R. Kainuma et al., EFFECT OF ALLOYING ELEMENTS ON MARTENSITIC-TRANSFORMATION IN THE BINARY NIAL(BETA) PHASE ALLOYS, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 27(9), 1996, pp. 2445-2453
The characteristics of the B2(beta) to L1(0)(beta') martensitic transf
ormation in NiAl base alloys containing a small amount of third elemen
ts have been investigated by differential scanning calorimetry (DSC),
X-ray diffraction (XRD), and transmission electron microscopy (TEM). I
t is found that in addition to the normal L1(0) (3R) martensite, the 7
R martensite is also present in the ternary alloys containing Ti, Mo,
Ag, Ta, or Zr. While the addition of third elements X (X: Ti, V, Cr, M
n, Fe, Zr, Nb, Mo, Ta, W, and Si) to the binary Ni64Al36 alloy stabili
zes the parent beta phase, thereby lowering the M(s) temperature, addi
tion of third elements such as Co, Cu, or Ag destabilizes the beta pha
se, increasing the M(s) temperature. The occurrence of the 7R martensi
te structure is attributed to solid solution hardening arising from th
e difference in atomic size between Ni and Al and the third elements a
dded. The variation in M(s) temperature with third element additions i
s primarily ascribed to the difference in lattice stabilities of the b
cc and fee phases of the alloying elements.