Methods for testing the adhesion and layer strength of a surface layer

Abstract

Method for testing the adhesion and layer strength of a surface layer applied to a first side (2) of a substrate (1), wherein the substrate (1) is formed by a cylinder wall (1) of a crankcase of an internal combustion engine and the surface layer (3) is formed by a running surface coating applied to the cylinder wall (1), comprising the following steps: • Creating a recess (5) in the substrate (1), wherein the recess (5) extends into the substrate (1) from a second side (4) of the substrate (1) facing away from the first side (2) on which the surface layer (3) is located, and is limited in depth by a base surface (6), • Inserting a pressure body (7) in an insertion direction (8) into the recess (5) until an end face of the pressure body (7) abuts the base surface (6), wherein a cross-section of the recess (5) is larger than a cross-section of the pressure body (7) so that there is no undercut between the pressure body (7) and the recess (5), • Pressing the pressure body (7) against the base surface (6) so that the pressure body (7) moves, where the surface layer (3) is a metal-containing surface layer, the pressure body (7) is inserted into the recess (5) from the second side (4) and the recess (5) is made from an outer side of the cylinder wall (1) forming the second side (4) and the reaction force acting on the pressure body (7) or the pressure force exerted by the pressure body (7) on the base surface (6) is measured over the displacement path of the pressure body (7) during the pressing of the pressure body (7) against the base surface (6).

Description

[0001] The present invention relates to a method for testing the adhesion and layer strength of a surface layer according to the preamble of patent claim 1.

[0002] From DD 280 823 A1 a method for testing the quality of thermally sprayed protective layers is known, wherein an opening filled by a blind plug, which is provided in a test specimen, is over-sprayed with the protective layer, the blind plug is then removed and a test pressure is then applied to the protective layer by means of a rubber bladder until it breaks.

[0003] CN 101 109 696 A discloses a method for testing non-metallic surface coatings. In this method, a recess is created in a painted substrate into which a test stamp can be inserted from the side. The recess extends close to the surface layer. By applying force to the test stamp, the surface layer is lifted slightly from the substrate, from which conclusions can be drawn about the adhesion strength of the surface layer.

[0004] To date, there is no suitable test method for reliably verifying the adhesion and coating strength of a metallic surface or functional layer. Known methods, such as the tensile bond test, do not produce usable results due to their lack of adhesive strength. For example, the surface quality of the running surface coatings of crankcase cylinder bores can currently only be assessed through microscopic evaluation.

[0005] The technical background of the present invention also includes the • DE 198 29 478 C2, • US 1 653 714 A, • US 2 875 608 A, JP 2002 - 214 123 A and • Erichsen GmbH & Co. KG: Paint and Varnish Testing Machine Model 200 - Technical Description. October 2010.

[0006] The object of the invention is to provide a method for testing the adhesion and layer strength of a functional layer which is simply designed and which enables reliable statements regarding the adhesion and layer strength of such functional layers.

[0007] This object is achieved by the features of patent claim 1. Advantageous embodiments and further developments of the invention can be found in the subclaims.

[0008] The invention is based on a method for testing the adhesion and coating strength of a surface layer applied to a first side of a substrate. The substrate is a cylinder wall of a crankcase of an internal combustion engine, which can be made as a cast part from a light metal alloy, such as an aluminum alloy.

[0009] According to the invention, a recess is first created in the substrate, wherein the recess extends into the substrate from a second side of the substrate facing away from the first side of the substrate (on which the surface layer is located) and is limited in depth by a "base or bottom surface." The recess can be produced, for example, by milling or other machining methods.

[0010] Subsequently, a pressure or test specimen is inserted into the recess from the second side in one direction until it rests against the base surface. A compressive force is then applied to the pressure or test specimen. The pressure specimen generates a shear force in the surface layer. The compressive force should be adjusted or gradually increased until the pressure specimen shifts, i.e., until the surface layer and any remaining "residual wall thickness" of the substrate "give way." The surface layer is destroyed in the process.

[0011] According to a further development of the invention, it is provided that the base surface of the recess is designed to be substantially flat and, accordingly, a pressure body is used which also has a substantially flat end face which comes into contact with the base surface.

[0012] It is essential that the recess and the pressure body are designed in such a way that the pressure body can be easily inserted into the recess from the second side. Viewed in the insertion direction of the pressure body, the cross-section of the recess must therefore be at least slightly larger than the cross-section of the pressure body. An undercut, as is the case with the CN 101 109 696 A mentioned above, must therefore not be present.

[0013] The recess can be created so deep that it reaches almost or directly to the surface layer. In the case of a cylinder crankcase, the recess can be machined from the outside of the cylinder wall. The recess is preferably created in the form of a groove.

[0014] According to the invention, the surface layer is a metal-containing (e.g., iron-containing) surface layer. If the method is applied to a crankcase of an internal combustion engine, the surface layer can, in particular, be a metal-containing running surface coating applied to the inside of the cylinders of the crankcase.

[0015] The surface layer is a surface layer applied to the substrate by thermal spraying.

[0016] According to the invention, while the pressure body is pressed against the base surface, the "reaction force" occurring at the pressure body or the compressive force exerted by the pressure body on the base surface is measured over the displacement of the pressure body and, according to a further development of the invention, recorded. The measurement and recording can be performed analogue or digitally. Ultimately, the goal is to generate a "force-displacement diagram" that shows how the reaction force occurring at the pressure body or the compressive force exerted by the pressure body on the base surface changes over the displacement, which allows conclusions to be drawn about the adhesion and layer strength of the surface layer.

[0017] After the measurement process, a comparison of the recorded force-displacement curve with a reference curve can be carried out and a decision can be made as to whether deviations between the recorded force-displacement curve and the reference curve are tolerable.

[0018] A predefined "quality parameter function" can be used. Using such a quality parameter function, a quality parameter or quality index can be calculated from the curve (e.g., integral) of the deviation between the recorded force-displacement curve and the reference curve. This quality parameter or quality index serves as a measure of the quality of the surface layer and the strength with which the surface layer adheres to the substrate.

[0019] According to the invention, it is provided that the pressure body is further displaced in the insertion direction even after the first cracks have appeared in the surface layer and / or after a first partial detachment of the surface layer from the substrate.

[0020] The recess or groove is milled from the outside through the aluminum of the cylinder wall to just below the surface coating forming the cylinder bore. A thin "wall" of aluminum may remain beneath the surface coating. The compressive force can be applied using a punch from a tensile testing machine. This creates a shear force in the surface coating in the edge area of ​​the recess. Depending on the adhesion and layer strength of the surface coating, this shear force either destroys the bonding element or the surface coating itself.

[0021] By recording a force-displacement diagram, the adhesion and layer strength can be quantitatively determined. This allows the determination of a quality index that provides information about the functional layer quality (internal cohesion of the functional layer) and the adhesion strength of the surface layer (the bonding of the surface layer to the substrate).

[0022] The method according to the invention is very efficient and cost-effective and is suitable for testing all metallic layers on substrate surfaces.

[0023] The invention is explained in more detail below in conjunction with the drawings. Fig. 1 The basic principle of the invention in schematic representation; Fig. 2, Fig. 3 micrographs of a cylinder wall at different stages of the testing process.

[0024] Fig. Figure 1 shows a cross-section through a substrate 1, which may, for example, be the wall of a cylinder of a crankcase of an internal combustion engine. A metallic, e.g., iron-containing, surface layer 3 is applied to a first side (e.g., the inside of the cylinder wall of a crankcase). The surface layer 3 can be applied, for example, by thermal spraying, in which fine liquid or viscous metal particles are catapulted onto the first side 2 of the substrate 1.

[0025] To test the adhesion and layer strength of the surface layer 3, a groove-like recess 5 is first milled into the substrate from a rear side 4 of the substrate 1 facing away from the first side 2. The recess 5 can extend almost or directly to the surface layer 3. The depth of the recess 5 is limited by a base area 6, which is formed either by the surface layer 3 itself or by a residual wall thickness of the substrate 1 remaining after milling.

[0026] Subsequently, a pressure body 7 (e.g. cylindrical stamp or similar) is inserted into the recess 5 in an insertion direction 8, ie essentially perpendicular to a tangential plane of the surface layer 3 in the test area. The pressure body is brought with its front side into contact with the base surface 6. Subsequently, the pressure body is pressed against the base surface 6 by means of a pressing device not shown in detail here with a gradually increasing force F, so that the pressure body 7 is displaced. "Displacement" means that the surface layer 3 and any remaining wall thickness of the substrate 1 is destroyed, which in the Fig. 2, Fig. 3. With increasing "advancement" of the pressure hull 7, cracks gradually develop in the surface layer 3 (cf. Fig. 2) or there is a gradual detachment of the surface layer 3 from the first side 2 of the substrate 1, which in Fig. 3 is shown.

Claims

[1] Method for testing the adhesion and layer strength of a surface layer applied to a first side (2) of a substrate (1), wherein the substrate (1) is formed by a cylinder wall (1) of a crankcase of an internal combustion engine and the surface layer (3) is formed by a running surface coating applied to the cylinder wall (1), comprising the following steps: • Creating a recess (5) in the substrate (1), wherein the recess (5) extends from a second side (4) of the substrate (1) facing away from the first side (2) on which the surface layer (3) is located into the substrate (1) and is limited in its depth by a base area (6), • Inserting a pressure body (7) in an insertion direction (8) into the recess (5) until an end face of the pressure body (7) rests against the base surface (6), wherein a cross section of the recess (5) is larger than a cross section of the pressure body (7), so that there is no undercut between the pressure body (7) and the recess (5), • Pressing the pressure body (7) against the base surface (6) so that the pressure body (7) moves, where the surface layer (3) is a metal-containing surface layer, the pressure body (7) is inserted into the recess (5) from the second side (4) and the recess (5) is manufactured from an outer side of the cylinder wall (1) forming the second side (4), and wherein, during the pressing of the pressure body (7) against the base surface (6), the reaction force occurring at the pressure body (7) or the pressure force exerted by the pressure body (7) on the base surface (6) is measured over the displacement path of the pressure body (7). [2] Method according to claim 1, characterized by that a recorded force-displacement path is compared with a reference path and a decision is made as to whether deviations between the recorded force-displacement path and the reference path are tolerable. [3] Method according to claim 2, characterized bythat by means of a predetermined quality characteristic function, a quality characteristic is formed from a curve of the deviation between the recorded force-displacement path curve and the reference curve, which quality characteristic is a measure of the quality of the surface layer (3) and of the strength with which the surface layer (3) adheres to the substrate (1). [4] Method according to one of claims 1 to 3, characterized by that the pressure body (7) continues to be displaced in the insertion direction (8) even after the first crack has occurred in the surface layer (3). [5] Method according to one of claims 1 to 4, characterized by that the pressure body (7) is further displaced in the insertion direction (8) even after a partial detachment of the surface layer (3) from the substrate (1). [6] Method according to one of claims 1 to 5, characterized bythat the recess (5) is created so deep that it reaches almost or directly to the surface layer (3). [7] Method according to one of claims 1 to 6, characterized by that the surface layer (3) has been applied to the substrate (1) in the form of an iron-containing layer. [8] Method according to one of claims 1 to 7, characterized by that the surface layer (3) has been applied to the substrate (1) by thermal spraying. [9] Method according to one of claims 1 to 8, characterized by that a substrate (1) made of a light metal alloy is used. [10] Method according to one of claims 1 to 9, characterized by that the recess (5) is created in the form of a groove. [11] Method according to one of claims 1 to 10, characterized bythat the base surface (6) is substantially flat and a pressure body (7) with a likewise substantially flat or conical end face is used.

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