Progress in Light Metals, Aerospace Materials and Superconductors

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Authors: E. Tal-Gutelmacher, Dan Eliezer, Thomas Boellinghaus
Abstract: Ti-6Al-4V alloy has proven to be technically superior and cost-effective materials for a wide variety of aerospace, industrial, marine and commercial applications. The mechanical properties of Ti-6Al-4V are very sensitive to the microstructure obtained after the thermo-mechanical treatment. The duplex structures provide good tensile ductility, fatigue strength, resistance to microcrack growth and crack initiation, and are often used in demanding fatigue critical tasks. However, although Ti-6A-4V is considered to be reasonably resistance to chemical attack, severe problems can arise when it comes in contact with hydrogen-containing environments due to its susceptibility to hydrogen embrittlement. The objective of this paper is to investigate the absorption and desorption behavior of external hydrogen on a duplex-annealed Ti-6Al-4V alloy. While investigating the desorption profile, we seek to better understand the thermodynamics and the kinetic nature of the interaction between traps and hydrogen atoms, with specific emphasis on the investigation of the impact of these interactions on the microstructure of the studied aerospace applicative titanium alloy. In order to achieve these goals, thermal desorption spectroscopy (TDS) was applied and the data obtained from this analysis was supported by a variety of other experimental techniques, such as LECO hydrogen determinator, XRD and microstructure investigations by means of optic and electronic microscopy. Hydrogen was found to influence significantly the microstructure of the alloy. The process of hydrogen evolution was found to be a very complex process, being affected mainly by the phase transformations that may occur during the thermal analysis.
1367
Authors: Yong Qing Zhao, J.F. Wei, Wei Lu Wu, P. Guo
Abstract: Titanium and its alloys are widely used in industries due to their excellent comprehensive properties. However, their high-cost limits their applications in civil, therefore the research on low cost titanium technology is necessary. In the present study, the semi-solid deformation behavior of Ti14 burn resistant alloy was investigated. The results indicated that Ti2Cu melting phases within grains and at grain boundaries grow to form coarse grain boundaries and network structures during Ti14 alloy semi-solid deformation. Its microstructure was coarse and the grain boundary was wide after semi-solid forging, leading to low plasticity at room temperature. Recrystallizing heat treatment leads to fine microstructure, which is similar to that of conventional forging, resulting in improvement of tensile mechanical properties. The mechanical properties of semi-solid forging are similar to that of conventional one at high temperature.
1373
Authors: Qing Zhou, Goroh Itoh, Mitsuo Niinomi
Abstract: Because of its excellent environmental resistance and cold-working capacity, beta titanium alloy Ti-15-3 has attracted more and more attention in aerospace manufacture industry. Another beta titanium alloy, Ti-29-13, has been recently developed for biomedical implant materials. The mechanical properties of three alloys including two β and one α+β are presented, particularly the characteristic of β alloy differing from that of α+β alloy. The high temperature deformation behaviors of two alloys are also presented. Excellent formability of Ti-15-3 highlights the metal sheet application in commercial and military airplane. Band structure in Ti-29-13 has been found. Thermalmechanical processing is carried out to reduce the band structure and improve the elongation.
1379
Authors: Hui Qin Chen, Hao Zhuan Lin, L. Guo, Chun Xiao Cao
Abstract: The hot deformation behavior of TC11 with an equiaxed α+β pre-form microstructure was investigated by hot compression tests in the temperature range 800°C–1090°C and strain rate range 1×10-310s-1. Several approaches have been used in this investigation, which include analysis of shapes of stress–strain curves, kinetic analysis and microstructure observation. The experimented results showed that, (1) In the β phase field, the alloy exhibits dynamic re-crystallization. The apparent activation energy in this domain is estimated to be 183kJ/ mol, which is close to that for self-diffusion in β. The re-crystallized grain size may be governed by competing of diffusion and dynamic re-crystallization rate at deforming conditions. (2) In the α+β phase field, the alloy exhibits super-plastic deformation behavior at 0.001-0.01s-1 and 980°C -850°C, and the apparent activation energy estimated in this domain is about 600 kJ/mol, which is much higher than that for self-diffusion in α-titanium due to β volume fraction is not constant over the test temperature range.
1383
Authors: Xiao Teng Wang, Hong Yuan Fang, Fusahito Yoshida
Abstract: In this study, depth sensing nano-indntation test combined with in-situ atom force microscope (AFM) is carried out to investigate the plastic/viscoplastic behavior of beta titanium alloy. The indentation experiment results show that with the increasing nominal indentation strain rate, the hardening effect becomes stronger in the loading part, while the creep induced softening behavior becomes stronger in the unloading part. The residual penetration depth is deeper when the indentation strain rate increases. A new quantity named nominal hardness/modulus ratio is defined to characterize the plastic behavior of beta titanium at micro region.
1389
Authors: Xiu Hua Zheng, Bilal Dogan, Karl Heinz Bohm
Abstract: Ti-6242 alloys have been widely used in aero-engine applications due to high temperature strength and creep resistance. The γ-TiAl based intermetallics are considered as candidate materials to replace the current materials weed at high temperatures. The present paper reports on the microstructural and mechanical characterization of γ-TiA/Ti6242 diffusion bonds. The emphasis is put on the better understanding of microstructural development during diffusion process and mechanical properties of diffusion bonds. The process variables of temperature, pressure and time were optimized to produce joints with sound microstructure and bond quality for mechanical characterization. The micro and standard tensile tests were applied to determine bonding strength of joints. Metallographic and fractographic examinations on diffusion joints and tested specimens were carried out using SEM coupled with EDX. The concentration profiles of elements from EDX analysis combined with SEM/BSE investigation demonstrated that the strong inter-diffusion of main elements Al and Ti across the bonding interface occurred during DB process leading to the formation of a noticeable diffusion zone consisting of fine* α2/α grains. The micro tensile tests showed that the preference of fracture on base materials far from the bonding line, but a more marked tendency to brittle failure along bonding interface shown by the standard tensile test results, indicating a significant sample size effect on mechanical property measurements.
1393
Authors: Kun Wang, Jian Ping Liu, Zheng Yi Fu, Wei Min Wang, Hao Wang, Jin Yong Zhang, Yong Peng, Qing Jie Zhang
Abstract: The combustion synthesis and densification process for titanium diboride and iron layered materials in the process of Self-propagating high-temperature synthesis of titanium diboride, variation of the initial temperature, amount of diluent and particle size of raw materials had effect on the adiabatic temperature, fraction of melted product and propagation rate of the combustion process, were studied by theoretical calculation and experimental analysis. The result showed that divided by a combustion temperature 3050K, either in the high temperature range or in the low temperature range, the calculated process activation energies were 140 KJ/mol or 355 KJ/mol respectively, which revealed two different reaction process mechanisms. Interfacial bonding between TiB2+Fe cermet and Fe substrate was analyzed by EPMA, which showed interfacial bonding of two-layered product was obtained by the dissolution and the diffusion of Ti in the Fe substrate and joining of Fe binder with Fe substrate. The fractures of joints took place in the TiB2+Fe cermet layer rather than at the interface.
1401
Authors: Shu Hua Li, Fu Chi Wang, Cheng Wen Tan, Zhi Yong Chen, Zhi Sun
Abstract: Adiabatic shear properties of pure titanium-TA2 have been investigated using specially designed specimen in a Hopkinson pressure bar at high strain rate of 103s- 1. Microstructural characteristics was investigated using scanning electrion microscopy as well as transmission and high resolution transmission electrion microscopy .The results showed that the shear stress and adiabatic sensitivity for rolled 45% TA2 are higher than forged TA2. Comparing the adiabatic shear bands (ASB) both in the forged and rolled TA2, no evidence in morphology alteration was found except to shear band widths. The transmission electron micrograph of the ASB in forged and rolled TA2 showed the grain size reduction from ~20μm to 200nm. No deformation twins have been observed in ASB. The selected area electron diffraction patterns of the ASB showed reflections of multiple grains, forming discontinuous rings which can be indexed as h.c.p. structure of α-Ti. This indicates that the ASB consists of fine grains of α-Ti and the α-Ti→ β-Ti transformation did not occur.
1409
Authors: E. Tal-Gutelmacher, Dan Eliezer, Thomas Boellinghaus
Abstract: Ti-6Al-4V and β-21S (Ti-15Mo-3Al-3Nb-0.3Si, wt%) titanium alloys were exposed to a hydrogen-containing environment, introduced by Gas-Tungsten Arc welding via a mixed Ar + 5% H2 shielding gas. The different characteristics of hydrogen absortion/desorption behavior and trapping in the welded Ti-6Al-4V and β-21S alloys were studied by means of thermal desorption spectroscopy (TDS). Thermal spectra analysis is supported by data from a variety of other experimental techniques, e.g., Leco hydrogen determinator and microstructure investigations. In the specimens welded in hydrogen-containing environment, no cracking was observed. However, the complex process of hydrogen desorption was found to be significantly affected by the microstructure developed in the alloys after welding. The unique microstructural morphology, the presence of potential irreversible trapping sites and phase transitions (oxide dissociation) were considered to be the potential parameters affecting the hydrogen desorption behavior from the alloys.
1413
Authors: J. Zhang, Anja Kutzsche, K. Rosenberg, Christoph Leyens, Bernd Viehweger
Abstract: A novel canning technology to forge gamma-TiAl alloys was developed at the BTU Cottbus. A TiAl specimen was encapsulated with multilayer stainless steel foil and glass. The steel foil layers prevented the heat loss through radiation and the glass layer reduced the temperature decrease through conduction. First, the effect of steel foil on the cooling rate was investigated. Cooling curves were recorded for TiAl specimens without steel foil layer, with 1, 2, 3 and 4 layers of steel foil, as well as with 3 coated steel foil layers, respectively. While the unprotected specimen cooled from 1200 °C to 1100 °C within 12 s, the specimen with 3 coated steel foil layers needed 52 s for the same temperature decrease. The efficiency of the glass layer was examined with forging of steel specimens. The cooling rate during forging of the specimen with a glass layer was only half of that without a glass layer. Based on the results, Ti-45Al-0.5Mo-0.5Cu-0.2Si specimens, canned with steel foil and glass, were successfully forged at strain rates of 0.1 s-1 and 0.04 s-1 with warm dies which were heated to 500 °C. Visual and metallographic examinations revealed no cracks, pores or micropores. The microstructures are fine-equiaxed grains.
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