Miaoquan Li

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.

Effect of Processing Parameters on Microstructure and Mechanical Properties in High Temperature Deformation of Ti-6Al-4V Alloy

Abstract The effect of the deformation temperature, deformation degree, strain rate and their interaction on the microstructure and mechanical properties in the high temperature deformation of Ti-6Al-4V alloy was investigated. The experimental results show that the deformation degree and strain rate have significant influence on the microstructure and mechanical properties, in which finer microstructure and higher tensile strength can be obtained at a middle deformation degree and a higher strain rate. The interactions between the deformation temperature and the deformation degree or the strain rate in the high temperature deformation of Ti-6Al-4V alloy are significant, especially being deformed at the temperature just under the β transus, the ductility and tensile strength are sensitive to all of processing parameters including their interactions. So the interactions should be considered to optimize the processing parameters in order to meet the requirements of the mechanical properties.

Formation mechanisms of high quality diffusion bonded martensitic stainless steel joints

Abstract Diffusion bonding of martensitic stainless steel was conducted at different times. Based on the interface characteristic and shear strength, bonding mechanisms were discussed. Results showed that the bonding quality was controlled by void shrinkage and interface grain boundary migration. Large voids with scraggly edges changed to small voids with smooth edges, leading to an increase in interface bonding ratio. Two cases of interface grain boundary migration were revealed: interface grain boundary migration at the triple junction induced by the reduction in grain boundary energy and strain induced interface grain boundary migration resulted from the stored energy. Owing to the void shrinkage and interface grain boundary migration, the shear strength of the joint matched that of the base material.

Experimental investigation and modelling of microstructural variables of Al-4Cu-Mg alloy

Abstract The effects of process parameters on microstructural evolution, including grain size and shape factor of the α solid particles during semisolid compression of an Al–4Cu–Mg alloy, were investigated. Experiments were conducted at deformation temperatures of 540, 560 and 580°C, strain rates of 0˙001, 0˙01, 0˙1 and 1 s–1, and height reductions of 20, 40 and 60%. All of the optical micrographs and quantitative metallography showed that deformation process parameters significantly affect the microstructure during semisolid compression of Al–4Cu–Mg alloy, which appears to have a fuzzy characteristic. According to the experimental results from the semisolid compression of Al–4Cu–Mg alloy, a model has been established to describe microstructural evolution by applying a fuzzy set and artificial neural network, which integrates the learning power of neural networks with fuzzy inference systems. The model presented in the present paper can be applied to predict the microstructural changes at deformation temperatures of 540–580°C and strain rates of 0˙001–1 s–1. The maximum relative difference of grain size is 9˙34%. The predicted results are in satisfactory agreement with the experimental results.

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.

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.

A set of microstructure-based constitutive equations in hot forming of a titanium alloy

Abstract A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further, a set of mechanism-based constitutive equations were proposed, in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations, the contributions of different mechanisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correlation of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.

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.

Variation effect of strain rate on microstructure in isothermal compression of Ti-6Al-4V alloy

Isothermal compression of the Ti-6Al-4V alloy at the deformation temperatures of 950 and 980°C, height reductions of 30% and 60%, and strain rates of 0.001, 0.010, 0.100 and 1.000 s−1 was conducted, wherein the variations of microstructure with strain rate were investigated. The experimental results showed that the variation of the microstructure with the strain rate under one condition was significantly different from that under another condition, which meaned that the interaction between the processing parameters was great. The optimization of the strain rate under one condition was not suitable for another condition. Therefore, selecting the forging equipment and optimizing the strain rate should be based on simultaneously considering the deformation temperature and height reduction.

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.