Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 718

Effects of build layout and orientation consisting of (a) height from the build plate (Z-axis), (b) distance between samples, and (c) location in the build plate (X-Y plane) on porosity, NbC fraction, and hardness in electron beam melted (EBM) Alloy 718 were studied. The as-built samples predominantly showed columnar structure with strong Ë\u82001Ë\u83 crystallographic orientation parallel to the build direction, as well as NbC and ÎŽ-phase in inter-dendrites and grain boundaries. These microstructural characteristics were correlated with the thermal history, specifically cooling rate, resulted from the build layout and orientation parameters. The hardness and NbC fraction of the samples increased around 6% and 116%, respectively, as the height increased from 2 to 45 mm. Moreover, by increasing the height, formation of ÎŽ-phase was also enhanced associated with lower cooling rate in the samples built with a greater distance from the build plate. However, the porosity fraction was unaffected. Increasing the sample gap from 2 to 10 mm did not change the NbC fraction and hardness; however, the porosity fraction increased by 94%. The sample location in the build chamber influenced the porosity fraction, particularly in interior and exterior areas of the build plate. The hardness and NbC fraction were not dependent on the sample location in the build chamber. © 2018, The Author(s).First Online: 17 September 2018</p

Additive manufacturing of titanium alloys for biomedical applications

Titanium alloys have been extensively used in medical field, especially for load-bearing implants due to their excellent properties such as high strength and great corrosion resistance. In addition to the well-known CP-Ti and Ti-6Al-4V alloy, many beta type titanium alloys comprising of non-toxic and non-allergic elements have being developed for the next generation of bone implant materials. However, the hard machinery and high cost of materials removal arising from the conventional manufacturing processes are the two main obstacles of various potential applications of titanium alloys. As emerging advanced manufacturing technologies, additive manufacturing techniques are providing the ideal platform for the creation of these customized devices, where three dimensional complex parts could be realized by sequential production of two dimensional layers. Thus, additive manufacturing facilitates the manufacturing of parts with almost no geometric constraints and is economically feasible down to a batch size of one. This chapter mainly review the recent progress of the additive manufacturing (via selective laser melting and electron beam melting) of titanium alloys and their products, including the processing optimization, microstructure, mechanical properties and fatigue properties for different types of titanium alloys (CP-Ti, Ti-6Al-4V and Ti-24Nb-4Zr-8Sn) and their porous structures