Martensitic transformations definitions

Such transformations have been extensively studied in quenched steels, but they can also be found in nonferrous alloys, ceramics, minerals, and polymers. They have been studied mainly for technical reasons, since the transformed material often has useful mechanical properties (hard, stiff, high damping (internal friction), shape memory). Martensitic transformations can occur at rather low temperature ( 100 K) where diffusional jumps of atoms are definitely frozen, but also at much higher temperature. Since they occur without transport of matter, they are not of central interest to solid state kinetics. However, in view of the crystallographic as well as the elastic and even plastic implications, diffusionless transformations may inform us about the principles involved in the structural part of heterogeneous solid state reactions, and for this reason we will discuss them. 

This transformation has many characteristics of martensitic transformations in metals, with definite orientation relationships between the two structures. The orientation relationships conform to the following [69-71] ... 

The shear-like , cooperative , and military (Christian, 1965) characteristics of martensitic transformations are universally recognized, but few explicit definitions exist. As late as the 1950s some refused to recognize that a martensitic transformation could occur in materials other than steels (Crussard and Philibert, 1956). More recently Cohen et al. (1979) concluded that ... 

Martensitic phase transformations are discussed for the last hundred years without loss of actuality. A concise definition of these structural phase transformations has been given by G.B. Olson stating that martensite is a diffusionless, lattice distortive, shear dominant transformation by nucleation and growth . In this work we present ab initio zero temperature calculations for two model systems, FeaNi and CuZn close in concentration to the martensitic region. Iron-nickel is a typical representative of the ferrous alloys with fee bet transition whereas the copper-zink alloy undergoes a transformation from the open to close packed structure. ... 

Characteristics and implementation of the treatments depend on the expected results and on the properties of the material considered a variety of processes are employed. In ferrous alloys, in steels, a eutectoid transformation plays a prominent role, and aspects described by time-temperature-transformation diagrams and martensite formation are of relevant interest. See a short presentation of these points in 5.10.4.5. Titanium alloys are an example of the formation of structures in which two phases may be present in comparable quantities. A few remarks about a and (3 Ti alloys and the relevant heat treatments have been made in 5.6.4.1.1. More generally, for the various metals, the existence of different crystal forms, their transformation temperatures, and the extension of solid-solution ranges with other metals are preliminary points in the definition of convenient heat treatments and of their effects. In the evaluation and planning of the treatments, due consideration must be given to the heating and/or cooling rate and to the diffusion processes (in pure metals and in alloys). 

Figures 10 and 11 partially illustrate this phenomena, where individual martensite plates are shown. It can be noticed that these plates occur at preferential sites in definite orientation to others indicating an autocatalytic or chain type transformation. While some of these strained regions are activated by thermal fluctuations, other regions need additional free energy of activation. When warmed to room temperature some strained regions tend to relax however, the existing, untransformed regions are still in a more highly strained, unrelaxed position than they were in the previous cycle, since...

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