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Al–Zr–O coatings with various compositions at Ts = 500–
700 C, using pulsed magnetron sputtering of Al and Zr
metal targets in argon ? oxygen background gas. Their
coatings consisted of a mixture of a crystalline and amor-
phous (a) phases: c-Al2O3 with a-ZrO2, when the ZrO2
content was below 8 at%., or a mixture of t-ZrO2 with
a-Al2O3, when the Al2O3 content was below 7.5 at%.
Amorphous or nano-crystalline minority phase in grain
boundaries was conjectured by Klostermann et al. because
they did not appear in the x-ray diffraction (XRD) spectra
[10]. Coatings with all other compositions were XRD
amorphous. The c-Al2O3 coatings had H = 30 GPa, while
the amorphous coatings had H = 10–13 GPa. Klostermann
et al. [10] suggested that segregation to a nc-Al2O3/a-ZrO2
structure (nc—nano-crystalline) is energy activated and
could be accomplished with high-energy ion flux. Trinh
et al. [11, 18, 19] deposited Al2O3–ZrO2 coatings using
various modes of magnetron sputtering at a temperature
range of Ts = 300–810 C. Deposition of Al2O3–ZrO2 with
low ZrO2 content resulted in amorphous coatings. However,
with higher ZrO2 content, the structure changed to a nano-
structure of a-Al2O3/c-ZrO2 [18] (c—cubic phase) or
a-Al2O3/t-ZrO2 [19], depending on the deposition method.
Both Al2O3 [20, 21] and ZrO2 [22] were deposited by
vacuum arc deposition (VAD). Brill et al. [20] and Rosen
et al. [21] reduced the crystallization temperature of Al2O3
by negatively biasing the substrate, and used the bias
voltage, Vb, to control the energy of ions impinging onto
the substrate. By these means, the formation temperature of
a-Al2O3 was reduced from 800 to 600 C by increasing Vb
to -300 V [20], and c-Al2O3 was deposited under Vb =
-300 V and deposition temperature Ts as low as 200 C
[21]. Recently, Kim et al. [23] deposited nano-multilayerd
structures of alternating Zr–O/Al–O layers using Zr and Al
cathodes in a VAD system. The Zr layers contained t-ZrO
nano-crystallites. Crystallites with a-Al2O3 structure were
observed only when the substrate was negatively biased in
the 100–150 V range. However, there are no published
reports of multicomponent Al2O3–ZrO2 coatings fabricated
by simultaneously depositing of Al and Zr plasmas in
oxygen background using VAD.This article reports on the deposition of Al2O3–ZrO2
coatings using a VAD system in which two cathodes were
mounted on one plane [24–26]. This system was used
previously for depositing multicomponent and multilayer
nitride coatings [26, 27], but not for oxides. The results are
pided into two parts. The first part reports on arc
behavior, i.e., ion current, arc voltage, and cathode spot
motion. This information was necessary to develop the
Al2O3–ZrO2 deposition processes. The second part reports
on deposition and characterization of the Al2O3–ZrO2
coatings. The coating structure, hardness, adhesion, and
tribological behavior are presented and discussed.
Experimental setup and procedure
A triple-cathode VAD system was used with two variant
magnetic filter configurations: (1) a straight plasma duct,
described previously [24, 25] and (2) a 1/8 torus magnetic
duct for macroparticle filtering. The plasma gun (Fig. 1a)
was equipped with two cathodes, Al and Zr, which were
mounted in two of three holes which were equally spaced
along the circumference of a 100-mm diameter circle
centered on the system axis [26, 27]. In this study, both
cathodes had a frustum cone shape with front and back
base diameters of 49 and 54 mm, respectively, and a height
of 15 mm. The straight duct (Fig. 1b) mainly was used