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Creating and disseminating novel nanomechanical characterisation techniques and standards

Final Report Summary - NANOINDENT (Creating and disseminating novel nanomechanical characterisation techniques and standards)

Executive summary:

The project NANOINDENT has the aim to gather, improve, catalogue and present characterisation techniques, methods and equipment for nanomechanical testing. European-wide activities coordinated by a virtual centre contributed to a significant improvement of existing nanoindentation metrology and to reveal structure-properties relationship at the nanoscale. These methods are the only tools to characterise nanocomposite, nanolayer and interface mechanical behaviours in the nanometre range. Work laid down a solid base of efforts for defining and preparing new standards to support measurement technology in the field of nanomaterials characterisation. Steps included development of the quasistatic and the dynamic nanoindentation method and its application to new fields, application of modified nanoindenters to new fields as nanoscratching and nanowear measurement and firm and uniform determination of instrumental parameters. The virtual centre disseminated information using the 'Nanocharacterisation database' built on two levels: on a broader level partners built an inventory of nanomechanical materials properties, and, in a narrower circle, they concentrated on exchange of nanomechanical characterisation data gained during the project.

Indirect connections to the stakeholders by the webpage with a build-in interactive database were complemented by direct events, such as participation in 17 workshops and conferences by oral and poster presentations, and 12 regular technical reports in international journals.

These activities lead to detailed descriptions of novel characterisation techniques. The development induced in standardisation and the presented description of good practices will support design of intrinsically safe nanomaterials for wide, successful industrial applications.

Project context and objectives:

Instrumented (nano)indentation has a leading and even more increasing role in determination of mechanical properties of thin films and coatings applied in many branches of science, industrial product development, high tech production and quality control. In general this method (and its close relatives like nano-scratch test) is the only possibility to determine any mechanical parameters of these films and coatings. Although nanoindentation based on the Oliver-Pharr (O&P) method has a considerably long history of nearly two decades, and although a lot of metrological developments were done in this field, the basic concept of nanoindentation does not exceed that of the O&P method which is a solid base to determine the hardness and Young's modulus of the material, but is not suited to widen the application range. European Commission (EC) traditionally supports the metrological development in this field, valuable standardisation and metrological development resulted from the projects founded by EC (see the projects under the acronyms FASTE, REMAST and INDICOAT). To overcome the threshold set by the application of various interpretations of O&P method in different branches of equipment the project aims to give a solid starting point for developing and regulating some metrological problems, for developing measurement standards and extending quantitativity and traceability in new fields of application.

The coordination of work on these fields was divided in several vertical branches, and was based on several round robins, carried out on carefully selected samples and measurement processes developed in course of the project:

1. development of the classical (quasistatic) nanoindentation method and its application to newer fields as thin films an plastics.
2. monitoring the application of dynamic nanoindentation on instruments of different producers.
3. the application of modified nano-indenters to new fields as scratching and wear measurement.
4. firm and uniform determination of instrumental parameters, checking the customer satisfaction.
5. defining new standards in the field of nano-mechanical testing.

These five vertical branches of the work represent the technical Work package (WP)s of the project. Brach 1 and 2 was combined in a common indentation WP, all other branches consisted a separate WP.

These four WPs consists the technical keel of the project and had horizontal connections to each other: the carefully selected samples and testing programs used for the various round robins, the network of round robins itself.

The project had 3 main decision-making milestones:

- The first main milestone was just after the start of the project, a brain storming like kick-off meeting. In this meeting the precise, detailed objectives of each branch of the project, and the first set of project samples was chosen.
- At the same meeting the schedule for investigations (measurements connected to the round robins and evaluation) were fixed for the first half of the project: three, six month long periods were planned for carrying out the quasistatic-indentation, the scratching and the dynamic-indentation round robins on the selected three common samples: fused quartz, sapphire and polycarbonate.
- The results of this period were discussed at the mid-term meeting, the second main milestone in the project, in May 2010 in Berlin and the workplan for the second half of the project was established. In the discussion turned out, that in all three research directions a relevant conclusion could be drawn. These conclusions are listed in the next chapter of this report.
- At this second main milestone, (mid-term meeting in Berlin) some corrections to the original workplan and deliverable schedule was introduced and the and the 'GO' signal for a second round robin on newly defined samples was given.
- The second half of the project was similarly organised as the first, the test were carried out in three periods.
- At the third main milestone of the project, on the final meeting and workshop in Thessaloniki in Jun 2011 the conclusion for the second period and the whole project was drawn. At this point the project's time was practically over and the remaining two months was used for preparing the project reports due in month 36.
- The main output of project NANOINDENT is several ideas for standardisation, some of which are under consideration in some standardisation bodies and some of which serve as the core of a follow-up project in 2012.

Project results:

The project's efforts were divided in four technical WPs, so the results are listed in this system.

Preparation of standard methods of nanoindentation techniques (WP2)

Notwithstanding that the most developed field among the project's themes was quasistatic nanoindentation, important conclusions were drawn in this field.

Deliverable D2.1a1 and D2.1a2 presented the result reached in this WP (WP2) regarding the classic, quasistatic nanoindentation:

- a common exchange data format could enhance data exchange and trough this uniformity and transparency of data evaluation in nanoindentation;
- instrument stiffness and tip area function calibration should be carried out more carefully than it is usual in everyday measurement practice and as it is suggested by instruments user manuals;
- options as variable instrument stiffness and varied form of area function should be considered in evaluation software development;
- the usage of a single evaluation software for evaluation of test data of various instruments resulted in a significant decrease of inaccuracy;
- the usage of two standard samples for determining instrumental stiffness and tip area function resulted in a significant decrease of inaccuracy.

Deliverable D2.1b2 presented the results reached in this WP2 regarding the influence of surface roughness:

- roughness has an effect both on the mean value and data spread of measured hardness and reduced modulus in nanoindentation tests;
- the effect depends both on amplitude and characteristic length of roughness;
- the results are in line with simulation results;
- further work on simulation in the real parameter range is needed (and will follow).

Deliverable D2.2 was dealing with dynamic nanoindentation. In the course of the project turned out, that dynamic test results made by different equipment are less comparable than expected at project proposal, so this task sustained considerable delay (it was postponed from month 18 to month 36). It was found that each interpretation of dynamic nanoindentation is reliable on its own, but the different interpretations are not compatible, and the results are even less compatible with results of macroscopic dynamic mechanical analysis results. This area needs ongoing standardisation work to overcome these problems.

Deliverable D2.3 presented the result reached in WP2 regarding the influence of pile-up and sinking-in:

- a sign was found in the differential hardness versus penetration depth curve for building up a pile-up in course of indentation in form of a characteristic, curved decrease in the graph;
- for the correction of the error caused by the pile-up a method was suggested, which is based on image analysis of Atomic force microscopy (AFM) maps taken from the indents.

Deliverable D2.4 presented the results reached in WP2 regarding the influence of work-hardening: a sign was found in the differential hardness versus penetration depth curve for work-hardening, but this evidence is not strong enough for giving a firm statement. Further test are suggested in this field.

Preparation of standard methods of nano-scratching (WP3)

Deliverable D3.1 and D3.2 presented the result reached in WP3 in the field of nanoscratching and nanowear:

- Newly developed analysis procedure for determining critical pressure - effectively quantifying the scratch hardness - has been successful in quantifying the scratch test;
- In nanoscratch tests it is generally recommended to use spherical probes of the radius of 2-5 micrometre, as smaller probes may be difficult to accurately characterise and are subject to damage when scratching hard samples.
- Conventional, quasistatic, spherical-tip nanoindentation can be used to determine the area function for the scratching probes.
- Scratch hardness at a given applied scratching load on fused silica have all been quantitatively determined for the first time.
- The scratch hardness varies with load at low load, as expected, due to the non-fully-developed plastic zone in the elastic-dominated tests.
- Ramped and constant load tests showed no fundamental difference in the extent of deformation.
- Deformation in low pass repetitive scratching (nanowear) of the sapphire (0001) was much greater than in single progressive load nanoscratch tests. The difference is due to the number of wear cycles and a 3-body wear mechanism is implicated. This finding suggests that nano-wear measurements can provide valuable additional information not present in ramped or constant load single scratches.
- The study of the progressive load, constant load and repetitive nanoscratch testing of the model systems (Fused silica, polycarbonate, 350 nm or 1 300 nm amorphous carbon coated Si, 500 nm and 1 500 nm TiN coated M42 steel) has led to significant progress in determining and clarifying the key test parameters and expected data for input into a best practice guide for nanoscratch testing and subsequent standardisation activity. The best practice guidelines are an annex to D3.2.
- Film thickness and scratch orientation relative to grinding marks were shown to have a large influence on the critical loads obtained in the progressive load nanoscratch test on coated M42 steel samples.
- A contact pressure (scratch hardness) analysis originally developed for very thin films on silicon has been shown to be effective for these 500-1 500 nm TiN coatings on tool steel and 500-1 000 nm Diamond-like carbon (DLC) coatings on Si and has potential for the determination of scratch hardness without recourse to microscopic post-test analysis of scratch tracks.
- Analysis on the soft DLC coatings has shown that the onset of failure may be when the maximum von Mises stress is within the coating or substrate. This influences the critical load and the delamination hardness.
- Additionally, two approaches have been evaluated for determining the interfacial and ploughing contributions to the total measured friction in the nano-scratch test with good agreement between them. The interfacial friction was found to be lowest for the DLC coatings.

Defining standards and good practices (WP4)

The results listed in deliverable D4.1 and other findings of the project found diverse application in the standardisation process of nanoindentation and its related techniques mainly in international standards organisations as European Committee for Standardisation (CEN) and International Organization for Standardisation (ISO).

The project NANOINDENT initiated or contributed to several New Working Item Proposals in the current revision of ISO 14577 (metallic materials - instrumented indentation test for hardness and materials parameter) in technical committee ISO TC 164 / SC 3 (Hardness testing).

Part 1-3 (2002) now under systematic revision in ISO TC164 SC3:

- Resolution No. 210 taken during the 34th ISO TC meeting in Tsukuba (September 2009) mandated Dr Griepentrog (leader of WP5 in NANOINDENT) to collect comments on the Systematic Revision of ISO 14577-1 -2 and -3 by 31 December 2009 and to submit a New Work Item Proposal to SC 3 secretariat by 31st January 2010. SC 3 secretary is mandated to launch then a three month enquiry on the NWIP.
- In 2010 this NWIP got 114 comments and an ad-hoc group was nominated for the revision of ISO 14577. From the 15 group members 5 specialists were experts of a NANOINDENT partner.
- At the last meeting of ISO TC 164 SC 3 at NIST premises in Boulder Colorado, United States (18-23 October 2010) Dr Michael Griepentrog (leader WP5) was the acting chair of the meeting. Comments and resolutions, inspired by NANOINDENT were accepted by SC 3.
- At the same meeting adopted resolution No. 217 and mandated the ad-hoc Working Group to prepare the revised Drafts of ISO 14577 Parts 1 to 3 for CD enquiries. The CDs were submitted to SC 3 secretariat by 31st March 2011.
- Further the ad-hoc working group is mandated to prepare a NWIP for ISO 14577-4. The NWIP was submitted to the SC 3 secretariat by 31 March 2011. SC 3 secretary was mandated to launch a three-month enquiry on the NWIP.
- Based on cooperation and input from NANOINDENT the NWIP was prepared and the results of enquiries were available at the end of July 2011. Final discussion on this topic will be during the next meeting of ISO TC 164 SC3 in September 2011 in Paris.
- In resolution No. 224 SC 3 mandated the ad-hoc working group to prepare a scope and a proposal for integrating dynamic instrumented indentation testing methods (including indentation creep and nano impact testing) into ISO 14577 in 2011. This could include preparation of a NWIP for a 5th part of ISO 14577.
- There are some European standards in (macro)scratching (DIN EN 1071-3, DIN EN ISO 1518), it is high time to start work on standardisation of nano-scratching.

Harmonised steps for the identification of instrumental parameters (WP5)

Deliverable D5.1 and D5.2 presented the result reached in WP5 in the field of finding out the real instrumental parameters:

- the instruments used by partners of project NANOINDENT consists a wide selection of type and age of instrumented indentation equipment;
- thermal drift data varied from instrument to instrument considerably, but all drift data were within a reasonable range;
- depth and force noise data varied from several nm down to less than 1 nm. This noise is generally acceptable for the hardness tests involved in the project, but in some cases are considerably larger than instrumental paramers published by producers;
- the instruments participating in the project have appropriate accuracy, operatibility for the owners.

Potential Impact:

The most important target of the project was to create a solid basis for future standards, which aim is fulfilled as it was listed in detail in the previous section. The contribution to the revision of ISO 14577 standard, and the base for starting standardisation in nanoscratch testing are the most important two achievements.

Although the main impact of the project was planned and is achieved in the field of standardisation, other important results are the following:

- The best area function determination process described in deliverable D2.1 is not completely new, it's elements were well known before the project, but these statements were never proved on such a wide basis and using a soft sample, polycarbonate. Further work has been done in the optimisation of area function on very low contact depth, it means low load, where instrumental noise factors are more important and even the choice of the mathematical form of area function is crucial.
- The area function determination by AFM imaging is a promising option, but as the O&P evaluation method is a closed system requiring data only, which are acquired by nanoindentation, the introduction the AFM as a second instrument introduces inaccuracies, which are not present, or which are corrected for in the closed system of O&P method. So the development of AFM - Adhesion frequency (AFM-AF) determination needs some further work.

The project NANOINDENT matched the objectives of the call of the Seventh Framework Programme by fully reflecting the strategic objective of activity mastering nanoscale complexity in materials and specifically the Nanosciences, nanotechnologies, materials and new production technologies (NMP) call 2.1-3 'Characterisation of nanostructured materials' as it aimed to build an expert group for a special service (elaboration of standards and maintaining a database) and making 'preparatory technical work' for elaborating common standards in metrology of nanomechanical testing. It stimulated, encouraged and facilitated the participation of several Small and medium-sized enterprise (SME)s, and small and remote research centres in the activities of the thematic areas of the Cooperation programme, and it established a research intensive cluster across the European Union (EU) regions. In addition the project achieved the main objective of NMP to 'improve the competitiveness of European industry' by supporting small, innovative enterprises in product development and 'generate knowledge to ensure its transformation from a resource-intensive to a knowledge-intensive industry' by building knowledge database, generating new knowledge and spreading this knowledge over Europe.

The proposal improved a young gap-filling technology with extreme scientific content and application in the nanomechanical control processes of surface active and bulk nanotechnology. It reinforced the European competitiveness and position in nanotechnology (a strategic knowledge-based field) in application and instrument production. It generated knowledge on leading a quality assurance method in nanotechnology. Each individual point and milestone in the project brought substantial innovation with respect to the current state of the art.

Our project aspired to reach significant breakthrough in two fields: spreading information on fine art of nanomechanical testing as wide as possible in the scientific-technical community of Europe, and deepening the knowledge, metrology and standardisation of the same method to people who are applying this method for nanomaterial characterisation. In the first aim particular emphasis was laid on spreading information to scientific stakeholders at conferences, scientific journals and through our homepage over the sophisticated techniques to characterise the hardness, elastic modulus, friction, adhesion, fracture toughness of nanosized materials. For people involved in nanomechanical characterisation methods, the project was giving the possibility to use a unique database of measurement methods, standard samples and good practices to solve the actual metrological problems and reach significant improvements in determining nano-mechanical parameters, as hardness on soft samples (e.g. tissues and polymers). The large interest of diverse research groups in joining the project as associated partners proved this concept brilliantly. The materials property database on the homepage also provided a uniquely broad range of materials data connected to nanomechanical investigations.

In summary the current state of the art was a fertile ground to implement our project. It will bring substantial innovation in a number of fields, represented by the WPs of the project, in which individual progress will be manageable and sustainable.

List of websites:

Dissemination and exploitation activities went well beyond the usual publication in scientific journals and presentation at conferences. The aim to gather, inventory and process information for future standards by creating best practices of nanomechanical testing methods, equipment was reached primarily in standardisation (first revision of ISO 14577 standard, suggesting 'good practices' in nanoscratch testing) and through spreading information using the project's homepage When an interested group of scientists agree and come to a common footing, such routines and proceedings quickly disseminate not only among themselves, but inside the community as a whole.

Concerning exploitation, it is difficult to underestimate the gains of this successful project. On one hand European equipment manufacturers can easily outdo their counterparts by adopting the best practices developed in the project in their devices. On the other hand academia will benefit from the fact that all future measurements will have the same meaning globally.

NANOINDENT has a broader impact than a strictly European project since results attained have world-wide implications. The outcome serves as a basis for current and future standardisation steps, but it is in itself enough to guide stakeholders, who are leading producers of nanoindentation equipment and recognised researchers and who will apply the developed best practices in their instruments and everyday work.