Abstract
The presence of defects like porosity and lack of fusion can negatively affect the properties of the materials manufactured by Selective Laser Melting (SLM). The optimization of the manufacturing conditions allows reducing the number of defects, but there is a limit for each manufacturing material and process. To expand the manufacturing envelope, a remelting after every layer of the SLM process has been used to manufacture Ti6Al4V alloy samples using an SLM with a CO2 laser. The effect of this processing method on the microstructure, defects, hardness, and, especially, the corrosion properties was studied. It was concluded that the laser remelting strategy causes an increment of the α and β phases from the dissolution of metastable α’. This technique also provokes a decrease in the number of defects and a reduction of the hardness, which are also reduced with lower scanning speeds. On the other hand, all the corrosion tests show that a low scanning speed and the laser remelting strategy improve the corrosion resistance of the Ti6Al4V alloy since parameters like the Open Circuit Potential (OCP) and the Polarization Resistance (Rp) are nobler and the mass gain is lower.
Highlights
Additive Manufacturing (AM) has become one of the most promising manufacturing techniques
Ti6Al4V specimens were successfully fabricated by L-PBF equipped with a CO2 laser, and a process of laser remelting in each layer was established and was applied to the manufacturing of the samples
The application of a second laser pass reduced the porosity of the samples and caused a slight reduction of the hardness, which was still greater than that of non-AM samples
Summary
Additive Manufacturing (AM) has become one of the most promising manufacturing techniques. The SLM technique can fabricate near-net-shape pieces with complex and topologically optimized pieces without an increment of cost [2] This allows the manufacturing of unique and personalized parts in different fields like jewelry [3], transport industry, aerospace field [4]; or biomedical sector [5]. While porosity is related to gas entrapped during the solidification or the sublimation of some alloy elements, the lack of fusion is linked to a low amount of energy during the melting of the powder [10] These defects are critical of the use of the SLM samples in the aerospace field because they have a strong impact on their toughness and fatigue resistance. Using lower laser power of very high scanning speeds causes lacks of fusion, as the irradiated powder is not fully molten, leaving unmolten particles within the microstructure of the material
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