4 Prakt. Met. Sonderband 51 (2017) 
structural materials has led to a paradigm shift for the designer. Now it is possible to use the almost 
unlimited geometrical freedom of AM techniques for making the most intricate components in real 
materials, giving engineers new degrees of freedom for component design (Fig. 2). One example in 
the turbomachinery industry is the re-design of cooling configurations in components for better 
thermal efficiency (Fig. 3). For a detailed description of AM methods, such as SLM where 
“successive layers of metal powder are fully molten and consolidated on top of each other by the 
energy of a high intensity laser beam”, the reader is referred to the literature. 
The use of AM processes with actual structural materials like steel and non-ferrous alloys, such as 
nickel-base superalloys or aluminium, was driven by the aim of achieving material properties close 
to those of bulk material conventionally processed. However, designers will have to take into 
account some microstructural peculiarities resulting from AM processing. In particular, SLM 
produces extremely fine-grained microstructures due to high thermal gradients and rapid 
solidification. On the one hand, this might be advantageous for some applications requiring high 
static and dynamic strength. On the other hand, components requiring high creep strength may not 
be well suited to being made by SLM. Another problem could be the high residual stresses that 
remain in the part after AM. If they are not relaxed by stress relief annealing, the superposition of 
residual and applied stresses can lead to cracking in service, as the case study described under 3. 
will demonstrate [1] - [8]. 
REE. ws ARE 
[ xy scanner | laser 
leveling laser beam 
Ss m . 
yste window 
, 
powder 
. —— part 
movable 
satform 
Fig. 1: Selective Laser Melting (SLM) as an Additive Manufacturing (AM) process [19]