Effects of the Zr and Mo contents on the electrochemical corrosion behavior of Ti–22Nb alloy

Ti–22Nb–xZr and Ti–22Nb–xMo (x = 0, 2, 4, 6, in atom percent) were prepared by an arc melting method. The alloys were solution‐treated at 1073 K for 1.8 ks followed by quenching them into ice water, and the electrochemical corrosion behavior in a 0.9% NaCl solution at 25 °C and neutral pH range of the solution‐treated alloys was evaluated by using electrochemical impedance spectroscopy, polarization curves and an equivalent circuit analysis. It was found that the microstructure of the solution‐treated Ti–22Nb alloy mainly contains β phase with small amount of α″ phase, and the addition of Zr or Mo to a Ti–22Nb alloy is efficient to stabilize the β phase. The resulting impedance parameters and passive current densities indicated that the corrosion resistance of the Ti–22Nb alloy was promoted significantly with the addition of Zr and Mo.     

Damage characterization and modeling of a 7075-T651 aluminum plate

In this paper, the damage-induced anisotropy arising from material microstructure heterogeneities at two different length scales was characterized and modeled for a wrought aluminum alloy. Experiments were performed on a 7075-T651 aluminum alloy plate using sub-standard tensile specimens in three different orientations with respect to the rolling direction. Scanning electron microscopy was employed to characterize the stereology of the final damage state in terms of cracked and or debonded particles. A physically motivated internal state variable continuum model was used to predict fracture by incorporating material microstructural features. The continuum model showed good comparisons to the experimental data by capturing the damage-induced anisotropic material response. Estimations of the mechanical stress–strain response, material damage histories, and final failure were numerically calculated and experimentally validated thus demonstrating that the final failure state was strongly dependent on the constituent particle morphology.     

Ferromagnetic shape memory flapper

A new method for propulsion using a Ni₂MnGa ferromagnetic shape memory flapper is introduced. We optically examine the magnetic field induced strain of pure shear by means of a state of the art generator that provides alternating magnetic fields of 7000 Oe at frequencies of up to 100 Hz. Preliminary measurements show local shear deformation of about 5%, which open new frontiers in propulsion mechanisms.     

Influence of Nb content on martensitic transformation and mechanical properties of TiNiCuNb shape memory alloys

In present work, microstructure, martensitic transformation behavior and mechanical properties of (Ti₅₀Ni₄₀Cu₁₀)_100−xNb_x (x = 0, 5, 10, 15 at.%) alloys were investigated as a function of Nb content. The addition of Nb to TiNiCu alloy leads to the presence of β-Nb phase. During cooling and heating, the alloys show one-step B2 ↔ B19 transformation. As the Nb content increases, the transformation temperatures almost linearly decrease and the transformation hysteresis monotonously increases due to the decrease of middle eigenvalue of the phase transformation matrix. The addition of Nb is effective in improving the elongation because of the introduction of β-Nb phase. With the increase of Nb content, both the yield strength and the critical stress to induce martensitic transformation increase, resulting in the improved superelastic strain.     

Influence of Cu content on high temperature oxidation behavior of AlCoCrCuxFeNi high entropy alloys (x = 0; 0.5; 1)

Studies on the oxidation behavior of high entropy alloys from the Al-Co-Cr-Cu-Fe-Ni metallic system were conducted. Three different high entropy alloys were synthesized using arc-melting method: AlCoCrFeNi, AlCoCrCu_0.5FeNi and AlCoCrCuFeNi, with their crystal structures being respectively BCC, BCC and BCC + FCC. All alloys were oxidized in the air atmosphere at temperature of 1273 K for different time periods. Basing on the thermogravimetric result, the oxidation rate of the materials decreased with the increase of Cu content and the values of parabolic constants were on the level similar to those observed in Ni-Al intermetallic alloys. In all cases the oxide scale consisted of α-Al₂O₃, which exhibited poor adhesion to the surface during the cooling process, what was especially visible in alloys with Cu addition. In all oxidized samples a tendency towards formation of the Al-depleted FCC phase directly beneath the scale was observed. The phase constitution of all materials changed significantly during the oxidation process, with multiple new phases appearing in the system.     

Theoretical calculations of the surface tension of Ag(1−x)-Cu(x) liquid alloys

The surface tension of silver-copper binary liquid alloys is calculated, in the frame work of Eyring theory. The calculations were made for different compositions (mole fraction, x_Cu = 0, 0.2, 0.4, 0.6, 0.8 and 1), in the temperature range 1100-1800 K. The surface tension decreases with temperature increase, at a fixed copper fraction x_Cu, and increases with increasing copper content. The calculated results are appropriately compared with existing literature data.     

Kinetic arrest behavior in martensitic transformation of NiCoMnSn metamagnetic shape memory alloy

High-field magnetic measurements were carried out in order to investigate behaviors of field-induced reverse martensitic transformation and kinetic arrest of NiCoMnSn metamagnetic shape memory alloy. In the thermomagnetization curves, it was confirmed that the reverse martensitic transformation temperature decreases 67 K by applying magnetic field of 5 T, while in the magnetic field cooling process under 5 T, martensitic transformation does not occur down to low temperatures. Equilibrium magnetic field, defined from the critical magnetic fields of the metamagnetic evidence in the magnetization curves, exhibits almost constant below about 100 K, suggesting that the entropy change becomes zero, which is considered to cause kinetic arrest behavior.     

Microstructure and martensitic transformation of cast TiNiSi shape memory alloys

The martensitic transformation behavior, second phases and hardness of Ti₅₁Ni_49−xSi_x shape memory alloys (SMAs) with x = 0, 1 and 2 at.% are investigated. The transformation temperature of one stage martensitic reaction B2 ↔ B19′ is associated with the forward (M_s) and reverse (A_s) martensitic transformations, respectively. All experimental DSC results such as martensitic transformation peaks (M*) and reverse martensitic transformation peaks (A*) are increased and became sharper with increasing Si-content. The microstructure investigation of the studied SMAs (Ti₅₁Ni_49−xSi_x) showed that there are two types of precipitated second phase particles. The first one is Ti₂Ni which mainly located at grain boundaries and intermetallic compound of Ti₂(Ni + Si) phase distributed inside the matrix. The volume fraction of these two phases is increased with Si content. Additionally, a small amount of Si remained in solid solution of the matrix of Ti₅₁Ni_49−xSi_x SMAs. Moreover, hardness of Ti₅₁Ni_49−xSi_x SMAs is increased as the Si-content increases.     

TiAlSi intermetallic formation and its impact on the casting processing in Al–Si alloys

The effect of titanium additions on the formation of primary TiAlSi intermetallics and resulted cast microstructure in Al–Si alloys has been studied. The precipitation temperature, growth kinetic and morphology of TiAlSi intermetallics as well as the solubility limit of Ti in Al–Si alloys were experimentally evaluated. The impact of primary TiAlSi intermetallic particles on the casting process related problems was investigated on the large scale of industrial production. The influence of Ti in the occurrence of feeding blockage and wormhole defect during ingot casting was described. The perspectives of Ti addition in Al–Si cast alloys were discussed. It is proposed that the Ti level in the most Al–Si cast alloys should be controlled within 0.10 wt.%.