Experimental Procedure

Sample Preparation

Prepare a flat and smooth specimen surface by grinding and polishing to a mirror finish. Remove dust, oxides, or contaminants to ensure reliable contact between the indenter and the material. A smooth surface minimizes measurement errors in depth and contact area.

Instrument Setup and Calibration

Switch on the nanoindenter and allow thermal stabilization. Calibrate the load frame and displacement sensor. Determine the indenter area function using a standard reference material (e.g., fused silica) to account for tip rounding and geometric imperfections.

Indentation Parameters Selection

Select the maximum load (or depth), loading rate, hold time. Ensure that the chosen load produces indentation depths less than ~10% of the sample thickness (for coatings) to avoid substrate influence.

Indentation Testing

Perform multiple indentations at different locations on the surface. Maintain sufficient spacing between indents (at least 3–5 times the indentation size) to prevent overlap of plastic zones. During each test, continuously record load P and penetration depth h to obtain the load–displacement (P–h) curve.

Data Extraction

From each unloading curve, determine the initial unloading stiffness S. Calculate the contact depth h_c, projected contact area A_c, hardness H = P_max/A_c, and reduced modulus E_r. Use the elastic relation to compute the specimen’s elastic modulus E.

Repeatability and Averaging

Repeat the test for several indents (typically 8–10) and compute the average hardness and modulus values with standard deviation to ensure consistency.

Wear Resistance Correlation

Using the measured properties, calculate the ratios H/E and H³/E².