AW Rayment

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

• Motivations for Approaches to Controlled
  Atmosphere Indentation

• High Temperature Oxidation Problems -
  Thermodynamics

• High Temperature Oxidation Problems - Kinetics

• Design and Characteristics of a Controlled
  Atmosphere System

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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, 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.

• 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.

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Talk Outline

• Motivations for Approaches to Controlled
  Atmosphere Indentation

• High Temperature Oxidation Problems -
  Thermodynamics

• High Temperature Oxidation Problems - Kinetics

• Design and Characteristics of a Controlled
  Atmosphere System

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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
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O2 Partial Pressures to Avoid Oxidation of Carbon
Nickel

• ?G ?G0 RT ln(K)
• K 1 / p(O2)
• for ?G 0,
• p(O2) exp(?G0/RT)

O2 partial pressures necessary for these
reactions to become thermodynamically
unfavourable are in general below the achievable
range
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Talk Outline

• Motivations for Approaches to Controlled
  Atmosphere Indentation

• High Temperature Oxidation Problems -
  Thermodynamics

• High Temperature Oxidation Problems - Kinetics

• Design and Characteristics of a Controlled
  Atmosphere System

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Reported Erosion Rates for Diamond
Readily achievable O2 pressures (10-5 bar) bring
erosion rates down to acceptable levels (lt0.1 ?m
min-1), even at high T (1000C). Argon (for
back-filling to 1 atm) typically contains about
10 ppm of O2 (partial pressure of 10-5 bar).
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Reported Oxidation Rates for Nickel
Growth rate exhibits parabolic kinetics,
After 1 hour at 1000C, oxide thickness is
several µm at 1 bar of O2, whereas at 10-6 bar it
is a small fraction of a µm.
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Talk Outline

• Motivations for Approaches to Controlled
  Atmosphere Indentation

• High Temperature Oxidation Problems -
  Thermodynamics

• High Temperature Oxidation Problems - Kinetics

• Design and Characteristics of a Controlled
  Atmosphere System

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Chamber Dimensions and Specifications
Plan
Enclosed volume 1 m3 Total chamber mass 1
tonne Pneumatic actuator struts for lid lifting
Elevation
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Views of Chamber, with Nanoindenter in situ
Vibration-damped table inside chamber 12
separate electrical feedthroughs All Indenter
components vacuum-safe
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Evacuation and Back-filling of the Chamber
Oxygen Monitor
Simple rotary pump for initial roughing High
speed turbo-molecular pump About one hour to
reach 10-6 bar Deflection of evacuated
chamber base lt 1 mm Double O-rings for reduced
leakage rates Indenter normally operated under
1 bar Ar Standard purity Ar has 5-30 ppm
oxygen Back-filling time 5 minutes
Turbo-molecular pump
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Summary

• At high T (ie above 300-400C), oxidation of
  diamond, possibly of (metallic) specimens, are
  problematic

• The O2 partial pressures required to make such
  reactions thermodynamically unfavourable are not
  achievable

• However, p(O2) 10-5 bar (eg 10 ppm O2 in an
  inert atmosphere), which is readily achievable in
  a vacuum chamber, reduces rates of oxidation to
  acceptable levels

• Problems of water condensation below ambient T
  are also eliminated by use of a vacuum chamber

• A (vertical axis) chamber, recently designed
  installed at Cambridge, now being commissioned
  for nanoindentation, should therefore allow
  operation over a wide range of T

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Turbo pump limits
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Turbo pump times
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Schematic of the system
KF 40-25 adaptor /Oxygen sensor
Argon/air venting valve
LF-160 centre rings, o rings and clamps
T adaptor
LF160 for feedthroughs with blank
Indentor
Control system
420 RUG 160-160 CF-LF adaptor
Argon turbo brake valve
Argon supply
KF 40-25 adaptor Pressure sensor
Turbo pump CF 160
Chamber
LF-160 centre rings, o rings and clamps
CF-160 centre rings, o rings and clamps
Piping for Argon
Vent to outside
Exhaust trap
Back flow trap
Roughing pump Edwards
A Rayment July 2006
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Working regions
10ppm etch rate lt0.1 um/min
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