This paper describes characteristic profiles of explosibility and ignitability of metal powders as well as their possible hazards, in most cases, in comparison to those of organic dusts. Metals are mostly pure materials and their physical and thermochemical properties are well known, so that it was tried to explain their performances on the basis of their properties, which may help the estimation of explosibility and ignitability of metal powders that are not yet known.

Crystals of new compounds α-Yb(Al_1−xT_x)B₄ (orthorhombic, space group Pbam) (T = Fe, x = 0~0.100; T = Cr, x = 0~0.015) with YCrB₄-type were grown from Yb₂O₃, metal Fe or Cr and crystalline boron powders under an Ar atmosphere at 1773 K for 5 h. The obtained Yb(Al_1−xT_x)B₄ crystals were measured for hardness and magnetic susceptibility. The values of micro-Vickers hardness for Yb(Al_1−xFe_x)B₄ and Yb(Al_1−xCr_x)B₄ were in the range of 15.7(1.5)~16.8(1.5) GPa, and 13.3(2.7)~14.8(1.5) GPa, respectively. It is presumed that this difference is due to the difference in the size of the atomic radius of Fe or Cr. The magnetic susceptibility of Yb(Al_0.995Fe_0.005)B₄ shows a sharp paramagnetic increase at low temperatures, likely due to impurities or defects.

Other transition metal carbides NbC, TaC, WC, and ZrC added TiC–SiC composite ceramics were sintered at 1800°C and 1850°C using a resistance-heated hot pressing machine. The raw materials TiC, α-SiC and the reaction products TiC-based solid solutions were detected in the ceramics. The highest Young’s modulus value of 477 GPa was obtained for the ceramics with 17 mol% TaC. The Vickers hardness of TiC–SiC composite ceramics was increased by the addition of TaC, ZrC, and a small amount of NbC, reaching 21 GPa at 12 mol% TaC. There was a correlation between the hardness of TiC–SiC composite ceramics and the average grain size of TiC. The fracture toughness of TiC–SiC composite ceramics was increased with increasing WC amount below 5 mol%, and TaC below 12 mol%. The addition of 12 mol% TaC to TiC–SiC composite ceramics was increased not only the hardness but also the fracture toughness, its value reaching 6.1 MPa m^0.5.

Recently AM became one of the most revolutionary metal forming technologies in certain market fields in the world. Powder makers focus on supplying powder suitable for this new market. Big users and AM machine makers tend to acquire powder makers in order to secure the performance, quality and economics of their products. Often times, users of AM machines and AM machine makers are not familiar with metal powder manufacturing technology, because metal powders are made primarily for PM (Powder Metallurgy) or surface coating.

This review intends to summarize the demands of metal powder for AM industry and various metal powder manufacturing technologies for it. AM methods require powder with different characteristics, as melting together and solidifying are totally different from solid state sintering and AM does not need conventional compactibility of powder at all. On top of it, handling of metal powder before printing or jetting is the new demands.

Various Metal powder manufacturing technologies have been developed and some of them are commercially used for PM and surface coating. Depending on AM method and material. the optimum metal powder manufacturing technology should be chosen. The authors show typical grades suitable to each printing method and material.

With the ongoing trend in the weight savings of transportation equipment, the application of lightweight materials is gradually increasing. The magnesium alloys are the lightest metallic materials for practical use, and are regarded as environmentally-friendly, biocompatibility materials. Furthermore, they may exhibit good damping capacity and superelasticity. In the powder metallurgy, the sintering progress of the magnesium alloy powder would be inhibited because an oxide film is easily formed on the surface of its powder due to the high chemical reactivity of this metal. In contrast, the powder coated with a suitable oxide film would be resistant to oxidation and combustion because it is shielded from air. An industrial sintering process can probably be used for magnesium alloys when the dense and thin oxide film on the powder surface balances the competition for inactivating and sintering.

Iron-based powder mixtures for the powder metallurgy (PM) process commonly contain solid lubricants. Both zinc stearate (ZnSt) and N,N’-ethylenebis(stearamide) (EBS), which are conventional lubricants in this field, exhibit the similarly adequate lubrication performances. However, their effects on the powder mixture flow ability are different; that is, ZnSt exhibits the better flow abilities than EBS. In this study, the adhesive and frictional properties of the five surface combinations (Fe-Fe, Fe-EBS, Fe-ZnSt, EBS-EBS, and ZnSt-ZnSt) were investigated using surface forces and resonance shear measurement. The adhesion forces obtained for all combinations were almost the same. On the other hand, frictions for Fe-EBS and EBS-EBS combinations, obtained from resonance shear measurement, were larger than others at low applied load (<ca. 1.0 mN). This result suggests that the frictional properties of lubricants at low applied load determine the powder mixture flow abilities.