Quasi-static and Impact Nanoindentation to Study Deformation Mechanisms in Metals

Lead Research Organisation: University of Cambridge
Department Name: Materials Science & Metallurgy

Abstract

Nanoindentation is an attractive technique, allowing study of local mechanical characteristics in a versatile and cost-effective manner. The two MML indenters in the Gordon Laboratory represent the current state of the art. Hot and cold stages have been developed, allowing operation at up to ~800 C and down to -170 C. Impact indentation can be carried out so as to generate (transient) local strain rates ranging up to about 10^4 s^-1. One of the two systems can be operated in vacuum or under controlled atmosphere, greatly reducing the incidence of specimen oxidation and diamond tip erosion at high temperature, and also eliminating condensation at low temperature. Furthermore, a suite of FEM modelling routines has been developed, allowing quasi-static material constitutive relations, and residual stress levels in particular specimens, to be inferred from nanoindentation data, with good degrees of reliability and accuracy.

The proposed work will involve development of these capabilities, particularly relating to impact mode indentation. This will require enhancement of the current modelling suite, and comprehensive characterisation of the dynamics of indenter motion. This should allow the extraction of strain rate sensitivity information, over ranges of strain rate for which conventional testing presents severe difficulties. These techniques will be applied to "reference" materials, such as pure copper, and also to alloys of particular interest. These include (depleted) uranium, which will be supplied by AWE. Such alloys can exhibit pronounced superelastic deformation at relatively low strains and methodology will be developed for the extraction of parameters characterising such behaviour. The effect of ageing on these alloys will also be investigated, which will be facilitated by the capacity for heat treatments to be carried out in situ on the indenter stage (inside the vacuum chamber). AWE will fund a PhD studentship, which will be oriented particularly towards these alloys and the role of superelastic deformation in their overall mechanical behaviour.

Planned Impact

Beneficiaries
1) Commercial firms supplying nanoindenters. MicroMaterials Limited (MML) is the UK market leader. Since the work will be carried out on MML machines (albeit ones that have been modified and enhanced since their purchase), transfer of scientific and technological information will be particularly effective.
2) Organizations with an interest in expanding the range of information obtainable via nanoindentation. There are many such bodies. The development of methodology for extraction of material response data at high strain rate, and over a wide range of temperature, will be of particular interest. AWE has recognized that such testing could play an important role for them.
3) Organisations with an interest in new information about the nanoindentation response of certain types of materials, including those in which martensitic transformations can be stimulated by imposed strain (and are hence likely to exhibit shape memory behaviour). Correlations will be established with microstructural development in certain such alloys, and the effect of ageing at elevated temperature. AWE will supply the material and fund the associated PhD studentship. They expect to derive substantial benefit. Furthermore, there are many other (industrial and research-oriented) organizations in the UK likely to benefit from improved understanding of the behaviour of such alloys, and from insights arising from these novel testing procedures.

Dissemination, Impacts and Timescales
Publication in the open literature, and a project website, will be key dissemination mechanisms. There will be close contact with the partners, fostered by quarterly meetings and by periods spent in Cambridge by Giles Aldrich-Smith (AWE) and several members of staff from MML. A nanoindentation Symposium (CAMTEC III) will be held in Cambridge (March 2014), following two earlier events (see www.msm.cam.ac.uk/mmc/index.php/events/camtec-ii). As previously, financial support will come largely from commercial organizations involved in supply of nanoindenters.
Impact will partly be in the form of wider and more varied usage of nanoindentation, with expansion in possible ranges of strain rate and temperature. Improved methodologies for extracting material property data, including close integration of FEM modeling with material response and loading system characteristics, will also promote wider usage. Such advances will be particularly relevant to suppliers of nanoindenters, including MML, bringing economic benefits to the UK. Since the work is relevant to MML's current marketing strategy, these benefits could materialise within a short time scale (~3-5 years). Benefits to AWE, and other organisations involved in testing and use of advanced alloys, will take the form of cost savings and improved versatility arising from future testing strategies, in which nanoindentation is likely to figure strongly. This may well lead to reductions in certification time for new alloys. Benefits will also flow from specific property data generated within the project. These benefits are also likely to materialise within the short to medium term.

Publications

10 25 50
 
Description This grant has laid the groundwork for a significant breakthrough regarding the evaluation of bulk mechanical properties from instrumented indentation data, which is a longstanding and important goal. This has come about from a focussed set of projects over a period of about 8 years, funded by EPSRC and AWE. The approach involves development of a systematic methodology, and an associated user-friendly software package. This involves iterative FEM modelling of the indentation process, using trial material property values as input data, and comparison of the outcomes with experimental data, until convergence is obtained. An EPSRC proposal currently being assessed covers the final tranche of research required to bring this work to fruition.
Exploitation Route These findings are being taken forward. This is being done via the creation of a suite of software packages (SEMPID - Software for the Extraction of Material Properties from Indentation Data), in collaboration with AWE, where systematic testing is now being undertaken. It's likely that a spin-out company will be created specifically to market the products that emerge. The properties covered in the first package will be plasticity parameters (yield stress and work hardening characteristics), but work is already in hand on a package aimed at creep parameters (for both primary and secondary creep). A further period of research is required, but it's already clear that products of real utility and value will emerge within about 2-3 years.
Sectors Aerospace, Defence and Marine,Construction,Digital/Communication/Information Technologies (including Software),Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Transport

URL http://www.ccg.msm.cam.ac.uk/research-areas/fine-scale-mechanical-interrogation
 
Description These findings are being used in the form of development and testing of software packages. Details are given in the Key Findings section.
First Year Of Impact 2015
Sector Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Title Extraction of Creep Properties from Nanoindentation Data 
Description A procedure has been developed for the extraction of (primary and secondary) creep parameters from nanoindentation data 
Type Of Material Improvements to research infrastructure 
Year Produced 2013 
Provided To Others? Yes  
Impact Plans are being implemented for developing user-friendly software for implementation of these procedures and making this widely available to the indentation community. 
 
Title SEMPID 
Description This is a suite of software packages (Software for the Extraction of Material Properties from Indentation Data), designed to be used in conjunction with experimental data obtained during instrumented indentation to obtain material properties. The first of these packages, which is in the most advanced state, relates to plasticity parameters (yield stress and work hardening characteristics). 
Type Of Material Improvements to research infrastructure 
Year Produced 2016 
Provided To Others? Yes  
Impact Trial versions are being tested by researchers at AWE. 
URL http://www.ccg.msm.cam.ac.uk/initiatives/sempid/sempid
 
Description AWE 
Organisation Atomic Weapons Establishment
Department Materials Science
Country United Kingdom 
Sector Private 
PI Contribution Development of new methodologies, and associated software, for evaluation of material properties from indentation data
Collaborator Contribution Testing of trial versions of software, supply of unknown samples for blind testing, extensive discussions, joint publications etc
Impact Four joint publications have emerged. There have been six AWE grants, covering post-doctoral fellowships, PhD studentships, contracts with a spin-off company etc. A PhD studentship with an EPSRC DTC (in Nuclear Materials) is pending.
Start Year 2007
 
Description Hysitron 
Organisation Max Planck Society
Department Max Planck Institute for Physics
Country Germany 
Sector Academic/University 
PI Contribution Hysitron is a world leader in manufacture and supply of fine scale mechanical testing facilities. Developments in the Gordon Laboratory on methodologies for using indentation data to obtain materials properties have been supported by Hysitron.
Collaborator Contribution Hysitron have been involved in joint proposals and have supplied materials and resources for testing programmes in the Gordon Laboratory. They make frequent visits and participate in the CAMTEC Symposium series, which is based in Cambridge.
Impact An agreement is pending on joint development of a new type of testing facility for meso-scale indentation, to be used in conjunction with dedicated (SEMPID) software.
Start Year 2006
 
Description Link with Micromaterials Limited 
Organisation Micro-Materials Ltd.
Country United Kingdom 
Sector Private 
PI Contribution There is an ongoing collaborative link between the Gordon Lab and Micromaterials, mainly focussed on technical development of nanoindentation technology and procedures.
Collaborator Contribution Technical information passes in both directions between Micromaterials and the Godon Lab.
Impact Much of the recent collaboration has been concentrated in the area of high temperature nanoindentation, including techniques for heating of specimen and indenter tip, control of thermal drift and the provision of environments for reduction of specimen and tip oxidation.
 
Company Name PLASTOMETREX LTD 
Description Plastometrex was set up to exploit the outcomes from several research projects carried out within the Gordon Laboratory over the past 10-15 years, including several with EPSRC funding. The idea being exploited is that of using iterative FEM simulation of the indentation process to obtain the stress-strain relationship of the material being tested. Since indentation testing is a much quicker and more convenient operation than conventional tensile testing, this is a very attractive prospect. In order to obtain bulk properties, however, the scale of the indentation must be greater than the maximum possible using "nanoindenters", so a new type of machine, combining a relatively high load capability with accurate measurement of load-displacement plots or residual indent profiles, needed to be designed and manufactured. Commercial sales of this facility, integrated with the necessary software, are now starting. 
Year Established 2018 
Impact The company, which was established in 2018, but effectively started operations in 2019, has already made considerable progress and is starting to have a significant impact. Several industrial trials have been carried out and a number of companies have expressed strong interest. The first commercial sale has already been agreed, with delivery planned for May 2020, and it is anticipated that there will be several more later in the year. A number of papers have been published covering various aspects of the technology and a patent has been filed. The Plastometrex website is currently undergoing a major overhaul, expected to be complete by the end of April 2020. Partnerships are currently being set up with several firms. The number of employees is expected to rise above 10 this year.
Website https://www.plastometrex.com/
 
Description CAMTEC Symposium series 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The CAMTEC symposium series has been arisen partly in conjunction with an ongoing EPSRC project. It concerns nanoindentation and similar types of fine scale mechanical characterisation. A two-day symposium is held in Cambridge every 4 years, with attendance by invitation only (and no fee payable). It is supported entirely by contributions made by industrial exhibitors. Typical attendance has been about 60-80 people.

The CAMTEC series is very highly regarded and there is always competition for invitations. It is an excellent opportunity for widespread technical discussions.
Year(s) Of Engagement Activity 2006,2010,2014
URL http://www.ccg.msm.cam.ac.uk/camtec
 
Description Development of SEMPID software package 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact This activity involves the creation of user-friendly software (SEMPID - "Software for the Extraction of Material Properties from Indentation Data") for implementation of procedures that have been developed in the project for the extraction of mechanical properties (plasticity and creep characteristics) from instrumented indentation data. This is an ongoing activity.

This part of the project activity is supported by AWE, and also by Micromaterials - both being partners in the research programme. AWE already utilise procedures developed in the project, but this software will streamline that utilisation, and also make it accessible to a wide range of potential users.
Year(s) Of Engagement Activity 2014
URL http://www.ccg.msm.cam.ac.uk/sempid