Thermal spray is a continuous, directed, melt-spray process in which particles (e.g., 1–50 μm in diameter) of virtually any material are melted and accelerated to high velocities, through either a combustion flame or a dc or rf nontransferred thermal-plasma arc. The molten or semimolten droplets impinge on a substrate and rapidly solidify to form a thin “splat.” The deposit is built up by successive impingement and interbonding among the splats. The splats accumulate into a wellbonded deposit, generally > 10 μm thick.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400026853

Thermal Spray: Current Status and Future Trends

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

Octave bandwidth operation of Y-junction stripline and microstrip circulators is predicted using Bosma's Green's function analysis. The width of the coupling transmission lines is found to be a significant design parameter. Theoretical and experimental results are presented which show that wide lines and a smaller than usual disk radius can be used to obtain wide-band operation. A microstrip circulator is reported which operates from 7-15 GHz. Also presented are an analysis of the input impedance and an approximate equivalent circuit for the Y-junction circulator which shows the relationship between Bosma's equivalent circuit and that of Fay and Comstock.

Wide-Band Operation of Microstrip Circulators

In a method and apparatus for forming a three-dimensional object, successive layers of metal are welded together to build the object. After each layer is formed a complementary material is placed adjacent the layer. In this manner, layers of material form a block of welded metal and complementary material. Then, all or a portion of the complementary material which serves as a support structure during forming can be removed. The welded layers are milled to a final shape either after each layer is formed or after all layers have been made. Existing CNG machines can be easily modified to practice the method.

Method and apparatus for fabrication of three-dimensional metal articles by weld deposition

Thermal spraying has been present for over a century, being greatly refined and optimised during this time, becoming nowadays a reliable and cost-efficient method to deposit thick coatings with a wide variety of feedstock materials and substrates. Thermal sprayed coatings have been successfully applied in fields such as aerospace or electricity production, becoming an essential component of today's industry. To overpass the traditional capabilities of those coatings, new functionalities and coherent responses are being integrated, opening the field of functional and smart coatings. The aim of this paper is to present a comprehensive review of the current state of functional and smart coatings produced using thermal spraying deposition. It will first describe the different thermal spraying technologies, with a focus on how different techniques achieve the thermal and kinetic energy required to form a coating, as well as the environment to which feedstock particles are exposed in terms of temperature and velocity. It will then deal with the state-of-the-art functional and smart coatings applied using thermal spraying techniques, with a discussion on the fundamentals on which the coatings are designed, the efficiency of its performance and the industrial applications, both current and potential. The inherent designing flexibility of thermal sprayed functional and smart coatings has been exploited to explore exciting new possibilities on many different fields. Applications such as anti-bacterial and anti-fouling coatings, superhydrophobic surfaces, electrical and heating devices for functional coatings and self-healing, self-lubricating and sensors for smart coatings are here presented and discussed. All these exciting developments pave the way for the numerous applications that are to come in the next decade, making the field of thermal sprayed coatings a unique opportunity for research.

/pdf/beyond-traditional-coatings-a-review-on-thermal-sprayed-18jvpi9dt9.pdf

Beyond traditional coatings, a review on thermal sprayed functional and smart coatings

The arc‐plasma spray deposition has been successfully applied to fabrication of planar ferrite microwave integrated circuits. Powdered commercial sintered microwave ferrites were deposited at rates up to 2 mils/min on 1 sq in. dielectric substrates by arc‐plasma spray deposition. Process controls produced densities >99% theoretical and also maintained stoichiometric agreement between deposited films and starting material. Annealing expanded <0.1 μ grains to useful sizes of 1 to 20 μ and controlled cation distribution. Special annealing techniques were necessary for ferrites having volatile products such as Ni–Zn compounds. Magnetic and microwave properties of several deposited Mg–Mn ferrites and CeYIG agreed closely with bulk values. Remanence ratios up to 0.87 were noted. Practical application of arc‐plasma deposition required material compatibility studies at high temperature. These considerations often superseded microwave properties as criteria for material section.

D. H. Harris

Papers

Polycrystalline Ferrite Films for Microwave Applications Deposited by Arc‐Plasma