Composite wire for use in additive manufacturing and thermal spraying made from layered and jointly formed strips

Anja Oswald, Haitham Saleh, Theodor Stuth1*

1 hplcas GmbH

*t.stuh@hpulcas.com

In additive manufacturing, bodies are produced in layers by welding; in thermal spraying, melted droplets are accelerated onto activated surfaces. The elements of the alloy that are required to build up metallic layers or bodies come either from a powder bed or from sprayed powder or wire. In wire-based production, it can be advantageous not to introduce the elements as an alloy, but as a composite material. Such material composites already exist as filler wires, which are characterized in that a metal jacket is filled with powder. Hpulcas GmbH, Freiberg, has developed a process by which the alloying elements are introduced as layers of a composite wire. The wire is made of - preferably high-purity - layered strips that are - with a certain delay - jointly formed by profiling with subsequent reduction by rolling and drawing. The high purity of the starting material not only reduces the corrosion of the welded surfaces or bodies, it also has the function, e.g. for combinations of Ni, Fe and Ti with Al, to allow the use of strip instead of powder and to allow recrystallization annealing of the composite.

The benefits of making parts by additive manufacturing or layers from composite strip formed into wire are:

 Low input of trace elements, esp. oxygen, compared with filler wire, where powder is used. This is specifically relevant for the use of Al, which is necessary to obtain alloys with high temperature resistivity

 Due to the use of strip instead of powder, the intended composition of elements can be met with high accuracy so that reproducible coatings can be produced

 The wire made from strip is fully dense in contrast to filler wires made with a powder filling. Therefore, laser and electron beam welding can be applied without splashes occurring.

 An alloy is only produced from the layered constituents upon welding. Segregation of elements is effectively hindered by the high cooling rates. Alloys can be produced, which can not be provided in wire form, e.g. as they are too brittle.

 Resulting from the use of high purity strip, the compound wire can be recrystallization annealed, even if the melting temperature of one constituent (as Al) is lower than the recrystallization temperature of an element provided with a standard degree of purity (e.g. Ni 200). Consequently, NiAl, FeAl and TiAl can be produced in soft form, which allows inner coating of tight bores, as cylinder bores. Recrystallization allows to produce thin wire, which is a prerequisite to produce thin layers.