Understanding the complex mechanical behavior of stainless steel based composite coatings is important for engineering applications. The focus of this research was on gaining a fundamental understanding of the structure/property relationships that exist during structure formation of the coatings made by new low pressure cold spraying with propellant gas at the temperatures of 800-1000°C (warm spray). While composition is one of the key parameter in determining the final microstructure, the specific warm spray powder shock consolidation parameters (particle velocity and gas temperature) were found to have significant effects on the development of composite structure formation and mechanical properties. Microstructural examination and modeling results revealed that the strain localization mechanism differs from that of adiabatic shear band formation that results in large differences in the ensuing microstructure of the composite coating and its properties.

Surface preparation is very important for reliable adhesive bonding of cold sprayed coatings to the substrate. In this work, the grit blasting of low-carbon A516 steel substrates with Al 2 O 3 particles was studied and the roughness parameters Ra and Rt of the grit blasted surfaces were then measured. The influence of alumina grit size on the roughening of the A516 steel substrate, and the resulting effect on the roughness of the Cu coating – steel interface were studied. The results showed that variations of the grit blast size had significantly affected the resultant surface roughness of the substrate. The adhesive strength of the formed copper coatings on A516 steel substrates depends on the surface roughness and hardness of the base material. The adhesive strength about 110-200MPa was achieved. The specific features of the Cu coating-A516 steel interface topography were examined and discussed.

The main purpose of this study was to form cold sprayed copper coatings on A 516 low carbon steel, which is considered a prospective material for manufacturing used nuclear fuel containers. The 3 mm-thick Cu coatings were formed using the high pressure cold spray method with N 2 as the propellant gas. To increase the adhesion strength of the deposited coatings a copper sublayer was formed first, using He as the propellant gas. The deformation of copper particles during the deposition process was studied. The obtained SEM images of the Cu layer-A 516 low carbon steel substrate cross-sections demonstrated that the Cu sublayer had a dense microstructure, and local jet-metallic mixing areas. The Cu particles were deformed considerably more severely in the sub-layer than in the following layers. The steel substrate underwent severe deformation due to the impact of Cu particles. The mutual severe deformation of Cu particles and steel substrate resulted in a considerable increase of adhesion strength up to 120MPa. The structure of coatings and coating-substrate interface was studied by OIM, SEM and EDS.

Due to the demand for improved fuel economy as well as increased safety features, weight reduction is one of the major aims in the automotive industry. Future lightweight automotive components for the next car generation will probably use lots of magnesium alloy. These will form galvanic couples with other materials and may induce phenomena accelerating the corrosion rate of automotive components. The materials used were magnesium alloy AZ31B and several types of cold sprayed coating. The relative performance of each cold sprayed corrosion preventive compounds (CPC) was assessed in combination with the materials under several different electrochemical and accelerated corrosion tests. Baseline data for AZ31B with no CPC applied was also collected. CPC characteristics and properties are also included and discussed. The studies on bare Mg/Steel couples validated accelerated corrosion but found that CPC cold sprayed coatings mitigate corrosion rates. Thus Mg/Fe interfaces with defect-free cold sprayed coatings CPC can prevent buildup of corrosion products and reduce galvanic corrosion of automotive components.

The study of corrosion protection of magnesium and aluminum becomes increasingly important as the use of these alloys increases rapidly in the automotive and aerospace industries due to their advantages of light-weight, adequate mechanical properties and moderate cost. Corrosion, however, limits the application of magnesium and aluminum alloys. Fasteners, spot welds of dissimilar materials and their galvanic corrosion is of major concern in automotive applications. The paper presents first results of Low Pressure Cold Spray (LPCS) of Al based coatings for corrosion protection. The corrosion protection provided by these coatings was evaluated by electrochemical measurements in 1M NaCl electrolyte. The microstructures and electrochemical behavior of the coated joints were investigated. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed.

The FeAl intermetallic compound offers a combination of attractive properties such as thermal barrier, good strength at intermediate temperatures and an excellent corrosion resistance at elevated temperatures under oxidizing, carburizing and sulfidizing atmospheres. So they have attracted considerable attention as potential candidates for structural and coatings applications at elevated temperatures. However, the application of these intermetallics has been limited due to lack of deposition techniques and their low ductility at room temperature. To overcome the drawbacks we apply Low Pressure Cold Spray (LPCS) with following sintering for improving coating ductility and structure. The aim of this paper is to present the first results of FeAl intermetallic compound synthesis with this technique. A CS deposit is built up by the successive impact of individual powder particles that are the ‘‘building blocks’’ of the deposit. Sintering is applied to utilize reactions between the particles and obtain complex intermetallic compound. The microstructures and properties of the coatings were characterized by SEM, EDX and thermal diffusivity tests to define the structure formation mechanisms.

In this study, low-pressure cold spraying was used to deposit Al and Al-Al 2 O 3 composite powders on different substrate materials, including steel, aluminum, and magnesium alloy. Corrosion performance was evaluated by electrochemical testing in 1M NaCl electrolyte and microstructure was examined by means of SEM analysis. The results show that the corrosion potential of Al-Al 2 O 3 coatings depends on the content of alumina and that its presence does not appear to accelerate dissolution and failure of passivation oxide films. The investigation also revealed that pure aluminum coatings on aluminum alloy substrates can act as sacrificial anodes, thus providing corrosion protection.

Hydroxyapatite Composite (HAC) Coatings made by Low Pressure Gas Dynamic Spray (LPGDS) on the grit blasted Ti alloy substrate were studied. The powder feedstock for the HAC coating by LPGDS was prepared by mixing HA powder with Phosphate Glass particles in polyvinyl alcohol, drying and stirring. As-sprayed HAC films on the substrate were heat-treated by two steps (400-500°C and 600-900°C) and their physical characteristics were investigated by scanning electronic microscopy (SEM), X-ray diffractometer (XRD). During sintering-heat treatment, HA particles were consolidated and melted to form a dense and homogeneous coating layer which exhibits the grain structure. Application of HA-glass feedstock is found to be effective for Cold Spray HA based coatings.

A new approach is explored to achieve the aluminum alloy powder layer from nanoparticle contained metallic powder mixture feedstock by Low Pressure Gas Dynamic Spray (LPGDS) or Cold Spray (LPCS). In this approach, mixtures of micron-sized aluminum powder (average size of 10 µm) and alloying nano-powder of Cu, Si and TiC (200-500 nm), at appropriate proportions to compositions of Al-5wt%Cu, Al-5wt%Cu-0.75wt%Si and Al- 5wt%Cu-5wt%TiC with polymer binder were prepared by stirring. Then, the powder mixture was compacted into pellets, dryed, and further milled to obtain the particle agglomerates (average size of 50 µm) . The powder feedstock were sprayed by LPCS. In this paper, we investigate the spraying behavior Al-based nanoparticle contained powder mixtures the microstructural development and mechanical properties of deposited layers using a microindentation, scanning probe microscopy, scanning electron microscopy and energy dispersive X-ray analysis.

The corrosion behavior of Al alloys, produced by cast and powder (Low Pressure Gas Dynamic Spray or Cold Spray) technologies, was examined in 3% sodium chloride solution from the viewpoint of localized corrosion. The susceptibility to localized corrosion is known to be strongly affected by intermetallic phases present in the alloy’s microstructure. The influence of individual cathodic and anodic intermetallic phases was investigated by using a microelectrochemical setup and by electrochemical methods. The optical and scanning electron microscopy data reveal that the cast and powdered alloys experience localized corrosion due to presence of the intermetallic phases which results in the micro-corrosion effects such as exfoliation corrosion, intergranular or crevice corrosion, and most severely pitting. Cast material has lower corrosion properties because of the higher heterogeneity of the structure as compared with powder sprayed composite.

Thermal spraying processes are well known in industry for providing relatively dense components. The Gas Dynamic Spray (GDS) technologies are a growing alternative, especially after the great success of certain applications such as plasma and thermal spray formed components. One of the advantages of GDS is the possibility to obtain complex thin-walled shapes of various powder materials and composites. The optional post-spraying processes such as sintering, sizing and little machining may be applied. Using the low pressure radial injection GDS method, some new thin wall components have been formed. The process involves the automatic mechanical removal of sprayed ring components from a mould. Both the structure and properties of powdered material along with the GDS technology itself were studied. The main spraying and mould parameters were found to achieve high durability of moulds, which allowed the realization of a large scale GDS forming technology.