Theoretical and technological aspects of production mechani‑cally alloyed powders for the production of coatings and products by additive methods

The established regularities of the formation of powders based on iron and nickel, obtained by the method of mechanical alloying and intended for the deposition of thermal spraying coatings, as well as the manufacture of products by layer‑by‑layer synthesis. The structure, phase composition and properties of materials are investigated. Powders consist of particles with a size of 20–70 microns, differ in the submicrocrystalline type structures, and nonequilibrium phase composition. Thermal spray coatings made of them have a set of properties that significantly exceed the properties of coatings made of commercially available materials. The diameter of the grains of the material obtained by the SLМ method from the synthesized powder is 1.5–2.0 times smaller than that produced from the powder of 316L steel, and the heat resistance is higher.

Measuring Residual Strain and Stress in Thermal Spray Coatings Using Neutron Diffractometers

Background During thermal spray coating, residual strain is formed within the coating and substrates due to thermo-mechanical processes and microstructural phase changes. Objective This paper provides a comprehensive guide to researchers planning to use neutron diffraction technique for thermal spray coatings, and reviews some of these studies. Methods ENGIN-X at the ISIS spallation source is a neutron diffractometer (time-of-flight) dedicated to materials science and engineering with high resolution testing. The focus is on the procedure of using ENGIN-X diffractometer for thermal spray coatings with a view that it can potentially be translated to other diffractometers. Results Number of studies involving neutron diffraction analysis in thermal spray coatings remain limited, partly due to limited number of such strain measurement facilities globally, and partly due to difficulty is applying neutron diffraction analysis to measure residual strain in the thermal spray coating microstructure. Conclusions This technique can provide a non-destructive through-thickness residual strain analysis in thermally sprayed components with a level of detail not normally achievable by other techniques. Neutron sources have been used to measure strains in thermal spray coatings, and here, we present examples where such coatings have been characterised at various neutron sources worldwide, to study residual strains and microstructures. Graphic Abstract

Influence of Thermochemical Treatment on the Surface Properties of Finish Turned Wire Arc Sprayed 17Cr Steel Coatings

Structural features of thermal spray coatings, e.g., porosity, can be beneficial as oil retention volumes in tribological systems in order to improve emergency running properties. While thermal spray coatings can already have a considerable degree of porosity depending on the coating conditions, the finish machining, e.g., by turning, has a significant influence on the final surface properties. Effects like near-surface deformation and subsequent closing of pores during the machining process should be prevented. In the present study, the influence of thermochemical surface hardening on the surface topography of wire arc sprayed 17Cr steel layers after finish turning was investigated. Successful surface hardening by gas nitriding was shown by light microscopic and phase analyses. The surface properties after the various treatment steps were characterized by the surface roughness parameters Ra and Rz, the valley void volume Vvv, and the Abbott curves. A rise of the valley void volume can be beneficial in tribological applications in which a suitable oil retention volume is required. Accordingly, a thermochemical treatment combined with an appropriate subsequent finishing process is suitable to significantly influence the surface properties of thermal spray steel coatings.