Deformation Of Titanium Alloy Research Articles

Study on milling flatness control method for TC4 titanium alloy thin-walled parts under ice fixation

Thin-walled parts are characterized by weak rigidity and are very prone to deformation during machining, which directly affects the machining accuracy and performance of the parts, so controlling the machining deformation of thin-walled parts is an urgent process problem to be solved. To address such problems, this paper proposes a flatness control machining method based on ice holding of workpieces. The method uses frozen suction cups to solidify liquid water to achieve stress-free clamping of workpieces. We conducted a low-temperature tensile test to investigate the low-temperature mechanical properties of the material. Comparative tests of ice-free and low-temperature ice-fixed milling were conducted to compare and analyze the changes of flatness and milling force in the two working conditions, to investigate the influence of machining parameters on the flatness of thin-walled parts, and to reveal the mechanism of low-temperature milling of ice-fixed workpieces. In addition, the low-temperature milling performance of titanium/aluminum alloy based on ice-fixation was compared. The results show that TC4 has good plasticity, high flexural strength ratio and strong resistance to deformation at low temperatures. Compared with no ice-holding, ice-holding machining effectively improves the flatness of the workpiece, and the order of the machining parameters affecting flatness is: feed rate > milling depth > spindle speed. The milling forces under ice-holding conditions were all greater than those without ice holding. The stiffness and hardness, resistance to damage and deformation of titanium alloy at low temperature are greater than those of aluminum alloy. This method provides a new method for high-precision machining of thin-walled parts.

Calculation Method of Curvature Radius and Bending Deformation of Titanium Alloy under Multiple Laser Shocks

TC4 titanium alloy plate was processed under multiple laser shocks and bending deformation was studied. A method was proposed to determine the curvature radius of bending deformation of metal plate under multiple laser shocks based on the theoretical model of curvature radius of bending deformation and the eigenstrain field was calculated by a modified finite element analysis method. Effect of shock wave peak pressure and the number of impacts on the curvature radius was studied. Results show that bending deformation increases rapidly at the beginning and then it stops growing. Bending deformation increases rapidly with the increase of the number of impacts and it cannot increase after three impacts.

Analysis of deformation and microstructure evolution during the hot deformation of titanium alloy

The paper presents theoretical and experimental analysis of deformations and microstructural evolutions in the hot cogging process of Ti-6Al-4V alloy. A three–dimensional thermal – plastic coupled finite element model is employed to study the mechanical and thermal interaction between the forging anvils and the workpiece. To explore the distributions of effective strain, effective stress, mean stress and temperature of the specimens have been systematically studied. Attention has been paid to deformation, temperature, stress and strain inside the specimens and these parameters have been used to determine the evolution of the microstructure in deformed samples during hot cogging process. A comparison of theoretical with experimental results shows that the developed model may be used to accurately predict deformations and microstructural parameters.

Thermal and physico-mechanical properties of antifriction solid lubricant for cold plastic deformation of titanium alloys

The results of the investigations of thermophysical characteristics, thermomechanical and mechanical properties of epoxy-polysiloxane nanocomposites with different contents of modifying additives in the presence of fine-grained antifriction fillers. It is shown that the joint influence of the modifier (polysiloxane particles) and filler (graphite) on the formation of the composite structure during the hardening results in the essential improvement of its physico-mechanical properties. The optimal formulation of a composition to be used as an antifriction solid lubricant for a cold plastic deformation of titanium alloys is determined.

Recent Advances in EBSD Deformation Analysis

Abstract High-speed, high-fidelity techniques used to analyze texture and dislocation content enable greater understanding of the influence of texture on deformation of titanium alloys than previously possible. This article describes a study in which specimens were examined using graphical slip band analysis to understand the influence of microstructure, alloy content, and loading orientation on the surface deformation response of titanium.

繰返し負荷を受けるTi合金の不均一変形に関する結晶塑性解析

繰返し負荷を受けるTi合金の不均一変形に関する結晶塑性解析

Superplastic Behaviour and Microstructural Evolution in Stepped Tensile Deformation of Titanium Alloy

The effect of stepped tensile deformation at 850, 900, 950 °C on the elongation, microstructure, and mechanical characteristics of titanium alloy has been investigated. The stepped uniaxial tension (stepped-UT) was composed of the following three steps in sequence: constant speed tension, clearance stage, and maximum m superplasticity tension (MaxmSPT). Results showed that the maximum elongation of TC6 alloy between 850 and 950 °C through the Stepped-UT was 2053%, in which the first engineering strain of constant speed tension was 2.0, the following clearance time was 15 min, and the MaxmSPT was finally carried on until failure. And the optimal elongations obtained by the MaxmSPT and constant speed tensile method were 1347 and 753.9% at 850 °C, respectively. The true stress-strain curves showed the strain rate sensitivity index m of the alloy in the stepped-UT was higher than the one in the single step of the MaxmSPT. Moreover, the microstructure of TC6 alloys in the stepped superplastic deformation was observed and the grain refinement was found. The grain refinement and true stress-strain curves of TC6 alloys were all affected by preplanned engineering strain and temperatures. The results also showed the joint action of the dynamic recrystallization and static or meta-dynamic recrystallization refined the grains, improved the structure property, and induced the plasticity enhancement.

3D finite element simulation of microstructure evolution in blade forging of Ti-6Al-4V alloy based on the internal state variable models

The physically-based internal state variable (ISV) models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The constants of the present models could be identified based on experimental results, which were conducted at deformation temperatures ranging from 1093 K to 1303 K, height reductions ranging from 20% to 60%, and the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s−1. The physically-based internal state variable models were implemented into the commercial finite element (FE) code. Then, a three-dimensional (3D) FE simulation system coupling of deformation, heat transfer, and microstructure evolution was developed for the blade forging of Ti-6Al-4V alloy. FE analysis was carried out to simulate the microstructure evolution in the blade forging of Ti-6Al-4V alloy. Finally, the blade forging tests of Ti-6Al-4V alloy were performed to validate the results of FE simulation. According to the tensile tests, it is seen that the mechanical properties, such as tensile strength and elongation, satisfy the application requirements well. The maximum and minimum differences between the calculated and experimental grain size of primary α phase are 11.71% and 4.23%, respectively. Thus, the industrial trials show a good agreement with FE simulation of blade forging.

Modeling the cold deformation of titanium alloys

A model is proposed for simulating the cold deformation process of titanium alloys. The emphasis is on the description of the physical metallurgical processes and not the detailed mathematical formulation and calculations. The model will be a useful step toward understanding cold heading, an important metal processing technology.

Internal state variable models for microstructure in high temperature deformation of titanium alloys

There exists an interaction between microstructural evolution and deformation behavior in high temperature deformation of titanium alloys. And the microstructure of titanium alloys is very sensitive to the process parameters of plastic deformation process. In this paper, on the basis of plastic deformation mechanism of metals and alloys, a microstructural model including dislocation density rate equation and grain growth rate equation is established with the dislocation density rate being an internal state variable. Applying the model to the high temperature deformation process of Ti60 titanium alloy, the average relative errors of grain sizes between the experiments and the predictions are 9.47% for sampled data, and 13.01% for non-sampled data.

Temperature and Strain Rate Effects on Plastic Deformation of Titanium Alloys

Since titanium alloys are the most promising structural materials for the high velocity vehicles, the impact tensile strength of the materials is presently investigated. Three kinds of aging treatments on the beta-titanium alloy were performed, and the tensile deformation behaviors were identified in the wide range of the temperature and the strain rate. The stress－strain relations of the titanium alloy significantly depend on the temperature and the strain rate investigated. Thermally activated process concept was applied to explain the experimental results, and the stress-strain relations at high strain rates were well understood with taking account of adiabatic heating effect. It has been found that the stress-strain curves depend on the microstructures, while the temperature and the strain rate effects are almost independent of the different aging treatments.

An experimental investigation of phase transformation superplastic diffusion bonding of titanium alloy to stainless steel

The solid-state direct diffusion bonding of a near α-phase titanium alloy to an austenitic stainless steel by means of the phase transformation superplasticity (PTSP) caused by the cycles of heating and cooling has been carried out. The test results showed that, under the conditions of Tmax = 890°C, Tmin = 800°C, cyclic number of heating and cooling N = 10 cycles, specific pressure P = 5 MPa, heating rate Vh = 30°C/s and cooling rate Vc = 10°C/s, the ultimate tensile strength of the joint reached its maximum value (307 MPa), and the bonding time was only 120 s. In the phase transformation superplastic state, the deformation of titanium alloy has a character of ratcheting effect and it accumulates with the cycles of heating and cooling. The observations of tensile fracture interface showed that both the brittle intermetallic compound (FeTi) and the solid solution based on β-Ti were formed on the interface, and the more in quantity and the smaller in size the solid solutions are, the higher the ultimate tensile strength is.

Mechanical anisotropy and stress–strain rate characteristics in superplastic deformation of titanium alloys

Uniaxial tension and compression tests have been carried out on two titanium based alloys, Ti–6Al–4V in the form of extruded tubes and forged plates and Ti–3Al–10V–2Fe sheets, to study anisotropic behaviour during superplastic deformation. The following were observed: (i) originally round cross-section became elliptical after deformation; (ii) the flow stresses and strain rates were dependent on the orientation of the specimens; and (iii) the strain anisotropy became less severe as the strain rate increased. These characteristics of anisotropy were related to the original microstructure (e.g. the mechanical fibring of the α grains) and the microstructural evolution during superplastic deformation. New constitutive equations for describing anisotropic superplastic deformation have been proposed to explain the effect of strain rate or stress on anisotropy.

Character of strengthening of an initially orthotropic material when subjected to simple and complex loadings. Communication 3: Experimental study of mechanical anisotropy

The results of an investigation into plastic deformation of titanium alloy with initially anisotropic elastic mechanical characteristics are presented. The limit of applicability of classical plasticity theories for complex loadings is determined. A rating dependence is plotted in generalized coordinates: principal tangential stress and principal shear strain.

Plastic deformation of titanium alloys under simple loading and its mathematical modeling

Results of an experimental investigation of the regularities of plastic deformation of titanium alloys in a plane stress state are analyzed. Tests were performed by loading thin-walled tubular specimens by an axial force and internal pressure under conditions of a proportional increase in the loads. The alloys are found to be transversely isotropic materials whose isotropic surface coincides with the cylindrical surface of the specimen. The process of plastic deformation of the alloys under simple loading is shown to be described well by equations of a previously proposed deformation theory of the plasticity of transversely isotropic media.

Criteria of optimization of extrusion of titanium alloys

Deformation of titanium alloys by cold extrusion is a difficult and complex technology due to occurrence of cracks in products and relatively low tools life. An attempt of optimum selection of extrusion conditions (for prior determined range of process parameters) has been undertaken in the work and lack of cracks within products has been established as a main criterion of optimization. On the basis of the adopted model of metal flow and the stream function method the ratio of utilization of plasticity margin has been calculated for rods of WT3-1 and OT4-1 titanium alloys in forward extrusion. Experimental verification of the model has been also carried out. Finally conclusions concerning suitability of the model under consideration for optimization of forward extrusion have been drawn.

Features of the plastic deformation of titanium alloys in impulse loading

1. An increase in the rate of impulse loading of VT1-0 α-titanium strengthens twinning in the {1123} planes but with a lower rate the material deforms both by slip in the (0001) plane and by twinning in the\(\{ 10\overline 1 2\} \) plane (with the formation of prismatic loops and cleaved dislocations). The described transition corresponds to deformation of the α-phase with a reduction in temperature, when the probability of cleavage of dislocations increases. 2. The results of tests of VT30 β-titanium alloy under conditions of impulse loading showed that an increase in the impulse loading rate, the same as for α-titanium, increases the probability of cleavage of dislocations. However, the structure of β-titanium is very sensitive to the presence of alloying elements in the alloy.

Effect of elevated temperature on the deformation of titanium alloys subjected to biaxial stress

1. The small scatter in the family of stress—strain curves confirms the single stress—strain curve hypothesis for VT6S and VT14 at 300°C. 2. The limit curves for these alloys are contracted isotropically with increased temperature. An approximation to the Saint-Venant condition was noted only for the elastic curves of both alloys and the plastic curve of VT6S.

The martensitic transformation during deformation of titanium alloys with metastable ? phase

1. It was established by x-ray analysis that metastable β and α" phases can transform during plastic deformation. 2. The large difference between the ultimate and yield strengths observed in titanium alloys quenched to metastable β phase decreases greatly with increasing degrees of cold plastic deformation. This limits the use of the high plasticity of quenched α+β titanium alloys. 3. The region was determined in which β phase is mechanically unstable in binary titanium alloys with Mo, V, Nb, Ta, Fe, and Cr (alloys containing up to 20%Mo, 20%V, 50%Ta, 4%Fe, or 12%Cr). 4. The addition of aluminum substantially increases the tendency of metastable β phase to transform during deformation. The addition of eutectoid-forming elements (Fe, Cr, Mn) to alloys containing elements isomorphous with β titanium (Mo and V) with composition close to the critical composition inhibits the martensitic transformation during deformation. 5. Lowering the temperature from room temperature to −196° negligibly reduces the tendency of metastable β phase to transform during deformation.

Peculiarities of the deformation of titanium alloys under plane stress

Peculiarities of the deformation of titanium alloys under plane stress