Cold spray (CS) is a progressive method for the deposition of metals and alloys whose principles involve considerable plastic deformation of the produced material at extreme strain rates. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the PAS method was used to characterize the deformation character at the lattice level and quantify the open-volume defects in four cold sprayed metals: Al, Cu, Ni, and Ti. As counterparts, bulk samples of these materials with ultrafine-grained structures were also produced by high-pressure torsion (HPT), a process exceeding cold spray in the total deformation, but having several orders of magnitude smaller strain rates, and by a traditional cold rolling process. The results show that the CS and HPT processes lead to the formation of similar lattice defects (dislocations and vacancy clusters), and both exhibit significantly higher dislocation densities than conventionally cold-rolled materials. Further, the vacancy clusters present in CS and HPT materials were not present in the rolled counterparts due to the lower vacancy production rate.

Recently a Ti–TiAl 3 metal–intermetallic laminate (MIL) composite attracts growing attention because they have potential application in honeycomb or sandwich components of airplanes and as biomaterial with good bio-compatibility. Of the available processing techniques, diffusion bonding of elemental titanium and aluminum foils is an effective low-temperature method to synthesize the composite, allowing growth of the intermetallic layer. However, application of assembling and multi-pass cold rolling operations leads to fact that this technology is complex and expensive. The use of Cold Spray technology instead of aluminum foils utilization and multi-pass cold rolling to produce the Ti–TiAl 3 MIL composites is believed to be more effective. However, reaction diffusion kinetics of Ti-Al particulate composite differs from that of classical MIL composite and needs to be studied. The task of this paper is to define microstructural changes of Tl-TiAl 3 composite coating during cold spraying and reaction sintering. The optical microscopy, SEM, EDS, X-ray and microhardness examinations are presented and discussed.

Cold gas dynamic spraying has shown to be a promising approach for fabricating titanium structures directly from powder in the absence of a controlled atmosphere. This study investigates the effect of annealing on the microstructure, hardness, and tensile properties of commercial purity titanium deposited under cold spray conditions. Equiaxed grains with ultrafine grain structure are observed in the annealed samples. A physical based model is proposed for recrystallization of cold-sprayed titanium deposits and the results are compared with conventional cold-rolled and annealed titanium products.

To maintain surface roughness of process rolls in cold rolling steel plants, WC-Co coatings have been known to be effective ones. In this study, a high pressure/high velocity oxygen fuel (HP/HVOF) process was used to obtain WC-Co coatings. To get the best quality of coatings, WC-Co coatings are sprayed with numerous powders made by various processes. These powders include agglomerated sintered powders, fused-crushed powders, extra high carbon WC-Co powders and (W 2 C, WC)-Co powders. After spraying, properties of coatings such as hardness, wear resistance. X-ray diffraction, and microstructures were analyzed. For coatings produced by agglomerated-sintered powders, hardness of the coating increased as power levels and the number of passes were increased. In case of the coatings produced by fused-crushed powders, a very low deposition rate was obtained due to a low flowablity of the powders. In addition, the WC-Co coatings sprayed with extra carbon content of WC-Co did not show improved hardness and wear resistance. Also, some decomposition of WC was observed in the coating. Finally, the coatings produced by (W 2 C, WC)-Co powders produced higher hardness and lower wear resistance coating.

Characterization of flame sprayed and furnace fused NiCrBSiC alloy coatings with two different carbon contents and 15~45 wt.% WC-Co addition is described in terms of microstructure, microhardness, and differential thermal analysis. Microstructural development of these coatings before and after fusing treatment is discussed to identify the precipitates in the coatings. Optimum fusing conditions (time and temperature) for wear testing sample are investigated in terms of microhardness and porosity of the coatings. Wear performance of these coatings is also investigated by two-body and three-body abrasive and dry sliding wear experiments. Optimum tungsten carbide content of the coatings is also selected to improve wear performance and thus enhance the service life of the process roll for cold rolling steel plant. Finally, microstructure and microhardness of the furnace and induction fused coatings are compared with emphasis on the interface between the coating and the steel substrate.

Cladding is a common method of providing corrosion protection of aluminum alloys, which forms an anodic layer in direct and intimate contact with the alloy sheet during cold roll processing. A structural aluminum alloy is clad in a thin layer of a higher purity alloy that is more galvanically reactive. Common examples include 1230 clad on 2024, and 7072 clad on 6061 and 7075. If this clad layer is damaged or removed the underlying structural alloy is exposed and susceptible to corrosion and/or stress corrosion cracking. Kinetic Metallization is a low temperature deposition technique compliant with MIL-STD-3021 that enables repair or replacement of worn or damaged clad layers. Aluminum or Al-Trans coatings are deposited as a new clad coating, and can be subsequently polished to the same mirror finish as the original clad surfaces. This paper presents the techniques developed for repairing worn or damaged Al clad surfaces using the economical Kinetic Metallization process and the qualification tests performed to date for various feedstock powder formulations (Ref 1).

Aluminium alloys are widely used for transportation facilities, because of light weight and high corrosion-resistance. If there are some cracks in transportation, sometimes they repair by welding. However, it is difficult to weld aluminium materials. Because, Aluminium has high specific thermal conductivity and high coefficient of thermal expansion compared with that of steel. The cold spray technique is known as a new technique not only for coating but also for thick depositions. It has many advantages, i.e. dense coating, high deposition rate and low oxidation. Therefore, it has a possibility to apply the cold spray technique instead of welding to repair the cracks. What seems to be lacking, however, is deposition mechanisms and mechanical properties of deposition produced by low pressure type cold spraying. This is a very important issue for applying the cold spray to repair some structures. In this study, elucidation of deposition mechanisms and evaluation of mechanical properties for the low pressure type cold sprayed aluminium depositions were investigated. As a result of elucidation of deposition mechanisms, it can be clear that the particle deposition needs to activate the surface by several impingements. Furthermore, as a result of evaluation of mechanical properties, the cold sprayed specimen showed higher strength than the monolithic specimen in the case of compressive loading to the coating.

Through analyzing and predicting the development trend of tomorrow iron & steel industry in China and the effect of the improvement of the industry technology on the varying trend of the demand of steels, it appears that thermal spraying technology has a good chance for further developments. This paper presents the development of the thermal spray technology in Baosteel Company and its application in the iron & steel industry. It describes and analyzes the thermal spraying applications on mould narrow plates for CCL, CGL sink rolls, continuous annealing hearth rolls and cold mill processing rolls etc. It also introduced the work done by Baosteel Company on the development of thermal spray technology and the development of the softwares and experimental set-ups for the surface engineering lab. Various aspects such as corporation and “Both Payoff”, to the self-innovation in thermal spray technology, combination of the application technology with the manufacturing technology, pre-maintenance and complete life cycle service, etc, provide countermeasures on how to expand the application of thermal spraying technology in China iron & steel industry.

Tailoring strength and ductility in additive manufacturing or repair is key to successful applications. Therefore, cold spraying must be tuned for maximum amounts of well-bonded internal interfaces as well as sufficient softening of the highly workhardened deposit. Zinc (Zn) with its low melting temperature is an ideal model system to study phenomena associated with high strain rate deformation and local temperature distributions, both, in single impacts and thicker deposits. Bonding and recrystallization can be facilitated by covering selected wide parameter regimes in cold spraying. Despite the low temperatures, Zn single splats already show recrystallization at internal interfaces, the respective amounts then scaling with increasing process gas temperatures. At higher process temperatures, deposits are almost fully recrystallized. The recrystallization seems to improve bonding at internal and at deposit-substrate interfaces. Under optimum conditions, an ultimate deposit cohesive strength of up to 135 MPa and an elongation to failure of 18.4% are reached, comparable to that of laser-manufactured or bulk Zn parts. This demonstrates a welltuned interplay between high amounts of bonded interfaces and softening by recrystallization that allows for deriving bulk-like performance of cold sprayed material without additional posttreatments. Correlations between microstructures, mechanical properties, and fracture mechanisms supply information about prerequisites needed for reaching high ductility as obtained in damage and failure modes of deposits and bulk materials in global and local approaches.

Cold spraying is a novel coating method in which coating is formed by mechanical deformation of sprayed metal particles. This heavy deformation causes structures, which need recrystallization heat-treatment in order to gain back the materials natural deformability. Aluminum, copper, nickel and Ni-20%Cr were cold sprayed and heat-treated at several temperatures. Coatings were sprayed using nitrogen as process gas. Substrate material was carbon steel. Heat-treatment temperatures were chosen from near room temperature to below coating materials melting temperature. As-sprayed and heat-treated coatings were characterized in microstructure, hardness, phase structure and electrical resistivity. It was found that 200ºC was enough to increase electric conductivity to 87% of pure copper. By heat treatment ductility was able to be increased and hardness subsequently decreased.

Extensive laboratory testing and field usage have shown that innovative surfacing techniques have produced cost effective maintenance systems and are providing long-term benefits. Self-fusing (sometimes known as self-fluxing) alloys containing tungsten carbide (WC), applied by PTAW, HVOF and SF (Spray Fusion) brazing processes are investigated. The process used and the effect of process parameters on the wear resistance of these coatings is evaluated. The test results show that the same self-fusing alloy applied by SF compared to PTAW have proven superior in severe erosive and abrasive applications. The case histories presented will cover a variety of applications including the use of HVOF versus hard chrome plating and the improvement in wear resistance of SF applied self-fused coatings versus PTAW. These comparisons are useful in providing new, higher performance solutions, in helping to overcome today's tougher surfacing and environmental requirements

Interparticle bonding is considered the most important factor in cold sprayed coatings, determining mechanical properties as well as physical and chemical behaviors. In this study, a Cu feedstock with low oxygen content is deposited with relatively high spray pressure and temperature in order to improve interparticle bonding and obtain a coating cohesive strength. Mechanical bonding between deposited particles is deduced from fracture morphology and the deformation behavior of Cu particles is simulated by finite element analysis.

Cold spray (CS) is characterized as a solid-state process of high deposition efficiency for metallic coatings as well as additive manufacturing of metals. However, due to high velocity impact and extensive deformation of particles during CS, the as-received coatings or deposits may present anisotropic characteristics which could influence the performance of deposits. Hence this study aims to investigate the anisotropic behaviors of CS copper deposits in a systematic way. The microstructure and micromechanical properties of the deposits both in the cross-section (v-face) and in the parallel plane to the surface (p-face) were characterized. Tensile tests were performed at various loading angles with respect to the nozzle moving direction in the p-face. It is revealed that there exist strong microstructural and mechanical anisotropies in CS deposits. Different interparticle interaction results in more severe particle impact deformation in v-face than p-face, with larger elastic modulus and microhardness values. The tensile tests show an unexpected anisotropy in both ultimate tensile strength and elongation, with the highest performance occurring at the angle of 20°. The in-plane tensile anisotropy could be attributed to the parallel multiple passes. Therefore, a novel weave-spraying method was proposed, which can greatly reduce the tensile anisotropy of CS deposits.

Deposition of copper by cold gas dynamic spraying has attracted much interest in recent years because of the capability to deposit low porosity oxide free coatings. However, it is generally found that as-deposited copper has a significantly greater hardness, and potentially lower ductility, than bulk material. This paper will describe work undertaken to investigate the effect of annealing heat treatments on the structure and mechanical properties of freestanding cold sprayed copper. After de-bonding from substrates these tracks were annealed for one hour at a range of temperatures up to 600 °C. Optical microscopy, scanning electron microscopy and X-ray diffraction were all employed to examine the microstructure. The peak widths in XRD were analysed according to the Hall – Williamson method so that changes in grain size and microstrain (i.e. dislocation content) could be quantified. Mechanical behaviour of the deposits was studied by microhardness measurements and tensile testing. The influences of annealing on mechanical properties are rationalised in terms of microstructure evolution and its effect on strengthening and recrystallization mechanisms in metals. The softening behaviour of cold sprayed Cu is explained considering the low stacking fault energy of Cu and the possibility of dynamic recystallization occurring during spraying.

Trends of thermal spraying technology in Japanese steel industry is summarized by investigating the patent applications filed in Japan Patent Office in the past 20 years from FY1990 to FY2009. The total number of patents filed in 8 Patent Offices (Japan, United States, Europe, China, Korea, Russia, Brazil and India), retrieved by the International Patent Classification symbol C23C4/00 (IPC index key: Coating by spraying the coating material in the molten state ), is 15,082. The ratio of patent applications filed in each Patent Office is as follows: JP (39%), US (22%), EP (17%), CN (9%), KR (6%), RU (3%), BR (3%) and IN (1%). The database used in this study is from commercially available “PatBase”. Number of patent applications of thermal spray technology (C23C4/00) in Japan is 4,369. Among these patents, the ratio of patents related to steel industry filed by major Japanese steel companies is 13% of total patents of every industrial segment in Japan. These patents are classified according to (1) coating applications in the process of steel production lines, (2) performances and effects obtained by coatings, .and (3) coating materials. In this paper, current status and future trend of thermal spray technology in Japanese steel industry is discussed.

Cold spray additive manufacturing technology (CSAM) is a progressive method of 3D print of metals and alloys. Its inherent work principles allow production of the components below the material melting points, thereby avoiding several undesired material degradation processes. Among other inherently associated phenomena, the work principles of CSAM involve extreme plastic deformation of the materials, triggering formation of several types of lattice defects. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the first historical analysis of CSAM materials by PAS was carried out. For the demonstration, four different base metals were selected (Al, Cu, Ni, Ti). For these, the character of dislocations and vacancies was observed and the respective densities were quantified. The results show that the extremely high strain rate in the cold spray process prevents recovery of vacancies by diffusion to sinks. The deformation-induced vacancies agglomerate into small vacancy clusters. Hence, metals deposited using CSAM contain not only dislocations but also vacancy clusters. Both kinds of defects were detected by positron annihilation spectroscopy.

The fracture toughness of pure Al, Cu, Ni, and Ti deposited by cold spraying was investigated to gain a better understanding of the damage process and quantify material performance. Rectangular specimens of self-standing deposits with fatigue pre-cracks were tested in three-point bending. KIC values were obtained from J-R curves and stress-strain curves were plotted. The cold-sprayed deposits exhibited significantly lower fracture toughness than the same wrought materials, and fractographic analysis revealed either ductile or cleavage intergranular fracture as the major failure mode.

The fatigue performance of conventional structural steel with an applied thermal barrier coating (TBC) was evaluated via cyclic bending. Tests were carried out for as-received and grit-blasted substrates as well as for samples with thermally sprayed bond coats and topcoats. Failure mechanisms were identified and changes in fatigue resistance were assessed based on results obtained for different loading amplitudes supplemented by fractographic analysis.

Cold Spraying (CS) is a thermal spray process capable of producing dense and thick coatings by the spraying of powders under high velocity and relatively low temperature. The high deposition efficiency and the thickness of each pass make possible the use of CS to produce freestanding parts, as an additive manufacturing process (CSAM). Traditionally, CS is performed spraying perpendicularly to the substrate, which ensures maximum deposition efficiency among other benefits. This, however, presents two main disadvantages for CSAM. First, by keeping the spraying angle constant, there is not much control on the final geometry of the part being built, and, second, the resultant part’s properties show anisotropy depending on whether this property is measured along the spraying axe or not. In this work, we present a method (Metal Knitting) that aims to help reduce both disadvantages. Metal Knitting is based on the performance of certain spraying movements that build near squared shapes step-by-step like in a knitting process. The principle of the method and examples are presented in this work, as well as some results on the anisotropy of 316L stainless steel freeform parts obtained by CSAM, measuring the tensile stress, hardness, and evaluating the microstructure in different directions of the material. The effect of annealing on the material properties is also investigated.

The Cold Gas-Dynamic Spray Method (CGSM) is a means of producing coatings or free-standing structures from powder feedstocks, on metallic, polymeric or ceramic substrates, through the use of high particle velocities obtained by the control of gas dynamics in converging-diverging nozzles. The method expands the existing temperature-velocity domain of thermal-spray technology by permitting formation of coatings at relatively low temperatures with spray patterns governed largely by the gas dynamics of the nozzle. The coatings are formed by the energetic impact of the feedstock particles, whereby inter-particle bonding appears to be governed by the deformation of the particles accompanied by creation of copious amounts of fresh surface area available for interparticle bonding. Because of the novelty of the process, very little basic information exists regarding the mechanical properties and microstructure of the coatings. This work reports the outcome of investigations aimed at more clearly understanding the mechanical properties and microstructural characteristics of prototypical CGSM coatings formed from commercial copper and steel powders. Techniques include optical, scanning and transmission electron microscopies, microhardness and residual stress measurements. Early results suggest the materials to have significantly different properties than coatings made by more traditional thermal spray or cladding processes.