Mechanism of texture and microstructure evolution during warm rolling of Ti–6Al–4V alloy

Ti–6Al–4V (Ti64) plates were subjected to rolling at 600°C and 800°C, respectively, for reductions up to 90% reduction in thickness. The mechanism of texture and microstructure evolution during rolling was studied in the present study. Extension twins of coherent nature were observed in the samples rolled up to 50% of reduction. The deformation was relatively inhomogeneous in the samples rolled at 600°C compared to that at 800°C. Visco-plastic self-consistent (VPSC) simulation showed that relative activity of pyramidal <c+a> slip was higher during rolling at 800°C compared to that at 600°C. The average activity of slip systems per grain was less than five for the samples rolled at 600°C and this might be responsible for the strain heterogeneity in the large grains. Further, twinning activity was found to be limited to a true strain of 0.5, as supported by the microstructural observation. VPSC simulation also showed the presence of contraction twins in the samples which was further supported by X-ray texture measurement. Dominant basal texture was observed in the samples irrespective of the temperature of rolling.     

On the absence of shear cracking and grain boundary cavitation in secondary tensile regions of Ti–6Al–4V–0.1B alloy during hot (α + β)-compression

Deformation instabilities, such as shear cracking and grain boundary cavitation, which are observed in the secondary tensile region of Ti–6Al–4V alloy during compressive deformation in the (α?+?β)-phase field, do not form in Ti–6Al–4V–0.1B alloy when processed under the same conditions. This has been attributed to the microstructural modifications, e.g. the absence of grain boundary α and adjacent grain boundary retained β layers and a lower proportion of 90^o-misoriented α-colonies that occur with boron addition.     

Evolution of texture and grain boundary microstructure in two-phase (α + β) brass during recrystallization

The evolution of texture and microstructure during recrystallization is studied for two-phase copper alloy (Cu–40Zn) with a variation of the initial texture and microstructure (hot rolled and solution treated) as well as the mode of rolling (deformation path: uni-directional rolling and cross rolling). The results of bulk texture have been supported by micro-texture and microstructure studies carried out using electron back scatter diffraction (EBSD). The initial microstructural condition as well as the mode of rolling has been found to alter the recrystallization texture and microstructure. The uni-directionally rolled samples showed a strong Goss and BR {236}?385? component while a weaker texture similar to that of rolling evolved for the cross-rolled samples in the α phase on recrystallization. The recrystallization texture of the β phase was similar to that of the rolling texture with discontinuous ?101? α and {111} γ fiber with high intensity at {111}?101?. For a given microstructure, the cross-rolled samples showed a higher fraction of coincident site lattice Σ3 twin boundaries in the α phase. The higher fraction of Σ3 boundaries is explained on the basis of the higher propensity of growth accidents during annealing of the cross-rolled samples. The present investigation demonstrates that change in strain path, as introduced during cross-rolling, could be a viable tool for grain boundary engineering of low SFE fcc materials.     

Strain behavior of the hydrogenated submicrocrystalline Ti–6Al–4V alloy

Comparative studies of the influence of 0.002–0.12 mass % hydrogenation on the structure and phase composition of the submicrocrystalline and coarse-grained Ti–6Al–4 V alloys are performed. The evolution of the strain processes in the hydrogenated alloy is studied for both alloys upon tension at a temperature of 293 K depending on the hydrogen content and alloy state. It is established that the presence of hydrogen in the nanostructured Ti–6Al–4 V alloy in the solid solution leads to a decrease of its yield stress and an increase of its tensile strength and total strain before failure. The possible reasons for the increased duration of the uniform strain stage and the effect of strain hardening of the alloy in the presence of hydrogen in the solid solution are discussed.     

Structure of the B2 phase in Ti–25Al–25Mo alloy

The structure of the B2 phase has been investigated in Ti–25Al–25Mo alloy using Rietveld refinement of X-ray and neutron diffraction data in as-cast and solution-treated conditions. Different initial structure models have been used for the refinement. The site occupancy of the various chemical constituents in the B2 phase has been calculated and compared with earlier investigations. The relative merits of neutron diffraction over X-ray diffraction for structural refinement of the B2 phase in Ti–25Al–25Mo alloy have been demonstrated.     

Crystallographic features of the approximant H (Mn7Si2V) phase in the Mn–Si–V alloy system

The intermetallic compound H (Mn₇Si₂V) phase in the Mn–Si–V alloy system can be regarded as an approximant phase of the dodecagonal quasicrystal as one of the two-dimensional quasicrystals. To understand the features of the approximant H phase, in this study, the crystallographic features of both the H phase and the (σ → H) reaction in Mn–Si–V alloy samples were investigated, mainly by transmission electron microscopy. It was found that, in the H phase, there were characteristic structural disorders with respect to an array of a dodecagonal structural unit consisting of 19 dodecagonal atomic columns. Concretely, penetrated structural units consisting of two dodecagonal structural units were presumed to be typical of such disorders. An interesting feature of the (σ → H) reaction was that regions with a rectangular arrangement of penetrated structural units (RAPU) first appeared in the σ matrix as the initial state, and H regions were then nucleated in contact with RAPU regions. The subsequent conversion of RAPU regions into H regions eventually resulted in the formation of the approximant H state as the final state. Furthermore, atomic positions in both the H structure and the dodecagonal quasicrystal were examined using a simple plane-wave model with 12 plane waves.     

Microstructure evolution and properties of Al/Al–Mg–Si alloy clad wire during heat treatment

In this paper, heat treatment was carried out on Al/Al–Mg–Si alloy clad wire, and microstructure evolution and properties of Al/Al–Mg–Si alloy clad wire during heat treatment were investigated. During solution, contents of Mg and Si in inner matrix increased due to dissolution of primary Mg₂Si, and they also increased in outer matrix because Mg and Si diffused across the interface. Tensile strength of the clad wire increased firstly and then decreased, and elongation continuously increased, while conductivity continuously decreased with the increase in solution time. In aging process, Mg₂Si precipitated in both inner core and outer layer, and the content and average diameter of the precipitate increased with the increase in aging time. The content of precipitate was higher, and the average diameter was bigger in inner core. Tensile strength of the clad wire increased firstly and then decreased with the increase in aging time, and the elongation continuously decreased, while the conductivity continuously increased. The peak tensile strength of 202 MPa occurred at 8 h, when the corresponding elongation was 20 % and the conductivity reached 56.07 %IACS. Even tensile strength of the prepared clad wire approximately equaled to that of Al–0.5Mg–0.35Si alloy 203 MPa, the conductivity was obviously improved from 54.2 to 56.07 %IACS.     

Interaction behaviors at the interface between liquid Al–Si and solid Ti–6Al–4V in ultrasonic-assisted brazing in air

Power ultrasonic vibration (20 kHz, 6 μm) was applied to assist the interaction between a liquid Al–Si alloy and solid Ti–6Al–4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti–6Al–4V surface, chemical dissolution of solid Ti–6Al–4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2–20 μm diameter-sized pits formed on the Ti–6Al–4V surface. Propagation of ultrasonic waves in the liquid Al–Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti–6Al–4V substrate, excessive chemical dissolution of solid Ti–6Al–4V into liquid Al–Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al–Si and Ti–6Al–4V can be produced by ultrasonic-assisted brazing in air.     

Strength of the Ti–6Al–4V Titanium Alloy under Conditions of Impact and Short Pulse Loading

Physics of the Solid State - The strength and resistance of the Ti–6Al–4V titanium alloy to solid particle erosion have been studied in as-delivered state and after the equal-channel...     

High-rate erosion of Ti–6Al–4V ultrafine-grained titanium alloy obtained via intensive plastic torsional deformation

Testing results for Ti–6Al–4V ultrafine-grained titanium alloy obtained via intensive plastic torsional deformation (IPTD) are presented. To estimate the effect of IPTD treatment on the behavior of this material under erosion conditions, special experimental techniques were developed. The ultrafine-grained alloy was tested alongside with the traditional coarse-grained titanium alloy in an erosion wind tunnel in an air flow with corundum particles as an abrasive material. The erosion resistance of the material was estimated from the mass loss of specimens. Despite a considerable increase in the static strength characteristics, the nanostructured material did not demonstrate any increase in its erosion resistance in comparison with the initial alloy.     

Ultrasonic cavitation erosion of gas nitrided Ti–6Al–4V alloys

Ultrasonic cavitation erosion experiments were performed on Ti–6Al–4V alloys samples in annealed, nitrided and nitrided and subsequently heat treated state. The protective oxide layer formed as a result of annealing and heat treatment after nitriding is eliminated after less than 30 min cavitation time, while the nitride layer lasts up to 90 min cavitation time. Once the protective layer is removed, the cavitation process develops by grain boundary erosion, leading to the expulsion of grains from the surface. The gas nitrided Ti–6Al–4V alloy, forming a Ti_xN surface layer, proved to be a better solution to improve the cavitation erosion resistance, compared to the annealed and nitrided and heat treated state, respectively. The analysis of the mean depth of erosion rate at 165 min cavitation time showed an improvement of the cavitation erosion resistance of the nitrided samples of up to 77% higher compared to the one of the annealed samples.     

Raman characterization of Ti–6Al–4V oxides and thermal history after kinetic friction

Raman spectroscopy is applied to study the surfaces of a pair of tantalum and titanium alloy samples after high-speed dry friction. The surface of titanium alloy (Ti–6Al–4V) shows titanium oxides on the rubbing surfaces. Raman spectra enable to differentiate the allotropic phases of anatase or rutile. The presence of these phases is the signature of the local thermal history during the friction tests. Moreover, Raman mapping allows localizing area the flash temperatures that may have been produced by the friction between sample asperities.     

Microstructure and mechanical properties of V–4Ti–4Cr alloy as a function of the chemical heat treatment regimes

The regularities of the formation of a heterophase structure and mechanical properties of V–4Ti–4Cr alloy as a function of thermomechanical and chemical heat treatments are studied. The regimes of thermomechanical treatment which provide the formation of a heterophase structure with a homogeneous volume distribution of oxycarbonitride nanoparticles with a size of about 10 nm and an increase in the volume content and thermal stability of this phase and which provide an increase in the temperature of alloy recrystallization are developed. The formation of the heterophase structure results in a substantial (up to 70%) increase in the short-term high-temperature strength of the alloy at T = 800°C. The increase in the strength is achieved while keeping a rather high level of plasticity.     

Structure and Phase Composition of Ti–6Al–4V Alloy Obtained by Electron-Beam Additive Manufacturing

Russian Physics Journal - The paper presents the fabrication of Ti–6Al–4V alloy specimens using two operating modes of the electron beam additive manufacturing (EBAM). The structure,...     

The influence of strain rate on the visibility of dislocations in transmission electron microscopy images of deformed Ti–6 wt% Al–4 wt% V and in Timet 550

Samples of Ti–6?wt%?Al–4?wt%?V and Timet 550 (Ti–4?wt%?Al–4?wt%?Mo–2?wt%?Sn–0.5?wt%?Si) have been subjected to strain rates between 10^?1 and 10³?s^?1and detailed examination of the dislocation structure in the α grains has been carried out using transmission electron microscopy (TEM). For samples deformed to a strain of 0.1 at 10^?1?s^?1, detailed analysis of the defects can be carried out using all diffracting vectors and the presence of (c +?a) dislocations and a dislocations thus confirmed. In contrast, for samples strained to the same strain of 0.1 but at 5?s^?1, it is not possible to obtain images of dislocations when using any diffracting vectors other than 0002. Thus the presence of dislocations which have a Burgers vector containing a c component can be confirmed in the samples strained at 5?s^?1 but the presence of a-component dislocations can only be inferred from TEM of these samples because of the difficulty of obtaining images with diffracting vectors other than 0002. Limited observations on samples strained at 10³?s^?1 show that similar difficulties are found in imaging dislocations as are found in samples deformed at 5?s^?1 but at this strain rate, the highest used, the difficulties are reduced since images can be obtained in some grains using diffracting vectors other than 0002. These results are discussed in terms of the nature of damage as a function of strain rate and the factors that influence contrast from dislocations in crystals.     

Effect of Sn and Al additions on the microstructure and mechanical properties of amorphous Ti–Cu–Zr–Ni alloys

Amorphous Ti–Cu–Zr–Ni alloys with minor addition of Sn and Al were prepared by melt spinning technique.The effects of Sn and Al additions on the microstructures and mechanical properties of glassy ribbons were investigated.The amorphous state of ribbons was confirmed by x-ray diffraction and transmission electron microscopy,where those ribbons with Sn addition exhibited a fully amorphous state.The characteristic temperature indicates that Ti_(45)Cu_(35)Zr_(10)Ni_5Sn_5 alloy has a stronger glass-forming ability,as proven by differential scanning calorimetry.Ti_(45)Cu_(35)Zr_(10)Ni_5Al_5 alloy showed a better hardness of 9.23 GPa and elastic modulus of 127.15 GPa and good wear resistance.Ti_(45)Cu_(35)Zr_(10)Ni_5Sn_5 alloy displayed a pop-in event related to discrete plasticity according to nanoindentation.When the temperature is below 560 K,Ti_(45)Cu_(35)Zr_(10)Ni_5Sn_5 alloy mainly exhibits elasticity.When the temperature rises between 717 K and 743 K,it shows a significant increase in elasticity but decrease in viscoelasticity after the ribbon experiences the main relaxation at 717 K.When the temperature is above 743 K,the ribbon shows viscoplasticity.