Wyniki wyszukiwania - BazTech

1

Cavitation and grain growth during superplastic forming

Tan M. J., Liew K. M., Tan H.

Journal of Achievements in Materials and Manufacturing Engineering

|

2007

|

Vol. 24, nr 1

307-314

EN

Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic forming. Design/methodology/approach: Superplastic alloys exhibit the extremely large elongation to failure by their high strain rate sensitivity. Cavities have widely been observed during superplastic deformation of metals and alloys and lead to the degradation of material properties such as tensile, creep, fatigue and stress-corrosion behavior. In this work, a finite element method is developed, which considers the grain growth and the effect of material damage. Findings: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. The microstructural mechanism of grain growth during superplastic deformation is also studied. A new model considering the grain growth is proposed and applied to conventional superplastic materials. The relationships between the strain, the strain rate, the test temperature, the initial grain size and the grain growth respectively in superplastic materials are discussed. Practical implications: The effect of variation of strain rate sensitivity (in value) on the strain limit of the superplastic deformation is investigated, and the theoretically calculated values are compared with the experimental results. Originality/value: A new microstructure model based on the microstructural mechanism of superplastic deformation has been proposed. This model has been successfully applied to analyze conventional superplastic materials.

2

Analysis of cavitation and its effects on superplastic deformation

Tan M. J., Liew K. M., Tan H.

Journal of Achievements in Materials and Manufacturing Engineering

|

2007

|

Vol. 25, nr 2

7-10

EN

Purpose: To study the effects of cavitation on the superplastic deformation using finite element method. Design/methodology/approach: Using constitutive equations for superplastic deformation, and taking into account the effects of grain growth and cavitation growth, Zn-Al and LY12CZ alloys are used for simulations to show effects of m values, elongation-to-failure values, percentage cavities and effects of imposed hydrostatic pressure during superplastic forming processes. Findings: During superplastic deformation, cavitation damage increases with the increase in strain. For high strain rate sensitivity, necking develops which leads to final fracture; whereas for low strain strain rate sensitivity, the final fracture is due to cavitation growth. Research limitations/implications: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. Originality/value: A three dimensional viscoplastic finite element programe, taking into account of microstructural mechanisms, such as test temperature and cavity growth has been developed for superplastic deformation.

3

Superplasticity studies in a beta titanium alloy

Tan M. J., Zhu X. J., Thiruvarudchelvan S., Liew K. M.

Archives of Materials Science and Engineering

|

2007

|

Vol. 28, nr 12

717-721

EN

Purpose: In the present study, the Superplastic Forming and deformation behavior as well as related mechanisms of this titanium alloy were investigated. Design/methodology/approach: The high temperature deformation of a beta titanium alloy (Ti-15V-3Cr-3Sn-3Al) was studied in this work. Uniaxial tensile tests were carried out at 650, 750, 850 and 950°C with an initial strain rates from 10 -1 s -1 to 10 -4 s -1. The effects of temperatures and initial strain rates on the superplasticity of this alloy were studied. Findings: The studies showed that dynamic recrystallization took place during high temperature deformation and this process not only decrease the average grain size of the alloy but also increase the misorientation angle. Microstructure evolution during high temperature forming as well as related mechanisms were also investigated. Practical implications: The investigation of microstructure of beta titanium alloy as related phenomens during high temperature deformation are important for achieving desired mechanical behavior of the material. Originality/value: The Superplasticity studies in a beta titanium alloy as well as related mechanism are investigated.