Elongated Grains Research Articles

Investigation of the recrystallization behavior of cold-rolled A1050 thin sheets based on misorientation measurements and grain boundary information

The recrystallization behaviors of severely cold-rolled A1050 thin sheets (100μm thick) with a reduction area of 98.3% were examined in detail. The thin sheets consisted of elongated and banded grain structures with typical β-fiber (Brass-S-Copper) texture components. Based on electron backscatter diffraction (EBSD), microstructural features such as misorientation measures of the kernel average misorientation (KAM) and grain boundary information of the lattice misorientation angle and axis were characterized. The elongated grains with representative orientations near Copper and S components possessed slightly greater KAM values than those near Brass. During annealing, newly recrystallized grains mainly contained the representative orientations near Copper and S, as opposed to Brass. Low angle grain boundaries (LAGB) observed between the recrystallized and deformed β-fiber grains revealed the occurrence of subgrain growth. The typical recrystallization Cube and Goss textures were also found during annealing. An equi-axed Cube grain growing inside deformed grains with the representative orientation near Copper reveals widespread grain boundary misorientation. An ellipsoidal Goss texture grows up along the two deformed bands with equivalent near-S orientations. One band is mainly consumed by Goss, and the other band prevents it from growing inward by means of grain boundaries with 60∘〈111〉. Various grain boundary misorientations reveal the dynamic evolution of the newly recrystallized grains.

Systematic Investigation into Laser Powder Bed Fusion of Ti-5553 through Single-track and Multi-layer Studies for Tailored Manufacturing Solutions

Laser Powder Bed Fusion (LPBF) is recognized as an appealing fabrication process for producing metallic parts with customized properties. In the current research, a comprehensive approach is employed to systematically correlate single-track and multi-layer fabrication, aiming to generate a reliable process map, assess the effect of process parameters on the properties of LPBF-made Ti-5553, and guide the manufacturing of tailored structures. Based on single-track morphology, melt pool geometry, and multi-layer density, 30 combinations of laser power and scanning speed were categorized into three groups to identify the desirable process parameters. The investigation of single-tracks and multi-layers reveals that deeper melt pools, created with higher energy input, result in a more elongated grain structure, higher α phase content, increased strength and hardness, and reduced ductility. It is observed that achieving higher ductility involves a slight decrease in strength. Specifically, a substantial increase of ∼65% in ductility occurs with only a ∼3.5% reduction in strength. Also, it is found that the volumetric energy density (VED) alone is not sufficient as a design parameter, and the significant process parameters (e.g., laser power and scanning speed) should be considered, as two samples with the same VED yield different properties.

The role of processing temperature for achieving superplastic properties in an Al-3Mg-0.2Sc alloy processed by high-pressure torsion

Experiments were conducted to systematically assess the superplastic properties and the microstructural changes of an Al-3Mg-0.2Sc alloy processed by 10 HPT revolutions at room temperature (RT ≈ 300 K) or at 450 K after subsequent tensile testing at temperatures from 473 to 723 K over a wide range of strain rates. The HPT processing at RT led to the development of elongated grains with an average size of ∼140 nm whereas the grain structures were equiaxed and slightly larger (∼150 nm) after HPT at 450 K. After HPT processing at RT, the Al-Mg-Sc alloy exhibited true superplastic flow at low homologous temperatures and attained a maximum elongation of ∼850 % at 523 K. Nevertheless, the elongations decreased at temperatures T ≥ 623 K and an elongation higher than 400 % was only achieved at 673 K for a strain rate of ε˙ = 4.5 × 10−3 s−1. The material processed by HPT at 450 K displayed superior microstructural stability and substantially higher superplastic ductilities. Elongations of >1100 % were attained at 673 K for strain rates from 3.3 × 10−4 to 1.0 × 10−1 s−1 and a record elongation of ∼1880 % for an HPT-processed metal was achieved at 1.5 × 10−2 s−1 at 673 K. High strain rate superplasticity was also reached for an extended range of temperatures and strain rates. Analysis of the data confirms a stress exponent of ∼2 which is consistent with superplastic flow by grain boundary sliding accommodated by dislocation glide and climb.

Preparation of high-tensile-ductility and high-conductivity alumina dispersion-strengthened copper via a cold spray additive manufacturing-friction stir processing composite process

The solid-state forming capabilities of cold spray additive manufacturing (CSAM) offer a new method for creating nano-reinforced materials. However, the interface of the deposits often fails to form strong metallurgical bonds, leading to mechanical defects that weaken the material. This study investigates the preparation of highly plastic nano-alumina dispersion-strengthened copper by combining CSAM with friction stir processing (FSP), both solid-state techniques. The results show that FSP treatment fuses the interfaces of the deposited particles, transforming the microstructure from multi-scale, elongated grains to a uniform ultrafine-grained (UFG) structure. The average grain size reduces from 3.1 μm to 0.86 μm, and the proportion of high-angle grain boundaries increases from 42.5 % to 85.2 %. This treatment significantly enhances both mechanical and electrical properties. The ultimate tensile strength increases from 210 MPa to 450 MPa, elongation at break improves from 1 % to 35 %, and electrical conductivity rises from 70 % IACS to 81 % IACS. These findings demonstrate the potential of the combined CSAM-FSP approach for producing high-performance nano-alumina dispersion-strengthened copper with superior mechanical and electrical properties.

Oxygen-rich combustion behaviors and mechanisms of a new Ni-Cr-based superalloy fabricated by selective laser melting

The mechanical and combustion behavior of a new Ni-Cr-based superalloy, fabricated by selective laser melting in an atmosphere with an oxygen concentration greater than 99.5 %, was investigated through the analysis of microstructural morphology, elements distribution and combustion kinetics. The results show that heat treatment eliminated the anisotropy of the as-built microstructures and improved the tensile strength. The studied superalloy can be ignited with a combustion threshold of about 2.5 MPa–3 MPa. The burning length and burning rate increase with the increase of pressure. The selective combustion of Al, Ti, Nb, Cr, Fe, Mo, and Cu elements occurred, resulting in the dissolution of γ′, γ", and δ precipitates and formation of holes at the grain boundaries in the heat-affected zone. The microstructures exhibit large elongated grains in the melting zone and column grains in the heat-affected zone along the heat dissipation direction. The combustion products are a mixture of oxides exhibiting dendritic structures in terms of selective combustion, density, and melting point. The findings from this study enhance our comprehension of the combustion process in nickel-based superalloys, offering valuable data and guidance for the advancement of new oxygen-rich combustion-resistant superalloys.

Understanding process parameter-induced variability for tailoring precipitation behavior, grain structure, and mechanical properties of Al-Mg-Si-Mn alloy during solid-state additive manufacturing

Additive friction stir deposition (AFSD), a solid-state additive manufacturing technique, has excellent industrial application potential, particularly for Al alloys. However, in-depth process parameter-microstructure-property correlations are lacking, especially regarding precipitation behavior. In this work, AFSD of Al-Mg-Si-Mn alloy with various process parameter combinations was performed to understand the variation (by ∼ 70 %) in the nano/microhardness, concerning the precipitation behavior. The low nano/microhardness sample exhibited dissolution of the β” strengthening phase. However, higher nano/microhardness samples showed varying microstructural features with high dislocation density owing to fine-scale pre-β” precipitation and another sample possessed inhomogeneous β” phase distribution and β’ precipitation at the grain boundaries, thus exhibiting reprecipitation during AFSD. The variation in the grain structure was such that the high nano/microhardness samples exhibited large, elongated grains (∼11 to 13 µm) and low recrystallization fractions (∼16 –18 %) suggesting a predominantly non-recrystallized microstructure. Conversely, the lowest nano/microhardness sample exhibited the smallest grain size (∼5 µm) and, a higher recrystallization fraction (∼42 %). These findings demonstrate extensive variation in the precipitation behavior, grain structure, and mechanical properties due to the process parameters. Future applications can leverage this knowledge to tailor the microstructure and mechanical properties based on the identified process parameter combinations.

Short fatigue crack growth and retained austenite in steels processed via quenching and partitioning

Previous research has consistently found that introducing metastable retained austenite (RA) as a second phase retards the failure of steel under fatigue. However, the reasons for this benefit are not understood. Accordingly, the properties of RA most advantageous to resist fatigue are not known. Within this context, this paper examines the interaction between second-phase RA and short fatigue crack growth in a steel processed via quenching and partitioning, using quasi in situ electron backscatter diffraction experiments. Results show that most RA transforms into martensite under the plastic strain surrounding the crack. They also reveal various mechanisms whereby RA transformation delays short fatigue crack propagation; transformation-induced crack closure (TICC), crack deflection and branching, and roughness-induced crack closure (RICC). Crack deflection and branching are driven by a tendency of cracks to propagate towards transformed RA, which is against the previous assumptions in the literature. Furthermore, the impact of crack deflection/branching on retardation is more powerful than that of TICC acting alone. Microstructures including second-phase RA should avoid RA-lean areas and promote elongated RA grains, with relatively large size, and major axis normal to the preferential crack growth direction. Untransformed RA within the plastic zone (i.e. overstabilized) does not contribute to crack retardation.

Microstructure and mechanical properties of cellular (Ti,M)(C,N)-based cermets fabricated by pre-granulation and subsequent vacuum sintering

Cellular (Ti,M)(C,N)-based cermets were fabricated through pre-granulation followed by vacuum sintering. In this study, (Ti,Mo)(C,N) and (Ti,W,Ta)(C,N) solid solutions were utilized as hard phase components in agglomerates. The effects of the (Ti,M)(C,N) powders on the microstructure and mechanical properties of cellular cermets were studied. Cermet A, incorporating (Ti,Mo)(C,N) in the agglomerates, exhibited a cellular microstructure with double-layered agglomerates distributed in the matrix. By contrast, cermet B, which included (Ti,W,Ta)(C,N) in the agglomerates, exhibited a notable contrast between the agglomerates containing irregular elongated grains and the matrix. The mechanical properties of the cellular cermets were analyzed comprehensively in conjunction with the fractal dimension. Compared with cermet A, cermet B exhibited more transgranular fractures within the matrix, with dimples and tearing ridges visible in the agglomerates. Additionally, increased crack deflection, bridging, and bifurcation were observed near the interface, considerably impeding crack propagation. Overall, cermet A with significantly refined grains demonstrated higher hardness and TRS. The fracture morphology and crack propagation in cermet B were more complex and layered, resulting in the enhanced fracture toughness.

Fabrication of high-performance nanostructured CsPbI3/Si perovskite photodetector by pulsed laser deposition: Challenges and prospects

The inorganic perovskite CsPbI3 is a promising material for optoelectronic applications like photodetectors and solar cells due to its suitable bandgap and excellent properties. In this work, nanostructured CsPbI3 thin films were deposited on glass and silicon substrates by pulsed laser deposition (PLD) at laser fluences ranging from 5.7 to 10 J/cm2. Systematic characterization revealed that increasing the laser fluence significantly enhances the crystallinity, phase purity, optical emission intensity, charge carrier concentration (up to 1.38 × 1012 cm−3), and mobility (up to 164.7 cm2/Vs) of the CsPbI3 films. An optimal laser fluence of 10 J/cm2 resulted in large, elongated grains over 280 nm, tightly packed films with minimal defects, and a suitable bandgap of 1.83 eV CsPbI3/Si heterojunction photodetectors were fabricated, with the device made at 8.5 J/cm2 exhibiting maximum responsivity of 8 A/W at 600 nm, detectivity exceeding 1014 Jones, external quantum efficiency up to 17.5 × 102 %, and a high ON/OFF ratio of 225 under illumination. The photodetector performance was strongly correlated with the optimized structural order, morphology, and optoelectronic quality achieved by careful control of the laser fluence during PLD. This work highlights PLD as an effective technique for realizing high-quality CsPbI3 films with tailored properties for advanced photodetection and photovoltaic applications.

Powder Bed Fusion-Laser Beam of IN939: The Effect of Process Parameters on the Relative Density, Defect Formation, Surface Roughness and Microstructure.

This study investigates the effects of process parameters in the powder bed fusion-laser beam (PBF-LB) process on IN939 samples. The parameters examined include laser power (160, 180, and 200 W), laser scanning speed (400, 800, and 1200 mm/s), and hatch distance (50, 80, and 110 μm). The study focuses on how these parameters affect surface roughness, relative density, defect formation, and the microstructure of the samples. Surface roughness analysis revealed that the average surface roughness (Sa) values of the sample ranged from 4.6 μm to 9.5 μm, while the average height difference (Sz) varied from 78.7 μm to 176.7 μm. Furthermore, increasing the hatch distance from 50 μm to 110 μm while maintaining constant laser power and scanning speed led to a decrease in surface roughness. Relative density analysis indicated that the highest relative density was 99.35%, and the lowest was 93.56%. Additionally, the average porosity values were calculated, with the lowest being 0.06% and the highest reaching 9.18%. Although some samples had identical average porosity values, they differed in porosity/mm2 and average Feret size. Variations in relative density and average porosity were noted in samples with the same volumetric energy density (VED) due to different process parameters. High VED led to large, irregular pores in several samples. Microcracks, less than 50 μm in length, were present, indicating solidification cracks. The microstructural analysis of the XZ planes revealed arc-shaped melt pools, columnar elongated grains aligned with the build direction, and cellular structures with columnar dendrites. This study provides insights for optimizing PBF-LB process parameters to enhance the quality of IN939 components.

Microstructure, Mechanical, and Corrosion Performance of AA4343/AA3003/AA4343 Laminated Sheets Subjected to Cryorolling and Annealing

The effects of cryorolling (CR), hot rolling (HR), and different annealing temperatures on the microstructure, mechanical, and corrosion performance of AA4343/AA3003/AA4343 laminated sheets are studied. Compared with the HR samples, the microstructure of the CR samples presents a significant decrease in the size of elongated grains and significantly large second‐phase particles Al(Mn, Fe)Si in the AA3003 alloy. Grains in CR samples subjected annealing at 200–300 °C become finer. Increasing to 400–550 °C, the grains begin to grow, and the Si is diffused into the core layer. A comparison of HR and CR processing reveals a significant increase in the yield strength from 153 to 209 MPa and the ultimate tensile strength from 168 MPa to 217 MPa of the laminated sheet. Potentiodynamic polarization measurements and immersion tests are conducted to assess the corrosion morphology. After being immersed in a 3.5% NaCl solution for two weeks, the clad surface of the laminated sheet exhibits uniform corrosion products and pitting corrosion, which shows the pitting corrosion depth of the CR sample improved compared to the HR sample. The study suggests that both CR and annealing can be useful for enhancing the mechanical properties, and corrosion morphology of laminated sheets.

Strong and tough 3D-(SiC–Si3N4)/Al co-continuous composite with enhanced interfaces

Materials with high specific strength and toughness are urgently needed in the fields of electronic packaging, armor, and aerospace. SiC/Al composites show good potential for these applications but the problem of mutual exclusion of strength and toughness still needs to be solved. Herein, we propose a new strategy to simultaneously enhance its strength and toughness from the perspective of structural optimization and interface enhancement. Inspired by the nacre structure, a 3D-(SiC–Si3N4)/Al co-continuous composite was prepared by freeze-casting combined with the pressure infiltration method. During the process, elongated Si3N4 grains were introduced into the ceramic framework to design the internal lamella wall structure and increase the contact area with the aluminum substrate. Moreover, a favorable interfacial bonding was designed between Si3N4 and Al to improve interface wettability. The reliable microstructure of porous 3D-(SiC–Si3N4) preform was tailored through the adjustment of initial solid loading and the α-Si3N4 component. The effects of initial solid loading and the α-Si3N4 component on the microstructure, interfacial wettability, and mechanical properties of the final composites were investigated. The results showed that the SiC–Si3N4/Al composites possess high flexural strength (769 MPa) and fracture toughness (15.1 MPa m1/2), which is superior to data reported in general literature. Numerous elongated β-Si3N4 grains are produced on the ceramic skeleton, forming an interlocking structure with the aluminum matrix, which increases the contact area with the aluminum substrate. A chemical reaction layer was formed at the interface of the composite, greatly improving the interfacial bonding strength. This work provides a promising design guideline for developing and optimizing high-strength and tough composite.

Research and Analysis of TC4 Titanium Alloy Cutting Based on Crystal Plasticity Theory

Abstract Based on the crystal plasticity theory, the changes in TC4 titanium alloy before and after cutting, especially the changes in cutting forces, chip temperature, morphology, and quality, were analyzed in this study. Initially, a polycrystalline plasticity model for the TC4 titanium alloy was established. Following that, a crystal plasticity polycrystal finite element cutting simulation model is developed to perform cutting simulations. This model represents the mechanical behavior of the micro grains of TC4 titanium alloy during the deformation and cutting processes. Further, it validates the internal grain plastic deformation and the effect on the metallography of TC4 titanium alloy before and after cutting. The results show a good consistency between experimental and simulation data. The grain size increases gradually from the center to the edge of the cutting area, with the phenomenon of equiaxed grains becoming more apparent, leading to the formation of elongated fine grains. During the cutting process, grains interlock and fracture, exhibiting strong anisotropy.

Structural and dielectric properties of Eu3+,B3+ co-doped CoNb2O6 ceramic

The boron co-doped CoNb2O6:xEu3+, yB3+ (x=1, 3, 6, 9, 12 mol%, y=10 mol%) ceramics were obtained by the molten salt method, which has advantageous properties such as short reaction time, low sintering temperature, improved homogeneity, and crystallinity. The ceramic samples were examined by structural and dielectric analyses. In X-ray diffractions, the orthorhombic columbite type CoNb2O6 structure was obtained, and also a minor EuNbO4 phase was detected with increasing Eu3+ doping concentrations. Additionally, increasing Eu3+ concentration led to a slight increase in crystallite size, and two theta peak shifts occurred towards higher angles associated with shrinkage in the lattice or reduction in the lattice constant. In SEM examinations, a slight increase was observed in grain sizes from 1 to 9 mol% Eu3+ in the range of 1-30 m, while some decrease occurred in grain sizes at 12 mol%, and there was an evident increase in plate-shaped and elongated grains. The dielectric constant (ε') of the ceramic samples increased with increasing Eu3+ concentration and reached approximately 35 and 0.24 at 20 Hz for 9 mol% Eu3+, respectively. The increase in dielectric loss with increasing Eu3+ was associated with an increase in ionic conductivity, in which Eu3+ substitution does not suppress oxygen vacancies or make them more ordered.

Improvement in Grain Size Distribution Uniformity for Nuclear-Grade Austenitic Stainless Steel through Thermomechanical Treatment.

In this work, thermomechanical treatment (single-pass rolling at 800 °C and solution treatment) was applied to nuclear-grade hot-rolled austenitic stainless steel to eliminate the mixed grain induced by the uneven hot-rolled microstructure. By employing high-temperature laser scanning confocal microscopy, microstructure evolution during solution treatment was observed in situ, and the effect of single-pass rolling reduction on it was investigated. In uneven hot-rolled microstructure, the millimeter-grade elongated grains (MEGs) possessed an extremely large size and a high Schmid factor for slip compared to the fine grains, which led to greater plastic deformation and increased dislocation density and deformation energy storage during single-pass rolling. During subsequent solution treatment, there were fewer nucleation sites for the new grain, and the grain boundary (GB) was the main nucleation site in MEGs at a lower rolling reduction. In contrast, at a higher reduction, increased uniformly distributed rolling deformation and more nucleation sites were developed in MEGs. As the reduction increased, the number of in-grain nucleation sites gradually exceeded that of GB nucleation sites, and in-grain nucleation preferentially occurred. This was beneficial for promoting the refinement of new recrystallized grains and a reduction in the size difference of new grains during recrystallization. The single-pass rolling reduction of 15-20% can effectively increase the nucleation sites and improve the uniformity of rolling deformation distribution in the MEGs, promote in-grain nucleation, and finally refine the abnormally coarse elongated grain, and eliminate the mixed-grain structure after solution treatment.

Mechanical Properties and Microstructural Evolution of 6082 Aluminum Alloy with Different Heat Treatment Methods

The influence of solid solution treatment (SST), artificial aging treatment (AAT), and deep cryogenic-aging treatment (DCAT) on the mechanical properties and microstructure evolution of 6082 aluminum alloy was investigated. The tensile test was performed to obtain the true stress–strain curves through an electronic universal testing machine. The results show that the yield strengths of the SST specimens in all three directions are the lowest, of less than 200 MPa. In addition, the maximum elongation of the SST specimen is over 16% and the value of in-plane anisotropy (IPA) is 5.40%. For the AAT specimen, the yield strengths of the AAT alloy in three directions have distinct improvements, which are beyond 340 MPa. However, the maximum elongation and the IPA were evidently reduced. The yield strength and elongation of the DCAT alloy exhibit a slight enhancement compared with those in the AAT condition, and the corresponding IPA is 0.61%. The studied alloy specimens in all conditions exhibit ductile fracture. The DCAT alloy has the highest density of precipitates with the smallest size. Therefore, the dislocation pinning effect of the DCAT specimens are the strongest, which exhibit the highest yield strength accordingly. In addition, the uniformly distributed precipitates in the matrix with a large ratio of long and short axes can suppress the anisotropy caused by elongated grains.

Revealing the inhomogeneous nature of microstructure and texture evolution in the cold-rolled CoCrFeMnNi alloy during static recrystallization

In the present investigation, equiatomic CoCrFeMnNi high entropy alloy (HEA) was subjected to 80% cold rolling (as-rolled) followed by isothermal annealing treatment at 700 °C for different time periods. Microstructural characterization was performed using electron back-scattered diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques on the as-rolled and annealed samples. The as-rolled microstructure consisted of elongated grains mainly composed of strong α-fiber and weak γ-fiber textures. The as-rolled sample showed the formation of ingrain SBs in the γ-fiber grains, which served as preferential sites for grain nucleation. The annealing treatment of as-rolled samples at 700 °C cause static recovery (SRV) before 5 minutes of heat-treatment, whereas static recrystallization (SRX) was observed after 5 minutes of heat-treatment in the CoCrFeMnNi alloy samples. A faster rate of recrystallization kinetics was observed after 15 minutes of heat-treatment. The annealing treatment reduced the intensity of α-fiber and enhanced the Copper, Cube and P ({011}<122>) texture components. Copper components originated from coarse recrystallized grains, which were the results of localized grain growth phenomena. Unusual behavior of banded featured α-fiber grains was observed during the annealing process. These banded grains in the partially annealed samples consisted of subgrain-boundaries and showed a delayed response to recrystallization as compared to grains with other orientations. Stored energy (SE) and Taylor factor (M) calculations were also used to understand the delayed recrystallization response of the banded featured/retained deformed grains. The microhardness value of the as-rolled sample was approximately 450 Hv, which decreased to around 230 Hv for the fully recrystallized grains.

Microstructure, tensile strength, and hardness of AA5024 modified with ZrH4 additions produced by laser powder bed fusion

This work investigates the effect of ZrH4 additions on a commercial AA5024 aluminum alloy produced via Laser Powder Bed Fusion (L-PBF) where pre-mixed powders of AA5024 and ZrH4 were used. The microstructure was characterized using light and scanning electron microscopy assisted by energy-dispersive X-ray spectroscopy, and electron backscattered diffraction. The mechanical properties were evaluated by hardness and tensile measurements. The ZrH4 additions modify the microstructure. Regions without particles originate the large and elongated grains, while regions with undissolved ZrH4 or formed particles during solidification originate a fine equiaxed microstructure. The fine-grained region is typically located at the boundary of the melt pools, while the coarse-grained region is formed within the melt pools. There is substantial grain refinement with additions higher than 2.0 wt% ZrH4, nearly eliminating the coarse-grained region. The grain size does not differ in the fine-grained region for the different ZrH4, cross-sections (perpendicular or along the printing direction), or printing parameters. The 〈110〉 crystallographic fiber texture is identified, and a few particular texture components are more pronounced, such as the Cube {001} 〈100〉, the rotated Cube {001} 〈110〉, the Goss {011} 〈001〉, and Z {111} < 110>. Low texture index values are obtained in the fine-grained region, indicating the highly isotropic microstructure. The hardness and tensile strength increase with the increase in ZrH4 content for the as-built condition. A saturation in tensile strength is reached after 1.0 wt% ZrH4 additions.

Microstructure characteristics of the 2A50 aluminum alloy in radial forging and isothermal treatment conditions

A novel recrystallization and partial melting process combined radial forging was proposed to prepare long axial 2A50 aluminum alloy semi-solid billets. Microstructure characteristics of the forged and isothermal treated samples were investigated. Results demonstrate that initial elongated grains (fibrous structure) and low angle grain boundaries were substituted by spherical equiaxed grains and high angle grain boundaries when the sample was heated at 585 °C for 10 min. Deformed textures of the forged 2A50 aluminum alloy were remarkably weaken after isothermal treatment. The average grain size and shape factor increased with the increased temperature and holding time. Long holding time resulted in some dendrites. The liquid films at the grain boundaries thickened with the increase in temperature and holding time. Grains growth and spheroidization were determined by coarsening and Ostwald ripening mechanisms. The coarsening rate constant k of grains at 575 °C was 378.5 μm3/s.

МАТЕМАТИЧНА МОДЕЛЬ ВПЛИВУ ПОВОРОТУ ВИДОВЖЕНИХ ЗЕРЕН НА ПРОЦЕС ВИСОКОТЕМПЕРАТУРНОГО ДЕФОРМУВАННЯ КЕРАМІКИ НА ОСНОВІ НІТРИДУ КРЕМНІЮ

The speed of direct high-temperature extrusion of ceramics based on silicon nitride was analyzed. The influence of rotation of elongated grains on mass transfer processes and deformation rate is established. The influence of the parameters of the high-temperature deformation process on the deformation rate is shown. An equation is proposed that describes the effect of rotation of elongated grains on the strain rate. The described equation of strain rate can be used to create technological processes of plastic deformation of ceramic materials.