*3.2.1 Input control of nickel-based alloys*

Before using nickel-based alloy powders in additive manufacturing, the first step is to ensure that the powder corresponds a number of requirements listed in the incoming inspection chapter. Exclusively PREP and PA processes to avoid high oxide content (**Figure 14**) should produce nickel alloy powders with high Al and Ti content.

#### **Figure 14.**

*Inconel 718 powder (a) PREP, (b) GA, (c) L-DED microstructure from PREP powder, and (d) L-DED microstructure from GA powder.*

*Features of the Powder Application in Direct Laser Deposition Technology DOI: http://dx.doi.org/10.5772/intechopen.108853*

#### **Figure 15.**

*Nickel-based alloy EP648 powder (a) IGA, (b) EIGA, (c) L-DED microstructure from IGA powder, and (d) L-DED microstructure from EIGA powder.*

Defects in Nickel Alloys got by the L-DED technology.

For nickel alloys, as well as for steels, the content of some light elements should be strictly regulated: no more than 0.01 wt.% S and P, no more than 0.02% O. An increased amount of oxygen is usually associated with the presence of oxide inclusions on the surface and inside the powder. As a result, inclusions that were on the surface and inside the powders will be detected in the structure of the deposited samples. Their localization can be different, but mainly they are localized at the layer's boundaries. Also, the internal porosity of the powder, which occurs in powders got by the GA method, will negatively affect (**Figure 15**).

#### **3.3 Titanium alloys**

Wide interest in the titanium and titanium alloys associated with a unique range of characteristics. At the same time, they are difficult to process. As a result, they are widely used in additive manufacturing.

Features of titanium alloys also appear in the production of powders. Only inert gases can be used for protection and as energy carriers in the production of powders.

The most studied and widespread titanium alloy is Ti-6Al-4 V alloy [41–44]. However, there are also works by the authors on the use of other titanium powders in additive manufacturing [45–47].

Many studies have shown dependence of the L-DED process parameters on the structure and properties formation in titanium alloys [48–51].

### *3.3.1 Input control of titanium alloys*

The main attention in the input control of titanium powders is paid to the content of light impurities. Input control is carried out under the methodology presented in Section 1.6. Also, basic information on titanium powders can be found in ASTM B988–13 [51].

Opposed from steels and nickel superalloys, the low thermal conductivity of titanium causes the particle size of the powder to affect the grain size in the L-DED structure. This was shown in Section 1.1.

Since powders of titanium alloys are got by plasma atomization and PREP, they are characterized by a low content of satellites on the surface. The main problem encountered in such powders is the variation in chemical composition.

**Figure 16** shows SEM images of the surface of various powders, numbered respectively A1, A2, B1, B2.

The results of the study of L-DED material obtained from the considered powders showed that the most significant influence is exerted by light impurities in the powder [18]. **Figure 17** shows that powder B1 has an increased hydrogen content. This high hydrogen content has a significant effect on increasing hardness and reducing ductility, and porosity has also been found in the structure.

As can be seen from the L-DED figures, a sample made from a powder with a high hydrogen content has low ductility. No significant effect of the fraction on the properties was found.

#### **Figure 16.**

*Images of the powder surface from a scanning electron microscope in BSE mode: (a) A1 powder (45–100 μm), (b) A2 powder (106–180 μm), (c) B1 powder (45–100 μm), and (d) B2 powder (160–200 μm).*

**Figure 17.** *Light impurities content influence on properties of L-DED Ti-6Al-4 V.*
