Time-temperature-transformation, ITT

A molten metal alloy would normally be expected to crystallize into one or several phases. To form an amorphous, ie, glassy metal alloy from the liquid state means that the crystallization step must be avoided during solidification. This can be understood by considering a time—temperature—transformation (ITT) diagram (Fig. 2). Nucleating phases require an incubation time to assemble atoms through a statistical process into the correct crystal structure... 

Aronhime, M. T., Gillham, J. K. Time-Temperature Transformation (ITT) Cure Diagram of Thermosetting Polymeric Systems. Vol. 78, pp. 81-112. 

Isothermal Transformation Diagram. To separate the effects of transformation temperature from those of heat flow, it is essential to understand the nature of the transformation of austenite at a given, preselected temperature below the A. Information needed includes the starting time, the amount transformed as a function of time, and the time for complete transformation. A convenient way to accomplish this is to form austenite in specimens so thin (usually about 1-mm thick) that heat flow is not an issue, rapidly transfer the specimens to a Hquid bath at the desired temperature, and foUow the transformation with time. The experiment is repeated at several other transformation temperatures. On the same specimens, the microstmcture and properties of the transformation products can be assessed. These data can be summarized on a single graph of transformation temperature versus time known as an isothermal transformation (IT) diagram or, more usually, a time—temperature—transformation (ITT) diagram. A log scale is used for... 

We consider a plot of specific volume as a function of temperature as shown in Figure 21.1. This is a form of a time-temperature-transformation (ITT) diagram for a glass. On cooling the liquid from a high temperature, two phenomena may occur at the point of solidification, T. ... 

Gillhami ] [72] developed a time-temperature transformation ( ITT) diagram (Fig. 2.18) to represent the curing process. The ITT diagram is a plot of the log of time on the x-axis versus the curing temperature on the y-axis. There are five distinct regions in the diagram ... 

From equations (10) to (23), the time-temperature-transformation (ITT) curve can be obtained. The critical cooling rate Rc necessary for amorphous phase formation with a melt quenching method can be evaluated from TTT curve calculated and ap>proximated as follows... 

The nearly two dozen phase diagrams shown below present the reader with examples of some important types of single and multicomponent systems, especially for ceramics and metal alloys. This makes it possible to draw attention to certain features like the kinetic aspects of phase transitions (see Figure 22, which presents a time-temperature-transformation, or ITT, diagram for the precipitation of a-phase particles from the P-phase in a Ti-Mo alloy Reference 1, pp.358-360). The general references listed below and the references to individual figures contain phase diagrams for many additional systems. 

The kinetics of solid-state phase transformations are often summarized in time-temperature-transformation (TTT) diagrams. The ITT diagram shows... 

Problem 6.7. Figure 6.42 gives a set of rate of transformation [F(t)] curves for the crystallization of a glass. Using this information, calculate and plot (using a computer program of your choice) a ITT (time-temperature-transformation) diagram for this crystallization that includes curves for 10,50, and 90% transformed with temperature on the vertical axis versus log (time) on the horizontal axis. 

Problem 6.6. Figure 6.41 is a ITT diagram for 1054 steel. The heavy line to the left is for 1% transformed and the heavy line to the right is for 99% transformed. The dashed line in the middle is for 50% transformed. Calculate and plot (using the computer application of your choice) the rate of transformation for 300-750 °C at 50 C intervals by taking the times for 50% transformed and dividing 50% transformed by the time. Plot the temperature on the vertical axis and the rate of transformation on the horizontal axis. 

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