AW Rayment & TW Clyne Department of Materials Science & Metallurgy University of Cambridge, UK Design and Commissioning of a Chamber for Controlled Atmosphere Nanoindentation

Talk Outline Motivations for & Approaches to Controlled Atmosphere Indentation Motivations for & Approaches to Controlled Atmosphere Indentation High Temperature Oxidation Problems - Thermodynamics High Temperature Oxidation Problems - Thermodynamics Design and Characteristics of a Controlled Atmosphere System Design and Characteristics of a Controlled Atmosphere System High Temperature Oxidation Problems - Kinetics High Temperature Oxidation Problems - Kinetics

Stability Problems with Indentation in Air At High Temperatures, Indenter (Diamond) may Oxidise (Erode). Products Gaseous, so expect Constant Erosion Rate. Tips can become Blunted and Tip Life may be Short. At High Temperatures, Indenter (Diamond) may Oxidise (Erode). Products Gaseous, so expect Constant Erosion Rate. Tips can become Blunted and Tip Life may be Short. At High Temperatures, Specimens may Oxidise. Products usually Solid, so Rate will probably decrease with Time. Products likely to Interfere with Indentation, even when Thin. At High Temperatures, Specimens may Oxidise. Products usually Solid, so Rate will probably decrease with Time. Products likely to Interfere with Indentation, even when Thin. At Low Temperatures (below Ambient), Strong Tendency for Condensation in Vicinity of Specimen. Likely to Inhibit reliable Indentation. At Low Temperatures (below Ambient), Strong Tendency for Condensation in Vicinity of Specimen. Likely to Inhibit reliable Indentation. Due to Need for Mechanical Access to Specimen, via Delicate Sensors, Very Difficult to Avoid these Problems by Isolation & Shrouding with Inert Gas, use of Dessicants etc. Due to Need for Mechanical Access to Specimen, via Delicate Sensors, Very Difficult to Avoid these Problems by Isolation & Shrouding with Inert Gas, use of Dessicants etc.

Talk Outline Motivations for & Approaches to Controlled Atmosphere Indentation Motivations for & Approaches to Controlled Atmosphere Indentation High Temperature Oxidation Problems - Thermodynamics High Temperature Oxidation Problems - Thermodynamics Design and Characteristics of a Controlled Atmosphere System Design and Characteristics of a Controlled Atmosphere System High Temperature Oxidation Problems - Kinetics High Temperature Oxidation Problems - Kinetics

Ellingham Diagram for Oxidation of Carbon & Nickel At 1 atm pressure, large negative free energy changes for oxidation of C & Ni (& other metals), over the complete T range, so these reactions are strongly favoured thermodynamically

O 2 Partial Pressures to Avoid Oxidation of Carbon & Nickel O 2 partial pressures necessary for these reactions to become thermodynamically unfavourable are in general below the achievable range  G =  G 0 + RT ln(K) K = 1 / p(O 2 )  for  G = 0, p(O 2 ) = exp(  G 0 /RT)

Talk Outline Motivations for & Approaches to Controlled Atmosphere Indentation Motivations for & Approaches to Controlled Atmosphere Indentation High Temperature Oxidation Problems - Thermodynamics High Temperature Oxidation Problems - Thermodynamics Design and Characteristics of a Controlled Atmosphere System Design and Characteristics of a Controlled Atmosphere System High Temperature Oxidation Problems - Kinetics High Temperature Oxidation Problems - Kinetics

Reported Erosion Rates for Diamond Readily achievable O 2 pressures (~10 -5 bar) bring erosion rates down to acceptable levels (<~0.1  m min -1 ), even at high T (~1000˚C). Argon (for back-filling to 1 atm) typically contains about 10 ppm of O 2 (partial pressure of bar).

Reported Oxidation Rates for Nickel Growth rate exhibits parabolic kinetics, After 1 hour at 1000˚C, oxide thickness is several µm at 1 bar of O 2, whereas at bar it is a small fraction of a µm.

Talk Outline Motivations for & Approaches to Controlled Atmosphere Indentation Motivations for & Approaches to Controlled Atmosphere Indentation High Temperature Oxidation Problems - Thermodynamics High Temperature Oxidation Problems - Thermodynamics Design and Characteristics of a Controlled Atmosphere System Design and Characteristics of a Controlled Atmosphere System High Temperature Oxidation Problems - Kinetics High Temperature Oxidation Problems - Kinetics

Chamber Dimensions and Specifications Enclosed volume ~ 1 m 3 Enclosed volume ~ 1 m 3 Total chamber mass ~ 1 tonne Total chamber mass ~ 1 tonne Pneumatic actuator struts for lid lifting Pneumatic actuator struts for lid liftingElevation Plan

Views of Chamber, with Nanoindenter in situ Vibration-damped table inside chamber Vibration-damped table inside chamber 12 separate electrical feedthroughs 12 separate electrical feedthroughs All Indenter components vacuum-safe All Indenter components vacuum-safe

Evacuation and Back-filling of the Chamber Simple rotary pump for initial roughing Simple rotary pump for initial roughing High speed turbo-molecular pump High speed turbo-molecular pump About one hour to reach ~ bar About one hour to reach ~ bar Deflection of evacuated chamber base < 1 mm Deflection of evacuated chamber base < 1 mm Double O-rings for reduced leakage rates Double O-rings for reduced leakage rates Indenter normally operated under ~1 bar Ar Indenter normally operated under ~1 bar Ar Standard purity Ar has ~ ~5-30 ppm oxygen Standard purity Ar has ~ ~5-30 ppm oxygen Back-filling time ~ 5 minutes Back-filling time ~ 5 minutes Turbo-molecular pump Oxygen Monitor

Summary However, p(O 2 ) ~ bar (eg 10 ppm O 2 in an inert atmosphere), which is readily achievable in a vacuum chamber, reduces rates of oxidation to acceptable levels However, p(O 2 ) ~ bar (eg 10 ppm O 2 in an inert atmosphere), which is readily achievable in a vacuum chamber, reduces rates of oxidation to acceptable levels A (vertical axis) chamber, recently designed & installed at Cambridge, & now being commissioned for nanoindentation, should therefore allow operation over a wide range of T A (vertical axis) chamber, recently designed & installed at Cambridge, & now being commissioned for nanoindentation, should therefore allow operation over a wide range of T Problems of water condensation below ambient T are also eliminated by use of a vacuum chamber Problems of water condensation below ambient T are also eliminated by use of a vacuum chamber The O 2 partial pressures required to make such reactions thermodynamically unfavourable are not achievable The O 2 partial pressures required to make such reactions thermodynamically unfavourable are not achievable At high T (ie above ~ ˚C), oxidation of diamond, & possibly of (metallic) specimens, are problematic At high T (ie above ~ ˚C), oxidation of diamond, & possibly of (metallic) specimens, are problematic

Turbo pump limits

Turbo pump times

Chamber 420 RUG CF-LF adaptor Turbo pump CF 160 LF-160 centre rings, o rings and clamps CF-160 centre rings, o rings and clamps LF160 for feedthroughs with blank T adaptor KF adaptor Pressure sensor Argon turbo brake valve Indentor Roughing pump Edwards KF adaptor /Oxygen sensor Back flow trap Argon supply Piping for Argon Argon/air venting valve A Rayment July 2006 Schematic of the system Exhaust trap Vent to outside Control system

Working regions 10ppm etch rate <0.1 um/min