Aiming Xiong

Prediction of the mechanical properties of forged TC11 titanium alloy by ANN

Abstract In this paper, an artificial neural networks (ANNs) has been applied to acquire the relationships between the mechanical properties and the deformation technological parameters of TC11 titanium alloy (approximately corresponding to ASTM Ti–6Al–6V–2Sn), using the data from the isothermal compression test and the conventional tensile test of forged TC11 titanium alloy at room temperature. In establishing these relationships, the deformation temperature and the true strain were taken as the inputs, whilst the ultimate tensile strength, the yield strength, the elongation and the area reduction at fracture were taken as the outputs, respectively. The activation function in the output layer of the model obeyed a linear output, while the activation function in the hidden layer was in the form of a sigmoid function. Comparison of the predicted and experimental results shows that the ANN model used to predict the relationships of the mechanical properties of the forged TC11 titanium alloy has good learning precision and good generalization. The neural network method presented in this paper has been found to show much better agreement with the experimental data than the existing methods (for example, quadratic regression analysis), and to have the advantage of being able to treat noisy data, or data with strong non-linear relationships.

Deformation behavior of TC6 alloy in isothermal forging

Isothermal compression of the TC6 alloy was carried out in a Thermecmaster-Z (Wuhan Iron and Steel Corporation, P.R. China) simulator at deformation temperatures of 800∼1040 °C, strain rates of 0.001∼50.0 s−1, and maximum height reduction of 50%. The deformation behavior of the TC6 alloy in isothermal forging was characterized based on stress-strain behavior and kinetic analysis. The activation energy of deformation obtained in the isothermal forging of the TC6 alloy was 267.49 kJ/mol in the β phase region and 472.76 kJ/mol in the α+β phase region. The processing map was constructed based on the dynamic materials model, and the optimal deformation parameters were obtained. Constitutive equations describing the flow stress as a function of strain rate, strain, and deformation temperature were proposed for the isothermal forging of the TC6 alloy, and a good agreement between the predicted and experimental stress-strain curves was achieved.

An adaptive constitutive model of the Ti-6.29Al-2.71Mo-1.42Cr alloy in high-temperature deformation

In this paper, an adaptive constitutive model has been acquired with the help of a fuzzy set and an artificial neural network, so as to represent the deformation behavior of the Ti-6.29Al-2.71Mo-1.42Cr alloy in high-temperature deformation. In establishing this model for the constitutive relationship of this alloy, the process parameters of deformation temperature, strain rate, and strain were taken as three inputs, and the flow stress was taken as an output. Data from “teaching samples” and testing samples were obtained from the experimental results in the isothermal compression of the Ti-6.29Al-2.71Mo-1.42Cr alloy. By comparison of the calculated results with the experimental data from the testing samples, it was verified that the present adaptive constitutive model to predict the flow stress of the Ti-6.29Al-2.71Mo-1.42Cr alloy has good learning precision and generalization.

Acquiring a novel constitutive equation of a TC6 alloy at high-temperature deformation

The TC6 alloy produced in Baoji nonferrous metals work, Xian, China, is one of the best titanium alloys with good resistance against heat and corrosion and is widely used in the aviation and aerospace industries. In this paper, isothermal compression tests were conducted on the TC6 alloy in the Thermecmastor Z simulator, at temperatures between 800 and 1040 °C at strain rates between 0.001 and 50 s−1 to a 50% height reduction. The experimental results are presented as variations of flow stress with deformation temperature, strain rate, and strain. On the basis of the present experimental results and deformation behavior, a constitutive equation for the TC6 alloy was proposed by employing an Arrhenius-type equation. The activation energy of deformation (Q) and work-hardening index (n) are found to be a function of strain. The present equation is in good agreement with the experimental data.

Deformation behaviour and new constitutive equation utilising the grain size of commercial TC6 titanium alloy

Abstract Isothermal compression tests on a commercial TC6 titanium alloy have been conducted at deformation temperatures of about 800 – 1040°C, strain rates of 0.001 – 50 s-1 and height reductions of 30 – 50%. The microstructural evolution is represented through the measured grain size of the prior α-phase. Meanwhile, a new constitutive equation, which includes the grain size, is established for high temperature deformation behaviour. The procedure required to formulate a constitutive equation from the experimental results is presented. The constitutive equation to model the behaviour of the TC6 titanium alloy during high temperature deformation is validated and its formulation is presented. The results show that the present equation is satisfactory for describing the behaviour of the TC6 titanium alloy during high temperature deformation. The maximum difference between the calculated and the experimental results is less than 15%.

Fabrication and microstructure evolution of semi-solid LY11 alloy by SIMA

For semi-solid metal forming, it is essential to fabricate the semi-solid materials with spheroidal microstructure. Among several fabrication techniques of the semi-solid materials, (strain-induced melt activation (SIMA) is an ideal candidate with the advantages of simplicity and low equipment costs. In this paper, the microstructure evolution of LY11 alloy (approximately corresponding to ASTM 2017) was investigated in the SIMA process, which had two essential stages: deformation and isothermal heat treatment. The deformation stage was conducted using a CSS-1100C material testing machine and the isothermal heat treatment stage was performed in a resistance furnace. Different levels of deformation temperatures, ram velocities, isothermal temperatures, and holding times were used in this investigation. The microstructure of LY11 alloy was observed by a NEOPHOT-1 optical microscope. The results indicated that the processing parameters must be selected properly to obtain the fine, uniform and spheroidal microstructure by SIMA. The deformation-recrystallization mechanism for microstructure evolution in SIMA process was supported by experimental evidence.

New model of microstructural evolution during isothermal forging of Ti-6Al-4V alloy

Abstract An artificial neural network model of microstructural evolution, in particular grain size and volume fraction of α phase, has been established and trained with the help of experimental results obtained using Ti—6Al—4V alloy subjected to homogeneous deformation under high temperature. The measurement of microstructural variables was carried out using a Leica microscope. By comparison of the calculated results with the experimental data from training specimens and testing specimens, it has been verified that the proposed model can be applied to compute the microstructural evolution of formed Ti—6Al—4V alloy.

Analysis of high flow stress and microstructural evolution of TC6 titanium alloy during isothermal forging

Abstract Elevated temperature true stress – strain curves have been determined for the isothermal deformation of a TC6 titanium alloy using hot compression testing in the deformation temperature range 800 – 1040°C, strain rate range 0.001 – 50 s-1 and reduction in height of 30 – 50%. The experimental results show that the flow stress of TC6 titanium alloy is strongly dependent on process parameters, especially on the deformation temperature and strain rate. The peak stress and steady stress of such an alloy have the same characterisation, which increases with higher strain rate and lower deformation temperature. During isothermal forging, microstructural characterisation, including volume fraction, grain size, and grain pattern of prior α phase, varies with different temperatures, height reductions, and strain rates.

Effect of process parameters on microstructural variables of a commercial TC6 titanium alloy disc

Abstract The interaction between the deformation behaviour and the microstructure evolution is the main characteristic in the forging process of titanium alloy and this interaction is researched using finite element (FE) simulation. Coupled simulation of deformation behaviour with microstructure evolution has been carried out by means of a new constitutive equation presented by Li et al. (Mater. Sci. Technol., 2004, 20, 1256–1260). The effect of deformation temperature, hammer velocity,height reduction and shear factor on the microstructure variables, including grain size and volume fraction, has been studied in the forging process of the TC6 titanium alloy disc with deformation temperatures of 880–940°C, hammer velocities of 1·2–12 000 mm min−1 and shear factor (m) of the friction of 0·1–0·4. The simulated results show that deformation temperature, hammer velocity and height reduction have a significant effect on themicrostructure evolution and this effect is more significant on the microstructure evolution in hot forging than that in isothermal forging. The simulated results are in good agreement with the experimental results.

FE Simulation of Grain Size during the Isothermal Forging of a TC6 Titanium Alloy Disc

Isothermal compression tests were conducted at Thermecmaster-Z simulator, and grain size of the prior a phase was measured at a Leica LABOR-LUX12MFS/ST microscope for quantitative metallography. A methodology to establish a constitutive equation with grain size was proposed with the help of the experimental results. Combining FEM and the present constitutive equation at high temperature deformation, grain size of the prior a phase was simulated during the isothermal forging of a TC6 titanium alloy disc. The present results illustrate grain size and distribution of the prior a phase in the forging process of TC6 titanium alloy disc in detail. The maximum difference between the calculated results and the experimental is not more than 15%.