MicroMaterial Vantage Systems

Application areas include Aerospace (thermal barrier coatings); Automotive (hard coated components, paints, brake pads, etc.); Biomedical; Thin Film Coatings (PVD, CVD films); Polymers, Semiconductors, Biomimetic to name a few.

At the University of Southampton the NanoTest Vantage systems have been used to explore mechanical properties of thermal barrier coatings to explore the hierarchical structures of bones, teeth and other complex natural systems.

• Nanomechanical properties of hydroxyapatite like coatings formed by bioactive glasses, arginine and calcium silicate for dentine protection
• The effects of substrate dilution on the microstructure and wear resistance of PTA Cu-Al-Fe aluminium bronze coatings
• Microstructure characterisation of hypereutectoid aluminium bronze composite coating
• Nano-scale wear characterization of CoCrMo biomedical alloys
• The importance of the film structure during self-powered Ibuprofen salicylate drug release from polypyrrole electrodeposited on AZ31 Mg
• Microstructure characterisation of hypereutectoid aluminium bronze composite coating
• Nanomechanical properties of bird feather rachises: exploring naturally occurring fibre reinforced laminar composites
• Pulsed electron beam surface melting of CoCrMo alloy for biomedical applications

The NanoTest Vantage uses electromagnetic force application and capacitive depth measurement to measure the elastic and plastic properties of materials on the nano-scale.

• Indentation testing
• Hardness and modulus mapping
• Depth profiling
• Creep properties
• Wide load range

Hardness and modulus mapping

Rather than targeting specific unique sites, it is often useful to look at the distribution of hardness and modulus across a large area of interest. This can highlight areas of non-uniformity due to structural anomalies, variation in surface treatments or simply changes in properties at joints and boundaries. The stability of the NanoTest Vantage ensures excellent reproducibility of results over the duration of the test period.

Depth profiling load/partial-unload technique

Traditionally indentation was performed at one depth in the material. However, it is often of interest to investigate how hardness and modulus vary from the surface into depth in the sample. The ‘load/partial-unload’ technique included in the NanoTest software allows load cycling which allows hardness and modulus measurements to be made at different depths in the sample in just one indent cycle.

Indentation Creep

In addition to providing reliable measurements of hardness and modulus, excellent system stability enables tests of longer duration, such as indentation creep experiments. These can be used to reliably extract properties such as the stress exponent or creep compliance and, in conjunction with the high temperature module, the activation energy for creep processes.

Nano-impact testing is particularly suitable for high strain rate contact testing. The strain rates of nano-impact testing are typically 100-1000 s ^-1 , much greater than the nano-indentation strain rates of 0.0001 – 0.01 s ^-1

Advantages:

• Single impacts for work hardening, dynamic hardness and yield stress
• Repetitive high strain impacts for fatigue
• Clear identification of cycles to failure
• Rapid, automated determination of S-N curves
• Complements nano-indentation techniques when toughness is important and hardness alone is insufficient

Nano-impact testing was originally designed to assess the toughness and fatigue fracture resistance of thin films and coatings. Nano-impact testing is also able to mimic highly loaded repetitive contact situations. This includes assessing the durability of high speed machining tools for hard to cut aerospace materials and the erosive wear of aerospace engines in normal working environments.

In laboratory studies there is a high degree of correlation between results of nano-impact tests and the performance of coated systems operating in extreme intermittent contact environments

Repetitive contacts are true impact events. The probe repeatedly leaves the surface of the sample and impacts at the same location every time.

Nano-impact testing on the NanoTest Vantage is simple, rapid and flexible. The instrument can be bought with Nano-impact capabilities or an Impact module is available for an existing instrument.

A number of parameters can be controlled to vary the severity of the test and its duration including:

• Probe geometry
• Acceleration distance
• Coil force
• Impact angle
• Number of cycles
• Test frequency

The progression of damage is monitored by recording the position of the impacting diamond probe throughout the test. A cube corner diamond indenter is often used as its geometry induces high contact strain. This high strain is useful for inducing fracture within a short test run.

Thin films and coatings (from a few nm to about 1 µm thick) need to be optimised both in the mechanical properties and tribological performance. Typically, this is done with a combination of indentation and scratch tests. Conventional scratch test conditions are not appropriate for these types of materials as they were developed for testing thicker coatings. Instead the nano-scratch & wear module can provide what is needed.

The sample to be tested is moved perpendicular to the scratch probe whilst the contact is either held constant or ramped at a user-defined rate. Throughout the test the probe penetration depth and tangential (frictional) load are continuously monitored. Single and multi-pass tests are possible.  Multi-pass tests allow the investigation of nano-wear and micro-wear.

In operation, components in a wide variety of applications undergo vibrational wear. Fretting tests are regularly run on the macro-scale in order to examine material behaviour under these conditions. The nano-fretting module allows investigation of fretting and reciprocating wear at the micro/nano scale filling the previous metrology gap.

This capability allows examination of the effect of small oscillatory micro-motion on the durability of complex systems such as hip prostheses where small particles trapped between the ball and socket can slowly damage the contacting surfaces.

• Benefits of the NanoTest fretting module:
• High cycle wear behaviour
• True fretting behaviour on the nano-scale
• Reciprocating sliding wear
• Integrated friction sensing for improved data interpretation
• Flexibility to simulate in-service conditions