Amorphous alloys have attracted extensive attention due to their unique atomic arrangement and excellent properties. However, the application in practical engineering is seriously limited due to the size, crystallization and other problems. Laser additive manufacturing technology has the characteristics of high heating, cooling rate and point by point melting deposition, which provides a new idea for the preparation of amorphous alloys. Zr 50 Ti 5 Cu 27 Ni 10 Al 8 amorphous alloy was prepared on the surface of pure zirconium substrate by selective laser melting technology. The composition and structure of the samples were characterized. The results show that the samples are mainly composed of amorphous phase, and the crystallization mainly occurs in the superimposed zone of heat affected zone. With the decrease of laser power, the area of crystallization zone and the number of crystallization particles decrease. However, if the laser power is too low, there will be non-fusion defects and cracks, which will seriously affect the forming quality and amorphous rate of amorphous alloy.

Ferritic steels are commissioned as one of the preferred structure materials for the boilers of nuclear and thermal power plants. The mechanical characterization and microstructural evolution of shielded metal arc welded dissimilar joint between ferritic SA213T91 (T91) and ferritic SA213T22 (T22) steels has been investigated by virtue of microstructures, micro-hardness, XRD and SEM/EDS analysis. Comparative performance of distinctive zones in the weldment i.e. heat affected zone, base metal and weld pool has been explored. The T91 HAZ and T22 HAZ zones of the weldment are observed to have high micro-hardness by virtue of martensitic morphology along with the presence of delta ferrite in T91 HAZ and carbide as well as intermetallics in T22 HAZ.

In glass mold industry, a surface treatment by laser cladding of a Ni based powder on cast iron is performed with a 4-kW continuous diode laser. For this, a robot programming method named "Wavering" was used. This method allows to cover large surfaces (higher than 5 mm). The cast iron substrate used during this work is employed for its heat exchange properties in glass mold Industry. However, it has drawbacks which are weak wear, corrosion, and abrasion resistance. Conventional techniques used to protect the molds, like Plasma Transferred Arc (PTA), affect the molds microstructure, but also the thermal and mechanical properties. The laser cladding of the Ni based alloy allows to protect the molds without affecting the cast iron thermal properties (and reduce the Heat Affected Zone length). The purpose of this research is to produce a well bonded Ni based melted powder without pores or cracks on large and curvilinear surfaces with the wanted geometry. The impact of the process parameters such as laser power, scanning speed and frequency on the coating geometry was investigated with an experimental design technique using the ANOVA (Analysis of variance) method. It was used to determine and represent the influence of each process parameter on the coating geometry (width, height, and circularity). This ANOVA analysis led to a parameter combination to optimize the Ni coating and the cast iron substrate quality by considering the industrial geometrical constraints. The bonding quality and the cracking behavior are also investigated on optimized parameters. Finally, it appears that laser cladding process leads to a better coating on curvilinear surfaces than other process like PTA.

Laser cladding is a very promising technology from a metallurgical point of view. The benefits are low heat input into the substrate, high cooling rates resulting in a fine microstructure of the coating and an excellent metallurgical bonding to the substrate. The main disadvantage of laser cladding, however, is poor process efficiency, which causes high processing costs. In order to gain interest on the industrial level an optimisation of the energy management, for example reducing the energy loss through conduction, is necessary. Improved process efficiency and reduced processing time can be realized by a hybrid technology of coupling laser with a plasma arc. The feed can be coaxial to the plasma gun in form of powder. The main advantage of this process is that the processing area as well as the powder is preheated and activated by a transferred arc. The laser power is mainly used for heating up the feedstock material till melting temperature. The experimental results prove the theoretical considerations. Compared to laser cladding an increase in cladding speed and a lower energy input are reached. Further the efficiency towards material can be nearly doubled, reducing stock costs. At last the heat-affected zone is reduced, which offers the possibility to process crack sensitivity materials.

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 powder of HSS (HSS23, AISI M3:2) was deposited by pulsed-PTA method on to low alloyed steel substrate. The influence of pulsation frequency was evaluated on the surface of deposits and on their cross sections by both light microscope and by Vickers hardness measurement apparatus and extreme properties mapping (XPS). Surfacing parameters at current frequency from 0 to 200Hz were tested during deposition of single weld bead. Dilution and heat affected zone were evaluated and compared for all tested parameters. The presence of retained austenite after deposition was determined by X-ray diffraction. The beads deposited with different frequencies differ in their shape, dilution degree, microhardness and penetration depth. It was found that the microhardness increases with current frequency.

In Laser Cladding, a differentiation must be made between cladding by brazing and cladding by welding regarding process parameters and the resulting material properties. Results of investigations of bronze cladding on steel parts produced by Laser Deposition Brazing will be presented. This means that a strong metallurgical bond is realized by diffusion processes by Laser Deposition Brazing, but the steel base material is not molten. The coatings were characterized by hardness distribution measurements from the bronze cladding to the steel substrate, by measuring the size of the heat-affected zone and by porosity measurements. This combination of a steel substrate and a local bronze coating is used industrially in many tribological applications, such as plain bearings or hydraulic pumps etc. The bronze offers excellent tribological properties. In some cases, the bronze is used as a complete solid part. However, applying the bronze locally to a steel base body instead of using a complete solid bronze component, offers the advantage of the higher modulus of elasticity of the steel, which provides greater stability of shape with regard to possible elastic deformations as these coated parts are exposed to high mechanical loads, it is essential that a high coating quality is achieved by laser cladding and that the properties are extensively and purposefully characterized. The production technology, the characterization and the industrial applications of such bronze coated steel parts are presented and explained in this contribution.

Laser cladding shows an increasing interest to apply high-quality tailored surface coatings, as well as 3D-deposits for repair and additive manufacturing of metallic parts. The industry is requesting powerful technologies that maintain the quality advantages of the laser technology, but also make the process more productive, as well as time and cost efficient. At Fraunhofer IWS a Laserline fiber-coupled diode laser of 20 kW power has been employed for over a decade to develop competitive coating solutions. The deposition rates achieved with this technology are comparable to those of common PTA technique, while at the same time bringing significant advantages in terms of reduced heat affected zone, distortion and savings in material resources.

Innovative short arc technology is gaining high interest for low temperature joining strategies exemplified by the soldering of zinc coated steels and the joining of steel/aluminum hybrid joints. Controlled short arc allows on one hand a very low heat input in the component, so that melting of the base material can be limited. On the other hand it is possible to use low temperature melting filler wires, as for example zinc wire. New development in controlling short arc have been performed in the last year and reached its maturity for welding production (e.g. Cold Metal Transfer (CMT) of Fronius or Cold Arc in EWM). In both cases the short arc is controlled after drop transfer. One way to perform control is a high dynamic wire feed, which allows high dynamic retracting wire end. Another possibility represents a new type of highly dynamic inverter switching, combined with very fast digital current control, to reduce drastically the peak power in the arc when the short arc is reignited. The consequence of this is a no-sputter, low heat processing procedure. The arc is considerably colder due to the power reduction on re-ignition, which means that a lower heat input is possible.

Titanium alloys are used in several fields due to their outstanding high specific strength, low density and excellent corrosion resistance, but the low wear resistance confines their applicability. The performance of CVD and PVD coatings is limited by the low hardness of the substrate, which cannot supply sufficient support, and conventional thermal spray coating materials do not provide the excellent corrosion properties. Laser alloying also often results in a decreased corrosion resistance and additionally in embrittlement. The use of boron for laser alloying or dispersing of diborides permits the incorporation of extremely hard boride phases without significant decrease of the matrix materials corrosion resistance and ductility, as there is no solubility of boron in titanium. Laser alloying with boron paste and dispersing of TiB 2 in Ti6Al4V surfaces is carried out with CO 2 lasers and an adapted inert gas shower apparatus. Typically a melt pool depth of 200 - 300 µm is achieved and the boride precipitates permit an increase of the surface hardness from 350 HV0.05 in the initial state to about 800 HV0.05. The surface area is characterized by means of optical microscopy, SEM and EDXS. Vacuum plasma spraying is used to provide a technology for deposition of TiB 2 layers with defined thickness prior to laser treatment on surfaces with complex shape and in order to evaluate the direct applicability of thermally sprayed TiB 2 coatings.

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.

HVOF-, arc- and plasma sprayed coatings are widely used for wear protection. Today these type of layers are dominant if thin coatings from 50 up to 500 µm and low heat input into the work piece are required. The main disadvantage of thermally sprayed coatings is the adhesion to the substrate and the early failure when cyclic loaded. In both cases a metallurgical bonding to the substrate can improve the life cycle time. Plasma transferred arc (PTA) welded coatings show a metallurgical bonding to the substrate. The main disadvantages of this coating technology are the dilution of about 5%, the heat input into the substrate and that nowadays all welding positions seem to be impossible to carry out. In this paper the theoretical background for welding thin coatings (less than 500 µm) with a decreased dilution and in all welding positions is given and experimentally proved.

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 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.

Over recent years, with the drive for new higher power, higher efficiency Gas Turbine engines, manufacturers have had to look at new alloys and new coating techniques to achieve and support the industry requirements. Repair technology has therefore had to keep pace with the OEM advances and much research and development has been undertaken in developing new repair processes. Many of the alloys now used are directionally solidified or single crystal, which until now have been deemed irreparable by traditional welding techniques. Recent developments in the use of lasers have not only rendered these alloys salvageable but have also reduced the overall repair time and therefore the cost. This paper looks at the use of laser technology as a repair process for gas turbine components, touching briefly on laser cutting and drilling but concentrating mainly on laser powder feed welding and its applications.

This paper presents a concept to develop a practical method to join dissimilar materials by the cold spray process currently not possible with conventional technologies. The novel aspect of the process includes the development of a joint design using cold spray as the enabling technology to join dissimilar materials. The emphasis in this study will be on the method used in the joining of cast ZE41A-T5 magnesium and wrought 6061 aluminum by the cold spray process (CSP) in combination with friction-stir welding (FSW) and the subsequent materials characterization. Microstructural analysis by electron and optical microscopy, along with mechanical test results will be presented. Comparisons will be made to conventional joining techniques and the importance, as well as the applications of this technique, will be discussed.

Additive Manufacturing processes such as laser metal deposition (LMD) are often used in repairing processes where material is deposited onto existing components. During the LMD process, thermal stresses and deformations of the substrate can occur. This deformation results from a multitude of effects throughout the manufacturing process. To precisely measure the time-temperature-deformation history, an experimental setup combining in situ deformation measurement and thermography is conceived. 3D deformations are measured using a stereo camera system observing a stochastically distributed speckle pattern applied on the surface of the substrate. Additionally, the temperature is measured on the underside of the substrate by means of thermal camera. Material is applied using LMD on the opposite side of the measurement therefore there is no chance of the laser beam interfering with the optical measurement of temperature and deformation or damaging the measurement equipment. Due to the areal nature of the measurement system chosen, it is possible to achieve high temporal and spatial resolution to identify critical heat distributions and welding path strategies, which lead to deformation. This work proposes a novel measurement setup and provides possible use cases for optimizing path planning during additive manufacturing processes based on three exemplary path geometries.

One of the most widely accepted and versatile materials used with many coating deposition methods is austenitic stainless steel 316L. This is due to the combination of good corrosion and mechanical properties that are suitable for numerous varying applications. As a result of our familiarity with 316L we assume the properties achieved will be within the expected frame as described in the literature. Deposition techniques and component size and shape have an impact on the heating and cooling variations which will then affect the microstructure of the final coating. This in turn will result in variations in the properties achieved. Some of these numerous factors such as: deposition technique, component geometry and size, impurities in the substrate and chemistry of the substrate will be considered. The influence of these factors on the microstructure and the definitive properties of 316L will be presented.

High power diode lasers (HPDL) at the level of ? 6 kW are efficient cladding tools in heavy engineering applications where thick (up to 5 mm) wear and corrosion resistant coating layers are required. Large beam geometry makes possible the overlap of thick 20 mm wide cladding tracks side by side without coating defects. Compact size and closed cooling water circulation enable HPDL cladding process to take place also at a site of new or worn high-value machine parts, which have worn in operation or been damaged already during overseas transportation. Instead of moving parts of several tons’ weight, it would be perhaps more cost efficient to transport HPDL cladding unit.

The aim of this work was to determine the behavior of multi-layered structures under high heat fluxes. A direct simulation by the implicit finite difference method was used to predict the transient temperature distribution in each layer of the multimaterial. The influence of the thickness of layers was also studied. Experimentally, high heat fluxes were produced using a HVOF gun operated with a methane-oxygen mixture and internally cooled samples. Multi-layered deposits were vacuum plasma sprayed onto a copper block containing coolant channels for a circulation of water. Transient and static tests were performed with heat fluxes up to 100 MW/m 2 and durations of a few minutes to several hours.