# Wire Arc Additive and High-Temperature Subtractive Manufacturing of Ti-6 Al-4V
## 3 Mechanical Properties of the Built Titanium Alloy
An oxygen/nitrogen analyzer (HORIBA, Ltd., EMGA-900) was used to analyze light elements such as O\({}_{2}\), and an EDX (AMETEK, EDAX) was used to analyze other elements. We considered that one of the causes of the slightly smaller elongation was the influence of O\({}_{2}\) concentration in the deposited object. The local shield and cover were developed to reduce the O\({}_{2}\) concentration in the fabricating atmosphere, but their effect might have been limited. Table 4 presents the elemental analysis results of the specimen, and the wire material supplied to the WAAM process. For reference, values for the aircraft standard AMS4911 for Ti-6 Al-4V are also given in the table. The O\({}_{2}\) concentration in the test specimen was 0.232%, slightly higher than the upper limit of O\({}_{2}\) concentration of 0.20% for the aircraft standard ASM4911 of Ti-6 Al-4V. The slight difference in the oxygen concentration in the parts, 0.2% and 0.23%, may be one of the reasons for the reduction in elongation. Nevertheless, the O\({}_{2}\) concentration might be sensitive to elongation. The values of N and H in the modeled object were slightly larger than those in the wire material, but not by a problematic amount. The amount of Al was also smaller than the value in the wire material. It is considered that vaporization occurred under the high-temperature state in the plasma during the process, resulting in a decrease of component amounts. Figure 10: Diagram of the stress-relief annealing process. Figure 9: Dimensions of the tensile test piece and its picture with strain gauge. Finally, we compared the mechanical properties of the Ti-6 Al-4V objects and other metal additive manufacturing. The comparison targets were as follows: (1) WAAM with a local shield and cover supplying Ar gas shown in this paper; (2) WAAM process using the same equipment but with the whole working area enclosed in an Ar-filled chamber to keep O\({}_{2}\) concentration to less than 1% (tested by the authors); (3) WAAM with local shield without a cover supplying Ar gas by [PERSON] et al. [7]; (4) electron beam + wire supplied in the vacuum chamber by [PERSON] et al. [8]; and (5) PBF based on selective laser melting by [PERSON] et al. [9] Table 5 lists the tensile strength, 0.2% proof stress, and elongation for each method. The values of the forging material standard JIS H 4657 are given as a reference. Compared to the [PERSON] et al. case using a local shield, the tensile strength and 0.2% proof stress were slightly lower, and the breaking elongation slightly larger with the lower cover added to the local shield. On the other hand, it can be seen that elongation exceeded 10% in the case where the building area was a closed chamber to control O\({}_{2}\) concentration, and in the vacuum case of the electron beam + wire. For reference, in the case of the PBF method, the tensile strength showed a high value of 1100 MPa, but the elongation was as low as 7%. In the case of powder material, since the surface area is large relative to the volume of the material, it is necessary to consider antioxidation in the stock state. In that respect, it is advantageous that the wire's surface area/volume ratio in the material state is small. Since O\({}_{2}\) concentration is kept low when a closed chamber or vacuum atmosphere is used, it leads to higher elongation, over 10%, whereas a local shield did not achieve elongation over 10%. However, fabricating larger objects requires a larger chamber volume. A local shield is easy to install for a larger WAAM machine. Moreover, on the hybrid machine combining the additive process and subtract machining processes, it is also easy to apply the local shield.