Influence of Metal Base Material on Mechanical Characteristics of Arc-Deposited Coatingsatings
Authors:   Karpenko Physico-Mechanical Institute of NAS of Ukraine, Hvozdetskii Volodymyr , Student Mykhajlo ,   Karpenko Physico-Mechanical Institute of NAS of Ukraine, Zadopozna Khrystyna ,   Karpenko Physico-Mechanical Institute of NAS of Ukraine, Markovych Sergiy ,   Central Ukrainian National Technical University
Published: February 2025

Aluminum alloys are characterized by low abrasive wear resistance, which significantly hinders their widespread use in technological environments, especially in the presence of abrasive particles. Recently, there has been a trend to replace steels with aluminum alloys with wear-resistant coatings. This makes it possible to reduce, firstly, the weight of parts, and secondly, carbon dioxide emissions into the atmosphere and the greenhouse effect. In the process of spraying wear-resistant coatings on a steel base, significant tensile stresses arise in the coating, which can lead to the appearance of micro and macro cracks in the coatings. There is no reliable data in the literature on the cohesive strength and level of stresses that are formed in powder wire coatings sprayed on a base of aluminum alloys, which hinders the development of a technology for restoring aluminum alloy parts by electric arc spraying.
The purpose of the work: to investigate the mechanical characteristics of electric arc coatings sprayed on samples of aluminum alloy D16 and compare them with the mechanical characteristics of coatings sprayed on a steel base with the same parameters.
For spraying, an electrometallizer with a coating spraying system with two vertically arranged air channels was used to form a supersonic air flow velocity (with a Mach number of 2). Electric arc coatings sprayed on a steel or aluminum base have a typical lamellar structure. When using a supersonic air jet (pressure 1.2 MPa) compared to a subsonic (pressure 0.6 MPa) coating has a more dispersed structure and a smaller number of pores.In the structure of coatings sprayed onto an aluminum base, significantly fewer pores and microcracks were recorded. On the surface of aluminum alloys, there is always a natural refractory film with Tpl = 2050°C, which significantly reduces the adhesion strength of coatings to the aluminum base. The use of an exothermic charge (FeCr+B4C) increased the temperature of the melt droplets to 2400°C, which facilitated the melting of the surface film Al2O3 and the fusion of droplets with the aluminum base, and as a result, the adhesion strength of the coating to the base increased by 70% to 50 MPa. To assess the operability of coatings, a new parameter was introduced, namely the ratio between the values of the residual tensile stresses of the first kind and the cohesive strength - σcol/σv. It was determined that the formation of cracks begins at the values of this indicator σcol/σv  0,75, while at σcol/σv  0,85 a network of cracks appears in the coatings.
Conclusions. 1. The use of a supersonic air jet for spraying coatings increases the kinetic energy of the droplets forming the coating, and, as a result, increases the cohesive strength of the coatings and reduces the magnitude of the residual tensile stresses of the first kind in them on a steel and aluminum base.
2. The ratio of the residual tensile stresses of the first kind in coatings σcol to their cohesive strength σv (σcol/σv) is proposed to be used as an indicator of the coating's resistance to cracking. Based on the analysis of the obtained coatings, it is shown that cracks begin to form in coatings for which the indicator σcol/σv  0.75, while at σcol/σv  0.85 a network of cracks appears in the coatings.
3.The level of tensile stresses of the first kind in coatings sprayed onto an aluminum base is lower than in coatings sprayed onto steel, which is due to the greater coefficient of thermal expansion of the aluminum alloy D16 than that of steel St3.