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Abstract Al2O3–ZrO2 coatings were deposited using a
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vacuum arc deposition system equipped with two co-planar
cathodes. The plasma was injected into a cylindrical
magnetic duct through annular anode apertures toward a
substrate or an electrostatic ion current probe positioned on
the duct axis, in vacuum and in a low-pressure oxygen or
argon ? oxygen background. Ion current and arc voltage
measurements and visual observation of the cathode spots
were used to find stable arcing conditions, using a straight
plasma duct configuration. The cathode spot operation and
transport of the plasma beam in the duct were studied as a
function of arc current (Iarc = 25–200 A) and oxygen or
oxygen ? argon pressures (P = 0.1–1.5 Pa). Coatings 5073
were fabricated by exposing Si or WC–Co substrates
simultaneously to Al and Zr plasmas using a 1/8 torus filter
configuration in O2 ? Ar pressures. The coating compo-
sition, structure, microhardness, adhesion, and wear
behavior were studied as functions of the deposition
parameters. Favorable conditions for stable arcing were
obtained with Iarc = 75 and 100 A for Al and Zr plasmas,
respectively. The ion current decreased, and the arc voltage
increased with the oxygen pressure. Behavior of the ioncurrent and arc voltage suggested that cathode poisoning
started at P = 0.5 Pa. Deposition rates were 0.3-0.6 lm/
min, depending on the substrate position. All coatings were
‘‘Zr rich’’, i.e., the Zr:Al ratio was in the range of 1.2–5.6
depending on the substrate position and deposition condi-
tions. The coatings with higher ZrO2 concentration were
harder and had better resistance to wear. The coating’s
hardness reached a maximum of *22–24 GPa at a depo-
sition temperature of 500 C or a negative bias voltage of
75–100 V.
Introduction
Oxides, e.g., Al2O3, are promising as wear-resistant coating
materials for protecting cutting tool edges during high
temperature operation, due to their superior high temper-
ature stability [1]. However, being ionic compounds, they
are generally more brittle than carbides and nitrides of
transitional metals and also less adherent to tool substrates
[2].
Al2O3 and ZrO2 coatings, as well as Al2O3–ZrO2 coat-
ings with different Al2O3:ZrO2 ratios were studied previ-
ously. Al2O3 is used in cutting tool applications as a bulk
material for cutting inserts, and in wear-resistant coatings
for cutting tools—as an intermediate or top layer in mul-
tilayer coatings [1, 3]. Al2O3–ZrO2 coatings were depos-
ited by various techniques, such as electrochemical
deposition [4] and plasma spray [5–7] which were used for
thick coatings as well as physical vapor deposition (PVD)
[8–11], mainly used for thin coating deposition. Addition
of ZrO2 to Al2O3 improved mechanical properties in
structural bulk ceramics [12], and thick Al2O3–ZrO2
coatings deposited by plasma spray [6, 7] and electron
beam evaporation [8]. ZrO2 is presently used mainly foroptical and thermal barrier coatings [13]. Addition of
Al2O3 to ZrO2 stabilized ZrO2 in its tetragonal phase
(t-ZrO2)[9]. Moreover, ZrO2 and Al2O3 have almost no
mutual solubility [14], and thus may be deposited as a two-
phase nano-structure with greater hardness (H) than pre-
dicted by the mixture rule [15].
Most articles discussing PVD of Al2O3–ZrO2 coatings
focused on using Al2O3 to stabilize the t-ZrO2 phase [9, 16,
17]. For example, by controlling the Al2O3/ZrO2 ratio in
nano-laminate coatings, t-ZrO2 was deposited using reac-
tive d.c. magnetron sputtering at a low substrate tempera-
ture of Ts = 150 C[9]. Klostermann et al. [10] deposited