G.M. Hood

The diffusion of iron in aluminium

Abstract The diffusion of radioactive 59Fe has been measured in both single crystals and polycrystalline specimens of aluminium in the temperature range 520 to 660°c. The material for the diffusion samples was between 99·99 and 99·999% pure aluminium. The temperature dependence of the diffusion coefficient for single crystal specimens could be expressed by in the temperature range 580 to 660°c. The results are not in agreement with values previously published for this system by Hirano, Agarwala and Cohen (1962). The earlier results are thought to be in error as a result of tracer hold-up at the surface-oxide film on the aluminium specimens. This effect was overcome in the present work by implanting the 59Fe tracer atoms below the surface-oxide layers using a 40 kev 59Fe ion beam. Analysis of the data indicates the activation energy for diffusion is dominated by an iron-vacancy repulsive interaction term. Calculations of the difference between the activation energies for self and solute diffusion in alumin...

Ultra-fast solute diffusion in α-Ti and α-Zr

Abstract Diffusion of 63Ni in polycrystalline α-Ti and of 59Fe, 60Co and 63Ni in α-Zr has been measured. In α-Zr, single crystals were used for studies of Ni and Go diffusion, while the experiments on Fe diffusion were done on polycrystalline specimens. All the solutes studied exhibited extremely fast diffusion compared to self-diffusion in the host metals. It is suggested that these solutes diffuse by an interstitial mechanism and that very fast solute diffusion in the b.c.c. forms of Ti and Zr may be predominantly of an interstitial nature.

The diffusion of manganese in aluminium

Abstract Measurements of 55Mn and 56Mn tracer diffusion in single crystal and polycrystalline specimens of 99.999% pure Al have been made in the range 460 to 660°C. A least-mean-square fit of the data points yields The present results are in fair agreement with the work of Fricke (1967). They are not, however, consistent with previous 54Mn tracer diffusion studies in Al made by Lundy and Murdock (1962). It appears that the discrepancy may have resulted from the presence of an isotopic impurity in the work of Lundy and Murdock.

α-Zr self-diffusion anisotropy

Self-diffusion coefficients (D) have been measured in nominally pure (NP) α-Zr single crystals (= 50 ppm Fe) in the range 867–1107 K, in directions either parallel (Dpa) or perpendicular (Dpe) to the c-axis. Measurements were also made on high-purity (HP) α-Zr single crystals (< 1.0 ppm Fe) at 1110 K. The diffusion profiles were determined by sectioning and radio-tracer (95 Zr) counting. Sectioning was done with a sputtering device, or a microtome (some NP experiments at 1107 K). D values for NP Zr are about an order of magnitude higher than the corresponding values for HP Zr. Diffusion anisotropy is complicated. The sputter-sectioned NP Zr specimens show increasing anisotropy ratios (AR = Dpa/Dpe), from 1.0 to 3.2, with decreasing temperatures, whereas AR = 0.53 for both the microtome-sectioned NP and sputter-sectioned HP Zr: the low AR value is consistent with expectations based on intrinsic self-diffusion in hcp metals with c/a < 1.633.

Co tracer diffusion in Al

Abstract Measurements of 60Co diffusion in Al single crystals have been made at 930, 913. 804 and 724 K. The results support previous work on this system by Peterson and Rothman (1970). Analysis of the combined results yields the equation D=5.06 × 10−2 exp (−1.82 eV/k B T)m2 s−1.

The correspondence between self-diffusion properties and melting temperatures for α-Zr and α-Ti

Abstract Determinations of hypothetical hcp (α-phase) melting temperatures (Tmα) for Zr and Ti have been updated and the results considered in terms of common correspondences between self-diffusion properties of the elements and their melting temperatures (Tm). The present Tmα values for Zr and Ti are 1990 ± 6 and 1707 ± 4 K, respectively. The value for Zr is significantly higher than comparable values found earlier. These Tmα values and current data for self- and substitutional diffusion in α-Zr and α-Ti lead to reasonable accord with a common self-diffusion/Tm relationship for metals.

A Mössbauer study of single-crystal Zr-0.065 at% 57Fe

Abstract Single crystals of Zr-0.065 at% Fe (95% 57Fe), from a common parent, have been studied by Mossbauer spectroscopy, using both transmission and conversion-electron modes. In the “as grown” state the Fe is present as the meta-stable phase, t-Zr2Fe. Vacuum annealing, in the range 795–973 K, results in gradual decomposition of t-Zr2Fe and the diffusion of Fe from the bulk to the surface, where it forms the stable Zr3Fe phase. The kinetics of Zr3Fe formation show fair accord with the known diffusion properties of Fe in α-Zr. Some results for other dilute Zr(Fe) single crystals are reported.

A positron annihilation study of vacancy recovery in quenched single crystals of Al-1·2 × 10−2 at.% In

Abstract Abstract Doppler-broadening measurements of positron annihilation in single crystals of Al-1·2 × 10−2 at.% In have been made in terms of the customary peak, S, and wing, W, lineshape parameters. Results have been obtained for samples in both well-annealed and quenched (from 753 K) states, as well as for quenched samples as a function of isochronal annealing. In the as-quenched state, S and W are increased and decreased, respectively, by 4% and 16%, with respect to the corresponding annealed state values. The bulk of recovery of both S and W occurs in a nearly linear (with temperature) interval between about 300 and 400 K, by which tempera ture (400 K) W exhibits strong super-recovery. The W parameter returns, in a complex fashion, towards its annealed state value over the range 400–500 K; in this same interval, S rises from close to its annealed state value to a peak at 450 K before falling again towards its reference value. The recovery features observed here are in marked contrast to results fr...

Diffusion of Hf and Nb in Zr19%Nb

Abstract Diffusion of Hf and Nb in large-grained bcc Zr19%Nb has been studied. Diffusion coefficients of Hf, D(Hf), were measured in the range 620–1173 K and D(Nb) was measured at 920 and 1167 K. The Elf diffusion profiles were determined by SIMS and the Nb profiles by microtome sectioning and radio-tracer counting. The Hf data show a smooth, temperature-dependent behaviour through the monotectoid temperature, 875 K, and may be characterised by D ≃ 10 −9 × exp(−1.4(eV/ kT )m 2 /s. D (Nb) tends to be lower than the corresponding values for D (Hf). Overall, diffusion of Hf and Nb are characteristic of diffusion in bcc Zr. Surface hold-up (oxide film) at low temperatures was overcome by using ion-implanted Hf diffusion sources. The results are compared with earlier work and discussed in terms of diffusion mechanisms and the β-phase transformation of commercial Zr2.5Nb.

The anisotropy of Hf diffusion in α-Zr

Abstract Hf diffusion coefficients (D) have been measured (∼ 870–1100 K) in directions parallel (Dpa)and perpendicular (Dpe) to the c-axis of double-faced, single-crystal specimens of both high purity (HP) and nominally pure (NP) α-Zr. The diffusion profiles were measured by secondary ion mass spectrometry. Hf diffusion in HP α-Zr is characterised by an activation energy of about 3.0 eV and a pre-exponential factor of about 10−5 m2/s The anisotropy ratio, Dpa/Dpe, is ∼ 1.0 for the NP specimens. A dependence of D on diffusion time/depth is indicated for some experiments on NP Zr.