Studies on Young's modulus and microhardness of laser fused surfaces: Sm-Co on the stainless steel and Sm-Fe on the duralumin substrates have shown the heterogeneity of depth properties with local maximum in areas not containing micro cracks. Maximum hardening was obtained for Sm-Fe system. Found that hardening of laser fused layers and the increase their resistance to compression and tension on the stainless steel substrate is associated with the formation of multicomponent alloys (Fe17.8Ni25.6Cr5.6C11.0Sm32.1and Fe64.3Ni1.9Cr16.6C5.5Sm8.4) due to the diffusion of atoms of the substrate and depends on the availability of the micro crack’s grid of and the alloy microstructure. The high Al diffusion speed from duralumin substrate in the fused layer, formed from Sm powder, and then from Fe powder, led to the segregation of Al on the surface, formation of triple oxide (AlSmO3) with maximum microhardness and Young's modulus. Further decrease of both parameters is associated with the formation of micro cracks, but a local maximum connects with strong decreasing of microcrack’s density and formation of Al2Sm layer.
A robotic laser technological complex has been used for the laser powder fusing (LPF) of samarium (Sm) and iron (Fe) or Sm and cobalt (Co) powders on duralumin (AMG-3) substrates in argon flow conditions for the creation of thick (0.3–0.5 mm) ferromagnetic coatings. For the Sm-Fe system in the first step of Sm powder laser fusing the chemical interaction between Sm powder and Al atoms from the melted AMG-3 substrate resulted in the formation of Al2Sm in both cases: with and without perpendicular magnetic field (samples Nos. 6 and 4). The perpendicular magnetic field during LPF on the AMG-3 substrate resulted in the formation of the additional compound Fe5Al8 for sample No. 6. The formation of SmxFe alloy in the second step of Fe LPF was blocked due to the lower chemical activity of Fe atoms compared to Sm, and the high resistance of Al2Sm. But for Sm-Co system the interaction between Sm and Co atoms was not blocked and SmCo5 as a majority crystalline phase was formed. Samples Nos. 4 and 6 based on the Al2Sm and Fe5Al8 compounds were very weak ferromagnetic phases at 300 K with low coercivity, but a strong ferromagnetic ordering with Curie temperature of 70 K was observed at lower temperatures. This ordering increased by 100 times the saturation magnetisation, residual magnetisation and coercivity at 4K. The mechanism of such type of magnetic ordering is not clear at present. The two chopped pieces of the sample No. 5 showed ferromagnetic properties (saturation magnetization of (±27,8 emu/g and ±20.5 emu/g) and coercivities of 130-140 Oe and 300-320 Oe ) that determines only by SmCo5 grains inside the fused layer. The increase of coercivity for SmCo5 grains correlates with increase of area of grain boundaries inside the fused layer.
Comparative study of laser welding method has been carried out at four different methods of welding in Sm-Co system on two types of substrates: stainless steel and duralumin and at two types of argon gas flow in the place of melting. The comparison of compositions and magnetic properties of welded coatings has been done for all formed samples. It was established that SmCo8.5 compound conserves only after laser welding of SmCo8.5 tablets with additional contribution of oxides that results to strongly decrease of saturation magnetization and coercivity as compared with SmCo8.5 films. In the case of the standard argon gas flow and using of Sm and Co powders the quick melting of the stainless steel substrate surface occurs that results to strong diffusion of transition metals to the welded layer and formation of Sm-based, noncrystalline alloy with only two crystalline phases (Co0.72Fe0.28 and Co), which demonstrate soft ferromagnetic properties. The formation of Sm-Co chemical compound is blocked when the Co welding carried out after Sm welding due to formation of Sm oxides on the welding surface. In the conditions of a stable argon atmosphere around the sample the pure Co and Sm crystals have been formed with weak ferromagnetic properties.
A modern robotic laser complex with neutral gas supply system of argon to protect the powders from oxidation has been used for laser welding of Sm and Co powders on stainless steel and duralumin substrates. X-ray diffraction investigation of crystalline structure showed that oxidation of mainly Sm occurs during laser welding and following cooling at the standard argon flow. The main ferromagnetic phases: Co and Co-Fe alloy on stainless steel substrate (sample No 3) and SmCo5 on duralumin substrate (sample No 5) were determined by data of magnetic measurements, including temperature magnetization measurements and magneto-optic Kerr microscopy. It was observed that sample No 3 at T = 300 K showed ferromagnetic properties with small coercive force (about 300 Oe) and high saturation magnetization of 44 emu/g. With temperature decreasing its magnetization monotonically increases to 50 emu/g and coercivity increases in three times that determined with ferromagnetic ordering of Co and Co-Fe alloy grains at various temperatures. The sample 5 showed weak ferromagnetic properties (saturation magnetization of ±27.8 emu/g and coercive force of 130-140 Oe) that determines only by SmCo5 grains inside the welded layer. Small coercive force for SmCo5 grains correlates with big sizes of its magnetic domains (20-150 μm).
Thin (50-90 m) non-doped and doped (by Al atoms) Mg2Sn0.6Si0.4 and Mg2Sn0.4Si0.6films with roughness of 1.9-3.7 nm have been grown by multiple deposition and single annealing at 150 °C of multilayers formed by repetition deposition of three-layers (Si-Sn-Mg) on Si(111) p-type wafers with 45 Ω-cm resistivity. Transmission electron microscopy has shown that the first forming layer is an epitaxial layer of hex-Mg2Sn(300) on Si(111) substrate with thickness not more than 5-7 nm. Epitaxial relationships:hex-Mg2Sn(300)|| Si(111), hex-Mg2Sn[001]|| Si[-112] and hex-Mg2Sn[030]||Si[110] have been found for the epitaxial layer. But inclusions of cub-Mg2Si were also observed inside hex-Mg2Sn layer. It was found that the remaining part of the film thickness is in amorphous state and has a layered distribution of major elements: Mg, Sn and Mg without exact chemical composition. It was established by optical spectroscopy data that both type films are semiconductor with undispersed region lower 0.18 eV with no= 3.59 ± 0.01, but only two direct interband transitions with energies 0.75-0.76 eV and 1.2 eV have been determined. The last interband transition has been confirmed by photoreflectance data at room temperature. Fourier transmittance spectroscopy and Raman spectroscopy data have established the formation of stannide, silicide and ternary compositions.
Two step laser’s welding of Sm and Fe powders on duralumin substrate in the argon gas flow has been firstly tested. It was established that oxidation of Sm atoms with formation of Sm2O3 and SmO during laser welding of duralumin substrate is the main reason of not forming of the SmFex compound, which can be appeared on the second step of Fe laser welding. The next reason is a strong interaction between Al and Sm atoms at the interface with a substrate with formation of Al2Sm compound, consisting from paramagnetic atoms. So, an additional protection from oxidation needs during laser welding. Magnetic properties of coatings formed by layer-by-layer laser welding from Sm and Fe powders on duralumin AMg-3 substrate welded with and without external magnetic field have been studied by methods of field and temperature magnetization measurements and study by vibromagnetometer method at room temperature (300 K). A strong paramagnetic contribution of AMg-3 substrate has been proved. Al2Sm grains without substrate have shown soft ferromagnetic properties at 300 K independently from using an external magnetic field. An interesting phenomenon has been found at cooling coatings down to 4 K: magnetic ordering of Al2Sm domains with Curie temperature about 70 K.
The testing of welding of Sm and then Fe powders was carried out on laser complex to create ferromagnetic coatings of (1-2) μm thickness in conditions of argon flow. X-ray diffraction analysis showed that oxidation of Sm and Fe occurs, but the main contribution of Fe grains in the structure was proved. It was established that in the conditions of the additional magnetic field (0.2 T) the crystallization of single Fe grains (5-20 μm) with formation of a mesh structure in Sm oxide matrix occurs on the whole thickness of the welded layer. The dissolution of Sm on the depth of 1.0-1.3 μm was observed inside the substrate with the formation of high density Sm oxide’s grains (2-10 μm), when the additional magnetic field is absent during laser welding. The Fe laser welding results in the formation of elongated Fe grains to a depth of 60-100 μm framed. Regardless of the microstructure samples showed similar magnetic loops with high saturation magnetization (110-112 emu/g), low coercivity (0-100 Oe) and near zero residual magnetization that corresponds to soft magnetic coatings with main contribution of Fe grains. Magnetic ordering was found in both coatings with Curie temperature of 50 K.
A strong nonlinear increase in the photoluminescence intensity under laser excitation at room temperature is found for porous silicon obtained by anodic oxidation. It is shown that the maximum photoluminescence intensity correspond to samples of anodically oxidized porous silicon in the intermediate oxidation state. Laser excitation is found to increase the intensity of vibrational modes in the O3 – SiH, Si-O-Si and Si-O-H configurations with respect to the Si-Hn mode intensity in IR absorption spectra. It is experimentally confirmed that the oxide structure on the surface of silicon crystallites and the structure of the Si/SiO2 interface determine to a great extent the photoluminescent characteristics.
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