Determining interface strength of glass-metal bi-layer laminates. using cross-push method

Transcription

1 Key Engineering Materials Online: ISSN: , Vol. 351, pp doi: / Trans Tech Publications, Switzerland Determining interface strength of glass-metal bi-layer laminates using cross-push method Yiwang Bao 1, a, Sijian Gao 1, b, Yanfei Han 1, c and Ming Guan 1, d 1 China Building Materials Academy, Beijing a ywbao@csgc.org.cn, b gaosijian@263.net, c hyf7202@sina.com, d guanping@cbmamail.org.cn, Keywords: bond strength; cross-bonded sample; glass-metal laminates; Abstract. Bond strength of metal-glass bilayer laminate was determined via a simple testing approach using cross-bonded sample and a special fixture. Tensile and shear strength in the interface for glass-metal composite were obtained by this way. It is demonstrated that the strength can be accurately determined when it is lower than the glue strength but it is invalid if the strength is higher than the glue strength. The specimen preparation and testing principle is introduced for determining the interface bonding strength of coatings. Introduction Ceramic and glass coatings have been widely used as important functional materials due to their attractive functions in optic and chemical protection to engineering or biomechanical structures[1-4]. Many of their applications are related to surface and interface properties. It is apparent that the quality and reliability of the joint parts mainly depend on bond strength. Over the years, the fast development of brittle coatings creates great requirement for new methods to measure the bond strength accurately and conveniently. Therefore, it is significant to develop an effective method for measuring the bond strength between solid materials. Based on the bond strength data, the mechanical properties of metal-glass bilayer laminate can be designed by adjusting the bond strength and layer thickness [5, 6]. Moreover, bond strength is also important for evaluating the properties of coating and glue [7, 8]. There are various approaches for evaluating bond strength of solid materials [9, 10]. Most of the existing methods are based on bending test, such as 3-point bending test and 4-point bending test. Although those testing methods have widely been used for special objective, none of them can be used for measuring the bond strength in uniaxial tension,and general testing method for determining tensile bond strength has not been established to date. Recently, a new method using cross-bonded sample was proposed to measured bond strength of metal-ceramic bonding parts and quite ideal results have been obtained [11]. However, in some cases, the cross-bonded sample is difficult to prepare directly from a component, especially for film or coatings on metals. In order to evaluate the interface strength of brittle coating by using the cross-bonded sample, a modified cross-bonding technique was developed for measuring tensile and shearing bond strength between the coating and substrate. Based on this method, the tensile and shear bond strength of metal-glass bilayer laminate were measured. The results indicate that the compressive test with cross-bonded sample is a simple approach for estimating the bond strength of coating. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-10/05/16,17:59:47)

2 Key Engineering Materials Vol Principle of the Method The specimen for this work is prepared by the following procedures. First the metal-glass bilayer laminate were cut into bar samples with mm 3 in size. And a steel bar of mm 3 in size was also prepared as a bonding bar. Two parallel notches were cut on the glass coating cross the beam sample by using wire saw to a depth same as the thickness of the glass coating. The distance of two parallel notches equals to the width of the steel bar (4mm in this test), as shown in Fig.1. Bonding the steel bar on the glass coating of the glass-metal beam sample between the two notches with high-strength glue (UV glue was used in this work), then a cross-bonded sample was produced. The displacement between two notches, d, should equal to the width of the steel bar. Fig.1 Schematic diagram of sample with notches and the cross-bonded sample with the steel bar The measurement of tensile and shear bond strength can be performed by mounting the cross-bonded sample with different forms in a fixture made of hard metal. The experimental description on the loading form and fixture for the testing of tensile bond strength is schematically shown in Fig.2. Fig.2 Schematic diagram of fixture configuration and loading form for measuring tensile bond strength. The upper end of the pressure head is machined into arc shape at two perpendicular directions to avoid unsymmetrical stress in the sample, and the lower surface of the pressure head was stuck with a soft tape for keeping uniform contact between the pressure head and the sample. The soft tape is also stuck on the upper surface of the fixture for the same purpose. The tests can be carried out using universal mechanical testing machine, with a crosshead speed of 0.5mm/min, for both tensile and shearing tests. The tensile bond strength is calculated by the following equation:

3 128 Composite Materials V σ = A (1) t P ct / Where P ct is the critical load to debonding in tensile test and A is the bonded area. Fig.3 illustrates the testing method of shear bond strength measurement, loading form and sample configuration. The horizontal bar of the cross-bonded sample should contact well with one of the upper surface of the fixture. The uniaxial compressive load was applied on the erect bar which supported by the interfacial shear stress. Shear bond strength is then determined by the equation: τ = P cs / A (2) Where P cs is the critical load in shear test. In both the tension and shear tests, the sample should be inserted into the fixture fluently without friction, and the length inserted into the fixture should be at least 2mm shorter than the height of the fixture to ensure that the applied stress is completely on the bond section during loading. Generally, the mean value and standard deviation of test data should be obtained from a group of specimens containing over 6 samples. Fig.3 Schematic diagram of fixture and loading form for measuring shear bond strength. Experiment and Discussion The materials used in this work is a titanium alloy beam samples (3 4 40mm 3 in size) coated with ~0.3 mm glass film. Two notches normal to the beam were cut on the glass coating by wire saw. The distance between them is same as the width of the steel bar (about 4mm). The steel bar was stuck-on the coated sample between two notches with high-strength structural adhesive. The bond strength of samples was measured at room temperature and 0.5mm/min cross-head speed with universal testing machine. The fracture area for strength calculation was measured after the tests, using optical scale microscope. Fig.4 (a, b) and Fig.4 (c, d) show the fracture sections of metal-glass laminate sample under shearing and tensile stress, respectively. Fig.4 (a, c) show the glass coating separated from titanium alloy beam sample on the steel bar under tensile and shearing stress. Fig.4 (b, d) show interfacial sections of metal-glass laminate sample under tensile and shearing stress. In this test, the interfacial shearing strength was obtained to be 26MPa and the tensile strength was 8MPa.

4 Key Engineering Materials Vol Fig.4 Fractured section viewing from the steel bar (a, c) and from the substrate (b, d) of metal-glass laminate sample under tensile (a, b) and shearing stress(c, d) Since specimens for uniaxial uniform tension is difficult to prepare for brittle material, most tests for bond strength measurement are performed using bending method, which provides overestimation of the bond strength because the strength in uniform tension is lower than the bending strength. The compression test with cross-bonded sample was found to be an effective and convenient testing method for determining both the tensile and shearing bond strength of samples. Using this method, a simple compressive load can produce an approximately uniform tensile stress and shearing stress at interface. In addition, both the fixture and the cross-bonded sample are very easy to prepare and the equations of strength calculation are clear and simple. Since the cross-bonded sample has two interfaces, one is the interface of the coating-substrate, another is the interface between the coating and steel bar. For some coatings with the interface strength higher than the bonding strength of the glue, the measured strength reflects only the glue strength, rather than the interface strength of the coating. In this case, at least, it can be predicted that the interface strength should be higher than the measured value. It is worth noting that the stiffness of the bars should be high enough to keep the stress in the section uniform. Conclusions 1) The interface strength (tensile and shearing) of glass coating on substrate can be evaluated simply using cross-bonded sample with the coating layer in between two perpendicular bars, by means of a compressive load and a simple fixture. 2) When the interface strength between the coating and the substrate is higher than the bonding strength of the glue, the measured strength value represents the glue strength, and fracture would occurs from the interface between coating surface and steel bar.

5 130 Composite Materials V Acknowledgments This work was supported by the National Outstanding Young Scientist Foundation (No ) and International cooperation project of Chinese ministry of Sci & Tech. (DFA51010). Reference [1] Cook R F and Pharr GM: J. Am. Ceram. Soc. Vol. 73(1990), p. 787 [2] Peterson IM, Pajares A, Lawn BR, Thompson VP and Rekow ED: J. Dent. Res. Vol. 77(1998), p.589 [3] Pajares A, Wei L, Lawn BR and Berndt CC: J. Am. Ceram. Soc. Vol. 79(1996), p.1907 [4] Miranda P, Pajares A, Guiberteau F, Cumbrera FL and Lawn BR: Acta Mater. Vol. 49(2001), p.3719 [5] Rebillat, F, Lamon J, Naslain, R, Lala-Curzio, E, Ferber, MK, Besmann TM J. Am. Ceram. Soc. Vol.81 (1998) p.965 [6] Sainz, MA, Miranzo, P, Osendi MI J. Am. Ceram. Soc. Vol.85 (2002), p.941 [7] Lee, KY, Case, ED J. Mater Sci. Vol.35 (1996), p.107 [8] Besmann, TM J. Am. Ceram. Soc. Vol. 73(1990), p.2498 [9] Heck K, Kolotyluk D, Metal-Ceramic Bond Strength, unpublished report. [10] Morrell, R (1995) British Ceramic Transactions, Vol.94 (1995), p.1 [11] Bao Y. W. Zhang H. B., and Zhou Y. C. Materials Research Innovations Vol.6 (5-6) (2002), p. 277

6 Composite Materials V / Determining Interface Strength of Glass-Metal Bi-Layer Laminates Using Cross-Push Method /