Brittle-to-ductile transition (BDT) temperature (TBD) was evaluated according to temperature dependence of tensile properties under different strain rates from 10−5to 10−1s−1in two-phase Ti-47Al-2Mn-2Nb and Ti-47A1–2Mn-2Nb-0.8 TiB2alloys with nearly lamellar microstructure. Based on the strain rate dependence of the determined TBD values, apparent BDT activation energies were determined using Zener-Hollomon factor. Tensile fracture surfaces were observed using a scanning electron microscope while deformation substructures were investigated by transmission electron microscopy. It was found that the BDTT of both alloys increased sharply with the strain rate and that the minor addition of 0.8 vol% TiB2reduced TBD by about 100K at the same strain rate. The TiB2addition also decreases the apparent BDT activation energy from 324 to 256 kJ/mol. Both of these values approximate to self- or inter-diffusion of Ti and Al atoms in TiAl phase. Transgranular fracture and dimple fracture were found dominant in fracture surfaces below and above TBD, respectively. The most common 1/2<110] ordinary dislocations were found to begin climb at mound TBD. All this evidence, as well as a theoretical calculation using the Nabarro Model, add up to a conclusion that the BDT is controlled by dislocation climb in both alloys.

The compressive ductilities of Ni3Al-Zr-B base alloys with sole addition of magnesium (0.02∼0.06wt.%) and combined addition of magnesium(0.02wt.%) and silicon(0.54∼1.08wt.%) respectively responding to strain rate rising from 10-4sec-1 to 10-1 sec-1 have been studied in a high temperature range of 1073∼1273K. The results show that the compressive strains at rupture(CSR) of the alloys have been greatly improved by sole addition of magnesium and the alloys with combined addition of magnesium and silicon reveal even higher CSR values, furthermore, at temperatures of 1073K and 1273K, the strain rate dependence of CSR reveals to be anomalous, i.e, the CSR value increases as the strain rate rises, and then declines until it surpasses the peak value, which is corresponded to the strain rate of 10-3 sec-1 and 10-3 sec-1 respectively.

The beneficial effect of magnesium and silicon exists in their competence of reducing strain rate sensitivity exponent values. The mechanisms of the anomalous ductilizing behavior in the Ni3Al as affected by ternary elements are discussed.

The superplastic behavior of a NiAI and Ni3Al duplex alloy was investigated. It was found that the alloy exhibits superplastic behavior over a narrow temperature range, from 975 °C to 1025°C at the strain rate of 1.52 × 10-4 s-1. A maximum tensile elongation of 149% was obtained at 1000°C with the strain rate sensitivity up to 0.375. The superplastic deformation of the duplex alloy can be approximately described by an empirical equation of the form: ε = Ao2.67 exp(-303,000 / RT). Optical microstructure and TEM observation show that the superplastic behavior mechanism of the investigated alloy is a process of continuous recovery and recrystallization during deformation.

The influence of Ti addition on the high temperature oxidation behaviors of FeAl intermetallic alloys in air at 1000°C and 1100°C have been investigated. The oxidation kinetics of FeAl alloys were examined by the weight gain method and oxide products were examined by XRI), SEM, EDS and EPMA. The results showed that the oxidation kinetic curves of both Ti-doped and binary Fe-36.5A1 alloys were described as different parabolas followed the formula: (ΔW/S)2 =Kpt. The parabolic rate constant, Kp values are about 2.4 and 3.3 mg2cm-4h-1 for Fe-36.5A1 alloy and about 1.3 and 2.0 mg2cm-4V-1 for Fe-36.5Al-2Ti alloy when oxidizing at 1000°C and 1100°C respectively. The difference between Fe-36.5Al and Fe-36.5Al-2Ti alloy is not only in the surface morphology but also in the phase components. In the surface there is only α-Al2O3 oxide for the Fe-36.5Al alloy while there are α-Al2O3 and TiO oxide for the Fe-36.5Al-2Ti alloy. The effects of Ti addition on the oxidation resistance of FeAl alloy were discussed based on the micro structural evidence.

Tensile properties of a two-phase γ titanium aluminide with duplex microstructure are tested under different strain rates from 5×10-5 to 5×10-3S-1 at temperature from 1123K to 1273K. It is found that there exists approximate linear relationship between the flow stresses and the logarithm of the strain rate at different temperatures. The strain rate sensitivity can be explained by thermal activation theory, and dislocation climbing is identified as the rate controlling mechanism

Monte Carlo computer simulations with embedded atom method potentials are used to study the structure and energy of symmetric tilt grain boundaries in Ni3Al at high temperatures and compared with those at absolute zero, which is conducted with static relaxation method. The effect of stoichiometry and boron addition on the structure and energy of grain boundary are also investigated. The simulation results show that there exists more compositional disorder at grain boundaries than in the bulk in non-stoichiometric Ni3Al with and without boron. At absolute zero the grain boundary consists of periodically distributed structural units which are distorted with the increasing temperature. The effect of temperature on the structure and energy of grain boundaries in Ni3Al with and without boron was discussed.

The effects of microalloying elements, Y(0.02at%, 0.04at% and 0.06at%) and Nb(0.2at%, 0.5at% and 0.8at%) on the wettability of intermetallic Fe-40A1 with polycrystalline α-Al2O3 were investigated experimentally by means of sessile drop method. The addition of 0.02at%Y and 0.04at%Y showed no significant effects on the wettability. However, the addition of 0.06at%Y improved the wettability in temperature range from 1673K to 1823K. The addition of different amount of Nb were not beneficial to the FeAl-Al2O3 wettability under conditions investigated. The SEM study of the shear fractured surfaces showed that the additions of Y and Nb coursed Al2O3 particles more adherent to FeAl matrix, compared with the case of pure Fe-40A1. The degree of adherence varied with the amount of Y and Nb. These phenomena are discussed in terms of interfacial reactions and interfacial bonding.

The Mössbauer measurements at room temperature have been carried out on the B2 intermetallic compound Fe-40Al and its Mn or Ti containing alloys. The results show that all the Mössbauer spectra of Fe-40Al and its Mn or Ti containing alloys are approximately one-peak singlets. The Fe atoms in these alloys show no significant magnetic moment. The spectra of Mn or Ti containing alloys have been fitted with two Lorentzian lines by the method of least squares. By studying the isomer shifts and other parameters of these fitted lines, it have been shown that Mn atoms occupy both Fe and A1 sublattices, Ti atoms occupy preferentially Fe sublattice, however, a few of Ti atoms occupy A1 sublattice only as Ti concentration is over certain amount (∼5-at%).

The embedded atom type potentials and static relaxation method combined with steepest gradient computational technique have been used to simulate the grain boundary cohesive energies, the distribution of electron density and stress field in the grain boundary region, and other related problems of [100], [110] and [111] symmetric tilt grain boundaries in Ni3 Al with different grain boundary geometrical index and composition. Their relations with the segregation of boron, behaviors of the grain boundary, and especially the stoichiometrical effect of B induced ductility have also been studied and discussed.

At 515° C with a constant strain-rate of 6.7× 10−3 min−1,tensile specimen of LC4 aluminum alloy with an initial average grain size of 8.7μm exhibited good superplasticity. A fracture elongation of 4649% was obtained. Under such deformation conditions, the m-δrelationship belongs to the mL=mmax type , with a maximum m value of 0.78 at 94% strain. The m-δ relationship can be expressed as δI(%)= (CI ×0.0067(mI−0.5) −1) × 100. During superplastic deformation, three kinds of structural evolution take place, namely the formation of precipitate-free zones adjacent to grain boundaries due to diffusional creep, grain coarsening and cavity generation. The m-δ relationship of superplasticity of the alloy mentioned above can be explained on the basis of the structural evolution during superplastic deformation.