Coarse Columnar Grains Research Articles

The effects of specimens geometry on solidification conditions and microstructure formation in laser powder bed fusion fabricated Ti–6Al–4V alloys

Laser powder bed fusion (LPBF) excels at creating intricately shaped parts, which will result in variations in solidification conditions, microstructure formation and mechanical properties. To address this issue, three distinct shapes: cubic, pyramidal and inversed pyramidal Ti–6Al–4V alloy specimens were fabricated using LPBF technology. The effects of specimen geometry on microstructure formation, transformation as well as its effects on mechanical properties were investigated in the present study. Our results show that specimen geometry significantly affects the thermal gradient, influencing nucleation and growth during fabrication. EBSD (Electron Backscatter Diffraction) characterization reveals that the primary β-phase grows in columnar grains in cubic specimens, coarse columnar grains along lateral faces in pyramidal specimens, and nearly equiaxed grains in inverted pyramidal specimens, leading to a significant reduction in texture. Nanoindentation tests show higher nanohardness in the top parts of cubic and pyramidal specimens compared to the bottom parts, while inverted pyramidal specimens have consistent nanohardness throughout. This variation is due to differences in solid solute concentration, melt pool undercooling, and thermal histories during and post solidification processes respectively. TEM results indicate that the fine lath phase on the top parts has transformed into β-phase, while the bottom parts remain as α′ phase, highlighting a disparity due to different thermal cycling times and temperatures.

Mechanical property, corrosion behavior and cytocompatibility of CoCrMo for dental application: A comparative study of cast and laser powder bed fusion

In this work, by employing powders sourced directly from the original ingot for additive manufacturing, we enabled a comparative overview of the performance between CoCrMo manufactured via laser powder bed fusion (LPBF) and those in their original cast condition. Microstructural analysis revealed that the cast (CT) alloy predominantly consisted of coarse grains with distribution of sigma phase, while the LPBF process resulted in a refined grain structure devoid of the sigma phase. The tensile strength tests demonstrated that the LPBF-derived CoCrMo alloy had substantially greater tensile strength, and ductility compared to CT alloy. Corrosion tests indicated superior corrosion resistance in the LPBF alloy, albeit with a lower metal ion release. In vitro assays confirmed that LPBF CoCrMo alloys displayed favorable cytocompatibility. Consequently, it is concluded that the CoCrMo alloy processed through laser powder bed fusion exhibited enhanced mechanical performance and corrosion resistance. These improvements are primarily attributed to the transformation of the original coarse columnar grain structure through the LPBF technique.

Infrequent trigonal crystal system CoNb thin films: investigation of growth behavior, microstructure and magnetic properties

Magnetic films with excellent initial permeability, high resonance frequency, suitable anisotropy fields, and well compatibility are highly desirable for on-chip inductors and transformers. Here, Co90Nb10 thin films with different thicknesses are grown on Si substrates of different orientations using an electron beam evaporation technique. A rare trigonal crystal structure of the CoNb films was observed and was virtually unaffected by substrate orientation. Films grown exhibit thickness-dependent magnetic behavior: coercivity initially decreases and then increases, while the in-plane anisotropy field progressively diminishes. Meanwhile, the initial permeability increases initially before decreasing, and the resonance frequency continuously decreases as the thickness increases. The resultant Co90Nb10/Si (111)-50 nm film displays a high μi of 496 and a great fr of 2.1GHz. The improved magnetic performance originates from the smaller crystallite size, smoother surface roughness, and suitable in-plane anisotropy field. Moreover, the in-plane anisotropy transition to the out-of-plane anisotropy in the Co90Nb10 films whose thickness exceeds 70nm, which is attributed to the growth of the coarse columnar grains once the critical thickness is exceeded. This study demonstrates the correlation between the growth behavior, microstructure, and magnetic properties of CoNb thin films, presenting a new potential for utilizing Co-based thin films in high-frequency applications.

Effect of laser parameters on microstructure and mechanical properties of Al–Ni–Sc–Zr alloys fabricated by laser powder bed fusion

The processability, microstructure and mechanical properties of a near eutectic AlNiScZr alloy fabricated by laser powder bed fusion (LPBF) are investigated. The optimal processing windows for the LPBF alloy are determined. The results indicate that laser power exerts a predominant influence on the relative density of the as-built alloy. Elevated laser power can lead to increased relative density. Laser scanning speed exerts a significant impact on the microstructure and mechanical properties of the as-built alloys. An increase in the laser scanning speed can facilitate the growth of coarse columnar grains in the coarse grain region and suppress the formation of ultrafine equiaxed grain bands. Furthermore, the increase in the laser scanning speed can result in a reduction in the size of the cells, which in turn leads to an enhancement in the strength of the alloys. This study examines the evolution of the microstructure and mechanical properties of the as-built alloy as a function of laser scanning speed. By elucidating the relationship between laser parameters, microstructure and mechanical properties, the objective is to provide fundamental guidance for tuning the solidification structures and mechanical properties of LPBF AlNiScZr alloys by selecting appropriate laser parameters.

LNG storage tanks 9% Ni steel weld inspection via phased-coherent TFM and SVD enhancement

ABSTRACT 9% Ni steel is commonly utilised in liquefied natural gas storage tanks due to its strong resistance to corrosion and oxidation. However, the welds in these tanks are prone to serious defects, necessitating thorough non-destructive testing. Unfortunately, when inspecting nickel-based alloy welds using phased array ultrasonic testing (PAUT) technology the ultrasonic waves are scattered and attenuated because of the coarse columnar grains. To address this challenge, this paper introduces a based on SVD enhancement directivity corrected circular coherence factor weighted TFM imaging algorithm (SVD-DC-CCF). Initially, the CCF matrix is corrected by the directivity and energy attenuation compensation factors, then weighted with the TFM pixel point amplitude. Subsequently, the weighted amplitude matrix undergoes singular value decomposition (SVD), followed by the establishment of an enhancement factor to reconstruct the amplitude matrix. The proposed algorithm is evaluated through experiments on three types of defects in a 30.0 mm thick 9% Ni steel T-shaped fillet weld test block. Results demonstrate superior signal-to-noise ratio (SNR) and enhanced image resolution. Compared to TFM results, the SNR increases by 4.97 dB, 4.25 dB, and 4.96 dB, respectively, while the array performance index (API) decreases by 9.80%, 34.39%, and 22.22%, respectively.

Multi-scale microstructure and its synergetic strengthening effect in stress rupture life of Inconel 718 fabricated by high-deposition-rate laser directed energy deposition

Superior elevated temperature properties are critical for the application of Inconel 718 in hot-end components. The utilization of high-deposition-rate laser directed energy deposition (HDR-LDED) increases the microstructural diversity of Inconel 718, which accordingly provides more opportunities for properties improvement. Herein, Inconel 718 alloy with a multi-scale microstructure were fabricated by HDR-LDED followed by customized heat treatment. The coarser columnar grains (width ∼300 μm) were obtained with γ" phase (diameter ∼33.74 nm and volume fraction ∼15.16 %) distributed homogeneously in the grain and the fine Laves phases (length ∼3.69 μm; width ∼1.94 μm; aspect ratio ∼1.99 and volume fraction ∼1.55 %) in the inter-dendritic region. This multi-scale microstructure possesses an excellent stress rupture life of 342.9 h with the elongation of 13 % at 650 °C, which far exceeds that of the forging (106 h, 4.2 %), It is attributed to the reduced number of transverse grain boundaries, the finer Laves phase accommodating many dislocations, and γ" phase promoting the formation of stacking faults, Lomer-Cottrell locks and nanotwins. The findings demonstrate the great potential of additively manufactured microstructure in properties enhancement, and may be enlightening for the development of novel customized high-temperature alloys.

Role of TiC on the microstructure, tensile property and thermal stability of laser powder bed fusion fabricated AlSi10Mg alloy

The incorporation of ceramic particles is frequently employed to enhance the printability of high-strength aluminum (Al) alloys in laser powder bed fusion (L-PBF). However, their influence on the long-term thermal stability and elevated temperature mechanical properties of the Al alloy is seldom studied. This study aims to address this gap by investigating the role of micron-sized TiC particles in the microstructure, long-term thermal stability, and elevated temperature tensile properties of an L-PBF-fabricated AlSi10Mg alloy. The results indicate that highly dense TiC/AlSi10Mg samples can be fabricated, featuring fine equiaxed grains rather than the coarse columnar grains typically formed in the AlSi10Mg alloy. This columnar-to-equiaxed transition is attributed to the residual TiC and the in-situ formation of Al3Ti particles, which act as nucleating agents. Moreover, the incorporation of TiC significantly enhances the long-term thermal stability of the AlSi10Mg alloy by improving the stability of the eutectic network and retarding the coarsening of Si particles by inhibiting Si diffusion. Compared to the AlSi10Mg counterpart, the TiC/AlSi10Mg composite exhibits a higher hardness retention ratio (56 % versus 45 %) after thermal exposure at 400 °C for 192 h. The residual TiC and in-situ formed Al3Ti have high thermal stability and can impede dislocation motion, thereby contributing to enhanced long-term thermal stability. This study offers insights into the design of L-PBF ceramic-reinforced Al alloys with improved thermal stability for high-temperature applications.

Electron beam welding of the novel L12 nanoparticles-strengthened medium-entropy alloy Ni41.4Co23.3Cr23.3Al3Ti3V6: Microstructures, mechanical properties, and fracture

Although low levels of vanadium-doping can enhance the friction stress and strength of L12-nanoparticles strengthened medium-entropy alloys (MEA), how high concentrations of vanadium affect the weldability, microstructure, mechanical properties, and fracture behavior remains unknown. In this work, we designed a vanadium-doped, L12-nanoparticle-strengthened MEA Ni41.4Co23.3Cr23.3Al3Ti3V6 (at.%), which showed a high fracture toughness of 238 MPa × m1/2, a high friction stress of 410 MPa, and a Hall-Petch strengthening coefficient of 782 MPa × μm1/2. Pieces of the HEA were joined using electron-beam welding (EBW). Strong yet ductile defect-free joints were produced which had coarse columnar grains (88 μm) with a {110}<001> texture in the fusion zone, which was larger than the equiaxed grains in the heat-affected zones (14.9 μm) which had strong {110}<001> and relatively weak {110}<112> texture. In contrast, the base materials had fine grains (2.2 μm) with a strong {110}<111> and a relatively weak {110}<112> texture. The EBWed MEA showed a high yield strength of 599 MPa, a high ultimate tensile strength of 939 MPa, a good fracture strain of 20 %, and a fracture toughness of 198 MPa × m1/2, which were 75 %, 83 %, 58 %, and 83 %, respectively, of the values of for the thermo-mechanically treated counterpart. The reduced strength arose from the coarse columnar grains, while the reduced fracture strain and fracture toughness could be ascribed to the reduced deformation twinning and the absence of annealing twins, which produced a poor strain hardening capability. The EBWed MEA exhibited abundant dislocation networks, indicating that a high concentration of vanadium inhibited the occurrence of stacking faults and nanoscale deformation twins.

Microstructural characteristics and mechanical properties of Al-Cu alloys fabricated via 8-shaped oscillating laser wire additive manufacturing

Al–Cu alloy components fabricated by laser wire additive manufacturing (LWAM) generally present coarse columnar grains and poor mechanical properties. This study proposes a new strategy, integrating an 8-shaped beam oscillation and laser directed energy deposition, to solve these issues. The impacts of oscillation frequencies and amplitudes on the energy flux distribution and macro morphology of the single-bead deposited layer are investigated. The influences of beam oscillation on the microstructural characteristics and tensile properties of Al–Cu alloys fabricated by oscillating laser wire additive manufacturing (O-LWAM) are revealed. A high-frequency oscillating laser achieves a uniform energy flux distribution and improves the surface quality of the deposited layer. The <100> texture in the O-LWAM specimen decreases markedly owing to the columnar to equiaxed transition. The Cu element content at grain boundaries in the O-LWAM specimen is reduced by 52.6 %. The ultimate tensile strength of O-LWAM specimens in the horizontal and vertical orientations reach 334.2 and 327.3 MPa, respectively, which increased by 40.7 % and 64.6 % compared to those of the LWAM specimen. The substantial enhancement in strength and plasticity is attributed to fine-grain strengthening.

Modelling grain refinement under additive manufacturing solidification conditions using high performance cellular automata

Despite increasing applications of additively manufactured parts, they still suffer from anisotropic mechanical properties and can experience cracking due to coarse columnar grain structures induced by metal 3D printing. Microstructural control is promising avenue to overcome these challenges, but requires deeper understanding of factors controlling solidification, particularly regarding grain refinement. Addressing this gap, this study explores grain refinement in Al-Cu alloys with a process-microstructure linking cellular automata-finite difference (CAFD) approach supported by single-track laser surface remelting (LSR) experiments. To enhance the understanding of nucleation behaviour in alloys under additive manufacturing solidification conditions, this research analyses the influence of nucleation parameters on the post-LSR microstructures. Additionally, this study explores the computational dimensions of microstructure modelling, testing CA mesh sensitivity effects and benchmarking our CAFD models on two high-performance computing platforms. The CAFD model captures well the key microstructural features observed in LSR Al-Cu alloys with and without grain refiner addition. It is shown that the maximum nucleation density has a significant effect on the final microstructure, resulting in different proportions of coarse columnar grains resulting from epitaxial solidification, newly nucleated thin columnar grains, and equiaxed grains.

Heat and mass transfer behavior in CMT plus pulse arc manufacturing

The metal transfer mode, temperature distribution, flow behavior, and microstructure characteristic in the process of cold metal transfer plus pulse (CMT+P) arc manufacturing were investigated by the in-situ observation and numerical simulation. A novel coupling model for droplet-pool interaction under the CMT+P arc was established, along with a new heat source model that considered Marangoni forces on droplets. These innovations provided significant insights into the heat and mass transfer mechanisms in the CMT+P hybrid arc manufacturing process. The results show that the droplets generated by the CMT+P hybrid arc exhibited a mixed transfer mode: short-circuit transfer in the CMT period and projected transfer of one droplet per pulse during the pulse period. The short-circuit transfer was more stable than the projected transfer, attributed to the smooth transfer of droplets to the molten pool through the liquid metal bridge, dominated by surface tension and Marangoni forces. The main energy of the molten pool was provided by droplets, which had a dominant ability to melt the substrate. However, the liquid metal bridge in the CMT period slowed down the heat transfer to the molten pool and had significant oscillating and stirring effects. During the pulse period, the droplet was accelerated and projected transfer by gravity and electromagnetic force. After solidification, the microstructure exhibited an alternating distribution of columnar and equiaxed grains from the bottom-up in the monolayer deposited layer, with a deflected fusion interface towards the scanning direction. At the top of the deposited layer, coarse columnar grains were distributed obliquely or laterally, inhibiting the growth of equiaxed grains and forming a distinct boundary with the equiaxed grains below.

In-situ microalloying of Al-Cu-Sc alloy manufactured by beam oscillating wire laser directed energy deposition: Grain refinement and properties improvement

Al-Cu alloys manufactured by wire laser directed energy deposition (WLDED) usually exist coarse columnar grains. The novelty of this study is adding Sc to Al-Cu alloy of beam oscillation wire laser directed energy deposition (O-WLDED), achieving grain refinement by in-situ microalloying of Sc. An Al-Cu alloy part and an Al-Cu-Sc alloy part are prepared by O-WLDED, respectively. Furthermore, how the Sc affects the microstructure and mechanical properties is explored and discussed. The in-situ microalloying of Sc provides more nucleation sites for grains and promotes the columnar to equiaxed transformation. The average grain size of the overlapping zone decreases from 21.64 to 14.32 μm, and that of the remelting zone decreases from 18.67 to 7.83 μm. The grain refinement is significant. The contents of θ-Al2Cu and θ'-Al2Cu at grain boundaries of the Al-Cu-Sc alloy reduce since Al3Sc particles precipitated from the Al matrix can hinder the segregation of Cu. The ultimate tensile strength and elongation of the Al-Cu-Sc alloy reach 433 MPa and 11.8 %, respectively, respectively 117 MPa and 2.6 % higher than those of the Al-Cu alloy.

Effect of powder composition on WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion (L-PBF) of WE43 magnesium alloy has a promising application prospect in the fields of lightweight parts and biodegradable implants. Grain refinement in these components is expected for high strength and controlled biodegradation, however, grain structure of WE43 is sensitive to composition and processing. L-PBF WE43 exhibited significant diversity on the microstructure and properties with the fluctuation of powder composition, and the influencing mechanism remained unclear. In this study, L-PBF samples were fabricated with high formation quality using four different WE43 powders, in which the content of Nd and Zr were purposely adjusted. Their microstructure, tensile properties and corrosion resistance were characterized. L-PBF specimens composed of fine equiaxed grains were obtained from Mg-3.56Y-2.45Nd-1.14Gd-0.40Zr powder, achieving ultimate strength of 316 MPa and elongation of 15%. With the minor decrease of Nd and Zr content, which was still in the range of present standards of WE43, L-PBF specimens respectively exhibited abnormal grain growth and coarse columnar grains, leading to tremendous deterioration of mechanical properties and corrosion resistance. During the multiple layers of fusion and solidification, Zr promoted the columnar-to-equiaxed transition and generated finer grains, while Nd exerted pinning effect in the heat affected zone to keep the fine grains from abnormal grain growth. The results firstly demonstrate the significant influence of the minor change of alloying elements on the performance, and indicate that a stricter compositional standard of WE43 powder is necessary to achieve reliable properties for the L-PBF process.

Improving the formability and quality of CMT additively manufactured aluminum thin-wall parts via laser stabilization effect

In the recent past, the deposition efficiency has been one of the most concerned problems in aluminum additive manufacturing. In this research, a comparative study on the formation quality, microstructures and mechanical properties of aluminum alloy thin-wall structures between the oscillating laser-arc hybrid additive manufacturing (O-LHAM) and wire-arc additive manufacturing (WAAM) at high deposition speed was performed. The formation quality of the additively manufactured thin-wall parts under O-LHAM was significantly improved compared with WAAM. The molten pool overflow was significantly eliminated due to the higher support force on the molten pool, thus the surface roughness Sa and the maximum surface height difference Sz of O-LHAM thin walls were reduced by 13% and 22%, respectively. Compared with thin wall manufactured via WAAM, the microstructure of O-LHAM mainly consisted of coarse columnar grains and showed anisotropic characteristics due to the increased heat accumulation. Moreover, owing to the higher porosity in the interlayer combination regions of WAAM sample, the elongation of thin walls manufactured via O-LHAM was higher than WAAM in both horizontal and vertical directions, reaching 36.8% and 32.5%, respectively. This work will provide more guidance on thin-wall additive manufacturing with high deposition efficiency.

Stable superelasticity with large recoverable strain in NiTi alloy via additive manufacturing

We report a stable superelasticity with large recoverable strain in Ni51·2Ti48.8 (at.%) shape memory alloy (SMA) via additive manufacturing of laser powder bed fusion (LPBF). Microstructure analysis indicates that the LPBFed SMA samples have a non-homogeneous microstructure of two different grain zones, i.e., the coarse columnar one and the fine cellular one. Specifically, the coarse columnar grain zone accounts for a predominated content as high as ∼79 vol% and has a relatively low dislocation density. In contrast, the fine cellular one has a low content of ∼21 vol% yet a high dislocation density. Especially, all LPBFed non-homogeneous SMA samples exhibit a strong (100) texture with high intensities of 40.2–56.1, accompanied by homogeneous coherent Ti4Ni2Ox nanoprecipitates. Constant-stress cyclic compression shows that the LPBFed sample with 79 vol% coarse columnar grain zone and 52.8 (100) texture presents stable superelasticity with large recoverable strains, 5.71 % from 15 to 30 cycles at high loading of 1200 MPa. Such a large recoverable strain herein is superior to those in NiTi SMAs fabricated by various methods. Basically, the stable superelasticity is attributed to the strong (100) texture against plastic deformation and the pinning effect of the homogeneous coherent Ti4Ni2Ox nanoprecipitates on dislocation motion during cyclic loading. Meanwhile, the large recoverable strain originates from the high ability to accommodate new dislocation in the high content columnar grain zone. This work can provide significant insights into design of high-performance NiTi SMAs and further accelerate their engineering application by additive manufacturing.

Enhancing strength and ductility of graphene and ZrO2 nanoparticles hybrid reinforced AA2024 composite fabricate by laser powder bed fusion

The AA2024 aluminum alloy is difficult to manufacture by laser powder bed fusion (L-PBF) due to its crack sensitivity. This work introduces a novel crack-free graphene nano-platelets (GNPs) and ZrO2 nanoparticles hybrid-modified AA2024 alloy suitable for laser powder bed fusion (L-PBF). The columnar-to-equiaxed transformation caused by nanoparticles-inducing nucleation sites eliminates the cracks. A bimodal microstructure consists of coarse columnar grains and ultrafine equiaxed grains, which are formed in the as-built composites. Compared with the L-PBF prepared AA2024 alloy and 1 wt% ZrO2/AA2024 composite, the (0.2 wt% GNPs + 1 wt% ZrO2)/AA2024 composite exhibit the highest tensile strength of 382 MPa and elongation of 16 %. The introduction of GNPs and ZrO2 nanoparticles provide dual increment in both tensile strength and ductility compared with single ZrO2 nanoparticles modified AA2024. Following further T6 heat treatment, the tensile strength increased significantly to 624 MPa, but the elongation decreased dramatically to 5.6 %. In-depth analysis was provided of the strength and ductility improvements induced by GNPs/ZrO2 nanofiller in this investigation.

Multi-gradient structures by cold extrusion of strongly textured continuously cast commercially pure aluminum

During extrusion, the material is subjected to a heterogeneous deformation that results in the formation of gradients of microstructure and thus mechanical properties. In this study, using continuously cast commercially pure aluminum as a reference material, we show how a cast structure with coarse columnar grains affects the formation of these gradients during extrusion at room temperature. Characterization of the initial material as well as the extruded round bars by optical and electron microscopy, X-ray diffraction as well as by means of mechanical testing documents the formation of four characteristic annular sections. For extrusion along the casting direction there is a <100>/<111> double-fiber textured center with lowest hardness, followed by a <111> single-fiber textured ring with a hardness plateau, a double-fiber textured region with grains arranged alternatingly in an iris-like shape, and an (ultra-)fine grained surface layer with highest hardness. For extrusion opposite to the casting direction we find similar characteristics of the center section. With increasing distance from the center follow another double-fiber textured section with increasing hardness, a <111> single-fiber textured ring with nearly homogeneous hardness and a surface layer with a slightly rotated <111> fiber and highest hardness. The key finding is that the macroscopic anisotropy of the cast material, resulting from the grain size, crystal orientation and growth direction of the columnar grains, determines the local material flow during extrusion and thus leads to the formation of these different complex multi-gradient macrostructures that may provide unique properties for complex applications such as light-weight safety-relevant components.

Isotropy of fatigue crack growth in hybrid additive manufactured Ti6Al4V ELI titanium alloy

In the present paper, the effects of macrostructure and microstructure on fatigue crack growth (FCG) behavior of wire and arc additive manufacturing (WAAM) and hybrid additive manufacturing with in-situ rolling (HAMR) were investigated in three sampling directions for Ti6Al4V ELI. The results demonstrate that WAAMed samples exhibit coarse columnar grains with zigzag boundaries, interlayer heat affected band (HAB), and basketweave microstructures. The fatigue crack growth rate (FCGR) is lowest in the Y-X direction while being similar between the X–Y and X-Z directions, indicating significant anisotropy. This difference can be attributed to changes in plastic region size and internal slip characteristics near the crack tip caused by variations in macrostructure and microstructure. After applying HAMR with quasi-β heat treatment, interlayer HABs are eliminated, resulting in uniform equiaxed grains and colony microstructures. The FCGR curves in three directions significantly overlap without any observed anisotropy, which are lower than those obtained for traditionally forged materials. Therefore, the isotropic FCGR of plastic materials can be reduced by achieving a nearly flawless metallurgical quality and ensuring uniform equiaxed grain matching with the corresponding critical colony size and fine thickness lamellae. The findings suggest that the application of quasi-β heat treatment in conjunction with HAMR offers a promising high-efficiency manufacturing technique for producing isotropic titanium alloy forgings characterized by exceptional damage tolerance.

Inconel 718 alloy reinforced with nano-sized WC particles and graphene nanoplatelets: Microstructure, wear resistance and electrochemical properties

The coarse columnar grain structure of additively manufactured metals diminishes material performance, hence the transition from columnar grains to equiaxed grains is extensively investigated. The microstructure of composite materials and the properties of Inconel 718 are positively influenced by both nano-sized tungsten carbide (nano-WC) and graphene nanoplatelets (GNPs), which act as reinforcing phases. The study employs directed energy deposition (DED) technology for the fabrication of Nano WC/GNPS-IN718 composite materials. Th emicrostructure, wear resistance, and corrosion resistance properties of both Inconel 718 and its composite materials were systemically investigated. The findings discover the microstructure of the composite material consists of γ/M7C3 phases with precipitation of carbides such as (Nb,Ti)C. Utilizing nano WC and graphene as lubricants, and carbides like (Nb,Ti)C as strengthening phases, the composite material exhibits a grain size refinement of approximately 3.36 % compared to IN718. The grain orientation in the XOY plane predominantly aligns along the <001> direction. The Nano WC/GNPS-IN718 composite material exhibited a 1.264-fold increase in average microhardness compared to the IN718 alloy. Notably, the friction coefficient and wear rate were only 77 % and 18.75 %, respectively, of those observed in the IN718 alloy. Furthermore, the corrosion current density of the Nano WC/GNPS-IN718 composite material was 30.8 % of that observed in IN718, with a polarization resistance 4.08 times higher than that of IN718.

The comprehensive study on texture evolution and recrystallization behavior of twin-roll strip casting Fe-50 %Co alloy

The iron-cobalt soft magnetic alloy exhibits excellent properties such as high saturation magnetic induction, high magnetic permeability, and high Curie temperature, making it widely used in areas like aviation generators and electric motors. However, traditional iron-cobalt alloy strip materials often suffer from a high magnetic anisotropy constant, which hinders their performance in practical applications. In this study, twin-roll strip casting was employed to produce Fe-50Co soft magnetic alloy cold-rolled strip materials. The research findings reveal that the initial microstructure of the Fe-50Co alloy strip prepared through twin-roll strip casting is primarily composed of coarse columnar grains and equiaxed grains, with a strong {001} orientation for the columnar grains. Notably, a significant number of Σ3 grain boundaries are present within the cast strip. These grain boundaries effectively reduce dislocation accumulation during the cold rolling process and subsequently minimize the nucleation sites for γ-texture during subsequent annealing. Furthermore, a strong {001}<uv0> texture is formed in the finished strip material after cold rolling and annealing, resulting in superior magnetic properties. The alloy exhibited excellent magnetic properties after annealing at 900 ℃ for 5 h followed by furnace cooling to 750 ℃ with the cooling rate of 50 ℃/h and then to 300 ℃ with the cooling rate of 180 ℃/h, the B5000 was ∼ 2.417 T, P1.5/400 was ∼22.651 W/kg and P2/1000 was 183.51 W/kg. These findings provide valuable insights for the development of Fe-50Co alloys with excellent magnetic properties.