Dynamic nanoindentation testing: is there an influence on a material’s hardness?

Figures & data

Table 1. Investigated material selection, covering face-centered cubic (FCC), body-centered cubic (BCC) and hexagonal closed packed (HCP) metals as well as FQ, GC and GaAs.

Material	Lattice type	Microstructure	Young’s modulus, E (GPa)	Strain-rate sensitivity (m)
Au	FCC	SX (1 0 0)	75 ± 1	0.008 ± 0.001
Au	FCC	UFG 250 nm	79 ± 2	0.017 ± 0.002
Cu	FCC	SX (1 1 1)	121 ± 2	0.005 ± 0.001
Ni	FCC	SX (1 0 0)	196 ± 2	0.003 ± 0.002
Ni	FCC	NC 30 nm	205 ± 2	0.021 ± 0.001
V	BCC	UFG 200 nm	144 ± 1	0.013 ± 0.001
Ta	BCC	SX (1 0 0)	169 ± 1	0.045 ± 0.005
Fe	BCC	CG 100 µm	195 ± 2	0.015 ± 0.001
Cr	BCC	SX (1 0 0)	293 ± 5	0.050 ± 0.003
Cr	BCC	UFG 300 nm	291 ± 2	0.013 ± 0.001
W	BCC	SX (1 0 0)	397 ± 7	0.030 ± 0.002
W	BCC	UFG 890 nm	407 ± 9	0.024 ± 0.002
Zr	HCP	CG 45 µm	109 ± 1	0.026 ± 0.003
Zr	HCP	UFG	127 ± 2	0.024 ± 0.002
Ti	HCP	CG 55 µm	125 ± 1	0.025 ± 0.003
Ti	HCP	UFG	192 ± 3	0.014 ± 0.002
GaAs	Zinc blende	SX	114 ± 1	0.043 ± 0.003
Glassy C	–	amorphous	34 ± 1	0.014 ± 0.002
FQ	–	amorphous	72 ± 1	0.010 ± 0.001

Note: The Young’s moduli were obtained from CSM measurements, and m values from nanoindentation jump tests. UFG Zr contains omega phase.

Figure 1. Comparison of hardness—displacement profiles for (a) Ni SX and (b) Cr SX for tests with and without CSM. Evidently, the different techniques result in significantly different H levels for Cr SX but not for Ni SX.

Figure 2. Load—displacement curves of LC (multiple unloading) and CSM measurements on Ni SX and Cr SX demonstrate that the hardness difference originates from the dwell segments of the LC tests (see the insets), while the plastic loading curves match up well.

Figure 3. Development of the actual indentation strain-rate defined as , in contrast to the approximate solution for a hold segment of a quasi-static indentation experiment. Evidently, the approximate solution breaks down during constant load regimes.

Figure 4. (a)–(c) Strain-rate profiles of three common nanoindentation techniques for Cr SX. The red circles indicate the range that can be used to obtain mechanical properties by the Oliver and Pharr analysis. Note that for dynamic (CSM) testing (c) the anticipated strain-rate is achieved, while for static (LC) tests (a, b) it differs by one order of magnitude.

Figure 5. (a) Experimental and theoretical hardness difference as expected from Equation (3) between static and dynamic tests in dependence of the strain-rate sensitivity. (b) Low strain-rate CSM experiments confirm that the hardness difference is mainly rooted in differing strain-rates used to determine the hardness.