Demydenko O. Regularities of formation of structure and properties of powder composite materials on the basis of iron and self-fluxing alloys of multipurpose function.
The dissertation on competition of a scientific degree of the candidate of technical sciences on a specialty 05.16.06 - powder metallurgy and composite materials. – Igor Sikorsky Kyiv Polytechnic Institute, Kyiv, 2021
The work is devoted to the establishment of regularities of structure formation, physical and mechanical properties and operational characteristics of composite materials iron - self - fluxing multifunctional alloy obtained using various technologies of powder metallurgy.
The processes of wetting iron and its alloys with melts of self-fluxing iron-based alloys are investigated in the work. It is shown that the melt of the self-fluxing alloy wets the surfaces of iron and its alloys. Increasing the degree of alloying of steels impairs their wettability, due to the presence of carbides, which are known to impair wettability. Between steels and self-fluxing iron-based alloys there is an interaction with the formation of new phase components in the form of layers, the width of which depends
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on the temperature and interaction time. Also, the width of the layers is affected by the degree of alloying of steels, with increasing degree of alloying decreases the degree of
interaction between the components.
The presence of interaction is confirmed by the change in the content of elements
near the transition zones. In self-fluxing alloys based on iron, the content of chromium and nickel changes - it decreases, and in iron and its alloys the content of these elements increases.
The processes of compaction of composite material using various technologies of powder metallurgy are studied. It is established that in the materials obtained by pressing followed by sintering in a protective medium, porosity is present as a phase component, caused by the formation of closed porosity at the initial stages of sintering. The mechanism of sintering of the investigated materials is established, according to which the cause of residual porosity in sintered materials is the gas pressure in closed pores, which counteracts the acting Laplace forces.
The influence of technological parameters of compaction and composition of composite materials based on iron and self-fluxing alloys based on iron on the formation of the final structure is established. Self-fluxing alloy based on iron, which during sintering is in the liquid phase during crystallization forms layers between parts of the iron powder. With a self-fluxing alloy content of 20% or more, a frame structure is formed. Increasing the content of self-fluxing alloy increases the hardness. The high hardness is due to the fact that in the sintering process there was a self-reinforcement due to the formation of a frame of self-fluxing alloy, which at high hardness has a fairly high impact strength.
The study of mechanical characteristics shows that with increasing content of self-fluxing alloy for materials obtained by pressing followed by sintering in a protective environment, the tensile strength decreases, and the tensile strength remains virtually unchanged. It is known that the characteristics of materials largely depend on the quality of the contact surface between the components. On the one hand, increasing the amount of self-fluxing alloy provokes the dissolution of impurities, such as iron oxides, and improving the contact surface, and on the other hand, increasing the content of the brittle component reduces the overall strength of the material and consequently compensates for the properties. The highest values of physical and mechanical characteristics are observed for materials with a frame structure and the content of self- fluxing alloy based on iron within 20%.
Some operational properties of materials are studied. It is established that the resistance to wear with a fixed abrasive, in the conditions of gas-abrasive wear, resistance to corrosion depend on the method of obtaining materials, their composition and structure. The best indicators of wear resistance and corrosion resistance have materials with a content of self-fluxing alloy based on iron 20 – 30 % and honeycomb structure.
In addition, as mentioned above, when sintering materials, depending on the method of obtaining them in its structure, a framework of wear-resistant self-fluxing alloy is formed, which is an obstacle to the action of abrasives and aggressive media.
