Papers by Author: Miao Quan Li

Abstract: The growth behavior of 300M steel was investigated on a Gleeble-3500 simulator at the heating temperatures ranging from 1273 K to 1453 K and the heating rates ranging from 0.83 K/s to 40 K/s. The grain size of austenite was measured by using SISC IAS V8.0 image analysis software on Olympus PMG3 microscope. The experimental results showed that the coarse grains of austenite occurred at the heating temperature above 1413 K and the grain size of austenite increased with the increasing of heating temperature and decreased with the increasing of heating rate. The grain boundaries of austenite became flat and the angel of grain boundaries tended to 120˚ with the increasing of heating temperature. The grain boundaries of austenite increased and changed from flat to bend with the increasing of heating rate.

Abstract: Isothermal compression of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy is conducted on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1173 K to 1333 K, the strain rates ranging from 0.001 s-1 to 10.0 s-1 at an interval of an order magnitude and the height reductions ranging from 50% to 70%. The primary grain size is measured at an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software. A multi-scale constitutive model coupling the grain size, volume fraction and dislocation density is established to represent the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation, in which the flow stress is decomposed a thermal stress and an athermal stress. A Kock-Mecking model is adopted to describe the thermally activated stress, and an athermal stress model accounts for the working hardening and Hall-Petch effect. A genetic algorithm (GA)-based objective optimization technique is used for determining material constants in this study. The mean relative difference between the predicted and experimental flow stress is 5.98%, thus it can be concluded that the multi-scale constitutive model with high prediction precision can efficiently predict the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation.

Abstract: A constitutive equation has been established to describe the effect of grain size on the deformation behavior of Ti-6.62Al-5.14Sn-1.82Zr alloy during the high temperature. In this paper, firstly a steady flow stress model is proposed, and a function relating to the grain size is introduced to modify the steady flow stress model. Meanwhile, a microstructure model established by the fuzzy neural network method is applied to calculate the grain size of prior α phase during the high temperature deformation of Ti-6.62Al-5.14Sn-1.82Zr alloy. The calculated flow stress using the present constitutive equation shows a good agreement with the experimental flow stress of the Ti-6.62Al-5.14Sn-1.82Zr alloy. The relative maximum error was not more than 15%.

Abstract: Isothermal compression tests were carried out on the Ti-5.6Al-4.8Sn-2.0Zr-1.0Mo alloy with and without hydrogen. A series of experiments including the optical microstructure and TEM (Transmission Electron Microscope) were performed to the compressed samples. The results show that hydrogenation not only increases the fraction ofβ phase, but also activates the propagation of the dislocation and formation of the twins, which are benefit for plastic or superplastic formability.

Abstract: Superplastic compression of the Ti-6.62Al-5.14Sn-1.82Zr alloy were carried out at a Thermecmaster-Z simulator at deformation temperatures of 960°C, 980°C, 1000°C and 1020°C, strain rate of 0.001 s-1, 0.01 s-1 and 0.1 s-1, and height reduction of 50%, 60% and 70%. The α phase decreases with the increasing of deformation temperature, and the grain size of α phase has a slight variation with the deformation temperature. The strain rate affects both the morphologies and the grain size of α phase, and the optimal strain rate makes the grains be fine. The optimal height reduction also makes the α phase be fine and well distributed on the matrix of Ti-6.62Al-5.14Sn-1.82Zr alloy after superplastic compression.

Abstract: The Chinese nickel-base powder metallurgy (PM) superalloy FGH96, which was processed through hot isostatic pressing, is very difficult to deform. FGH96 superalloy has better superplasticity in special deformation conditions and superplastic isothermal forging is the best formation method at present. The accurate constitutive equations of the FGH96 alloy was established depended on the isothermal compression experiments. A two dimensional and thermomechanical coupled axisymmetric finite element(FE) model in which both part and die were taken in consideration was established to fully simulate the FGH96 superalloy turbine disk superplastic isothermal forging process. Some physical parameters about the turbine disk forging process, such as load, stress field and strain field were calculated at different temperature within the forging range of FGH96. The regularity of peak equivalent stress acted on die cavity surface, yield limit and ultimate strength of die material during the forging process was found. Based on the regulation, peak equivalent stress acted on cavity surface must be extremely less than yield limit of die material, the optimized processing parameter 1050°C that is the best deformation temperature for the alloy was determined. That was proved better in practice and high quality disk was forged.

Abstract: In this paper, the flow stress model has been established based on the isothermal compression data at deformation temperature of 800~1050oC, strain rate of 0.001~0.1 s-1 with the help of the Zener-Hollomon parameter and the Arrehnius’ equation. For the forging of Ti-6.0Al-2.0Zr-1.0Mo-1.0V alloy with 3.0 mm in thickness and 66.0 mm in height, the equivalent stress, strain, strain rate distribution and temperature rise in the superplastic extrusion process have been simulated through FEM. The simulated results show that the punch velocity has significant effect on the equivalent stress, temperature rise and extrusion load.

Abstract: Deformation behavior of a commercial TC6 titanium alloy at elevated temperature has been investigated using isothermal tension tests. By SEM, the fracture mechanism has been analyzed through the morphologies of failure surface. The superplasticity of the TC6 titanium alloy improves with an increase of deformation temperature and a decrease of initial strain rate. The optimal process parameters are the combination of 950 c o and 0.001s-1, and the limit elongation could reach 267%. The tough fracture is main pattern in the failure of the TC6 titanium alloy. The fracture begins at the boundaries between the matrix and the impurity, and it presents the much more tough fracture characteristic with an increase of deformation temperature and a decrease of initial strain rate.

Abstract: 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%.