Effect of thermal cycling on the structure of quenched alloys of the Ti−Ta−Nb system

Conclusion In alloys of the system Ti–Na–Nb, it is possible to obtain -martensite in which both reversible and irreversible phase transformations occur upon thermal cycling. Reversible phase transformations are observed preferentially in alloys where tantalum atoms predominate among th dopants, and the -martensite has a certain degree of rhombic distortion of the crystal lattice.A. A. Baikov Institute of Metallurgy, NIID. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 25–27, March 1992.     

Effects of the colony size on the fracture toughness of TiAl−Mo−B alloys

The effect of the colony size on the fracture toughness of Ti−46.5Al−1.5Mo−xB (x=0.1, 0.6, 1.0) alloys was investigated. The colony size was varied by a heat treatment in the alpha-single phase region and by directional solidification (DS). The colony size decreased as the boron content increased. Fracture toughness was measured at room temperature by a three-point bend test. The heat-treated Ti−46.5Al−1.5Mo−0.1B alloy, which had a colony size of ∼350 μm, showed the best fracture toughness, and the fracture toughness decreased rapidly as the boron content increased. The fracture toughness of the DS ingots was similar with different compositions and was lower than that for the heart-treated Ti−46.5Al−1.5Mo−0.1B alloy. This study confirms that the colony size plays a major role in determining the fracture toughness of TiAl alloys with a lamellar microstructure.     

Effect of microalloying on the structure and properties of alloys in the Al−Si−Cu system

Conclusions  

Correlation between the oxide impedance and corrosion behavior of Zr−Nb−Sn−Fe−Cu alloys

The correlation between the oxide impedance and corrosion behavior of two series of Zr−Nb−Sn−Fe−Cu alloys was evaluated. Corrosion tests were performed in a 70 ppm LiOH aqueous solution at 360°C for 300 days. The results of the corrosion tests revealed that the corrosion behavior of the alloys depended on the Nb and Sn content. The impedance characteristics for the pre- and post-transition oxide layers formed on the surface of the alloys were investigated in sulfuric acid at room temperature. From the results, a pertinent equivalent circuit model was preferably established, explaining the properties of double oxide layers. The impedance of the oxide layers correlated with the corrosion behavior; better corrosion resistance always showed higher electric resistance for the inner layers. It is thus concluded that a pertinent equivalent circuit model would be useful for evaluating the long-term corrosion behavior of Zr−Nb−Sn−Fe−Cu alloys.     

Enhancement of the glass forming ability of Cu−Zr−Al alloys by Ag addition

The thermal stability and glass forming ability of Cu_50-xZr₄₃Al₇Ag_x (x=0, 1, 3, 5, and 7) bulk metallic glass alloys have been investigated. The glass forming ability in the Cu−Zr−Al−Ag alloys increased proportionally to the Ag content and show good correlations with thermal parameters such as ΔT_x(=T_x-T_g), T_rg(=T_g/T₁) and γ(=T_x/(T_g+T₁)). For the Cu₄₃Zr₄₃Al₇Ag₇ alloy, fully amorphous rods of 8 mm diameter were successfully fabricated by copper mold casting. Mechanical tests on this composition revealed also remarkable properties with compressive strength around 2000 MPa and large ductility.     

Structure and properties of high-temperature alloys with the effect of shape memory in the system Cu−Al−Nb

Conclusion Martensite transformation in alloys of the system Cu−Al−Nb occurs at temperatures much above 200°C. The hysteresis of the reversible martensite transformation is 108–128°C, which is less than for alloys of the system Cu−Al−Ag [3]. Alloys of the system Cu−Al−Nb possess a high effect of shape memory and an elevated ductility and strength. The degree of recovery of shape for an alloy with 2.56% Nb exceeds 90% at σ_Г MPa and δ₂₀=12.7% Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 32–34, August, 1999.     

On the physicochemical mechanism of modification of Al−Si alloys

Conclusions  

On the relation between the chemical composition and the strength of high-temperature deformable Al−Cu−Mg alloys under various kinds of static tests

Conclusions  

Effect of alloying on the segregation of embrittling phases in aging of alloys of the Mn−Cu system

Conclusions  

Relation between phase transformations and mechanical properties of alloys in the Ti−Al−W−Zr system

Conclusions  

Indirect evaluation of the long-term oxidation properties of Al−21Ti−23Cr and Al−37Ti−12Cr coating materials for TiAl alloy

The most pertinent coating materials in the Al−Ti−Cr alloy system to improve the high temperature oxidation resistance of a TiAl alloy, with respect to oxidation properties, resistance to thermal stress, and chemical compatibility, are the two-phase alloys of Al−21Ti−23Cr (L1₂+Cr₂Al) and Al−37Ti−12Cr (γ+TiAlCr). In this study, cyclic oxidation tests at 1000 °C and 1200 °C were performed for the specimens coated with both materials of 10 im thickness. Furthermore, breakaway oxidation caused by the formation of a rutile TiO₂ scale was observed, though both bulk alloys showed very stable oxidation behavior. This phenomenon was resulted from the depleted Al content in the coating layer due to Al₂O₃ oxide growth and interdiffusion with the substrate. Considering the decrease of Al content due to oxide growth, the Al−21Ti−23Cr coating with the initial higher Al content was more effective for long-term oxidation protection of the TiAl alloy. On the other hand, when the Al content changes due to the interdiffusion with the substrate, the Al−37Ti−12Cr coating with a smaller compositional gradient with the TiAl substrate was more effective than the Al−21Ti−23Cr coating. Cyclic oxidation tests at 1000 °C and 1200 °C confirmed that for the longer lifetime of coating materials the initial Al content was more important than the smaller compositional gradient with the substrate. Consequently, the Al−21Ti−23Cr coating was considered as more effective one for the long-term oxidation resistance of TiAl alloys.