Depth-sensing indentation measurements with Vickers and Berkovich indenters
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Depth-sensing indentation measurements with Vickers and Berkovich indenters B. Rother Forschungsinstitut f¨ur Edelmetalle und Metallchemie, Katharinenstr. 17, D-73525 Schw¨abisch Gm¨und, Germany
A. Steinera) Joint Research Centre of the Commission of the EC, Inst. for Advanced Materials, I-21020 Ispra, Italy
D. A. Dietrich Ingenieub¨uro Dr. Dietrich, Hauptstr. 64, D-09235 Burkhardtsdorf, Germany
H. A. Jehn Forschungsinstitut f¨ur Edelmetalle und Metallchemie, Katharinenstr. 17, D-73525 Schw¨abisch Gm¨und, Germany
J. Haupt and W. Gissler Joint Research Centre of the Commission of the EC, Inst. for Advanced Materials, I-21020 Ispra, Italy (Received 12 February 1996; accepted 10 March 1998)
Depth-sensing indentation measurements are performed with two different Vickers indenters and one Berkovich indenter. The sample materials were mirror polished Ag, Al, Au, Ni, and Ti samples. From the load-indentation depth data, the conventional hardness plots as well as the first derivative are calculated. The latter procedure yields a specific volume related density of deformation energy in the probed material. That specific energy density is shown to be a constant material parameter for extended indentation depths and for different Vickers indenters. Vickers and Berkovch indenters delivered within the error margin the same results.
I. INTRODUCTION
Depth-sensing indentation measurement with depth resolution in the nm-range is an increasingly popular technique for mechanical characterizations of thin films, subsurface layers, and surface regions of bulk materials. They are preferably used for the determination of hardness under load and the elastic modulus (see, e.g., Ref. 1). The reliability of the technique is, however, still limited by insufficient understanding of the indentationrelated deformation processes. A serious drawback results from the mathematical definition of indentation hardness under load Hc as the ratio of applied load P to the contact area between the indenter and the testpiece under the test load as Hc
P , bh 2
(1)
with the geometry factor b of the ideal indenter shape and the indentation depth h. Tip rounding of the indenter, material buckling at the rim of the indent, and uncertainties of the zero point detection generally falsify the a)
Present address: Roth & Rau Oberfl¨achentechnik, Gewerbering 10, D-09358 W¨ustenbrand, Germany. J. Mater. Res., Vol. 13, No. 8, Aug 1998
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relation between indentation depth and contact area as defined by the term b ? h2 in Eq. (1) (see, e.g., Ref. 2) Contact areas at low indentation depths are particularly affected by these issues which are commonly termed indentation size effects (ISE).3 It should additionally be mentioned that, if Eq. (1) only refers to the “loading curve,” both plastic and elastic deformations are sensed. For separation of elastic and plastic effects, the “unloading curve” has to be considered additionally and this is not the subject of the p
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