Mechanical and structural features of Nb coating layers deposited on steel substrates in a vacuum chamber

Abstract

In this paper analyzed was the influence of implementation of inert Ar gas and a mixture of inert plasma Ar / He gases in a vacuum chamber on the deposition of reactive niobium (Nb) powder. The aim of this paper was to deposit coating layers of high density, without oxide content, that will find application in the field of biomedicine. Detailed examination was performed of mechanical properties of microhardness using the HV0.3 method, of tensile bond strength by tensile testing and of the microstructure of the coating layers in the deposited state and after etching. For etching a solution of nitric acid HNO3 and hydrofluoric acid HF in a ratio of 1:1was used. It was found that inert gases, at low pressure prevent the reaction of gases with the metal droplets of molten Nb powder particles during the plasma spray deposition process. The density of the deposited coating in vacuum chamber is higher than that of coatings which are deposited at atmospheric pressure with reactive plasma gases N2 and H2. This is attributed to the elimination of thin oxide and nitride films at the interlamellar Nb contact, substantially increasing the ductility of the coating, eliminating the micro cracks through the deposited layers, which was confirmed by metallographic examination of samples. Tests have shown that VPS - Nb coating layers have mechanical properties and microstructure which completely enable the use of the coating on implants.