Size Effect Analysis and Experimental Study of Microhardness Indentation of Metal Materials

The micro Vickers hardness of DT4A, 97NiBe and electroless Ni-P coating was tested by microhardness test and SEM. A model was established from the fitting curve by drawing the relationship between load and indentation diagonal line length. Based on the theory of material mechanics, the physical meaning of each parameter was determined in the model. According to the physical meaning of the parameters, the reason for the indentation size effect at micro-nano scale was explained. The results show that the microhardness indentation size effect of metal materials is remarkable. The corrected models are P_0 = a_1d + a_2d^2 and \rmH\rmV_\rmmicro = 0.189\;1 \times (\dfraca_1d + a_2). These models can well describe and explain the indentation size effect. The physical meaning of parameter a₀ is a physical quantity to accurately reflect the load error of the equipment in the uncorrected model. The physical meaning of parameter a₁ is a physical quantity related to elastic modulus, contact stiffness, microhardness and macrohardness. The physical meaning of parameter a₂ is a compression stress required for the indenter to be pressed into specimen surface to form plastic deformation during test loading. It is approximately 5.288 times the macro hardness value. The change of contact stiffness of indentation surface is a main reason for the indentation size effect. The contact stiffness calculation model of hardness indentation surface was worked out: S = 7Ed - 7a_1.