From Nanoindentation to Microhardness to Tensile Strength: Correlation Coefficients Estimates as a Function of Microstructure in Eutectic SnBi Alloy

Abstract

Determining strength to hardness correlation coefficients on nano and microscale in correspondence to microstructure and composition leads the way to inexpensive, non-destructive ways to predict tensile strength of bulk materials, which is important for developing preventive maintenance procedures in a variety of industries. Nanohardness and microhardness tests were performed on an in-house prepared eutectic SnBi alloy. Elemental composition and eutectic morphology were verified by scanning electron microscopy and energy dispersive spectroscopy. The linear correlation coefficient, C₁ = H_IT/H_v, between nanoindentation hardness and Vickers microhardness was determined based on experimental measurements. A value of C₁ > 1.25 was obtained, exceeding the expected value for polycrystalline alloys C₁ = 1.25. The Tabor factor, k = H_v/σ at 8% strain, is well known to be about 3 for polycrystalline alloys. However, for the eutectic alloy, the estimated Tabor factor was consistently greater than 3. The stronger correlation in both cases suggests the presence of an unaccounted factor contributing to both C₁ and k. Comparison to coefficients estimated from data available for other alloy systems is discussed.