A. Biscarini et al., Martensitic transitions and mechanical spectroscopy of Ni50.8Ti49.2 alloy containing hydrogen, ACT MATER, 47(18), 1999, pp. 4525-4533
Hydrogen additions [n(H) =H/(Ni + Ti) =0.003; 0.008; 0.013; 0.021; 0.029; 0
.045 at.] to a Ni50.8Ti49.2 alloy produce several effects in the elastic an
d anelastic properties of the material. At temperatures between 100 and 150
K hydrogen atoms act as fixed pinning points for dislocations, as they can
cel a newly observed dislocation relaxation. At low H contents (0 < n(H) le
ss than or equal to 0.008) the internal friction peak PAM (PRM) associated
with austenite/martensite (A --> M) or R-phase/martensite (R --> M) transit
ions dramatically increases with increasing the H content, while the dip oc
curring in the Young's modulus (E) vs temperature curves becomes gradually
wider and shallower. The enhancement of peak PAM (PRM) can be accounted for
in terms of a mechanism involving the excitation of collective vibration m
odes (dyadons) of twin boundaries interacting with H or the stress-induced
motion of parent/product interfaces. The widening of the dip in the Young's
modulus is due to the introduction by H of a two-step transition (A --> R
--> M). With increasing the H content n(H) from 0.008 to 0.045 the height o
f peak P-AM (P-RM) decreases and a higher temperature peak (PH) appears and
progressively grows becoming the only internal friction feature for nH = 0
.045. With increasing H content the thermal hysteresis in the E(T) curves o
ccur ring over the coexistence region of the A and M (R and M) phases decre
ases due to the inhibition caused by H of the martensitic transition. Peak
PH is most likely associated with stress-induced motion of H in solid solut
ion within the R-phase or within a hydride. (C) 1999 Acta Metallurgica Inc.
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