Titanium Alloy Sheet Research Articles

超弾性チタン合金薄板を用いた展開式ノズルの基本概念と試作結果

This paper proposes a new concept of a deployable nozzle made of superelastic titanium-alloy sheet. A concrete design of deployable nozzle is determined by FEM analyses based on the condition of a kick motor on a certain launch vehicle. A 1/4-scale model of the nozzle was produced in trial and its storing and deploying test was completed.

Investigation of the Welding Capability of Aluminum and Titanium Alloy Sheets with IF Steel Sheets by Resistance Spot Welding Method

Bu çalışmada, 1 mm kalınlığındaki yüksek mukavemetli ve derin çekilebilir IF 180 çeliğinin yine 1 mm kalınlığındaki ticari saf titanyum (ASTM Grade 2) ve 5754 alüminyum alaşımı ile noktasal kaynak edilebilirliği araştırılmıştır. Kaynak işlemleri elektrik direnç nokta kaynağı yöntemiyle farklı kaynak akımları (10 kA, 12,5 kA ve 15 kA), kaynak süreleri (10, 15 ve 20 çevrim) ve elektrod kuvvetlerinde (5 kN, 10 kN ve 15 kN) gerçekleştirilmiştir. Kaynaklı numunelerin kaynak çekirdek çapı, elektrod dalma derinliği, sertlik ve çekme-makaslama testi sonuçları incelenerek mekanik özellikleri irdelenmiştir. Sonuç olarak, kaynak parametrelerinin IF 180 - 5754 Al alaşımı kaynak çiftinin mekanik özellikleri üzerinde IF 180 – Ti-Gr2 alaşım çiftine göre daha büyük etkiye sahip olduğu görülmüştür. Kaynak akımı ve elektrod kuvvetinin her iki kaynak çiftinde çekirdek çapı, elektrod dalma derinliği ve maksimum çekme kuvvetini önemli oranda etkilediği tespit edilmiştir.

Orientation dependent behavior of tensile-creep deformation of hot rolled Ti65 titanium alloy sheet

The mill products like sheet always have one or more severe textures inevitably, and its effect on mechanical properties is not a negligible issue. The orientation dependent tensile-creep behavior induced by rolling texture of Ti65 titanium alloy sheet has been systematically investigated at 650 ℃. There are some anisotropic characteristics between TD and RD of Ti65 sheet. The UTS and TYS of TD are higher than RD at 650 ℃. Besides, the creep endurance time of TD (172.6–174.5 h) is about three times longer than RD (55.6–65.1 h) at 650 ℃ and 240 MPa. Moreover, the grains are inclined to form Texture Ⅲ (1¯ 2 1¯ 6)[1 2¯ 11] and (01 1¯ 3)[1 2¯ 11] after creep along with TD, but to form Texture Ⅰ (1¯ 2 1¯ 0)[10 1¯ 0] after creep along with RD. Finally, the crack initiation site is different during creep in TD and RD. The reason for anisotropic properties of tensile and creep has been summarized in two aspects: (ⅰ) the change of the SFs (Schmid factors) value between TD and RD; (ⅱ) the difference of creep mechanism between TD (grain boundary sliding) and RD (dislocation slip). Anisotropy of Ti65 sheet should be fully considered to increase structural efficiency in the engineering design and application.

Springback prediction of TC4 titanium alloy V-bending under hot stamping condition

In this paper, the springback of TC4 titanium alloy under hot stamping condition was studied by means of experiment and numerical analysis. Firstly, an analytical model was established to predict the V-shaped springback angle Δα under the stretch-bending conditions. The model took into account of blank holder force, friction, property of the material, thickness of the sheet and the neutral layer shift. Then, the influence of several process parameters on springback was studied by experiment and finite element simulation using a V-shaped stamping tool. In the hot stamping tests, the titanium alloy sheet fractured seriously at room temperature. The titanium alloy has good formability when the initial temperature of the sheet is 750–900 °C. However, the springback angle of formed parts is large and decreases with increasing temperature. The springback angle Aa decreased by 50% from 0.5° to 0.25°, and the angle Δβ decreased by 46.7% from 1.5° to 0.8° when the initial temperature of sheet increased from 750 °C to 900°C. The springback angle of titanium alloy sheet increases gradually with the increase of the punch radius, because of the increase of elastic recovery, the complex distribution of stress, the length of forming region and the decreasing degree of stress. Compared with the simulation results, the analytical model can better predict the springback angle Δα.

Study on rolling of a new near-α titanium alloy: Microstructure refinement and dual-scale silicides evolution

In this study, a novel near-α titanium alloy sheet with dual-scale silicides was successfully fabricated by rolling in α+β two phase field. The microstructure refinement, dual-scale silicides evolution and their influence on the tensile properties were systematically investigated. The results indicate that the preheating before rolling and the reheating between rolling passes play vital roles in the process of microstructure refinement. Thus, a new microstructure refinement mechanism was proposed considering the heat treatment besides the rolling deformation. The dual-scale silicides exhibit obvious differences in size, shape and distribution. The mean size of large-scale silicides is about 1.58 μm while the one of small-scale silicides is only 152 nm. The sheet with dual-scale silicides shows an outstanding room temperature tensile strength (1370 MPa) but an ordinary 650 °C tensile strength (513 MPa). This is because the strengthening mechanisms can be attributed to the microstructure refinement, dual-scale silicides and the residual substructures at room temperature. At 650 °C, however, the matrix softening is dominant due to the directionally arranged α/β microstructure has a low flow resistance at high temperature.

Numerical and experimental study on formability of TC4 alloy in a novel multi-layer sheet hot stamping process

In this study, a novel modified hot stamping process is proposed to prevent the heat loss of titanium alloy sheet during transferring and stamping. A technology which is two steel sheets clamping one titanium alloy sheet (the sandwich structure) to transfer and deform was used in the multi-layer sheet hot stamping process. The formability of TC4 alloy under the triple-layer sheet hot stamping condition was studied by means of experiment and numerical simulation. The influence of sheet temperature, stamping speed, and blank holder force on the depth and thickness uniformity of parts was analyzed. The results show that the deep-drawing depth of titanium alloy parts is improved and the thickness uniformity of parts is better by using the triple-layer sheet hot stamping process proposed in this paper. On the one hand, the flow stress of the TC4 alloy is low because of the less heat loss in the triple-layer sheet hot stamping process. On the other hand, the TC4 alloy sheet can be deformed better because of the changing of the friction situation of the titanium alloy sheet. And the contact force between titanium alloy sheet and steel sheet is less because of the protection of two steel sheet under the triple-layer sheet hot stamping condition. With the sheet temperature increasing, the deep-drawing depth of titanium alloy parts increases by 22.2% from 27 mm of 750 °C to 33 mm of 900 °C. Compared with the single-layer sheet hot stamping process, the stamping depth of titanium alloy parts obtained by the triple-layer sheet hot stamping process increases by 135.7% at 900 °C, and the local thinning of titanium alloy sheet is improved. Due to strain rate strengthen and the uniform distribution of sheet temperature, the thickness uniformity of parts is improved with the increase of stamping speed. Based on the microstructure observation tests, it is can be seen that more equiaxed α phase of TC4 alloy parts can be obtained by the triple-layer sheet hot stamping process.

Surface Quality of Ti-6Al-4V Titanium Alloy Parts Machined by Laser Cutting

This paper investigates high power CO2 laser cutting of 5mm-thick Ti-6Al-4V titanium alloy sheets, aiming to evaluate the effects of various laser cutting parameters on surface roughness. Using multiple linear regression, a mathematical model based on experimental data was proposed to predict the maximum height of the surface Sz as a function of two laser cutting parameters, namely cutting speed and assist-gas pressure. The adequacy of the proposed model was validated by Analysis Of Variance (ANOVA). Experimental data were compared with the model’s data to verify the capacity of the proposed model. The results indicated that for fixed laser power, cutting speed is the predominant cutting parameter that affects the maximum height of surface roughness.

Multi-objective optimization of the resistance spot welding process using a hybrid approach

This study proposed an approach to optimize the process parameters using the entropy weight method combining regression analysis in the resistance spot welding process. Based on the central composite experimental design, tests were carried out with three levels of process parameters for spot-welded titanium alloy sheets. Multiple quality characteristics, namely nugget diameter, maximum displacement, tensile shear load, and failure energy, were converted into a comprehensive welding quality index. The weight for each quality index to obtain the comprehensive welding quality index was determined based on the grey entropy method. The welding heat input for each welding joints was calculated based on the dynamic power signal in the welding process. The mathematical model correlating process parameters and the comprehensive welding quality index was established on the basis of regression analysis. The relationship between the welding process parameters and welding heat was also quantified using a regression model. The effects of welding process parameters on welding quality and welding heat were also discussed. To optimize multi-performance characteristics, the desirability function was employed. The verification test results proved that the method proposed in this paper effectively optimized the welding parameters and kept the welding heat input as low as possible at the same time. Welding current is the most significant parameter affecting the welding quality followed by welding time. This can be owing to its direct influence on the amount of heat supplied to the welding zone during the welding process. The method proposed in this study can serve as a guidance and recommendation for resistance spot welding welders to guarantee welding quality and meet the needs of high production and effective energy saving.

Thickness Measurement of Titanium Alloy Sheet Based on Eddy Current Method With a Novel Simplified Model

This article proposes a novel simplified model that describes the real part (in-phase component) of the difference in pickup coil voltage when an eddy current (EC) sensor consisting of two coils (excitation and pickup coils) is placed above the titanium (Ti) alloy sheet. A parameter that encapsulates the coil geometry factors is integrated into the classical Dodd–Deeds model, and then, the model is simplified by combining with the electromagnetic properties of Ti alloy. The use of the simplified model provides a thickness measurement method for Ti alloy sheets. The measured thickness can be calculated directly from the calibration signal by using the model, without the need to predict response by solving the forward model in advance. Experimental measurements were conducted on TC4 (Ti-6Al-4V) Ti alloy sheets of different thicknesses with a developed EC sensor and measurement system. The experiment verified the proposed model and measurement method. The experimental results shown that the maximum measurement error is less than 2.86%, which is greatly lower than the permissible error of the current industry standard. This study provides a theoretical basis and a fast method for EC thickness measurement of Ti alloy.

Development of adhesion preventing method during deep drawing of TP340 titanium sheets

ABSTRACT Generally, the adhesion of titanium alloys easily occurs between die and blank during press forming because the sliding and contact surface of die and blank with high surface pressure. In the case of titanium alloy sheets, it is especially difficult to prevent the adhesion. Thus, the various studies to prevent the occurrence of adhesion during press forming of titanium alloy sheets were carried out. For example, deep drawing with oil lubrication and with diamond-like carbon (DLC) coated die, it was difficult to prevent the adhesion, so the combination of DLC coated die and lubrication oil were utilised and the adhesion was prevented. Hence, it is necessary to develop the preventing method of the adhesion on die during deep drawing process. We have focused on the prevention of titanium surface oxide film peeling during deep drawing process to prevent the adhesion. We have developed the method to prevent the adhesion during dry deep drawing process. In this study, the compressed air was applied into die and the blank holding force with vibration technique was utilised during dry deep drawing of TP340 sheets. As a result, the occurrence of adhesion was prevented significantly by the application of developed methods.

Novel thermoplastic fiber metal laminates manufactured with an innovative acrylic resin at room temperature

In the current study, the mechanical characteristics of a new generation of thermoplastic fiber metal laminates (FMLs) manufactured by vacuum-assisted resin infusion (VARI) at room temperature are investigated. For this end, Ti-6Al-4V alloy sheets, ultra-high molecular weight polyethylene (UHMWPE) fabric, carbon fabric, and two hybrid laminates with different layups are manufactured by a novel liquid methyl methacrylate (MMA) thermoplastic resin, Elium®. Prior to fabricating and testing, a multi-step surface treatment is followed to improve the bonding strength between the titanium alloy sheets and fiber-reinforced polymer composite (FRPC) laminates. ASTM standard tests are conducted in tension, compression, shear (both intralaminar and interlaminar) as well as flexural to evaluate the mechanical characteristics of the newly developed hybrid titanium composite laminates (HTCLs). The results are compared with those of equivalent monolithic composites as well as traditional FMLs in the literature to determine the possibility of replacing epoxy resins with Elium® for fabricating different types of FMLs, namely HTCLs. In addition, the results are verified by a recently developed homogenization method, that is the mechanics of structure genome (MSG), which is used in parallel with the rule of mixture (ROM) to verify the experimental results of HTCLs and their constitutive FRPC laminates. The results show equivalent mechanical properties of the newly developed HTCLs compared to those of traditional thermoplastic HTCLs with the advantages of fabricating at room temperature, increasing the production rate, eliminating the residual thermal stresses, and the requirement for post-stretching HTCL panels.

Thermal Behavior of Single-Crystal Diamonds Catalyzed by Titanium Alloy at Elevated Temperature

Single-crystal diamonds are considered as the best tool material for ultra-precision machining. However, due to its low thermal conductivity, small elastic modulus and strong chemical activity, titanium alloy has poor machinability and is a typically difficult-to-machine material. Excessive tool wear prevents diamonds from cutting titanium alloy. This study conducts a series of thermal analytic experiments under conditions of different gas atmospheres in order to research the details of thermochemical wear of diamonds catalyzed by titanium alloy at elevated temperatures. Raman scattering analysis was performed to identify the transformation of the diamond crystal structure. The change in chemical composition of the work material was detected be means of energy dispersive X-ray analysis. X-ray photoelectron spectroscopy was used to confirm the resultant interfacial thermochemical reactions. The results of the study reveal the diffusion law of the single-crystal diamond under the action of titanium in the argon and air environment. From the experimental results, the product of the chemical reaction corresponding to the interface between the diamond and the titanium alloy sheet could be found. The research results provide a theoretical basis for elucidating the wear mechanism of diamond tools in the titanium alloy cutting process and for exploring the measures to suppress tool wear.

Improved tensile properties of a novel near-α titanium alloy via tailoring microstructure by hot-rolling

Novel near-α titanium alloy sheets with improved tensile properties at room temperature and 650 °C were fabricated by hot-rolling. When rolled at 1000 °C, the sheet exhibits a duplex microstructure. When the rolling temperature is above 1025 °C, the basket-weave microstructure is obtained. Compared with the as-forged alloy, the intragranular microstructures of sheets are obviously refined. With increasing the rolling temperature, both volume fraction and mean size of silicieds decrease, and these silicides disappear completely when rolled at 1100 °C. The tensile strengths at both room temperature and 650 °C are significantly improved by hot-rolling. The UTS of all sheets at room temperature exceeds 1300 MPa. When rolled at 1100 °C, the UTS and elongation at 650 °C are 711 MPa and 24.4%, respectively. The strengthening mechanism at both room temperature and 650 °C is mainly attributable to the refined intragranular α platelets. In addition, the micro-voids are mainly induced by decohesion of the silicide/matrix interface at room temperature but by matrix damage at 650 °C.

Mechanical properties of dissimilar Ti-Al resistance spot welds

Abstract In this study, the mechanical behavior of titanium (ASTM Grade 2) alloy sheet, resistance spot welded with 5754 aluminum alloy, was investigated with respect to nugget formation and mechanical properties. The welding operations were performed using resistance spot welding at various welding currents (10, 12.5 and 15 kA), welding times (10, 15 and 20 cycles) and electrode forces (5, 10 and 15 kN). The weld nugget diameter and nugget center height, hardness, and tensile-shear test results of the welded samples were examined, and the mechanical properties were compared. As a result of the tests, it was seen that the welding parameters have a significant effect on the mechanical properties of the titaniumaluminum alloy welding joints. The tensile-shear load of the resistance spot welded joints increased as the welding current increased, and welding time increased for 15 cycles. On the other hand, when the electrode force increased, the tensile-shear load decreased markedly.

Investigation of Microstructure, Mechanical Properties, and Numerical Modeling of Ti6Al4V Joints Produced by Friction Stir Spot Welding

In this work, lap-joined titanium alloy sheets have been successfully spot welded using friction stir spot welding (FSSW). Fully consolidated spot welds of thin Ti6Al4V sheets were obtained with a convex scrolled polycrystalline cubic boron nitride probe. The influence of processing parameters on FSSW was evaluated through a finite element analysis (FEA). Numerical results showed that von Mises stress and strain distributions were non-symmetric in the stir zone, whereas higher temperatures were observed in the region next to the tool pin. The welding microstructures showed different effects due to temperature gradients and material flow. The tool configuration played a significant role when determining the spot weld quality, since it directly influences the flow behavior of FSSW. It was observed that, in the stir zone, the microstructure suffered a transformation from α to β. The effect of welding parameters and the development of a FEA for the friction stir spot process were explored in the current investigation.

Microstructure and texture variations in high temperature titanium alloy Ti65 sheets with different rolling modes and heat treatments.

Ti65 alloy (Ti-5.8Al-4.0Sn-3.5Zr-0.5Mo-0.4Si-0.3Nb-1.0Ta-0.8W-0.05C) is the newly developed high temperature titanium alloy optimized from Ti60 alloys. The long-term service temperature of the alloy is as high as 650 °C, which is unattainable with the previous high temperature titanium alloy. It has excellent strength and excellent creep resistance, and has great application prospects in the aerospace industry. In the current study, the evolution of microstructure and texture of Ti65 alloy sheets developed by unidirectional rolling (UDR) and cross rolling (CR) followed by solution and aging treatment was investigated. The microstructure of the UDR sample consists of equiaxed , lamellar and few elongated , and the texture is the combination of minor B-type and major T-type texture, with the main component of basal {0001} fiber texture and , respectively. Due to more active slip system resulted by transformed direction, the microstructure of the CR sample consists of more elongated , and the <0001> texture characterized as R-type texture forms in addition to B/T-type texture. With aging temperature increasing, the microstructures for both transform to duplex microstructure, and the thicknesses of lamellar increase. B-type texture becomes stronger, while T/R-type texture are weakened, which is caused by the combination of recrystallization, spheroidization, and variant selection. An abnormal increasing of T/R-type texture but constant B-type texture happens in the CR-600 sample, which is related to high recrystallization fraction. It is expected that the research results can provide useful references for the rolling of high temperature titanium alloy sheets and the precise control of microstructure/texture.

Thermal Contact Resistance between Aero Engine Compressor Blade and Flexible Fixture

In the process of two-pass micro plasma arc welding of titanium alloy sheet, based on the thermal contact resistance theory, a three-dimensional transient heat transfer finite element model of contact heat transfer between titanium alloy sheet and flexible fixture was established. The effects of contact upper surface temperature, micro-contact thermal resistance, micro-gap thermal resistance, DC and pulse welding on thermal contact resistance were investigated, and the simulation and experimental results were compared. The results show that the thermal contact resistance increases as the temperature increases when the temperature of the contact upper surface (titanium alloy sheet) is in the range of 290–350 K. The effect of micro-contact thermal resistance on the thermal contact resistance is 26.1%–46.3% larger than the micro-gap thermal resistance. The thermal contact resistance of pulse welding is 3.1%–3.5% larger than DC welding. The error of simulation and experimental results of weld pool depth is 8.6%, which verifies the reliability of the model.

Impacts of laser cladding residual stress and material properties of functionally graded layers on titanium alloy sheet

Laser cladding induces high tensile residual stress (RS), which can compromise the quality of a specimen. Therefore, it is critical to accurately predict the RS distribution in cladding and understand its formation mechanism. In this study, functionally graded material (FGM) layers were successfully deposited on the surface of a titanium alloy Ti6Al4V sheet by laser cladding technology. A corresponding thermo-mechanical coupling simulation model of the laser cladding process was developed to investigate the formation mechanism of RS in the laser cladding FGM layers. The results show that high tensile RS forms in cladding components. Subsequent cladding can effectively alleviate the RS in cladding components although the position of maximum RS remains unchanged. The measurement results of the longitudinal RS on the top and bottom surfaces of cladding components by the X-ray diffraction (XRD) method agreed with the simulation results, thereby proving the accuracy of the simulation. In addition, the formation mechanism of RS in the laser cladding FGM layers was revealed by discussing the individual impact of each material property on RS. It was indicated that the RS distribution in the laser cladding FGM layers was significantly affected by material properties (in particular, coefficient of thermal expansion and Young’s modulus), except for the temperature gradient induced by the laser cladding process.

Mechanical properties of dissimilar Ti-Al resistance spot welds

AbstractIn this study, the mechanical behavior of titanium (ASTM Grade 2) alloy sheet, resistance spot welded with 5754 aluminum alloy, was investigated with respect to nugget formation and mechanical properties. The welding operations were performed using resistance spot welding at various welding currents (10, 12.5 and 15 kA), welding times (10, 15 and 20 cycles) and electrode forces (5, 10 and 15 kN). The weld nugget diameter and nugget center height, hardness, and tensile-shear test results of the welded samples were examined, and the mechanical properties were compared. As a result of the tests, it was seen that the welding parameters have a significant effect on the mechanical properties of the titaniumaluminum alloy welding joints. The tensile-shear load of the resistance spot welded joints increased as the welding current increased, and welding time increased for 15 cycles. On the other hand, when the electrode force increased, the tensile-shear load decreased markedly.

Relationship among microstructure, mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation

The relationship among microstructure, mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation at 800 °C was investigated. In the test, the original sheet exhibited relatively low flow stress and sound plasticity, and increasing the heat treatment temperature resulted in an increased ultimate tensile strength (UTS) and a decreased elongation (EL). The deformation mechanism of TA32 alloy was dominated by high angle grain boundaries sliding and coordinated by dislocation motion. The coarsening of grains and the annihilation of dislocations in heat-treated specimens weakened the deformation ability of material, which led to the increase in flow stress. Based on the high-temperature creep equation, the quantitative relationship between microstructure and flow stress was established. The grain size exponent and α phase strength constant of TA32 alloy were calculated to be 1.57 and 549.58 MPa, respectively. The flow stress was accurately predicted by combining with the corresponding phase volume fraction and grain size. Besides, the deformation behavior of TA32 alloy was also dependent on the orientation of predominant α phase, and the main slip mode was the activation of prismatic 〈a〉 slip system. The decrease of near prism-oriented texture in heat-treated specimens resulted in the enhancement of strength of the material.