ELFT HÍRADÓ

[Kádár György <kadargy AT mfa.kfki.hu>]

MFA Szeminárium

Valeriu CHIRITA (Linköping):
A Formula for Increased Strenght in
TiN-based Ternary and Quaternary Compounds

2009. február 12.-én, szerdán 11:00 órakor
az MTA Műszaki Fizikai és Anyagtudományi
Kutatóintézet Tanácstermében,
KFKI 26. épület I. emelet

Minden érdeklődőt szívesen várunk

Kádár György (MFA)
kadargy AT mfa.kfki.hu

(TiN-based thin films, such as Ti1-xAlxN and their alloys, are known to 
have excellent mechanical and thermal properties. In this lecture we 
report the initial results of our ab-initio investigations of two novel 
ternary compounds, Ti1-xWxN and Ti1-xMoxN, obtained by alloying TiN with 
W, respectively Mo, in concentrations of up to 50%. The elastic 
constants as well as the bulk, shear and Young's moduli of these 
compounds were evaluated using density functional theory calculations 
within the generalized gradient approximation, and compared with the 
corresponding properties of TiN and Ti1-xAlxN. Significantly, we found 
that the addition of W and Mo resulted in substantial increases in bulk 
modulus values compared to TiN (up to 15%) and Ti1-xAlxN (up to 30%). At 
the same time, we observed a dramatic decrease (up to 50%) in the values 
of C44, and a reversal of the Cauchy pressure, C12-C44, from negative to 
positive, results indicative of significantly increased ductility in 
these compounds. Both of these trends are in total contrast to what is 
known for Ti1-xAlxN, which exhibits increased C44/brittleness and lower 
bulk modulus values as the Al content is increased. We also 
investigated, in the same manner, the effects of alloying Ti0.5Al0.5N 
with W and Mo, in concentrations of up to 6% and observed a similar 
trend in increasing hardness and ductility. However, in the case of 
quarternary TiAl(W/Mo)N, the impact of W and Mo addition was 
considerably more moderate, as the increase in bulk modulus, 
respectively decrease in C44, were in the 5% range. As it will be shown, 
these results demonstrate and help understanding the mechanisms through 
which W and/or Mo additions modify the atomic bonding in these 
compounds, from a strong angular/directional character, towards a more 
metallic type of bonding. This type of electronic structure information 
is essential in designing compounds with different mechanical properties 
and tailoring them to a variety of applications.)