https://bura.brunel.ac.uk/bitstream/2438/13101/1/FullText.pdf

Cold spraying - A materials perspective

Cold spray is a solid-state coating deposition technology which has recently been applied as an additive manufacturing process to fabricate individual components and to repair damaged components. In comparison with fusion-based high-temperature additive manufacturing processes, cold spray additive manufacturing (CSAM) has been shown to retain the original properties of the feedstock, to produce oxide-free deposits, and to not adversely influence underlying substrate materials during manufacture. Therefore, CSAM is attracting considerable attention from both scientific and industrial communities. Although CSAM is an emerging additive manufacturing technology, a body of work has been carried out by various research groups and the technology has been applied across a range of manufacturing areas. The purpose of this paper is to systematically summarize and review the CSAM-related work to date.

Cold spray additive manufacturing and repair: Fundamentals and applications

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.

https://link.springer.com/content/pdf/10.1007%2Fs11666-016-0473-x.pdf

The 2016 Thermal Spray Roadmap

Solid-state additive manufacturing and repairing by cold spraying: A review

Cold Spray involves the deposition of metallic powder particles using a supersonic gas jet. When the nozzle standoff distance is small, a bow shock is formed at the impingement zone between the supersonic jet and the substrate. It has long been thought that this bow shock is detrimental to process performance as it can reduce particle impact velocities. By using computational fluid dynamics, Particle Image Velocimetry and Schlieren imaging it was possible to show that the bow shock has a negative influence on deposition efficiency as a result of a reduction in particle velocity. Furthermore, the existence of the bow shock was shown to be dependent on the length of the nozzle's supersonic potential core. Experiments were carried out with aluminium, copper and titanium powders using a custom-made helium nozzle, operating at 2.0 MPa and 20 °C, and a commercial nitrogen nozzle operating at 3.0 MPa and 300 °C. In all cases, it was found that there is a direct relationship between standoff distance and deposition efficiency. At standoff distances less than 60 mm, the bow shock reduced deposition efficiencies by as much as 40%.

Standoff distance and bow shock phenomena in the Cold Spray process

This paper reports on the development of a novel freeform fabrication technique using a cold spray (CS) system. In the CS process, metallic powder particles are accelerated in a supersonic gas jet and impacted with a substrate at speeds in excess of 600 m/s. The non-melting nature of its deposition mechanism ensures that the sprayed material is free from thermally induced tensile stresses, while the underlying substrate remains unchanged. The process is seen as a viable method for additive manufacturing because of its high deposition rates and controllable spray jet. A process was developed to investigate the potential of non-thermal freeform fabrication and was coined Cold Gas Dynamic Manufacturing (CGDM). Here, additive and subtractive techniques were combined to enable the production of complex geometries. Whereas most CS facilities concentrate on the application of wear or corrosion-resistant coatings, CGDM is dedicated to the production of freeform components, whilst still retaining an inherent coating ability. The process can produce functional forms using novel manufacturing strategies that are unique to CS. This paper presents information on the process, and details the various strategies employed during component fabrication. It was possible to construct components from many materials, including titanium, which exhibited freeform surfaces, internal channels and embedded devices. A breakdown of the process economics is also provided, with and without helium recycling.

Cold gas dynamic manufacturing: A non-thermal approach to freeform fabrication

Laser-assisted Cold Spray (LCS) is a new coating and fabrication process which combines the supersonic powder beam found in Cold Spray (CS) with laser heating of the deposition zone. LCS combines some advantages of CS: solid-state deposition, high build rate and the ability to deposit metals onto a range of substrates, with reduced operating costs which arise from not using a gas heater and replacing helium with nitrogen as the process gas. A system has been developed to impact metallic powder particles onto a substrate which is locally heated using a diode laser. A pyrometer and control system are used to record and maintain impact site temperature. In this study,

The laser-assisted cold spray process and deposit characterisation

Thick metal coatings are currently deposited via two well established routes, Laser or arc based cladding, and thermal spray. A new coating technique known as Laser-assisted Cold Spray (LCS), which aims to expand on the capabilities of the two process routes currently available, is under development at the University of Cambridge in the UK. LCS is a development of the Cold Spray process (CS) in which coatings are built up from powder particles which are entrained within a gas stream and accelerated through a de Laval nozzle, impacting the substrate at supersonic speeds that exceed a material dependent critical velocity.

The laser-assisted cold spray process

A process and apparatus are disclosed for the deposition of a layer of a first material onto a substrate of a second material. Powder particles of the first material are entrained into a carrier gas flow to form a powder beam directed to impinge on the substrate. This defines a powder beam footprint region at the substrate. The powder beam and the substrate are moved relative to each other to move the powder beam footprint relative to the substrate, thereby to deposit the layer of the first material. A laser is operated to cause direct, local heating of at least one of a forward substrate region and a powder beam footprint region. The laser beam direction is defined with reference to a plane coincident with or tangential to a surface of the substrate at the centre of the laser beam footprint in terms of an elevation angle from the plane to the laser beam direction and in terms of an acute azimuthal angle from the movement direction to the laser beam direction. The elevation angle is 80° or less and the azimuthal angle is ±60° or less. In the apparatus, there are provided at least three laser sources arrayed around the powder beam footprint, the angular spacing between the laser sources being 120° or less.

Deposition of coatings on substrates

The importance of metal coating technologies drives the continuous improvement of metal deposition techniques for application in a wide range of industrial sectors. This work presents the foundations of a new process technology for the deposition of Ti and Ti64 coatings on various substrates using supersonic powder streams and impact site laser heating. Full density metallic deposits are obtained under appropriate impact conditions without the need for transiting the melting point of the deposited material or substrate leading to large energy savings. Details of the experimental approach will be presented along with the general characteristics of the titanium coatings produced using this novel coatings method.

M Bray

Papers

Cold gas dynamic manufacturing: A non-thermal approach to freeform fabrication

The laser-assisted cold spray process and deposit characterisation

The laser-assisted cold spray process

Deposition of coatings on substrates

Supersonic laser deposition of Ti and Ti64 alloys