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INTERNAL FRICTION STUDY OF Nb-M-H ALLOYS
(M = Ti, Zr, Cr, Mo)
O. Yoshinari, N. Yoshikawa, H. Matsui, M. Koiwa
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C10, supplbment au n012, Tome 46, dbcembre 1985
page
C10-95INTERNAL FRICTION STUDY OF Nb-M-H ALLOYS (M
=Ti,
Zr, Cr, Mo)
0. YOSHINARI, N.YOSHIKAWA, H. MATSUI AND M. KOIWA*The Research I n s t i t u t e f o r Iron, S t e e l and Other Metals,
Tohoku, U n i v e r s i t y , Sendai
980,
Japan
'Department o f Metal Science and Technology, Kyoto
U n i v e r s i t y , K y o t o
606,
Japan
Abstract - Low frequency lnternal friction(Q1Hz) of Nb-2at%M-H alloys (M=Ti,zr,Cr,~o) has been measured over a temperature range from 5 to 300 K. Relaxation peaks are observed below 100 K for specimens containing Ti and Zr, but not for the other specimens. These peaks are considered to be due to relaxation of substitutional(M)-interstitial(H) complexes. The characteristics of the peaks are discussed in comparison with those in V-base alloys.
I-INTRODUCTION
It is well known that the diffusivity or the terminal solid solubility of hydrogen is affected by the addition of alloying elements. This is interpreted in terms of trapping of hydrogen; substitutional foreign atoms and hydrogen form substitutional-interstitial (s-i) complexes.
Several authors have suggested the presence of the s-i complexes by using anelastic technique. Cannelli and Cantelli/l/ and Cannelli, Cantelli and K@iwa/2/ observed internal friction peaks due to Ti-H complexes in Nb-Ti alloys. Tanaka and Koiwa/3,4/ reported the result of internal friction measurements on vanadium containing Ti, Zr, Mo, Nb, Cr, Fe or Cu. They found relaxation peaks for specimens containing Ti or Zr but not for other specimens. Similar relaxation processes were also observed in Fe- and Ni base alloys containing hydrogen by magnetic after effect measurements/5,6/.
In this paper we report low frequency internal friction measurements in niobium alloys containing hydrogen. The results are compared with that of V alloys/3,4/ and Nb-Ti alloy/l,2/
Nb-2at%M (M=Tl,Zr,Cr,Mo) alloys were prepared by arc-meltlng Nb(99.9%, Hermann Corp.) wlth appropriate amounts of alloying elements. Speclmen wlres of 1 mm In dlameter were made by swaglng and drawlng. The specimens were wrapped with zlrconlum foils, sealed In evacuated quartz tubes and annealed at 1373 K for 2 h. Thls treatment 1s known to be effective for removal of oxygen or nltrogen In V/7/ and also In Nb/8/. Hydrogen charglng was made electrolytically and the H concentration,
CH, was estimated from the Increase In electrrcal reslstlvlty,
Ap.
A relatlon Ap(~Rcm) = 0.71 C (at%) was used to calculate C.
Ij
Internal frlctlon was measured In a
newsy
deslgned lnverted torslon pendulum over a temperature range from 5 to 300 K,6 The measuring frequency was about 1.2 Hzand the straln amplitude was about 2x10 ln the maxlmum surface shear straln. The measurements were performed under constant heatlng (0.5 - 1 K/mln).
JOURNAL
DE
PHYSIQUE
111-RESULTS AND DISCUSSION
Figure 1 shows the internal friction versus temperature curves for Nb-2at%M-lat%H (M=Ti,Zr,Mo,Cr) and Nb-lat%H. Below 100 K, peaks are observed for specimens with Zr and Ti, while the internal friction is almost constant for the other specimens. The nature of these peaks is considered to be the same as that of the peaks observed for V-Ti and V-Zr alloys by Tanaka and ~oiwa/3,4/. In the higher temperature range (200-300 K), peaks are observed for all the specimens except for Nb-Ti; these peaks are identified as the hydride precipitation peak/9/. In the intermediate temperature range (100-200 K), additional peaks are observed for pure Nb and Nb-Cr. These peaks are interpreted as the hydrogen cold-work peaks; dislocations formed around hydride precipitates are considered to be responsible.
Detailed investigations were made for Nb-Ti and Nb-Zr alloys.
Nb-Ti-H Figure 2 shows the effect of the hydrogen concentration on the internal friction for Nb-2at%Ti below 100 K. The change of relative rigidity modulus, G/G(O K), is also shown in the figure. For low CH(<0.2at%), a small peak (PT1) appears around 80 K. This peak disappears above 0.4at%H and a new peak(PT2) appears around 60 K. PT2 increases its height linearly with C and shifts towards lower temperatures. For C >1.3at%, the peak remains at the same pemperature and its height begins to decrease. H
The internal friction of Nb-Ti-H alloys has been measured by Cannelli et a1./1,2/ at a frequency of about 20 kHz. Their observations on a Nb-2at%Ti alloy is summarized as follows. With the'addition of hydrogen a peak(P1) appears at about 130 K (0.36at%H), and shifts towards lower temperatures: 110 K(0.57at%H) and 100 K(0.70at%H). The activation energies estimated from the half peak width, E
W'
deerease from 0.124 to 0.075 eV with increasing C
.
The height of the peak 1s proportional to CH. The defect responsible for this peaE was proposed to be a single Ti atom with one or more hydrogen atoms. The shift of the peak with increasing C was explained by assuming that (1) there exist titanium-hydrogen complexes witA different numbers of hydrogen atoms: Ti-H, Ti-H Ti-H.-.,
( 2 ) higher order2'. 3
complexes have lower activation energies for reorientatlon; wlth the increase in C
H'
the fraction of the higher order complexes increases so that the apparent peak temperature of the whole relaxation process would shift to lower temperatures. A small subsidiary peak P is observed at a lower temperature(s70 K), which has been tentatively ascribed to t6e orientation of H around Ti-Ti complexes.
The peak PT2 observed in the present experiment is naturally identified as the peak P1 from the similarity of the behaviour. For the peak PT2, the peak height and the relaxation strength estimated from the modulus defect are summarized in Table. By assuming a Gaussian distribution of the relaxation time, and comparing the relaxation strength and the observed peak height, the'distribution parameter, 6 , in the Nowick-Berry analysis/lO/ is estimated. The activation energy, E, is determined from the peak width by using the relation, E=2.63k r (~)/A(I/T), where k is the
2
Boltzmann constant, A(l/T) is the peak width and r2(B) is the relative peak width. The activation energy E thus determined is 0.13 eV, which is much larger than the values estimated from the half peak width without taking into account the distribution in relaxation time.
The height of the peak PT2(1.2 Hz) is five times as large as that of P1(20 kHz), when compared at the same hydrogen concentration. This difference is larger than that expected from 1/T dependence of the relaxation strength. Note that, in general, the concentration of defect complexes is dependent on temperature dictated by binding energy; with increasing temperature the number of s-i complexes should decrease. The observed change in the peak height can be reasonably explained by assuming a binding energy of about 0.03 eV.
(1) The lowest concentration examined by Cannelli et al. was 0.36atBH. At lower concentrations, the peak may be observed.
(2) At the peak temperature of the relaxation, the concentration of the relevant complexes is so small as to produce a peak of detectable size.
(3) At a high frequency, the peak temperatures of PT1 and PT2 becomes so close as to produce a single broad peak.
At present, it is not known which of the above three is responsible.
Nb-Zr-H In the case of a Nb-Zr specimen, the trend is somewhat different from that of the Nb-Ti specimen. Figure 3 shows the internal friction and the rigidity modulus change for a Nb-2at%Zr specimen with increasing C ; at least three peaks seem to exist. With increasing CH, a peak, PZ1 appears arouni 70 K at first, and the peak height passes a maximum at C =0.15at% and gradually decreases for higher C
.
For C >0.15at%, new peaks PZ2 and ~ 1 3 appear around 6 0 and 40 K, respectively. ~Ete peak ~ g 2 shifts toward higher temperatures and it becomes difficult to distinguish PZ2 from PZ1. The height of PZ3 increases with CH and no longer varies for C >0.5at%.H
Such a saturation of the peak height was also noted in the previous investigation on V-Ti-H alloys and has been associated with the initiation of the hydride precipitation. The critical concentration for the saturation is about 0.5at%, while it is about 1.3at8 for the Nb-2at%Ti; for the suppression of hydride precipitation Ti seems to be more effective than Zr.
The major peak PZ3 may be considered to correspond.to PT2 or the relaxation of Zr-H complexes. In contrast to PT2, however, the peak PZ3 does not shift with CH: If the emphasis is placed on the trend of the peak shift, the peak PZ1 (possibly
together with PZ2) should be associated with PT2. Further investigations are required for the understanding of the nature of the peaks in Nb-Zr-H alloys.
IV-SUMMARY
The present investigation has revealed that Ti and Zr form s-i complexes with hydrogen in Nb, while no corresponding relaxation was.observed for specimens with Cr and Mo. This trend is exactly the same as that observed for V-base alloys. In this respect, it can be said that the V-M-H and Nb-M-H alloys exhibit very similar behaviour.
The peak PT2 or P /1,2/ in Nb-Ti-H alloys is considered to correspond to a peak 1
observed in V-Ti-H alloys/3,4/. As seen in the Table, the peak height is very much smaller for the former. This may suggest a larger anisotropy of the lattice distortion around a Ti-H complex in V than in Nb. However, a detailed comparison should be made by taking into account the peak width or the distribution in the relaxation times.
- 1
Table Peak temperature, TP, peak height, Qm
,
relaxation strength,A ,
-
distribution parameter,
6,
activation energy, E, and pre-exponential factor of the relaxa ion time,-1
T for the s-i relaxations in Nb-Ti, b-Zr and V-Ti alloys. Qm /at%H ard A/~?.%H are evaluated from the slope of Piy-C and b-Ccurves. H H
- 1
system ref. freq.peak TP Qm/at$H A/atlg
6
E log(tO) (HZ) (K) (xi0 ) (xi0 ) (ev) ( s )Nb-Ti-H Dresent 1.2 PT1 80- 83 5 Nb-Zr-H present 1.2 PZ2 50- 42 PZ3 40 40 100 0.9 0.04 - 5.3 V-Ti-H /3,4/ 0.8 61- 82 72 180 1.1 0.11 - 9.4 Nb-Ti-H 1 2 20 k P1 100-130 1.7 REFERENCES
/1/ Cannelli, G. and Cantelli, R., J. de Phys. 42 (1981) C5-793.
/2/ Cannelll, G., Cantelli, R. and Koiwa,
M.,
~ h i l . Mag. A46
(1982) 483./3/ Tanaka, S. and Koiwa, M., J. de Phys.
42
(1981) C5-781. /4/ Tanaka, S. and Koiwa, M., Scripta Metall.15
(1981) 403.C10-98 JOURNAL
DE
PHYSIQUE569.
..
/6/ Holler, B. and Kronmuller, H., Phil. Mag. A
45
(1982) 607./7/ Yoshinari, O., Konno, T., Suma, K. and Koiwa, M., J. Less-Common Met.
81
(1981) 239./8/ Yoshinari, O., Thesis of Tohoku University (1980). /9/ Koiwa, M. and Yoshinari, O., Reported in this conference.
/lo/ Nowick, A. S. and Berry, B. S.. "Anelastic Relaxation in Crystalline Solids", Academic Press, New York (1972).
Temperature K
Pig.l The internal friction vs. temperature curves for Nb-lat%H Nb-2at%M-lat%H (M=Cr,Mo,Ti,Zr) alloys.
Temperature K Temperature K
