Commercial Pure Titanium Sheet Research Articles

An Experimental Study on the Frictional Behavior of Ultrathin Metal Sheets at Elevated Temperatures.

Hot forming is an effective approach for improving the formability of ultrathin metal sheets, such as those made of stainless steel and pure titanium. However, the increased friction coefficient between the tool and the high-temperature metal sheet negatively affects material flow during hot forming, potentially resulting in severe local thinning or even cracking. This study explores the frictional behavior of 0.1 mm thick ferritic stainless steel (FSS) and commercially pure titanium (CP-Ti) sheets at elevated temperatures. A friction testing apparatus was developed to measure the friction coefficients of these metal sheets from room temperature (25 °C) up to 600 °C. The friction coefficient of the FSS sheet increased monotonically with temperature, whereas that of the CP-Ti sheet first increased and then decreased. Post-friction testing microscopic examination demonstrated that built-up edges formed on the surfaces of the friction blocks when rubbed against the stainless steel, contributing to the higher friction coefficients. This study provides a foundation for understanding frictional behavior during the hot forming of ultrathin metal sheets.

Evolving asymmetric and anisotropic hardening of CP-Ti sheets under monotonic and reverse loading: Characterization and modeling

Commercially pure titanium (CP-Ti) sheets are promising to manufacture high-performance and lightweight components in many fields such as aerospace, marine, energy, electrics and healthcare. However, due to its low symmetric hexagonal close-packed (HCP) structure and complex thermal-mechanical processing history, CP-Ti sheets may exhibit significant asymmetry and anisotropy under monotonic and reverse loading. Therefore, the coupling effect of loading-path dependent asymmetric and anisotropic hardening behaviors of CP-Ti sheets need to be systemically characterized and accurately described under monotonic and reverse loading paths. In this study, firstly, the rheological tests were performed to systemically explore the evolving asymmetric and anisotropic hardening behavior of CP-Ti sheet under monotonic and reverse loading modes. With the help of anti-buckling support fixture and DIC system in tension and compression tests, the coupling effect of asymmetric and anisotropic hardening under monotonic and reverse loading of CP-Ti sheet was identified. Secondly, a loading-path dependent constitutive modeling framework was constructed in which the stress invariants-based model (SIM) integrated with distorted hardening (DH) under reverse loading (RL) conditions (SIM+DH+RL) were considered. Within the proposed modeling framework, a judging criterion of stress reversal for explicit solution method and an activation criterion of different reverse loading modes were introduced. Finally, the proposed SIM+DH+RL model was implemented, calibrated and further applied to simulate typical V-/U-bending of CP-Ti sheets. The results show that the proposed SIM+DH+RL model can significantly improve the prediction accuracy of V-/U-bending springback with the relative errors less than 7.8% and 2.1%, compared with 15.2% and 12% relative errors of Mises+IH, 19.5% and 7.3% relative errors of SIM+DH, 15.1% and 8.4% relative errors of Yoon2014+IH, 14.5% and 5.2% relative errors of CPB06+IH, and 17.3% and 11.5% relative errors of Hill48+IH. It is noted that for the thickness distributions after V-/U-bending springback, the above used models have similar prediction accuracies with the relative errors less than 1.8%.

Constitutive modeling of commercial pure titanium sheet based on non-associated flow rule and differential hardening

The commercial-pure titanium (CP-Ti) sheet has attracted a great interest from biomedical and aerospace industries because of its strong mechanical advantages such as lightweight, high strength, good formability, and corrosion-resistance. However, strong anisotropic features, such as evolutionary yield surface and strength difference in tension and compression, of the CP-Ti require advanced constitutive modeling compared to standard advanced high strength steel sheets. This study took into account the differential hardening behavior and the changing R-value of CP-Ti sheet observed during the uniaxial tensile and bulge tests in developing a material model. The observed behaviors are modeled by Hill48 quadratic function based on non-associated flow rule with equivalent plastic work dependent evolutionary parameters. The developed material model was then implemented into a user material subroutine (VUMAT) for ABAQUS/EXPLICIT and used to simulate a circular deep drawing to verify the developed model. Simulation results are compared with those of a material model coupling Yld2000–2d yield function with associated flow rule. The comparison shows that the developed material model provides not only a good agreement with the experiment for yield and potential surfaces but also accurate predictions in forming simulations.

Transformation textures in pure titanium: Texture memory vs surface effect

Surface effect-induced phase transformation heat treatment is performed on cold-rolled commercial pure titanium sheet to change and control the transformation texture. The results show that the type of final transformation texture changes from the texture memory effect type texture of TD-split basal to the surface effect type texture of 〈11−20〉//ND with the increase of heating temperature in helium atmosphere. At a low heating temperature of 920 °C and 1000 °C, the textures in sheets exhibited texture memory effect, while in the high heating temperature of 1100 °C, it showed the effects of both anisotropy in elastic modules of HCP titanium crystals and transformation strain. During the cooling phase, the surface effect can promote the preferred nucleation of α-phase grains on the plate surface, and then grow to the center layer of sheet along the ND direction. In the process of preferential nucleation of surface grains, texture memory effect and surface effect are a competitive process. The result of competition often shows that the small grains with tilted basal orientation (red) and cylindrical orientations (blue-green) are nucleated on the surface together, and the grains with blue-green orientation have the advantage of growth, leading to different grain morphology and microstructure. In addition to heating temperature and protective atmosphere, the degree of recrystallization before phase transformation also significantly affects the type of transformation texture. These differences in transformation texture and microstructure are explained according to the mechanism changes of the factors influencing the variant selection.

Design and fabrication of special fixture for different weld configurations of commercial pure Titanium sheet in laser beam welding process

Titanium and its alloys have been used in several areas such as aerospace, automobile, marine and medical industries due to its several superior properties from other materials. In Laser Beam Welding (LBW) process, a variety of advantages such as very narrow heat affected zone, high depth to width ratio, high productivity and low residual stress are obtained. In the present study, trials were conducted in commercial pure titanium (Grade 2) material to ensure feasibility and to make different weld configuration such as lap joint and T joint in Nd: YA G single-sided during the laser beam welding process. Distortion and colorization of the welded joints were avoided by providing firm clamping and uniform shielding gas (99% pure industrial argon) using a custom-made fixtures arrangement. Hence, the quality of weld configurations of the lap joint and T joint are investigated in regard to weld morphology.

Crystal-plasticity finite-element simulation of time-dependent springback in a commercially-pure titanium sheet

A crystal-plasticity finite-element method was used to examine the deformation mechanism of time-dependent springback in a commercially-pure titanium sheet. To reproduce the viscoplastic behavior of the sheet, the material parameters were calibrated to reproduce the strain-rate dependency of the stress-strain curve under uniaxial tension. A two-dimensional draw bending process was simulated and the change in the sidewall curvature was evaluated. The simulation results showed that the curvature increased with the elapsed time after unloading, consistent with experimental results reported elsewhere. The deformation mechanism during the process was discussed in terms of evolution of stress and relative activities of slip and twinning systems.

Effect of Planar Anisotropy and Tension-Compression Asymmetry of CP-Ti on its Deep Drawing Behavior at Room Temperature

The planar anisotropy (PA) and tension-compression asymmetry (TCA) of the commercially pure titanium (CP-Ti) were investigated through uniaxial tension and compression experiments at room temperature. By deep drawing experiment, the formability and the earing profile for the CP-Ti were studied at room temperature. The deep drawing simulations using the hardening rules of uniaxial tensile or compression curves were compared with experimental results. The results show that the CP-Ti has obvious PA, and the plastic strain ratiosr0,r45andr90are 1.47, 1.64 and 2.05, respectively. The CP-Ti sheet shows the tension-compression asymmetry of yielding and hardening. The TCA also shows obvious PA. The tension-compression yield strength ratio of 0°, 45° and 90° to the rolling direction are 1.12, 1.08, 1.04, and the tension-compression hardening exponent ratio are 0.86, 0.8 and 0.62, respectively. The simulative results without considering TCA indicate that the forming force, the wall thickness and earing profile are not in good agreement with the experimental ones. Therefore, the earing appeared in 45° is contribution of the PA and TCA. The TCA will reduce the thickness of the deep drawing parts, increase the earing ratio and affect the drawing force.

Effect of pre-annealing deformation on the recrystallized texture and grain boundary misorientation in commercial pure titanium

The effects of rolling reduction followed by annealing (at 650°C) on commercial pure titanium sheet are investigated. The microstructure, texture and misorientation angle distributions after rolling and annealing are observed by electron back scatter diffraction (EBSD). It is found that, when the rolling deformation was low (20%) or medium (40%), a fraction of non-TD-split basal texture is inherited from the deformed state and remains even after long time (60min) annealing. However, heavy rolling deformation (85%) causes a strong and typical TD-split basal texture in the deformed and annealed states. In addition, the misorentation angle distributions are relatively homogeneous for the recrystallized samples with a low or medium pre-annealing deformation. But with heavy pre-annealing deformation, the misorientation angle distributions exhibits two peaks, around 15–30° and 70–80°. The texture and misorientation angle evolution mechanisms are discussed in this work. The study shows the possibility to tailor the texture and the misorientation angle distribution of commercial pure titanium sheet by ordinary rolling process.

Tribological behaviors between commercial pure titanium sheet and tools in warm forming

The tribological conditions between tools and sheet are the major factors affecting the product quality, forming limits and service life of tools in thin-walled titanium components warm forming. Using the orthogonal design based twist compression test in the temperature range of 25–300 °C, the significant factors affecting the coefficient of friction (CoF) and the influencing rules in CP-3 titanium sheet warm forming are clarified and discussed by changing tribological conditions such as tool material, lubrication, temperature and normal pressure. The results show that the significant factors affecting the CoF are lubrication, surface roughness, tool material, sliding velocity, normal pressure and temperature; compared with unlubricated condition, the graphite and MoS2 greatly improve the friction condition and the maximum reduction of the CoF is 0.318; the CoFs of Cr12MoV/CP-3 and QAl10-3-1.5/CP-3 tribo-pairs show a similar tendency: the CoFs increase with increasing surface roughness and sliding velocity, and increase firstly then decrease with increasing normal pressure and temperature.

OS0110 反転負荷を受ける純チタン板における双晶活動

OS0110 反転負荷を受ける純チタン板における双晶活動

Effects of stress state on texture and microstructure in cold drawing-bulging of CP-Ti sheet

Three different stress states of the combination of tensile (t) stress and compressive (c) stress, t–t, t–c and t–c–c, exist in the deformed commercially pure titanium (CP-Ti) sheet during cold drawing-bulging. The textures and microstructures in the different stress state regions were investigated by means of XRD and TEM analysis. Similar development of texture and microstructure is achieved with less thickness strain under multiaxial stresses in drawing-bulging than in cold rolling. The results show that texture and microstructure are much sensitive to multiaxial stresses. Twinning is more easily activated under compressive stress than tensile stress. Prism 〈a〉 slip is heavily affected by tensile stress, resulting in a remarkable change of the intensity of (0°, 35°, 0°) texture, while pyramidal 〈c+a〉 slip, forming (20°, 35°, 30°) texture, weakens with the increase of thickness strain in spite of stress state.

Microstructure and texture of commercially pure titanium in cold deep drawing

The development of microstructure and texture during cold deep drawing of commercially pure titanium (CP-Ti) was investigated. Three parts, stretching region, drawing region and flange region, were sequentially formed in the deep drawing process of the hemispheric surface part, with reference to deformation modes and strain regimes. Results show that the plastic strain is accommodated by dislocation slip and deformation twinning in the whole deep drawing process. The texture of the CP-Ti sheet and its drawn part consists of rolling texture component and recrystallization texture component. The intensity and type of the initial texture varied during the drawing process are related to the production of deformation twinning and dislocation slip. Twinning weakens the initial texture by randomizing the orientations of crystals, especially for the recrystallization texture. The recrystallization texture in the drawing region disappears due to the significant forming of twinning. Furthermore, over drawing would result in the predominance of dislocation slip and the texture is strengthened.

工业纯钛板激光冲击形变的特征微结构

工业纯钛板激光冲击形变的特征微结构

Flow stress behavior of commercial pure titanium sheet during warm tensile deformation

The flow stress behavior of commercial pure titanium (CP-Ti) sheet was studied by uniaxial warn tension tests at temperatures ranging from 623 K to 773 K and strain rates from 5.0 × 10 −2 to 8.3 × 10 −4 s −1. A mathematical model using an updated Fields–Backofen (FB) equation was established to describe the flow stress behavior of CP-Ti during warm tensile testing. The results show that the flow stress of CP-Ti is evidently affected by both deformation temperature and strain rate, i.e., the flow stress decreases with the decrease of strain rate and the increase of deformation temperature, and a typical characteristic of dynamic recrystallization softening. The flow stress curves analyzed by FB equation shows good agreement with experimental flow curves for different temperatures and strain rates for CP-Ti sheet.