Nano indenter g200

Commercial duplex stainless steel produced by Baoshan Iron and Steel Co., Ltd., Shanghai, China was used as the study object. A 20 × 20 × 8 mm duplex stainless steel sample with clear grain boundaries was obtained by hand grinding, mechanical polishing, and slight electrolytic etching in a 20% NaOH solution. Then, the sample was observed under an optical microscope. The nanoindentation tests were conducted on a Nano Indenter G200 (Agilent Technologies, Santa Clara, CA, USA), with the XP Berkovich indenter selected. The experimental temperature was 25 °C. Six unidirectional indentation experiments were performed on austenite and ferrite in the region away from the grain boundaries using a displacement-controlled mode with a peak displacement of 1500 nm and a thermal drift of 0.05 nm/s.

SEM images were acquired by using a field emission SEM (JSM-7500F, JEOL), and the samples needed to be coated with a gold film (a thickness of ~3–5 nm) beforehand. The optical microscopy images were obtained using a Motic BA400 microscope equipped with a charge coupled device camera. The pH of the solutions was calibrated by using a precision pH meter PHS-25 (INESA) with a resolution of 0.01. The Young’s modulus of the SU-8 microstructures was measured by using an Agilent Nano Indenter G200 equipped with an XP-style actuator, and the continuous stiffness measurement method was adopted. The measurement was carried out using a Berkovich diamond tip at 30 °C with a relative humidity of 20%.

The instrument used in this experiment is the Nano Indenter G200 nano-indentation instrument (Agilent, Santa Clara, CA, USA) for indentation experiments. Before the experiment, the samples were taken out of the freezer and thawed in a water bath at 37 °C. In order to prevent the sample from moving during the experiment, the samples were placed in a fixed bottom column and bonded. In this experiment, a cylindrical indenter was selected, and the radius (R) of the indenter was 100 μm. The areas with PDL thickness greater than 0.2 mm were found under the microscope for experimenting, and five experiment points were selected for each region.
The schematic diagram of the nano-indentation mechanical experiment of the cylindrical indenter is shown in Figure 2. The loading rate of the experiment was set to 0.5 mN·s⁻¹, the peak load was 3 mN, and the holding time was 200 s [32 (link)]. Then, unloading was performed. Finally, the obtained data were derived to obtain the load-indentation depth curves and the displacement-time curves. The displacement-time curves were divided by the PDL thickness to obtain the PDL strain-time curves.

Mechanical properties of stainless-steel substrates with and without deposited TO films were studied by nanoindentation technique (NanoIndenter G200, Agilent Technologies, USA). Continuous stiffness measurements mode was used to determine elastic modulus and hardness of the TO-deposited porous films. The nanoindenter was equipped with a Berkovich three-sided diamond pyramid indenter with centerline-to-face angle of 65.3° and a 17.8 nm radius at the tip of the indenter. The nanoindentation was carried out using a constant indentation strain rate of 0.05 s⁻¹, continuous stiffness measurements amplitude was 2 nm with a frequency of 75 Hz and indent depth of 300 nm. The device is equipped with an optical microscope. Series of 15–25 indents were made for each sample probe, to obtain a better statistics as well as to cover large surface area. Distance between every measured point was 100 μm.

Prior to nanoindentation, the Y-42° plane of a commercial LiTaO₃ single crystal wafer was carefully polished to a mirror surface. The surface morphology was detected by optical profiler (Newview 800, Zygo, Middlefield, CT, USA), as exhibited in Figure 1. Surface defects like tiny scratches or embedment of abrasives could not be observed on the polished surface. In addition, the surface roughness was about 1.1 nm on the area of 0.832 × 0.832 mm². Nanoindentation load-holding tests were performed on Agilent Nano Indenter G200 (USA) at an ambient temperature of 23 °C by air conditioning. All the mechanical measurements were compliant with ISO 14577. The effective spherical tip radius was estimated by calibrating the standard fused silica. The loading rate and holding time were fixed to 2 mN/s and 500 s, respectively. The peak loads ranged from 1 to 20 mN for 0.76 μm tip, 2.5 to 50 mN for 2.95 μm tip and 25 to 450 mN for 9.8 μm tips, respectively. To minimize the thermal drift influence, all the holding tests were carried out until thermal drift decreased to 0.03 nm/s. Meanwhile, drift correction which was calibrated at 10% of the maximum load during the unloading process, was strictly performed. To ensure the reliability of the creep results, more than eighteen nanoindentation measurements were conducted for each test.