Correlation of Nanoindentation and Conventional Mechanical Property Measurements
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Correlation of Nanoindentation and Conventional Mechanical Property Measurements Philip M. Rice1 and Roger E. Stoller2 1 IBM Almaden Research Center, San Jose, CA, USA,[email protected] 2 Oak Ridge National Laboratory, Oak Ridge, TN, USA, [email protected] ABSTRACT A series of model ferritic alloys and two commercial steels were used to develop a correlation between tensile yield strength and nano-indentation hardness measurements. The NanoIndenterII® was used with loads as low as 0.05 gf (0.490 mN) and the results were compared with conventional Vickers microhardness measurements using 200 and 500 gf (1.96 and 4.90 N) loads. Two methods were used to obtain the nanohardness data: (1) constant displacement depth and (2) constant load. When the nanohardness data were corrected to account for the difference between projected and actual indenter contact area, good correlation between the Vickers and nanohardness measurements was obtained for hardness values between 0.7 and 3 GPa. The correlation based on constant nanoindentation load was slightly better than that based on constant nanoindentation displacement. Tensile property measurements were made on these same alloys, and the expected linear relationship between Vickers hardness and yield strength was found, leading to a correlation between measured changes in nanohardness and yield strength changes. INTRODUCTION Ion irradiation provides samples well suited to investigation of microstructural evolution by transmission electron microscopy (TEM). However, special techniques are required to obtain mechanical property data from such specimens because the thickness of the irradiated area is only a few micro-meters. The high-precision NanoIndenter-II® [1] was used in this work to measure the change in hardness caused by radiation damage as a function of distance from the irradiated surface. Since the corresponding radiation-induced microstructure can be characterized by TEM, the relationship between microstructural and mechanical property changes can be investigated. This study was undertaken to determine the effects of minor solutes on radiation-induced property changes in model ferritic alloys, and the results of the microstructural investigations have already been published [2,3]. This paper focuses on the work done to develop a correlation between the nanoindentation data and conventional mechanical property measurements. The model alloys used in this study are described in Table 1. They have been used by the University of California, Santa Barbara (UCSB) in neutron irradiation experiments [4] and by AEA Technologies (AEAT) in thermal aging studies [5]. The AEAT heat treatment was similar to that listed in Table 1, 16 hours at 770˚C, but their material was water quenched [5,6]. The asreceived microstructure of the alloys was characterized by TEM, and an extensive description of the observations was published in Ref. [7]. COMPARISON OF VICKERS HARDNESS AND YIELD STRENGTH Experiments were conducted using the model ferritic alloys and two commercial alloys to provide a ba
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