrate to be 2.4 O.IGPa. 

Based on its apparent simplicity, scratch testing is frequently applied to estimate the cohesive and adhesion bond strengths of hydroxyapatite coatings (for example Arias et al., 2003 Zhang et al., 2006 Dudek and Adamczyk, 2013). However, the interpretation of the recorded traces is difficult as the test results are affected by scores of intrinsic and extrinsic parameters that tend to falsify the conclusion drawn. 

ASTM C1624-05. (2010a) Standard Test Method for Adhesion Strength and Mechanical Failure Modes of Ceramic Coatings by Quantitative Single Point Scratch Testing, American Society for Testing Materials. 

Examples of loss of adhesion during the scratch test (according to Butler et al [68,41]... 

It is clear that the scratch test is the only viable method of determining the adhesion of thin hard coatings which adhere well to hard glass substrates. It is equally clear that the test cannot be applied without great care being used in the interpretation of the results. Irrespective of the particular coating-substrate combination under examination, a number of points need to be kept in mind. 

Thus we may conclude that the scratch test can be used to characterize the strength of the interface quantitatively. The determination of the onset of adhesion... 

There are numerous techniques known for adhesion and delamination testing, some of the most common being a tape test, stud-pull test, scratch test, and an indentation test [1]. In the tape test, a tape is pulled off the surface containing a scratch, which provides the failure initiation. In the stud pull test, a stud held with thermosetting epoxy is pulled off the film surface. The indentation test, wherein a ball is pressed into the surface, is used for hard coatings, and the failure pattern indicates acceptable behavior. In the scratch test, where an indenter moves in both vertical (loading) and horizontal (sliding) directions, an acoustic emission sensor allows for detection of the initiation of fiacture, while the scratch pattern indicates the type of failure. 

The Universal Nano-i-Micro Materials Tester (UNMT) has been developed to perform a variety of the common adhesion tests [2]. During any of them, it can simultaneously measure contact or surface electrical resistance displacement, deformation, or depth of penetration contact acoustic emission temperature forces in all three directions and digital video of the contact area. This report covers evaluation of the adhesion and delamination properties of coatings by the scratch test. 

The scratch tests are very similar to the nanoindentation tests and can be considered side by side. In both teclmiques, a prime tip is used for the adhesion measurements by dragging across the measuring surface under an increasing load, which results in an indentation. Scratch and indentation tests are suitable for the analyses of the coatings and thin films [100]. Sharp diamond indenters are usually used for the adhesion and scratch resistance determination between the substrate and coating. These techniques can fail for the analyses of hard coatings on soft substrates due to no detectable failures as a result of small critical loads. Therefore,... 

T. Sander, S. Tiemmel, S. Wartzack, A modified scratch test for the mechanical characterization of scratch resistance and adhesion of thin hard coatings on soft substrates. Surf. Coat. Technol. 206, 1873-1878 (2011)... 

In a scratch test, a diamond or WC, conical or pyramidal indentor is sheared across a specimen under a controlled normal load while monitoring the tangential force [117]. The adhesive bond and the tangential plowing force determine the total work performed by frictional forces. The coefficient of friction is determined from the ratio of the tangential to the normal load. 

Scratch tests have been used to evaluate the adhesion of thin films to a ceramic substrate. 

Coating adhesion The film adhesion can be qualitatively assessed by Rockwell and scratch test methods. These test procedures do not always yield reliable results, due to limitations of the test procedures (Bouzakis et al. 2011a). The evolution of the inclined impact test renders possible the accurate and quantitative coating adhesion evaluatiOTi (Bouzakis et al. 2010b). 

Adhesion is defined as the physical attraction or joining of two substances, especially the macroscopically observable attraction of dissirmlcir substances. There cire many techniques to study adhesion, namely pull-off tests, interfacial fracture tests, blister tests, mapping of interfacial properties, probe modification, and scratch tests. 

Conventional Tests of adhesion are not well suited to measurement of thin dims. The scratch test has been used to characterize the adhesion of thin hlms, such as plasma-polymerized polymers or evaporated metals, on hard substrates. 

In early work on the test, it was argued that the critical load was determined only by the properties of the interface, the radius of the stylus and the hardness of the substrate. On this basis, the scratch test would give a measure of fundamental adhesion (see Adhesion - fundamental and practical). However, there are many reports of dependency on the thickness and mechanical properties of the thin film, even several of those upon which supposedly similar styluses were used. 

A simple form of the scratch test is used for assessing paint adhesion (see Paint constitution and adhesion). The scratch test, as described in this article, is perhaps best regarded as a useful comparative method of characterizing thin film adhesion. The test variables used should be carefully characterized and caution exercised in comparing results obtained in different laboratories. 

European Standards Committee, Advanced Technical Ceramics - Methods of Test for Ceramic Coatings — Part 3 Determination of Adhesion and Other Mechanical Failure Modes by a Scratch Test, European Standard prEN 1071-3, March 5, 2001. 

Scratch test D E PACKHAM Assessment of thin film adhesion... 

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