National Physical Laboratory Mark Gee

The National Physical Laboratory UK’s National Measurement Institute Founded in people Scientists Engineers Support staff 75% of funding from DTI GOCO since 1995 Occupying new building

Expertise at NPL spans the physical, materials and life sciences Photometry/Colour Pressure RF and Microwaves Radioactivity Radiometry Scientific Software Time Physical-chemical measurements for life sciences Biometrology Nanotechnology Acoustics Dimensional Electromagnetics Ionising Radiation Environmental Air Quality Lasers Mass and force Materials Thermal Optical communications Photonics

Tribology at NPL Sliding wear –Effect of machine dynamics –Effect of tribochemistry –Measurement of low wear Abrasion –WC/Co –Wear-Corrosion Microscale tribology

Before Wear After Wear Before Wear After Wear Correlated and Subtracted Images Profile from above 3D Optical Microscopy Similar to confocal microscopy Height data combined with image data Dataset correlation Real volume measurement

Modified ASTM G65 Test System

Results for WC/Co Hardmetals

Archard law (wear is proprotional to load) is not obeyed for all abrasives Wear does not always stop when hardness of sample is greater than hardness of abrasive (cf sand results) Effect of abrasive size

Conformal or Non-conformal Geometry Try to get flat on flat –Alignment an issue –Need careful design to obtain self-aligning samples Non-conformal (typically ball on flat) – contact conditions and hence mechanisms change with time Mild Steel on Bearing Steel

Evaluation of Wear Brass DiscBearing Steel Disc

Effect of Humidity – Reaction with Environment Alumina with water vapour SEI BEI

Effect of Test System Dynamics Changed loading system in tests on alumina 50 N load, 0.1 ms -1, pin on disc

Effect of Test System Dynamics

Micro Load Scratch Tester Features Designed to be cost effective Uses off the shelf high technology components where possible –Flexure bearings for no friction artefacts –2 mm recirculating ball screw linear slide –6 mm servo motor+gearbaox Designed for in-situ SEM operation Single and multiple repeated scratch Operation down to ~0.3 mN load Friction measurement Future Vision Tool for characterisation of performance of nanostructured and low friction materials Foremost EU project Mechanisms of wear in WC/Co hardmetals Context Measurement of micro-scale contacts in MEMS applications Measurement of single asperity contact in conventional macroscopic tribological contacts

Coarse Grained Hardmetal, 300 mN 25  m Radius Indenter Single Scratch Triple Scratch Same Area

Knowledge Transfer IAG Organise meetings Paper output, particularly Good Practice Guides Direct interaction with industry in projects

Good Practice Guides Unlubricated sliding wear Monolithic abrasive wear Ball cratering wear Gas erosion Coatings Wear-Corrosion

Standards Participation CEN 184 WG5 ceramic coatings –Micro-scale abrasion, now published –Reciprocating wear –Pin-on-disc wear –Scratch testing ISO TC 206 ceramics and ceramic coatings –Micro-scale abrasion of ceramic coatings –Pin-on-disc of ceramics ASTM G99 –Many standards ISO TC 199/ SC4 –Abrasion of hardmetals Wear standards database, 1995, 400 standards

CEN 352 Nanotechnology Techniques for evaluation of tribological performance of sliding contacts Not SPM (AFM, FFM) Loads between 100  N and 100 mN Contact size between few nm and 10  m Participants from Spain, Portugal, Belgium (2), UK (2), Netherlands Also on ISO TC 229 work programme – participants from China, Denmark, France, Spain, USA