Study of quality criteria for two-phase iron-based composite coatings formed by plasma spraying

Abstract

The increasing relevance in the field of repair and restoration of machines and mechanisms is acquiring gas-thermal methods of applying functional coatings to the working surfaces of parts of machine assemblies. The purpose of gas-thermal coating methods is to provide and obtain special physical and mechanical properties of the surface of the part, as well as to restore worn-out components and mechanisms after their long-term and intensive operation. Plasma spraying of composite coatings is an effective method of gas-thermal treatment of the surface of a part. In this paper, a study was conducted on the optimal selection of material for plasma spraying of a part, taking into account its operational features and types of wear of working surfaces. In particular, the operating conditions of the screw of the conveying conveyor are analyzed. The technological features of the application of composite materials by plasma spraying technology are considered. The theoretical selection of a two-phase dispersed-filled composite for application to the working surfaces of the screw in order to restore and harden it has been carried out. Studies and analysis of one of the main indicators of the quality of the formed coating after plasma spraying – the magnitude of the resulting residual stresses (stretching and compression) have been carried out. Taking as a basis the kinematic modes and geometry features of the working surfaces of the screw, as well as the criteria for the formation of the thickness of the sprayed layer, the calculation equations for determining the residual stresses arising on the screw and cylindrical surfaces of the screw of the conveying conveyor are obtained. It is concluded that in order to achieve the required physical and mechanical properties of the coating, the volume fraction of the filler in the matrix of the PG-SR4 composite powder should be in the range of 20–25%. Therefore, it is possible to use in practice a particulate-filled composite of the NiСrВSiFе type with 20–25% reinforcing TiC filler particles in order to restore parts of machines and mechanisms.

Hardening of the plasma spraying coating dispersed additional phase of titanium carbide

“…Ввиду особенностей технологии плазменного напыления внутренняя макроструктура формируемого композитного покрытия будет стохастической, при этом в процессе формирования покрытия случайными становятся форма, размеры и свойства мелкодисперсной фазы, так и их локализация в основной матрице [18].…”

“…Следует отметить, что с помощью формулы (4) описывает напряжение сдвига композитного материала до образования в нем дислокационных петель. При этом, как отмечено в ряде работ [17][18][19], напряжения сдвига композитного покрытия согласно теории Орована практически в два раза расходятся с экспериментальными величинами, полученных в лабораторных условиях.…”