This work presents a comparative study on the in-situ alloying of NiTi shape memory alloys (SMAs) by directed energy deposition (DED), selective laser melting (SLM) and selective electron beam melting (SEBM) processes using pre-mixed Ni-Ti powders. The influence of process parameters on the microstructural homogeneity, phase formation and thermomechanical properties of NiTi alloy has been systematically studied. DED could build solid NiTi alloys with good interlayer fusion and phase transformation characteristics. However, a substantial amount of uniformly dispersed Ti2Ni intermetallics can embrittle this material. SLM-built NiTi parts show a tradeoff between microstructural inhomogeneity and keyhole defects when the energy densities are varied. In addition, the strong exothermic reaction in Ni-Ti powder mixtures during printing can disturb the melt pool, making it challenging to elaborate this material and obtain desired phases by using SLM. Moreover, SEBM is found to be unsuitable to in-situ synthesize this highly reactive material due to the lack-of-fusion vs. powder-ignition dilemma in the mandatory preheating step. It is suggested to adopt DED to in-situ alloy NiTi parts when using the elementally blended powders as feedstocks.

Friction stir welding is a solid-state welding technology capable of joining metal parts without melting. The microstructure of the material evolved during the process from columnar grain along the thermal gradient in the melt pool to fine equiaxed grains. A significant decrease in microhardness in the stir zone was observed with the lowest hardness at approximately 3 mm from the weld centre. The decrease in the microhardness is mainly attributed to the dissolution of hardening precipitates in the aluminium matrix. Defects in the weld were observed due to insufficient heat input. Heat input could be increased with the increase in rotational speed of the welding tool, with some improvements in strength.

Aluminium reinforced with multi-wall carbon nanotubes was produced using friction stir processing and selective laser melting. Very fine grains were successfully achieved in both methods with high Vickers hardness values. Cavities were present in selective laser melting of AlSi10Mg reinforced with multi-wall carbon nanotubes parts resulting in higher stress concentration brittle fracture appearance. The high laser absorption and higher thermal conductivity of multi-wall carbon nanotubes resulted in the formation of the cavities in the melted parts. However, the fractography images showed dimpled like appearance indicating a ductile fracture mechanism. Multi-wall carbon nanotubes were observed at the fracture sites indicating the presence of a crack-bridging mechanism. In comparison to carbon nanotubes reinforced aluminium by friction stir processing, selective laser melting produces aluminium reinforced aluminium with better mechanical properties.

polymeric drug-delivery devices play an important role in drug administration. However, the current polymeric drug delivery device fabrication methods lack precision. This impairs the quality of the devices, resulting in a decrease in the efficiency and effectiveness of drug delivery. The concept of building parts layer by layer out of powdered raw materials makes selective laser sintering (SLS) a suitable process for fabricating polymeric matrix drug delivery devices. The current SLS process is not capable of processing two or more materials separately. This work, explores the possibilities of using SLS to perform a dual material operation by developing two process models. The two processes can then be integrated to form a dual or multimaterial fabrication technique and act as a foundation for future work in multimaterial applications such as polymeric drug delivery device fabrication. Accordingly. two papers are presented.In this paper, Part 2, the emphasis is on a secondary powder-deposition method, which is an electrostatic technique based on electrography. Developed toner on the photoconductor is scraped off using mechanical shearing and is deposited using an electrostatic force by electroplating. Results have shown that by reducing the distance between the photoconductor and surface of deposition, the resolution of the printout can be refined. Other important factors include the efficiency of powder removal from the photoconductor, printing speed, and the traversing speed during deposition.

Polymeric drug delivery devices play an important role in drug administration. However, the current polymeric drug delivery device fabrication methods lack precision. This impairs the quality of the devices, resulting in a decrease in the efficiency and effectiveness of drug delivery. The concept of building parts layer by layer out of powdered raw materials makes selective laser sintering (SLS) a suitable process for fabricating polymeric matrix drug delivery devices. The current SLS process is not capable of processing two or more materials separately. This work explores the possibilities of SLS per-forming a dual material operation by developing two process models. These two processes can then be integrated to form a dual or expanded multimaterial fabrication technique and act as a foundation for future work in multimaterial applications such as polymeric drug delivery device fabrication. Accord-ingly, two papers are presented. In this paper, Part 1, the focus is on the first process, which is a "space" creation technique in which a "space" is created by varying the density of a first representative material using heat during sintering. Three methods – one based on a vacuum and a place method, and the other two based on two variations of a laser compacting method – were tested. Results have shown that by varying the laser power during sintering, it is possible to create channels in which a second material can be deposited.