Joining and surfacing of advanced materials

The application of advanced materials, i.e. advanced ceramics, glasses, intermetallic phases and various type of composites, not only depends on their manufacture processes including a great input of know-how, but also on their abilities for processing, among which the joining processes play an important role. The uses of advanced materials are changing rapidly, with a major emphasis on technical applications, especially the components of machines, apparatus and technical devices expected to withstand very heavy exploitation conditions. Furthermore,these materials are becoming more complex, in terms of being strengthened and toughened by transformation processes as well as by the addition of other ceramic or metallic materials including nanomaterials. The successful use of advanced materials requires the development of equally advanced joining materials, processes and technology. Some selected examples of results of joining advanced materials with the use of various procedures as well as surface modification of structural components with the use of advanced materials obtained in the Welding Engineering Department of Warsaw University of Technology, Poland, are presented.     

Graded plasma spraying of premixed metalceramic powders on metallic substrates

The mismatch between the thermal expansion coefficients of ceramics and metals and the differential stresses it causes at the interface create problems in metal to ceramic joining. Research has been con-ducted to solve this problem in thermal barrier coating technology. Previous studies have considered met-al-ceramic multilayers or graded-coatings, which include a metallic bond coat. In this study, a graded plasma-sprayed metal-ceramic coating is developed using the deposition of premixed metal and ceramic powders without the conventional metallic bond coat. Influences of thickness variations, number, and composition of the layers are investigated. Coatings are prepared by atmospheric plasma-spraying on In-conel 718 superalloy substrates. Ni-Cr-Al and ZrO₂ -8 % Y₂O₃ powders are used for plasma spraying. Ad-hesive and cohesive strength of the coatings are determined. The concentration profile of the elements is determined by x-ray energy-dispersive analysis. The microstructure and morphology of the coatings are investigated by optical and scanning electron microscopy (SEM). Results show that the mixed metal-ce-ramic coating obtained with the deposition of premixed powders is homogeneous. The morphology and microstructure of the coatings are considered satisfactory.     

Technology of braze welding absorber tubes to copper foil in solar collectors by the GTA method

The classification of aluminium alloys on the basis of main alloy elements and usability for heat treatment is presented. The essential problems occurring in welding of aluminium and its alloys are mentioned. The most advanced methods of joining these materials are described. Results of investigations into the possibility of joining of thin walled elements of aluminium alloys by low heat input arc welding methods, plasma arc welding and hybrid laser+MIG welding are also presented.     

Deposition of metallic coatings on polymer surfaces using cold spray

Current coating technologies such as plasma spray, High Velocity Oxygen Fuel (HVOF) or laser cladding involve the delivery of molten materials during the deposition process. However, such techniques are not well suited to the deposition of metallic coatings on polymers and composites. Cold spray (CS) has attracted much industrial interest over the past two decades. In this method, a material in powder form is accelerated on passage through a converging-diverging nozzle to high speeds via a high pressure coaxial carrier gas jet. The high impact kinetic energy deforms the particles, which creates effective bonding to the substrate.This paper presents the results of an initial study on the potential of the CS process to produce metallic coatings on non-metallic surfaces such as polymers and composites for engineering applications. Experimental and Computational Fluid Dynamics (CFD) results when spraying copper, aluminium and tin powder on a range of substrates such as PC/ABS, polyamide-6, polypropylene, polystyrene and a glass-fibre composite material are presented and analyzed.     

Synthesis of the Ni–Zn–Sm ferrites using microwaves energy

This work reports the preparation of Ni–Zn–Sm ferrite powders by combustion reaction using microwaves energy and XRD characterization. The influence of the fuel type used was investigated. The metallic nitrates and fuels (urea, glycine or 1:1 mixture) were heated in microwave oven for 5 and 10 min using the power of 450 and 630 W. Ni–Zn–Sm ferrite and traces of secondary phases were observed in the powders obtained with glycine and mixture (1:1). The powers obtained with urea presented low cristallinity, only the main peak of the Ni–Zn–Sm ferrite phase was observed.     

Aqueous processing in materials science and engineering

Reviews of aqueous processing in JOM have traditionally focused on hydrometallurgical process routes. This article, however, addresses the application of aqueous processing in materials engineering and presents some promising developments that employ aqueous-based routes for the manufacture of high-tech components and specialty products. Such applications include producing metallic and ceramic powders; etching; surface modification by electroplating and electroless plating; manufacturing jewelry and intricate components by electroforming; and producing advanced ceramics, composites, and nanophase materials by sol-gel and biomimetic processing.     

In situ joining of dissimilar nanocrystalline materials by spark plasma sintering

Joining of nanocrystalline materials will be a great challenge. In this paper, a reaction synthesis-based in situ joining technique was developed for joining dissimilar nanocrystalline materials by use of the spark plasma sintering (SPS) process. The joining technique combines the nanocrystalline material processing and joining operations into a single process.     

微波技术在金属材料制备中的应用现状

微波技术如何应用于金属材料制备是当前材料研究工作的重要方向之一.本文在分析微波场与金属的相互作用后,简要介绍了微波技术在金属间化合物合成、金属粉末冶金材料烧结、金属材料熔炼及焊接等方面的研究进展.     

Joining similar and dissimilar advanced engineered materials

The typically specialized property combinations associated with advanced materials, combined with a desire for monolithic structures to maximize efficiency and performance, requires their effective joining. Through proper joining process selection and parameter optimization, both similar and ultimately dissimilar combinations of materials can be joined to produce high-performance components and systems.     

Progress in joining of advanced materials Part 2: Joining of metal matrix composites and joining of other advanced materials

Abstract

Advanced materials generally require novel joining techniques. Developments in new materials research should be conducted hand in hand with work on weldability and joining capacity aspects. Sound joint quality for any new material has always been considered a milestone in a research and development scheme for a new material, particularly in terms of widespread applications. Better understanding of the microstructure–mechanical properties relationships of the bonded or welded joints will feed back to the materials development activities both in conventional and new materials areas. The two joining processes diffusion bonding and laser welding are considered in this literature review, since these processes are capable of joining a wide range of materials of interest in the aerospace industry, as well as in many other industrial applications, and offer remarkable advantages over conventional fusion welding processes. Of particular interest is the ability to join the more difficult aerospace alloys with minimal component distortion and high reproducibility of joint quality. The purpose of the review is to outline progress made in this area and to make suggestions for future work. Part 1 (STWJ, 1998, 3, (3), 105–126) dealt with solid state joining, fusion joining, and joining of intermetallics, while Part 2 covers joining of metal matrix composites and joining of other advanced materials.     

TiNi合金连接技术的研究现状及发展趋势

简述TiNi合金的性能及应用，着重论述了TiNi合金连接技术的研究现状，简要分析了TiNi合金现有连接方法的不足，并对TiNi合金连接技术需进一步开展的研究工作做了展望。     

Metallization of Thin Al2O3 Layers in Power Electronics Using Cold Gas Spraying

A successful combination of insulating substrates with conducting metal coatings produced by cold spraying could open new industrial application areas like the fabrication of power electronic components. For minimizing the number of industrial process steps, insulating ceramic layers should ideally be processed by thermal spray techniques. Thus, this study investigates the impact behavior and coating formation of ductile metallic feedstock powders onto brittle ceramic coatings. With respect to high electrical conductivity of the metallic lines and good electrical insulation of the ceramic interlayer, copper was cold gas sprayed on previously thermally sprayed Al₂O₃ coatings. Successful cold coating formation requires different strategies for the activation of the ceramic layer to increase adhesion and to avoid brittle failure. These both can be achieved either by applying a bondcoat on the ceramic layer or using heated substrates during the cold spray process.     

An investigation on microstructures and mechanical properties of explosive cladded C103 niobium alloy over C263 nimonic alloy

Futuristic aerospace applications such as advanced turbojet and scramjet engines used in subsonic, supersonic, and trans-atmospheric flights require materials with ever-increasing temperature and load bearing capabilities for improved performance. The materials C103 niobium alloy and C263 nimonic alloy are widely employed in the manufacturing of scramjet engine components. Efforts to join these two materials by fusion welding process have revealed that they are metallurgically incompatible due to the extreme propensity to form brittle intermetallics. The possibility of interdicting interlayer is explored to overcome the formulation of intermetallics and the attempts have not yielded fruitful results. Explosive welding/cladding is one of the possible ways to join these materials, as it is a solid state joining process.     

Progress in joining of advanced materials: Part 1: Solid state joining,fusion joining,and joining of intermetallics

Abstract

Advanced materials generally require novel joining techniques. Developments in new materials research should be conducted hand in hand with work on weldability and joining capacity aspects. Sound joint quality for any new material has always been considered a milestone in a research and development scheme for a new material, particularly in terms of widespread applications. Better understanding of the microstructure–mechanical properties relationships of the bonded or welded joints will feed back to the materials development activities both in conventional and new materials areas. The two joining processes diffusion bonding and laser welding are considered in this literature review, since these processes are capable of joining a wide range of materials of interest in the aerospace industry, as well as in many other industrial applications, and offer remarkable advantages over conventional fusion welding processes. Of particular interest is the ability to join the more difficult aerospace alloys with minimal component distortion and high reproducibility of joint quality. The purpose of the review is to outline progress made in this area and to make suggestions for future work. Part 1 deals with solid state joining, fusion joining, and joining of intermetallics, while Part 2 will cover joining of metal matrix composites and joining of other advanced materials.     

Characterization of thermal sprayed hydroxyapatite powders and coatings

Calcium phosphate materials such as hydroxyapatite (HA) have biocompatible properties that can promote osteogenesis or new bone formation. Thermal spraying is an economical and effective process for coating the hydroxyapatite onto metal. It has been reported that plasma spraying changes the degree of crystallinity as well as the phase composition of the HA. This article reports the preparation and characterization of HA powders and coatings by two thermal spray processes (plasma and combustion flame) and suggests that the state of the starting powder adversely affects the coating characteristics. The raw HA powders are synthesized through a chemical reaction involving calcium hydroxide and orthophosphoric acid. Phase analysis using an X- ray diffractometer revealed that the synthesized powder consists of predominantly the HA phase. Calcined and crushed HA powders of various size ranges were fed into the plasma jet to produce HA coatings on metallic substrates. In addition, some HA powders were sprayed into distilled water by plasma spraying and combustion flame spraying to study powder melting characteristics. Other samples were plasma sprayed onto a solid rotating target to study atomization and impact behavior. The morphology of the rapidly solidified powders and thermal sprayed coatings were examined by scanning electron microscopy (SEM). An X- ray sedimentation particle size analyzer, laser diffraction particle size analyzer, and image analyzer performed the particle size analysis. Preliminary results indicate that particle cohesion, size range, and thermal treatment in the plasma affect the phase and structure of the as- sprayed coating, and some post- spray treatment may be necessary to produce a dense and adherent coating with the desired biocompatible properties.     

Polyethylene–Carbon Nanotube Composite Film Deposited by Cold Spray Technique

Carbon nanotubes (CNTs) are high-performance materials because of their superior electrical conductivity, thermal conductivity, and self-lubrication, and they have been studied for application to polymer composite materials as fillers. However, the methods of fabricating polymer composites with CNTs, such as injection molding, are too complicated for industrial applications. We propose a simple cold spray (CS) technique to obtain a polymer composite of polyethylene (PE) and CNTs. The composite films were deposited by CS on polypropylene and nano-porous structured aluminum substrates. The maximum thickness of the composite film was approximately 1 mm. Peaks at G and D bands were observed in the Raman spectra of the films. Scanning electron microscopy images of the film surface revealed that PE particles were melted by the acceleration gas and CNTs were attached with melted PE. The PE particles solidified after contact with the substrate. These results indicate that PE–CNT composite films were successfully deposited on polypropylene and nano-porous structured aluminum substrates by CS.     

Aluminum-silicon carbide coatings by plasma spraying

An aluminum base composite (Al-SiC) powder has been developed for producing plasma sprayed coatings on Al and other metallic substrates. The composite powders were prepared by mechanical alloying of 6061 Al alloy with SiC particles. The concentration of SiC was varied between 20 and 75 vol%, and the size of the reinforcement was varied from 8 to 37 μm in the Al-50 vol% SiC composites. The 44 to 140 μm composite powders were sprayed using an axial feed plasma torch. Adhesion strength of the coatings to their substrates were found to decrease with increasing SiC content and with decreasing SiC particle sizes. The increase in the SiC content and decrease in particle size improved the erosive wear resistance of the coatings. The abrasive wear resistance was found to improve with the increase in SiC particle size and with the SiC content in the composite coatings.     

Investigation on reactive diffusion bonding of SiCp/6063 MMC by using mixed powders as interlayers

Mixed Al–Si, Al–Cu and Al–Si–SiC powders were used as interlayers to reactive diffusion bond SiCp/6063 MMC. The microstructure and the effects of bonding parameters on the shear strength of SiCp/6063 MMC joints were investigated. The results show that SiCp/6063 MMC joints bonded by using the interlayers of mixed Al–Si, Al–Cu powders have a dense joining layer of high quality. The mass transfer between the bonded materials and the interlayers during bonding leads to the hypoeutectic microstructure of the joining layers. Using mixed Al–Si–SiC powder as an interlayer, SiCp/6063 MMC can be reactive diffusion bonded by a composite joint. Because of the SiC segregation, however, there are a number of porous zones in the joining layer. This is responsible for the low shear strength of the joints, even lower than those reactive diffusion bonded by using the interlayers of mixed Al–Si and Al–Cu powders. Ti added in the interlayer obviously improves the joint strength reactive diffusion bonded by using the mixed Al–Si–SiC powder.     

Research on Quality and Reliability of Cold-Pressing Joining Between Aluminum and Stainless Sheets

Lightweight forming was one of the main ways to achieve energy conservation and emission reduction in advanced manufacturing. However, the cold-pressing process was easier to realize dissimilar sheets joining and could reduce the weight of both the material and the structure; therefore, this process was widely used. Taking aluminum and stainless sheets joining as an example, this study designed three kinds of joining schemes based on the theory of materials mechanics. It was concluded that the increase of the load pressure made the joining parts of the two sheets fitted quickly, but it decreased the joining thickness through the research of different joining project results. In the joining process, defects such as overlap, warping, protrusions, pitting, and partial cracking led to decreasing surface quality and reliability of the joining part. It was demonstrated by the sheet specimen unidirectional tensile test that the “embedding” and the “interlocking” were the main mechanisms of cold-pressing joining.     

Metallization of Various Polymers by Cold Spray

Previous results have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fiber reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a benchmark substrate. The CFRP used in this work has a thermosetting matrix, and the ABS, PEEK and PEI are all thermoplastic polymers, with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders, tin, copper and iron, were cold sprayed with both a low-pressure system and a high-pressure system at various conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermosetting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI. Based on the results, a method is proposed to determine the feasibility and deposition window of cold spraying specific metal powder/polymeric substrate combinations.