In order to develop a new oxide-dispersion strengthened Cu alloy for heat sinks of fusion helical reactors, Cu alloy powders containing Ti, Fe and Y were prepared by atmosphere controlled gas atomization, and the effect of oxygen was investigated. The microstructure of the Cu alloy powder had a typical solidification structure regardless of the alloying element and gas species. The Fe atom was uniformly solid-soluted in the matrix, while the Ti and Y atoms were swept out from the matrix to the grain boundaries and particle surfaces during solidification. The average particle size and aspect ratio of the obtained powders decreased with the use of the N₂+O₂ gas mixture. This is due to the lower surface tension of Cu in the oxygen atmosphere, suggesting that the frequency of the strip breakage stage in the gas atomization process was suppressed due to the formation of oxide film on the particle surface.

The effect of carbon elements on the microstructures and mechanical properties of pure Ti alloys fabricated through extruded powder metallurgy route was investigated. Furthermore, the strengthening mechanism of extruded materials was also investigated quantitatively. In Ti-C materials, the lattice parameter in c-axis of α-Ti increased due to solid solution of carbon atoms in the most stable octahedral interstitial sites. As the carbon contents increased, tensile strength was increased while maintaining a high elongation at break. The 0.2% yield stress of Ti-2.0 mass% TiC increased by 242 MPa compared with pure Ti. The elongation at break value exceeded 35.0% for all specimens. According to this analysis, it was clarified that F_m value of Ti-C materials was 2.90 × 10^-10 by using Labusch model. The estimated strengthening improvement using these values was significantly agreed with the experimental results of PM Ti alloys with carbon solution atoms. Furthermore, the strengthening mechanism of the alloys was quantitatively clarified that carbon solution strengthening was the dominant factor in this study.

In this study, Ti-Zr-Sc sintered alloys with excellent biocompatibility were fabricated from the elemental mixture of pure Ti, ZrH₂ and ScH₂ powders, and their microstructures and mechanical properties were investigated to clarify the strengthening mechanism. In particular, the effect of scandium (Sc) used as the third alloying element on the strengthening behavior by grain refinement, oxygen (O) and Sc solid solution, and Sc₂O₃ particle dispersion was quantitatively evaluated by using the theoretical strengthening models. 0.2% YS of Ti-Zr-Sc alloys decreased with Sc content in the range of 0~1.0 at.% Sc, and increased in the range of 1.0~2.5 at.% Sc. In the former, the added Sc elements reacted with O solutes to form Sc₂O₃ particles and resulted in a significant decrease of O solid solution strengthening effect. On the other hand, when Sc content was over 1.0 at.%, the strengthening effects by both Sc solid solution and Sc₂O₃ dispersion were effective, and cause a remarkable increment of 0.2% YS of Ti-Zr-Sc sintered alloys.

The microstructural and mechanical properties investigation on powder metallurgy (PM) Ti-Zr composite alloys dispersed with TiC particles via sintering and hot rolling process was carried out in this study. PM Ti-Zr-TiC composites were fabricated from the pre-mixed pure Ti, metal Zr and TiC powders, and heat treatment was applied to the sintered materials to homogenize Zr solid-solution in α-Ti matrix. XRD analysis results of these rolled composite materials indicated complete solid-solution of Zr elements. Microstructures observation clarified the binary Ti-(10-20%)Zr alloys had a mean grain size of around 4 µm, which was much smaller compered to pure Ti material with 10 µm grain diameter. According to the tensile test results, Ti-Zr alloys showed a remarkable increment of tensile strength due to Zr solid-solution and α-Ti grain refinement, and also had a large elongation. On the other hand, since Young’s modulus gradually decreased with increased in Zr content, TiC particles were added into Ti-10%Zr alloy to improve the modulus. The uniform dispersion of (2.5-5 wt%)TiC particles in the matrix resulted in the increase of both Young’s modulus and tensile strength. The experimental values of Young’s modulus showed a good agreement with the calculated ones by using the law of mixture.

Ti-Si alloys with fine α-Ti grains and Si solutes were fabricated by laser powder bed fusion (LPBF) process and subjected to hot rolling to form ultrafine grains at the submicron level from fine acicular grain structures. The relationship between the microstructures and mechanical properties of each Ti-Si alloy sample was investigated, and the quantitative strengthening analysis was carried out to find the main strengthening factor by using the theoretical models of grain boundary strengthening, solid solution strengthening and precipitation hardening mechanism. Grain refinement was observed with increasing Si content, which was due to the solute drag effect of Si solute atoms as well as Zener pinning by the precipitation of ultrafine Ti₃Si particles of about 50 nm in the Ti-0.7%Si material. The 0.2% YS values were 1.5 to 2.2 times higher than those of Ti-0%Si samples under sufficient ductility of 17-20% elongation. Quantitative analysis using each strengthening model revealed that grain boundary strengthening by grain refinement was the main strengthening factor for all specimens of LPBF Ti-Si alloys.

α+β dual phase Ti-(0~6 wt.%) Fe alloys were prepared via sintering and hot rolling process to clarify the effects of Fe contents and the rolling temperature on their microstructures and crystalline orientation. With an increase in the Fe content, the volumetric fraction of the β-Ti phase, contains high Fe solutes, drastically increased. When hot rolled at 750°C (α+β dual-phase temperature), each phase grew immediately after rolling and suppressed each other’s grain growth, resulting in fine microstructure formation and uniform residual strain. In Ti-Fe alloys rolled at 1000°C (single β-phase temperature), a very small amount of residual strain was observed, and acicular α-Ti grains with random crystalline orientations were formed due to the phase transformation from β-Ti grains after rolling.

In this study, titanium (Ti) alloy with carbon (C) solid solution was fabricated by laser powder bed fusion (LPBF) from Ti-TiC mixture powder to investigate the effect of C solid solution on microstructure and tensile properties of LPBF Ti alloy. XRD and TEM analysis showed that part of TiC particles was decomposed from the surface during melting process of LPBF and C was solid soluted in α-Ti for Ti-(0.09~0.4 wt%) C. The solid solution of carbon changed the microstructure of the LPBF Ti alloy to fine acicular microstructure due to the martensitic phase transformation. This was also observed in Ti-0.4 wt% C, where solid solution of carbon was not confirmed, suggesting that in Ti-0.4 wt% C, C was once solid solution and precipitated as TiC after phase transformation. LPBF Ti-C alloys showed good strength-ductility, UTS and elongation at break for Ti-0.2 wt% C were 746 MPa and 26.3%, respectively.