The utilization of “anisotropy” is becoming an important direction for realizing highly-functionalized products overcoming the current functional limits for materials with isotropic properties. In particular for the use in aerospace and biomedical industries, some products are exposed to anisotropic stress fields. Therefore, the products should be anisotropic along the functional axis. Additive manufacturing (AM) technology was originally specialized to fabricate the complicated structures in an arbitrary way. However, when it comes to metal AM, the control of material anisotropy has received an increasing attention in recent years. In this review article, the latest findings regarding the control of mechanical anisotropy through the modifications of macroscopic porous structure, microstructure, and crystallographic orientation by powder-based metal AM technologies are introduced. The powder-based metal AM is able to control a wide range of anisotropy from crystallographic texture to pore structure, however, their simultaneous control is yet challenging. Attainment of this heightens the value of metal AM technology and enhances the AM products’ functions.

This review paper presents a brief background of a concept for both alloy design and process design in order to enhance properties of pure titanium applying a combination of mechanical milling (MM) and spark plasma sintering (SPS) process. Powder processing, such as MM, is one of an effective technique for the enhanced properties of the powders. Especially, adding stearic acid as a process control agent (PCA), is significantly effective for not only reducing cold weld, but also strengthening the matrix in pure titanium during the MM process. SPS is the advanced consolidation technique for the powders synthesised by the MM process with relatively shorter sintering time and lower sintering temperature. The properties for two types of developed titanium materials fabricated by the MM-SPS process with PCA will be introduced.

Mechanical and tribological properties of powder metallurgy (PM) α-titanium (Ti) materials with dissolved nitrogen atoms were evaluated in this study. Pin-on-disk wear test was carried out under dry condition, where a SKD61 disk specimen was used as a counter material. The elemental mixture of Ti and TiN powders was compacted and sintered in vacuum, and then extruded to the full-dense PM Ti rods. During sintering in vacuum, TiN particles were completely decomposed via reaction with Ti powder. Nitrogen atoms originated from TiN were dissolved into α-Ti matrix, and resulted in the remarkable improvement of micro-hardness and tensile strength. The additional heat treatment on the sintered Ti materials was effective to improve further elongation in tensile test because the localization of dissolved nitrogen atoms was decreased. The friction coefficient of nitrogen dissolved Ti material was extremely lower and more stable compared to pure Ti specimen employed as a reference material. The wear loss of the former was significantly smaller than that of the latter specimen. This is because of superior wear resistance of α-Ti material with nitrogen solid-solution due to a large increment of micro-hardness of Ti matrix.

Silicon carbide (SiC) has drawn a significance attention in recent decades for its excellent properties such as high oxidation resistance, high hardness and low density. However, an important drawback for SiC manufacturing is its poor sinterability due to its highly covalent nature of bonding. This work investigates the effect of dispersion in particle size distribution (PSD) on the sinterability of SiC ceramics. In the present work, two types of SiC powders, consisting powders of sizes 0.3 μm and 2.5 μm, were subjected to mechanical milling in order to produce various patterns of particle size distributions. Subsequently, milled powders were sintered by spark plasma sintering. This sintering technology is used on account of its rapid heating and short time sintering. This work also suggests the usage of coefficient of variation, Cv as an appropriate parameter to indicate the dispersion level in PSD range investigated.

Porous metals show some unique properties, which bulk metals cannot exhibit. Especially, iron-based porous metals are expected to be applied to structural components because of their high strength, high rigidity, low material cost and so on. In this research, we synthesized porous Fe/TiB₂ composites by Fe-Ti-B combustion reaction. Iron, titanium and boron powders were blended to synthesize 30 to 60vol%TiB₂ particles in Fe matrix after the combustion synthesis reaction. Four kinds of iron powders (powder size: < 53 μm, < 150 μm, 600 μm and 850-1000 μm) were used. The blended powder was heated to induce the combustion synthesis reaction. When < 53 μm and < 150 μm iron powders were used, irregular shaped and open pores were formed. On the other hand, when 600 μm and 850-1000 μm iron powders were used, spherical pores whose sizes and shapes were similar to those of iron powders were formed.

Spherical powder with excellent fluidity is generally considered to be a suitable raw material powder for additive manufacturing (AM), as opposed to irregularly shaped powder produced by pulverization. The authors have investigated the possibility of obtaining a mixed powder comprising irregularly shaped Ti-6Al-4V alloy powder and spherical Ti-6Al-4V alloy powder. The powders were produced by the hydride-dehydride process and the plasma atomization process, respectively. The fluidity of the mixed powder was confirmed to be an acceptable level for AM and the chemical composition and tensile properties of the AM product using the mixed powder were same as those of the AM product using 100% spherical powder.