Abstract
The phenomena of the first order phase transition (two-dimensional melting) of grain boundary at temperatures 0.6 - 0.9 TS0 (of the solid state melting point), discovered by the author (1971), is a fundamental property of solid crystalline materials. This finding leads to a principal revision of the scientific concepts of the solid state of substance. The phenomenological description and justification of the finding are developed. The generalized equation of Clausius-Clapeyron type for two-dimensional phase transition was obtained by applying the mathematical tools of the film thermodynamics. The equation has been used for calculating the grain boundary phase transition(GBPhT) temperature TSf of any metal, which TSf value lies within the range of (0.55 - 0.86) TS0. The investigation outcomes are applied to develop the methodology for more effective hard coating formation by synthesis of nanosize nitrides and carbonitrides in surface layers of steels and nickel alloys using a thermo-chemical processing (TChP). Production of an overall nitrogen concentration gradient from 4% to 0.5% at within surface layers leads to formation of modified coatings with a stepped change in properties. The mechanical behavior of new tools at the industrial tests indicated a higher heat resistance (nickel alloys), high resistance to surface wears and fragile breaks-down (chromium tool steels). A short overview of the results of some graded alloys characterization is presented.
Highlights
The analysis of a surface layers status had been executed by author and presented in number of publications earlier [1] [2]
The background of our investigation is the statement of Frenkel that the melting point of a solid state is specified as “jumping” of a vacancy concentration from 10−3 - 10−4 up to 10−1
Within the framework of these rough approaches the concentration of vacancy and the temperature of solid-liquid phase transition of grain boundaries appeared to differ from the volume stated above
Summary
The analysis of a surface layers status had been executed by author and presented in number of publications earlier [1] [2]. According to the concept, applied in the study the formation of the vacancy in a surface layer should be caused by its transfer from the middle of solution both at constant system mass and at constant surface It was resulted in the equation for vacancy concentration Xv in the surface, How to cite this paper: Minaev, Yu.A. The valuation of the vacancy concentrations for some of metals (Cu, W, Ag, Mo, Mg, Na, Al, Ti, Cr, Co, Ni, Fe, Au) gives Xv/Nv = 1000 It means, that near solidification temperature TS0 the vacancy concentration in a surface layers of a solid metals is the same, as in a liquid state [1]
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