Misoriented 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.

Modelling freckles and spurious grain formation in directionally solidified superalloy castings

Segregation channels with misoriented spurious grains, known as freckles, are an unacceptable casting defect in superalloy turbine blades. A digital-twin method to predict segregation channels was proposed in our previous studies; however, the formation of spurious grains was ignored. Here, we extend the digital twin methodology by incorporating dendrite fragmentation, which is recognized as the predominant mechanism in the formation of spurious grains. The flow-induced fragmentation process has been refined to account for the timing of dendrite pinch-off. A three-phase mixed columnar-equiaxed solidification model was used to track the motion of the crystal fragments. Directional solidification experiments for superalloy casting were conducted in an industrial-scale Bridgman furnace, and the distribution of spurious grains in the freckles was metallographically analysed. Excellent simulation-experiment-agreement was achieved. Based on this study, the formation of spurious grains within the segregation channels is mainly caused by the flow-driven fragmentation mechanism. Experimentally measured freckles can be reproduced only if the timing of the dendrite pinch-off is considered.

Misorientation Angle Study on Cleavage Fracture Propagation Surfaces of a Grade a Ship Steel, through Charpy and Four-Point Double-Notch Bend Tests

Misorientation Angle Study on Cleavage Fracture Propagation Surfaces of a Grade a Ship Steel, through Charpy and Four-Point Double-Notch Bend Tests

Flexible nanoimprint lithography enables high-throughput manufacturing of bioinspired microstructures on warped substrates for efficient III-nitride optoelectronic devices

III-nitride materials are of great importance in the development of modern optoelectronics, but they have been limited over years by low light utilization rate and high dislocation densities in heteroepitaxial films grown on foreign substrate with limited refractive index contrast and large lattice mismatches. Here, we demonstrate a paradigm of high-throughput manufacturing bioinspired microstructures on warped substrates by flexible nanoimprint lithography for promoting the light extraction capability. We design a flexible nanoimprinting mold of copolymer and a two-step etching process that enable high-efficiency fabrication of nanoimprinted compound-eye-like Al2O3 microstructure (NCAM) and nanoimprinted compound-eye-like SiO2 microstructure (NCSM) template, achieving a 6.4-fold increase in throughput and 25% savings in economic costs over stepper projection lithography. Compared to NCAM template, we find that the NCSM template can not only improve the light extraction capability, but also modulate the morphology of AlN nucleation layer and reduce the formation of misoriented GaN grains on the inclined sidewall of microstructures, which suppresses the dislocations generated during coalescence, resulting in 40% reduction in dislocation density. This study provides a low-cost, high-quality, and high-throughput solution for manufacturing microstructures on warped surfaces of III-nitride optoelectronic devices.

Misorientation of Grains in Fatigue of Harmonic Structured Steel Observed by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation

Misorientation of Grains in Fatigue of Harmonic Structured Steel Observed by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation

Three-dimensional configuration of crystal plasticity in stainless steel assessed by high resolution digital image correlation and confocal microscopy

In polycrystalline austenitic stainless steels, a comprehensive three-dimensional configuration of crystal plasticity in relation to microstructure is required to elucidate the deformation behaviors during mechanical loading. In the present work, a combination of backscattered electron image (BSE) based high-resolution digital image correlation (HR-DIC) and laser scanning confocal microscopy (LSCM) was employed to simultaneously investigate in-plane and out-of-plane deformations at the sub-grain scale in 316 stainless steel. The high spatial resolution and precise alignment provided by the three-dimensional deformation assessment enable the identification of specific slip and twinning systems. This is achieved through the minimization of the residual L2 norm between the in-plane components of experimental and theoretical strain tensors. Dominant slip and few mechanical twinning activities are initiated at the early-stage of yielding, and their frequency and intensity increase with the applied load. The hierarchical networks formed by nanotwins, along with the presence of grain and annealing twin boundaries, serve as obstacles for slip glide, leading to substantial twin–slip interaction and grain boundary strengthening. As a consequence of wide mechanical twins formed by parallel nanotwins coalescence and strain localization at the twin boundary, slip transmission occurs, resulting in an effective accommodation of external stress. Furthermore, the consistent observation of out-of-plane roughness, in alignment with twinning Burgers vector predictions, offers valuable insights into the significant deformation gradient occurring in the vicinity of boundaries. This deformation gradient is influenced by the neighboring mechanical twinning activities, indicating strong obstacle to twin transmission and high back-stresses resulting from the highly misoriented grain boundary.

Solidification Crack Free Welding Strategy via Ultra High Precision Laser Scanning at a Single Grain of Directionally Solidified and Single Crystal Superalloys

In this study, possibility of solidification crack-free welding of directionally solidified CM247LC and single crystal CMSX-4 superalloys was metallurgically investigated using single-mode fiber laser scanning. The key metallurgical factors of solidification cracking have been identified as the formation of highly misoriented solidification grain boundaries (low level of epitaxial growth behavior) at the fusion zone that affects the repulsive force between two adjacent dendrites and dendrite coalescence undercooling at the terminal stage of weld solidification. In particular, under extremely low heat input and ultra-high-speed laser beam scan conditions (welding speed: 1,000 mm/s, heat input: 2 J/mm, and energy density: 65 J/mm<sup>2</sup>), an effective fusion zone could be achieved within a single directionally solidified grain of CM247LC alloy owing to the characteristics of single-mode fiber laser. The fusion zone successfully showed a 99.9% of epitaxial growth achievement ratio (that is, low fraction of highly misoriented solidification grain boundaries at the fusion zone) without solidification cracking. Based on these results on CM247LC alloy, solidification crack-free welds could be successfully achieved using quadruple-pass and square-type weld geometries.

A phenomenological understanding of the novel design of hierarchical structure for 1 GPa ultrahigh strength and high toughness combination low alloy steel

In the present study we propose a novel design of hierarchical structure with the aim to obtain high strength of 1 GPa and low temperature toughness in a heavy low alloy steel plate by intercritical quenching and tempering (IQ&T). The hierarchical microstructure consisted of bimodal prior austenite grains with complex microstructure obtained via intercritical quenching from 810 °C and tempering at 500 °C. The large size grains with average diameter of ∼22 μm consisted of tempered martensite and fine intercritical ferrite. While the surrounding fine grains with average diameter of ∼12 μm consisted of tempered lower bainite and tempered lath martensite. Ultra-high yield strength of 998 MPa and tensile strength of 1059 MPa were obtained for the novel hierarchical microstructure steel, which was similar to the conventional quenched and tempered (Q&T) steel. Whereas, the low temperature impact energies at both −40 and −80 °C were ∼100% higher for the hierarchical microstructure steel than the conventional Q&T steel. The significant improvement of low temperature toughness is attributed to the synergistical effect of hierarchical microstructure. The fine intercritical ferrite in large grains increased the plastic deformation ability during impact and was beneficial for formation of dimples, and the surrounding fine grains offered high density of large mis-orientation grain boundaries to deflect crack propagation, leading to high impact energy at low temperature.

Crystal plasticity-based analysis and modelling of grain size and strain path dependent micro-scaled deformation mechanisms of ultra-thin sheet metals

Multi-stage microforming is increasingly used in manufacturing of the miniaturized parts with complex structures and geometries. Optimization design of this type of manufacturing process, however, is still challenging due to its unknown intrinsic nature of the process. In the multi-stage deformation and microforming, the size effect (SE), the strain path change (SPC), and the intragranularly misoriented grain boundary (IMGB) generated in previous forming stage, are the main factors governing the deformation behaviors of ultra-thin sheets. To gain thorough insights into their influences on deformation and elucidate the associated micro-scaled mechanisms, SS 316L ultra-thin sheets with the thickness of 0.1 mm and different mean grain sizes (d¯) were used for two-stage tensile tests under the conditions with distinct pre-strain εpre and intersection angle θSPC (the angle between the previous loading direction and subsequent one). Mechanical tests reveal that increasing εpre and θSPC reduces the yield stress and hardening rate in SPC tension, but this reduction gets smaller after increasing d¯. This is because more IMGBs with complex pattern are formed in relatively large grains, raising the permanent deformation resistance inside grains in subsequent tension. To model the IMGB-induced hardening, the SPC-induced softening, and the SE-induced concurrent facilitations to the hardening and softening, an enhanced crystal plasticity constitutive relation was established. The physical essence that IMGB obstructs dislocation movement, is used to model the IMGB-induced hardening based on the interactions between the main slip planes and IMGBs. The hardening facilitation caused by increasing grain size is implicitly incorporated in determining the saturated slip resistance. Modelling of the SPC-induced softening is based on the high Schmid factor grain fraction and its influences are governed by pre-strain and the defined SPC parameter. The softening facilitation caused by coarsening grains is modelled in establishing the initial slip resistance in SPC deformation. The proposed simulation procedure and constitutive relationship help with accurately predicting the mechanical response and microstructure evolution in micro-scaled SPC deformation, and also provide a basis for modelling and design of the multi-stage microforming of complex miniaturized parts.

A theoretical and deep learning hybrid model for predicting surface roughness of diamond-turned polycrystalline materials

Polycrystalline materials are extensively employed in industry. Its surface roughness significantly affects the working performance. Material defects, particularly grain boundaries, have a great impact on the achieved surface roughness of polycrystalline materials. However, it is difficult to establish a purely theoretical model for surface roughness with consideration of the grain boundary effect using conventional analytical methods. In this work, a theoretical and deep learning hybrid model for predicting the surface roughness of diamond-turned polycrystalline materials is proposed. The kinematic–dynamic roughness component in relation to the tool profile duplication effect, work material plastic side flow, relative vibration between the diamond tool and workpiece, etc, is theoretically calculated. The material-defect roughness component is modeled with a cascade forward neural network. In the neural network, the ratio of maximum undeformed chip thickness to cutting edge radius R TS, work material properties (misorientation angle θ g and grain size d g), and spindle rotation speed n s are configured as input variables. The material-defect roughness component is set as the output variable. To validate the developed model, polycrystalline copper with a gradient distribution of grains prepared by friction stir processing is machined with various processing parameters and different diamond tools. Compared with the previously developed model, obvious improvement in the prediction accuracy is observed with this hybrid prediction model. Based on this model, the influences of different factors on the surface roughness of polycrystalline materials are discussed. The influencing mechanism of the misorientation angle and grain size is quantitatively analyzed. Two fracture modes, including transcrystalline and intercrystalline fractures at different R TS values, are observed. Meanwhile, optimal processing parameters are obtained with a simulated annealing algorithm. Cutting experiments are performed with the optimal parameters, and a flat surface finish with Sa 1.314 nm is finally achieved. The developed model and corresponding new findings in this work are beneficial for accurately predicting the surface roughness of polycrystalline materials and understanding the impacting mechanism of material defects in diamond turning.

Influence of Flank Wear on the Microstructure Characteristics of the GH4169 Metamorphic Layer under High-Pressure Cooling.

Since the flank has an important influence on the surface of a workpiece, and as microstructure flaws of the surface metamorphic layer are a key factor that affects the service performance of a part, this work studied the influence of flank wear on the microstructure characteristics of the metamorphic layer under the conditions of high-pressure cooling. First, Third Wave AdvantEdge was used to create a simulation model of cutting GH4169 using tools with different flank wears under high-pressure cooling. The simulation findings emphasized the impact of flank wear width (VB) on the cutting force, cutting temperature, plastic strain, and strain rate. Second, an experimental platform was established for cutting GH4169 under high-pressure cooling, and the cutting force during the machining process was recorded in real time and compared with the simulation results. Finally, an optical microscope was used to observe the metallographic structure of the GH4169 workpiece section. The microstructure characteristics of the workpiece were analyzed using a scanning electron microscope (SEM) and electron backscattered diffraction (EBSD). It was discovered that, as the flank wear width increased, so did the cutting force, cutting temperature, plastic strain, strain rate, and plastic deformation depth. The relative error between the simulation results of the cutting force and the experimental results was within 15%. At the same time, near the surface of the workpiece, there was a metamorphic layer with fuzzy grain boundaries and refined grain. With an increase in flank wear width, the thickness of the metamorphic layer increased from 4.5 μm to 8.7 μm and the grain refinement intensified. The high strain rate promoted recrystallization, which caused an increase in the average grain boundary misorientation and high-angle grain boundaries, as well as a reduction in twin boundaries.

Liquation crack-free welding strategy for 247LC DS superalloy by control of pipeline diffusion via ultra-high-speed laser beam scanning

Under completely suppressed constitutional liquation of MC carbide, unexplored 247LC superalloy single-mode fibre laser welds experience unexpected liquation cracking. These cracks continuously propagate from a solidification crack, particularly at highly misoriented and epitaxially grown solidification grain boundaries, and dominated by pipeline diffusion of impurities. Two novel metallurgical preconditions were identified which, if satisfied, ensure complete suppression of liquation cracking of 247LC superalloy welds. These preconditions are (i) the constitutional liquation of MC carbide at the heat-affected zone and (ii) pipeline diffusion of impurities at the fusion zone. It is also highly recommended that the welding is carried out in a single directionally solidified grain under scanning conditions, avoiding the formation of highly misoriented solidification grain boundaries.

Microstructure-based intergranular fatigue crack nucleation model: Dislocation transmission versus grain boundary cracking

Intergranular fatigue crack nucleation has been reported to occur commonly at high angle grain boundaries (HAGBs) but seldom at low angle GBs (LAGBs) during persistent slip band (PSB)-GB interactions. However, the mechanistic understanding of the role of GB misorientation angles in affecting the GB fatigue cracking remains limited due to the lack of quantitative descriptions. Here a theoretical framework based on the competition between dislocation transmission across GB and GB cracking is established for investigating the GB fatigue crack nucleation. We show that, HAGBs usually provide higher resistances to dislocation transmissions compared with LAGBs, causing a more significant dislocation pile-up and stress concentration, which facilitates the GB crack nucleation. But the quantitative analysis indicates that even at HAGBs with poor plastic compatibility, the critical stress of GB cracking is much larger than the critical transmission stress. This demonstrates the crucial role of GB fatigue damage accumulation, which is associated with PSB extrusion growth, in promoting GB crack nucleation. In this study, the critical stress of dislocation transmission is derived in terms of the energy balance, and the nucleation criterion of GB crack is formulated using the fracture theory, both of which display the dependence on GB misorientation angles and grain sizes. It is found that the GB fatigue cracks preferentially nucleate at HAGBs with poor plastic compatibility and large grain sizes. The competition between dislocation transmission and GB cracking at varying fatigue cycles are also discussed. This theoretical framework offers quantitative analyses for the GB crack nucleation during PSB–GB interactions, clarifies the role of microstructures in affecting the critical cycles of GB cracking, and might offer important guidelines for designing fatigue-resistant metallic materials.

Formation of locked-lamellar grains in a slightly hypoeutectic Al-Al2Cu alloy during thin-sample directional solidification

We studied the formation and growth of locked-lamellar microstructures in a thin sample of a slightly hypoeutectic Al-Al2Cu alloy. The coupled-growth dynamics, including early stages and steady-state regimes, was observed optically in real time during directional solidification. The orientation of the α (Al) and θ (Al2Cu) crystals was measured ex situ in a series of eutectic grains by X-ray Laue microdiffraction. A nucleation event of a θ crystal on a pre-existing α crystal, and the subsequent growth of a eutectic grain with a type-C orientation relationship, that is, with a coincidence of {123}-α and {100}-θ planes, were observed in situ. In type-C eutectic grains, lamellar locking occurred parallel to the low-energy coincidence plane. A regular (floating) coupled-growth dynamics was observed in misoriented eutectic grains.

EBSD analysis of spark plasma sintered SS316-B4C composite

The Electron Backscatter Diffraction (EBSD) method has been characterized as a potential tool for analysing the microstructural changes that occur during the sintering processes and it possesses the ability to depict misorientation diagrams, pole figures and grain size distribution. The present work focuses on observing the microstructure evolution of the prepared 316 stainless steel with 10 wt% of B4C samples sintered at the temperatures of 800, 900, and 1000 °C using the Spark Plasma Sintering (SPS) method. The samples are in the equiaxed form of recrystallized grains and they are elongated. Further, the samples sintered at 900 °C are equally recrystallized compared to other samples sintered at 800 and 1000 °C, where the microstructure is partially recrystallized with a high fraction. The result is explicable, by increasing the carbon content it causes the reduction of grain boundaries as well as decreases the migration rate of twin boundary generation. Hence, twin character loss is accelerated by the increase of carbon content with low-angle boundaries, and because of the typical drag effect, it has been discovered that the dynamically recrystallized grain size is reduced. The partitioning of these microstructures is done to differentiate the sintered sample and the recrystallized grains, based on the Grain Orientation Spread (GOS) map. The experimental investigation has suggested that the samples sintered at 900 °C has a more favourable microstructure analysis than the other samples sintered at 800 °C and 1000 °C, respectively.

Molten pool effect on mechanical properties in a selective laser melting 316 L stainless steel at high-velocity deformation

Microstructural modification for the molten pool can improve mechanical properties of the selective laser melting 316 L stainless steel (SLM 316 L SS) at high-velocity deformation and can promote application of the SLM 316 L SS in the field of high-velocity deformation. Mechanical properties of the SLM 316 L SS with different volumetric energy densities (VED) were obtained at high-velocity deformation by using a split Hopkinson pressure bar (SHPB). With strain rate increased, compressive strength of the SLM 316 L SS peaked at the strain rates of 1200 s −1 - 1450 s −1 . Analyzed molten pool and mechanical properties of SLM 316 L SS at the strain rate of 1200 s −1 - 1450 s −1 , the SLM 316 L SS with volumetric energy density of 145.83 J/mm 3 had a combination of minimum overlap ratio of molten pool and maximum single pass molten pool width, which brought maximum pool size and exhibited excellent impact energy and compressive strengths, reaching 1185 MPa and 125.4 MJ/m 3 , respectively. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize molten pools of the SLM 316 L SS. Microcracks appear along molten pool boundaries of the failed specimens was found and poor deformation coordination ability due to the misorientation of grains on both sides of molten pool boundaries makes the molten pool boundary as the weak region. Overlap ratio of the molten pool and theoretical width of the single pass molten pool are considered to be main factors in determining the molten pool size, which in turn determines mechanical properties of the SLM 316 L SS at high-velocity deformation. Further, in the process of dynamic compression deformation, microcracks were formed at the molten pool boundary, which lead to failure of the SLM 316 L SS. • Strain rate sensitive index of the SLM 316 L SS changes from positive to negative. • Failure of the molten pool boundary leads to the instability flow. • Molten pool size has a major effect on mechanical properties of the SLM 316 L SS. • Deformation band across cellular structure was found at high-velocity deformation. • Damage of the molten pool boundary is the main failure mechanism.

Evolution of superconductivity dependence on substrate temperature with thickness of Fe(Se,Te) coated conductors deposited on metal tapes

Fe(Se,Te) films of different thicknesses were deposited on metal tapes by pulsed laser deposition at different substrate temperatures. It is found that the substrate temperature dependence of superconductivity changes with the Fe(Se,Te) film thickness. When fabricating thin Fe(Se,Te) films with a thickness of about 150 nm, moderate substrate temperatures are conducive to balancing the influence of texture and stoichiometry on superconductivity, contributing to the obtainment of good superconductivity. When the Fe(Se,Te) films’ thickness is about 300 nm, the optimal substrate temperatures are lowered due to the determination of film superconductivity by the inhomogeneity of longitudinal chalcogen distribution via the cooperation of Te loss in the long-term-ablated target and the attraction of metal ions in the buffer layer. In addition, with a further increase in thickness from 300 to 600 nm, the self-field critical current of thick Fe(Se,Te) films continuously increases, but the critical current density increases first and then decreases, which is thought to be a result of the misoriented grains or non-superconducting phase due to the large deviation between the actual deposition temperature and the set substrate temperature, and the Se excess in the film. In addition, the 450-nm-thick Fe(Se,Te) film exhibits excellent self-field and in-field performances at 4.2 K: 1.308 MA/cm2 at self-field and over 0.5 MA/cm2 at 9 T. Point pinning, which is the local lattice disturbance randomly distributed in the film observed by transmission electron microscopy, dominates over the entire temperature range.

Superplasticity of a friction stir processed overaged WE54 magnesium alloy

• The coarse-grained overaged WE54 alloy was refined to 1 µm by severe FSP. • Thus, deformation mechanism at high temperature changed from solute-drag creep to GBS. • Comparison of Mg alloys showed that heavier solutes give less superplastic response. • The accommodation process for GBS is hindered by low solute diffusion rates. The coarse-grained WE54 magnesium alloy was heat treated in order to have minimum hardness minimizing the effects of precipitates and solid solution. Friction stir processing (FSP) was applied in severe conditions to obtain fine, equiaxed and highly misoriented grains, with grain sizes even less than 1 µm. The high severity of processing demonstrated to have a strong impact in the microstructure. Consequently, the processed materials exhibited excellent superplasticity at the high strain rate 10 −2 s −1 , and temperatures between 300 and 400 ºC. The maximum tensile superplastic elongation of 756% was achieved at 400 ºC thanks to the operation of grain boundary sliding mechanism (GBS). Besides the new data obtained through tensile testing, the paper deals with a transcendental question regarding the large differences in strain rate values at a given stress in the superplastic regime at maximum elongation compared to other magnesium-based alloys. With this is mind, 19 magnesium alloys from 22 different investigations were analyzed to give some light to this behavior that never was treated before. It is proposed that this behavior has to be attributed to the accommodation process, necessary for GBS to occur, which is hindered by reinforcing solutes.

Influence of structural properties on the ferroelectric behavior of hexagonal AlScN

The direct impact of structural quality on the ferroelectric properties of hexagonal Al1–xScxN with an Sc-content of x = 0.3 was investigated using dynamic hysteresis measurements, high-resolution x-ray diffraction (HRXRD), and atomic force microscopy. The films investigated were deposited on p-doped (001)-Si substrates by reactive pulsed DC magnetron sputtering under different gas mixtures to vary the structural quality and surface morphology between samples. Misoriented grains were identified as ferroelectrically inactive, as these grains resulted in an underestimation and distortion of the ferroelectric quantities. In fact, a high amount of misoriented volume was found to have a significant effect on the coercive electric field, as this is mainly determined by the crystal strain in the ferroelectric [0001]-oriented regions, independent of its origin. Furthermore, it was concluded that the crystal quality does not have a pronounced effect on the coercive field strength. Conversely, the polarization in the film is mainly determined by the crystal quality, as a difference of 1° in the HRXRD FWHM of the ω-scan resulted in a 60% loss of polarization. The amount of polarization was influenced to a lesser extent by the misoriented grains since the ferroelectric volume of the layers was only slightly overestimated. This reveals that optimizing reproducible and transferable properties, such as crystal quality and surface morphology, is more reasonable, as the film with the lowest misoriented volume and the highest degree of c-axis orientation showed the highest polarization.

In-situ thermal cleaning of the sapphire substrate and temperature effect on epitaxial AlN

The impact of thermal surface cleaning on epitaxial AlN thin films grown on sapphire is investigated in this study at various temperatures. The sapphire substrate is cleaned in a hydrogen environment. Structural, optical, and surface morphology properties of the samples are investigated by using high-resolution X-ray diffraction, Raman spectroscopy, UV–visible spectroscopy, and atomic force microscopy, respectively. Because wastes from the surface of sapphire, which begins to decompose after 1200 °C, cannot be entirely removed at such a low temperature, grain distribution and grain size in the nucleation layer are impacted. Moreover, when a sapphire is cleaned at a high temperature, the rate of breakdown of oxygen atoms from the surface rises, and islands appear on the surface. Roughnesses on the sapphire surface cause misoriented grains and deteriorated the structure. The surface of the sapphire, which is cleaned at 1245 °C, was both sufficiently cleaned and not etched too much, uniformly distributed, and large-sized particles formed in the nucleation layer. Thus, the AlN thin film has grown with high quality in terms of structure, optics, and surface. Experimental results have demonstrated that the in-situ thermal cleaning temperature has a critical influence on the properties of the AlN.