Study On Aging Phase Transformation Process And Properties In Constant Elastic Alloy

By means of transmission electron microscope (TEM), tensile experiments and Vickers-hardness measurement, it is investigated that the aging transformation process and influence of time, temperature and pre-deformation on properties of Ni42CrTiAl alloy.Firstly, On the basis of a rebuilt thermodynamic model, using the available data, we draw the conclusions that 508C is the temperature at which the Spinodal decomposition takes place and prove the result in subsequent experiment. We analysis the phenomena of serration "sideband", which is showed in X-ray diffraction pattern of Ni42CrTIAl alloy aged at various times and temperatures, and conclude that it results from the atoms of Ti and Al distribution un-uniformly. The early stage of phase transformation of Ni42CrTiAl alloys begins by Spinodal decomposition mechanism to form the rich and the poor solute zones. Then a concomitant ordering of solute atoms appears in the rich zone to form an ordered embryo of y ' phase.Secondly, based on the result of the early stage of phase transformation of Ni42CrTiAl alloy, we discuss the process of nucleating and growing of the Y ' phase. On one hand, the dispersed, uniform and fine precipitates improve the strength and toughness of the studied alloy. On the other hand, at some range of temperatures, if suitable densities of solute atoms exist, such as in grain boundary, Celluar precipitation will take place through nucleation and growth to form a stable structure, which is unfavorable to the properties of materials.Thirdly, the influence of pre-deformation on phase transformation and properties of alloy is studied. The pre-deformation leads to increase of the strain of materials and the density of dislocation. The former adds the drive force to the phase transformation and the latter provide the position of nucleation and promote the interaction of pre-formation and dislocation.Studying the whole phase transformation, we find that not only the Spinodal wavy, but also the phase in the peak aging are of the level of thenanometer, and the growth rate of the nanosized phase and structure is slower. This results from the bigger atomic size factor, which promotes the concomitant reaction of Spiondal and ordering, and prevents the further growing of the strengthening phase and structure. The phenomena provide the new ideas for the application and exploitation of bulck nano-materials.