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The objective of this work was to create Co-based coatings (compositionally close to Stellite 6) on compacted graphite and gray cast iron substrates with a high power laser (2 kW continuous Nd:YAG) cladding process. The relationships between the relevant laser cladding parameters (i.e. laser beam scanning speed, laser power and powder feeding rate) and the main geometrical characteristics of a single laser track (height, width, dilution, etc.) were examined. A gradual variation of a single processing parameter was used for an appropriate experimental analysis and statistical correlations study between main processing parameters and geometrical characteristics of an individual laser track. These relations lead to the design of a laser cladding processing map that can be used as a guideline for the selection and further tuning of proper processing parameters for laser cladding of extensive layer. The coatings with thickness from 1.0 to 3.3 mm were created on flat substrates without cracks and other major defects. The microstructural features of these coatings were studied using optical microscopy, scanning electron microscopy (Philips XL30 FEG), EDS (EDAX) and XRD. Mechanical properties were determined using microhardness measurement, scratch test (CSM Revetest) analysis at room temperature and using the tribotesting (CSM HT Tribometer) at room and elevated (up to 525°C) temperatures.

Residual stress analysis in Co-based laser clad layers by laboratory X-rays and synchrotron diffraction techniques de Oliveira, U.; Ocelik, Vaclav; De Hosson, J.T.M. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. AbstractThick Co-based coatings were prepared by laser cladding technique on C45 steel substrates with different geometries. Microstructural observations were realized using optical, scanning electron and orientation imaging microscopy. The residual strain state on the surface of a clad layer was determined by the sin 2 Ψ-technique using laboratory X-rays. The diffraction of synchrotron radiation in θ-2θ was used to acquire information from the bulk of the materials. Internal stress was characterized through the depth and width of the coatings. Elastic moduli required for stress state calculation were measured by the nanoindentation technique and also estimated from moduli of γ-Co single crystal. A misorientation between principal strain direction and cladding direction was observed on the surface of Stellite 20 coating. The stress profiles inside clad layers reveal the influence of scanning speed, clad layer shape, laser tracks overlap and stress release component due to crosssectioning. The strong texture inside the coatings affects diffraction conditions, the precision of the measurements and also ability to collect experimental data.

Microstresses in a thick laser clad Co-based coating on steel substrate were investigated with 3D X-ray microscopy using an intense synchrotron microfocused beam. The microstructure was examined with light microscopy and field emission scanning electron microscopy equipped with X-ray energy dispersive spectroscopy and Electron Back Scattering Diffraction (orientation imaging microscopy). Microhardness and scratch resistance variations inside the coating are related to the local microstructure influenced by additional heating and by melt convection during the laser track overlapping. The residual microstrains were accessed with a high spatial resolution defined by the size of the synchrotron microbeam. Type II residual strains and stresses on the level of individual grains and dendrites were analyzed in terms of tensor invariants, hydrostatic and von Mises shear stress, along the depth of a slightly diluted clad track. The upper part of the coating shows a constant spread of hydrostatic stresses between −500 and 500 MPa; towards the bottom of the track the spread of these stresses increases almost linearly with depth. A correlation between the microstructural features and the spread of the hydrostatic microstresses was found. It is concluded that microstresses in individual neighboring grains are inhomogeneously dispersed.

This paper concentrates on thick and crack-free laser clad coatings (up to 3 mm). The coating material is a chromium-molybdenum-tungsten-vanadium alloyed high-speed steel that shows high wear resistance, high compressive strength, good toughness, very good dimensional stability on heat treatment and very good temper resistance. It will be demonstrated that laser cladding of MicroMelt 23 powder offers a relatively wide processing window resulting in the formation of thick, microstructurally uniform, hard, crack-and defect-free coating on ordinary steel substrates. Microstructural observations using light and field emission gun scanning electron microscopy with EDS and EBSD attachments together with internal strain measurements using diffraction of X-rays revealed the reason for low susceptibility to crack formation. An intensive martensitic transformation inside small austenitic cells surrounded by hard carbides following the rapid solidification process compensates the tensile strain and finally results in compressive stresses at the coating surface. Laser cladding on different steels substrate geometries will be demonstrated together with hardness profiles and their dependence on cladding conditions.