Accession Number : ADA508364


Title :   Energy Barriers and Hysteresis in Martensitic Phase Transformations


Descriptive Note : Journal article


Corporate Author : MINNESOTA UNIV MINNEAPOLIS DEPT OF AEROSPACE ENGINEERING AND MECHANICS


Personal Author(s) : Zhang, Zhiyong ; James, Richard D ; Muller, Stefan


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a508364.pdf


Report Date : Aug 2008


Pagination or Media Count : 40


Abstract : We report results from a systematic program of changing composition of alloys in the system TiNiX, X= Cu, Pt, Pd, Au, to pursue certain special lattice parameters that have been identified previously with low hysteresis. We achieve lambda sub 2 = 1, where lambda sub 2 is the middle eigenvalue of the transformation strain matrix, for alloys with X = Pt, Pd, Au. In all cases there is a sharp drop of the graph of hysteresis vs. composition at the composition where lambda sub 2 = 1. When the size of the hysteresis is replotted vs. lambda sub 2 we obtain an universal graph for these alloys, which also agrees with trends in an earlier combinatorial study of alloys in the system TiNiCu. Motivated by these experimental results, we present a new theory for the size of the hysteresis based on the growth from a small scale of fully developed austenite martensite needles. In this theory the energy of the transition layer plays a critical role. New methods for calculation the optimal layer are developed that rely on Gamma-convergence arguments, the small parameter being lamba sub 2 - 1. The limiting energy of the transition layer is found to be governed by a nonstandard linear elasticity problem. Overall, the results point to a simple systematic method of achieving low hysteresis and a high degree of reversibility in transforming materials.


Descriptors :   *MARTENSITE , *HYSTERESIS , *PHASE TRANSFORMATIONS , NICKEL ALLOYS , TITANIUM ALLOYS , AUSTENITE , CONTINUUM MECHANICS , FATIGUE LIFE , TRANSITIONS


Subject Categories : Physical Chemistry
      Metallurgy and Metallography
      Electricity and Magnetism
      Thermodynamics


Distribution Statement : APPROVED FOR PUBLIC RELEASE