Page 419 - Handbook of Materials Failure Analysis

2 Influence of Deposition Parameters on PVD Coating Properties 417

and Czyz ˙niewski’s investigations of TiN and CrN arc-evaporated coatings did not
confirm these relations [45,46].
With increasing substrate temperature, the microstructure of the Cr-N coatings is
changing from a columnar form to a “more dense and uniform” structure, and the
surface becomes more and more smooth [26,45]. On the other hand, in Gahlin
et al. [39], the opposite results were obtained: the increase of substrate temperature
caused an increase of roughness of TiN and CrN arc-evaporated coatings and an
increase of metal drop density. In ion plating and vacuum arc evaporation, with
increasing substrate temperature the size of grains increased [29].
Ion energy in ion-beam assisted magnetron sputtering had influence on the grain
size, microstrain, hardness, and fracture toughness [15,19]. In the case of the CrN
coating, an increase of ion energy up to 800 eV decreased a grain size and hardness,
and increased fracture toughness, but further increase of ion energy caused an oppo-
site effect [19]. However, microstrain increased continuously with an increase of ion
energy, but a rate of microstrain increase slowed down with an increase of this depo-
sition parameter.
In nitrogen-based coatings, arate of nitrogen flow and the ratio of Ar/N 2 during the
coating deposition had an influence on coating structure, hardness, and adhesion
[9,11,30]. In reactive magnetron sputtering method, an increase of nitrogen flow rate
caused nearly linear increase of nitrogen amounts incorporated in Cr-N coating [30],
andalsoincreasedcrystallinesizeandlatticeparameter[9].Withanincreaseofnitrogen
flowfrom20to60 sccm,thecoatinghardnessintheCr-Ncoatingincreasedfrom26.9to
44.9 GPa [9]. This increase was likely caused by an increase of compressive residual
stressduetotheinsertionofnitrogenatomsintheCrNstructureandanincreaseoflattice
˚
parameter from 4.2068 to 4.2566 A. However, further increase of nitrogen caused a
decrease of coating hardness [30]. In opposition to the hardness, with the increase of
content of nitrogen in these Cr-N coatings the critical load, which is often treated as a
measure of adhesion, decreased [30]. On the other hand, the hardness of Cr-based coat-
ingsdecreaseswithincreasingargonandnitrogenflowrateataconstantAr/N 2 ratio[11].
Not only deposition parameters have influence on PVD coating properties
(Table 16.2). An increase of coating thickness causes a change of a preferred growth
orientation [9,55] and microstructure [59], and has an influence on residual stress and
coating hardness [9,33,55,57,58]. An experimental data show opposite results.
According to Barata et al. [9], an increase of thickness of CrN coating from 2.5
to 4.2 μm deposited by reactive r.f. magnetron sputtering caused a decrease of coat-
ing hardness from 44.9 to 27.1 GPa, while an increase of thickness from 2.5 to 5 μm
of TiN, TiAlN, and TiCN coatings deposited by arc ion plating caused an increase
of coating hardness from 700 to 3000 HV [58]. Also, an increase of thickness from
4to12 μm of TiN coating deposited by cathodic arc evaporation caused an increase
of coating hardness from 21.7 to 27.4 GPa [33]. Chou et al. [55] have shown that
as thickness of TiN coating increased from 0.32 to 0.75 μm the most intensive
increase of coating hardness was noted, further increase of coating thickness had
a slightly influence on coating hardness. Moreover, the increase of TiN coating