Phase Transformation Properties Research Articles

The Effect of Ti Addition on Microstructure and Magnetic Properties of Nanocrystalline FeAl40 Alloy Powders Prepared by Mechanical Alloying

Recent research on nanocrystalline FeAl alloys has shown that these alloys are of high importance due to their promising structural and mechanical properties, particularly magnetic behavior. This work aims at studying the synthesis, structural and magnetic characterization of nanocrystalline FeAl alloy powders, prepared by a mechanical alloying process (MA), as well as the effect of Ti addition on the magnetic properties of a compound. The powder morphology, phase transformation, crystallite size, micro-stress evolution, and magnetic properties were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), and vibrating samples magnetometer (VSM). It has been found that at the final stage of mechanical alloying the bcc-disordered FeAl phase and nanocrystalline Fe(Al, Ti) solid solution occurred for the FeAl40 and FeAl40Ti3 alloys, respectively. The milling time and the addition of titanium affect the powder morphology and decrease the size of the particles. The average crystallites size of 17.2 and 11.2 nm was reached at the end of 30 h of milling, and the lattice strain increased up to 0.3 and 0.21% for the FeAl40 and FeAl40Ti3 alloys, respectively. Also, the magnetic properties attributed to microstructural changes were investigated. It has been established that the change in magnetic behavior occurs mainly due to the formation of a supersaturated Fe(Al, Ti) solid solution. Magnetic properties of the samples are highly influenced by the addition of the Ti element into FeAl40 alloy, as well. The magnetism of the FeAl40Ti3 compound is reported to be higher than that of FeAl40.

High elongation of medium-manganese steel containing 1.0 wt.% Al after a short intercritical annealing time

ABSTRACT This paper presents research on the phase transformation, microstructure, and tensile properties of medium-manganese steel containing 1.0 wt.% Al (1.0Al) after a short intercritical annealing (IA) time at different IA temperatures using thermodynamic simulation, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and uniaxial tensile tests. The results show that the addition of 1.0Al can expand the size of the IA temperature range from 208 to 272 °C and shifts the range to higher temperatures, and this increases the fractions of the retained austenite in the steel when the IA time is short. Most of the retained austenite transforms to α’-martensite during the tensile test. Part of the retained austenite transforms to α’-martensite in the early stage and contributes little plasticity. The other part of the retained austenite transforms in the middle or late tensile deformation stage and improves the mechanical properties. The mechanical properties of the steel are remarkable, with a tensile strength above 1000 MPa, elongation above 35%, and strength × ductility above 35,000 MPa% when the IA temperature is 700 °C and the IA time is 3 min.

The effect of boron substitution on the glass-forming ability, phase transformation and optical performance of zinc-boro-soda-lime-silicate glasses

The influence of boron oxide on glass-forming ability, phase transformation, and optical properties of new zinc-boro-soda-lime-silicate (ZBSLS) glass system with formulation 60–x(ZnO)x(B2O3)40(SLS) where x=0, 1, 5, 10 and 15wt.% using the conventional melt-quenching technique was comprehensively studied. The glass powder samples were subjected to true density measurement using Helium Pycnometer. Besides, the XRD and FTIR spectroscopy was used to examining the phase and structural rearrangement in the ZBSLS glass system. The XRD result emphasizes the glass samples (G3, G4, and G5) in amorphous nature when boron concentration is more than 5wt.% in the ZBSLS glass matrix. Also, the UV–Vis spectra were observed within 200–800nm. At that point, the data from optical absorbance was converted to justify the optical band gap energy using Mott and Davis theory. The optical band gap energy show increment behavior from 4.35 to 5.25eV for direct allowed transition and 3.25–4.30eV for indirect allowed transition with the progress of boron concentration, respectively.

Influence of Hydrofluoric Acid Leaching and Roasting on Mineralogical Phase Transformation of Pyrite in Sulfidic Mine Tailings

Under the oxidative roasting process, pyrite, as a major mineral in sulfidic mine tailings, can transform to iron oxides. Generated iron oxides, if exhibiting enough magnetic properties, can be recovered via magnetic separation resulting in partial mine tailings valorization. However, due to the presence of various minerals and sintering possibility, it is advantageous to remove impurities and increase the pyrite content of mine tailings prior to the roasting procedure. In this case, hydrofluoric acid that has no influence on pyrite can be used to leach most inorganic minerals, including aluminosilicates. Therefore, this study investigated and compared the influence of the roasting process with and without hydrofluoric acid leaching pretreatment on mineralogical phase transformation of pyrite and magnetic properties of thermally generated minerals. Several tests and analyses were performed to study mineralogical phase transformation, morphology, elemental composition, surface characterization, and magnetic properties. Results of this study indicated that without acid leaching pretreatment, pyrite was mainly transformed to hematite. However, via acid leaching, fluorine, as a more electronegative element over oxygen, entered the compound and neglected the role of oxygen in thermal oxidation, instead reducing sulfur content of pyrite to only form pyrrhotite.

Structure stability and magnetic properties of Fe-doped Co2VGa Heusler alloys: Insights from first-principles calculations

In this work, we report an interesting phenomenon with respect to the coexistence of martensite phase transformation (MPT) and half-metallic properties in Fe doped Co2VGa Heusler alloys, which is predicted theoretically according to the ab initial calculations based on density functional theory (DFT). The effects of Fe partial substitution for Co, V or Ga atoms on the structural stability, MPT, electronic structure and magnetic properties in Co-V-Ga system alloys have been systematically investigated. It was found that Co2-xFexVGa (x = 0, 0.25, 0.5, 0.75, 1), Co2V0.75Fe0.25Ga and Co2VFe0.25Ga0.75 alloys are stable in highly ordered L21-type structure. The magnetic analysis indicates that the magnetic moment decreases with the increase of Fe content in Co2-xFexVGa (x = 0, 0.25, 0.5, 0.75, 1) alloys, whereas it increases with the increase of Fe content for V or Ga partially replaced by Fe atoms. According to the calculated results, MPT can take place in Co2V0.5Fe0.5Ga and Co2VFe0.5Ga0.5 Heusler alloys. All the studied alloys exhibit high spin polarizability, especially in the alloys of Co or V partially replaced with Fe.

Microstructure, phase transformation and mechanical property of porous NiMnGa alloys prepared by one-step sintering

This article investigated microstructure, martensitic transformation and mechanical property of porous NiMnGa alloys fabricated by one-step sintering method using Mg powder as a pore former. The overall pore size was decreased with decreasing Mg content due to the reduction of aggregation tendency of Mg particles. Residual Mg existed mainly in the pore wall (interfacial areas between NiMnGa and Mg) due to interfacial reactions. The porous alloys with different porosity exhibited one-step martensitic transformation with close transformation temperatures and the temperature of martensitic transformation was lower for the porous alloys than the original NiMnGa powder. The porous NiMnGa alloys exhibited a low compressive strength and ductility due to the existence of pores. The porous NiMnGa alloys with continuous pore wall structure could be a better candidate than NiMnGa particles to form composites with ductile matrix.

Heating parameter optimization and optical properties of Nd:YAG transparent ceramics prepared by microwave sintering

Nd-doped YAG transparent ceramics were prepared by microwave sintering. In this paper, the green bodies from high-purity commercial powders were sintered from 900 °C to 1750 °C for different lengths of time (0.5–2 h) by microwave heating. By optimizing the microwave heating parameters (the heating rate at different stages of microwave sintering, sintering temperature and holding time), the microstructures and optical properties of transparent ceramics can be effectively improved. The phase transformation, densification process and optical properties of Nd:YAG transparent ceramics were discussed. The liquid phases strongly absorb microwave radiation and affect the sintering results of samples during microwave sintering. The highest in-line transmittances of Nd:YAG transparent ceramic fabricated at 1750 °C for 2 h were 76.5% at 400 nm and 80.6% at 1064 nm. The fluorescence emission spectra and lifetime depending on different heating conditions were also discussed.

Effect of Cold Rolling and Aging on the Microstructure and Mechanical Properties of Ti-Nb-Zr Alloy

The effect of cold rolling deformation and aging treatment on the phase transformation, microstructure evolution, and mechanical properties of a new Ti-Nb-Zr metastable β-titanium alloy was investigated by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and mechanical property testing. The results show that the alloy exhibited excellent phase stability that no stress-induced α″ phase transition occurred during cold rolling and that the plastic deformation mechanism was related to dislocation slipping. Interestingly, even under the same aging treatment at 300 °C for 2 h, the aging products for the unrolled and cold-rolled alloys are β + ω and β + α, respectively. The alloy with cold deformation produces a large number of dislocation defects, and grain boundaries inhibit the nucleation of the ω phase, while the α phase tends to nucleate at the dislocations and grain boundaries and promote the precipitation of the α phase. Compared with solution treatment and aging, the aging treatment after cold deformation has high-strength matching and its ideal elastic modulus can satisfy the requirements for dental implants.

Comparison of Wear Performance of Austempered and Quench-Tempered Gray Cast Irons Enhanced by Laser Hardening Treatment

The current research studied the effects of laser surface hardening treatment on the phase transformation and wear properties of gray cast irons heat treated by austempering or quench-tempering, respectively. Three austempering temperatures of 232 °C, 288 °C, and 343 °C with a constant holding duration of 120 min and three tempering temperatures of 316 °C, 399 °C, and 482 °C with a constant holding duration of 60 min were utilized to prepare austempered and quench-tempered gray cast iron specimens with equivalent macro-hardness values. A ball-on-flat reciprocating wear test configuration was used to investigate the wear resistance of austempered and quench-tempered gray cast iron specimens before and after applying laser surface-hardening treatment. The phase transformation, hardness, mass loss, and worn surfaces were evaluated. There were four zones in the matrix of the laser-hardened austempered gray cast iron. Zone 1 contained ledeburite without the presence of graphite flakes. Zone 2 contained martensite and had a high hardness, which was greater than 67 HRC. Zone 4 was the substrate containing the acicular ferrite and carbon-saturated austenite with a hardness of 41–27 HRC. In Zone 3, the substrate was tempered by the low thermal radiation. For the laser-hardened quench-tempered gray cast iron specimens, three zones were observed beneath the laser-hardened surface. Zone 1 also contained ledeburite, and Zone 2 was full martensite. Zone 3 was the substrate containing the tempered martensite. The tempered martensite became coarse with increasing tempering temperature due to the decomposition of the as-quenched martensite and precipitation of cementite particles. In the wear tests, the gray cast iron specimens without heat treatment had the highest wear loss. The wear performance was improved by applying quench-tempering heat treatment and further enhanced by applying austempering heat treatment. Austempered gray cast iron specimens had lower mass loss than the quench-tempered gray cast iron specimens, which was attributed to the high fracture toughness of acicular ferrite and stable austenite. After utilizing the laser surface hardening treatment, both austempered and quench-tempered gray cast iron specimens had decreased wear loss due to the high surface protection provided by the ledeburitic and martensitic structures with high hardness. In the worn surfaces, it was found that cracks were the dominant wear mechanism. The results of this work have significant value in the future applications of gray cast iron engineering components and provide valuable references for future studies on laser-hardened gray cast iron.

Evolution of crystallographic orientation, precipitation, phase transformation and mechanical properties realized by enhancing deposition current for dual-wire arc additive manufactured Ni-rich NiTi alloy

Ni-rich NiTi alloys were deposited using the in-situ alloying wire arc additive manufacturing (WAAM) method, with varying deposition currents from 80 A to 120 A. The effects of deposition current on the crystal orientation, precipitation, phase transformation and mechanical properties of the WAAM-deposited NiTi alloys were investigated. The results show that increasing the deposition current during the WAAM process would result in noticeable coarsening of B2 grain and an increased volume fraction of high angle grain boundaries (HAGBs). Also, the texture intensity gradually decreased with increasing deposition current. The fabricated components are dominated by the B2 phase with quantities of Ni4Ti3 precipitates in all samples. When increasing the deposition current during the WAAM process, the size of Ni4Ti3 precipitates generally increased and gradually decomposed into a stable Ni3Ti phase which could be detected in the sample produced at 120 A. Furthermore, all of the characteristic phase transformation temperatures increased with the deposition current while the ultimate tensile strength dropped from 927.9 MPa to 613.8 MPa and elongation reduced from 8.7 % to 5.6 %. The cyclic loading-unloading tests revealed that similar trends for the evolution of irreversible strain (εir), recoverable strain (εre), recovery ratio, and elastic energy storage efficiency (η) during cycling were obtained in all samples processed with different deposition currents. The highest εre of 3.2 % and the highest recovery ratio of 53.9 % were obtained in the sample processed with 80 A at an applied stress of 700 MPa for ten cycles. The change of mechanical properties with varying deposition current is due to a combination of factors including precipitation hardening effect, grain refinement effect, and crystal orientation. These results can be useful for optimizing WAAM process parameters to fabricate NiTi components with acceptable structural properties.

Preternatural Hexagonal High-Entropy Alloys: A Review

Recently, various topics on high-entropy alloys have been reported and great amounts of excellent properties have been investigated, including high strength, great corrosion resistance, great thermal stability, good fatigue and fracture properties, etc. Among all these research activities, high-entropy alloys tend to form face-centered-cubic (FCC) or body-centered-cubic (BCC) solid solutions due to their high-entropy stabilization effect, while the hexagonal structures are rarely reported. Up to now, the reported hexagonal high-entropy alloys are mainly composed of rare-earth elements and transitional elements. Their phase transformation and magnetic properties have also aroused wide concern. This study summarizes the above results and provides the forecast to the future.

Phase transformation, thermodynamics and kinetics property of Mg90Ce5RE5 (RE = La, Ce, Nd) hydrogen storage alloys

The Mg90Ce5RE5 (RE = La, Ce, Nd) alloys were prepared by a vacuum induction furnace and their microstructure, phase transformation, thermodynamics and kinetics property were systematically studied by XRD, SEM, TEM, and PCT characterization methods. The result shows that the activated alloys are composed of Mg/MgH2 and corresponding REH2+x with nanoscale. The REH2+x grain with Ce and La or Nd functional group have lower nucleation potential barriers than CeH2+x grains as the nucleation location, thus improve the hydrogen absorption kinetics of these alloys among which the Mg90Ce5Nd5 alloy can absorb 90% of the hydrogen within 2 min at 320 ºC. In addition, the Mg90Ce10 alloy has the lowest activation energy with 103.2 kJ mol−1 and the fastest desorption kinetics, which can release 5 wt% of the hydrogen within 20 min at 320 ºC. This is a correlation with grain size and the in-suit formed CeH2.73/CeO2 interface. Moreover, the co-doping Ce and La or Nd can effectively disorganize the thermodynamic stability of Mg-based hydrogen storage alloys to a certain degree, but the dehydrogenation kinetics of that still is restricted by the recombination energy of hydrogen ions on the surface.

Microstructural stability, phase transformation and mechanical properties of a fully-lamellar microstructure of a Mo-modified high-Nb γ-TiAl alloy

Microstructural instability modes, phase transformation and mechanical properties evolution of a fine-grained fully-lamellar Ti–44Al–6Nb–1Mo−0.3(B, Y) (at.%) alloy were investigated systematically. During isothermal exposure at application temperatures, dramatic discontinuous precipitation of γ and βo (ωo) grains proceeded along boundaries of prior lamellar colonies, i.e. via a transformation of L(α2/γ) → γ + βo (ωo). Meanwhile, the internal lamellar structures degraded by α2-lath dissolution and simultaneous γ-lath coarsening. Furthermore, thermal loading was found to contribute to the above decomposition processes. However, almost no βo and βo (ωo) grains formed in the interiors of lamellar structures. The precipitation of equilibrium phases γ, β and ωo abided by normal crystallographic orientation relations with their respective parent phases. The present microstructural decomposition was considered to be essentially induced by thermodynamic instability of α2 laths and high interfacial energy of nanoscaled lamellar structures. Finally, it was demonstrated that this microstructural degradation caused both high-temperature strength and room-temperature ductility to deteriorate.

Influences of Cr Content on the Phase Transformation Properties and Stress Change in V–Cr–O Thin-Film Libraries

VO2-based thin-film libraries with a continuous composition spread of Cr were obtained by reactive cosputtering. Gradual changes in the crystalline structures of VO2 were observed in the thin-film ...

Phase Transformation, Surface Topography and Mechanical Properties of Hydrothermal Aged Laser treated Cubic Versus Tetragonal Zirconia Ceramics

Phase Transformation, Surface Topography and Mechanical Properties of Hydrothermal Aged Laser treated Cubic Versus Tetragonal Zirconia Ceramics

Synergistic effects of stretching/polarization temperature and electric field on phase transformation and piezoelectric properties of polyvinylidene fluoride nanofilms

This study aims to investigate the dependence of crystalline structure and piezoelectric properties of polyvinylidene fluoride stretched films (up to four times their initial length) as a function of temperature, polarization under constant field as well as varying electric field at constant polarization temperature. X-ray diffraction analysis indicates that α → β phase transformation occurs below 80 °C; meanwhile, the crystallinity is improved with stretching temperature reaching 44% compared to 32% for un-stretched. FTIR analysis confirms the results obtained by XRD, as new functional groups, shift of peaks position as well as reduction in their relative intensity are observed. It is found that the piezoelectric coefficient (d33) decreases with increasing temperature, while it increases with the electric field. The obtained results are discussed on the basis of the dependence of (d33) as a function of phase (α + β + amorphous) composition and the degree of crystallinity associated with various vibrational modes and the arrangement of hydrogen and fluorine atoms (corresponding charge H+ and F−) from either sides of PVDF skeleton chains arising upon the influence of thermomechanical treatment, polarization and electric field.

Effect of accumulative roll-bonding process on phase transformation and magnetic properties of polycrystalline cobalt

In this paper, the cobalt was deformed by accumulative roll-bonding (ARB) process. The phase transformation behavior of cobalt during accumulative rolling and its effect on the magnetic properties of polycrystalline cobalt were investigated. Twinning occurs in α-Co phase with hexagonal closepacked (HCP) structure during the ARB process, and a large number of twin boundaries hinder the phase transformation from β-Co phase to α-Co phase. {0001} texture forms in α-Co phase during rolling deformation, however, the intensity of {0001} texture decreases with the growth of twins. The coercivity of polycrystalline cobalt gradually decreases with the increasing rolling deformation, which can be attributed to the evolutions of phase and texture.

Effect of Al2O3 particle size on the microstructure, phase transformation and mechanical properties of hot pressed Al2O3-CA6-ZrO2/Ni multi-phase composites

Al2O3-CA6-ZrO2/Ni multi-phase composites were fabricated by vacuum hot pressing sintering at 1650 °C under the pressure of 30 MPa for 30 min. The microstructural evolution rule of the composites was investigated as a function of Al2O3 particle size. Upon increasing the Al2O3 particle size to 30 μm, the generated CA6 underwent a transformation from unfixed type to a plate-like pattern and to a combined CA6-Al2O3 matrix, whereas the fracture mode of m-ZrO2 changed from an intergranular fracture to an intergranular and transgranular mixed type due to the improved interface binding energy. Additionally, satisfactory mechanical properties of the composites were achieved when the Al2O3 particle size was 30 μm. Under the synergistic effect of different strengthening and reinforcing phases, the inhomogeneous distribution caused by poor wettability between Al2O3 and Ni was effectively solved by the distributions of “intercrystalline type” and “intracrystalline type” for the Ni phase. The mechanisms of the microstructural evolution, phase transformation and improved mechanical properties are discussed in detail.

Phase transformation and mechanical properties of Ti-(10–30)Zr–3Mo–1Sn alloys

Studies on three Ti–xZr–3Mo–1Sn (x=10–30 at.%) alloys found that the influences of Zr on phase transformation and mechanical properties are closely tied to its effect on β-phase stability. It decreases the β-transus by ~8.8 °C/at.%, suppresses the formation of α-phase or martensite during cooling and enhances the room temperature super-elasticity. The influence of Zr on lattice transformation strain is weak with the calculated maximum transformation strains of ~8% in all three alloys regardless of their large differences in Zr content. The largest recoverable strain of ~3.8% was obtained in alloy 30Zr after heat treatment at 600 °C. Heat treating at 600 °C produces a α+β dual phase structure with unique texture patterns in alloys 10Zr and 20Zr. Although texture patterns of α and β phases can be understood based on their crystal orientation relationship, mechanisms that caused these textures remain unknown. Aging at 200 °C for a short time increases the super-elastic strain without sacrificing material ductility and total recoverable strain.

In situ fabrication of a titanium-niobium alloy with tailored microstructures, enhanced mechanical properties and biocompatibility by using selective laser melting.

A titanium-niobium (Ti-Nb) alloy with tailored microstructures, enhanced mechanical properties and biocompatibility was in situ fabricated by selective laser melting (SLM) using a blended powder with 25wt.% Nb content. The effect of laser energy density from 70J/mm3 to 110J/mm3 on the phase transformation, microstructure, and mechanical properties of the SLM-printed Ti-25Nb alloy was investigated. The results indicate that the energy density of 110J/mm3 results in the highest relative density and homogeneous element distributions in the alloy. The α' and β phases with an orientation relationship of [023]β//[-12-16]α' were identified through X-ray diffraction and transmission electron microscopy, and their proportions are crucially determined by the laser energy density. With an increase in the energy density, the microstructure of the Ti-25Nb alloy varies from acicular-shaped grains to coarsened lath-shaped grains and to lath-shaped grain+cellular-shaped subgrains, due to the decrease in cooling rate and the rise in temperature gradient. The yield strength and microhardness of the printed Ti-25Nb alloy decrease with the increase in energy density from 70J/mm3 to 100J/mm3, and then increase to the highest values of 645MPa and 264HV at 110J/mm3, respectively. This variation of mechanical properties is dependent on both the coarsening of α' phase and the formation of β (Ti, Nb) solid solution. Besides, the SLM-printed Ti-25Nb alloy exhibits both the excellent in vitro apatite-forming capability and better cell spread and proliferation compared to pure Ti.