Thixoforming : Semi-solid Metal Processing

Figure 8.15 Monolayer g-Al2O3 (a) and TiAlN/g-Al2O3 bilayer (b).
8.4 Multifunctional PVD Composites for Thixoforming Mouldsj257
pressure (0.2 Pa) and a high target power density (78 Wcm 2 ). The deposited
coatings offer a high critical scratch load (70 N), very high hardness (28 GPa) and
high Young s modulus (351.8 GPa). After the promising results of this material
screening, this type of coating is being further developed for coating on industrialsized
coating units to coat tool inserts for application and forming experiments.
8.4.1.4 Upscaling g-Al2O3 from a Laboratory-scale Unit to an Industrial Coating Unit
The upscaling of a deposition process developed on a laboratory coating unit to an
industrial coating unit still remains a challenge. Especially the transfer of oxidic
coatingsisdifficult,becauseof theirhysteresisbehaviourduringdeposition.Thereare
different adjustable parameters, such as pumping speed of the turbopump [the Z400
laboratory coater has a 5.5 times higher pumping capacity than the CemeCon
(W€urselen, Germany) CC800/9 SinOx industrial unit] and the power density is twice
as high in the Z400. Furthermore, the gas inlet in the laboratory coater is located near
the substrate, whereas in the CC800/9 SinOx unit it is attached next to the cathodes.
Theseparametersstronglyinfluencethecoating behaviourandthecoatingproperties.
8.4.1.5 Experimental Details for the Development of g-Al2O3 on an Industrial
Coating Unit
Deposition is performed using a four cathode setup in a two-by-two dual cathode
arrangement on a CemeCon CC800/9-SinOx industrial coating unit. The coatings
are produced by co-sputtering of two TiAl targets and two Al targets. The size of the
TiAl targets is 88 500 mm. The Al targets have a purity of 99.2%. For the Ti 50Al 50
targets the purity is about 99.5% for the titanium and of 99.9% for the cylindrical
aluminium inserts within the sputter track. During deposition, the samples are
moved in a planetary motion to ensure a constant film thickness distribution at the
substrates. Before deposition, the samples are ion etched in an argon atmosphere.
For this substrate cleaning process, an m.f. power source is used. The coatings are
deposited using a MELEC pulse power supply (SPIK 2000A). For the (Ti1 xAlx)N
interlayer a total pressure of 500 mPa by reactive sputtering in a mixed atmosphere of
argon and nitrogen is used. The deposition of the Al 2O 3 top layer is performed by