Using an electron beam melting (EBM) printing machine (Arcam A2X, Sweden), a matrix of 225 samples (15 rows and 15 columns) of Ti-6Al-4V was produced. The density of the specimens across the tray in the as-built condition was approximately 99.9% of the theoretical density of the alloy, ρT. Tensile strength, tensile elongation, and fatigue life were studied for the as-built samples. Location dependency of the mechanical properties along the build area was observed. Hot isostatic pressing (HIP) slightly increased the density to 99.99% of ρT but drastically improved the fatigue endurance and tensile elongation, probably due to the reduction in the size and the distribution of flaws. The microstructure of the as-built samples contained various defects (e.g., lack of fusion, porosity) that were not observed in the HIP-ed samples. HIP also reduced some of the location related variation in the mechanical properties values, observed in the as-printed condition.
Additively-manufactured Ti-6Al-4V (Ti64) exhibits high strength but in some cases inferior elongation to those of conventionally manufactured materials. Post-processing of additively manufactured Ti64 components is investigated to modify the mechanical properties for specific applications while still utilizing the benefits of the additive manufacturing process. The mechanical properties and fatigue resistance of Ti64 samples made by electron beam melting were tested in the as-built state. Several heat treatments (up to 1000 °C) were performed to study their effect on the microstructure and mechanical properties. Phase content during heating was tested with high reliability by neutron diffraction at Los Alamos National Laboratory. Two different hot isostatic pressings (HIP) cycles were tested, one at low temperature (780 °C), the other is at the standard temperature (920 °C). The results show that lowering the HIP holding temperature retains the fine microstructure (~1% β phase) and the 0.2% proof stress of the as-built samples (1038 MPa), but gives rise to higher elongation (~14%) and better fatigue life. The material subjected to a higher HIP temperature had a coarser microstructure, more residual β phase (~2% difference), displayed slightly lower Vickers hardness (~15 HV10N), 0.2% proof stress (~60 MPa) and ultimate stresses (~40 MPa) than the material HIP’ed at 780 °C, but had superior elongation (~6%) and fatigue resistance. Heat treatment at 1000 °C entirely altered the microstructure (~7% β phase), yield elongation of 13.7% but decrease the 0.2% proof-stress to 927 MPa. The results of the HIP at 780 °C imply it would be beneficial to lower the standard ASTM HIP temperature for Ti6Al4V additively manufactured by electron beam melting.
Powder Bed Additive Manufacturing is a relatively novel 3D-printing method of fabrication metallic components predominantly working with pre-alloyed powders. Laser or electron beam melt the powder in each layer according to the cross-section of the printed model. The combination of freedom of design and high mechanical properties of resulting material make PB-AM popular for different industrial applications including biomedical implants and aerospace part production. Titanium alloys and especially Ti-6Al-4V are among the most popular materials for additive manufacturing. It is mainly due to its high strength to weight ratio, biocompatibility, and high fatigue and corrosion resistance. Selective electron beam melting is already well-known effective additive manufacturing technology for wide range of applications. The high mechanical properties are provided due to vacuum environment of the process and specific temperature conditions. The final microstructure and required properties could be controlled by the adjustment of internal process parameters such as beam power (BP), beam scan rate (BR), hatching distance (HD) -distance between beam traces, and layer thickness (LT). In the current research the hatching strategy for SEBM manufacturing of Ti-6Al-4V was optimized and its influence on the mechanical properties and microstructure of the resulting components was analyzed. It was found that optimized HD with additional proper placement of components on the start platform can help to shorten the lead time without compromising the mechanical properties.
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