In-Line Observation of Laser Cladding Processes via Atomic Emission Spectroscopy

Direct metal deposition (DMD) can be used for the cladding of surfaces as well as repairing and additive manufacturing of parts and features. Process monitoring and control methods ensure a consistent quality during manufacturing. Monitoring by optical emission spectroscopy of the process radiation can provide information on process conditions and the deposition layer. The object of this work is to measure optical emissions from the process using a spectrometer and identify element lines within the spectra. Single spectra have been recorded from the process. Single tracks of Co-based powder (MetcoClad21) were clad on an S235 base material. The influence of varying process parameters on the incidence and intensity of element lines has been investigated. Moreover, the interactions between the laser beam, powder jet, and substrate with regard to spectral emissions have been examined individually. The results showed that element lines do not occur regularly. Therefore, single spectra are sorted into spectra including element lines (type A) and those not including element lines (type B). Furthermore, only non-ionised elements could be detected, with chromium appearing frequently. It was shown that increasing the laser power increases the incidence of type A spectra and the intensity of specific Cr I lines. Moreover, element lines only occurred frequently during the interaction of the laser beam with the melt pool of the deposition layer

Residual Stresses in Steel Specimens Induced by Laser Cladding and their Effect on Fatigue Strength

AbstractResidual stresses resulting from circumferential laser cladding of fatigue test specimen of austenitic steel X5CrNi18-10 and heat treatable steel 42CrMo4 with Stellite 21 are evaluated by neutron diffraction. Below the interface of cladding and base material the former shows compressive residual stresses, the latter shows tensile residual stresses. Locations of crack initiation during fatigue testing correlate to the findings. Austenitic steel specimens crack at the surface whereas heat treatable steel components and specimens crack close to the interface. Fatigue strength of both material systems drops due to laser cladding whereby the drop of heat treatable steel is significant. It can be concluded that residual stress distribution needs to be optimized in order to conserve maximal fatigue strength

Spectral Visualization of Alloy Reactions during Laser Melting

Laser materials processing includes rapid heating to possibly high temperatures and rapid cooling of the illuminated materials. The material reactions can show significant deviations from equilibrium processing. During processing of complex materials and material combinations, it is mainly unknown how the materials react and mix. However, it is important to know which chemical elements or compounds are present in the material to define the alloy. In addition, their distribution after rapid cooling needs to be better understood. Therefore, such alloy changes at rapid heating induced by laser illumination were created as pre-placed and pre-mixed powder nuggets. The energy input and the material ratio between the powder components were varied to identify characteristic responses. For the detection of reaction durations and mixing characteristics, the vapor plume content was assumed to contain the necessary information. Spectral measurements of the plume were used to identify indicators about process behaviors. It was seen that the spectral data give indications about the chemical reactions in the melt pool. The reactions of iron ore components with aluminum seem to require laser illumination to finish completely, although the thermite reaction should maintain the chemical reaction, likely due to the required melt mixing that enables the interaction of the reacting partners at all