Density Of Grain Boundaries Research Articles

Achieving High Strength-Ductility Synergy in Low-Alloyed Mg-Li-Er Extrusion Alloys via Tailoring Bimodal-Grained Structure.

Low-alloyed Mg-Li-Er alloys were developed in this study and a bimodal-grained structure was obtained by varying the trace Er content and extrusion temperature. The alloys displayed a good strength-ductility synergy, i.e., a tensile yield strength (TYS) of 270 MPa and an elongation (EL) of 19.1%. Microstructural characterization revealed that the formation of numerous submicron Mg24Er5 particles favored a high density of low-angle grain boundaries (LAGBs) inside the deformed grains and inhibited dynamic recrystallization (DRX). The resultant coarse unDRXed grains with a strong basal texture and considerable LAGBs, together with the fine DRXed grains, contributed to the high strength-ductility synergy.

High pressure coupled with Cu deficiency boosts thermoelectric performance in BiCuSeO oxides

Low carrier concentration and mobility have been the primary obstructions to improving the electrical transport properties of BiCuSeO thermoelectric oxides, particularly for excessively low carrier mobility, heavily impeding the development of its thermoelectric performance. Herein, high-pressure technology is adopted to tune the electronic structure motivating carrier mobility, incorporated with the contribution of Cu deficiency to carrier concentration, achieving high carrier mobility of 25 cm2V−1s−1 and outstanding electrical conductivity of 2834.57 Sm−1. Moreover, high densities of grain boundaries and dislocations are introduced by high pressure, accompanied by the effect of Cu vacancies, suppressing phonon transport and depressing lattice thermal conductivity, finally realizing an acceptable zT of 0.56 at 823 K in BiCu0.97SeO. This work demonstrates that high pressure can be compatible with other methods, realizing synergetic optimizations in coupled parameters and thus improving thermoelectric performance in BiCuSeO oxides.

Effect of grain size on spall fracture of CrCoNi medium-entropy alloy under Taylor-wave loading

The effect of grain size on spall properties of medium-entropy alloy CrCoNi under Taylor-wave loading is investigated. Three different grain sizes, 300 μm, 20 μm, and 3 μm, are explored. The free surface velocity histories are measured to obtain such quantities as dynamic yield strength and spall strength. With decreasing grain size, there is a slight decrease in spall strength, but a significant increase in damage rate. The shock-recovered samples are characterized with scanning electron microscopy and electron backscatter diffraction. In coarse-grained samples, voids tend to nucleate within grain interiors, while in fine-grained samples, voids nucleate preferentially at grain boundaries (GBs). Molecular dynamics simulations show that the nucleation of intergranular or intragranular voids is dominated by GB–slip and slip–slip intersections, respectively. The higher GB density results in more extensive GB–slip intersections, consistent with the experimental results.

Unconventional grain fragmentation creates high-density boundaries for efficient CO2-to-C2+ electro-conversion at ampere-level current density

Electrocatalytic CO2 reduction reaction (CO2RR) to produce multi-carbon products (C2+) is one of the most sustainable manners to achieve net-zero carbon emissions. Among many approaches, enriching grain boundaries (GBs) in copper (Cu) catalysts has been demonstrated to enable enhancement for C2+ production. However, it still lacks effective strategies to controllably synthesize abundant GBs, rendering efficient C2+ production a persistent challenge, especially at ampere-level current density. Herein, we propose a novel strategy, which can achieve unconventional grain fragmentation during thermal annealing and thus create controllable GB densities. The catalyst with the utmost GB density exhibits a peak C2+ faradaic efficiency of ca. 70.0 % in H-type cell and 68.2 % in flow cell; even more impressively, it delivers an ultra-high C2+ current density of 0.768 A cm−2, outperforming most recently reported results. A combination of in situ spectroscopies and theoretical calculations reveal that the enrichment of GBs yields more active sites for a higher *CO coverage, leading to promotion of the *CO-*CO coupling process and ultimately high C2+ production performance.

Crystallographic study on microstructure evolution and mechanical properties of coarse grained heat affected zone of a 500 MPa grade wind power steel

The effect of different welding heat inputs on the microstructure and mechanical properties of the simulated coarse grained heat affected zone (CGHAZ) of high-strength wind power steel with yield strength of 500 MPa has been investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Charpy impact tests have demonstrated that there exists an optimum heat input of ∼20 kJ/cm that allows optimum impact toughness to be obtained for the CGHAZ. It was shown that this is related to the refined bainitic structure and the highest density of high-angle grain boundaries (HAGBs) with misorientation angle of more than 45°. In crystallographic visualization studies, it was shown that the weakest variant selection occurs for the bainite transformation in the optimal heat input, leading to the highest density of HAGBs with each Closed-packet group containing two or three Bain groups and showing a staggered arrangement structure. The contribution that can effectively deflect and prevent crack propagation during impact experiments has to come from the block boundary. However, it was also found that the center segregation induced by C and Mn reduces the low-temperature impact toughness of the core sample before and after simulated welding, and affects the fluctuations of impact toughness and fatigue performance of simulated CGHAZ. Mn segregation can have a genetic effect on the welding heat affected zone, inducing a lower temperature martensitic transformation, which in turn leads to a decrease in low-temperature toughness and fatigue crack arrest performance.

Grain-Boundary Engineering Boosted Undercoordinated Active Sites for Scalable Conversion of CO2 to Ethylene.

The development of highly selective and energy efficient technologies for electrochemical CO2 reduction combined with renewable energy sources holds great promise for advancing the field of sustainable chemistry. The engineering of copper-based electrodes facilitates the conversion of CO2 into high-value multicarbon products (C2+). However, the ambiguous determination of the intrinsic CO2 activity and the maximization of the density of exposed active sites have severely limited the use of Cu for the realization of practical electrocatalytic devices. Here, we report a scalable strategy to obtain a high density of undercoordinated sites by maximizing the exposure of grain-boundary active sites using a direct chronoamperometric pulse method. Our numerical investigations predicted that grain boundaries modulate the adsorption behavior of *CO on the Cu surface, which acts as a key intermediate species associated with the production of multicarbon species. We investigated the consequence of grain-boundary density on dendric Cu catalysts (GB-Cu) by combining transmission electron microscopy, in situ Raman spectroscopy, and X-ray photoelectron spectroscopy with electrochemical measurements. A linear relationship between the Faradaic efficiency of the C2+ product and the presence of undercoordinated sites was observed, which allowed to directly quantify the contribution of the grain boundary in Cu-based catalysts on the CO2RR properties and the formation of multicarbon products. Using a membrane electrode assembly electrolyzer, the high grain-boundary density Cu electrodes achieved a maximum Faradaic efficiency of 73.2% for C2+ product formation and a full-cell energy efficiency of 20.2% at a specific current density of 303.6 mA cm-2. The GB-Cu was implemented in a 25 cm2 MEA electrolyzer and demonstrated selectivity of over 62% for 70 h together with current retention of 88.4% at the applied potential of -3.80 V. The catalysts and electrolyzer were further coupled to an InGaP/GaAs/Ge triple-junction solar cell to demonstrate a solar-to-fuel (STF) conversion efficiency of 8.33%. This work designed an undercoordinated Cu-based catalyst for the realization of solar-driven fuel production.

Oxidation behaviors of a Ni–Cr–W based superalloy with different microstructures

Oxidation behaviors of a Ni–Cr–W based superalloy were investigated in terms of microstructural characteristics. It was found that the specimens with small grains present a better oxidation resistance owing to their higher density of grain boundaries. Based on analyses of the products of oxidation, the oxidation kinetics, the morphologies and the structures of oxide scales, the oxidation mechanisms correlated with the outward diffusions of metal cations were proposed. The results of this work indicated that grain refinement is one of effective measures to enhance the oxidation resistance of the investigated alloy.

The mechanism for the superior isotropic mechanical properties attained in a cross rolling TiNb alloy

In the present study, the Ti–41Nb (wt.%) alloy featuring a microstructure composed of β and α″ phases have been prepared through the application of the Cross Rolling (CSR) technique to achieve a near-isotropic superior mechanical behavior. The experimental findings revealed that the CSR sample exhibits a uniform β matrix, randomly dispersed α″ martensite and a high density of dislocations and grain boundaries. Subsequent experiments unveiled that the CSR sample displays an almost isotropic mechanical response across three typical directions, Rolling Direction (RD), a 45° deviation from RD, and Transverse Direction (TD), evidenced by comparable stress-strain curve profiles and ultimate tensile strength (UTS) values. Due to the randomly distributed textures and high density of dislocations and grain boundaries, the stress-induced martensitic (SIM) transformation exhibits a similar characteristic in three typical directions, that is, the SIM transformation took place homogeneously and continuously. Consequently, the CSR sample can achieve a near-isotropic and outstanding mechanical performance due to the similar characteristics of martensitic phase transformation and the strengthening effect brought by the high density of dislocations and grain boundaries.

A mechanistic study of grain boundary behaviour during irradiation-induced growth in zirconium

Grain boundaries play a significant role during deformation and can exhibit both beneficial and adverse effects on deformation behaviour during irradiation. For instance, macroscopic irradiation growth is increased by the presence of a high density of grain boundaries. Grain boundaries can act as sinks for point defects and barriers to dislocation motion. Thus, a mechanistic assessment of the impact of grain boundaries is essential for better understanding irradiation-induced deformation. The interplay between irradiation-induced microstructure and mechanical properties has been an area of research for many decades, but many uncertainties remain. In the present work, the deformation fields adjacent to grain boundaries in pure zirconium are investigated by using high angular resolution electron backscatter diffraction (HR-EBSD) after a period of irradiation growth. It is observed that the extent of grain boundary deformation is associated with the crystallographic orientation difference between adjacent grains. High-angle grain boundaries function as a deformation constraint, whereas a significant grain boundary migration occurs at some low-angle grain boundaries, which likely act as an active diffusion path for the irradiation-induced point defects. In addition, the change in residual strain fields associated with the irradiation damage is quantified with respect to a non-irradiated reference. A net change in the state of residual elastic strain in the order of ∼10−3 has been estimated for ∼8 dpa proton irradiation. Furthermore, the origin of residual elastic strain and lattice misorientation concentration along (0002) traces are discussed.

Influence of TiB2 Incorporation on Microstructural Evolution in Laser-Clad FeCrV15 + TiB2 Deposits

Vanadium carbide (VC)-reinforced Fe-based hard facings are pivotal in enhancing the wear resistance of tools prone to mechanical damage. This study investigates the impact of titanium diboride (TiB2) addition (at varying laser power and powder federate) on the microstructure, hardness, wear resistance, and corrosion resistance of high-carbon ferrochrome FeCrV15 clad coatings for agricultural and mining applications. Laser cladding techniques were employed to deposit coatings on steel substrates, and the samples were subjected to comprehensive material characterization, including microhardness testing, wear studies, and electrochemical polarization. Results reveal that TiB2 addition led to visible reactions during deposition, resulting in decreased hardness compared to pure FeCrV15 coatings. Moreover, TiB2 incorporation adversely affected the anti-corrosion properties of the coatings, although FeCrV15 coatings exhibited superior corrosion resistance compared to FeCrV15 + TiB2 coatings. Tribological evaluations showed that all coatings exhibited better anti-wear capabilities compared to the steel substrate, with varying degrees of improvement influenced by TiB2 concentration and laser beam power. Overall, FeCrV15 deposits demonstrated superior anti-wear and anti-corrosion properties compared to FeCrV15 + TiB2 coatings and attributed to increased convergence of carbide particles and higher grain-boundary density. This research contributes to understanding the intricate interplay between carbide reinforcement and matrix structure in Fe-based hard facings, providing insights for optimizing coating performance in demanding industrial applications.

Effect of Pre-Weld Heat Treatment on the Microstructure and Properties of Coarse-Grained Heat-Affected Zone of a Wind Power Steel after Simulated Welding

The effect of pre-weld heat treatment on the microstructure and low-temperature impact toughness of the coarse-grained heat-affected zone (CGHAZ) after simulated welding was systematically investigated through the utilization of scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). The Charpy impact test validated the presence of an optimal pre-weld heat treatment condition, resulting in the highest impact toughness observed in the CGHAZ. Three temperatures for pre-weld heat treatment (690, 720 and 750 °C) were used to obtain three different matrices (Steel 1, Steel 2, Steel 3) for simulated welding. The optimal pre-weld heat treatment is 720 °C for 15 min followed by water quench. Microstructure characterization showed that there is an evident microstructure comprising bainite (B) in Steel 1 and Steel 2 after pre-weld heat treatment, while the addition of martensite (M) with the pre-weld heat treatment temperature exceeds Ac1 by almost 60 °C (Steel 3). These differences in microstructures obtained from pre-weld heat treatment influence the refinement of high-temperature austenite during subsequent simulated welding reheating processes, resulting in distinct microstructural characteristics in the CGHAZ. After the optimal pre-weld heat treatment, Steel 2 subjected to single-pass welding thermal simulation demonstrates a refined microstructure characterized by a high density of high-angle grain boundaries (HAGBs) within the CGHAZ, particularly evident in block boundaries. These boundaries effectively prevent the propagation of brittle cracks, thereby enhancing the impact toughness.

Effect of recrystallization on aging embrittlement and high temperature creep properties of AFA steel

As a kind of typical precipitate strengthened steel, alumina-forming austenitic (AFA) stainless steels usually suffer obvious aging embrittlement issue. Recrystallization treatment was performed by cold rolling followed with heat treatment at 1080 ℃ for a Fe-25Ni-15Cr-3.5Al based AFA steel to evaluate the effect of recrystallization on aging embrittlement. The materials before and after recrystallization were aged at 700 ℃ for 120 h to evaluate the effect of recrystallization on precipitation behavior. After recrystallization, the average grain size decreased and the density of grain boundaries increased obviously. The size of precipitates along grain boundaries was smaller and more uniform after recrystallization, and the precipitation of Cr rich phase was inhibited. Room temperature tensile test, Charpy impact, and creep behavior at high temperature of samples with different treatment states were measured and compared. The aging embrittlement of AFA steel was alleviated obviously after recrystallization. The creep resistant was also improved for sample treated by recrystallization and aging. The relevant mechanisms were discussed.

Microstructure evolution under different austenitizing temperatures and its effect on mechanical properties and mechanisms in a newly high aluminum bearing steel

A new type of lightweight high aluminum bearing steel had been developed based on the widely used high carbon chromium bearing steel. Via multi-scale experimental characterizations and theoretical calculations, here we mainly focused on the evolution of microstructure including precipitates under different quenching temperatures. Accordingly, the mechanical properties, mechanisms and fracture features of the new high-Al steel after tempering were characterized in detail. As austenitizing temperature rose, matrix of steel varied from multiphase structure of martensite, retained austenite (RA) and ferrite to the full martensite and RA. RA was found in all four samples with the austenitizing temperature from 850 °C to 1000 °C. In terms of precipitates, a transformation from M3C to M7C3 were observed. As a phase newly introduced by Al, AlFe3C (κ carbides) would dissolve into matrix at 900 °C. Eventually, the yield strength of the researched steel could reach 1430 MPa with an unnotched impact energy of 35 J. Theoretical results showed that high strength of researched steel was mainly caused by solid solution effect of carbon and high density of dislocation. In terms of toughness and fracture observation, high impact energy was attributed to the highest density of grain boundary, and also, κ carbides were found at the origin of secondary crack. This study highlighted the significant effect of Al addition and quenching process based on the traditional bearing steel, which showed a novel method and idea to reduce significantly the weight of bearings.

Precise Alkali Supply during and after Growth for High‐Performance Low Bandgap (Ag,Cu)InSe2 Solar Cells

Alkali treatments are crucial for low bandgap (Ag,Cu)InSe2 (ACIS) and Cu(In,Ga)Se2‐based solar cell performance. Traditionally, Ag‐alloying of CIS (ACIS) is grown on soda‐lime glass (SLG) at temperatures exceeding 500 °C, resulting in uncontrolled alkali diffusion from the substrate and variable photovoltaic properties. A substrate‐independent low‐bandgap ACIS growth process is introduced and the impact of controlled supplies of NaF and RbF alkali fluorides before and after absorber growth through precursor layers and post‐deposition treatments (PDT) are investigated. NaF and RbF precursor layers enhance carrier lifetimes and doping density, outperforming the previous SLG‐dependent strategy. Even small quantities of RbF significantly enhance device performance, while specific NaF amount during deposition are necessary to limit grain growth and achieve high doping densities and lifetimes. A certain density of grain boundaries appears crucial for high doping levels. Although subsequent NaF post‐deposition treatment (PDT) does not provide additional benefits with sufficient Na during growth, RbF‐PDT remains crucial. The best performance is achieved with a combination of NaF and RbF precursor layers along with RbF‐PDT, resulting in over 19% efficiency, 605 mV open‐circuit voltage (VOC), 73% fill factor (FF), a carrier density of 3 × 1016 cm−3, and a 700 ns lifetime. This approach supports high‐efficiency ACIS solar cell advancement, particularly for thin‐film tandem photovoltaic devices.

Effect of Boron on Microstructures and Low-Temperature Impact Toughness of Medium-Carbon CrMo Alloy Steels with Different Quenching Temperatures

The effect of boron (B) on the microstructures and low-temperature impact toughness of medium-carbon CrMo steel quenched at 870~1050 °C and tempered at 600 °C was studied via Charpy impact testing and microstructure characterizations. The results showed that with an increasing B content from 0 to 50 ppm, the low-temperature impact toughness deteriorated significantly at quenching temperatures (Tq) lower than 950 °C but increased at a higher Tq of 1050 °C. Undissolved M2B particles remained and coarsened during the holding process due to the low Tq, decreasing the critical stress required for crack initiation and deteriorating the impact toughness accordingly. However, this detrimental effect of B could be mitigated by a higher Tq, and the favorable influences on the impact toughness improvement could be attributed to (1) the finer M2B particles formed during quenching effectively pinning the austenite grain boundaries (GBs), leading to a finer block size and a high density of high-angle grain boundaries, which reduced the critical stress for crack initiation; and (2) the fact that the coarsening of M23C6 on the GBs during tempering was slightly suppressed by the segregated B, eventually increasing the energy required for crack propagation. However, the degree of the favorable effect due to B was still lower than the negative effect of a high Tq.

On machining-induced surface integrity of Inconel 718 fabricated by powder bed fusion

Additive manufacturing (AM) introduces unique grain feature and anisotropy in metals, as well as relatively poor surface quality, so the knowledge about the formation of post-machining-induced surface integrity needs to be extended. This study aims to understand the machining phenomena in orthogonal cutting of Inconel 718 produced via powder bed fusion of metals using a laser beam system (PBF-LB/M), paying particular attention to the cutting energy, chip formation, geometrical defects, and microstructural deformation. Experiments are conducted on both wrought (W 718) and PBF-LB/M (PBF 718) Inconel 718, whereby the cutting speed and the anisotropy of the workpiece in the raw state play an important role. The results indicate that less cutting energy is consumed when cutting PBF 718 in the direction perpendicular to its build direction (BD), followed by cutting in its BD. Denser shearing-induced slip lines and relatively continuous chip morphology are found when cutting PBF 718 in its BD, moreover, the effect of cutting speed on shearing deformation of columnar grains under this condition is analysed. More importantly, this study identifies a significant geometrical defect phenomenon which is unique to PBF 718 and highly depends on the cutting speed and anisotropy of grain feature. A detailed characterisation shows that this behaviour is caused by tearing within the grains in the matrix material and not by the presence of hard inclusions, which has rarely been reported in the literature. The microstructure in the subsurface area exhibits that the density of grain boundaries in the cutting direction plays the key role in plastic deformation, as the machining process mainly causes dragging behaviour in the area below the machined surface. Thus, cutting PBF 718 in the direction perpendicular to its BD shows similar deformation layer to W 718, while cutting PBF 718 in its BD displays much stronger subsurface deformation. The obtained results greatly help to understand the cutting phenomena in post-machining of additively manufactured Ni-based components, especially the integrity for a better functional surface.

Localized plastic strain accumulation in shape memory ceramics under cyclic loading

The premature failure of shape memory ceramics (SMC)s under cyclic loading is a critical issue limiting their applications as actuators and thermal protection layers. Martensitic phase transformation (MPT), essential for superelasticity and shape memory functionalities in SMCs, induces localized plastic deformations due to phase expansion. In polycrystalline materials, the accumulation of localized plastic strain serves as the primary mechanism for fatigue crack initiation under cyclic loading. In this research, a phase-field (PF) phase transformation model coupled with a viscoplasticity model is presented to study the effects of microstructural features, engineered pores, and sample size on plastic strain accumulation (PSA) during cyclic loading of SMCs. Our findings highlight that the grain boundaries (GB)s are critical regions with high PSA, with noticeable reductions observed by decreasing the grain boundary density (GBD). Additionally, we found that engineered pores effectively reduced cyclic PSA, however, we identified a threshold on the volume fraction of pores. Also, textured microstructures with certain characteristics demonstrate significant influence on PSA. A cross-correlation data analysis approach is employed to study the relationship between the studied microstructural features and PSA to facilitate the identification of the most important factors controlling the irreversible PSA during compressive cyclic loading. By mitigating the rate of PSA, significant enhancements in cyclic life before fatigue crack initiation can be achieved, enabling superior performance in practical applications.

A study on the thermal conductivity of proton irradiated CVD-SiC and sintered SiC, measured using a modified laser flash method with multi-step machining

CVD-SiC and sintered SiC (SPS-SiC) were proton irradiated at 340 ̊C receiving different levels of damage (0.05–0.25 dpa). A novel multi-step machining and measurement method using laser flash analysis (LFA) was developed to derive the thermal conductivity of the irradiated layer (∼46 µm). Before irradiation, the thermal conductivity of SPS-SiC was much lower than CVD-SiC, primarily due to its higher intrinsic defect concentration and smaller grain size which provide a greater density of barriers to phonon transmission. Following irradiation, major thermal conductivity degradation (∼90%) was found to occur to both types of SiC after only a low dose (∼0.1 dpa), with both saturating at a similarly low value (a few W/K⋅m), as the thermal resistivity due to the presence of high density of grain boundaries became less important. Thermal conductivity degradation after irradiation was primarily caused by point defects in both types of SiC, as reflected by Raman spectra.

Crystallization modulation and defect passivation in carbon-based perovskite solar cells using multifunctional group additive

Recently, carbon-based perovskite solar cells have attracted wide attention in academia and industry because of their simple preparation process, low cost, and adaptability to roll-to-roll industrial production. The combination of ternary perovskite composition and carbon electrode configuration is expected to meet the requirements of device performance and stability. However, low grain size, and high density of grain boundary and surface defect states result in serious non-radiative recombination, which is one of the main gaps between the carbon-based perovskite solar cells and metal-electrode-based devices. Based on the consideration of crystal tuning and defect passivation of ternary CsFAMA thin films, the additive molecule 5-(Difluoromethoxy)-2-mercapto-1H-benzimidazole (DMB) with multifunctional groups were introduced into the film. XRD show that the (100) and (200) crystal plane orientation growth directed by the DMB additive lead to the formation of the micro-sized perovskite. XPS suggests that DMB not only modulates the crystallization of the films but also exists at the grain boundaries, and realizes the passivation of undercoordinated Pb2+ defects and inhibits the generation of Pb0. The defect state density is significantly reduced, and the carrier lifetime is greatly improved. The possible mechanism for perovskite crystal growth as well as defect passivation based on Lewis acid-base coordination and hydrogen bond was also proposed. After the introduction of DMB, a power conversion efficiency of 14.40% was achieved, which was 13.4% higher than that of the control device. After nearly 1200 h of environmental stability test, the DMB modified device still retained 95% of the original efficiency. This work emphasizes the feasibility of simultaneously realizing the crystallization modulation and defect passivation of carbon-based perovskite solar cells using the additive with multifunctional groups, and provides a reference for the commercialization of carbon-based perovskite solar cells.

Structure and RF performance evolution of polycrystalline silicon charge capture layer for advanced RF-SOI in in-situ annealing process

In this paper, the structures and radio-frequency (RF) properties of high resistivity silicon (HR-Si) wafers with a polycrystalline silicon (Poly-Si) charge capture layer after in-situ annealing were investigated. The thermal treatment significantly improves the wafer warpage and optimize the resistivity of Poly-Si/HR-Si interfaces. By using spreading resistance profiling (SRP), energy dispersive spectrometer (EDS) and secondary ion mass spectrometry (SIMS) technology, the rise of interfacial resistivity may be as results of the pyrolysis of the native oxide and the diffusion of hydrogen atoms. The transmission Kikuchi diffraction (TKD) analysis exhibited that the grains were recrystallized during the annealing, leading to the transformation from the small angle boundaries (SAGBs) into low-Σ coincidence lattice grain boundaries (CSL GBs). The drop of the bulk resistivity of the Poly-Si layer is attributed to the reduction of the total grain boundary (GB) density and the increase of the low electro-activity GB density. Moreover, the microwave losses and non-linearity of the RF-SOI with embedded Poly-Si layer was evaluated by on-chip testing based on CPW. It was determined that the decrease in the Poly-Si resistivity only worsens the microwave losses but not the non-linearity.