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Analysis of the precipitation and growth processes in a high-temperature Fe-Ni alloy

Ducki K. J.

Journal of Achievements in Materials and Manufacturing Engineering

2008

Vol. 31, nr 2

226-232

Purpose: The influence of prolonged aging on the precipitation process of the intermetallic phases, carbide and boride in high-temperature Fe-Ni austenitic alloy has been studied. Taking advantage of the LSW theory, at attempt was undertaken to provide a quantitative description of the γ' phase particles growth as a function of temperature and aging time. Design/methodology/approach: The samples were subjected to a solution heat treatment at 980° C/2h/water, and then aged at 715, 750 and 780° C, with holding times 0.5-500 h. Structural investigations were conducted using transmission electron microscopy (TEM) and X-ray diffraction. Findings: Direct measurements on the electron micrographs allowed to calculate the structural parameters of the γ' phase: mean diameter, volume fraction and mean distance between particles. In accordance with the LSW theory, linear dependencies of changes in mean diameter as a function of t1/3 were elaborated and the activation energy (E) of the γ' phase coagulation process was determined. Practical implications: The obtained data of γ' phase particles growth as a function of temperature and aging time can be used to evaluate the degree of Fe-Ni alloys structure degradation and the distributions of temperatures during their operation at high temperatures. Originality/value: The paper touches upon the problem of the development of modern quantitative metallography methods with the use of thin foil technique and using theory LSW to describe a growth and coagulation processes of particles γ' phase in high-temperature Fe-Ni alloy.

Precipitation and growth of intermetallic phase in a high-temperature Fe-Ni alloy

Ducki K. J.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 18, nr 1-2

87--90

Purpose: The paper identifies the intermetallic phases, carbide and boride precipitating in the high-temperature Fe-Ni austenitic alloy during extended aging. Taking advantage of the LSW theory, at attempt was undertaken to provide a quantitative description of the γ’ phase [Ni3(Al,Ti)] particles growth as a function of temperature and aging time. Design/methodology/approach: The samples were subjected to a solution heat treatment at 980°C/2h/water, and then aged at 715, 750 and 780°C, with holding times 0.5-500 h. Structural investigations were conducted using transmission electron microscopy (TEM) and X-ray diffraction. Findings: Direct measurements on the electron micrographs allowed to calculate the structural parameters of the γ’ phase: mean diameter ( ), volume fraction (VV), and mean distance between particles (ld). In accordance with the LSW theory, linear dependencies of changes in as a function of t1/3 were elaborated for the analysed aging temperatures. From the slope of the Arrhenius straight line, the activation energy (E) of the γ’ phase coagulation process was determined, with its value estimated at 299kJ/mole. Research limitations/implications: The obtained data of γ’ phase particles growth as a function of temperature and aging time can be used to evaluate the degree of Fe-Ni alloys structure degradation during their operation at high temperatures. Originality/value: The paper touches upon the problem of the development of modern quantitative metallography methods with the use of thin foil technique.