ENCYCLOPÉDIE DE LA RECHERCHE SUR L’ALUMINIUM AU QUÉBEC 2013 | Page 52

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NOUVEAUX PRODUITS ET MATÉRIAUX À BASE D'ALUMINIUM
NEW ALUMINIUM BASED PRODUCTS AND MATERIALS
CARACTÉRISATION DE COMPORTEMENT À L'USURE D'Al-7075
RECOUVERT D'Al-Si NANOSTRUCTURÉ PAR INDENTATIONS NANO-IMPACT
CHARACTERIZATION OF WEAR BEHAVIOUR IN NANOSTRUCTURED
Al-Si CLADDED ON Al-7075 SUBSTRATE USING NANO-IMPACT INDENTATIONS
Characterization of wear behaviour in
nanostructured Al-Si cladded on Al-7075
using nano-impact indentations
Abhi Ghosh, J. Arreguin, M. Brochu and J. Milligan
INTRODUCTION

OBJECTIVE

• Nano-impact is a performance testing tool capable of measuring and tracking deformation at nanoscopic level
under dynamic stress conditions. Due to the dynamic nature of the stresses occurring during the
erosion/sliding, the wear behavior of a material is generally tested under dynamic conditions.
• Aluminium alloys such as Al-7075 have good strength and ductility, however, they possess poor surface
properties. For this reason, wear resistant materials such as Al-Si alloy are cladded to Al-7075 to obtain a
material system possessing optimum bulk properties along with excellent surface properties.
• Spherical nano-sized Si precipitates embedded in nano-sized grains of Al matrix form a perfect resistance
towards material removal, and hence towards sliding wear [1].

• Perform nano-impact tests for a range of loads on
Al-7075 and Al-Si.
• Understand the deformation behaviour at low loads,
where geometrically necessary dislocations (GND)
dictate the deformation mechanism.
• Comparision of deformation and wear behaviour for
nano-impact and nano-indentation for Al-Si coating
and AA-7075 substrate.

METHODOLOGY
1. Materials processing [1]:
Cryomillig:
4 hrs at 196 oC

Al-Si Powder

Al-Si powder
placed on
top of Al7075
substrate

T6S Heat
treatment:
1 h at 475 oC,
Stretch, 24 h
at 125 oC

Wrought Al7075

2. Resultant micro-structure:
Spark Plasma Sintering:
5 mins at 450 oC

3. Nano-impact testing:

Coating-substrate crosssection: [1]

Nano-impact tester

Indenter and sample positioning

Al-Si

Type
Interface
Al-7075

No. of Impacts

Load

Time

Samples

Impact/
Dynamic
hardness

1

10 mN to
100 mN

300 ms

Al-Si and Al7075

RESULTS & DISCUSSION
Nano-impact: Nix-Gao model and Geometrically Necessary Dislocations (GND)
Hardness vs. Residual Depth for Al-Si and Al-7075

GND Zone in low load indents [2]

Micrographs of indents at 100 mN

0,4

PRIX AXE 2 // AXE 2 AWARD

Nano-Impact Hardness (GPa)

0,35

Al-Si

0,3
0,25

Al-7075

Al-Si

0,2
0,15
0,1

Al-7075

0,05
0
2500

3500

4500

5500

6500

7500

8500

9500

Residual Depth (nm)

Comparision with Micro-hardness results:

Plasticity index and wear resistance: Effect of nanostructuring

Hardness by nano-impact and nano-indentation [3]:

Micro-hardness: Hardness vs. Depth

Static vs. Dynamic indentations: Hardness comparision

Static and Dynamic Plasticity Index:

140
120

Vickers Hardness

Abhi Ghosh
Javier Arreguin-Zavala
Mathieu Brochu
Jason Milligan
Université McGill

• Hardness vs. Depth curve for both Al-Si and Al7075 almost coincide, indicating them to have
the same resistance to dynamic stress.
• Ho, or Hardness at statistically stored
dislocations were same for both materials.
• Nix-Gao model: It states that a linear
relationship occurs between hardness and
residual depth. Nix-Gao model does not apply for
low loads at nano-impact test [2].
• GND zone: For the GND zone, an inverse relation
between hardness and depth applies. Hence,
hardness increased with decrease in indentation
depth for nano-impact tests.

Al-Si

100
80

Al-7075
Al-Si

60
40
20
0
0

5

10

15

20

Residual Depth (µm)

25

30

35

• GND zone: For larger static loads, the
Nix-Gao model applies. Microhardness values do not change with
increasing loads.
• Micro-Hardness values for Al-Si and
Al-7075 are almost equal.

Nano-Impact Hardness,
DHo
Nano-Indentation
Hardness, Ho

~0.12 GPa
1.3 GPa

Al-7075
0.11-0.13
GPa
0.94 GPa

• At static loading, nano-structured Al-Si is harder
than Al-7075. At dynamic loading, the hardness is
approximately same for Al-Si and Al-7075.
• Decrease in hardness at dynamic condition is due
to the lack of dislocation generation and hence
lack of strain hardening at high strain rate
deformation.

Al-Si
DHo/E using Nano-impact
Ho/E using Nano-indentation

0.150

Al-7075
0.00137
0.102

• H/E or Plasticity Index dictates the sliding wear resistance.
• Dynamic Stress conditions during sliding wear is represented more
appropriately by DHo/E or Dynamic Plasticity Index.
• Brittle Nano-grained Al matrix further embrittles due to high strain
rate deformation. Surface cracks cause enhancement of wear due to
“sink” and “pop-in” behaviour of the Si precipitates. Increased
strain-rate is the cause for a decreased wear-resistance of the Al-Si
coating [1].

REFERENCES

SUMMARY
•Dynamic Hardness vs. Depth profile for Al-Si and Al-7075 coincide, with DHo ~ 0.12 GPa.
•Decreased wear resistance of nanostructured Al-Si at dynamic conditions; surface cracks in Al matrix are
evident from indent micrographs.
•Nano-impact testing was used to predict the dynamic response of Al-Si and Al-7075 during sliding wear.

L’utilisation d’un équipement d’indentation à nano-incidence MicroMaterials™ a
permis d’étudier le comportement à la déformation de la surface d’un revêtement
d’Al-Si nano-structuré et du substrat Al-7075 sous-jacent. Afin de mener cette étude,
des tests ont été effectués à faible charge, à partir de 10 mN, où la déformation
est uniquement liée aux dislocations géométriquement nécessaires (GND).
L'augmentation des charges conduit à une stabilisation de la dureté, résultant en
une valeur de dureté Ho dans la zone de dislocations statistiquement stockées.
Les valeurs Ho obtenues à partir de nano-impacts se sont avérées beaucoup
plus faibles que les valeurs obtenues à partir de la nano-indentation dans des
conditions de chargement statique. La diminution des valeurs de dureté à haut
taux de dé