Abstract
Laser beams can be used to modify surface properties, such as increasing hardness. This can be achieved by
introducing and distributing carbides. It was previously shown that the deep penetration effect in combination with
a scanner moving the laser beam in a circular manner above the surface [1] promises to have a greater influence
on mixing and cross-sectional geometry compared to conventional heat conduction processes. However, the
mixing of the hard particles and the creation of rectangular tracks remains a challenge [2] since typically the track
depth correlates with the laser power. Using the correct laser power to achieve a welding depth matching the
cladding thickness in combination with a homogeneous distribution of the WC powder particles remains unsolved.
Therefore, this study aims to explain influences of dynamic beam shape modulation on track dimensions and
particle distribution. A two-stage process was used. In the first step, a powder mixture of spherical fused tungsten
carbide within a nickel-based superalloy was cladded using laser-powder directed energy deposition onto C45
(similar to AISI 1045; JIS S45C). The particles were present in spherical form in the nickel-matrix after cladding.
In a second step, the applied cladding layer was remelted using a high-intensity CIVAN laser beam to analyze the
impact of tailored heat input on track geometries, Fig. 1 (a). The laser power was varied and the dilution of the
cladding with the substrate was measured to identify if the dynamic high-frequency beam shaping can create more
homogeneous heat input and more rectangular track geometries.
A reasonable result in the distribution of particles by modulating the laser beam between a ring and a core geometry
were seen. For comparing the results, a laser energy dose distribution on the surface was introduced to characterize
the laser heat input distribution on the material. This takes the geometry of the laser beam, the travel motion and
the laser parameters into account. In combination with the metallographic analysis, it was shown that the
modulation of the cross-sectional beam profile at moderate frequency (500 Hz) leads to the highest homogeneity
of hard particle distribution, Fig. 1 (b). Without diluting into the substrate, a homogeneous material distribution
was realized. The key factor was the induced energy distribution and additional momentum on the melt pool
movement by the dynamic beam shaping.