Research on Selective Laser Melting of Ti6Al4V: Surface Morphologies, Optimized Processing Zone, and Ductility Improvement Mechanism

Abstract

Abstract:The quality and mechanical properties of titanium alloy fabricated using selective laser melting (SLM) are critical to the adoption of the process which has long been impeded by the lack of uniformity in SLM-fabrication parameter optimization. In order to address this problem, laser power and scanning speed were combined into linear energy density as an independent variable, while surface morphology was defined as a metric. Based on full-factor experiments, the surface quality of SLM-fabricated titanium alloy was classified into five zones: severe over-melting zone, high-energy density nodulizing zone, smooth forming zone, low-energy density nodulizing zone, and sintering zone. The mechanism resulting in the creation of each zone was analyzed. Parameter uniformity was achieved by establishing a parameter window for each zone, and it also revealed that under smooth forming conditions, the relationship of linear energy density to the quality of the formed surface is not linear. It was also found that fabrication efficiency could be improved in the condition of the formation of a smooth surface by increasing laser power and scanning speed. In addition, maximum elongation of the SLM-fabricated titanium alloy increased when the densified parts were processed using an appropriate heat treatment, from a low value of 5.79% to 10.28%. The mechanisms of change in ductility of the alloy were thoroughly analyzed from the perspectives of surface microstructure and fracture morphology. Results indicate that after heat treatment, the microcosmic structure of the alloy was converted from acicular martensite α' phase to a layered α+β double-phase structure, the fracture type also changed from quasi-cleavage to ductile fracture.

Effect of Laser Energy Density, Internal Porosity and Heat Treatment on Mechanical Behavior of Biomedical Ti6Al4V Alloy Obtained with DMLS Technology

“…The same orientation between the columnar grains and the direction of the tensile forces led to a reduction of the grain boundary resistance, which no longer constituted an effective obstacle to the dislocation movement and which could be subject to greater distortion [48,49]. Reducing the energy density by reducing the laser beam power and increasing the scanning speed resulted in defects between successive layers of material [50,51]. For highly porous samples, force was applied parallel to the layers and caused pores deformation consistent with the direction of force, whereby the stress concentration around the pores was several times lower, and consequently, the material was less susceptible to the initiation and propagation of cracks.…”

Mechanical Behavior Assessment of Ti-6Al-4V ELI Alloy Produced by Laser Powder Bed Fusion

“…The ability to produce a fine microstructure in components can lead to a higher strength but at the expense of reduced ductility and fracture toughness. Consequently, post-AM heat treatment has become an indispensable tool for the AM components in order to reduce some of the fabrication limitations and to obtain the desired mechanical properties [9][10][11][12][13][14][15][16][17]. While the challenge in AM may be defined by manufacturing components with a combination of superior strength, ductility, and fracture toughness in the as-built state [11,18,19], heat treatment of the component has always been a part of the manufacturing process for any manufacturing process.…”

Bioactivation Treatment with Mixed Acid and Heat on Titanium Implants Fabricated by Selective Laser Melting Enhances Preosteoblast Cell Differentiation

“…Selective laser melting (SLM) on Ti is a promising technology for solving these difficulties. In the SLM technique, small Ti particles are melted and fused layer by layer using a high-intensity laser, and computer-aided design was applied to make three-dimensional structures of the materials [6,7]. Therefore, SLM used to make materials with a high surface 2 of 16 roughness and personalized to the needs of the bone defect(s) of each patient.…”