MML European User Meeting 2007 - A Review

The 2007 MML European User Meeting was held in Fondettes, near the historic city of Tours, France on October 25th 2007.

  The Mayor of Fondettes welcomed over fifty NanoTest users from all corners of Europe to his town, and made all feel very welcome.

                                                               Download the Final Programme

 Review of the Scientific Programme

 The first session of the day was chaired by Prof. Bill Clyne of The Gordon Laboratory, Cambridge University.

  First speaker was Professor Mohan Ranganathan, an invited speaker from the University of Tours, who spoke about the selection of wear resistant coatings on low carbon steel. Prof Ranganathan showed the work his group carried out using a combination of nanoindentation, microwear and POD experiments were used to identify the optimum WC/C-based coating for an automotive application. 

  Prof Ranganathan was followed by Dr Dariusz Bielinski, an invited speaker from the Technical University of Lodz, Poland. Dr Bielinski gave a fascinating talk on the use of nanoindentation to monitor the ageing of polymer materials. At present the lack of reliable durability data on polymeric materials is a factor limiting their greater use, which currently stands at around 6-7% of the engineering component market. Dr Bielinski and his group have used hardness profiles and creep characteristics of surface layers of polymers and rubbers (CB/NR vulcanates, thermoplastic urethanes and elastomers, nanocomposites etc.) in order to investigate the effect of aging due to ion beam modifications, ozone and thermal degradation.  

Dr Alessandro Patelli, an invited speaker from CIVEN Nanofab, Venice, spoke on the use of nanoindentation and microscratch in industrial coating research at CIVEN, a new research centre close to Venice devoted to technological transfer of nanotechnologies to industry. The talk featured an overview of the different coatings (including decorative, protective, hardening, self lubricating and anti-sticking coatings) produced at CIVEN and their mechanical characterisation. The talk was an excellent example of how the combination of nanoindentation and microscratch can directly improve industrial processes. In particular Dr Patelli showed how the addition of nanoparticles to SiOx coatings can have a dramatic improvement in the fracture resistance of the glassy coating.

Session 2 of the day was chaired by Dr Bill Clegg, of the Gordon Laboratory, Cambridge University.

 Dr Sylvie Poissonnet of CEA Saclay, began session 2 with a discussion on nanoindentation studies of zirconium alloy during which Dr Poissonnet studied the influence of the oxygen content and of the cooling rate. Phase transformations of low-tin zircaloy-4, beta to alpha phase, were studied at CEA using a combination of nanoindentation together with Electron Probe Micro Analysis (EPMA) to established oxygen concentration. Dr Poissonnet described how homogeneous samples with various oxygen contents were produced and correlations between hardness and oxygen content were derived. Then, the group made a systematic study of the beta to alpha phase progress upon cooling at 1°C/s before final quenching. It was found that fluctuations of oxygen and associated local hardening depend on the final quenching temperature. 

 Mr Vitor Marques of Oxford University presented his work on the elevated temperature nanoindentation of lead free solders for aerospace applications. Mr Marques explained that although the aerospace industry was exempt from current EU regulations on lead-free solders until 2010, the issues will become design-critical at that point so research is already being carried out. He explained how intermetallics of Cu₃Sn and Cu₆Sn₅ form, and reflow processes promote their growth and are accompanied by voiding. He used indentation mapping (2000 indent grid) to precisely map the phase distribution across the complex solder joints. For his work on elevated temperature mechanical properties Mr Marques has used thin Pt layers (~ 5nm thick) to avoid oxidation whilst being able to perform indentations at 400-1000 nm depth as a function of temperature over the range 25-175C. Indentation creep curves were then used to determine creep exponents. 

Mr Jeff Wheeler of the Gordon Laboratory, Cambridge University, spoke on the recent advances which have been made at the Gordon Laboratory in nanoscale impact and scratch testing with the NanoTest. It was clear that the Gordon lab has made much progress in understanding the deformation of materials under impact loading in both high and low sampling rate testing. Mr Wheeler described how the basic understanding of single impacts has been extended using high sampling rate testing, and the fatigue/wear response of coatings on Aluminum and Titanium alloys has been characterised using low sampling rate testing. Complementary work was conducted using scratch techniques on the same coating systems, and the correlation of these two techniques to conventional wear testing was described. In most cases an excellent correlation was observed. 

Dr Ben Beake (Micro Materials Ltd) spoke about the evaluation of nanomechanical test approaches towards PVD coating optimisation for high speed machining of steel.

 This work featured a discussion on how the Plasticity Index (PI) can be used to predict the life of coated WC-Co tools with hard PVD coatings in various mechanical contact conditions such as high speed interrupted cutting (turning and milling). Dr Beake described how a correlation between the optimal value of this index and the severity of the cutting conditions was observed implying that the PI determined from nanoindentation can be used as a first approximation in determining whether or not a PVD coating could have the desirable mix of mechanical properties for a given cutting application. However, in tool operation increased plasticity (higher PI) is accompanied by several other factors, which may or may not be beneficial and the influence of these on tool life is discussed. Some limitations of the plasticity index as a sole predictor of coating performance can be addressed by performing additional novel nanomechanical tests, such as micro and nanowear, elevated temperature nanoindentation and nano -impact. Their regimes of usefulness for simulation and prediction of coating performance were discussed in the second part of the talk.   Nano-impact was shown to correctly rank coatings in terms of tool life in end milling and reproduce the shapes of the tool wear vs. cutting time traces. Elevated temperature nanoindentation results on tool coatings revealed that the PI increases with temperature, particularly when a loss of coating stability occurs in addition to thermally activated dislocations. In elevated temperature nano-impact tests, the probability and extent of fracture decreased markedly as temperature increases, consistent with the higher PI. Dr Beake showed how the results can be used to predict which coatings have longer life in interrupted cutting conditions. 

The first session after lunch was chaired by Prof Mohan Ranganathan, of Universite Francois Rabelais, Tours.

 First speaker was Dr Bill Clegg of the Gordon Laboratory, Cambridge University, who gave a very lively discussion on the deformation seen under indents in elemental semiconductor materials which undergo phase transformations from the diamond structure to the beta-tin phase. Dr Clegg showed conclusively that the close agreement between the phase transformation pressure and the measured indentation hardness in Si and Ge was due to the very low yield strength of the transformed phase. 

 Dr Stephane Jouannigot of LCTS, Bordeaux, France, spoke on the novel use of the NanoTest for push-out tests, in order to evaluate the fibre/matrix interfacial properties of carbon-carbon composites.  Single-fiber push-out tests were performed on two carbon-carbon composite materials. A testing procedure was established to obtain very thin samples which were strong enough to be manipulated safely. The samples were observed using optical microscopy and scanning electron microscopy to check that the fibers were correctly loaded and that the fibers and the matrix were not damaged during the tests. Dr Jouannigot presented results from two Carbon/Carbon composites: a reference sample with as-received fibers and a treated one with increased fiber/matrix bonds. The untreated sample exhibited some protruding fibers due to failure of the fibre/matrix bond during sample preparation and relaxation of the thermally induced stresses. Push-back-like tests were thus conducted on the protruding fibers. The analysis of the push-out test results allows the intensity of the fiber/matrix bond to be evaluated and the composites to be compared. 

 Ms. Laura Mera Álvarez from AIMEN, Spain spoke on the nanohardness assessment of salt bath nitrided layers. In Laura’s recent work, nanoindentation measurements were used in order to reveal the optimum nitriding time for the sursulf process of an AISI H13 tool steel. Rows of nanoindentations were performed over 11 samples nitrided under the same salt bath conditions where only the nitriding time was varied from 1 to 24 hours. The results were correlated and compared with microhardness measurements, and the microstructure of the nitrided H13 tool steel was evaluated by means of SEM observations. Features such as porosity and inhomogeneities of the nitrided layers seem to be hidden within the microhardness results. However, variations within the nanohardness profile were found to be a function of the microstructural variability. Thus, nanohardness results revealed the good reliability of the nanoindentation technique as a tool to asses material’s characteristics. On the other hand, nitriding times about 6 or 7 hours lead to the best hardness profiles due to the high hardness present in the nearest-surface region and the homogeneous microstructures formed. Lower nitriding times did not achieve the hardness and nitrided layer thickness required, while higher nitriding times did lead to the creation of soft microstructures associated to a scattered hardness profile.

The final session of the day was chaired by Dr Ben Beake, Micro Materials Ltd.

 The first speaker in this session was Mr. Jorge Nunes from Coimbra University, Portugal. Jorge presented the work he has been carrying out on the mechanical properties of functionally graded nanocomposite thin films of PTFE/316L produced by a sputtering process. The films show great promise for nitinol stent applications and Jorge combined his nanoindentation experiments with a wide range of other tests.

 Mr. Damien Joly of CEROC/University of Tours then presented two separate studies both showing how the NanoTest at Ceroc has been invaluable in solving industrial problems in the automotive industry. The first of these looked at how to characterize ageing phenomena in grey cast iron and the second considered using elevated temperature nanoindentation in combination with in-situ microscopic location of steel inclusions to map their hardness at high temperature.

 Finally Sandra Korte of the Gordon Laboratory, Cambridge University presented her work on the nanoindentation of In_xGa_1-xAs. The deformation behaviour of InGaAs over the full compositional range from GaAs to InAs was described in detail. Ms. Korte showed that existing data on a range of systems suggest a maximum in the yield stress or measured hardness occurs at some intermediate composition, for instance in ZnBeSe. In recent studies on InGaAs, a dependence of mechanical properties on composition has only been carried out in the range of normal dopant concentrations. Here, nanoindentation with different tip geometries was used to investigate the mechanical properties of InGaAs over its full compositional range, going into greater detail to either side of the maximum hardness at x ~ 0.25. Yield stress from spherical indentation, Berkovich hardness and Young modulus were reported for all samples.

 All in all it was a very strong scientific meeting, which was both beneficial and enjoyable for all. Micro Materials Ltd would like to thank all our speakers for sharing the work they have carried out with the NanoTest.