Spheroidization Process Research Articles

Thick and dense nitrogen-doped hafnium carbide ultra-high temperature thermal protection coating for outstanding ablation resistance up to 2600 ℃

Transition metal carbon-nitrides, typically represented by HfCN, have become the latest progress among the ultra-high temperature ceramics. In this study, single-phase solid solution HfCN coating was successfully synthesized from spray granulated HfC-HfN composite powder followed by employing the dual solid solution effects of radio frequency inductively coupled plasma spheroidization and supersonic atmospheric plasma spraying processes. The coating was nearly dense (only 2.3% in porosity) with a high thickness of ~ 270 μm. Compared with HfC coating, the HfCN coating exhibited higher hardness and elastic modulus. After plasma ablation at a high heat flux of 8.2MW/m2 for 200s, the HfCN coating exhibited a surface temperature of up to 2600 ℃ and can firmly protect the refractory tungsten substrate from oxidation failure. This outstanding performance illustrates that doping N element in HfC crystal can effectively improve the energy barrier for oxidation reaction and oxygen adsorption compared with typical HfC coating.

Crystallographic orientation and slip behavior of powder metallurgy Ti–6Al–4V via multi-directional forging

In this study, we present a microstructural and mechanical analysis of Ti–6Al–4V alloys processed by low-temperature multi-directional forging at 900 °C, achieving near-theoretical density (99.9%), with a tensile strength of 1070 MPa and elongation of 14.9%. The microstructure is defined by both continuous and discontinuous dynamic recrystallization occurring simultaneously, related to an increase in dislocation density. Significantly, this study reveals the interaction between crystallographic orientation and spheroidization during the forging process. Specifically, changes in crystallographic orientation include the asynchronous formation of new subgrains/grains, the disruption of the Burgers orientation relationship, and rotation around the <11 2‾ 0>axis, which not only increases the orientation differences between α lamellae but also enhances the spheroidization process. Moreover, our findings demonstrate that during deformation, the activation of basal and pyramidal slip systems is favored over prismatic slip, indicating that the forging process has enhanced slip activity. The average misorientation angle and the fraction of high-angle grain boundaries are quantified, providing a detailed characterization of the evolved microstructure. This study adopts a new perspective to examine the microstructural evolution during the multidirectional forging process in powder metallurgy, presenting findings that elucidate how multidirectional forging effectively controls.

Influence of post-deformation annealing conditions on microstructures and mechanical properties of hypereutectoid steel wires during cold drawing

Abstract This investigation delves into the complex influences of annealing conditions post-deformation, such as duration and heat levels, upon the microstructure, as well as the mechanical properties of hypereutectoid steel wires subjected to cold drawing. XRD and VSM analyses confirmed that higher annealing temperatures precipitated a notable increase in cementite volume, concurrently inducing the spheroidization of cementite lamellae. This transformation was evidenced by the expansion of cementite volume and the transition of cementite layers into a spherical morphology as the annealing temperature increased. The evolution of tensile strength in response to varying annealing temperatures and time revealed two distinct patterns. Initially, at lower annealing temperatures ranging between 200°C and 300°C, tensile strength exhibited an upward trajectory with increasing annealing time. This phenomenon can be attributed to age-hardening mechanisms, notably associated with solution hardening. As annealing time increases, the decomposition of cementite releases additional carbon atoms into the ferrite matrix. These carbon atoms act as effective barriers, hindering dislocation movement within the structure and consequently contributing to increased tensile strength. However, this increase in carbon content within the ferrite matrix also elevated the susceptibility to delamination phenomena. Conversely, at higher annealing temperatures of 400°C and 500°C, a contrasting trend was observed, characterized by a consistent decline in tensile strength post-annealing. This decline could be attributed to the phenomenon of aging softening, wherein the process of spheroidization and re-precipitation of cementite resulted in a reduction of dissolved carbon atoms within the ferrite matrix. Consequently, this led to a decline in tensile strength as well as a reduced incidence of delamination. In summary, the study explored how different annealing conditions affect the structure as well as the strength of hypereutectoid steel wires, revealing detailed mechanisms behind these changes.

The effect of LaSi2 content on the powder characteristics and coating structure of ZrB2-SiC

To investigate the effect of LaSi2 content on the properties of ZrB2-SiC composite powder and coatings, different amounts of LaSi2 were added to the ZrB2-SiC system. The composite powders were prepared using the induction plasma spheroidization process, and the coatings were fabricated using atmospheric plasma spraying. Results showed that LaSi2 significantly improves the density of both the powder and the coatings. As LaSi2 content increase to 15 vol%, the density of the powders increases to 2.75 g/cm3 and the porosity of the coatings decreases to 6.92 %. Our results suggest that LaSi2 can fully melt in the plasma jet field and act as a sealing phase to heal pores, thereby improving the performance of both the powders and subsequently, the coatings.

Improving wear and corrosion resistance of HVAF sprayed 316L stainless steel coating by adding TiB2 ceramic particles and CeO2

316L stainless steel is used in a wide variety of corrosion-prone locations. However, its low hardness and poor tribological properties limit its application under heavy wear conditions. In this study, 316L Fe-based composite coatings co-doped with TB2 hard phases and rare-earth CeO2 exhibited excellent wear and corrosion resistance. Firstly, 316L-TiB2 cermet powder and (316L-TiB2)/CeO2 composite powder with high sphericity and density were prepared by high energy ball milling (HEBM), spraying drying granulation (SD), plasma spheroidization (PS) process. Then, 316L coatings, 316L-TiB2 and (316L-TiB2)/CeO2 cermet coatings were deposited by high velocity air fuel (HVAF) spraying. Finally, the effects of TiB2 and CeO2 additions on the microstructure, wear and corrosion behavior of the coatings were investigated. The results showed that TiB2 hard particles and CeO2 were uniformly distributed in the HVAF sprayed 316L-TiB2 and (316L-TiB2)/CeO2 coatings. The wear resistance of the coating prepared by 316L Fe-based composite powder with TiB2 and CeO2 is significantly improved. The hardness of the (316L-TiB2)/CeO2 composite coating was increased from 269 Hv0.3 to 826 Hv0.3 for the pure 316L coating, while the volumetric wear rate was only 3.6 % of that of the pure 316L coating (110 × 10−5 down to 4 × 10−5 mm3/N). Electrochemical tests show that the corrosion resistance of the coating decreases with the addition of TiB2 alone, but it can be improved by doping CeO2. The 316L Fe-based coating prepared by adding TiB2 and CeO2 can significantly improve the wear resistance of the coating, while the corrosion resistance decreases only slightly.

High-temperature deformation behavior and microstructural evolution of TC17 alloy

The hot deformation behavior and microstructure evolution of TC17 alloy were investigated by hot compression tests at 700–950 ℃ with strain of 0.9 and strain rate of 0.001–10 s-1. A modified Arrhenius-type constitutive equation was established to describe the hot deformation characteristics. The spheroidization process of α phase was studied by scanning electron microscopy. The results show that the lamellar α phase forms a groove through the boundary splitting mechanism, and the gradually deepened groove eventually leads to the splitting of the lamellar α phase, and then diffuses to the surrounding under the termination migration mechanism. Finally, the lamellar α phase spheroidizes. The microstructure evolution during hot compression was analyzed by electron backscatter diffraction technique. The results show that the spheroidization of lamellar α phase is the main softening mechanism of TC17 alloy at low temperature. With the increase of temperature, dynamic recrystallization gradually transforms into the main softening mechanism of TC17 alloy. At the same time, the discontinuous dynamic recrystallization at the subgrain boundary and the continuous dynamic recrystallization at the subgrain rotation of TC17 alloy were found.

Constitutive Model and Microstructure Evolution of Ti65 Titanium Alloy.

The hot deformation behavior and mechanism of Ti65 alloy with a bimodal microstructure were investigated by isothermal compression experiments conducted on the Thermecmastor-Z simulator equipment at temperatures ranging from 950 to 1110 °C and strain rates ranging from 0.01 to 10.0 s-1. The Arrhenius constitutive model, based on strain compensation, and Grey Wolf optimization-neural network with back propagation model (GWO-BP), were both established. The differences between the experimental and predicted value of flow stress were compared and analyzed using the two models. The results show that the prediction accuracy of GWO-BP in the two-phase region is higher than that of Arrhenius model. In the single-phase region, both methods demonstrated high prediction accuracy. Compared to the single-phase region, the flow stress of Ti65 alloy shows a higher degree of softening in the two-phase region. During deformation in the two-phase region, the initial lamellar α phase transformed from a kinked and elongated morphology to a globularized topography as the strain rate decreased. Boundary-splitting was the primary mechanism leading to the spheroidization process. The degree of recrystallization increased with the increase in strain rate during the deformation in the single-phase region, while dynamic recovery and strain-induced grain boundary migration were the main deformation mechanisms at a lower strain rate. Discontinuous dynamic recrystallization may be the dominant recrystallization mechanism under a high strain rate of 10 s-1.

Microstructural evolution and spheroidization mechanism of powder metallurgy Ti-6Al-4 V alloys after high-temperature forging

After high-temperature forging and rapidly cooling, the microstructure evolution and spheroidization mechanism of powder metallurgy Ti-6Al-4 V alloy have been clarified. The spheroidization process is divided into two asynchronous stages. The initial stage is primarily characterized by the initial shearing and twisting of GBα grain boundaries, as well as the deformation of lamellar structure. Subsequently, the fragmentation of original GBα grain boundaries and the fracture of intra-granular α lamellae are observed. This process is accompanied by grain twisting and substructure formation, especially the division of lamellae through interface splitting and the segregation of local chemical elements. The differential accumulation of elements around the fractured and twisted grains suggests that element segregation and interfacial energy play a significant role in microstructure evolution. Therefore, the static spheroidization process largely depends on the formation and evolution of dislocation substructures, and the reduction of interfacial energy may be a key factor driving this process. These findings provide a theoretical basis for manufacturing metals with specific anisotropic properties by controlling microstructure evolution.

Eliminating the lamellar microstructure and improving the mechanical properties by optimizing the spheroidization of titanium alloys

Spheroidization of lamellar microstructure is the committed step to obtain the microstructure and mechanical properties required by titanium alloys. At present, the spheroidization of titanium alloys is mainly achieved through thermomechanical deformation and traditional heat treatment. This study first conducted hydrogenation treatment on cast Ti-6Al-4V alloy by cold rolling and cast Ti-6-Al-4V alloy by hot rolling. Then, spheroidization is carried out using two different methods: pulsed electric current and traditional heat treatment. The experimental results indicate that under the coupling effect of pulsed electric current and hydrogen, the original lamellar α phase in the cast Ti-6Al-4V alloy is broke, and the original strong preferred orientation disappears. In addition, the continuous lamellar β phase is decomposed into uniformly distributed β particles. Through the coupling effect of pulsed electric current and hydrogen, the mechanical properties of the cast Ti-6Al-4V alloy after spheroidization have also been significantly improved. The above experimental results are mainly attributed to the pulsed electric current promoting the elimination of dislocation and atomic diffusion in deformation cast Ti-6Al-4V alloy. At the same time, recrystallization is accelerated, thereby promoting spheroidization. The spheroidization process of coupling pulsed electric current with hydrogen provides a new and effective method for optimizing the original lamellar titanium alloy.

Mechanism of Crystallographic Orientation and Texture Evolution of Ti60 Alloy during Plane Strain Compression

The crystallographic orientation and texture evolution mechanism of equiaxed Ti60 alloy plates were investigated in this study through plane strain compression tests. The EBSD analysis revealed that the received plate contained two characteristic textures that were perpendicular to each other, i.e., c-axis//TD (Component 1) and c-axis//RD (Component 2), with the latter being caused by the change in direction of the TD texture that was generated during the previous unidirectional rolling process into an RD direction in the cross-rolling process. The results demonstrated that, with increasing the deformation temperature from 930 °C to 960 °C and 990 °C, the intensity of the c-axis//TD texture (Component 1) initially rose to a peak value of 5.07, which then—subsequently—decreased significantly to 2.96 at 960 °C and 3.11 at 990 °C. Conversely, the intensity of the c-axis//RD texture (Component 2) remained relatively unchanged. These texture changes were correlated with slip system activity and the spheroidization of the primary alpha phase. For the c-axis//TD texture, the initial intensity of the texture components during compression at lower temperatures could be attributed to the incomplete dynamic spheroidization process of the α phase, which leads to the reinforcement of the c-axis//TD due to prismatic slip. As the deformation temperature increased, the dynamic spheroidization process became more prominent, thereby leading to a significant reduction in the intensity of the c-axis//TD texture. In contrast, the c-axis//RD texture exhibited difficulty in activating the prismatic slip and basal slip; in addition, it also encountered resistance to dynamic spheroidization, thus resulting in negligible changes in the texture intensity.

Evolution of mechanical properties of ferrite and pearlite phases during spheroidization process and their relationship to the overall properties of low alloy steel

Mechanical properties of ferrite-pearlite low alloy steel are strictly determined by the properties of ferrite and pearlite phases. In this present paper, the evolution of mechanical properties of ferrite and pearlite phases during spheroidization process is investigated by using nanoindentation tests. Meanwhile, the overall mechanical properties of the material were measured using uniaxial tensile tests. Test results indicate that with the intensification of spheroidization of layered cementite in pearlite, the hardness and yield strength of pearlite phase decrease from 2.72 GPa to 1.73 GPa and 411.5 GPa–256.1 GPa, respectively. However, the mechanical properties of ferrite phase exhibit an opposite trend, with hardness and yield strength increasing from 1.6 GPa to 1.67 GPa and 188.1 GPa–208.4 GPa, respectively. Uniaxial tensile tests results indicate that overall yield strength of steel decreases significantly as the degree of spheroidization increases, from the original 276 MPa–229 MPa. Although the strength of pearlite decreased by 38%, the overall strength of alloy steel decreased by only 15% due to an 11% increase in ferrite strength. During spheroidization process, the relationship between pearlite hardness, yield strength, and interlayer spacing of cementite in pearlite can be expressed in Hall-Petch type relationships as: H=0.482×S−12+1.34 and σy=91.44×S−12+149; and the relationship between the strengths of ferrite-pearlite aggregate and ferrite and pearlite phases is σy=Vf1.95σf+(1−Vf1.95)σp.

Acceleration of Spheroidization in Low‐Density Ultrafine Pearlitic Steel by κ‐Carbide

The impact of κ‐carbide on the spheroidization process of low‐density ultrafine pearlitic steel (with 5 wt% Al and 5 wt% Mn additions) is investigated through isothermal annealing spheroidization. In the findings, it is demonstrated that κ‐carbides can significantly refine the lamellar spacing of low‐density ultrafine pearlite during the isothermal transformation. Additionally, under identical conditions, κ‐pearlite exhibits a higher number of ferrite/κ‐carbide interfaces. In the first stage of pearlite spheroidization, an abundance of dislocations and sub‐grain boundaries facilitate rapid fusion of the lamellar pearlite, while in the second stage, they provide a high‐speed diffusion pathway for carbon diffusion. Moreover, the reduced lamellar spacing shortens the distance for carbon and alloying elements diffusion, thereby promoting granular κ‐carbide formation and accelerating spheroidization in low‐density ultra‐fine pearlite.

Enhanced methylene blue adsorption by double alkali activation of highly porous glass microspheres prepared from waste glass

The remediation of water from organic pollutants, such as dyes and related compounds and the reuse of discarded glasses, represents fundamental challenges in highly industrialized countries. Porous glass microspheres have been proposed as efficient adsorbents in wastewater treatment, but their real application is problematic, especially from the perspective of their reuse and recycling. For the first time, the present paper describes the process of preparation and use of highly porous bodies with a specific surface area of nearly 20 m2/g fabricated from alkali activated glass microspheres and applicable for the removal of methylene blue as a model organic dye from wastewater. Alkali activation is applied both as an intermediate step (using 9 M KOH) for the conversion of waste glass into porous microspheres by flame spheroidization process, and as a final step (using 2.5 M NaOH), facilitating low temperature consolidation of the microspheres, and their transformation into porous structures. The experimental adsorption capacity of porous glass microspheres pellet was 122 mg/g. The high correlation coefficient indicates the applicability of Langmuir isotherm adsorption model.

Effects of heat treatment on microstructure and mechanical properties of squeeze casting AlSi9Mg alloy flywheel housings formed with local supplementary pressure

Targeted squeeze casting components of the thick-walled locations with local supplementary pressure (LSP) can effectively realize the local forced shrinkage, which is very significant for the elimination of shrinkage defects. In this paper, the effects of solid solution temperature, solid solution time, aging temperature and aging time on AlSi9Mg aluminum alloy flywheel housing with large wall thickness difference and complex structure formed with LSP were investigated. The results showed that the LSP effectively refined the microstructure and accelerated the spheroidization process of eutectic silicon, which reduced the heat treatment holding time significantly. The twinning growth of silicon particles effectively hindered the dislocation motion, relieved the stress concentration, and improved the strength. The fishbone-like AlSiMnFe phase were passivated after heat treatment. Heat treatment can enhance the plasticity by breaking and spheroidizing the coarse needle-like eutectic silicon, and enhance the strength by refining and homogenizing the β" phase precipitated in the alloy. The optimum heat treatment parameters are solid solution at 540 °C for 210 min and aging at 175 °C for 480 min. Under the optimum heat treatment condition, the ultimate tensile strength, yield strength and elongation for the position with LSP reached 306.1 MPa, 237.5 MPa, 13.29 %.

Study on the recycling of 100Cr6 powder by plasma spheroidization for Laser Powder Bed Fusion

Additive Manufacturing (AM) of steel parts is crucial in various industries such as medical, energy and transport. Laser Powder Bed Fusion (L-PBF) is a commonly used technique for producing such parts, but it can alter the properties of the unconsumed powder. This study aims to investigate the recycling of oxidized 100Cr6 powder using a plasma spheroidization process, focusing on its physical and chemical properties. The experiments reveal that the powder feed rate during spheroidization has an impact on the physical properties of the recycled powder, an optimized powder feed rate is found. Different washing and drying conditions are applied to the spheroidized powder and their influence on the powder's chemical composition is analysed through oxygen measurement. One of the washing and drying condition led to oxygen content even lower than the commercial powder. Additionally, three different hydrogen ratios in the plasma during the spheroidization process are investigated and it is found that increasing the hydrogen ratio can reduce the oxygen content in the processed powders.

Rapid Spheroidization Process of S Phase (Al2CuMg) in the As-Cast 2024 Al Alloy Induced by High-Energy Electropulsing.

The effect of electropulsing treatment (EPT) on the microstructure of the as-cast 2024 Al alloy at room temperature was investigated. The results show that EPT remarkably accelerated the spheroidizing of second phase (S phase) in the as-cast 2024 Al alloy. The mechanism for rapid spheroidizing of the second phase was proposed based on not only the accelerated dissolution, but also the growth of particles. The morphology and size of the secondary phase could be controlled by changing the cooling speed of the specimen after EPT. Furthermore, the dissolving process of the randomly distributed S phase was recognized as the combination effect of the two basic dissolving ways. Hence, the EPT can be applied to improve the microstructure and properties of the alloys.

Microstructure of the Advanced Titanium Alloy VT8M-1 Subjected to Rotary Swaging.

In this study, the microstructural behavior of the advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn-0.15Si (VT8M-1) alloy during rotary swaging (RS) was investigated. VT8M-1 has increased heat resistance and is considered a replacement for the Ti-6Al-4V alloy. It was shown that, during RS, the evolution of the primary a phase is characterized by the formation of predominantly low-angle boundaries according to the mechanism of continuous dynamic recrystallization. The density of low-angle boundaries increases three times: from 0.38 µm-1 to 1.21 µm-1 after RS. The process of spheroidization of the lamellar (a + b) component is incomplete. The average size of globular a and b particles was 0.3 μm (TEM). It is shown that the microstructures after RS (ε = 1.56) and equal-channel angular pressing (ECAP) (ε = 1.4) are significantly different. The temperature-velocity regime and the predominance of shear deformations during ECAP contributed to a noticeable refinement of the primary a-phase and a more complete development of globularization of the lamellar (a+b) component. EBSD studies have shown that RS leads to the formation of a structure with a higher density of low- and high-angle boundaries compared to the structure after ECAP. The results are useful for predicting alloy microstructure in the production of long rods that are further used in forging operations.

Dynamic Spheroidization Mechanism and Its Orientation Dependence of Ti-6Al-2Mo-2V-1Fe Alloy during Subtransus Hot Deformation.

The dynamic spheroidization mechanism and its orientation dependence in Ti-6Al-2Mo-2V-1Fe alloys during subtransus hot deformation were studied in this work. For this purpose, hot compression tests were carried out at temperatures of 780-880 °C, with strain rates of 0.001-0.1 s-1. Based on SEM, EBSD and TEM characterization, the results showed that the aspect ratio of the α phase decreased with increasing deformation temperatures and decreasing strain rates. At 880 °C/0.001 s-1, the aspect ratio of the α phase was the smallest at 2.05. The proportion of HAGBs decreased with increasing temperatures and strain rates, which was different from the trend of the spheroidization; this indicated that the formation of HAGBs was not necessary for the spheroidization process. Furthermore, the formation of the α/α interface was related to the evolution of dislocations and twin boundaries at high (880 °C) and low temperatures (780 °C), respectively. Moreover, the dependence of lamellar spheroidization on the crystallographic orientation tilt from the compression direction (θ) was clarified: when θ was between 45° and 60°, both the prism <a> slip and basal <a> slip systems were activated together, which was more favorable for spheroidization. This study could provide guidance for titanium alloy process designs and microstructure regulation.

Synthesis of single‐phase high‐entropy diboride powders and their spheroidization process

AbstractSpherical (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 powders with a uniform particle size distribution are successfully prepared using a novel industrial approach, which combines spray‐drying process and thermal plasma sintering technology together. In this, single‐phase (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 powders are first synthesized via a borothermal reduction process using a mixture of individual metallic oxides and boron powders as starting materials. The influence of boron powder content on the structure of prepared powders is researched. Then, (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 granules are prepared after wet‐grinding and spray‐drying process, which exhibit a spherical shape and homogeneous element distribution. RF induction thermal plasma is finally used to sinter the granulated particle, and the apparent density of sintered spherical powders is increased to 2.57 g/cm3 from 1.43 g/cm3. Such powders are in potential demand for additive manufacturing techniques, and the successful synthesis of spherical (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 powders may guide the way toward the preparation of many other spherical high‐entropy diboride powders.

Powder plasma spheroidization treatment and the characterization of microstructure and mechanical properties of SS 316L powder and L-PBF builds

A plasma spheroidization treatment was applied to stock stainless steel 316L powder for additive manufacturing. The normal and treated powders were compared both in the powder state as well as in the resulting laser powder bed fusion (L-PBF) builds. The plasma spheroidization process slightly increased treated powder aspect ratio and sphericity and shifted the size distribution to larger diameters relative to the normal powder. The normal powder was austenitic in nature whereas the plasma spheroidization process introduced a small fraction (∼3.5 vol %) of ferrite in the treated powder. Ferrite in the powder was not retained in the printed samples and was not shown to negatively affect the build quality. Porosity areal fraction was generally smaller in the treated powder builds. The normal powder builds had a 6% higher yield strength than treated, however the scatter was significantly larger in the 45° and horizontal orientations compared to the treated powder builds.