Experimental research of surface roughness and surface texture after laser cladding

Applied Surface Science, Volume 388, Part A, 1 December 2016, Pages 420-423

Damian Przestacki, Radomir Majchrowski, Lidia Marciniak-Podsadna

Abstract:The objective of the investigation was to identify surface integrity of machined parts after laser cladding. Surface analysis was made by using novel metrology methods: auto correlation and gradient distributions. An Infinite Focus Measurement Machine (IFM) has been used for the surface texture analysis. The study has been performed within a production facility during the prototyping process of new products. There are many methods available for geometric and surface topography measurements: contact and non-contact, micro and nanoscale approaches. An optical method based on the measurement of light reflected or scattered from the surface of an examined object can be used for this purpose. We have tested the application of an advanced 3D scanner for this purpose – optical scanner ATOS II. The scanner ATOS II represents the optical method, i.e. the digital light projection (DLP) method. The system consists of a projector and two digital cameras capable of supplying 1.4 million of measuring points per second. This method enables to scan elements from a few millimeters to a several dozen of meters in size. The roughness analysis is based on 2D measurements, which gave two-dimensional characteristics of the surface. In last decades, the metrology of the surface layer notes dynamical development as a science. During the last decades, many scientists and constructors became convinced that the third dimension should be added to the surface analysis. At present, 3D analysis of the surface geometry is widely accepted. In order to complete the topography analysis of the surface texture after laser cladding, our team worked out original program for 2D and 3D surface analysis. It was called TAS (topography analysis and simulation) and was based on Matlab software. Four modules were developed: the initial data processing module, basic parameters calculating module, data visualization module, and digital filtration module.

High temperature oxidation behavior of laser cladding MCrAlY coatings on austenitic stainless steel

Surface and Coatings Technology, Volume 270, 25 May 2015, Pages 243-248

J.C. Pereira, J.C. Zambrano, M.J. Tobar, A. Yañez, V. Amigó

Abstract:The development of coatings has become technologically significant in many industries. A common approach in high temperature applications is the production of new thermal barrier coatings (TBCs). Laser cladding (LC) can be an alternative method to thermal spraying in the production of high quality bond coats in TBCs. In this work, dense coatings that formed adequate metallurgical bonds with the substrate were obtained by overlapping coaxial laser cladding. The oxidation behavior of the coating specimens was assessed by air furnace oxidation tests at 1100 °C for up to 200 h. The coatings' microstructures are composed of a γ matrix phase and a β interdendritic phase, confirmed by X-ray diffraction (XRD). At high temperatures, the growth and formation of oxide layers protect the underlying coating and substrate from oxidation at elevated temperatures. The possible formation and morphology of oxides on the oxidized surface were evaluated using scanning electron microscopy (SEM), XRD and atom force microscopy (AFM). The evaluation of the thickness and phases present in thermally grown oxide scales was evaluated using field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy microanalysis (EDS), with a previous cut using the Focused Ion Beam Ga Column (FIB) method.

Fiber laser cladding of nickel-based alloy on cast iron

Applied Surface Science, Volume 374, 30 June 2016, Pages 197-205

F. Arias-González, J. del Val, R. Comesaña, J. Penide, F. Lusquiños, F. Quintero, A. Riveiro, M. Boutinguiza, J. Pou

Abstract: Gray cast iron is a ferrous alloy characterized by a carbon-rich phase in form of lamellar graphite in an iron matrix while ductile cast iron presents a carbon-rich phase in form of spheroidal graphite. Graphite presents a higher laser beam absorption than iron matrix and its morphology has also a strong influence on thermal conductivity of the material. The laser cladding process of cast iron is complicated by its heterogeneous microstructure which generates non-homogeneous thermal fields. In this research work, a comparison between different types of cast iron substrates (with different graphite morphology) has been carried out to analyze its impact on the process results. A fiber laser was used to generate a NiCrBSi coating over flat substrates of gray cast iron (EN-GJL-250) and nodular cast iron (EN-GJS-400-15). The relationship between processing parameters (laser irradiance and scanning speed) and geometry of a single laser track was examined. Moreover, microstructure and composition were studied by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD). The hardness and elastic modulus were analyzed by means of micro- and nanoindentation. A hardfacing coating was generated by fiber laser cladding. Suitable processing parameters to generate the Ni-based alloy coating were determined. For the same processing parameters, gray cast iron samples present higher dilution than cast iron samples. The elastic modulus is similar for the coating and the substrate, while the Ni-based coating obtained presents a significantly superior hardness than cast iron.

Characterization of hard coatings produced by laser cladding using laser-induced breakdown spectroscopy technique

Applied Surface Science, Volume 336, 1 May 2015, Pages 396-400

J.A. Varela, J.M. Amado, M.J. Tobar, M.P. Mateo, A. Yañez, G. Nicolas

Abstract:Protective coatings with a high abrasive wear resistance can be obtained from powders by laser cladding technique, in order to extend the service life of some industrial components. In this work, laser clad layers of self-fluxing NiCrBSi alloy powder mixed with WC powder have been produced on stainless steel substrates of austenitic type (AISI 304) in a first step and then chemically characterized by laser-induced breakdown spectroscopy (LIBS) technique. With the suitable laser processing parameters (mainly output power, beam scan speed and flow rate) and powders mixture proportions between WC ceramics and NiCrBSi alloys, dense pore free layers have been obtained on single tracks and on large areas with overlapped tracks. The results achieved by LIBS technique and applied for the first time to the analysis of laser clads provided the chemical composition of the tungsten carbides in metal alloy matrix. Different measurement modes (multiple point analyses, depth profiles and chemical maps) have been employed, demonstrating the usefulness of LIBS technique for the characterization of laser clads based on hardfacing alloys. The behavior of hardness can be explained by LIBS maps which evidenced the partial dilution of some WC spheres in the coating.

Laser cladding of aluminium on AISI 304 stainless steel with high-power diode lasers

Surface and Coatings Technology, Volume 253, 25 August 2014, Pages 214-220

A. Riveiro, A. Mejías, F. Lusquiños, J. del Val, R. Comesaña, J. Pardo, J. Pou

Abstract:The production of aluminium-based coatings on a stainless steel (AISI 304) substrate by side laser cladding, and using a high-power diode laser was experimentally studied. These coatings are very interesting for potential application such as fuel cells or catalytic converters.

Correlations between the main processing parameters (i.e. laser beam scanning speed, irradiance, and powder feeding rate) and the main geometrical characteristics of the clad track (height, width, and depth) were determined using a full factorial method. Furthermore, the microstructure of the coatings and the influence of the processing parameters on the costs associated to the process were examined. These relationships lead to the determination of processing maps in order to be used as a guideline for the selection of proper processing parameters for laser cladding of aluminium and alloys.