Among hardfacing processes using welding, laser cladding is nowadays one of the most efficient surface coating techniques. It is widely used to increase wear and corrosion resistance of machine parts as a result of the unique process characteristics such as low heat input (smaller heat affected zone), distortion free clad layers, lower dilution rate, finer coating microstructure as well as good metallurgical bonding at the coating/substrate interface. A wide range of new hardfacing materials and corrosion-resistant alloys are available on the market and in this study, different coatings of Ni-, Co- and Fe-based alloys as well as carbide-based metal matrix composites have been deposited by laser cladding for benchmarking purposes. Coatings were deposited onto mild steel substrates using a high-power diode laser. Coating microstructure and hardness were investigated as well as their tribological properties such as 2-body and 3-body abrasion, slurry abrasion and cavitation erosion resistance. Corrosion performance of coatings was also investigated with the salt spray test. Coatings are ranked according to their performance in the different tests and relationships between microstructure and coating properties are discussed.

The need for sustainable use of resources requires continuous improvement in the energy efficiency and development of new approaches to the design and processing of suitable materials. The concept of high entropy alloys (HEAs) has recently been extended to more general compositional complex alloys (CCAs) and multi-principal element alloys (MPEAs). One of the major challenges on the way to application of these alloys is the extensive design and selection efforts due to the great variety of possible compositions and its consequences for workability and resulting material properties. The favorable high-temperature strength of Ni-based and Co-based superalloys is ascribed to a defined γ/γ’ structure consisting of a disordered FCC A1 matrix and ordered L 12 γ’ precipitates. In the current work we extended this design concept to CCAs, allowing disordered BCC A2 and ordered B2 phases in additions or in substitution of the original γ/γ’ structure. We used a high-throughput screening approach combining CALPHAD-based computational tools with in situ alloying by means of laser cladding. Wall-type specimens with gradient composition in the system Al-Co-Cr-Fe-Ni-Ti with varying Al, Ti and Cr content were analyzed. The combined modelling and experimental screening approach was demonstrated to be a powerful tool for designing new high performance AM-ready feedstock.

Laser cladding is a technology that uses high-energy-density lasers to quickly melt and solidify alloy powder on the surface of the metal substrate to form a cladding layer with good performance. Especially, martensitic stainless steel is widely used as a cladding material due to its high hardness and wear resistance. In this work, the martensitic stainless steel layers were fabricated on the C45 steel substrate by the laser cladding with different process parameters. The results show that holes in the cladding layer is unavoidable. The laser cladding process parameters have the important influence on the residual stress in the cladding layer. Under the action of residual stresses, the holes in the cladding layer will be the source of cracks, which will cause cracks in the cladding layer.

In this study, pure spherical Ta powders made by induced plasma sphero technique were used in the laser cladding process. The powders were sent into high-energy laser zone and were melted at the surface of a steel substrate to create a Ta layer. The microstructure development in the Ta layer was investigated in a scanning electron microscope. The results showed that the layer was basically dense with some pore/crack defects. In the layer, typical dendritic crystalline structures were formed. With the help of an energy dispersive spectroscope, Fe was detected in the Ta layer. The top surface had about 5% Fe while at the bottom of the cladded layer 15% Fe was detected. So, the diffusion of Fe upwards occurred. With the participant of Fe, the microstructure of the Ta layer was changed. Thermocalc software was used to simulate the phase constitution at different Ta-Fe compositions. The results by the simulation basically agreed with the experimental observations.

Laser cladding is a technology that uses high-energy-density lasers to quickly melt and solidify alloy powder on the surface of the metal substrate to form a cladding layer with good performance. The alloy powder composition has a significant impact on the cladding layer performance, including hardness, wear resistance and corrosion resistance. In this work, the effect of Nb content on the microstructure types and phase precipitation rules in the martensitic stainless steel laser cladding layers was investigated through the thermodynamics software. The martensitic stainless steel cladding layers with different Nb content was fabricated on the 45# steel substrate by the laser cladding. The microstructure and element composition of the cladding layers were analysed by the scanning electron microscope (SEM) and the energy spectrum analyser (EDS). The hardness, wear resistance and corrosion resistance of the cladding layers were also discussed. The results show that the amount of Cr element in carbide (boride) gradually decreases, while the amount of Nb element in carbide (boride) gradually increases, with the increasing Nb element content from 0.6 wt.% to 2.2 wt.%. For the performance of the cladding layer, the increase in the content of Nb makes the hardness and wear resistance of the cladding layer increase first and then decrease, but the corrosion resistance gradually increases. Generally speaking, the comprehensive performance is better when the Nb element content in the cladding layer is about 1.4 wt.%. At this time, the microhardness of the cladding layer is about 780.00 HV 0.2 , and the self-corrosion potential is -350.87 mV.

Laser cladding or metal deposition (LMD/DED) is widely used for wear-resistant coatings, repair and additive manufacturing applications due to the excellent properties of the deposited material. However, processes on complex 3D surfaces are often a challenge because they require time-consuming programming. This is particularly the case when no CAD data is available for the parts on which metal coatings or structures have to be applied. As a solution, we describe a digital process chain that begins with a 3D scanning process within the laser cladding machine (either robotic or CNC type). Using special software, high-quality 3D models of the scanned parts are created. For coating applications, these models are visualized on a PC. The operator can define cladding areas with just a few clicks of the mouse. Based on predefined parameters, powerful software calculates all the required tool paths. An additional simulation step can be used to verify collision-free operation. Finally, robot or CNC programs are automatically generated that can be executed immediately. Similar software is used to create 3D parts directly from CAD files. Finally, by combining both approaches, 3D geometries can be printed directly onto existing 3D freeform parts using laser metal deposition/LMD, even if their shape is arbitrary and not well documented by CAD data.

Process monitoring and control methods during direct metal deposition (DMD) are used to ensure a consistent manufacturing quality of the process. In the optical regime, naturally occurring process emission provides therefore selective and specific element lines, which can be obtained by optical spectrometers. However, DMD processes are in the heat conduction regime and superimposed broad spectral emissions dominate the wavelength specific signals. The aim of this work is to investigate the occurrence of different elemental lines in DMD processes as well as deposition track cross-sectional dimensions. Therefore, experiments were simultaneously conducted by using a high-resolution spectrometer (resolution = approx. 47 pm FWHM at 522 nm and 55 pm FWHM at 407.5 nm) and a medium resolution spectrometer (resolution = 0.73 nm FWHM), which were coupled by a bifurcated optical fibre. A parameter study of 27 single track DMD experiments using Co-Cr-based (MetcoClad21) powder on low-alloyed tool steel C45W (1.1730) substrate material, varying laser power, scan velocity and powder feed rate was conducted. Series of spectra were obtained for all sets of parameters with a scan rate of 100 Hz. The individual wavelength spectrum was analysed and classified by an algorithm into two types. Type-A spectra, with specific element emission lines and Type-B spectra, without significant emission lines with mostly predominant thermal emission radiation. Each deposition track was coupled to cross-sectional dimensions, including height, welding depth and melted areas. In addition, certain elemental lines contained in Type-A spectra were verified by using data from the NIST atomic spectra database. The investigation indicates that the relative number of Type-A spectra with respect to the total quantity of spectra, correlates significant to the process parameters. All detected and identified element lines occurred to be non-ionised elements, especially Cr I, Fe I and Mn I lines were frequently observed.

In order to improve the quality of coating, the causes of defect are analyzed in this paper. The research innovative uses single factor experiment combined with MATLAB to fit out the relationship between porosity and laser power, scanning speed, thickness, overlap rate. The multivariate quadratic equation is derived in this paper. It provides a solution to avoid defects in the aspect of laser cladding process.

The purpose of this work is to study the effect of laser radiation on powder particles transported by gas during laser cladding. The temperature and velocity of particles entering the light field of a CO 2 laser were determined by measuring particle radiation as well as the scattered radiation of the diode laser, two independent methods. It is shown that under the action of laser radiation, the particles acquire additional acceleration due to the vapor pressure from the irradiated part of the particle surface. This sonic recoil vapor pressure can significantly affect the in-flight characteristics of powder particles in a gas jet. Particle velocities due to laser acceleration exceeded 100 m/s in a carrier gas with a flow rate less than 30 m/s. Particle temperature depends on several factors and was found to vary from ambient temperature to the boiling point of the powder.

Different surface protection technologies were investigated in a waste-wood fired fluidized bed boiler. This biomass fuel environment is more aggressive than those firing virgin wood due to the elevated presence of sodium, potassium, lead, and zinc, leading to the deposit of alkali metal chlorides in conjunction with ash on boiler tube surfaces. As laboratory tests are seldom representative of the complex firing, chemistry, temperature, and local heat flux encountered in actual operating conditions, five different commercial, near commercial, and development coatings were applied to a 1 m length of plain carbon steel tubing used in the furnace walls. The coatings were fully characterized and measured prior to installation and after exposure. Iron and nickel-based weld overlays, two high velocity thermal spray coatings, and a laser-clad nanosteel coating were tested. After exposure, the tube was extracted from the boiler and corrosion scales and material losses were evaluated in comparison to unprotected tube material.

This paper presents some of the successful applications and material combinations the authors have achieved with high-speed laser cladding

This paper discusses the challenges of constructing mathematical models of physicochemical and heat-mass transfer processes associated with reactive heterogeneous materials used in laser additive manufacturing. The results of calculations of thermocapillary convection induced by laser heating in an aluminum melt with an admixture of nickel particles are presented. Models of interphase and chemical interactions with the formation of intermediate phases and intermetallic compounds on nickel particles added to the melt during laser alloying or cladding are proposed, which make it possible to calculate the composition of intermetallic phases in the trace of the beam after crystallization and cooling.

This study demonstrates a two-step laser cladding process for copper substrates in which cold spraying is used as a powder preplacing method to overcome problems associated with the high laser reflectivity of copper as well as the effects of high-temperature oxidation. In the first step of the process, Inconel powders are cold sprayed onto pure copper, producing a layer with a thickness of about 250 μm and a porosity of 0.88%. This is followed by a 3.5 kW laser remelting treatment using a 1030 nm laser with a spot size of 2.5 mm. Examination and testing of the as-sprayed and remelted layers show how the laser treatment improves coating microstructure, hardness, density, and metallurgical bonding.

This study assesses the erosive wear performance of hard-phase-reinforced coatings developed for use on hammer drills employed in mining operations. Several laser-clad coatings consisting of a nickel matrix with various tungsten carbides were evaluated along with two Fe-based alloys, FeCrBSi and FeCrNiBSi, and a WC-CoCr reference layer deposited by HVOF spraying. Erosion tests were conducted in 15° steps up to an angle of 90° and coating performance was determined based on volume loss obtained by 3D profilometry. At low angles, the more brittle materials lost significantly less volume, but at 90°, wear-resistant steel performs almost as well as a hard-phase loaded coating. Laser-clad layers with spherical fused tungsten carbides (FTC) performed better overall than coatings with regular (angular) FTC.

This study assesses the applicability of high-speed laser cladding for producing iron-based alloy coatings, in particular, CrNi duplex steel, FeCrV, and FeCrNiB. Process parameters are optimized for 150 µm thick claddings on mild steel using different laser power levels, surface speeds, and preheating temperatures. Claddings are also produced on cylindrical substrates of different diameters to investigate dependency on component geometry. Duplex steel was found to be highly processable by high-speed laser cladding. In contrast, crack-free FeCrV claddings can only be produced on small diameter surfaces, and only with preheating, while FeCrNiB could not be applied at all without cracking.

In this study, nickel-base superalloy coatings are deposited on CrMoAl substrates by different spraying methods and the coatings are evaluated based on their microstructure, phase composition, surface and splat morphology, bond strength, and corrosion properties. In the experiments, NiCrAlY powders with a particle size range of 30-45 μm were sprayed by conventional air plasma and a new laser hybrid plasma spraying technique. The spraying parameters are presented along with test results, observations, and conclusions. The coatings produced by laser hybrid plasma spraying had an average porosity of 0.9%, a bonding strength of 117 MPa, and significantly better corrosion properties than the APS layers.

This paper describes a method for producing textured surface layers on vacuum chamber components that act as particle traps. The novel textures consist of a stainless steel core produced by direct energy deposit laser cladding covered with a twin-wire arc sprayed aluminum film. The process has been qualified for 20 nm and older IC architectures and is now implemented in production equipment. It has been proven to significantly increase preventive maintenance intervals, reduce particle levels, and enhance yield.

A common method to combat abrasive wear and prolong the life of a component is to hardface the exposed region by overlay welding. State of the art coatings for these applications consist of a nickel-based ductile matrix with hard tungsten carbide particles embedded in it. An alternative with low environmental impact in combination with high performance to cost ratio is to use iron-based alloys. Critical in affecting the abrasive and impact wear resistance of these alloys is the coating quality e.g. porosity, cracks, dilution from the substrate combined with chemistry, size and volume fraction of the hard phase particles formed during solidification. Selection of the process parameters is critical for producing sound clads with expected properties. This paper focuses on the properties of PTA welded and laser cladded M2, M4 and A11 high speed steel coatings. Clad quality, hardness, abrasive wear resistance and microstructure are presented and interpreted with support of thermodynamic simulations.

The influence of process gas composition on characteristics of laser cladding processes is studied in detail at the example of a 60 HRC nickel based self fluxing alloy powder. Typically pure nitrogen, argon or helium are used as process gases in laser cladding processes. Besides mixtures of these gases also addition of hydrogen, carbon dioxide and oxygen are applied studying their influence on thermal emission, weld penetration depth and homogeneity, powder usage and crack formation. Use of identical composition of carrier gas and laser process gas is compared to use of different carrier and laser process gases. Oxygen addition increases thermal emission, but does not result in increased weld penetration depth or crack formation tendency. Thereby homogeneity of weld penetration is improved in comparison to use of pure argon. Also, maximum hardness of claddings is achieved when adding oxygen.

The potential of additive manufacturing has reached a point where the techniques are considered highly relevant for production purposes. In general, the manufacturing industry greets the new approach with enthusiasm, as it offers innovative designs and potentially reduced production costs. However, questions arise concerning the durability of additively manufactured components. This paper describes industrial trials with laser cladding and precipitation hardening heat treatment of thin-walled structures with the 17-4 PH stainless steel alloy. Due to the great relevance of the AM production methods for the aviation industry, the mechanical strength of the alloy given by the MMPDS document is used as a baseline. In order to improve the properties of the produced specimens, hot isostatic pressing was applied. The results show that a post processing treatment consisting of a HIP cycle and a conventional precipitation hardening, vastly improves the mechanical strength and elongation values of printed specimens, causing them to exceed the specified values.