COMPUTER AIDED ENGINEERING FOR THERMO-MECHANICAL-METALLURGICAL ANALYSIS OF FORGING OPERATIONS OF TITANIUM ALLOYS

In this thesis a study on the forging processes of Ti-6Al-4V titanium alloy, with particular focus on the numerical applications and simulation design of hot forming methods, was done. The aim of this work is to collect all data concerning the material definition in terms of thermal, mechanical and microstructural properties of the selected alloy in order to filter all useful information to describe the behavior of the material under the characteristic conditions of the hot forging processes, taking into account both thermo-mechanical and metallurgical aspects involved during a such complex thermo-mechanical stage. Those information were collected and used to characterize the material properties, creating a first coupled characterization for the considered material with the aim of link both thermal-mechanical and thermal-microstructural behaviors in running numerical analysis of hot forging processes. The collected data was validated by means of comparison with a forging campaign of workpieces for aeronautical applications involved within the research project Titaform, which had the objective to study and determine a methodic design approach in set-up of precision hot forging of titanium alloys. After the first validation, all collected information were used to develop a self-consisten system based on the Johnson-Cook equation with the aim of creating a fully coupled constitive model for multiphasic titanium alloys which takes into account both thermal, mechanical and microstructural properties as function of field variables. The final objective considers the thermo-mechanical behavior of each main phase of Ti-6Al-4V alloy in order to carry out the contribution of each allotropic form during a non-isothermal deformation. Results showed a good agreement with experimental observations

Influence of geometrical ratios in forgeability of complex shapes during hot forging of Ti-6Al-4V titanium alloy

AbstractTitanium alloys are considered desirable materials when both mechanical properties and weight reduction are requested at the same time. This class of materials is widely used in application fields, like aeronautical, in which common steels and light-weight materials, like aluminum alloys, are not able to satisfy all operative service conditions. Most of manufacturing processes of titanium alloy components are based on machining operations, which allow obtaining very accurate final shapes but, at the same time, are affected by several disadvantage like material waste and general production costs. During the last decade, the forging processes for titanium alloys have attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a net shaped part with minimal need for machining. In this paper, a numerical analysis of the forging process design for an Ti-6Al-4V titanium alloy aerospace component is presented that focuses on the role of material evolution during thermomechanical processing. This component geometry is characterized by thin webs and ribs, and sharp corner and fillet radii. The numerical model was tested and validated by means of comparison with real experimental forgings in order to verify the quality in the prediction of material flow and microstructure evolution. Moreover, the analysis of forgeability of the same component with more critical geometrical ratios is considered in order to test the capability of code to support the forging sequence design in the case of a complex shape component

Dual phase titanium alloy hot forging process design: experiments and numerical modeling

Titanium alloys are considered desirable materials when both good mechanical properties and weight reduction are required at the same time. This class of materials is widely used in those fields (aeronautics, aerospace) in which common steels and light-weight materials, e.g., aluminum alloys, are not able to satisfy all operative service conditions. During the last decade, forging of titanium alloys has attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a near net shaped part with minimal need for machining. In this paper, a numerical model of the forging sequences for a Ti-6Al-4V titanium alloy aerospace component is presented. The model was tested and validated against experimental forgings. The model is then applied to predict loads final microstructure and defects of an aeronautical component. In addition to metal flow and die stresses, microstructural transformations (α and β phases) are considered for the determination of proper process parameters. It is found that transformation from α/β to β phase during forging and reverse transformations in post-forge cooling needs to be considered in the computational model for reasonable prediction of forging loads and product properties

Application of a rheological Model for Phase Transformation Prediction in Beta Processing of Titanium Alloys

The paper shows a description of a numerical model able to simulate a complete forming process of Ti-6Al-4V titanium alloy that is a multi-phasic alloy composed, at room temperature, by two main different phases, namely Alpha and Beta, which evolve during both cooling and heating processes. The characterization of the material behavior concerns both the thermo-mechanical and metallurgical data in order to set a valid tri-coupled thermo-mechanical-metallurgical analysis systems taking into account the effects and interactions of all the phenomena resulting from the coupling of thermal, mechanical and metallurgical events. The numerical model was used to simulate a double numerical campaign regarding the forging process of a complex shape and in-house Friction Stir Welding (FSW) experiments. All analyses are carried-out using the commercial implicit code DEFORM