A method for measuring the contact area in instrumented indentation testing by tip scanning probe microscopy imaging

Abstract

International audienceThe determination of the contact area is a key step to derive mechanical properties such as hardness or an elastic modulus by instrumented indentation testing. Two families of procedures are dedicated to extracting this area: on the one hand, post mortem measurements that require residual imprint imaging, and on the other hand, direct methods that only rely on the load vs. the penetration depth curve. With the development of built-in scanning probe microscopy imaging capabilities such as atomic force microscopy and indentation tip scanning probe microscopy, last generation indentation devices have made systematic residual imprint imaging much faster and more reliable. In this paper, a new post mortem method is introduced and further compared to three existing classical direct methods by means of a numerical and experimental benchmark covering a large range of materials. It is shown that the new method systematically leads to lower error levels regardless of the type of material. Pros and cons of the new method vs. direct methods are also discussed, demonstrating its efficiency in easily extracting mechanical properties with an enhanced confidence

Decrease of Nano-hardness at Ultra-low Indentation Depths in Copper Single Crystal

“…Therefore, it lies below the level of an undeformed surface and its shape corresponds to the well known behaviour of fused silica. Similar shape of the contact boundary for fused silica was detected with use of the post-mortem method proposed in [24]. The measurement of residual imprints to estimate the contact area was advised also in [39].…”

“…The methods applied to estimate the contact area can be classified into two subcategories [24]: direct methods where the load-penetration curve is used and post-mortem methods that rely on data extracted from the residual imprint. The direct methods are widely used in the instrumented nanoindentation as they do not need the time-consuming residual imprints measurements.…”

“…In particular, the measurement of the contact area is used to verify the results of direct methods. For instance, in [24] the methodology was proposed that bases on the analysis of profiles extracted from an AFM image to specify the contact boundary of a Berkovich tip in different materials. The residual imprints generated in numerical benchmark (a conical tip) and experimental benchmark (a Berkovich tip) were investigated and a good accuracy of the proposed methodology was shown.…”

Влияние Малоамплитудных Осцилляций Нагрузки На Наноконтактные Характеристики Материалов В Процессе Наноиндентирования

“…Площадь проекции отпечатков измерялась прямым методом обработки изображений отпечатков, получен-ных с помощью АFМ в полуконтактном режиме [36]. По этим данным была рассчитана твердость для z = 0, которая сравнивалась с рассчитанной на основе OPM.…”

“…Площадь остаточных отпечатков, рассчитанная независимым методом для z = 0 и 1 nm, т. е. прямым измерением площади отпечатков на основе изображе-ний, даваемых АFМ [36], не показывает существенного различия в микро-и нанодиапазонах глубин (от 100 до 2000 nm).…”