The fault density in 9R type martensites: A comparison between experimental and calculated results

Abstract In the crystallographic analysis of the b.c.c. into 9R (or 18R) martensitic transformations it is customary to decompose the transformation into a Bain distortion (which transforms the b.c.c. lattice into an f.c.t. lattice with tetragonality ψ = c f a f , and a subsequent lattice invariant shear (whose amount is determined from the invariant plane transformation condition). This shear can be converted into a fault density, which is measured with respect to the hypothetical f.c.t. structure. Experimental data of the fault densities from the 18R martensites in both Cu-Al (ψ = 1) and Cu-Zn-Al (ψ = 0.935) alloys are directly obtained by means of high resolution electron microscopy. On the other hand, the corresponding fault densities for both alloys are calculated in terms of the phenomenological theory of Wechsler-Lieberman-Read. A good agreement is found between the measured and calculated fault densities.

[1]  M. Wechsler.  On the theory of martensitic transformations. The generalized lattice invariant shear and the degeneracy of solutions for the cubic to tetragonal transformation , 1959 .

[2]  M. Ahlers.  On the stability of the martensite in β-CuZn alloys , 1974 .

[3]  G. Tendeloo,et al.  HREM imaging conditions for stacking sequences in 18R martensite of Cu-Al alloys , 1984 .

[4]  J. Mackenzie,et al.  The crystallography of martensite transformations II , 1954 .

[5]  K. Shimizu,et al.  Crystal Structure of Cu 30 Au 25 Zn 45 Martensite , 1976 .

[6]  C. M. Wayman,et al.  Electron microscopy of internally faulted Cu-Zn-Al martensite , 1977 .

[7]  C. M. Wayman,et al.  On the shape memory effect in internally faulted martensites , 1975 .

[8]  M. O'Keefe,et al.  The high resolution electron microscopy of stacking defects in Cu–Zn–Al shape memory alloy , 1983 .

[9]  S. Kajiwara.  Stacking Disorder in Martensite of Cu-Zn Alloy , 1971 .

[10]  H. Warlimont,et al.  The electron-metallography and crystallography of copper-aluminum martensites , 1963 .

[11]  L. Delaey,et al.  The variation of stacking order and structure-symmetry in copper-base martensites , 1970 .

[12]  S. Kajiwara.  Theoretical Analysis of the Crystallography of the Martensitic Transformation of BCC to 9 R Close-Packed Structure , 1976 .

[13]  S. Kajiwara,et al.  Stacking Faults in the Martensite of Cu-Al Alloy , 1965 .

[14]  M. Chandrasekaran,et al.  The basal plane stacking faults in 18R martensite of copper base alloys , 1984 .

[15]  T. Tadaki,et al.  Modified 2H and 9R Martensites in a Au-47.5at% Cd Alloy , 1977 .

[16]  J. Humbeeck,et al.  The stabilisation of step-quenched copper-zinc-aluminum martensite part II : Crystal structure and reordering , 1984 .

[17]  G. Tendeloo,et al.  On the Nature of Various Stacking Defects in 18R Martensite in Cu-Al Alloys. A Study by High Resolution Electron Microscopy , 1984, December 16.

[18]  F. Lovey,et al.  The structure of the modified 2H martensite in CuZnAl , 1983 .