Ekaterina Trush

Theme of master's work:

Studying of the structure and properties of azotized surfaces of moulds for increasing their working capacity

Scientific adviser: Onoprienko Vladimir

In the machine-building industry, the pressure casting method became wide-spread for production of cast from nonferrous alloy. One of the problems of the cast production is the securing of durable working efficiency of the press molds. In the casting process of the aluminum-base alloy, the major factors of breakdown of press molds are hydrodynamic amortization and metal penetration (sticking of the alloy to the form face followed by tearing off together with the part of the base material while cast extracting). For hardening of the press molds, the various technologic measures are used, such as hot-working steel and alloy, extensional hardenable and surface im-pregnation application of coating.
It was examined in the research paper the fracturing behavior of bearing sur-face of press molds from steel with the previous gas and ionic plasma nitriding.
In the course of micro graphical investigation of the press molds components o the surface of the angular parts of the bearing surface flow around by liquid metal, it was found out the edge cracking and metal penetration of aluminum alloy. The metal penetration was found also on the flat surface in the point of impact of melt stream. The diffusion layer was detected between the stuck aluminum and the material of the instrument. According to the results of the micro hardness testing and microstructure analysis it was determined that the intermediate layer is a solid solution Al in ni-trated α-Fe with intermetalliñ compounds Fe_õAl_ó in the form of needle-shaped crystals. The transition zone includes also a thin layer (not more than 10 microme-ter) of solid solution Al â α-Fe with the higher hardness than the base metal (ac-cordingly 8500 and 3800 Í/mm²), then it’s followed by the layer of ferrous alu-minides with hardness 9-10 êÍ/mm², thickness up to 20 micro meter.
It’s determined that in the course of gas nitriding the diffusion layer is formed with a complex nitride zone that doesn’t secure a high flame erosion stability in con-ditions of frequent thermal cycling. Ionic plasma nitriding under the special schedule provides the diffusion layer forming without nitride zone. The absence of flame ero-sion net decreased the sticking of aluminum but did not secure the required amortiza-tion that leads to the loss of the coupling density of the elements of press mold.