The physical, mechanical, and tribological properties of quasicrystalline coatings based on the Al65Cu23Fe12 alloy prepared by plasma spraying have been investigated. The specific features of the phase formation due to the competitive interactions of the icosahedral Ψ and cubic β phases have been elucidated. A correlation between the microhardness and the content of the icosahedral phase in the coating has been determined. The decisive role of the quasicrystalline phase in the formation of high tribological characteristics of the coatings has been revealed and tested.

http://iopscience.iop.org/article/10.1088/1757-899X/155/1/012014/pdf

Microstructures and Tribological Properties of Al-Cu-Fe quasicrystalline plasma sprayed coatings

In this paper the model of the cathode spot of a vacuum arc is considered in the framework of the drift-diffusion representation. It is shown that the main source of electrons, providing the current transport of vacuum arc, are ionization processes in the cathode zone, while the emission processes are an auxiliary source of initial electrons. The effects associated with the distribution of electron density in the plasma column of cathode spot, in particular the formation of a "plasma reaction zone" and "ionization wave", are discussed.

Numerical simulation of low pressure gas metal arc plasma

Multiple missions are being planned for lunar in-situ resource development initially requiring autonomous complex software-hardware system operations followed by a sustainable, long-term astronaut presence entailing the development of a lunar base camp. Radiation exposure from solar particle events (SPEs) presents a significant hazardous concern. In mitigating the radiation risk to autonomous robotic systems (ARS) including orbiters, satellite probes, landers, rovers, and other equipment at the lunar surface, component parts in the hardware are categorized according to their respective Radiation Design Margin (RDM). Ratio of the part failure level to the part radiation environment is the key activity of the missions’ hardness assurance program. Reliability of multi-state systems with multi-state components indicates the probability that system capacity meets a required demand when the system components and demand follows a multi-state behavior. Space radiation demand placed on ARS appears as an impending/ impacting flux for which comparative measureable analysis of various technologies applied may express the degree of reliability per ASR structural integrity and mission function. The aim of this paper is showcase multiple innovative technologies on radiation tolerance in the engineering designs of lunar spacecraft/ ARS. Keywords: radiation hardness, radiation shields, autonomous robotic systems 

Radiation hardening of spacecraft and other autonomous robotic systems: Lunar safety v2.0

The paper deals with modeling of elemental composition and properties of heterogeneous layers in multilayered shields to protect spacecraft onboard equipment from radiation emitted by the natural Earth's radiation belt. This radiation causes malfunctioning of semiconductor elements in electronic equipment and may result in a failure of the spacecraft as a whole. We consider four different shield designs and compare them to the most conventional radiation-protective material for spacecraft - aluminum. Out of light and heavy chemical elements we chose the materials with high reaction cross sections and low density. The mass attenuation coefficient of boron- containing compounds is 20% higher than that of aluminum. Heterogeneous shields consist of three layers: a glass cloth, borated material, and nickel. With a protective shield containing heavy metal the output bremsstrahlung can be reduced. The amount of gamma rays that succeed to penetrate the shield is 4 times less compared to aluminum. The shields under study have the thicknesses of 5.95 and 6.2 mm. A comparative analysis of homogeneous and multilayered protective coatings of the same chemical composition has been performed. A heterogeneous protective shield has been found to be advantageous in weight and shielding properties over its homogeneous counterparts and aluminum. The dose characteristics and transmittance were calculated by the Monte Carlo method. The results of our study lead us to conclude that a three-layer boron carbide shield provides the most effective protection from radiation. This shield ensures twice as low absorbed dose and 4 times less the number of penetrated gamma-ray photons compared to its aluminum analogue. Moreover, a heterogeneous shield will have a weight 10% lighter than aluminum, with the same attenuation coefficient of the electron flux. Such heterogeneous shields can be used to protect spacecraft launched to geostationary orbit. Furthermore, a protective boron-containing and nickel coating can be deposited onto a finished housing frame of space equipment.

https://iopscience.iop.org/article/10.1088/1757-899X/122/1/012033/pdf

O N Draganyuk

Papers

The heterogeneous anti-radiation shield for spacecraft*

Effect of Substitution of Mn and Ga Atoms by Fe Atom in the Mn2GaC MAX phase

The spin-state transition in ACo2O4 spinels (A=Be, Mg, Ca, Cd, Zn)