Surface Grain Size Research Articles

Synergistic effects of the surface grain coarsening and the grain boundary phase magnetism on the magnetic properties of Re-Fe-B (Re: Rare earth elements) magnets after the grain boundary diffusion

The grain boundary diffusion process (GBDP) is one of the most popular methods to enhance the coercivity of Re-Fe-B (Re: Rare earth elements) magnets. The surface grain coarsening is the common characteristic for the sintered Re-Fe-B magnets after GBDP. However, the effect of the coarse surface grains induced by GBDP on the magnetic properties has not been thoroughly studied. In this work, sintered Nd-Ce-Fe-B magnets were subjected to GBDP with Pr70Cu30 alloy and Pr60Tb10Cu30 alloy, respectively. The size of the coarse surface grains on the Pr70Cu30 alloy diffused magnet surface is far larger than that on the Pr60Tb10Cu30 alloy diffused magnet surface. The diffusion depth decreases with the size increase of the coarsened surface grains. Micromagnetic simulation reveals that for the magnet with the non-ferromagnetic grain boundary phase, increasing the polar surface grain size decreases the coercivity. However, the coercivity increases with the coarsening of the polar surface grain size for the magnet with a ferromagnetic grain boundary phase. Magnetic properties of the magnets after GBDP are synergistically affected by the polar surface grain size and the grain boundary phase magnetism.

Non-contact measurements of residual stress distribution and grain size in titanium alloys with laser ultrasonic system

In this study, a laser ultrasonic method is proposed for nondestructive non-contact measurement of both the residual stress depth profile and grain size in Ti-6Al-4 V alloy processed by warm shot peening (WSP). The method utilizes a pulsed laser to generate a surface acoustic wave (SAW) along the cross-section of the sample, and a laser interferometer to detect SAW signals. Laser ultrasonic measurements were performed on the samples treated by WSP at different temperatures (32, 100, 200 and 300 °C). A theoretical model for calculating the residual stress profile and a model to correlate the center frequency shift and the mean grain size of the sample were presented. The results obtained by the laser ultrasonic method were compared with those obtained by X-ray stress measurement, center-hole drilling (CHD), and electron backscattering diffraction (EBSD). The proposed method can measure and locate the maximum compressive residual stress (CRS) in a peened surface layer with a high spatial resolution of approximately 30 µm, allowing for precise extraction of the residual stress profile. This method can also provide an estimation of the grain size through the same experiment. The developed method is promising for the quick and nondestructive measurement of the residual stress profiles and grain size of surface treated metallic materials.

Finite element and experimental analysis of grain refinement caused by dynamic recrystallization during high-speed cutting of nickel-based superalloys

Nickel-based superalloys are subjected to complex mechanical and thermal loads during high-speed cutting, resulting in dynamic recrystallization behavior. The microstructure state is closely related to fatigue performance. In this paper, the Johnson-Mehl-Avrami-Kolmogorov model is used to predict the microstructure evolution of during high-speed cutting of superalloy GH4169. The finite element model of microstructure evolution considering dynamic recrystallization is established by user-defined subroutine on simulation platform. The error of cutting force obtained by experiment and simulation is within 12%. Serrated chips are obtained in high-speed cutting of superalloy GH4169. The typical characteristics of serrated chips such as peak, valley and peak-to-peak distance obtained by simulation are used to compare with the experimental results, and the error is within 20%. The dynamic recrystallization grain size increases as cutting speed increases. The promoting effect of increasing temperature on grain growth is greater than that inhibition effect of increasing strain rate, which leads to the increase of average grain size of machined surface.

Effect of laser shock peening on microstructure and mechanical properties of laser cladding 30CrMnSiNi2A high-strength steel

The effect of laser shock peening (LSP) on the microhardness and tensile properties of laser cladding (LC) 30CrMnSiNi2A high-strength steel was studied. After LSP, the microhardness of the cladding zone reached approximately 800 HV0.2, which was 25% higher than that of the substrate, while the cladding zone without LSP had an approximately 18% increase in its microhardness. Two strengthening processes were designed: groove LSP + LC + surface LSP versus LC + surface LSP. The former's tensile strength and yield strength were less than 10% weaker than those of forged materials, which is the best mechanical property recovery found in LC samples. The microstructural characteristics of the LC samples were analysed by scanning electron microscopy (SEM) and electron backscatter diffraction. Under the action of the laser-induced shock wave, the grain size of the LC sample surface was refined, the low-angle grain boundaries on the surface layer increased significantly, and the austenite grain length was reduced from 30–40 μm in the deep layer to 4–8 μm in the surface layer. In addition, LSP modulated the residual stress field, hence preventing the weakening effect of the LC process's thermal stress on the components' mechanical properties.

Carburization-induced microstructure evolution and hardening mechanism of 18CrNiMo7-6 steel

The microstructural evolution and hardening mechanism caused by carburizing heat treatment must be determined to improve the in-service functional performance of components used in advanced equipment for aerospace and other industrial applications. Carburizing heat treatment causes the microstructure to exhibit heterogeneous characteristics in the depth direction. In this study, the effects of carburizing heat treatment on the microstructure and hardening mechanism of 18CrNiMo7-6 steel were investigated. The experimental results show the residual austenite (RA) content in the carburized surface reached 56.2% and the RA content in the core was 0.1% after carburizing heat treatment. The kernel average misorientation (KAM) value, grain size, low angle grain boundaries (LAGBs) content, and dislocation density caused by carburizing heat treatment increased with increasing depth. After the carburizing heat treatment, considerable grain refinement occurred, and the minimum grain size of the carburized surface was 3.19 μm. The microhardness of the carburized layer first rose and then reduced, achieving a maximum of 686 HV, which was 57.7% higher than that of the quenching and tempering (uncarburized) samples. In addition, it was found that grain boundary and solution strengthening played a prominent position in the hardening mechanism of the carburized layer. This study has deepened the current understanding of the hardening mechanism of 18CrNiMo7-6 steel during carburizing heat treatment.

Effect of Te content on microstructure and thermoelectric properties of Bi–Te multilayers

Bi2Te3 is a thermoelectric material with high thermoelectric conversion efficiency near room temperature. The control of its components is an effective method to improve the thermoelectric properties of Bi–Te based materials. In this paper, seven-layer Bi–Te thin films with Te content ranging from 36.29% to 77.29% were deposited on non-rotating glass substrates by co-sputtering and the samples were rapidly thermally annealed in a nitrogen atmosphere. The films were characterized by x-ray diffraction, scanning electron microscopy, and Hall effect measurement methods, and the effects of the components on the film morphology and thermoelectric properties were investigated. The results showed that the films were composed of mainly Bi2Te3 after annealing. As the Te element content increased, the grain size in the film surface first increased and then decreased, the layers between the interfaces became less obvious, and the number of voids decreased. Subsequently, thin films with Te content between 60% and 75% were deposited on a rotating substrate; the thermoelectric properties were relatively high and stable after annealing. A film with Te content of 69.29% had a good crystallization quality and large grain size with a maximum power factor of 8.17 µW/(K2 cm) after annealing at 350 °C for 17 min.

Impact of different types of storage media on enamel surface roughness and granularity distribution of avulsed teeth (In vitro study)

Background: To investigate the effect of different types of storage media on enamel surface microstructure of avulsed teeth by using atomic force microscope.Materials and methods : Twelve teeth blocks from freshly extracted premolars for orthodontic treatment were selected . The study samples were divided into three groups according to type of storage media :A-egg white , B- probiotic yogurt , and C-bovine milk . All the samples were examined for changes in surface roughness and surface granularity distribution using atomic force microscope, at two periods: baseline, and after 8 hours of immersing in the three types of storage media. Results: Milk group had showed a significant increase in the mean of the roughness values at the test period, while the egg white and the probiotic yogurt groups showed decrease in the surface roughness at the test period. No significant changes was found in the grain size of enamel surface of the avulsed tooth in any types of three storage media at eight hours interval. The use of egg white and probiotic yogurt to store the samples may be beneficial in that they contain various ions and proteins that fill up enamel valleys, while the longer periods of milk exposure encourage the bacteria to continue fermenting lactose, resulting in continual acid generation and increased demineralization. Conclusion : Milk group demonstrated the highest roughness values, while the egg white group demonstrated the lowest roughness values of the teeth. No significant changes in the grain size of enamel surface of the tested teeth in any types of three storage media at eight hours interval .

Exploring three-point-bending fracture toughness of thick diamond films from different directions

In this study, the effect of defects on fracture toughness in different directions was investigated. Two diamond films with a diameter of 122 mm and as-deposited thicknesses of 2.2 and 1.5 mm, respectively, were deposited by DC arc plasma jet chemical vapor deposition. To accurately obtain the fracture toughness, the films were ground and polished to 1.6 and 0.8 mm, respectively. The results indicate that many defects, including pores, are introduced into the films during the growth process, particularly on the side close to the growth surface in thicker film. The size of pores reaches micrometres, which affects the fracture toughness under loading in different directions. Due to the minimum grain size, both films exhibit a maximum toughness of 8.2 and 10.0 MPa·m1/2, respectively, with growth-surface cracks. For the thinner sample, the maximum value is followed by that of the edge-surface cracks. As the grain size of the edge surface falls between that of the growth surface and that of the nucleation surface, the results indicate that fracture toughness is affected by grain size. However, the number of pores near the growth side increases when the thickness exceeds 0.8 mm. Pores reduce the toughness, resulting in the minimum fracture toughness (6 MPa·m1/2) of the thicker diamond film with edge-surface laser cracks. The sample with an edge-surface sharp pre-crack has a similar fracture toughness of 5.6 MPa·m1/2. This study provides guidance for selecting the applied load direction.

Domain structure and optical band gap of MnO2 doped (K,Na)NbO3-LiTaO3 thin films

In this paper, potassium sodium niobate lead-free piezoelectric thin films were prepared by sol-gel method. The electric domain structure and optical band gap of the thin films were regulated by doping Mn. It is found that Mn doping increases the grain size and density of KNNLT piezoelectric film surface. In addition, Mn doping can regulate the electric domain of thin films. Increasing Mn doping concentration can regulate the size and distribution of electric domain, and the ratio of 71° electric domain increases with the increase of doping concentration. The results show that the optical band gap decreases gradually with the increase of doping amount when the annealing temperature is 650 °C. The lowest optical band gap reaches 3.426 eV, and is lower than the undoped KNNLT films.

Effect of cold Pilger rolling followed by annealing on fatigue crack initiation in Zircaloy-4 alloy cladding tube

In this study, low cycle fatigue behavior of Zircaloy-4 alloy cladding tube manufactured by cold Pilger rolling and annealing was investigated at room temperature. Results revealed that fatigue cracks initiated toward the marked side on clamped position i.e. on outer wall of the tube. Besides, substantial microstrain and dislocation developed on the out wall surface of the tube during manufacturing stage, which playing a key role in the fatigue crack initiation of the specimens. Meanwhile, effects of grain size and texture of the out wall surface, inner wall surface and cross section remained almost indifferent in this regard.

Production and characterization of Tungsten Trioxide nanoparticles on porous silicon as photoconductive detector via pulsed laser deposition

The pulsed laser deposition (PLD) technique has been widely used to prepare and characterize Tungsten Trioxide (WO3) nanoparticles on Porous Silicon (PS) substrate produced on n-type Si (100) wafer using a Nd-YAG laser with a wavelength of 355 nm, a repetition rate of 1 Hz, and various laser ablated energy of 440 mJ, 640 mJ, and 840 mJ at room temperature. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL), Raman spectroscopy, are used to investigate the structural and morphological, electric properties and photodetector of the WO3NPS. In high laser ablated energy of 640 mJ and 840 mJ, the XRD analysis revealed that all of the reflection peaks of WO3 NPS can be triclinic WO3 structure, and they became polycrystalline. The size of surface grains grew larger when the energy pulse was increased. Current-voltage (I-V) measures, the electrical characteristics, like the height of the barrier (ΦB) and ideality factor (n) of Al/WO3NPs/PS/n-Si/Al heterojunction have been determined, as between 1.22 and 4.44 ideality factors. It was found that as the laser energy utilized increases, the photocurrent density decreases. The high responsivity curve from the photodetector device has migrated to the visible area as the energy gap has reduced. When the energy pulse was increased to 800 nm, the quantum efficiency of WO3 NPS photodetectors increased to 89%.

Effect of Microstructure Evolution and Corrosion Behavior on Phase Transformation of Nanocrystalline SUS304 Prepared by Dry Ice Shot Peening

Microstructure and corrosion behavior of nanocrystalline SUS304 by dry ice shot peening has been investigated in detail in term of phase transformation. SUS304 as metastable austenitic stainless has excellent corrosion resistance and induced martensite by shot peening process. However, the SUS304 has quite low strength which is difficult to wear as metallic component. The dry ice shot peening process was carried out on SUS304 surface for one and three hours. The microstructure was observed by transmission electron microscope (TEM) and scanning electron microscope (SEM) equipped with electron back-scattered diffraction (EBSD). The phase transformation was analyzed by X-ray diffraction (XRD). The corrosion testing was carried out in 3.5% NaCl solution. The result indicated that the grain size of SUS304 surface was finer by deformation due to dry ice shot peened process. The hardness was improved properly by the increasing the shot peened time, and the corrosion resistance was increased. The XRD results showed that three hours shot peening process induced martensite phase of SUS304 by 15 m thickness. It can be summarized that the dry ice shot peening can be induced phase transformation due to high deformation on the SUS304 surface

Improved in-vitro biocompatibility of LZ91 Mg–Li alloy by formation of nanostructured Ti coating through surface mechanical nano-alloying treatment

Abstract Surface mechanical nano-alloying treatment (SMNAT) was employed to fabricate a nanostructured Ti coating on LZ91 Mg–Li alloy. Microstructure, surface hardness and in-vitro biocompatibility of the Ti-coated sample were investigated in comparison with those of an untreated sample. Experimental results showed that a nanostructured Ti coating with a thickness of 35 to 60 μm was formed after SMNAT for 2 h. The average grain size in the top surface of the Ti coating was about 30 nm. The surface of the Ti coating is rougher than that of the untreated LZ91 sample, in which the values of Ra, Rq and Rz were 7.83, 9.57 and 14.85 μm, respectively. The hardness of the Ti coating top surface was about 483 HV. Cell proliferation and differentiation on Ti coated samples were enhanced relative to those on the untreated samples.

Correlation between X-Ray diffraction pattern and microstructure of surface of E690 high-strength steel induced by laser-shock processing

To examine the relationship between the X-ray Diffraction (XRD) pattern and microstructure of the surface of E690 high-strength steel induced by laser shocks, X-ray diffractometry and transmission electron microscopy (TEM) were used to detect the laser-impact zone on the steel surface to obtain its diffraction pattern and microstructural morphology, followed by the establishment of a surface microstructure response model of the E690 high-strength steel under laser shock. The grain size of the impacted surface decreased with an increase in laser power density (LPD). When the LPD reached 4.07 GW/cm2, Ostwald ripening was observed in the TEM images and the grain size increased during the later stages of spinodal decomposition. When the LPD was 5.09 GW/cm2, nanograins were detected on the surface of the laser-impacted area. The X-ray diffraction result on the surface of the E690 high-strength steel was consistent with the microstructural analysis using TEM, which proves that the microstructural response of E690 high-strength steel under laser shock can be described by the surface microstructure response model.

Investigation of layer-by-layer laser remelting to improve surface quality, microstructure, and mechanical properties of laser powder bed fused AlSi10Mg alloy

Laser Powder Bed Fusion (LPBF) is an innovative additive manufacturing technology. But it is also limited by the defects and surface quality. In this work, the layer-by-layer laser remelting (LR) method is applied to LPBF AlSi10Mg to improve the surface quality and mechanical performance. To account for the physical mechanism of the laser remelting, a three-dimension multi-physics coupled transient model is established. The numerical results indicate that the molten pool during the LR process is significantly expanded. The larger molten pool plays a great role in removing the defects. Moreover, the temperature gradient and cooling rate are simultaneously increased during the LR process, which has a considerable impact on the microstructure transformation. The densification, surface quality, including roughness, wettability, and residual stress, microstructure, and mechanical property are investigated after LR treatment based on experiments. The experimental results show that after LR treatment, the densification can be up to 99.4%. The surface hydrophilicity is limited due to roughness reduction. The average grain size of top and side surface can be decreased by 6.74% and 28.79% due to the increasement of cooling rate. The average microhardness and ductility can be improved due to grain refinement and defect elimination.

Effects of Sequential Operation with Heat Treatment and Mechanical Milling on Work Hardening for Superalloy GH4169

Engineering components are usually manufactured with sequential production processes. Work hardening due to previous production processes affects the machinability of the workpiece in subsequent operations. In this research, the surface work hardening of a workpiece manufactured by two sequential processes with heat treatment/milling (HT + M) and milling/heat treatment (M + HT) of superalloy GH4169 was investigated. First, the surface microstructure characteristics, including plastic deformation and grain size of the machined workpiece surface processed by the two sequential processes, were quantitatively presented. Then, the microhardness on the machined workpiece surface and its cross-section was measured and analyzed. Finally, a surface microhardness calculation model considering twin boundary deformation was proposed. Here, we also present the microstructure evolution principle of the machined workpiece surface by the two sequential processes. It was found that the degree of work hardening of HT + M machining was 179%, whereas that of M + HT was only 101%. The research results can be applied to the optimized selection of process sequence for manufacturing superalloy GH4169.

Effects of Microstructure on the Low-Temperature Toughness of an X80 × D1422 mm Heavy-Wall Heat-Induced Seamless Bend

The relationship between the microstructure and the low-temperature toughness of an X80 × D1422 mm heavy-wall heat-induced seamless bend was investigated, including the influence of microstructure on crack initiation and crack propagation. Using optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron backscattered diffraction, the microstructure and crystallographic orientation characteristics were studied. An instrumented impact tester was used to investigate the impact toughness. The results showed that during the hot bending process, there was a difference in the induction heating temperature and the cooling rate results in the uneven microstructure of the inner surface, center position, and outer surface of the bend. The center position was mainly composed of granular bainite and exhibited the best combination of strength and toughness. The ductile–brittle transition temperatures of the inner surface, center position, and outer surface were −88, −85, and −60 °C, respectively. In the process of impact deformation, the non-uniformly distributed strain concentration regions are likely to cause uneven distribution of plastic deformation and the nucleation of microcracks. The high ratio of high-angle grain boundaries and the smaller effective grain size of the inner surface and center position lead to higher crack growth absorption energy. The low crack propagation energy of the outer surface is attributed to the fact that the high-angle grain boundary does not effectively deviate or arrest the crack propagation, and multiple microcracks are connected to one another and cause fracture failure.

The active layer in gravel‐bed rivers: An empirical appraisal

AbstractThe vertical position of the streambed–water boundary fluctuates during the course of sediment transport episodes, due to particle entrainment/deposition and bedform migration, amongst other hydraulic and bedload mechanisms. These vertical oscillations define a topmost stratum of the streambed (i.e. the ‘active layer or active depth’), which usually represents the main source of particles entrained during long and high‐magnitude bedload transport episodes. The vertical extent of this layer is hence a capital parameter for the quantification of bedload volumes and a major driver of stream ecology in gravel‐bed rivers. However, knowledge on how the active depth scales to flow strength and the nature of the different controls on the relation between the flow strength and the active depth is still scarce. In this paper we present a meta‐analysis over active depth data coming from ~130 transport episodes extracted from a series of published field studies. We also incorporate our own field data for the rivers Ebro and Muga (unpublished), both in the Iberian Peninsula. We explore the database searching for the influence of flow strength, grain size, streambed mobility and channel morphology on the vertical extent of the active layer. A multivariate statistical analysis (stepwise multiple regression) confirms that the set of selected variables explains a significant amount of variance in the compiled variables. The analysis shows a positive scaling between active depth and flow strength. We have also identified some links between the active depth and particle travel distances. However, these relations are also largely modulated by other fluvial drivers, such as the grain size of the bed surface and the dominant channel macro‐bedforms, with remarkable differences between plane‐bed, step‐pool and riffle‐pool channels. © 2020 John Wiley & Sons, Ltd.

Effect of Rapid Thermal Annealing on Thermal Evaporated CdSe Thin Film for Solar Cell Application

Cadmium Selenide (CdSe) thin films have been deposited on a cleaned glass substrate by thermal vacuum evaporation method under the pressure of 10-5 torr. These CdSe thin films were also kept into a quart glass tube for rapid thermal annealing at 60 and 120 second using a 500 W halogen lamp for crystalline the structure. These thin films were characterized for structural, optical and thermo-electrical properties. The optical studies have been done using UV-VIS-NIR, shows that the transition of the deposited film is found to be a direct band gap of 1.74, 1.70 and 1.67 eV for asdeposited, 60 sec and 120 sec annealed thin films respectively. It was also found that absorbance has increased and transmission decreased with increasing annealing time, the change in the extinction coefficient with energy (hν) has been also measured. The Thermoelectric power (TEP) studies confirm the n-type nature of CdSe thin films but as well as annealing time increased the hole concentration increased resultant n-nature of CdSe thin film changing toward p-type nature, the Seebeck coefficient for different annealing time at as-deposited (RT), 60 seconds and 120 seconds have observed 549, 949 and 1031 μV/K respectively. The SEM result shows that with increasing annealing time the grain size and roughness of surface are increased. X-ray diffraction (XRD) studies indicate that the film is like a cubic crystal structure with average crystalline size (D) was measured using Scherrer formula and it is 16.44 nm.

Employing Cold Spray to Alter the Residual Stress Distribution of Workpieces: A Case Study on Fusion-Welded AA2219 Joints

Eight-millimeter-thick high-strength AA2219 aluminum alloy plates were successfully welded by variable polarity tungsten inert gas welding, and the effect of cold spraying (CS) process on the residual stress, microstructure and mechanical properties of the welded joints were investigated. The CS experiment was performed under different driving gas temperatures and pressures and with different powder types. The microstructure of the as-welded joints and as-coated joints was analyzed by optical microscopy and scanning electron microscopy, while the residual stress was measured by the blind-hole-drilling method. The results show that the CS process could significantly modify and re-distribute the residual stress of the welded joints. The maximum residual tensile stress of the welded joint has been significantly reduced by 111.9% and distributed more uniformly compared to the as-welded state. With the increase in gas temperature and/or pressure in CS, the residual tensile stress of joints was reduced, and even some compressive stress appeared. Among the powders of Cu, Al, and Ni, Cu particles have the best-improving effect. In addition, double-sided spraying treatment can reduce the residual tensile stress of both sides more effectively. Besides, the grain size of the joint surface after CS was refined.