**3. Laser direct energy deposition for standard construction alloys**

#### **3.1 Steels**

At the moment, iron-based alloys are actively used in additive manufacturing. Steels are mainly used in the form of a spherical powder in the DED and PBF technologies [28] and also in the form of a wire in the EBM [29], WAAM [30]. The application of the austenitic stainless steels class for additive manufacturing has been the most attractive. Martensitic transformation in these steels is absent and that allows to use them almost with no problems during deposition an air atmosphere [31]. It should be noted that the requirements for the chemical composition of steels, especially for the content of light impurity, should be strictly kept. It is also should control oxygen and trying to minimize it in powders to a level of 0.02%. When the porosity high level is observed in L-DED material, it is worth checking a sulfur, phosphorus, and nitrogen content.

Other steels classes, such as high-tensile-strength carbon steels and maraging steels, require more attention before using for manufacturing by the L-DED process. Development of post-processing is also necessary for that steel class. Steels with a high carbon content, which in turn are most often limited or difficult-to-weld, require careful selection of the process mode to avoid cracking because of a high level of stress during uneven heating and cooling [2, 32, 33]. Additional heating may also be required to equalize the temperature field [34].

Steels used for welded structures are best suited for the additive process.

To select the heat treatment parameters for a particular as-deposited alloy, one should rely on data already developed for other technological processes (rolling, casting). However, standard parameters should be considered as a starting point and research should be carried out to correct the modes of annealing, hardening, and tempering. Parameters such as temperature, time, cooling rate may change up or down. *Features of the Powder Application in Direct Laser Deposition Technology DOI: http://dx.doi.org/10.5772/intechopen.108853*

### *3.1.1 Input control of steel*

In order to use steel powder in additive manufacturing, the first step is to ensure that the powder meets several requirements listed in the incoming inspection chapter. Powders got by the PREP and PA methods have the best quality. However, PREP is practically not used to produce steel powders because of the high cost of the process. Plasma atomization will, of course, be the best option (**Figure 13**).

It is worth paying attention to the content of impurities of light elements. The content of sulfur and phosphorus should be only 0.01 wt.%. The oxygen content is often not regulated by guidelines; however, for steel powders for additive manufacturing, it should be controlled, its content in steel should not exceed 0.02 wt.%. An increased amount of oxygen indicates 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 grown samples. Their localization may be different, but mainly at the boundary of the layers.

The high content of satellites in steel powders got by gas atomization can lead to the appearance of defects in the form of pores and non-fusion in steels. In general, gas porosity is the most common defect found in steels got with the help of L-DED. However, a small number of individual pores or an accumulation of small pores practically does not affect the mechanical characteristics.

During L-DED of non-stainless steels, it is worth using vacuum drying of powders. In the case of suspected high humidity of powders, for example, in the presence of condensate inside the can or low fluidity of powders in the absence of many satellites on the surface of the particles, it is worthwhile to vacuum dry the powders between 120 and 140°C and at least under low vacuum.

### **3.2 Nickel-based alloys**

Nickel-based alloys are distributed the same as steel for additive manufacturing. But developed nickel alloys quantity list is the leading position for application in industry compared to the nomenclature of steels [35–37]. Main interests are heat-resistant nickel alloys [38–40], the microstructure of which is a complexly alloyed γ-solid solution of nickel and dispersed particles based on intermetallic compounds (γ<sup>0</sup> -phase Ni3(Al,Ti) and γ00-phase Ni3Nb).

Multicomponent alloying of the γ-solution and γ'-phase/γ00-phase is carried out in such a way as to ensure high phase and structural stability of the alloy [41]. Using

#### **Figure 13.**

*Additive manufacturing of 304 steel (a) plasma atomized powder, and (b) L-DED 304 steel.*

concentrated energy sources introduces their own characteristics into the processes of structure formation and significantly affects the mechanical properties of the material. Al, Ti, Nb, and Ta are responsible for the content of the γ<sup>0</sup> -phase and γ00-phase in nickel alloys. However, for materials used in additive manufacturing, it is recommended to use additional heating, for example, induction, if the total amount of Al, Ti in them exceeds 5 wt.%.

Strengthening of the γ-solid solution is achieved by alloying with using Co, Cr, Fe, Mo, W, Ta, Re. Strengthening of the grain boundaries is achieved by separating MC-type carbides based on Nb, Ti, Zr, as well as by selective microalloying of B, N, and rare earth metals (REM Y, La, Ce). High heat resistance of the material, grain boundary precipitates should be globular, have a size of 1 μm or less, and be dispersed along the grain boundaries, but at the same time they should not form a continuous grid. The possibility of formation of undesirable phases (σ-, μ-phases, Laves phases) should be minimized.

Despite the above difficulties, the use of additive methods for the manufacturing of products from heat-resistant nickel alloys is justified.
