STAGING OF THE CELLULAR DECOMPOSITION OF THE SUPERSATURATED SOLID SOLUTION Co - 13 at.%W

Abstract

The process of cellular decomposition staging of metallic supersaturated solid solutions was observed since the early investigations of this process using the method of optical metallography.The secondary cellular reaction is taking place in depleted reaction in the process of solid solution where  concentration is usually higher than the equilibrium temperature of alloying aging. The lower supersaturation of the solid solution causes the lower rate of the secondary cellular reactions, as well as the dispersion of the new microstructure. Although the secondary cellular response process is widespread and well-known, its systematic studies have not been conducted yet. According to the results of isothermal resistometric studies of cellular decomposition kinetics in lead-tin alloys the new method of distinguishing data for primary and secondary reactions was proposed. 

The purpose of this work is an experimental study of dilatograph of alloy Co-13 at. % W, aged in the temperature range 660-820 ° C by the cellular decomposition mechanism.

The experimental data on the  stage cellular decomposition are analyzed on the basis of the developed procedure of time derivatives analysis after alloy volume reduction.Submission of initial experimental isotherms in the coordinates dl/dτ-lg(τ), where  -l is the length of the test sample, τ - is the time of the alloy aging, it is possible to accurately determine the time time interval kinetical stages cellular decomposition.It was found that the alloy aging occurs during the primary and secondary reactions at all temperatures of the experiment.The product of the next stage of the cellular  reaction, which begins at the end of the previous reaction and proceeds at a substantially lower speed, are cell colonies of much less dispersion.

As a result of dilatograph investigation and application of the developed numerical data processing procedure, the stability of stage cellular decomposition in the Co - 13 at % W alloy temperature interval of aging 675 – 820°С was determined.It is established that at  675°С the process of cellular decomposition stage proceeds in three stages. In the temperature range up to 765°C, there is a two-stage decomposition of the solid solution, and at a temperature of 804°C and 820°C, close to the upper temperature limit of the cellular reaction behavior, only one decomposition stage is recorded.