NanoTest System - Four Publications Highlighting Unique Capabilities of NanoTest System from Micro Materials

Topics Covered

Capabilities Offered by Micro Materials NanoTest System
Micropillar Compression of Ceramics at Elevated Temperatures
Probing Mechanical Properties of Fully Hydrated Gels and Biological Tissues
Investigation into the Effect of Film Thickness on Nanowear with Amorphous Carbon-Based Coatings
Coating Optimisation for High Speed Machining with Advanced Nanomechanical Test Methods


Micro Materials Ltd are based in Wrexham, UK, which is located approximately one hour from the cities of Manchester and Liverpool.

Micro Materials provide innovative, versatile nanomechanical test instrumentation, and respond to developments in applications in response to customer and market requirements. The integrity, reliability and accuracy of our equipment is paramount, as is our relationship with our users.

Capabilities Offered by Micro Materials NanoTest System

The wide range of capability offered by the Micro Materials NanoTest system means that the system is active in a wide range of application areas. The following are examples of recent work published by the Micro Materials user base.

Micropillar Compression of Ceramics at Elevated Temperatures

This papera describes micropillar compression tests carried out using a flat punch indenter mounted on an MML NanoTest system. Tests were carried out on MgAl2O4 spinel, at a range of temperatures from room temperature to 400°C. The spinel deformed plastically at 200°C and above without a confining pressure. The yield stresses measured were consistent with those obtained elsewhere by compressing larger crystals under a high confining pressure, suggesting that micropillar compression has the potential to be a useful technique for studying plastic flow in brittle materials.

Compression of such micropillars requires an extremely stable system. The NanoTest ensured this stability at high temperature by using heaters in both the sample stage and diamond tip. This minimises thermal drift, thereby allowing micro-compression tests to be carried out at reasonably low strain rates.

Figure 1. Pillar after focused ion beam milling prior to deformation, viewed at an angle of 52°

The authors state 'Both sample and tip heaters are required to minimize thermal drift ... In both cases the rate was constant over the 20s period. The values obtained were 0.15 and 0.20 nm s-1 at 200 and 400°C respectively.'

The MML NanoTest system uses a unique horizontal loading mechanism, meaning electronics and measurement hardware are free from the influence of heat convection. This, combined with the separate heating of both sample and indenter, ensure makes the NanoTest stand out as the only option for high temperature measurements. PID loop control of both indenter and sample heating ensure excellent temperature stability, thus long duration creep tests.

aMicropillar compression of ceramics at elevated temperatures. Sandra Korte and W.J. Clegg Scripta Materialia 60 (2009) 807-810.

Probing Mechanical Properties of Fully Hydrated Gels and Biological Tissues

This innovative paperb from NanoTest users at MIT details the work they have done in conjunction with Dr Jim Smith of Micro Materials to validate a liquid cell which enables nano- to micro-scale indentation of fully immersed, hydrated polymers and tissues. This is done while maintaining the high precision force and displacement signals normally acquired with the NanoTest.

The group state, 'We anticipate that the platform will enable quantitative studies of tissue mechanics as a function of source, disease state, and exposure to soluble toxins or adjuvants, particularly as a function of submicrometer position within the tissue'

A range of hydrated gels and biological tissues were investigated using the cell, and the accuracy of measurement was validated using viscoelastoplastic analysis of relatively stiff, water-insensitive materials.

Figure 2. NanoTest configured for indentation in liquid, obviating vertical loading effects such as buoyancy and surface tension.

The authors highlight the advantages of the NanoTest's horizontal-loading configuration (shown above) which, in the words of the authors, 'Confers significant advantages for indentation in liquids, obviating vertical-loading effects due to variation in buoyancy and surface tension during vertical indenter displacement through liquid. In absolute terms such forces are quite small, but can be significant for the nanoscale forces and/or displacements relevant to compliant hydrogels (Kaufman et al., 2008) or tissues.'

The work demonstrates clearly that the NanoTest has the required sensitivity and repeatability to measure elastic properties of synthetic gels/biological tissues in a liquid environment.

bProbing mechanical properties of fully hydrated gels and biological tissues. Georgios Constantinides, Z. Ilke Kalcioglu, Meredith McFarland, James F. Smith, Krystyn J. VanVliet, Journal of Biomechanics 41 (2008) 3285-3289

Investigation into the Effect of Film Thickness on Nanowear with Amorphous Carbon-Based Coatings

NanoTest users at Aston University used the newly developed 'nanofretting' capability to perform nanoscale wear testing on a series of sputtered Cr doped amorphous C films.

The authors explain the background behind their workc as follows 'It is expected that carbon-based coatings may provide solutions to tribology issues associated with micro-scale devices involving moving mechanical arrays (MMAs), such as MEMS and other microscale engineering systems, due to the high hardness, high elastic modulus and chemical inertness of the films. These types of applications will require a low friction/wear carbon-based film of just a few nm or tens of nm thickness, operating under conditions of low contact pressure, low contact area, with small displacements.' These low pressure, low contact area conditions are perfectly replicated using the Micro Materials nanofretting option.

The authors expand further to state 'It was shown that mean contact pressures, contact radii and displacements relevant to MEMS and micro-scale engineering devices could be achieved over hundreds of thousands of oscillation cycles using a spherical ruby counter-body. Contact pressures of 60-2200MPa; contact radii of 2-7µm and displacements of 2-14µm were employed in this initial investigation.'

The results section state 'There was a clear exponential reduction of specific wear rate with reducing film thickness over the range of 2000-10 nm.' The authors state that 'such a clear relationship with quantified wear data as shown here has not previously been reported under conditions relevant to MEMS devices.' Furthermore 'a rapid reduction of specific wear rate (defined as volume of worn material per unit applied load per unit of slid distance) was observed during the first 3000 oscillation cycles. This was analogous to the 'running in' process observed with macroscopic tribology systems.'

Figure 3. Exponential reduction of specific wear rate with reducing film thickness over the range of 2000 - 10 nm.

Micro Materials offer a newly developed nanofretting option, which allows oscillation of sample whilst applying a known load. The user can vary both the frequency and amplitude of sample oscillation. The extremely low thermal drift experienced by the NanoTest allows long duration wear tests such as these to be carried out with no need for drift corrections. Various experiments may be scheduled to run automatically, ensuring best use of system time.

cAn investigation into the effect of film thickness on nanowear with amorphous carbon-based coatings. G.M. Wilson and J.L. Sullivan, Aston University, Wear 266 (2009) 1039-1043

Coating Optimisation for High Speed Machining with Advanced Nanomechanical Test Methods

This paperd describes how advanced nanomechanical testing has been used to evaluate key factors influencing tool life. These tests include: (1) a plasticity index at room and elevated temperature (2) high temperature indentation (3) fatigue fracture resistance

Results presented show that elevated temperature nanoindentation showed decreasing hardness and increasing plasticity index with temperature. In high-speed turning hot hardness is the dominant factor, whilst for interrupted cutting high hot hardness should be combined with improved plasticity for longer tool life. A novel test technique nano-impact, which is patented to Micro Materials, was used to simulate the interrupted contact.

Elevated temperature mechanical properties were determined from nanoindentation to 25-60 mN at 20-500°C.

From a combination of nanoindentation measurements and cutting tool tests on >3 µm hard PVD coatings on WC-Co substrates the authors showed a correlation between the plasticity index and tool life for the coatings studied. Furthermore, the elevated temperature data acquired revealed a range of coating mechanical behaviour at temperature that shows correlation with tool life.

Nano-impact, a novel test technique was used to simulate the interrupted contact (and cyclic loading) conditions occurring in milling applications and evaluate the fatigue fracture resistance of coated tools. It was reported that tests (at both room and elevated temperature) show correlation with tool life in end and face milling.

Figure 4. Clear correlation between end milling tests (top) with nano impact results (bottom) is shown.

The authors conclude 'the results from the various advanced nanomechanical tests ... can provide compelling data that correlate with tool life. With care, the techniques described can be used to aid reliable prediction of which coatings have longer life in severe cutting conditions.'

Elevated temperature nanoindentation can be carried out with excellent levels of system stability, due to the fact that both indenter and sample are heated to ensure isothermal contact. This work involved use of the unique NanoTest nano-impact technique, which is subject to an MML patent. These two unique capabilities can be combined to allow the user to carry out elevated temperature nano-impact.

dCoating optimisation for high speed machining with advanced nanomechanical test methods. B.D Beake, G.S. Fox-Rabinovich, S.C. Veldhuis, S.R. Goodes, Surface & Coatings Technology, 203 (2009) 1919-1925

About Micro Materials

Established in 1988, Micro Materials Ltd are manufacturers of the innovative NanoTest system, which offers unique nanomechanical test capability to materials researchers for the characterisation and optimisation of thin films, coatings and bulk materials. The current model, the NanoTest Vantage was launched on June 1st 2011.

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