What nanoindentation measures
Hardness and stiffness decide how a surface resists contact damage, scratching and wear. Conventional hardness testers measure the size of an indent under a microscope, which limits them to indents large enough to see and to hardness alone. A nanoindenter records the depth of the indent throughout the test, so it can measure films a fraction of a micrometre thick, single grains and phases, polymers and biological tissue, and return elastic modulus and time-dependent behaviour from the same indent.
How nanoindentation works
- The tip approaches the surface and detects contact.
- The load increases to a set maximum at a controlled rate while depth is recorded.
- The load is held, often to let creep settle, then removed while depth is still recorded.
- The unloading curve gives the contact stiffness and contact depth. With the indenter’s area function, they give hardness and elastic modulus (the Oliver & Pharr method in ISO 14577 and ASTM E2546).
Repeating this over a grid gives a property map; holding the load gives creep; oscillating it gives storage and loss modulus.
What to look for in a nanoindentation tester
- Direct load measurement. NANOVEA modules apply the load vertically with a piezoelectric actuator and measure it with an independent load cell, in a closed loop with a capacitive depth sensor. The load is measured, not inferred, and there is no cantilever or pivot.
- Resolution and noise at the bottom of the range. On the most sensitive range, the nano module resolves 0.006 µN and 0.003 nm (24-bit), with noise floors of 0.5 µN and 0.04 nm.
- Load range. Ranges of 80, 400, 1800 and 4800 mN cover soft gels to hard coatings; adding the micro module extends the same system to 400 N.
- Tip calibration. The Single Indent Area Function (European Patent No. 3076153) calibrates the tip area and gives a quantifiable quality check of the indenter.
- Positioning and imaging. Stage accuracy below 0.2 µm, a video microscope up to 100x, and on the PB1000 an integrated AFM or 3D profiler to image the residual indent.
- Throughput. FastMap places 100 indents in 5 minutes; automated multi-sample testing handles samples of different heights.
Indenter geometry
The tip determines the stress field under the indent. Berkovich is the standard nanoindentation tip; Vickers gives values comparable with microhardness testing and resists high loads; Knoop is elongated, for thin layers and directional differences in hardness, such as in fibre composites. Cube corner cracks brittle materials at low loads for fracture toughness. Conico-spherical tips suit soft metals, plastics and porous materials. Flat punches crush particles and measure yield strength, and knife tips test failure of cylindrical parts such as fibres.
Beyond hardness
The same load–depth measurement supports a wide set of tests: creep and relaxation of polymers and gels, nanoindentation DMA from 0.1 to 100 Hz with frequency and temperature sweeps, fracture toughness of glass and ceramics, stress–strain from spherical and cyclic indentation, and yield strength and fatigue with flat punches. On the same module, scratch tests measure coating adhesion.
Testing in service conditions
Many materials change with temperature and moisture, polymers above all. NANOVEA’s humidity-controlled study measured a polymer film’s hardness falling from about 0.60 GPa at 25% relative humidity to 0.31 GPa at 75%. The nano module runs in high-temperature, low-temperature, humidity and liquid modules, and in vacuum systems, so properties can be measured where the material works.
