jianliang lin, john j moore, s, myers, f. wang, b. mishra
DESCRIPTION
An Examination of Coating Architecture in the Development of an Optimized Die Coating System for Aluminum Pressure Die Casting. Jianliang Lin, John J Moore, S, Myers, F. Wang, B. Mishra Advanced Coatings and Surface Engineering Laboratory (ACSEL) Colorado School of Mines, Golden, Colorado. - PowerPoint PPT PresentationTRANSCRIPT
An Examination of Coating Architecture in the Development of an Optimized Die Coating System for
Aluminum Pressure Die Casting
Jianliang Lin, John J Moore, S, Myers, F. Wang, B. Mishra
Advanced Coatings and Surface Engineering Laboratory (ACSEL)
Colorado School of Mines, Golden, Colorado
Peter Ried,
Ried and Associates, LLC, Portage, Michigan
Why the Toughness is Critical for a Die Coating
• Premature failure of the die– Erosion– Wear
– Thermal fatigue
• General considerations:
– Adherent to and compatible with the die
material.
– Satisfies a range of specific mechanical,
chemical and physical properties required
by the forming process (High hardness
and low coefficient of friction)
– Thermally stable at die casting operation
temperature (oxidation resistance)
– Chemical inertness (non-wetting) with
liquid alloy, e.g. aluminum (corrosion
resistance)
– Able to accommodate the thermal residual
stresses induced by shot cycling
(temperature and pressure) during the
pressure die casting process. (Need High
toughness and low residual stress)
Can be effectively minimized by coating protection
Pitting area in the die formed under the
TiAlN/CrC coating after 12000 shot cycles in the
in-plant trial
Need high toughness, low residual stress coating
Coating cracks
Fe-Cr-Al-Si intermetallics
Coating
Substrate
The Concept of an Optimized Die Coating System
– Different architectures of the intermediate layer (CrAlN) will have different microstructure and properties
(mechanical, tribological, toughness, etc.)
– The purpose of our recent work is to investigate the effect of the intermediate layer architecture on the
coating structure and properties, especially the toughness and plasticity.
US Patent: PCT/US2005/17818------Designed on the philosophy of integrating the best properties from individual
coatings into a coating system to extend die life by minimizing premature die failure
Working Layer
Intermediate Layer
Adhesion Layer
Ferritic NitrocarburizedH13 substrate
(Cr,Al)2O3
CrN-CrAlN
Cr
Ferritic NitrocarburizedH13 substrate
Designed Coating Architecture
An Example Coating Architecture
Non-wetting with molten Al,
Good mechanical strength
High toughness, accommodation
of thermal stress, and crack
propagation resistance
Provide good adhesion to the die material
Increase the substrate strength to provide good support to the top layers
Three Different Intermediate CrAlN Layer Architectures
CrAlN Homogeneous
Al Rich compositionally graded
CrxNy
Cr1-xAlxN
CrN/AlNSuperlattice
Different Approaches for the Intermediate Layer
The composition of the CrAlN coating is consistent The composition of the CrAlN coating is consistent
through the coating thickness. The Al/(Cr+Al) atomic through the coating thickness. The Al/(Cr+Al) atomic
ratio in Crratio in Cr1-x1-xAlAlxxN coating was maintained constantly in N coating was maintained constantly in
the range of 55-60 at.% (optimized from our previous the range of 55-60 at.% (optimized from our previous
work)work)
The Al concentration was increased from The Al concentration was increased from
bottom to the top in CrAlN coating according bottom to the top in CrAlN coating according
to the Power Law with the exponent P=0.2 to the Power Law with the exponent P=0.2
(the black line) (optimized from our previous (the black line) (optimized from our previous
work)work)
CrN and AlN layers were alternately CrN and AlN layers were alternately
depositeddeposited with the bilayer thickness
of 2-10 nm
Graded CrN
Graded CrNLCr1-xAlxN
k
CrxNy
Cr
Will be focused in the current research
Coating Deposition System
Deposition system:
– Pulsed closed field unbalanced magnetron sputtering (P-CFUBMS)
Depositions of three CrAlN intermediate layer architectures
– For the homogeneous coating, the power densities and other deposition parameters were kept constantly
during deposition period;
– For the Al rich graded coating, the power density on the Al target was increased in accordance with the P=0.2
power law, while maintaining other deposition parameters constant.
– For the CrN/AlN superlattice, the substrate was rotated back and forth between Al and Cr target at different
power densities and settle times using a planetary rotation system.
Closed magnetic field lines
N2+Ar
EQP orificeEQP detector
Quadrupole lens and energy filter
Substrate
Superlattice CrAlN Intermediate Structure
Both homogeneous and graded CrAlN coatings exhibit a typical columnar structure, the columnar grain boundaries were clearly observed
Superlattice CrAlN coatings exhibit a bilayered structure, with extremely fine grain size and further improved dense structure
CrN AlN
Bilayer thickness of 7-8 nm
CrN/AlN superlattice
Dense structure with super fine grains
Homogeneous Graded (Al rich graded)
Dense columnar structure with fine grains
Dense columnar structure
Calculation of the Bilayer Period in CrN/AlN Superlattice Coatings
Where m is the order of the reflection, λ is the X-ray wavelength (λcu=1.54056), is the bilayer thickness,
and is the real part of the average refractive index of the film, which is of the order of 1x10 -5, By plotting
vs. m2 into a line, the bilayer thickness can be calculated from the slope of the line (about 5 nm for this
CrN/AlN coating)
2 3 4 5 6 7 8
0
400
800
1200
1600
2000
m=5m=4m=3
m=2
Inte
nsity
[Cou
nts/
Sec]
Diffraction Angle [2-Theta]
m=1
22
22
mSin
Low angle XRD: Confirming a layered structure, the bilayer thickness can be calculated from modified
Bragg’s law:
2Sin
Crystal Phase in CrN/AlN Superlattice Coatings
30 35 40 45 50 55 60 65 700
40
80
120
160
200
In
tens
ity [C
ount
/sec
]
Diffraction Angle [2-Theta]
c-CrAlN(200)
c-CrAlN(111)
c-CrAlN(220)
High angle XRD: showing the coating was crystallized in the cubic NaCl B1 structure (fcc), in which the (111),
(200) and (220) diffraction peaks were observed. There is no hexagonal wurtzite-type AlN phase observed in
the XRD pattern, therefore the AlN layers in CrN/AlN coatings exhibit an isostructural structure with CrN layer
The Plasticity of CrAlN Coatings with Different Architectures
0 50 100 150 200 250 300 350 400 450 5000
5
10
15
20
25
30
35
40
45
50
BA
CrN/AlN superlattice(Bilayer period=3.8 nm)
Single Layer CrAlN
50%
Elastic deformation
Displacement into the surface [nm]
Loa
d [m
N]
Plastic deformation
63%
O
The plasticity of CrAlN coatings with different structures was calculated from the ratio of the plastic deformation over the total displacement in the load-displacement curve:
Load-displacement curves obtained from Nano-
indentation tests
OBOA
ntDisplaceme Totalndeformatio PlasticPlasticity
The plasticity of three different CrAlN coating architectures were:
1) For Homogeneous: 50%
2) For Al rich graded CrAlN coating: 60%
3) For CrN/AlN superlattice coating: 63% (=3.8 nm)
Rockwell-C Indentation Test and Indent MorphologiesHomogeneous
Al rich graded
CrN/AlN superlattice
A HF adhesion strength quality as standardized in the
VDI guidelines 3198, (1991)
Load: 150 kg
HF1-HF4 define a
sufficient adhesion
HF5 and HF6 represent
insufficient adhesion
Similar to HF2
Better than HF1
Better than HF1
Wear Resistance of Graded and Superlattice CrAlN Layers
Test conditions:
- CETR microtribometer
- 3 N normal load
- 100 m sliding length
Graded p=0.2Al rich graded
Homogeneous
Superlattice
Decreased wear
depth
Decreased wear
debris
Summary of the Properties of the properties of Graded and Superlattice CrAlN layers
Hardness [GPa] 36.383.98 34.613.22 41.32.89 (=3.8 nm)
Young’s Modulus (E) [GPa]
369.929.3 378.4724.72 377.65314.21(=3.8 nm)
H/E 0.0984 0.091 0.109
Plasticity 50% 60% 63%
Residual Stress [GPa]
-4.8 -2.25 Characterization in progress
Lc [N]
28 42 Characterization in progress
Coefficient of Friction 0.38 0.45 0.35 (=5.4 nm)
Wear Rate (WN)[10-6mm3N-1m-1]
2.87 3.12 0.95 (=5.4 nm)
HomogeneousHomogeneous Al rich gradedAl rich graded CrN/AlN superlatticeCrN/AlN superlattice
Super hardness
Increased adhesion
Good wear resistance
Decreased residual stress
Good toughness
Summary
• The approaches to design and deposit an example surface engineered coating system for aluminum
pressure die casting applications have been introduced.
• The microstructure, mechanical and tribological properties of the CrN/AlN superlattice coatings were
investigated and compared with the homogeneous Cr0.42Al0.58N single layer coating and an Al rich
graded CrAlN coating.
• The superlattice CrN/AlN coating architecture produced a super hard (41 GPa), high toughness (63%
plasticity, no crack observed in the Rockwell-C indentation tests), and high wear resistance (low wear
rate of 0.95x10-6 mm3N-1m-1) with a bilayer period of 3.8~5.4 nm.
• It is expect that the superlattice CrN/AlN and Al rich graded CrAlN coatings are very promising coating
candidates for the aluminum high pressure die casting dies.
Future work:
Systematic investigate the effect of the CrN, AlN nanolayer thickness on the superlattice coating structure and
properties