Effect of Macro, Micro and Nano Loads on The Indentation Behavior of Ti-6Al-4V and Haynes 242 Alloys

Abstract

Indentation tests were conducted on Ti-6Al-4V and Haynes 242 alloys at macro, micro and nano load range using conventional and depth-sensing indentation instruments to study the load effects on the mechanical behaviour of the alloys. With the increase of indentation loads from macro to nano, a decrease in Young’s modulus and indentation hardness values was observed as a result of the indentation size effect in the alloys. During the loading procedure in macro, micro and nano indentations, the loading curves progressively moved upwards, showing the increase in resistance of the alloys with the increase in indentation load. Compared the depth-sensing instrumented indentation hardness of alloys with the conventional indentation hardness at micro loads, the magnitude of the depth-sensing instrumented indentation hardness is 10-25% greater than the conventional indentation hardness. The reason for this variation is explained as the depth-sensing instrumented indentation hardness is calculated at maximum load with the projected contact residual impression area, A_c, instead of the residual indenter impression projected area, A_r. So the indent pileup and sink-in play a major difference between the depth-sensing instrumented hardness and conventional indentation hardness. The outcome of the experimental work clearly indicates that for evaluation of the hardness usage of projected contact residual impression area provides more accurate results than when residual indenter impression projected area is used. The concept is synonmous to evaluation of engineering stress / strain and true stress / strain using original and actual cross sectional area respectively.