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Laser Surface Modification of Composite Ceramics on Base YAG-Al2O3

Adriana Escobar Martinez1, Marina Vlasova1, Pedro Antonio Márquez Aguilar1, Mykola Kakazey1

1Center of Investigation in Engineering and Applied Sciences of the Autonomous University of the State of Morelos

(CIICAp-UAEMor), Av. Universidad, 1001, Cuernavaca, Mexico.

Abstract

Laser treatment of composite ceramics on base of Y3Al5O12 with additives of Y2Ti2O7, Al2Y4O9, and Al2O3 is accompanied by the melting of the surface layer, the partial dissociation of Y3Al5O12, Y2Ti2O7 and Al2Y4O9, and also with formation of secondary Y3Al5O12 and Al2O3 phases and such new phases as YAlO3 with orthorhombic and hexagonal modifications. Content of all this phases depends on regime of irradiation and phase composition of ceramics. In result of directed laser treatment of composite ceramics the new type of ceramic material is formed. It consists from three layers with different thickness. The upper layer is enriched with YAlO3, the middle layer (the real body of track) contain mainly the textured YAG and then followed by the main part of ceramic material. Keywords: Y3Al5O12 composite ceramics, directed laser treatment, phase transformation

1. Introduction

In the investigation of the processes occurring in the laser treatment (heating) of compacted powder mixtures Al2O3–Y2O3–TiO2 in the mode of directed movement of the laser beam, was established [1-7] that, depending on the content of components in mixtures, their properties, density of blanks, mode of radiation (capacity and speed of the beam) takes place the melting of the composite material to a certain depth, the formation of new phases (products of interaction). Specific conditions of rapid heating and subsequent rapid cooling of the melt affect not only on macro-texturing of surface, but also on texturing of crystallites in this layer, on formation of different shapes and sizes of the crystallites, on thickness of zone melting-crystallization and sintering zone, on distribution and stabilization of air bubbles in the thickness of cooling melt, on forms of tracks. In principle, all changes materials in a narrow selected zone of heating can be explained with process of heat propagation [8-11]:

(1) where: ρ is the density of solid body, C is the heat capacity of material, χ is the thermal conductivity coefficient, Q is the density of heat sources in a solid body. In the case of divergent, not a parallel laser beam, due to formation of 3d-temperature gradient of heating, on the surface of compacts is formed concave track. Can assume that in the case of irradiation of ceramic surface, the heat propagation

also should obeys to the expression (1), but the influence of certain members will be largely determines by the mode of ceramics sintering (Tsint., tsint.) and a mode of laser irradiation (P and v). The aim of the present work is the investigation peculiarities of laser processing of ceramics sintered from mixtures of Al2O3–Y2O3–TiO2 at a temperature which is clearly lower the temperature which can be achieved during laser heating. The second objective is revealing the structural phase and morphological differences in the surface layer of ceramics and porous compacts as result of laser heating.

2. Experimental methods

In the present work, specimens were prepared from analytically pure Al2O3, TiO2, and Y2O3 powders. Powder mixtures x mol. % Al2O3 – y mol. % TiO2 – z mol. % Y2O3 were compacted in pellets with a diameter of 18 mm and a thickness of 2–3 mm under a pressure of 300 MPa. The compositions of compacts are presented in Table 1. The compositions of the mixtures were calculated so that, with increase in the Al2O3 content in the mixtures, the TiO2/Y2O3 molar ratio was constant and equal to 0.25. In the first stage, compacts were sintered at 1200 °C for 4 h and then at 1400 °C for 1 h. The surface of compacts and ceramic specimens was subjected to laser treatment. Laser irradiation was performed in an LTN-103 unit (continuous-action laser with λ = 1064 nm). The chosen modes of laser irradiation were as follows: the radiation power (P) was 45, 50, and 70 W. Moving samples was carried out using a linear stepper motor. Travel speed was: 0.075, 0.2, and 0.26 mm/s. The diameter of the beam (d) was 3 mm. After irradiation on surface of ceramics and compacts appear glossy concave tracks of different thickness. The material of tracks as on the surface of compacts and ceramics were investigated by the X-ray diffraction (XRD) method in Cu Kα radiation (a Siemens D-500 diffractometer). An electron microscopy study and electron-probe microanalysis was performed with a LEO 1450 VP type scanning electron microscope.

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3. Results 3.1. X-ray diffraction data The investigation of a series of tracks obtained on a base of mixtures with different contents of Al2O3 showed that the main phase is Y3Al5O12 (YAG) (see Table 1 and Fig. 1). The content of other phases are much smaller than that of YAG. The content of α-Al2O3 increases, and YAG decreases with increasing of alumina content in the initial powder mixtures (Fig. 2). Attention is drawn to the fact that in tracks on the surface of ceramics the YAG and Al2O3 content is greater than on the surface of compacts. The fraction of such secondary phases as Y2Ti2O7 and Al2Y4O9 in tracks of ceramics and compacts are several different. This is especially noticeable for samples with a high content of corundum (α-Al2O3) (see Table. 1, specimens N 4-7). Table I. Phase composition in the ceramics and tracks (TiO2/Y2O3= 0.25) N Composition of the

Powder Mixture Phase Composition

Al2O3, mol. %

Track on ceramics (P = 70 W, v = 0.075 mm/s)

Track on compact (P = 70 W, v = 0.075 mm/s)

1 50 40 10 Y3Al5O12 Little All2Y4O9, Y2Ti2O7, Traces Al2O3,YAlO3

Y3Al5O12 Little Y2Ti2O7 Traces Al2Y4O9

2 55 36 9 Y3Al5O12 Little All2Y4O9, Y2Ti2O7, YAlO3

Y3Al5O12 Little Y2Ti2O7 Traces Al2Y4O9

3 60 32 8 Y3Al5O12 Traces Y2Ti2O7, YAlO3

Y3Al5O12 Little Y2Ti2O7 traces Al2O3

4 65 28 7 Y3Al5O12 Traces Y2Ti2O7, YAlO3

Y3Al5O12 Little Al2O3 Al2Y4O9

5 70 24 6 Y3Al5O12 Traces All2Y4O9, YAlO3

Y3Al5O12, Al2O3 Little All2Y4O9,

6 75 20 5 Y3Al5O12 Traces All2Y4O9, YAlO3

Y3Al5O12 Al2O3 Little All2Y4O9, Al2O3,YAlO3

7 80 16 4 Y3Al5O12 Little All2Y4O9, YAlO3

Y3Al5O12 Little All2Y4O9, Y2Ti2O7, traces Al2O3,YAlO3

An analysis of diffraction peaks in the range 32º–34° for showed that for ceramic tracks they have a complex shape and consist of superposed peaks, namely, peaks of YAG

(420), YAP (112), and YAH (102) (Fig. 1 c, c’).

Fig.1. Fragments of X-ray diffraction patterns of tracks on ceramics (a, b, c) and compacts (a’, b’). For a, b, c: 50 mol. % Al2O3 + 40 mol. % Y2O3 + 10 mol.% TiO2. For a’, b’: 80 mol. % Al2O3 + 16 mol. % Y2O3 + 4 mol. % TiO2. P = 45 W, v = 0.075 mm/s. On c, c’ the view of YAG (420) peak with YAP (112) and YAH (102) peaks. Changing the size of Y3Al5O12 and α-Al2O3 crystallites (Fig. 3) is consistent with a change in the content of YAG in tracks (see. Fig. 2)

Fig. 2. Relative content of YAG (420) (a) and α-Al2O3 (104) (b) in tracks on ceramics (1) and compacts (2) depending on content of alumina in initial mixtures P = 70 W, v = 0.075 mm/s.

Fig. 3. Change the size of YAG (a) and α-Al2O3 (b) crystallites in tracks on ceramics (1) and compacts (2) depending on content of alumina in initial mixtures. P = 70W, v = 0.075 mm/s. The characteristic feature diffraction patterns of tracks are the deviation of the intensity of the peaks (lines) from standard values. This indicates the texturing of crystalline phases. The crystallographic texturing is characterized by the texture coefficient (TC) which is calculated by the formula [12,13]:

1

oo )hkl(I)hkl(I

n1

)hkl(I)hkl(I)hkl(TC

−

= ∑(2),

where I(hkl) are the measured intensities of the (hkl) reflections, Io(hkl) are the intensities according to the JCPDS cards, and n is the number of reflections used in the calculation. The values of the TC for YAG (420) are shown in Fig. 4.

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The content of the YAG phase, crystallites size, and TC are determined with irradiation mode (Fig. 5).

Fig. 4. Texture coefficient for YAG (420) and α-Al2O3 (104) (b) in tracks on ceramics (1) and compacts (2) depending on content of Al2O3 in the initial mixtures P = 70 W, v = 0.075 mm/s

Fig. 5. Change the relative content of YAG (a, a’), size of YAG crystallites (b, b’), and texturing coefficient (c, c’) in tracks on ceramics depending on capacity (a, b, c) and velocity (a’, b’, c’) of laser beam. Ceramics obtained from the 60 mol. % Al2O3 + 32 mol. % Y2O3 + 8 mol.% TiO2 mixture 3.2 SEM investigation At movement of the laser beam in the region of selective laser melting and subsequent cooling of the melt, which is accompanied by crystallization from melt the Y3Al5O12, α-Al2O3, Al2Y4O9, and Y2Ti2O7, appear tracks with a complicated texture in the form of arcs (Fig. 6 a, a’). This is due to the peculiarities of the melt propagation from the local zone of heating zone into region with a lower temperature (Fig. 6 с, с’).

Fig. 6. The view of tracks on the surface of ceramics (a) and compacts (a’), their cross-section (b, b’), and the simplified schema of material heating (c, c’) due to defocusing of laser beam and appearance of a number temperatures on the surface Depending on the regime of irradiation distance between arcs is changed (Fig. 7, Fig. 8). In Fig. 7 a, it can be seen not only a partial superposition of new portion of the melt on had already cooled layer (see Fig. 7 a’, c), but even the appearance of crests (ridges) (see Fig. 7 c). On the surface of tracks can be detected deposited ablation products in the form of aggregates of various sizes (on Fig. 7 d, d’ some of them indicated by arrows). Investigation of cross-sections had shown that shrinkage in the zone of maximum heating depends on the irradiation conditions, and the porosity of the material (see Fig. 6 b, b’, c, c’ and Fig. 8 d). So, the more power and lower velocity of laser beam movement, the greater the shrinkage. The porosity in ceramics is considerably less than in the compacts. For this reason in first case the shrinkage is less. It was found the body of tracks contains bubbles (Fig. 9 a-c). Formation of bubbles depends on velocity and the capacity (P) of laser beam to a greater extent than the phase composition of the ceramics. However, at use of average radiation power and low-speed movement of the beam can avoid blistering. On Fig. 9 b, d can be seen that the size of bubbles increases as the bubbles movement to the surface of tracks due to merging of small bubbles. Part of bubbles is stalled near the surface. 3.3. EDS investigation

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The EDS analysis of the surface of tracks formed on both the ceramics and compacts showed that, depending on the irradiation regime, elements such as O, Al, and Y were detected. At different places, their contents differ (Figs. 10, 11, Tables 2, 3). Titanium is registered only at the places of accumulation of ablation products deposited on the surface of tracks (Fig. 10 a, c, d). The distribution of the elements over the cross-section of track obtained at high powers of irradiation confirms the absence of titanium in the surface layer (Fig. 12 a, b). However, with decrease in the power of irradiation, titanium appears in the surface layer of tracks (Fig. 12 c). 4. Discussion Comparing the phase compositions of tracks on the surface of the ceramics and compacts, (see Table 1) we can conclude that, in the first case, the content of secondary phases such as Y2Ti2O7 and Al2Y4O9 is much smaller than that in tracks on compacts. This indicates that, in the zone of laser irradiation, more favorable conditions for the formation of YAG and α-Al2O3 including their formation as a result of the decomposition/dissociation of Y2Ti2O7 and Al2Y4O9 and formation of “secondary YAG and α-Al2O3” [14-18] are realized, (Fig. 2). This is confirmed by the recording of YAlO3 (YAP) (Fig. 1 c), the larger size of YAG and α-Al2O3 crystallites (Fig. 3), and the higher value of the TC (Figs. 4, 5). On the basis of the obtained data, it can be concluded that, in these two materials, the processes of heat transfer and heat distribution differ. For instance, in selective laser heating of ceramics, heat is consumed only on the melting of the material and on an insignificant change in the phase composition. During irradiation of compacts, heat is consumed on both melting and phase formation to a certain depth and on the formation of the sintering zone (Fig. 6 b, b’, c, c’). The ceramics and compacts differ substantially in porosity (and, hence, in density and thermal conductance). The compacts have a high porosity. This is why the values of the shrinkage and thicknesses of the melting–crystallization and sintering zones turn to be different (Fig. 9). The specificity of motion of the melt over the surface is set by the irradiation mode: the power of irradiation (P) and traverse speed (v) of the laser beam, which has a discrete character [19]. In this case, arcs, which can be considered as macrotexturing of the surface layer under the action of hydrodynamic forces, form [20–22]. In certain irradiation modes, the complete or partial overlaying of the melt on the previous cooled or solidified layer occurs (Fig. 6 a, a’, Fig. 7, and Fig. 8). Undoubtedly, the bonding (adhesion) of layers, their homogeneity, the morphology and texture of each layer depend on the toughness of the

upper and the lower layer, and the extent of propagation of the melt from the melting point of the upper layer to the point of its solidification on the lower layer, and, hence, on the interlayer temperature gradient [23]. In Fig. 7 a, d, d’, one can see not only the overlapping of neighboring layers, but also ejections of portions of the melt to high distances, which is characteristic of high values of P and v. In this case, the roughness of the surface can increase [24–26], and even asperities (crests) can form (Fig. 7 c). The shape of these crests enables us to assume the growth of crystallites (dendrites) from the gas phase as a result of evaporation, the decomposition of Y2Ti2O7, Al2Y4O9, Al2O3, and Y3Al5O12 at high temperatures [17, 18, 26-31], and subsequent deposition of particles/vapors on primary asperities, which are seen, e.g. in Fig. 7b.

Fig. 7. The view of tracks on the surface of ceramics (a,a’) and compact (b, c). For (a, a’) was used mixture 55 mol. % Al2O3 + 36 mol. % Y2O3 + 9 mol. %, P = 20 W, v = 0.075 mm/s. For (b) was used mixture 50 mol. % Al2O3 + 40 mol. % Y2O3 + 10 mol. % P = 70 W, v = 0.075 mm/s. For (c) was used mixture 84.6 mol. % Al2O3 + 6.4 mol. % Y2O3 + 9 mol.%- P = 120 W, v = 0.15 mm/s [1]. For (d, d’) was used mixture 80 mol. % Al2O3 + 16 mol. % Y2O3 + 34 mol.%- P = 45 W, v = 0.075 mm/s Analyzing the appearance and distribution of bubbles in the body of tracks and the pore-size distribution, we arrive at the conclusion that their formation depends directly on the irradiation mode (see Fig. 9). For instance, the higher the heating temperature of the surface (i.e., the larger the power of irradiation P), the greater the number of formed bubbles. According to [32–35], the most important process that determines the formation of gas bubbles is the disturbance of the composition of the melt as a result of reactions of thermal dissociation of compounds. The

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appearance of the YAP phase (according to X-ray data), the formation of pores after irradiation of the ceramics and the gradual disappearance of Y2Ti2O7 and Al2Y4O9 correspond to this process. Gas bubbles are accumulated along the crystallization front and can be captured by a growing crystal [34, 36, 37]. The capture of gas bubbles depends on the crystallization rate, which, in turn, depends on the speed of movement of the heating zone (see Fig. 9). The specificity of the distribution and change of the pore size is described by a model that takes into account the movement of a flow of certain viscosity, thickness, and initial pore-size distribution [38]

Fig. 8. Change the distance between arcs (a, b), width of tracks (c); on (d) shrinkage of ceramics (1) and compacts (2); on (e) thickness of zone crystallization (1) and ceramics (2) depending on the irradiation power (a, c) and the speed of beam movement (b, d) for ceramic specimen obtained from mixture 80 mol.% Al2O3 + 16 mol.% Y2O3 + 4 mol.% TiO2.

Fig. 9. The view of tracks cross section on ceramics (a, b, c) and distribution of bubbles inside volume of track (d). For (a) ceramics obtained from mixture 65 mol.% Al2O3 + 28 mol.% Y2O3 + 7 mol.% TiO2, P = 45 W, v = 0.075 mm/s. For (b, d) ceramics obtained from mixture 65 mol.% Al2O3 + 28 mol.% Y2O3 + 7 mol.% TiO2, P = 70 W, v = 0.075 mm/s. For (c) ceramics obtained from mixture 55 mol.% Al2O3 + 36 mol.% Y2O3 + 9 mol.% TiO2, P = 70 W, v = 0.075 mm/s. The microanalysis of tracks formed on the ceramics with a small Al2O3 content showed the depletion of the surface in titanium atoms (see Fig. 10, Table II), which agrees with the X-ray data (see Table 1) and the temperature of decomposition of Y2Ti2O7 in the melt (~ 750 ºC) [17]. At the same time, the surface is depleted of oxygen and is enriched in Y and Al, which indicates the simultaneous development of the following processes: phase transformations, complete or partial decomposition of compounds, and evaporation (ablation) [39- 44]. As a result, on the surface of tracks, YAlO3 is accumulated, and in the ablation products, titanium is registered.

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Fig. 10. The view of tracks on ceramic surface (a, b, c) and content of elements (a’, b’, c’) in places indicated on micro photos. Ceramics obtained from mixture 55 mol.% Al2O3 + 36 mol.% Y2O3 + 9 mol.% TiO2. For (a, a’) P = 70 W, v = 0.26 mm/s. For (b, b’) P = 70 W, v = 0.075 mm/s. For (c, c’) P = 45 W, v = 0.075 mm/s. On (d) aggregate from precipitated products of ablation and on (d’) content of elements in aggregate. The microanalysis of tracks formed on the ceramics with a high Al2O3 content (see Fig. 11, Table 3) also indicated the absence of titanium and the enrichment of the surface in aluminum oxide and YAG. In the ablation products deposited on the tracks, Al2O3 and Y2O3 are present which is consistent with the dissociation (ablation) process of Y2Ti2O7 and Al2Y4O9.

Fig. 11. The view of tracks on ceramic surface (a, b, c) and content of elements (a’, b’, c’) in places indicated on micro photos. Ceramics obtained from mixture 80 mol.% Al2O3 + 16 mol.% Y2O3 + 4 mol.% TiO2. P = 45 W, v = 0.075 mm/s. Table II. Content of elements in places on ceramic tracks marked on Fig

10 and calculated compositions Table III. Content of elements in places on ceramic tracks marked on Fig 11 and calculated compositions. Mode of irradiation: P = 70 W, v = 0.075 mm/s

Type of specimen

Content of elements, wt.%

Places of irradiation:

1 2 3 4 5 6

55 mol.% Al2O3 + 36 mol.% Y2O3 +9 mol% TiO2

O 35.4 33.18

33.2 31.73

48.3 24.31

Al 30.2 20.29

30.13 23.3

43.25 40.73

Y 34.4 46.53

36.67 44.79

8.45 35.04

Calculated composition, %

86YAG

17Al2O3

83YAG 17

Al2O3

80 YAG

20 Al2O

3

YAG

82.35Al2O3 16.97 YAG 0.68 YAlO3

~ 50 Al2O3

~ 50 Y2O

3

Type of specimen

Content of elements, wt.%

Mode of irradiation

P =70W, v=0.26 mm/s

P=70 W ,v=0.075 mm/s

P= 45W, v =0.075 mm/s

P =70W, v=0.075 mm/s

Places:1 2 3 4 5 6 7(ablation product)

55 mol.% Al2O3 + 36 mol.% Y2O3 +9 mol% TiO2

O 38.14 33.18 32.37 29.16 30.08 31.7 32.15

Al 19.86 20.29 20.72 27.61 24.71 19.3 15.22

Y 41.14 45.25 45.25 43.23 44.11 47.13 37.91

Ti 0.84 0 0 1.01 1.01 1.87 14.72

Calculated composition, %

59YAG 40YAP 1TiO2

96YAG 4YAP

99YAG 1YAP

55 YAG 45YAP

70 YAG 29YAP 1TiO2

70 YAG 28YAP 2TiO2

28 Al2O3 48 YAG 24 TiO2

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Fig. 12. The view of tracks cross section on ceramics and distribution of elements from the upper to bottom part of zone crystallization. Ceramics obtained from mixture 65 mol.% Al2O3 - 28 mol.% Y2O3 - 7 mol.% TiO2. For (a) P = 70 W, v = 0.26 mm/s. For (b) P = 70 W, v = 0.075 mm/s. For (c) P = 45 W, v = 0.075 mm/s. The results suggest that on the surface of tracks the surface layer (as "skin layer") with complex morphology and oxygen-depleted relative to the bulk part of the track is formed (Fig.12). The generalized scheme of ceramic material structure after laser surface treatment is shown in Fig. 13.

Fig. 13. A simplified scheme of the structure of the ceramic specimen after laser surface texturing. Y3Al5O12 is YAG, Y4Al2O9 is YAM, YAlO3 orthorhombic is YAP, YAlO3 hexagonal is YAH.

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5. Conclusions According to the obtained results, the laser treatment of the composite ceramics based on Y3Al5O12 is accompanied by melting and the formation of the surface layer enriched in the YAP, YAH, and Al2O3 phases as a result of different reactions proceeding simultaneously in different temperature zones of laser heating. The directed movement of the laser heating zone and subsequent cooling predetermine the directional solidification of the most representative YAG phase and, as a consequence, the crystallographic texturing of YAG crystallites. The degree of crystallographic texturing and the size of YAG crystallites depend on the heating–cooling mode of the surface and the YAG/Al2O3 phase ratio. In result of directed laser treatment of composite ceramics the new type of thee-layered ceramic material is formed. The upper layer is enriched with YAlO3, the middle layer (the real body of track) contain mainly the textured YAG and may be saturated with bubbles. The third layer is the primary ceramics. The formation of such macrostructure of ceramic specimens should be taken into consideration in the case of using of textured ceramic material for optical and other special applications. Acknowledgments The authors wish to thank CONACYT for financial support (Project 155731). References 1. M. Vlasova, M. Kakazey, P. A. Márquez Aguilar, V. Stetsenko, A. Ragulya and A. Bykov: "Phase formation in the region of laser irradiation of Al2O3–TiO2–Y2O3 oxide eutectic mixtures", MAT SCIE ENG, 2012, 1 (3), 1-7. 2. M. Vlasova, M. Kakazey, P. A. Márquez Aguilar, A. Ragulya, V. Stetsenko and A. Bykov: "Phase formation at selective laser synthesis in Al2O3–TiO2–Y2O3 powder compositions", Mater. Res. Soc. Symp. Proceedings, 2013, 1485, 65-70. 3. M. Vlasova, M. Kakazey, P. A. Márquez Aguilar, R. Guardian Tapia, V. Stetsenko, A. Bykov and S. Lakiza: "Phase formation and microstructure of ceramics at selective laser synthesis in Al2O3–TiO2–Y2O3 powder compositions", J. Advances in Ceramic Science and Engineering (ACSE), 2013, 2 (3), 120-129. 4. M. Vlasova, M. Kakazey, E. A. Juarez-Arellano, P. A. Márquez Aguilar, R. Guardian Tapia, V. Stetsenko, A. Bykov and A. Ragulya: "Laser synthesis of composite Al2O3 – Y2Ti2O7 ceramics from Al2O3–TiO2–Y2O3

powder mixtures", J. Advanced Microscopy Research (JAMR), 2013, 8 (1-9),186-194. 5. M. Vlasova, M. Kakazey, P. A. Márquez Aguilar, E.A. Juarez-Arellano, R. Guardian Tapia, V. Stetsenko, A. Bykov, S. Lakiza, and A. Ragulya: "Directed laser processing of compacted powder mixtures Al2O3–TiO2–Y2O3", Sci. Sint., 2013, 3, 251-260. 6. M. Vlasova, M. Kakazey, P. A. Márquez Aguilar, V. Stetsenko, A. Bykov and S. Lakiza: "Structural and Phase Evolution in Laser Treatment of Al2O3–TiO2–Y2O3 Powder Mixtures", J. Alloys Compd., 2014, 586, 5199-5204. 7. P. A. Márquez Aguilar, M. Vlasova, S. Lakiza‚ M. Kakazey, A. Bykov and V. Stetsenko: "Laser synthesis features of composite ceramics Y3Al5O12-Y2Ti2O7-Al2O3-Al2TiO5", Adv. Sci. Techol., 2014, v. 88, 4, 2014. 8. M. S. Brown, C. B. Arnold, "Fundamentals of Laser-Material Interaction and Application to Multiscale Surface Modification", in ‘Laser Precision Microfabrication’, Chapter 4, (eds.K. Sugioka et al.), 91-120, 2010, Springer Series in Materials Science 135, Springer-Verlag Berlin Heidelberg. 9. F. H. Mirzoev, V. Ya. Panchenko and L. A. Shelepin, "Laser control processes in solids", Adv. Phys. Sci., 1996, 166, 3-32. 10. Loong-Ee Loh, Chee-Kai Chua, Wai-Yee Yeong, Jie Song, Mahta Mapar, Swee-Leong Sing, Zhong-Hong Liu, Dan-Qing Zhang, "Numerical investigation and an effective modelling on the Selective Laser Melting (SLM) process with aluminium alloy 6061’, International Journal of Heat and Mass Transfer, 2015, 80, 288–300. 11. ‘Laser-Assisted Fabrication of Materials’, (eds. J. Dutta Majumdar and I. Manna), 1 Springer Series in Materials Science 161, 2013, Springer-Verlag Berlin Heidelberg. 12. S. Ruppi, "Deposition, microstructure and properties if texture-controlled CVD α-Al2O3 coatings", Int. J. Refract. Met. Hard Mater., 2005, 23 (4–6), 306–316. 13. F. J. Ester, A. Larrea and R. I. Merino, "Processing and microstructural study of surface laser remelted Al2O3-YSZ-YAG eutectic plates", J. European Ceram. Soc., 2011, 31(7), 1257-1268. 14. S. Wang, F. Yamamoto, T. Akatsu, Y. Tanabe and E. Yasuda, "Metastable precipitation in isothermally solidified YAG-alumina composites with off-eutectic composition Materials", J. Mater. Sci., 1999, 34, 3489 – 3494. 15. M. Marezio, J.P. Remeika and A. Jayaraman, "High-pressure decomposition of synthetic garnet", J. Chem Phys, 1966, 45, 1821-1824. 16. D. Hreniak , S. Gierlotka , W. Łojkowski , W. Stręk , P. Mazur and R. Fedyk, "High-pressure Induced Structural

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