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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Electric field enhanced diffusion welding of alloy 617: Microstructural characteristics and mechanical properties

This study investigated the microstructural characteristics and mechanical behavior of diffusion welded nickel-based Alloy 617 obtained by electric field-assisted sintering (EFAS) using various parameters. The interfacial microstructure exhibited different characteristics including good grain boundary (GB) migration across the interface in the samples diffusion-welded at 1100 °C and a flat interface in the samples joined at 1000 °C and 1050 °C. The interface consisted of fine Al 2 O 3 oxides, while precipitation of interfacial M 23 C 6 carbides was not observed. Grain boundaries migrated across the Al 2 O 3 oxides, leaving these oxides within the grains. Graded grain size was observed, with grain coarsening being more significant near the sample surface due to the temperature gradient induced by EFAS. Tensile testing revealed that the specimens fractured in the matrix away from the interface, indicting strong diffusion-welded joints. Further, the peak tensile strength of 807 MPa was obtained in the samples welded at 1000 °C due to minimal grain growth. The materials obtained at 1100 °C exhibited reduced tensile strength but improved ductility. Strain maps revealed by digital image correlation showed alternating high and low strain segments in the samples produced at 1000 °C and 1050 °C, indicating that the flat interfaces with no GB migration were less ductile compared to the matrix. A greater strain uniformity was observed along the bond interfaces with improved GB migration. The hardness reduced near the sample surfaces due to enlarged grains induced by temperature gradient. This study demonstrates that GB migration and enhanced mechanical strength can be achieved in diffusion-welded Alloy 617.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of Solidification Cooling Rates on Microstructures and Physical Properties of Fe-6.5%Si Alloys

Compared to the widely used Fe-3.2wt%Si steel, Fe-6.5wt%Si has superior electric and magnetic properties, including higher electrical resistivity, lower iron loss, higher permeability, and near zero magnetostriction. However, Fe-6.5wt%Si sheet is difficult to produce using traditional manufacturing processes as the high silicon content favors the formation of ordered phases that embrittle the material. Fortunately, these ordered phases can be suppressed if the alloy is cooled fast enough from a high temperature kinetically trapping the disordered solid solution or amorphous state. Planar flow casting is known for its rapid solidification rate. In order to consider it as a viable method to manufacture ductile Fe-6.5wt%Si sheets, the effect of cooling rate on physical properties of Fe-6.5wt%Si alloy are systematically investigated. In this work, various cooling rates are achieved by changing melt-spin wheel speeds, which significantly affect the solidification temperature profile and have profound effects on ordering, microstructures, textures, hardness, and magnetic properties. High cooling rates result in refined grains, reduced ordering, enhanced <100> out of the plane texture, decreased hardness, and increased coercivity. This study demonstrates a critical cooling rate at ~1.7 × 10 5 K/s, corresponding to a tangential wheel speed of 5-7 m/s, below which the hardness significantly increases in agreement with the sudden increase of the ordered phases that causes the material embrittlement.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure and creep properties of cast near-eutectic Al–Ce–Ni alloys

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al 11 Ce 3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al 3 Ni and Al 11 Ce 3 fibers, (iii) large ternary eutectic colonies, where the binary Al 3 Ni and Al 11 Ce 3 phases are alternating or intertwining within the individual, fine fibers (diameters of ~60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al 3 Ni and Al 11 Ce 3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. Additionally, the alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al 3 Ni particles which engulf finer, more stable Al 11 Ce 3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al 3 Ni and Al 11 Ce 3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructural and optical properties of nanocrystalline ZnO deposited onto vertically aligned carbon nanotubes by physical vapor deposition

Nanocrystalline ZnO films with thicknesses of 5 nm, 10 nm, 20 nm, and 50 nm were deposited via magnetron sputtering onto the surface of vertically aligned multi-walled carbon nanotubes (MWCNTs). The ZnO/CNTs heterostructures were characterized by scanning electron microscopy, high resolution transmission electron microscopy, and X-ray diffraction studies. No structural degradation of the CNTs was observed and photoluminescence (PL) measurements of the nanostructured ZnO layers show that the optical properties of these films are typical of ZnO deposited at low temperatures. The results indicate that magnetron sputtering is a viable technique for growing heterostructures and depositing functional layers onto CNTs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Fabrication, microstructure and mechanical properties of W-NiTi composites

Here, new two-phase tungsten-based composites containing 88 wt% tungsten powders and 12 wt% nearly equiatomic NiTi alloy deforming by martensite variant detwinning were fabricated by infiltration and hot pressing in this study. The change of Ti/Ni ratio in NiTi mater alloy and the effect of addition of Nb element on the microstructure, martensitic transformation and mechanical properties of W-NiTi composites were investigated by comparison of W-Ni 50 Ti 50 , W-Ni 44 Ti 56 , W-Ni 42 Ti 58 and W-Ni 42 Ti 53 Nb 5 composites. The results showed that brittle Ni 3 Ti formed in the W-Ni 50 Ti 50 and W-Ni 44 Ti 56 composites and brittle Ti 2 Ni formed in the W-Ni 42 Ti 58 composites while no brittle intermetallics formed in the W-Ni 42 Ti 53 Nb 5 composite. The W-Ni 42 Ti 53 Nb 5 composite exhibited the sharpest martensitic transformation with the largest transformation enthalpy among the four different composites. The W-Ni 42 Ti 53 Nb 5 composite exhibited a double-yielding phenomenon under compression with an ultimate compressive strength of 3820 MPa and a deformation of 50.4%. In-situ synchrotron high-energy Xray diffraction measurements revealed the first yielding was caused by the martensite reorientation of the NiTi matrix and the second was due to the commencement of massive plastic deformation of the reoriented martensite and is also attributed to the microscopic internal fracturing of the W particles.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of rare earth ionic doping on microstructures and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

Graphical abstract: The dielectric constant decreases monotonically with reduced RE doping ion radius and is more frequency independent compared with that of pure CCTO sample. - Highlights: • The mean grain sizes decrease monotonically with reduced RE doping ionic radius. • Doping gives rise to the monotonic decrease of ϵ{sub r} with reduced RE ionic radius. • The nonlinear coefficient and breakdown field increase with RE ionic doping. • α of all the samples is associated with the potential barrier width rather than Φ{sub b}. - Abstract: Ca{sub 1–x}R{sub x}Cu{sub 3}Ti{sub 4}O{sub 12}(R = La, Nd, Eu, Gd, Er; x = 0 and 0.005) ceramics were prepared by the conventional solid-state method. The influences of rare earth (RE) ion doping on the microstructure, dielectric and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics were investigated systematically. Single-phase formation is confirmed by XRD analyses. The mean grain size decreases monotonically with reduced RE ion radius. The EDS results reveal that RE ionic doping reduces Cu-rich phase segregation at the grain boundaries (GBs). Doping gives rise to the monotonic decrease of dielectric constant with reduced RE ionic radius but significantly improves stability with frequency. The lower dielectric loss of doped samples is obtained due to the increase of GB resistance. In addition, the nonlinear coefficient and breakdown field increase with RE ionic doping. Both the fine grains and the enhancement of potential barrier at GBs are responsible for the improvement of the nonlinear current–voltage properties in doped CCTO samples.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Low-Activation Fe-Cr-V Multicomponent Single-Phase Alloys

A ternary equiatomic and nearly equiatomic alloy composed of the low-activation elements Fe, Cr, and V was designed for potential application as low-activation structural materials for the first wall of fusion reactors. The optimal composition of the multicomponent alloy was determined by minimizing the Gibbs free energy for solid-solution formation. The microstructure, phase stability, and mechanical properties of the equiatomic and optimized Fe-Cr-V alloys were studied. The equiatomic alloy consisted of a body-centered-cubic (BCC) solid-solution phase with a small amount of a face-centered-cubic (FCC) solid-solution phase, whereas the optimized alloy consisted of a single BCC solid-solution phase in the as-cast state. The crystal grains of both alloys were equiaxial. No phase transition was observed in the optimized alloy after homogenization; however, for the equiatomic alloy, the FCC solid-solution phase disappeared and surface relief was observed. The Vickers microhardness and yield strength of the Fe-Cr-V alloys increased after homogenization compared with those of the as-cast alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Ti-4Al-1Mn Titanium Alloy

Mechanical behavior of Ti-4Al-1Mn titanium alloy has been studied in annealed, cold-rolled and heat-treated conditions. Room temperature tensile strength as well as % elongation has been found to be low with increasing amount of cold rolling. Lowering of strength in cold worked condition is attributed to premature failure. However, the same has been mitigated after heat treatment. Significant effect of cooling media (air and water) from heat treatment temperature on microstructure was not found except for the degree of fineness of α plates. Optimum properties (strength as well as ductility) were exhibited by samples subjected to 15% cold rolling and heat treatment below β transus temperature, which can be attributed to presence of recrystallized microstructure. In cold worked condition, the microstructure shows fine fragmented α plates/Widmanstätten morphology with high dislocation density along with a large amount of strain fields and twinning, which gets transformed to recrystallized equiaxed microstructure and with plate-like morphology after near β heat treatment. Prior cold work is found to have a significant effect on mechanical properties supported by evolution of microstructure. Twinning is found to be assisting in deformation as well as in recrystallization through the formation of deformation and annealing twins during cold working and heat treatment. Fracture analysis of the tested sample with prior cold work and heat-treated condition revealed quasi-ductile failure as compared to only ductile failure features seen for samples heat treated without prior cold work.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Heat Treatment and Combination of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Titanium Alloy Ti6Al2V2Zr1.5Mo

The heat treatment and cold rolling combinations have been carried out on titanium alloy Ti6Al2V2Zr1.5Mo, and microstructure evolution and mechanical behavior have been studied. Solution treatment below the β-transus temperature, followed by air cooling, resulted in higher microhardness/strength as compared to the same with water quenching. A sudden drop in microhardness/strength is observed in sample solution heat-treated above β-transus temperature followed by air cooling. The former is attributed to the additional presence of fine secondary α-phase formed by dynamic aging during air cooling as compared to water-quenched samples which did not have fine secondary α-phase. Solution treatment above β-transus temperature resulted in Widmanstatten microstructure with no significant fine secondary α in air-cooled samples. Among the studied conditions of cold rolling (CR), gain in strength of the alloy from annealed condition is significant with first 15% reduction and thereafter it is marginal for 30% reduction. Initiation of cracks at the edges has been observed in 30% CR. The microstructure of cold-rolled samples confirms the fragmentation of α-plates with the presence of high dislocation density. Heat treatment of cold-rolled samples resulted in significant reduction in strength from the as-cold-rolled conditions. The marginally lower strength than the as-received (annealed) or heat-treated alloy samples is due to the recrystallization in CR samples and the formation of Widmanstatten microstructure in air-cooled samples. The alloy does not have fine secondary α or regions with large dislocation density in this condition. The microstructure in the samples heat-treated (with air cooling) below as well as above β-transus temperature (after CR) is similar to air-cooled samples (without prior CR) with heat treatment above β-transus temperature. This indicates the reduction in recrystallization temperature with cold working, which is substantiated with the reduction in strength as well.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Mechanical Properties of Exothermic-Reaction-Assisted Friction-Stir-Welded Nickel-Aluminum Bronze Alloy

In the present work, nickel-aluminum bronze alloy is joined using conventional friction stir welding (CFSW) and thermite heat-assisted friction stir welding (THAFSW). In this experiment, preheating technology was utilized using the thermite reaction of Al-CuO powder. A substantial rise in temperature was observed during THAFSW which is beneficial to the eliminations of tunnel defect. In THAFSW, a large amount of α-phase was observed from the top to the center in stir zone as a result of the rise in temperature. Transverse tensile strength of the THAFSW and CFSW was improved by 27 and 14%, respectively, in comparison with base metal tensile strength. A higher microhardness values observed at the bottom of the stir zone in the THAFSW, while this was seen higher in the surface zone and the center zone in the case of CFSW. Tool wear was reduced during the THAFSW process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Mechanical Properties of Powder Thixoforged Amorphous Ni{sub 55}Nb{sub 35}Si{sub 10}-Reinforced Al Matrix Composites

Powder thixoforging was used to produce amorphous Ni{sub 55}Nb{sub 35}Si{sub 10}-reinforced Al matrix composites from recycled Al powders obtained from ball-milled Al520 end-milled billets. The amorphous reinforcing material was uniformly dispersed in the Al matrix and bonded adequately with it without undesired interfacial reactions. The compressive yield strength of composites with 45% reinforcement content increased 248% to 794 MPa over as-cast samples. The maximum elongation and hardness of samples were 15%, and 60.4 HRA, respectively. The relative density of the unreinforced thixoforged sample was 99.8%, indicating near-perfect compaction of Al powders. The maximum elongation, hardness, and compressive yield strength of thixoforged monolithic matrix alloys were, respectively, 40%, 56.9 HRA, and 747 MPa (a 228% increase in CYS over the cast alloy). In contrast, cold-forged samples showed only 82% increase in compressive yield strength over the as-cast alloy. Powder thixoforging introduced in this study—even without reinforcement—delivers better mechanical properties compared to cold forging most likely due to the refinement and modification of the microstructure during powder ball milling.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Effective Physical Contact Area on Microstructure and Mechanical Properties of Diffusion-Bonded TC4/1060Al Joints

In the present study, dissimilar TC4 alloy and 1060Al alloy were successfully diffusion-bonded at a very low temperature about 410 °C by improving the effective physical contact area. A sound joint with a crack-free interface and a high shear strength (128 MPa) is obtained with a combination of TC4 surface roughness of 109.90 μm (S{sub a}) and 1060Al surface roughness of 101.43 μm (S{sub a}), and customized parallel surface scratches. Under this condition, the two parent metals share the largest contact area during the physical contact stage of diffusion bonding process, which is consistent with the theoretical calculation. The results show that no Ti-Al binary intermetallic compounds are observed at the interface of the joints. The maximum shear strength of the joint reaches 128 MPa with optimized bonding parameters (410 °C for 120 min with a pressure of 20 MPa), which is higher than the shear strength of 1060Al (80 MPa) base metal. The fractography analysis indicates the joints failed with a ductile fracture at the 1060Al side.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microstructure and Mechanical Properties of 21-6-9 Stainless Steel Electron Beam Welds

Welds can either be stronger or weaker than the base metals that they join depending on the microstructures that form in the fusion and heat-affected zones of the weld. In this paper, weld strengthening in the fusion zone of annealed 21-6-9 stainless steel is investigated using cross-weld tensile samples, hardness testing, and microstructural characterization. Due to the stronger nature of the weld, the cross-weld tensile tests failed in the base metal and were not able to generate true fusion zone mechanical properties. Nanoindentation with a spherical indenter was instead used to predict the tensile behavior for the weld metal. Extrapolation of the nanoindentation results to higher strains was performed using the Steinberg–Guinan and Johnson–Cook strength models, and the results can be used for weld strength modeling purposes. The results illustrate how microstructural refinement and residual ferrite formation in the weld fusion zone can be an effective strengthener for 21-6-9 stainless steel.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Iron Content on Microstructure and Magnetic Properties of Sr{sub 0.3}La{sub 0.4}Ca{sub 0.3}n(Fe{sub 2}O{sub 3})Co{sub 0.4}

In this work, the hexagonal ferrite Sr{sub 0.3}La{sub 0.4}Ca{sub 0.3}n (Fe{sub 2}O{sub 3})Co{sub 0.4}, where n ranging from 5.5 to 6.0 with a step of 0.1, and magnetic powders and magnets were synthesized by solid-states reaction. The microstructure of the magnetic powders was investigated by X-ray diffraction (XRD). And then we can found that a single magnetoplumbite phase is obtained for magnetic powders as a result when 5.6 ≤ n ≤ 5.8. When the iron content in the magnetic powders increased continuously, the diffraction peaks of α-Fe{sub 2}O{sub 3} were observed. Scanning electron microcopy (SEM) was used to explore the micrographs of the magnets and the hexagonal-shaped crystals were found obviously. The magnetic properties of the M-type hexagonal ferrites Sr{sub 0.3}La{sub 0.4}Ca{sub 0.3}n(Fe{sub 2}O{sub 3})Co{sub 0.4} were studied by using vibrating sample magnetometry. The saturation magnetization (M{sub s}) first increased and then began to decrease with the n increasing. While the coercivity first decreased with the n from 5.5 to 5.9 and then increased when n ≥5.9. The coercivity (H{sub c}) of the hexagonal ferrite Sr{sub 0.3}La{sub 0.4}Ca{sub 0.3}n(Fe{sub 2}O{sub 3})Co{sub 0.4} reaches the maximum value (H{sub c} = 1130 Oe) when the iron content (n = 5.5).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ge{sub 1-y}Sn{sub y} (y = 0.01-0.10) alloys on Ge-buffered Si: Synthesis, microstructure, and optical properties

Novel hydride chemistries are employed to deposit light-emitting Ge{sub 1-y}Sn{sub y} alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge₂H₆ and deuterated stannane SnD₄. For y ≥ 0.06, the Ge precursor was changed to trigermane Ge₃H₈, whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge₄H₁₀ as the Ge source. The photoluminescence intensity from Ge{sub 1–y}Sn{sub y}/Ge films is expected to increase relative to Ge{sub 1–y}Sn{sub y}/Si due to the less defected interface with the virtual substrate. However, while Ge{sub 1–y}Sn{sub y}/Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge{sub 1–y}Sn{sub y}/Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge{sub 1–y}Sn{sub y}/Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge{sub 1–y}Sn{sub y}/Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si{sub 1–x}Ge{sub x}/Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron-microscopy techniques, including aberration corrected STEM imaging and EELS mapping of the average diamond–cubic lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Atomistic simulations of nanoindentation on nanoglasses: Effects of grain size and gradient microstructure on the mechanical properties

The use of nanoglass (NG) microstructures has been shown as an effective strategy to improve the ductility of rather brittle metallic glass alloys. To evaluate the effects of grain size and gradient design on the mechanical properties of NGs, we perform molecular dynamics simulations of nanoindentation on Cu 64 Zr 36 NGs. We consider samples with uniform 3 and 7 nm grain sizes as well as gradient microstructures with gradient grain sizes varying from 3 to 7 nm. Here, the results show that the deformation mechanism in NGs with small grain sizes is dominated by the activation and evolution of multiple shear transformation zones. Increasing grain sizes enhances the elastic modulus and hardness at the cost of reduced abrasion resistance. Though the average grain size at the indentation surface plays a crucial role in the deformation behavior of gradient NG models, their strain localization and plastic deformation states are affected by the grain sizes far from the indenter. Desired combinations of mechanical properties can be realized by different NG microstructure designs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of SMAT on microstructural and mechanical properties of AA2024

In recent days surface mechanical attrition treatment (SMAT) had attracted the attention of researchers as it produces a nano-crystalline surface with improved mechanical properties. In the present study Al-4%Cu alloy used in automobile and aerospace application is subjected to surface mechanical attrition treatment using steel shots. The microstructural changes introduced on the surface of the Al alloy was investigated using Scanning Electron Microscopy (SEM). The secondary phases formed during the SMAT process is been investigated using EDX and XRD analysis. The effects of SMAT on the mechanical properties were analyzed using a tensile testing. The SMA treatment had resulted in severe plastic deformation of the surface, thereby yielded a nanocrystalline surface with a grain size of 30 to 50 nm. Further, it is also found that the SMAT produced ultra nanocrystalline particles of Cu{sub 2}Al dispersed uniformly into α-Al matrix. These microstructural changes had resulted in considerable change in the mechanical properties of these alloys. The tensile strength of these alloys had increased from ∼212 MPa to 303 MPa while the fracture toughness increased up to 28% in 10 minutes of SMAT.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructural, Optical, and Magnetic Properties of Vanadium-Substituted Nickel Spinel Nanoferrites

The current study investigates the impact of vanadium substitution on the structural, magnetic, and optical properties of NiFe{sub 2−x}V{sub x}O{sub 4} (x ≤ 0.3) nanoparticles (NPs) produced by the cost-effective sol-gel route. The as-prepared spinel ceramic powders were examined by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The functional groups, spinel phase, and crystal structure were confirmed by XRD and FT-IR, respectively. The crystallites size decreased from 45.24 to 36.56 nm as the doping process increases. The plots of Tauc were drawn to determine optical band gap magnitudes of 1.291, 1.302, and 1.312 eV for x = 0.0, 0.2, and 0.3, respectively. The estimated saturation magnetization is maximum for pristine NiFe{sub 2}O{sub 4} NPs and decreases to minimum for NiFe{sub 1.7}V{sub 0.3}O{sub 4} NPs. The σ-H hysteresis loops have finite coercivity (between 125 and 169 Oe) and retentivity (between 9.36 and 14.04 emu/g) values. The calculated σ{sub r}/σ{sub s} ratios are lower than 0.500, assigning the uniaxial anisotropy for NiFe{sub 2−x}V{sub x}O{sub 4}. The effective anisotropy constants (K{sub eff}) are in the range of 0.824 × 10{sup 5} and 1.303 × 10{sup 5} Erg/g. The magnetocrystalline anisotropy field (H{sub a}) values are around 5.0 kOe. The characteristics of hysteresis (σ-H) curves and the order of magnetic data reveal the soft ferrimagnetic feature of as-prepared nanoparticle samples. From Mossbauer analysis, the variations in hyperfine magnetic field, quadrupole splitting, line width, and isomer shift have been evaluated. The distribution of cations showed that the octahedral B sites are occupied by all the ions of V{sup 3+}. Mossbauer spectra are composed of four Zeeman sextets and one doublet.

77 NANOSCIENCE AND NANOTECHNOLOGY↗