1. DFT calculations of metal/ceramic interfaces
Collin D. Wick, Shoutian Sun, Abu Mohammad Miraz, and B. Ramu Ramachandran
Collaborators: Shuai Shao and Wen J Meng

2. Thin ceramic coatings offer an important means for providing mechanical protection to machine tools and mechanical components
Reducing ceramic coating spallation is important for enhancing life of coated systems
Better adhesion between ceramic and metal and stronger resistance to shear are desired
Introducing an adhesion layers between metal substrate and ceramic coating is a common industrial practice
*The main goal is to find metal/ceramic combinations that maximize strength of interactions and resist spallation
Metal
“Compressive cracks” in a coating with excessively high residual stresses; taken from P. Ståhle et al. Wear vol issue. 12, pp , 2009.
Adhesion layer
(Cu, Ti, Cr)
CrN, TiN, VN
Calico Coatings (CrN)

3. There are two common ways to study systems atomistically
Use first principles
The VASP software is reasonably user friendly
Nearly every atom and atom combination can be examined without any initial fitting
Can be confident in most qualitative results extracted from the study
Electron density and density of states information can be extracted from the calculations
Smaller system sizes, up to around 103 atoms
Use molecular models
Can study much larger systems (orders of magnitude of that with first principles: 106 atoms)
Run simulations on much longer time scales.

4. We will use First Principles to Predict where Shear failure occurs and Which Metals and Ceramics have the highest Shear Strength
Can only investigate the interface between the adhesion layer and the ceramic
Limited to fairly small systems and only coherent interfaces
Can investigate many different molecular formulas due to the flexibility of first principles calculations
Metal
CrN, TiN, VN
Cu, Ti, Cr

5. We will determine the strength of adhesion between interfaces and barriers to shear movement for the first few metal layers
Work of adhesion shows which layer it is easiest to pull the metal/ceramic system apart.
The 2D Generalized Stacking Fault Energy (GSFE) gives the barriers for shear movement
Work of Adhesion
2D GSFE

6. Strongest adhesion at the surface is for Ti, while strongest adhesion overall is for Cr
Ti adhesion significantly drops away from the surface and is strongest with the VN ceramic
Cu has many different most stable faces with the ceramics. The weakest adhesion is with the CrN surface. For TiN and VN, Cu adhesion is weakest one molecular layer from the ceramic surface
Cr adhesion increases away from the ceramic interface, signaling stronger adhesion in its bulk than with the ceramic surface
Ti(0001)-XN(111)
Cu(001/111)-XN(001/111)
Cr(001)-XN(001)

7. The interface between Ti and TiN have by far the highest barriers for shear
The most stable interface is the Ti (0001)-TiN (111) surface
The smallest barriers for shear is in the 1st layer equal to J/m2 (around three times that further away from the interface).
0th Layer*
1st Layer
2nd Layer
3rd Layer
*Notice that the scale is much larger than others

8. Cr has similar barriers for shear in all layers
The most stable interface is the Cr(001)-TiN(001)
Cr has clear movement pathways in the x and y directions
Barriers are all near 3.8 J/m2, much greater than for Ti-TiN (0.12 J/m2)
0th Layer
1st Layer
2nd Layer
3rd Layer

9. Cu has smallest barriers at the interface
The most stable interface is the Cu(001)-TiN(001).
Cu has clear movement pathways in the x and y directions
The barrier is higher than Ti, but lower than Cr
1st Layer
0th Layer

10. For Cr, CrN has the lowest barriers for shear, while TiN has the highest barriers
This suggests that TiN will better resist shear displacement than CrN or VN
Cr has clear movement pathways for all systems
Cr(001)-CrN(001)
Cr(001)-VN(001)
Cr(001)-TiN(001)

11. As with Cr, Ti-CrN has the lowest barriers for shear with TiN having the highest
The Ti-CrN barriers for shear are significantly lower than for the other systems.
TiN appears to be the best overall material for resistance to shear failure
Ti(0001)-CrN(111)
Ti(0001)-VN(111)
Ti(0001)-TiN(111)

12. Conclusions
Ti forms very strong interactions with all ceramics, but are weakened near the interface.
Cr has similar if slightly weaker interactions with each ceramic than within its bulk structure.
Cu interactions vary significantly with each ceramic
TiN has highest barriers for shear displacement for Cr and Ti
Future work will examine more metal layers for all systems and….

13. See Poster on new MEAM potentials for ceramic-metal interactions (preliminary results for Ti-TiN)
We fit bulk and surface properties of Ti and TiN using our genetic parameter fitting algorithm
Also does a good job of reproducing GSFE and the work of adhesion between Ti and TiN
DFT
DFT
Ref.
New Model
Wad Ti(0001)-TiN(001) [J/m2]
2.83
4.91
2.13
Wad Ti(0001)-TiN(111)
6.06
9.90
6.95
New Model
Reference
. Y. Kim and B. Lee, 56, 3481–3489 (2008).