Mariacira Liberini

Influence of Powder Characteristics on Formation of Porosity in Additive Manufacturing of Ti-6Al-4V Components

This paper aims to study the genesis of defects in titanium components made through two different additive manufacturing technologies: selective laser melting and electron beam melting. In particular, we focussed on the influence of the powders used on the formation of porosities and cavities in the manufactured components. A detailed experimental campaign was carried out to characterize the components made through the two additive manufacturing techniques aforementioned and the powders used in the process. It was found that some defects of the final components can be attributed to internal porosities of the powders used in the manufacturing process. These internal porosities are a consequence of the gas atomization process used for the production of the powders themselves. Therefore, the importance of using tailored powders, free from porosities, in order to manufacture components with high mechanical properties is highlighted.

Microstructure of a Hot Forged Ti 5-5-5-3 Aeronautical Component

The changes in microstructure during the forging of a large Ti-5-5-5-3 component are studied. The effect of the different plastic strain and cooling rates experienced by the various zones of the component is analyzed and compared in terms of the microstructures that they induce. The results show that the microstructures vary in the different zones of the forging with the α phase spheroidization increasing with the amount of plastic strain sustained by the material. A correlation between the level of α phase spheroidization and the plastic softening of the forging has been found.

On the Investigation of the Portevin-Le Chatelier Effect in the Rolling of AA 5083

The aim of this paper is to investigate about the Portevin-Le Chatelier Effect (PLC) on a AA 5083 sheet. In order to study the minimizing of the PLC effect, three different rolling cyles have been carried out and an experimental campaign on the three different AA 5083 rolled has been carried out. In particular, the experimental campaign, to better understand the evolution of the phenomena during the rolling process, is based on: microstructural analysis, tensile tests and fractographic observations. Finally it has been found that the greater grain size the smaller the PLC effect, even if this effect cannot be totally removed, furthermore the PLC effect occurs only in the rolling direction. The best rolling cycle is the one that provide a hot rolling until 4mm, then a cold rolling up to 2mm and a final heat treatment of annealing.

Experimental study of the Portevin-Le Chatelier effect in AA 5754 sheets: Influence of the different rolling routes

This paper deals with the experimental study of the Portevin-Le Chatelier (PLC) effect in the rolling of AA 5754 ingots. Three different rolling cycles were investigated in order to minimize or avoid the occurrence of the PLC effect during the rolling process. A full experimental campaign including microstructural observations, tensile tests and fractographic observations was carried out on the rolled sheets in order better understand the phenomena occurring during the rolling process. It was found that is not possible to completely avoid the occurrence of the PLC effect, but by increasing the grain size through an heat treatment between two rolling passes and by adopting an higher thickness reduction for each rolling pass it is possible to reduce the occurrence of the PLC phenomenon. Moreover it was observed that the PLC effect happens only along the rolling direction.

Development of an innovative method to predict and to characterize the performances of Ti-6Al-4V LBW joints

Every manufacturing process leaves on the surface of the piece a typical “technology signature”. In particular, the laser welding leaves a feature at the edge of the weld bead called “undercut”. In this work an experimental campaign has been conducted on Ti6Al4V butt joints. In particular a Central Composite Design (CCD) with the central point repeated three times has been investigated. In the CCD there are two factors (power and speed of the fiber laser) and five levels for each factor. This paper deals with the investigation about the correlation between the severity of the undercut and the process parameters of the laser welding. In particular, through the confocal microscopy, the original geometry of the joint was accurately acquired and rebuilt in order to make a FEM model and simulate the mechanical behavior using Ansys14.5. Moreover, response surfaces and level curves were carried out to understand and predict the depth and the width of the undercut starting from the power and the speed of the lase...