**5. SLS/M formation of local zones of given configuration possessing magnetic properties**

inhomogeneous (i.e., functional graded, FG) nanostructures with different types of orderings

The most promising materials are lead-free phases (involving niobates of alkali metals and alkaline earth metals, bismuth ferrite, etc. with various additives) [26, 27]. These materials have giant macroresponses including ultrahigh Curie (*T*C ≥ 1400 K) and Neel (*T*N ≥ 1000 K) temper‐ atures providing a wide range of practical applications. They are ferroelectric, antiferroelectric, piezo- (magneto) electric solid solutions, and/or their based compositions due to greater polyfunctional characteristics in vicinity of new structured phases appearance with their

However, there are some negative factors impeding their application, which are related to the physical and chemical features of these objects (decomposition during the process of heat treatment, problems with poling, high volatility of the starting components, excessive grain growth due to recrystallization, low thermal stability, and mechanical strength, etc.), which could be solved by additive technologies. An urgent and significant problem of modern physical material science is the development of experimental and theoretical base of functional (and FG) materials fabrication which are free from the abovementioned drawbacks. A hybrid technology is based on the combination of traditional techniques (solid-phase synthesis, hot isostatic pressing (HIP)) and SLS/M technologies and uses dispersion—nanocrystallite powders and CAD of specific (M/NEMS) devices on the base of obtained materials [28, 29].

Fundamentals of the active elements creation were developed at the Samara branch of LPI [25] from functional (smart) materials by the SLS method with a hybrid combination of some traditional processes. The laser influence (LI) on multicomponent (including reaction capable) powdered compositions was studied. Well-known piezoelectric, hexaferrite, and hightemperature superconductivity (HTS) systems (PbTi1−*<sup>x</sup>*Zr*x*O3—named as PZT; Li0.5Fe2.52*x*Cr*x*O4 and BaFe12−*<sup>x</sup>*Cr*x*O19—spinels; SrFe12O19 and CoFe2O4—HTS) were fabricated [26, 30]. A hybrid layerwise SLS-SHS process (SHS is self-propagated high-temperature synthesis) was realized by means of the laser-controlled combustion reaction inside the oxide stoichiometric mixtures of the above said systems. The main achievement was a production of the 3D parts during the SLS-SHS hybrid process, as well as determination of optimal regimes for their following annealing and polarization (magnetization). The X-ray analysis of the sintered and annealed samples revealed the main phases, responsible for the ferroelectric, antiferroelectric, piezo- (magneto) electric activity of these ceramics. The possibility of association of several ap‐ proaches (we used PZT as a filler for poly(vinylidene fluoride) (PVDF) polymer) into a united technological process for layerwise syntheses of the FG structures and 3D parts with ferro‐ electric characteristics of different types of connectivity were also shown [28, 29]. The use of nano-PZT particles in PVDF matrix (which has its own piezoelectric properties) will allow to create such types of connectivity into hybrid AT, which do not exist in the nature, but can possess unique features. Regrettably, density of the synthesized ceramics reached only 3–4 g/

 (that makes up ~40–50% from the theoretical value for PZT) and, as an effect, instead of completely synthesized products, we received only mixture of the initial oxides with partly

(and different thermal, magnetic, piezoelectric, ferroelastic properties, etc.) [25].

accompanying extreme electro-(magneto-) physical parameters.

244 New Trends in 3D Printing

cm3

formed given active phases.

Mechanisms of formation of local zones of a specified configuration with magnetic character‐ istics during the melting (SLM/S) of nanoparticles additives of transition and/or rare-earth metals with a HTS ceramics in a polymer matrix are of great interest [11, 31].

However this issue was not given a sufficiently thorough study yet. Parts and/or tools of a complex configuration with selective local magnetic properties and multidirectional magnetic poles, which cannot be obtained by the machine treatment, can be easily reproduced by the SLM process. But the mechanisms of formation of such zones and the interaction of materials at the zones boundary have been studied partially only.

If at the moment of a rapid crystallization from the liquid phase into the solid one, the melted pool is influenced with a strong static magnetic field, then the resultant alloy microcrystal‐ lines will be arranged along the power lines and after cooling will keep their magnetiza‐ tion. This approach allowing to create local magnetic zones inside a solidified matrix in the longitudinal, transverse, or vertical direction, was proposed by us earlier [32]. By means of the passage by passage consistent cladding, it is possible to form in the vertical direction an overall solid coating of 3D parts with magnetic properties. The obtainment of the 3D part with volume zones of the predetermined magnetic properties is a challenge in materials science and manufacturing. The microstructure of the resultant material is determined by the joint mutual influence of the processes of rapid solidification and crystallization, direction‐ al cooling and phase transitions caused by repeated thermal cycles, and chemical composi‐ tion of the initial powders.

The rapid solidification may cause a volumetric heterogeneity of chemical elements that can lead to the metastable phases formation. The directional heat removal can determine both the preferred direction of the grains growth and crystallographic texture, thereby affecting the magnetic properties of the part [32]. The LI enables to choose the regimes of energy influence on the cladded layers of materials, ensuring the maintenance of the crystalline structure and a given grains size. The orientation of the grains in an external magnetic field characterizes the residual magnetic properties of the obtained material.

Other interesting tasks are the obtainment on nonmagnetic (polymer) substrates of quasizero-dimensional points (local zones) [11], quasi-one-dimensional magnetic passages from rare-earth nanoadditives (e.g., Samarium-based alloys) with different composition, two- and three-dimensional arrays based on them; determination of their morphology, crystalline and magnetic structure, the saturation magnetization, residual magnetization, and coercive force. In the paper [33], a model was considered allowing numerical determination of a resulting field velocity under the laser melting of aluminum in the external magnetic field. The model included heat-dependent characteristics of the material (surface tension and viscosity). A heterogeneous distribution of the magnetic flow density was determined by the experimental Hall data measured for the prototype. It was shown that a constant magnetic flow applied coaxially with the LI, exerts its influence upon the direction of the melted material flow and can be explained as a heterogeneity of electromagnetic destruction.
