One-step and iterative thermo-mechanical treatments to enhance Σ3n boundaries in a Ti-modified austenitic stainless steel

The article discusses the results of a study on low-strain thermo-mechanical (one-step and iterative) processing to enhance Σ3 ⁿ boundaries in a Ti-modified austenitic stainless steel (alloy D9). Solution annealed (SA) specimens were subjected to 10% thickness reduction by rolling followed by annealing at 1173, 1223, and 1273 K for 0.5, 1, and 2 h. Anomalous grain growth with moderate increase in Σ3 ⁿ boundaries was observed after annealing at 1,173 K for 0.5 to 2 h. Prolific multiple twinning with minimum deviation of Σ3 and Σ9 boundaries from ideal orientation was achieved after annealing at 1,273 K for 0.5 to 2 h. A significant disruption in random boundary connectivity was obtained in these conditions due to the presence of large number of Σ3-Σ3-Σ9/Σ3-Σ9-Σ27 triple junctions. Iterative processing (up to 4 cycles) employing 10% thickness reduction followed by annealing at 1,273 K for 0.5 h revealed fluctuations in the evolution of Σ3 boundaries. The Σ3 fraction increased after 2nd and 4th iteration and there is a drop after 3rd iteration. This was attributed to the increased driving force for grain boundary migration due to dislocation pile-up at twin boundaries during earlier iterations. A two step iterative processing comprising of 10% deformation followed by annealing at 1,273 K for 0.5 h is the recommended thermo-mechanical processing to achieve enhanced fraction of Σ3 ⁿ boundaries (~73%) in alloy D9.     

Retardation of grain growth in electrodeposited Cu by an electric field

The application of an external dc electric field E = 5 kV/cm during the annealing of electrodeposited Cu foil at 150–195 °C retarded grain growth. The time dependence of the grain size both with and without the field was

An analysis of grain-growth data in duplex materials on static annealing and during superplastic deformation

An analysis of data on grain growth in several duplex materials subjected to superplastic deformation (SPD) and to static annealing (SA) is presented. Also, for comparison, data of a single-phase alloy and a particle-strengthened one were considered. The theoretical equationD ⁿ -D _o ⁿ =Kt was employed, whereD andD _o are the instantaneous and initial average grain size, respectively,t is the deformation or annealing time,n is the kinetic exponent andK is the rate constant. When analysing the selectedD-t data sets, the fact thatD _o values were generally not small enough to be negligible in the above equation was taken into account. It is concluded: (i) for a given duplex allay, the coarsening mechanisms acting during SA and SPD are different, the kinetics being enhanced by concurrent deformation, and (ii) whatever the alloy, the value forn for grain growth under SPD is near to 2, (as for normal grain growth in single-phase materials).     

Influences of Ni–5 at.%W Alloy Substrates on the Epitaxial Growth and Surface Morphologies of CeO<Subscript>2</Subscript> Films Deposited by PLD

We fabricated CeO₂ films using pulsed laser deposition (PLD) for YBa₂Cu₃O_7−δ coated conductors on Ni–5 at.%W alloy substrates and investigated the effect of Ni–5 at.%W tapes on the epitaxial growth and surface morphologies of CeO₂ deposited on various substrates at various temperatures ranging from 650 to 770 °C. The texture and microstructure of substrates and CeO₂ films were measured by X-ray diffraction (XRD), optical microscope (OM), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). It was found that the texture and microstructure of Ni–5 at.%W substrates, such as Ni(111), grain size, the depth of grain boundary grooves and surface roughness, affected the growth of CeO₂ films. Especially, the depth of grain boundary grooves of substrates resulted in high intensity of CeO₂(111) peak and high surface roughness of CeO₂ films. We also found that high growth temperature effectively reduced the influence of substrate surface roughness on the epitaxial growth of CeO₂ films. CeO₂ films with high in-plane and out-of-plane alignments (Δφ=5.54°, Δω=3.40°) were obtained under optimum condition.     

Grain growth in nanocrystalline NbAl3 prepared by mechanical alloying

Grain growth and its kinetics were studied on an intermetallic compound, NbAl₃ powder prepared by mechanical alloying of elemental Nb and Al powders for 1.8 Ms in an argon atmosphere at ambient temperature. The initial and grown grain sizes were measured from the X-ray line broadening of as-alloyed and annealed powders. Isochronal annealing of mechanically alloyed powders from 573 to 1373 K indicated that substantial grain growth occurs only in a temperature range of 1048 to 1173 K and ceases at 1273 K regardless of anneal time. Accordingly isothermal annealing of 1.8 to 18 ks was carried out at 1048, 1073 and 1098 K to obtain the grain growth kinetic that is described by In (dD/dt) = In(r_o/3) –2.0 In D where D is the measured grain size and r _o a constant. This r _o depends on temperature according to r _o=r_o exp (– Q/kT) where Q is the activation energy for grain growth, k the Boltzmann constant and T the absolute temperature. Arrhenius plots of r _o against the reciprocal of temperature yield a straight line, from whose slope the activation energy for grain growth is deduced to be 162±2 kJ mol^–1. Of significance is the fact that the ultimate grain size at 1273 K is approximately 70 nm, which will not grow by further annealing even at 1373 K.On leave from Ibaraki University, Japan.     

Possibility of fabricating an inductive high-speed detector for electromagnetic radiation using thin YBa2Cu3O7−δ films

It is shown that an inductive high-speed nonequilibrium detector for electromagnetic radiation can be fabricated using thin YBaCuO films. An electronic detection regime has been obtained for the first time using a low-temperature inductive YBaCuO detector in the measuring frequency band Δf=1–50 MHz and it has been shown that no bolometric detection regime exists at operating temperatures far below the superconducting transition. The time constant of the low-temperature inductive YBaCuO detector in the electronic regime is determined only by the electron-phonon interaction time in the nodal regions τ _e-ph ^d . The detector has the following limiting characteristics: when the operating temperature is reduced from 10 to 1K, the time constant τ _D varies between 10 and 100 ps and the sensitivity D* improves substantially from 10⁹ to 4×10¹² W⁻¹ cm Hz^1/2. Pis’ma Zh. Tekh. Fiz. 25, 14–19 (January 26, 1999)     

The effects of temperature gradient and growth rate on the microstructure of directionally solidified Sn–3.5Ag eutectic solder

The mechanical properties (microhardness, tensile strength) of alloys are controlled by their microstructure, which depends strongly on temperature gradient (G) and growth rate (V). Thus, it is important to understand the relationships among G, V and microstructure (rod eutectic) of Sn–Ag solders. The Sn–3.5 wt% Ag eutectic alloy was directionally solidified upward with a constant growth rate, V (16.5 μm/s) at different temperature gradients, G (1.43–4.28 K/mm) and with a constant temperature gradient, G (3.93 K/mm) at different growth rates, V (8.3–500 μm/s) in a Bridgman–type directional solidification furnace. The rod spacings (λ) have been measured from both longitudinal section (parallel to the growth direction, λ _L ) and transverse section (perpendicular to the growth direction, λ _T ) of the samples. The undercooling values (ΔT) were calculated by using V, λ and system parameters (K ₁ and K ₂). It was found that the values of λ (λ _T , λ _L ) decrease while V and G are increasing. The relationships between rod spacing and solidification parameters (G and V) were obtained by linear regression analysis. The dependences of eutectic spacings λ on undercooling (ΔT) are also analyzed. λ² V, λΔT, ΔTV ^−0.5 and ΔTG ^−0.5 values were determined by using λ, ΔT, V and G values. The results obtained in this work are compared with the Jackson–Hunt eutectic theory and the similar experimental works. The experimental l_\textT ² \textV \lambda_{\text{T}}^{ 2} {\text{V}} value (159.3 μm³/s) is slightly lower than the result 174.6 μm³/s calculated from Jackson–Hunt eutectic theory.     

Densities,Viscosities, Speeds of Sound,and Refractive Indices of Binary Mixtures of 2-Octanol with Chlorobenzenes

Densities, ρ, viscosities, η, speeds of sound, u, and refractive indices, n _D, of binary liquid mixtures of 2-octanol with 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene have been measured over the entire range of composition at 298.15 K, 303.15 K, and 308.15 K and at atmospheric pressure. From the experimental data of the density, speed of sound, viscosity, and refractive index, the values of the excess molar volume, V ^E, deviations in isentropic compressibility, Δκ _S , and deviations in molar refraction, ΔR have been calculated. The calculated excess and deviation functions have been analyzed in terms of molecular interactions and structural effects.     

Densities,Viscosities, Speeds of Sound,and Refractive Indices of Binary Mixtures of 1-Decanol with Isomeric Chlorotoluenes

Densities, ρ, viscosities, η, speeds of sound, u, and refractive indices, n _D, of binary liquid mixtures of 1-decanol with o-chlorotoluene, m-chlorotoluene, and p-chlorotoluene have been measured over the entire range of composition at 298.15 K, 303.15 K, and 308.15 K and at atmospheric pressure. From the experimental data of density, speed of sound, viscosity and refractive index, the values of the excess molar volume, V ^E, deviations in isentropic compressibility, Δκ _S , and deviations in molar refraction, ΔR, have been calculated. The calculated excess and deviation functions have been analyzed in terms of molecular interactions and structural effects.     

Comparison study on the size and phase control of nanocrystalline TiO<Subscript>2</Subscript> in three Ti–Si oxide structures

Three types of Ti–Si binary oxides have been prepared by sol-gel processes. The effects of SiO₂ addition and annealing temperature on the grain size, phase transition, dispersion, and microstructure of nanocrystalline (nc) TiO₂ anatase in the three Ti–Si oxide structures have been comparatively investigated by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). The grain growth and anatase-rutile transformation (ART) of ncTiO₂ were found to depend not only on the SiO₂ content and annealing temperature, but also on the composite structure. Both the grain growth and the ART of ncTiO₂ proved to be significantly inhibited with increasing SiO₂ content for all of the Ti–Si samples, but the structure of intimately mixed Ti–Si binary oxide showed the best inhibiting ability under high-temperature annealing. This result might be attributed to variations in the large lattice strains in ncTiO₂, which were mainly induced by the substitution of Ti⁴⁺ by Si⁴⁺. Plausible mechanisms for the grain growth and ART of ncTiO₂ are proposed. To inhibit the grain growth of ncTiO₂, the addition of 10 and 30 mol% SiO₂ proved to be optimal for Ti–Si samples annealed at 773 K and 1273 K, respectively.     

Effects of pulsed magnetic annealing on Goss texture development in the primary recrystallization of grain-oriented electrical steel

As the condition of Goss component in primary structure of grain-oriented electrical steel plays a significant role for its abnormal growth in the subsequent secondary recrystallization, pulsed magnetic annealing was used to affect the development of Goss texture in primary recrystallized structure in this study. Specimens of one-stage cold-rolled electrical steel were annealed under pulsed magnetic field with the maximum strength 1T from three different directions—rolling direction, transverse direction, and normal direction at the temperature about 700 °C for 16 min, and then electron backscattering scanning diffraction technology was used to measure grains for texture determination. It was found that pulsed magnetic field not only decreases the average grain size of recrystallized structure but also affects the development of primary recrystallized texture varied with the change of applying direction due to that the magnetic field induces extraneous driving forces causing preferential grain growth and the preferential order can be listed from those with crystal orientation 〈100〉//H, 〈112〉//H, 〈110〉//H to 〈111〉//H. This research can be a guide to control the Goss texture development in primary recrystallization with pulsed magnetic annealing for deformed grain-oriented electrical steel.     

Influence of rotational motion of nitrogen molecules on the thermal expansion of solid solutions of Ar−N2: A new effect

The thermal expansion coefficient of solid Ar and of solid solutions of¹⁴N₂ in Ar (0.51; 2.24; 4.89 mol.%¹⁴N₂) has been investigated in the temperature range 1–16 K. Two new effects have been discovered for the behaviour of the impurity contribution Δα to the linear expansion coefficient, i.e., negative values of Δα atT<4.3 K for the solution with a nitrogen concentration of 0.51%, and independence of Δα on impurity content for two more concentrated solutions below 7 K. An explanation of the peculiarities mentioned is given. The comparison of the results obtained with the theoretical predictions has been made.     

Effect of the thickness of Bi–Te compound and Cu electrode on the resultant Seebeck coefficient in touching Cu/Bi–Te/Cu composites

The resultant Seebeck coefficient α of the touching p- and n-type Cu/Bi–Te/Cu composites with different thicknesses of t _Bi–Te and t _Cu was measured as a function of t, where t _Bi–Te was varied from 0.1 to 2.0 mm, t _Cu from 0.3 to 4.0 mm and t is the lapse time after imposing the voltage. The temperature difference ΔT is produced by imposing a constant voltage of 1.70 V on two Peltier modules connected in series. The resultant α of composites was calculated from the relation α = ΔV/ΔT, where ΔV and ΔT were measured with two probes placed on both end coppers. ΔV decreases abruptly with an increase of t below t = 5 min, while above t = 7 min, it tends to saturate to a constant value. The resultant α and saturated ΔV vary significantly with changes in t _Cu and t _Bi–Te. When a composite has a combination of t _Cu = 1.0 mm and t _Bi–Te=0.1 mm, the generating powers ΔW (=(ΔV)²/4R) estimated using the saturated ΔV and calculated electrical resistance R for the p- and n-type composites have great local maximum values which are 4–5 times as large as those obtained for the conventional combination of t _Bi-Te = 2.0 mm and t _Cu = 0.3 mm. It is surprising that the generating power ΔW is enhanced significantly by sandwiching a very thin Bi–Te material between two thick coppers, unlike the conventional composition of thermoelectric modules. On the other hand, when a composite has a combination of t _Bi–Te = 0.1 mm and t _Cu = 0.3 mm, the resultant α of the p- and n-type composites exhibited great values of 711 and −755 μV/K, respectively, so that the maximum resultant ZT of the p- and n-type composites reached extremely large values of 8.81 and 5.99 at 298 K. However, the resultant ZT decreases rapidly with an increase of t _Cu or t _Bi–Te. The resultant ZT is thus found to be enhanced significantly not only in superlattice systems but also in macroscopic composites. The present enhancement in ZT is attributed to the large barrier thermo-emf generated in the Bi–Te region shallower than 50 μm from the boundary.     

Kinetics of isothermal reactive diffusion between solid Fe and liquid Al

The kinetics of the reactive diffusion between solid Fe and liquid Al was experimentally observed using Fe/Al diffusion couples. The diffusion couples were prepared by an isothermal bonding technique and then immediately annealed in the temperature range of T = 1053–1093 K for various times up to t = 600 s. Owing to annealing, an intermetallic layer with a rather uniform thickness is produced at the Fe/Al interface in the diffusion couple and grows into the solid Fe specimen. The intermetallic layer consists of Fe₂Al₅ and FeAl₃, and the thickness is much smaller for FeAl₃ than for Fe₂Al₅. Hence, the growth of the intermetallic layer is predominantly governed by Fe₂Al₅. The total thickness, l, of the intermetallic layer increases with increasing annealing time, t, according to the parabolic relationship l ² = Kt. This may mean that the growth of the intermetallic layer is controlled by volume diffusion. If the temperature dependence of the parabolic coefficient K is expressed by the equation K = K ₀exp(−Q _K /RT), K ₀ = 126 m²/s and Q _K  = 248 kJ/mol are obtained from the experimental values of K at T = 1053–1093 K by the least-squares method. A mathematical model was used to evaluate the interdiffusion coefficient, D, of Fe₂Al₅ from K. The evaluation provides D ₀ = 2.55 × 10³ m²/s and Q = 259 kJ/mol for the dependence of D on T described as D = D ₀exp(−Q/RT). Thus, K is one fifth of D at T = 1053–1093 K, and Q _K does not necessarily coincide with Q. D is about two orders of magnitude greater for the values evaluated in the present study than for those extrapolated from the previously reported result at T = 823–913 K. The microstructure observation in a previous study suggests that such large values of D are attributed to the boundary diffusion in the intermetallic layer as well as the crystallographic anisotropy of Fe₂Al₅.     

3He Anomalously High Spin Diffusion in Solid Para-Hydrogen

NMR measurements of ³He spin diffusion coefficient in solid para-H₂ are carried out at the temperatures 0.45–1.5 K. The crystals have been grown under constant pressure 20–130 bar. The ³He concentrations in the initial para-H₂–³He gas mixtures were 0.1% and 0.3%. It is found out that the decay of echo amplitude vs both magnetic field gradient G and time interval τ between RF pulses is of non-exponential character, typical of one-dimensional diffusion in restricted geometry. The values of true spin-diffusion coefficient D _S measured are found to be ∼10⁻⁴ cm²/s at 20 bar. At 108 bar D _S value is one order of magnitude less. D _S does not depend on temperature. Such spin diffusion coefficient values seem to be anomalously high in comparison with well-known values of D _S =10⁻⁵ cm²/s for bulk liquid ³He at 27 bar and D _S =10⁻⁸ cm²/s for bulk solid ³He at 108 bar. The special experiments with the crystal annealing make it clear that the high spin diffusion here is connected with fast diffusion along dislocation lines.     

Investigation of the effect of solidification processing parameters on the rod spacings and variation of microhardness with the rod spacing in the Sn–Cu hypereutectic alloy

Sn–3 wt% Cu hypereutectic alloy was prepared in a graphite crucible under the vacuum atmosphere. The samples were directionally solidified upwards under argon atmosphere with different temperature gradients (G = 4.24–8.09 K/mm) at a constant growth rate (V = 7.64 μm/s) and with different growth rates (V = 2.24–133.33 μm/s) at a constant temperature gradient (G = 4.24 K/mm) by using a Bridgman type directional solidification apparatus. The microstructure of directional solidified Sn–3 wt% Cu alloy seems to be rod eutectic structure. The influence of the growth rate (V) and temperature gradient (G) on the rod spacing (λ) and undercooling (ΔT) were analysed. The values of λ²V, λ²G, ΔTλ, ΔTV^−0.5 and ΔTG^−0.5 were determined by using the Jackson–Hunt eutectic theory. The dependence of microhardness (HV) on the rod spacing (λ) was analyzed. According to present results, it has been found that the value of HV increases with the increasing the value of λ.     

Plasticity initiation and subsequent deformation behavior in the vicinity of single grain boundary investigated through nanoindentation technique

The initiation of plasticity and the subsequent state in the vicinity of a single grain boundary during indentation-induced deformation were investigated to understand an elementary step of a stress-strain behavior of polycrystalline materials. Nanoindentation measurements on several points on a single grain boundary and the grain interior of an interstitial-free steel and an analysis on the pop-in behavior and the plastic nanohardness were carried out. The pop-in load P ^c that was obtained on the loading curve is different for each measurement. However, the loading curves overlap one another and the unloading curves coincide as well after the pop-in event. The nanohardness Hn has no dependence on the P ^c in the range of 150–550 μN. The relation between P ^c and Δh can be expressed as a simple cubic polynomial function based on a geometrically necessary dislocation loop model. The fitted function differed for various grains with different crystallographic orientations.     

Characterisation of vacancy-like defects in III–V compound semiconductors using positron annihilation technique

Single crystals of GaP and InSb were irradiated by 3 MeV electrons at 20 K to a total dose of 4 × 10¹⁸ e ⁻/cm². Isochronal annealing in the temperature region 77–650 K followed the irradiation. In GaP, the positron lifetime measurement indicated the presence of irradiation-induced vacancies in the Ga-sublattice. The vacancies disappeared at two stages observed in temperature ranges 200–300 and 450–550 K. In InSb the positron lifetime was found to increase by 8 ps compared to that in as-grown crystals (i.e. 282±2 ps) after irradiation. The increase indicated the presence of irradiation-induced defects; the crystal was found to recover until 350 K with a sharp annealing stage at 250–350 K.     

Growth behavior of compounds due to solid-state reactive diffusion between Cu and Al

To examine experimentally the kinetics of the reactive diffusion between solid-Cu and solid-Al, sandwich Al/Cu/Al diffusion couples were prepared by a diffusion-bonding technique and then isothermally annealed in the temperature range of T = 693–753 K for various times up to 336 h. Owing to annealing, compound layers of the γ ₁, δ, ζ ₂, η ₂, and θ phases are formed between the Cu and Al specimens. The γ ₁, δ, ζ ₂, η ₂, and θ phases are the only stable compounds at T = 693–753 K in the binary Cu–Al system. At each annealing time, the thickness of the θ phase is much greater than those of the δ, ζ ₂, and η ₂ phases but smaller than that of the γ ₁ phase. Hence, the overall growth of the compound layers is governed by the γ ₁ and θ phases. The mean thickness of each compound layer is proportional to a power function of the annealing time. For the γ ₁ phase, the exponent m of the power function is 0.5 at T = 753 K. Such a relationship is called a parabolic relationship. As the annealing temperature T decreases, however, m gradually increases and then reaches to 0.66 at T = 693 K. On the other hand, for the θ phase, m is close to 0.5 at T = 723–753 K and becomes 0.42 at T = 693 K. In the γ ₁ and θ phases, grain growth occurs at T = 693–753 K. Thus, the layer growth of the θ phase is controlled by volume diffusion at T = 723–753 K but partially by boundary diffusion at T = 693 K. On the other hand, for the γ ₁ phase, volume diffusion is the rate-controlling process of the layer growth at T = 753 K, but interface reaction contributes to the rate-controlling process at T = 693–723 K. Consequently, the rate-controlling process varies depending on the annealing temperature in a different manner for each compound.     

Hot deformation behavior of an 8% Cr cold roller steel

An 8% Cr cold roller steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s⁻¹. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the microstructure evolution and the mechanism of flow instability. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 8% Cr steel; the efficiency of power dissipation decreased with increasing Z value; flow instability was observed at higher Z-value conditions and manifested as flow localization near the grain boundary. The hot deformation equation and the dependences of critical stress for dynamic recrystallization and dynamic recrystallization grain size on Z value were obtained. The suggested processing window is in the temperature range 1050–1200 °C and strain rate range 0.1–1 s⁻¹ in the hot processing of 8% Cr steel.