Toshimi Yamane

Plastic deformation of the intermetallic compound Al3Ti

Abstract Polycrystalline specimens of the intermetallic compound Al3Ti with the D022-type structure have been deformed under compression at 25–860°C. At temperatures below 620°C, specimens fracture with very small fracture strain since extremely localized deformation occurs and cracks are initiated in intensely deformed regions almost at yielding. At temperatures above 620°C, good compression ductility is observed. Yield stress starts decreasing rapidly with increasing temperature at around 330°C and becomes less temperature dependent above 630°C. The major mode of deformation of Al3Ti is twinning of the type (111)[112] which does not disturb the D022 symmetry of the lattice. However, at high temperatures, the four (111)[112]-type twinning systems are augmented by slip of the types [110], [100] and [010]. This would supply an explanation for the good compression ductility observed at temperatures above 620°C. Suggestions are made for further experimental work on alloying additions which may improve the du...

Oxidation resistance of intermetallic compounds Al3Ti and TiAl

The oxidation kinetics and morphological features of Al3Ti and TiAl were investigated. The oxidation resistance of Al3Ti is much better than that of TiAl, for example, by a factor of about 30 at 1000° C for 48 h. The big difference in the oxidation resistance is related to the characteristics of the external oxide scales of a protective Al2O3 or a mat of crystalline TiO2 formed on Al3Ti or TiAl, respectively. Sufficient aluminium transport from Al3Ti assists the formation of the Al2O3 scale which acts as a protective film against oxidation. The poor aluminium content of TiAl produces Ti3Al phase at the interface of TiAl and oxide scales and increases the diffusivity of titanium in the Al2O3 scale. The external crystalline TiO2 scale produced by the diffusion of titanium through the Al2O3 scale enhances oxidation of TiAl.

High temperature deformation of MoSi2 single crystals with the C11b structure

Abstract Single crystals of MoSi2 with the C11b structure have been deformed in compression at 900–1500°C. Slip of the {013}〈3 3 1〉- and/or the {013}〈3 3 1〉- type is activated depending on crystal orientation. The critical resolved shear stress (CRSS) for {013}〈3 3 1〉- slip is much higher than that for {013}〈3 3 1〉- slip . At about 1300°C where ductility is remarkably improved, 〈100〉- and 〈110〉-type ordinary dislocations are observed and the climb mobility of these dislocations is very high. The CRSS for {013}〈3 3 1〉- slip , which depends on orientation exhibits a slight anomalous peak at 1000–1100°C. The anomalous strengthening is interpreted by the cross-slip mechanism as similar to that in L12 ordered alloys. Ductility improvement of MoSi2 above about 1200°C is assisted by the formation of stacking fault which is closely related to the instability of the C11b against to the C40 structure.

Microstructural change of ultrafine-grained aluminum during high-speed plastic deformation

Abstract Effect of strain rate on microstructural change in deformation of the ultrafine grained (UFG) aluminum produced by severe plastic deformation (SPD) was studied. Commercial purity 1100 aluminum sheets were highly strained up to an equivalent strain of 4.8 by the Accumulative Roll-Bonding (ARB) process at ambient temperature. The ARB-processed sheets were found to be filled with pancake-shaped ultrafine grains surrounded by high-angle grain boundaries. The ultrafine grains had a mean grain thickness of 200 nm and a mean grain length of 1100 nm. The ultrafine-grained aluminum sheets were deformed at various strain rates ranging from 2 to 6.0×10 4 s −1 by conventional rolling, ultra-high-speed rolling, and impact compression. High-speed plastic deformation generates a large amount of heat, inducing coarsening of the ultrafine grains during and after deformation. On the other hand, it was also suggested that high-speed plastic deformation is effective for grain-subdivision, in other words, ultra-grain refinement, if the effect of heat generation is extracted.

The effect of orientation and lamellar structure on the plastic behavior of TiAl crystals

Abstract Crystals of binary TiAl (48.1–51.6 at.% Al) containing a single set of lamellae were grown using the floating zone method, and the spacings between the lamellae were changed by altering the crystal growth rate and the alloy composition. The plastic behavior of TiAl was found to depend strongly on the lamellar spacing and the angle between the loading axis and the lamellar planes. When the stress is applied parallel or perpendicular to the lamellar planes, shear deformation proceeds on {111} planes which cross the lamellae, the specimens are very strong and they exhibit low ductility. However, when the stress is applied at intermediate angles, slip occurs on {111} planes parallel to the lamellae at a low applied stress and good ductility is observed. The mode of deformation in the α2 phase, i.e. {11 2 1}〈 11 26〉 or 〈10 1 0〉〈 2 10〉 slip, strongly affects the plastic behavior of lamellar TiAl compounds. A fine and uniform distribution of lamellae is necessary to obtain high strength and good ductility.

Orientation and temperature dependence of yield stress and slip geometry of Ti3Al and Ti3Al-V single crystals

Single crystals of binary Ti3Al and ternary Ti3Al-V alloys with the D019 structure were deformed in compression at 20–900°C. Slip systems of the {1010}〈1210〉-type and the {1121}〈1126〉-type were observed in these alloys throughout the entire temperature range depending on orientation, but the {1121}〈1126〉-slip was limited to orientations near [0001]. the basal (0001)〈1210〉-slip activated in quenched Ti3Al. The CRSS for the {1010}〈1210〉-slip in the binary and ternary alloys decreases monotonically with increasing temperature. In the ternary alloy the CRSS for the {1010}〈1210〉-slip shows a violation of Schmids law, while the binary alloy obeys the CRSS law. When Ti3Al is deformed by {1121}〈1126〉-slip the CRSS for the slip exhibits an anomalous peak in the temperature-CRSS curve but the addition of vanadium suppresses the extent of the anomalous strengthening.

Deformation and improvement of ductility of the intermetallic compounds Al3 V and Al3(V, Ti)

Abstract Polycrystalline specimens of the intermetallic compounds Al3V and Al3(V, Ti) containing 1 - 25 at.% Ti with the D022 structure have been deformed under compression temperatures between 20 and 900°C. Al3V shows only a small fracture strain at low temperatures. The deformation is mainly controlled by the motion of 〈110〉-type dislocations without twinning. The activation of 〈110〉 and 〈010〉 slip in addition to 〈110〉 slip contributes to the ductility improvement at high temperatures. Ductility of Al3V has been found to be induced by the replacement of vanadium by titanium. For example, Al3(V0.95Ti0.05) shows 7% compressive fracture strain at room temperature. In Al3(V0.95Ti0.05) deformed at room temperature, not only dislocations but also numerous deformation twins and stacking faults are observed. Therefore, the improvement of ductility of Al3V by the partial replacement of vanadium by titanium arises from a substantial increase in the activity of the ordered twinning which is not operative in the bi...

Diffusion of cobalt, chromium, and titanium in Ni3Al

Diffusion studies of cobalt, chromium, and titanium in Ni3Al (γ′) at temperatures between 1298 and 1573 K have been performed using diffusion couples of (Ni-24.2 at. pct Al/Ni-24.4 at. pct Al-2.91 at. pct Co), (Ni-24.2 at. pct Al/Ni-23.1 at. pct Al-2.84 at. pct Cr), and (Ni-24.2 at. pct Al/Ni-20.9 at. pct Al-3.17 at. pct Ti). The diffusion profiles were measured by an electron probe microanalyzer, and the diffusion coefficients of cobalt, chromium, and tita-nium in γ′ containing 24.2 at. pct Al were determined from those diffusion profiles by Hall’s method. The temperature dependencies of their diffusion coefficients (m[su2]/s) are as follows: ~D(Co)= (4.2 ± 1.2) × 1O-3exp {-325 ± 4 (kJ/mol)/RT} ~D(Cr) = (1.1 ± 0.3) × 10-1 exp {-366 ± 3 (kJ/mol)/RT} and D(Ti)= (5.6 ± 3.1) × 101 exp {-468 ± 6 (kJ/mol)/RT} The values of activation energy increase in this order: cobalt, chromium, and titanium. These activation energies are closely related to the substitution behavior of cobalt, chromium, and titanium atoms in the Ll2 lattice sites of γ′; the cobalt atoms occupying the face-centered sites in the Ll2 structure diffuse with the normal activation energy, whereas the titanium atoms oc-cupying the cubic corner sites diffuse with a larger activation energy that includes the energy due to local disordering caused by the atomic jumps. The chromium atoms which can occupy both sites diffuse with an activation energy similar to that of cobalt atoms.

Slip systems and hardness in MoSi2 single crystals

Analyse par microscopie optique du glissement dans les monocristaux soumis a des essais de compression a 900 o C. Mesure de la durete entre 100 et 1200 o C

Plastic deformation of Ni2AlTi

Abstract Single-crystal and polycrystalline specimens of the intermetallic compound Ni2AlTi with the L21 structure have been deformed in compression at 923–1283 K. At temperatures higher than ∼965 K, specimens deform by slip along ⟨110⟨ directions. The observed slip planes vary with crystal orientation and, in general, they are indexed to be the high-index {hℏk} planes. However, the fundamental slip planes on which dislocations move are of the {110}, {001} and possibly {112} types. The critical resolved shear stress (CRSS) is lowest for the {110} ⟨110⟩ system and highest for the {001}⟨110⟩ system. The CRSS for these slip systems exhibits a strong temperature-dependence. Dislocation structures on the slip plane of the most predominant slip system have been studied as a function of the deformation temperature and crystal orientation. The most characteristic feature of the dislocation structure in Ni2AlTi is the occurrence of numerous dislocation nodes and networks. This has been discussed in term of the ela...