Annealed State Research Articles

Interfacial Microstructure in W/2024Al Composite and Inhibition of W-Al Direct Reaction by CeO₂ Doping: Formation and Crystallization of Al-Ce-Cu-W Amorphous Layers.

In this work, interfacial microstructure in W/2024Al composite and inhibition of the W-Al direct reaction by CeO2 doping were investigated. The composites were prepared through powder sintering, and after preparation the composites were treated by annealing at 823 K. For the prepared W/2024Al composite, a multi-phase thin layer composed of WAl12 and WAl5 compounds were formed at the interface due to the W-Al direct reaction. While doping CeO2 in the composite, Al-Ce-Cu-W amorphous substituting of W-Al compounds were formed at the interfacial reaction layer. In an annealed state, the composite with CeO2 doping shows a significant inhibitory effect on W-Al compounds, which was attributed to the crystallized layer that evolved from Al-Ce-Cu-W amorphous as an interfacial obstacle. The crystallization product for Al-Ce-Cu-W amorphous layer was identified as bcc-structure Al-Ce-Cu-W phase without any binary/ternary Ce-containing phases. Therefore, by doping CeO2 in W/2024Al composite, W-Al direct reaction was markedly inhibited during both preparation and annealing.

Microstructure and Hot Deformation Behavior of Twin Roll Cast Mg-2Zn-1Al-0.3Ca Alloy.

In the present work, the microstructure, texture, mechanical properties as well as hot deformation behavior of a Mg-2Zn-1Al-0.3Ca sheet manufactured by twin roll casting were investigated. The twin roll cast state reveals a dendritic microstructure with intermetallic compounds predominantly located in the interdendritic areas. The twin roll cast samples were annealed at 420 °C for 2 h followed by plane strain compression tests in order to study the hardening and softening behavior. Annealing treatment leads to the formation of a grain structure, consisting of equiaxed grains with an average diameter of approximately 19 µm. The twin roll cast state reveals a typical basal texture and the annealed state shows a weakened texture, by spreading basal poles along the transverse direction. The twin roll cast Mg-2Zn-1Al-0.3Ca alloy offers a good ultimate tensile strength of 240 MPa. The course of the flow curves indicate that dynamic recrystallization occurs during hot deformation. For the validity range from 250 °C to 450 °C as well as equivalent logarithmic strain rates from 0.01 s−1 to 10 s−1 calculated model coefficients are shown. The average activation energy for plastic flow of the twin roll cast and annealed Mg-2Zn-1Al-0.3Ca alloy amounts to 180.5 kJ/mol. The processing map reveals one domain with flow instability at temperatures above 370 °C and strain rates ranging from 3 s−1 to 10 s−1. Under these forming conditions, intergranular cracks arose and grew along the grain boundaries.

In situ analysis of the effect of high heating rates and initial microstructure on the formation and homogeneity of austenite

Decreasing processing time of a quench and temper heat treatment is of high interest for industry due to the possibility of cost reduction. One option to reduce processing time is to shorten the austenitizing cycle by applying high heating rates and minimum holding times. However, due to the high heating rates, the analysis of their influences on the formation kinetics of austenite and its crystallographic parameters is challenging. Thus, this work concentrates on the in situ analysis of the austenitization process by means of high-energy X-ray diffraction to study a range of heating rates applied to ferritic–pearlitic and soft annealed initial microstructures. The transformation kinetics from ferrite/pearlite and soft annealed state to austenite, the cementite dissolution behavior and the homogeneity of the freshly formed austenite were analyzed. The results indicate three distinct steps of austenite formation independent of initial microstructure and heating rate: (1) nucleation of carbon-rich austenite at cementite–ferrite interfaces, (2) growth of austenite phase fraction accompanied by a reduction of the carbon content, until reaching the mean carbon content of the steel, followed by growth of the austenite grain size, (3) regarding austenite homogeneity, the combination of austenitization temperature and initial microstructure are the main influencing factors.

Kinetics and dynamics of the regeneration of boron-oxygen defects in compensated n-type silicon

The effects of doping level, illumination intensity and temperature on the regeneration kinetics and dynamics of BO defects in compensated n-Si have been investigated. The regeneration rate, corrected with interstitial oxygen concentration and average injection level, is almost constant in n-type samples with different doping levels under the same regeneration condition. It is proportional to the average injection level during regeneration when the doping level and temperature are fixed. In comparison with previous studies using n-type silicon, the regeneration completeness is significantly improved, especially in samples with net doping levels higher than 1 × 1016 cm−3, due to the higher regeneration temperature and more stable surface passivation films. The remaining incompleteness is mostly dominated by the occupation of the annealed state (as opposed to the activated state). For rapid and complete regeneration, the optimal condition is applying high illumination intensities at around 200°C.

Micromechanical and microstructural properties of tungsten fibers in the as-produced and annealed state: Assessment of the potassium doping effect

Due to its high strength and low temperature ductility, tungsten fibers (Wf) have been widely used as reinforcement elements in metallic, ceramic and glass matrix composites to improve the strength, toughness and creep resistance. Materials designed for future fusion reactors also utilize the option of Wf reinforcement, i.a. with a copper (Wf/Cu) or tungsten (Wf/W) matrix. Wf/W composites are being intensively studied as risk-mitigation materials to replace bulk tungsten which is susceptible to embrittlement induced by neutrons resulting from fusion reaction. Operation of Wf/W in high temperatures (up to 1300 °C and even higher) fusion environment implies a risk of recrystallization and grain growth, which dimishes the attractive properties of tungsten fibers. In this work, we assess this modification of micro-mechanical and microstructural properties of tungsten fibers by means of nanoindentation, scanning electron microscopy, electron back-scattering diffraction analysis and corelate it with the ultimate tensile strength and fracture modes observed in the tensile tests. Both pure W and pottasium doped wires in the as-fabricated and annealed states are investigated and the results are compared with bulk tungsten, also exposed to several annealing temperatures. The results highlight the postive impact of potassium doping which shifts the threshold temperature for the grain growth by about 600 °C compared to pure tungsten wire. The results of the nanoindentation revealed systematic linear correlation with the ultimate tensile strength, which therefore offers a complimenatary way of micro-mechanical testing linking it with macro-scale properties of the wires.

The response of (GeS2)x(Sb2S3)(1-x) thin films to illumination and annealing

Amorphous (GeS2)x(Sb2S3)(1-x) films where 0.29 < x < 0.94 were prepared by thermal evaporation from previously synthetized bulk glass. The response of virgin and annealed states of films to the slightly over-band gap illumination with respect to the shift of the optical band gap (Egopt) and the slope of the optical absorption edge (B1/2) was studied. The magnitude of photo-bleaching and photo-darkening varied with the molar fraction of GeS2 (x) (the average coordination number CN) while a maximum of photo-sensitivity was observed, with respect to the experimental error of chemical composition determination, at CN ≈ 2.6 (x ≈ 0.80). The spectral sensitivity of photo-darkening was studied for the annealed state of the most sensitive thin film.

Effect of B on the thermal stabilization of cryomilled nanocrystalline Cu–Al alloy

Nanocrystalline Cu86Al12B2 alloy with an as-milled average grain size of ∼11 nm was synthesized by high-energy ball milling at cryogenic temperature. The alloy was then annealed up to 900 °C (or 0.87 Tm of Cu). Microstructural changes with annealing were assessed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and microindentation. TEM investigation indicates that the newly-developed alloy retains its nanoscale grain size after annealing at 900 °C. The present investigation complements our previous findings of the thermal stability of cryomilled binary Cu88Al12 and Cu86Al14 alloys, where excellent thermal stability was observed and attributed to the in-situ formation of nanoscale Cu–Al precipitates and their Zener pinning effect. First principle calculation shows equilibrium in Al–Cu–B prefers segregation of B in the grain boundary of Cu–Al alloy. Superior thermal stability of the Cu86Al12B2 alloy was primarily ascribed to the synergistic grain boundary pinning of CuAl2 and AlB12 intermetallic phases. Moreover, the alloy maintains a higher hardness than both Cu88Al12 and Cu86Al14 alloy. The grain size dependent Hall–Petch strengthening was found to be the dominant mechanism with substantial contributions from solid solution strengthening and Orowan strengthening in annealed state.

Experimental study of cold-drawn duplex stainless steel circular tubes under axial compression

Cold-drawing is one of the typical cold-forming techniques in producing stainless steel circular hollow sections (CHS). Compared with cold-rolling, cold-drawing can produce large scale stainless steel tubes which have wide applications in highly corrosive environment. Nevertheless, few researches have been carried out on the duplex stainless steel CHS columns. In this paper, cold-drawn duplex S22053 stainless steel CHS of three types of cross-sections were tested, including 8 material tensile coupon tests, 6 axially compressed stub column tests and 7 axially compressed long column tests. The material stress-strain curves of the cold-drawn CHS tubes, ultimate loads and failure modes of the stub and long columns were obtained. It has been revealed that material properties of cold-drawn stainless steel CHS tubes are close to those of the virgin plate in the annealed state. Moreover, all the stub columns show local buckling in “elephant foot” mode, while all the long columns undergo overall flexural buckling, among which a long column specimen with the nominal length of 700 mm（CHS-700） shows local buckling after the peak load due to the interaction of axial compression and second-order bending moment. Furthermore, comparing the test values with the predicted values based on the European, American, Australian/New Zealand and Chinese design codes, and the calculation methods available in literatures, it is concluded that the predicted values of the stub columns and the long columns with relatively large member slenderness are all lower than the test values, while the predicted values using the design methods except that in the Chinese design code are higher than the test values for the long columns with relatively small member slenderness. Chinese design code could provide safety predictions for cold-drawn duplex stainless steel CHS columns.

Fe–Ni Invar alloy reinforced by WC nanoparticles with high strength and low thermal expansion

Invar is a solid solution alloy that offers high-dimensional stability. It is challenging for traditional methods to strengthen Invar alloys without a significant increase in the coefficient of thermal expansion (CTE). In this work, WC nanoparticle-reinforced Invar nanocomposite was manufactured. The microstructures, mechanical properties, and thermal expansion behavior were investigated. It was found that the Invar alloy was effectively strengthened by WC nanoparticle reinforcement without significant elevation of its CTE. The Invar–WC nanocomposite exhibits an enhanced yield and tensile strength of 440 and 795 MPa, an increase of 60% and 77% from commercial Invar alloy, and a moderate ductility of 22.7% in annealed state. In cold-rolled state, The Invar–WC nanocomposite exhibits a high tensile strength of 1050 MPa, an increase of 46% from commercial Invar alloy, while retaining 4.5% ductility. A record low CTE value of 2.61 × 10−6/°C and an enhanced Young’s modulus of 185 GPa, up from 140 GPa, were also achieved. It was found that WC leads to a lower CTE at higher temperature compared to unreinforced Invar.

Effects of Ti and Gd for Ga substitution on microstructure, magnetic and mechanical properties of polycrystalline Ni-Mn-Ga magnetic shape memory alloy

Abstract The present study is focused on the influence of Ti and Gd doping at the Ga site on the microstructure, magnetic and mechanical properties of the polycrystalline Ni50Mn25Ga20-xZx (x = 0 or 5, Z = Gd, Ti) magnetic shape memory alloys. Microstructure investigations show that reference Ni50Mn25Ga25 and Ti-doped alloys, both in the as-cast and annealed state, are single phase materials, whereas Gd-doped sample reveals dendritic dual-phase structure with substantial distinction between Gd-rich and Gd-poor regions. Thermomagnetic measurements expose reversible martensitic transition in the Ni50Mn25Ga25 and Ni50Mn25Ga20Ti5 alloys, where Ti addition to NiMnGa composition leads to the decrease of phase transformation temperature from TM = 193 K for reference sample to TM = 172.5 K for Ti-doped material. Furthermore, the Ni50Mn25Ga20Gd5 alloy does not experience fully martensitic transition. Temperatures of magnetic transformation also varies with chemical composition and equals to 379 K, 318 K and 370 K for the annealed Ni50Mn25Ga25, Ni50Mn25Ga20Ti5 and Ni50Mn25Ga20Gd5 alloy, respectively. Mechanical properties investigation based on the nanoindentation measurements shows beneficial influence of doping elements on material hardness. In addition, planar distributions of hardness allow to deconvolute mechanical properties of each individual phase of the Ni50Mn25Ga20Gd5 alloy.

Microstructure Evolution and Texture Formation Behavior during High-Temperature Deformation in M1 Magnesium Alloy

Uniaxial compression tests are carried out in the M1 magnesium alloy at 723K under a strain rate of 5.0x10-2s-1 up to a strain of-1.3. Microstructure observation shows that grain distribution is heterogeneous and coarsened grain is observed in all deformation conditions. Mean grain size tends to decrease with increasing strain. Dynamic recrystallization and grain growth are occurred during deformation. (0001) texture which shown at annealed state is weakened with increasing strain, and texture component changed from (0,0) to (24,0) during deformation. The recrystallized grains have no strong preferred orientation about (0001), similar to the grains of growing.

The formation of a homogeneous α-alumina coating on a Ni-based superalloy from a layer stack deposited by cathodic arc evaporation

Cathodic arc evaporation was applied to form a layer stack on a Ni-based superalloy single crystalline substrate in a single in-situ vacuum deposition process. The initial layer was deposited using a target with the same nominal composition as the superalloy substrate. Subsequently, a second layer was deposited using a target with a composition of 70 at.% Al and 30 at.% Cr, and the deposition was conducted in flowing oxygen to form Al-Cr-O. The thermal stability of the layer stack was investigated by means of a heat treatment at 1100 °C in air. The substrate-like coating recrystallized at elevated temperature and showed epitaxial growth on the superalloy single crystal, according to transmission Kikuchi diffraction measurements. A thin layer of pure α-alumina formed on top of the substrate-like coating and a compact Al-Cr-O phase with corundum structure developed towards the top of the coating. Microstructural and chemical analyses of the coating architectures in the as-deposited and annealed states were performed by means of transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Rutherford backscattering spectrometry, and utilized to explain the recrystallization and diffusion processes in the layer stack.

Ion irradiation effects on commercial PH 13-8 Mo maraging steel Corrax

The effects of irradiation on the precipitation behavior of commercial PH 13-8 Mo maraging steel a.k.a. Corrax are investigated through in-situ ion irradiation. Samples of the alloy in its solution annealed state are irradiated up to 10 dpa at 573 and 773 K using 1 MeV Kr ions, in-situ in a transmission electron microscope in order to probe irradiation effects on the precipitation usually observed in this alloy under thermal aging. Indeed, the alloy is known to develop a relatively fine distribution of precipitates during thermal aging which gives the martensitic alloy its strength. The effects of irradiation are substantiated by comparing with the same material thermally aged at 773 and 873 K for similar amounts of experimental time. Both radiation and thermal aging induced segregation and precipitation are characterized using analytical transmission electron microscopy (TEM) techniques.The diffusion coefficients under irradiation are estimated using the point defect balance equations based on Rate Theory and then compared with the thermal diffusion coefficients, demonstrating the accelerated precipitation of β-phase and Laves-phase in the irradiation case at relatively lower temperature is attributed to the radiation-enhanced diffusion. In addition, a numerical model based on classical precipitate nucleation and growth theories is introduced and shows a relatively good agreement with the experimental results in terms of precipitate density. This study serves to generate baseline data on ion irradiation effects on Corrax to learn how this steel responds to irradiation.

Nd-Fe-B films with perpendicular magnetic anisotropy and extremely large room temperature coercivity

Abstract Nd-Fe-B films with perpendicular magnetic anisotropy are important for various applications. Most common process to prepare Nd-Fe-B thin films with perpendicular magnetic anisotropy is the heteroepitaxy process. Here, Nd-Fe-B thin films with perpendicular magnetic anisotropy were prepared by a two-step process. Amorphous and magnetically soft thin films were first deposited. Crystallized, magnetic hard thin films were obtained by rapid thermal annealing of the as-deposited films. A clear correlation between perpendicular magnetic anisotropy of annealed state and the domain configuration in the as-deposited state was noticed. Films prepared without substrate heating, with additions of Tb show perpendicular coercivity which is larger than 24 kOe.

Features of the surface relief of TiNi alloy in coarse-grained and ultrafine-grained states at room and elevated temperatures

The effect of coarse-grained (CG) and ultrafine-grained (UFG) structures processed by equal channel angular pressing on the formation and features of the surface relief during mechanical tensile tests at room and elevated temperatures was studied. The formation of the UFG structure leads to a significant increase in strength, but the ductility decreases. Coarse-grained samples in the quenched state after tensile tests have a developed relief and microcracks. After tensile testing of the annealed CG sample, a similar situation is observed. On samples in the UFG state, no developed relief and cracks were found. The surface of the UFG sample in the annealed state at a temperature of 500 °C shows a very weak relief, but no cracks are observed. Possible reasons of these effects are discussed.

Microstructural anisotropy, phase composition and magnetic properties of as-cast and annealed Ni-Mn-Ga-Co-Cu melt-spun ribbons

Ni-Mn-Ga-Co-Cu melt spun ribbons were investigated in the as-cast and annealed states. The initial microstructure of the ribbons was highly anisotropic along the growing direction and was characterized by three different regions of equiaxed, columnar and dendritic grains. At ambient temperature, the microstructure was composed of two martensitic phases, i.e. non-modulated and seven-layer modulated, and the high temperature L21 austenite phase. The stabilization of the austenite phase was a consequence of a strong grain size reduction, especially close to the “contact” side of the ribbons. Subsequent annealing at 823 K triggered atomic ordering, which promoted an improvement in the magnetization. Additional annealing at 1173 K brought about a substantial refinement of the microstructure. The ribbon structure changed to a single non-modulated martensite phase, whereas on a microstructural level, the grains and martensitic plates coarsened considerably. The annealed ribbons resembled oligo-crystalline materials and may cause interest for magnetic field-induced strain applications.

Possibility of Application of a 1565ch Alloy in the Automotive Industry

The ductility margins of a grade 5182 aluminum–magnesium alloy, which is traditionally used in the automotive industry, and a 1565ch aluminum–magnesium alloy having a higher magnesium content and microalloyed with zirconium are analyzed and compared. The mechanical properties, their anisotropy, and the microstructures of the alloys in the annealed state are studied, and forming limit and limiting stress diagrams are plotted. The stamping of a typical automobile-body part, namely, an inner hood panel, is simulated by the finite element method. The 1565ch alloy is found to have the ductility that is high enough for an automobile-body sheet: its ductility is comparable with that of the grade 5182 alloy and even slightly exceeds it in the uniaxial tension zone.

Phase Transition of As-Milled and Annealed CrCuFeMnNi High-Entropy Alloy Powder

The CrCuFeMnNi high entropy alloy (HEA) powder was synthesized by mechanical alloying. The effects of milling time and subsequent annealing on the structure evolution, thermostability and magnetic property were investigated. After 50[Formula: see text]h of milling, the CrCuFeMnNi HEA powder consisted of a major FCC phase and a small amount of BCC phase. The crystallite size and strain lattice of 50[Formula: see text]h-ball-milled CrCuFeMnNi HEA powder were 12[Formula: see text]nm and 1.02%, respectively. The powder exhibited refined morphology and excellent chemical homogeneity. The supersaturated solid solution structure of the as-milled HEA powder transformed into FCC1, FCC2, a small amount of BCC and [Formula: see text] phase in annealed state. Most of the BCC phase decomposed into FCC (mainly FCC2 phase) and [Formula: see text] phases, and the dynamic phase transition was almost in equilibrium at 900[Formula: see text]C. The saturated magnetization and coercivity force of the 50[Formula: see text]h-ball-milled CrCuFeMnNi HEA powder were respectively 16.1[Formula: see text]emu/g and 56.2[Formula: see text]Oe.

Phase, microstructure and magnetic properties of 45.5Fe-28Cr-20Co-3Mo-1.5Ti-2Nb permanent magnet

The 47.5-xFe-28Cr-20Co-3Mo-1.5Ti-xM; M = Nb; x = 0.5, 1, 1.5, 2.0, 2.5, 3.0 (wt%) permanent magnets have been investigated after solution annealing, thermomagnetic annealing and step-aging process. Alloys were prepared by vacuum melting and casting technique. Magnets with improved properties were developed through a modified thermal treatment cycle. Solution annealed specimens depict equiaxed α phase grain size of 250 µm while optimally thermomagnetic treated and step aged magnets yield ultra-fine Fe-Co nanorods (10 nm) precipitates in Cr-Ti-Nb matrix. The Nb addition to 47.5Fe-28Cr-20Co-3Mo-1.5Ti alloy expands the α phase structure by suppressing the nonmagnetic phases at annealed state and promotes shape anisotropy for spinodal phases in final treated samples leading to the improvements of magnetic properties. Spinodal phases preferentially aligned and elongated close to applied field direction and retained strong Goss {1 1 0}〈0 0 1〉 orientations. The 45.5Fe-28Cr-20Co-3Mo-1.5Ti-2Nb magnet reveals Hc of 86.9 kA/m, Br of 1.24 T and (BH)max of 57 kJ/m3. High coercivity and remanence in the magnets are attributed to the ideal shape anisotropy of Fe-Co rich nanorods or nanowires.

A comprehensive investigation of electrophysical and magnetoresistive properties of thin films based on permalloy and silver

Thin films based on Ni80Fe20 (Py) and Ag were prepared by electron-beam co-evaporation technique at room temperature. A composition of samples was studied using scanning electron microscope equipped with an energy dispersive detector to perform the x-ray spectrometry. The film structures in both as-deposited and annealed states consist of a Py ferromagnetic particles embedded in an Ag non-magnetic matrix. Results of the study of electrophysical properties demonstrate that metallic behavior of resistivity temperature dependences is observed for all films. Analysis of magnetoresistive properties demonstrates that the isotropic MR field dependences are observed for as-deposited and annealed up to 500 K thin films. The following increase of annealing temperature leads to the appearance of the MR anisotropy during both the transition from the perpendicular geometry to the longitudinal one and to transverse geometry.