Load- and Depth-Sensing Indentation Tester for Properties Measurement at Non-Ambient Temperatures
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LOAD- AND DEPTH-SENSING INDENTATION TESTER FOR PROPERTIES MEASUREMENT AT NON-AMBIENT TEMPERATURES KARL B. YODER* AND DONALD S. STONE** *Materials Science Program, University of Wisconsin-Madison, 1500 Johnson Dr., Madison, WI 53706 "**Department of Materials Science and Engineering, University of WisconsinMadison, 1509 University Avenue, Madison, WI 53706
ABSTRACT The ability to measure the temperature-dependence of the hardness of thin films is useful from both an applications and a scientific standpoint. For this reason, we have designed and constructed a load- and depth-sensing indentation tester combining sub-nanometer resolution with the ability to operate over a range of temperatures, currently 150K to 400K. This paper describes the new experimental apparatus and reports preliminary data on 440C stainless steel substrates with and without a 0.75 gim ZrN coating.
INTRODUCTION Load- and depth-sensing indentation testers are routinely used to probe mechanical properties of thin films [1-5]. Due in part to the need to maintain a low rate of thermal drift, conventional instruments are restricted to operating at room temperature. Removing this restriction allows mechanical properties measurements to be made at temperatures more appropriate to process and service conditions, and provides a useful tool for exploring strengthening mechanisms based on the temperature dependence of the hardness. In this paper, a load- and depth-sensing indentation tester combining subnanometer resolution with the ability to operate from 150K to 400K is described. Design modifications (principally the replacement of temperature-sensitive components such as the load cell springs) will extend the upper temperature range to at least 700K. Representative data of 440C stainless steel substrates and substrates with a 0.75 gtm ZrN coating are reported [6].
EXPERIMENTAL APPARATUS Mechanical Components The indenter, specimen, displacement transducer, load cell and translation stages are located inside the vacuum chamber of a JEOL 50A scanning electron microscope with gun and electron optics removed (fig. 1). The entire apparatus rests on an air table. The indenter shaft assembly consists of a piezoelectric (PZT) actuator mounted outside the chamber, connected to the indenter shaft via a pre-loaded bellows. Inside the chamber, the shaft is supported by a pair of phosphor-bronze leaf springs mounted on a canister that, in turn, is suspended from the chamber Mat. Res. Soc. Symp. Proc. Vol. 308. ©1993 Materials Research Society
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ceiling with thin, stainless tubing. The leaf spring arrangement allows controlled displacement in the z-direction, but resists indenter motion in the x- or ydirections. When a voltage is applied to the PZT actuator it shrinks, allowing the pre-loaded shaft to move downward toward the specimen. With a screw, the sample is mounted into a holder fixed to a hollow shaft running through the center of the load cell canister. This shaft is supported by a pair of leaf springs similar to those of the indenter-support springs
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