Thixoforming : Semi-solid Metal Processing

258j 8 Tool Technologies for Forming of Semi-solid Metals
Table 8.3 Process parameters for coating deposition.
Process parameters
Etching
phase
Interlayer
(Ti 1 xAl x)N
Top coat
c-(Al 2O 3)
Heating power (kW) 16 16 16
Process step time (s) 3600 8500 8000
Total pressure (mPa) Flow controlled 500 Flow controlled
M.f. voltage (250 kHz) (V) 650 — —
Bias voltage (V) — 80 (DC) 25 (pulsed m.f.)
Nitrogen flow (mln) — 60 —
Oxygen flow (mln) — — varied
Argon flow (mln) 150 Pressure controlled 250
Target power density (Wcm 2 ) — 13.7 7.95
Anode voltage (V) — 70 —
using two aluminium targets (target size 88 500 mm) using the dual cathode
arrangement (power 3500 W, pulse frequency 18.5 kHz). The process is flow controlled:
the argon is kept at 250 sccm while the oxygen flow is varied. The oxygen
partial pressure was controlled by adjusting a certain voltage at the cathodes. The
process parameters are listed in Table 8.3.
8.4.1.6 Results of the Deposition of g-Al2O3 on an Industrial Coating Unit
The properties of the deposited coatings are strongly dependent on the working point
in the hysteresis (Figure 8.16). To obtain the right coating properties for the dies,
different working points are examined. Two of these working points presented as an
example are compared using different thin-film analysis equipment such as phase
analysis (XRD), mechanical properties (nanoindentation) and SEM. One point is
chosen near the metallic sputtering mode at a cathode voltage of 560 V, and the
second one in the lower area at 460 V near the fully poisoned region. With an increase
in oxygen partial pressure, the deposition rate dropped from 40 nm min 1 at 560 V to
18 nm min 1 at 460 V.
Further investigations by using the XRD patterns in these working points show a
strong increase of the g-phase from 460 to 560 V. At 560 V, all important g-peaks can
be identified. For the g-Al2O3 the JCPDS card 10-425, for the substrate the JCPDS
card 25-1047 and for the cubic TiAlN interlayer the JCPDS card 38-1420 for TiN and
the JCPDS card 25-1495 for AlN are used [31]. These results were compared with
those for the g-Al2O3 coating of the laboratory coater (Figure 8.17).
This strong difference in the crystallinity can also be seen in the SEM images
(Figure 8.16). Comparing the different working points 460 and 560 V on the
industrial coating unit and the operation point of 310 V on the laboratory coater,
only 560 and 310 V show all 100% intensity peaks of g-Al2O3, the h400i and h440i.
With an increase in crystallinity of the deposited coating, the mechanical properties
also changed massively. The hardness and Young s modulus are obtained by using
nanoindentation. The hardness increased from 11.2 1.1 GPa at a deposition voltage