TITLE:
Phenomena of Intergranular Liquid Film Formation in Technology
AUTHORS:
Yu. A. Minaev
KEYWORDS:
Grain Boundaries, Phase Transition, Nitrided Coatings, Graded Alloys, Hard Metals
JOURNAL NAME:
Journal of Materials Science and Chemical Engineering,
Vol.3 No.1,
January
20,
2015
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.