Materials Science Forum Vols. 747-748

Abstract: Ti-Mo-Nb-Cr-Al-Fe-Si alloy is a new metastable β titanium alloy with excellent combination of strength and ductility. The β grain-growth exponent and the activation energies for β grain growth for the investigated alloy at specified temperature were computed by the kinetic equations and the Arrhenius-type equation. The rate of β grain growth decreases with elongating solution treated time and increases with the increasing solution-treated temperature. The β grain-growth exponents, n, are 0.461, 0.464 and 0.469 at 1113, 1133 and 1153K, respectively. The β grain growth activation energy is determined to be 274 KJ/mol.

Abstract: Titanium alloy are widely used in various fields, such as Aerospace, Marine and Medical. However, the technology of straightening for TC4 wire rod has not been effectively solved, and relevant research is quite rare. TC4 wire rod is difficult to be straightened under room temperature owing to its special properties. In order to solve this problem, this paper designed a parallel roll thermal straightening system and also developed an automatic intermesh calculation software based on Matlab GUI platform to precalculate the settings of straightening device under different temperatures according to straightening theory. Furthermore, numerical simulation method has been used for straightening process with ABAQUS software before the practical straightening experiment. Finally, using the calculated parameters the straightening experiment was carried out, and results show that this method is feasible and effective.

Abstract: A series of Ti-Mo-Sn alloys with different Mo contents from 7% to 15% (wt. %) were prepared, and the effects of Mo content and thermo-mechanical treatment on their microstructural evolution and mechanical behavior were investigated. The experimental results indicated that the β to α martensite transformation can be effectively suppressed with increasing Mo content. After cold rolling treatment, superior mechanical properties and low modulus were achieved in Ti-8Mo-4Sn alloy, with tensile strength of 1108MPa, yield strength of 1003MPa and low Youngs modulus of 53GPa. The influence of severe cold deformation on the macrostructure and mechanical properties was discussed based on the characterization of X-Ray diffraction and mechanical tests. It was demonstrated that the cold rolling induced fine α martensite and high density dislocations lead to the high strength of the Ti-Mo-Sn alloys. The fine α martensite as well as the β matrix with low stability guarantee low Youngs modulus.

Abstract: TG6 alloy is a new titanium alloy which has been designed to reach the service temperature of 600°C. The microstructural evolutions of TG6 alloy under different thermal mechanical treatments were studied. It was found that lamellar microstructures with basketweave α lamella are obtained for TG6 alloy forged in β field. The evolution mechanism is transformed from dynamic recrystallization to dynamic recovery and the thickness of α lamella increases with increasing forging temperature. The aspect ratio of α lamella decreases firstly and then increases with increasing deformation degree. Grain boundary α lath appears when the deformation degree is less than 40%. The thermal mechanical treatments, including deformation in β field firstly and then deformation in α+β field result in the transformations of the microstructures drastically. The deformation degree in α+β field decides the final microstructure. The deformation degree of 20% in α+β field results in partial globular α phase.

Abstract: The influences of sputtering current on deposition rate, composition, microstructure evolution and growth mechanism for titanium alloy coatings onto SiC fibers are explored by surface profiler, auger electron spectrometer, X-ray diffraction, scanning electron microscopy and atomic force microscope. The experimental results show that crystallization take place in all coatings with hexagonal structure (α-Ti). As sputtering current is increased, deposition rate and Al content increase, and Ti content decreases. Coating growth mode alsotransforms from V-shaped column grains to equiaxed grains as sputtering current increased. The column grains are generally not single grains, and more nanograins are composed

Abstract: Abstract. OM, XRD, SEM, EDS were used to test. and analyze the combustion products of TC4 and Ti40 alloys by layer-by-layer from reaction frontier to matrix The result shows that: titanium alloy can be divided into 4 sections, combustion surface (CS), molten zone (MZ), transitional zone (TZ) and influence zone (IZ). The CS is mainly consist of TiO₂, and with oxide of V. Cr₂O₃ and SiO₂ are detected on CS of Ti40. MZ of TC4 is in loose and porous state. There are lots of cracks and holes in the TZ and IZ; MZ of Ti40 is compact, between MZ and IZ there is a TZ which is rich of V and Cr, it can stop oxygen diffusing effectively. From the MZ to matrix, oxygen content reduces gradually, and oxide of Ti with different valence state is detected. Because of effect of oxygen, the hardness of the two alloy increase after combustion, increment of Ti40 is much greater than that of TC4.

Abstract: The effect of strain rate and deformation temperature on flow stress of TC18 titanium alloy was studied through heat simulating tests in 760~960 with temperature interval and the strain rate interval in 0.01~10s^-1. Relationship model of flow stress versus strain was established and hot deformation mechanics of TC18 titanium alloy was analyzed. The results show that the flow stress reduces obviously as the deformation temperature increases or the strain rate decreases. Dynamic recovery occurs at high strain rate above phase transformation point, while dynamic recrystallization occurs at low strain rate as well as at the temperature below phase transformation point.

Abstract: [(Mo,Sn)(Ti,Zr)₁₄]Nb₁ serial alloy compositions were designed using a cluster-plus-glue-atom model to receive BCC β-Ti alloys with low Youngs modulus (E) in Ti-based multi-component systems, where the square brackets enclose the coordination polyhedron cluster CN14 of the BCC structure and Nb is the glue atom. These serial alloys were prepared into rods with a diameter of 6 mm by copper-mould suction casting method. XRD and tensile test results indicated that all these alloy series possessed a monolithic BCC structure except [SnTi₁₄]Nb₁ and [(Mo_0.5Sn_0.5)Ti₁₄]Nb₁ due to Sn deteriorating BCC structural stability. A combination of Mo_0.5Sn_0.5 at the cluster center, as well as low-E Nb and Zr in the glue and cluster shell respectively, can reach simultaneously low E and high BCC stability, incarnated in the [(Mo_0.5Sn_0.5)(Ti₁₃Zr)]Nb₁ alloy which has the lowest E of 48 GPa in the suction-cast state.

Abstract: The effect of Nb on the equilibrium lattice parameters and relative stability between β and ω phases of Ti_1-xNb_x (0 < x 0.4) random alloys as well as their mechanical properties in body-centered-cubic crystallographic phase was investigated using the exact muffin-tin orbitals method in combination with the coherent potential approximation. It has been found that the calculated lattice parameters of the β phase agree well with the experimental data. For ω phase, the value of a increases almost linearly with increasing Nb concentration, while the opposite situation presented for c/a. Both Nb addition and increasing temperature enhanced the stability of β phase relative to ω phase. The critical Nb concentration for the complete stabilization of β phase at 300 K, 673 K and 1273 K was 22 at.%, 17 at.% and 9 at.%, respectively. The polycrystalline bulk modulus B, Youngs modulus E and shear modulus G increased monotonously with Nb addition and reducing the Nb concentration below 30 at.% resulted in lower E compared to that of Ti-6Al-4V. The calculated G/B values demonstrate that the bcc Ti_1-xNb_x (0 < x 0.4) random alloys should be intrinsically ductile.

Abstract: The effect of cryogenic treatment on the microstructure and properties of Ti-6Al-4V has been studied in this paper. The program controlled SLX cryogenic box was used to conduct the cryogenic treatment and the subsequent low temperature temper. The scanning electron microscope was used to study the morphology of microstructure and fracture surface. As the results show that the cryogenic treatment increases the elongation of Ti-6Al-4V from 16.5 percent to 24.5 percent, at the same time, the strength increases slightly, this indicates that cryogenic treatment can improve the comprehensive mechanical properties. The microstructure measurement revealed that there is a tendency of reduction in the precipitated particles after cryogenic treatment. The cross section is flat and the size of dimples is more uniform. It is concluded that the change in the precipitation particle had a great influence in the mechanical properties.