Why do we calculate austenite to martensite volume expansion using "tetragonal" austenite (a*(a/sqrt(2))*(a/sqrt(2)) and not the austenite lattice parameter cubed for the FCC system?
And, is it possible to also use the inverse approach? (i.e. "FCC" martensite against FCC austenite)
Chris, the strains vary with orientation in the austenite and so using a tetragonal description of austenite simplifies the calculation although there is no fundamental reason why the cubic description cannot be used provided that the strain differences along different axes are determined.
Thanks Martin - much appreciated.
See you at the Hume-Rothery seminar if you're there (https://www.iom3online.org/iom/frontend/reg/tOtherPage.csp?pageID=343544&ef_sel_menu=2577&eventID=689&eventID=689)
Because the cell transformation from FCC (austenite) to BCC (martensite) is through the BCT. BCT has more degree of freedom in lattice parameter (c-axis) compare to BCC. If BCT c-axis converge so that c = a = b than it'll become BCC lattice, but if somehow BCT still present than it cannot be approach BCC lattice.
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