Stress Annealing Research Articles

Investigations on the adhesion and fatigue characteristics of hybrid surface-treated titanium alloy

This study is critical for aiding the development of a hybrid treatment consisting of a tungsten-doped diamond-like carbon coating (WC/C) deposited atop shot-peened Ti-6Al-4V surfaces. Residual stresses, considered a key indicator of fatigue performance, were measured by X-ray diffraction (XRD). Rotating bending fatigue tests were carried out while microscopy allowed for fractographic analysis of resultant surfaces. Results show that despite the pronounced surface roughness produced by the shot peening treatment, the high residual compressive stresses, together with the refined and cold-worked microstructure were capable of marginally improving the fatigue performance of the shot peened Ti-6Al-4V compared to the untreated alloy. Conversely, following fatigue testing, the WC/C coating displayed extensive cracking which propagated prematurely into the substrate and yielded a reduction in fatigue limit. On the other hand, despite some annealing of the compressive residual stresses during the coating deposition treatment, the hybrid treatment yielded a reasonable improvement in the fatigue limit over the untreated condition. This result, coupled with the high coating hardness and adhesion, confirm this hybrid treatment's capability in retaining both the adhesive and fatigue performance of the Ti-6Al-4V alloy.

Effect of Stress Annealing on Structure and Magnetic Properties of Fe72.9si15.8b6.9nb3.2cu1co0.2 Amorphous Alloy

Effect of Stress Annealing on Structure and Magnetic Properties of Fe72.9si15.8b6.9nb3.2cu1co0.2 Amorphous Alloy

Mechanism of stress induced irreversible magnetic anisotropy in Fe-based alloy ribbons

Fe-based amorphous and nanocrystalline soft magnetic alloys are regarded as the significant dual-green energy-saving materials because of their superior magnetic properties and straightforward fabrication procedure. As such, they have attracted much attention in the fields of the electronic information and electrical power. In this work, Fe<sub>73.5</sub>Cu<sub>1</sub>Nb<sub>3</sub>Si<sub>13.5</sub>B<sub>9</sub> (%) amorphous alloy ribbon is subjected to various physical ageing treatments in nitrogen atmosphere. These treatments include annealing at 540 ℃ for 30 min under different tensile stresses and isothermal tempering without tensile stress for several cycles. The origin of stress-induced magnetic anisotropy is investigated through using dynamic strain analysis, the longitudinally driven giant magento-impedance effect, and synchrotron radiation X-ray diffraction. In the process of tensile stress annealing, it is found that the axial strain of ribbon is elastic strain when annealing temperature is below the glass transition point, and plastic strain when annealing temperature is above the glass transition point; the precipitation of nanocrystalline phase has a pinning effect on amorphous matrix, which slows down the strain rates and makes the tend stable. Additionally, isothermal tempering studies show that the stress-induced magnetic anisotropy and lattice plane anisotropy have different relaxation patterns. It is found through numerical fitting that the stress-induced magnetic anisotropy can reach a stable value of 0.144 by infinite tempering, whereas the lattice plane anisotropy can only relax to zero by finite tempering. A model of nanocrystalline grain distribution anisotropy is developed to re-examine the origin of stress-induced magnetic anisotropy. It supports a viewpoint that the nanocrystalline grain distribution anisotropy <inline-formula><tex-math id="M4">\begin{document}$\Delta \delta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221509_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221509_M4.png"/></alternatives></inline-formula> is responsible for the stress-induced irreversible magnetic anisotropy <inline-formula><tex-math id="M5">\begin{document}${K_{\text{d}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221509_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221509_M5.png"/></alternatives></inline-formula>, and that their relationship can be described as a following function: <inline-formula><tex-math id="M6">\begin{document}${K_{\text{d}}} = k\Delta \delta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221509_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221509_M6.png"/></alternatives></inline-formula>. Therefore, it is proposed that the stress-induced anisotropy originates from a synergistic interaction between the lattice plane anisotropy and the nanocrystalline grain distribution anisotropy in Fe-based alloy ribbon. This work has important implications for understanding the mechanism of the stress-induced magnetic anisotropy.

Vol4 num4-16 Magnetic properties and applications of glass-coated ferromagnetic microwires

The impact of post-processing on soft magnetic properties and the giant magnetoimpedance (GMI) effect of Fe- and Co-based glass-coated microwires is evaluated. A remarkable improvement of magnetic softness and GMI effect is observed in Fe-rich glass-coated microwires subjected to stress annealing. Frequency dependence of GMI ratio of stress-annealed Fe-rich microwires has been discussed considering frequency dependence of the skin penetration depth, δ, as well as magnetic anisotropy distribution within the metallic nucleus. Annealed and stress-annealed Co-rich microwires present rectangular hysteresis loop and single and fast domain wall propagation. However, Co-based stress-annealed microwires present high magnetoimpedance ratio. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.

Nanocrystallization, magnetic properties and bending ductility of antiferromagnetic Mn-doped FeSiBCuPC alloys induced by micro-compressive stress annealing

Insufficient amorphous forming ability (AFA) and thermal instability have always been the bottleneck restricting the application of high Fe content iron-based nanocrystalline soft magnetic materials. In this work, the effects of micro-compressive stress annealing (MCSA) on microstructure, soft magnetic and mechanical properties of high Fe content FeSiBCuPCMn alloys were systematically investigated. We demonstrate that Mn doping effectively increases the AFA of the alloys and improves the thermal stability of the amorphous matrix. The change of coercivity (Hc) is closely related to the grain size, which depends on the Mn content and annealing process. It clearly shows that a small amount of Mn doping (≤3 at%) and MCSA can inhibit the excessive growth of α-Fe grains and reduce the grain size. Moreover, the low Mn-doped amorphous alloys exhibit good bending ductility even after annealing at appropriate conditions. After MCS-annealing at 420 °C for 10 min, the Mn-doped Fe85−xSi1.3B9P4Cu0.5C0.2Mnx (≤3 at%) nanocrystalline alloys exhibit comprehensive and excellent soft magnetic and mechanical properties, such as high Bs of 1.79–1.87 T, low Hc of 4.6–9.9 A/m and low Hv of 737–867.

Tailoring of Magnetic Softness and Magnetoimpedance of Co‐Rich Microwires by Stress Annealing

Herein, detailed studies on the influence of stress annealing on the magnetic softness and giant magnetoimpedance (GMI) ratio of Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass‐coated microwires are provided. As‐prepared microwire presents linear hysteresis loops, moderate GMI ratio with double‐peak magnetic field dependence and low coercivity (4 A m−1), typically observed for wires with transverse magnetic anisotropy. However, after conventional annealing magnetic hardening and transformation of linear hysteresis loop into rectangular with coercivity about 90 A m−1 is surprisingly observed. It is shown that stress annealing allows preventing magnetic hardening and remarkably improving GMI ratio. Properly stress‐annealed samples present better magnetic softness: almost unhysteretic loops with coercivity about 2 A m−1 and magnetic anisotropy field about 35 A m−1. Observed stress‐annealing‐induced anisotropy is affected by the tensile stresses, applied during annealing and by the annealing temperature. From the frequency dependence of the maximum GMI ratio, the optimum frequency ranges for as‐prepared and stress‐annealed samples are determined. The observed stress‐annealing‐induced magnetic anisotropy and associated changes in magnetic properties and GMI effect are discussed in terms of internal stresses relaxation and related modification of the magnetostriction coefficient, “back stresses,” structural anisotropy, redistribution of internal stresses, and change of spatial distribution of magnetic anisotropy.

Wavelength tunable fiber Bragg gratings fabricated by stress annealing assisted femtosecond laser direct writing

The resonant wavelength is an important parameter of fiber Bragg grating (FBG). When FBGs are fabricated by femtosecond (fs) laser direct writing, it can be fine-tuned through the process of stress annealing. By changing applied stress, it can be permanently fine-tuned in the range of 20.76 nm relative to the original one, and the tunable sensitivity is 1.48 nm/MPa. Besides, the elastic limit strength of silica can be measured at high temperature by analyzing nonlinear shift of FBG resonance wavelength during the stress annealing process. The temperature sensing properties of FBG are measured from 20 °C to 1150 °C. The sensitivity and high-temperature stability of FBG are improved after stress annealing, which means that the fine-tuned FBG is still suitable for high-temperature sensing, high-power fiber lasers and other high-temperature conditions.

Engineering of magnetic properties and magnetoimpedance effect in Fe-rich microwires by reversible and irreversible stress-annealing anisotropy

Herein, by using both hysteresis loops and the Giant magnetoimpedance, GMI, measurements, the magnetic properties of amorphous FeSiBC microwires have been thoroughly analyzed paying attention on the influence of annealing (under stress or without stress) on the GMI effect and magnetic properties of Fe–Si–B–C microwires. We observed that stress annealing allows the induction of transverse magnetic anisotropy and the GMI effect improvement. This stress-annealing induced anisotropy depends on the stress-annealing conditions: annealing time and stress applied during the annealing and can be partially annealed out by subsequent furnace annealing. However, the reversibility of the stress-annealing induced anisotropy depends on the stress-annealing conditions. Particularly, most of the transverse induced magnetic anisotropy obtained by stress-annealing at high stresses values is irreversible. Stress-annealing followed by annealing without stress allows further improvement of the GMI effect in Fe–Si–B–C microwires in a wide frequency range.Coercivity, remanent magnetization, and magnetoimpedance ratio of FeSiBC microwires can be tuned by annealing conditions: annealing time and stress.All studied microwires present GMI hysteresis. The sample with the highest GMI ratio presents the lowest GMI hysteresis.Observed experimental results are discussed considering relaxation of internal stresses, compressive “back-stresses” arising after stress annealing and topological short range ordering.

Temperature memory effect of stress annealing-induced anisotropy in metallic glasses

Stress annealing (SA)-induced magnetic anisotropy is known in iron, nickel, and cobalt-based ferromagnetic metallic glass ribbons and it has already been used in commercial processes. Uniaxial elastic strain is introduced by SA and is quenched into the ribbons even after cooling and removing the external stress. The release of the uniaxial quenched strains is clearly observed as an anomaly in the linear thermal-expansion coefficient (LTEC) when the ribbon is reheated without stress. The rate of strain release corresponding to the LTEC anomaly reaches a maximum at the temperature at which the original SA was performed. We have observed this temperature memory effect over the whole temperature range from 280 to 400 \ifmmode^\circ\else\textdegree\fi{}C, which is below the crystallization temperature ${T}_{x}$. The observed results are explained well by the existence of a localized ``flow unit'' embedded in an elastic matrix, which is accepted as the origin of the shear band formation and rejuvenation of metallic glasses with ${T}_{g}$ (glass transition temperature) $<{T}_{x}$. Although ${T}_{g}$ is hardly visible in calorimetry measurements in most of the ferromagnetic metallic glass ribbons (${T}_{g}>{T}_{x}$), the results here indicate that the same important structural feature is common to metallic glasses with both ${T}_{g}<{T}_{x}$ and ${T}_{g}>{T}_{x}$. Because magnetization behavior is very sensitive to the existence of residual elastic strain which is difficult to evaluate in most of the metallic glasses, detailed studies and a revival of interest in ferromagnetic ribbons will help us to understand more about the nature of the localized flow unit, as well as nonaffine deformations.

Perovskite Oxides Tunable by Electromechanical and Electrothermal Couplings

Perovskite oxide thin films is an attractive material group due to their unique multi-functionalities. To broaden the impact of perovskite oxides to practical electronic device applications, their electrical properties will need to be tunable by external means. In this work, we show that electrical conductivity of perovskite STO (SrTiO3) thin films can be largely tuned by mechanical stress (electromechanical coupling) and thermal annealing (electrothermal coupling). The conductive atomic force microscope setup was carefully calibrated to enable precise measurements of electrical response upon application of varying forces, resulting in a high electromechanical coupling sensitivity of up to ~1,000 Sm-1MPa-1. The thermal annealing study also suggests that electrical conductivity of STO is strongly affected by the ambient temperature due to the varying amount of oxygen vacancies.

Laser-based powder bed fusion of 16MnCr5 and resulting material properties

Laser-based Powder Bed Fusion (LPBF) has evolved to a manufacturing technology for prototype and small scale production of gears. The case hardening steel 16MnCr5 is typically used and its material properties are well known and understood. However, the resulting material properties following the post-LPBF process sequence such as residual stress annealing, case hardening and hard finishing are widely unknown. This paper presents a study of processing 16MnCr5 with an EOS M270 LPBF-machine reaching 99.5 % relative density and above. The resulting microstructure and hardness of the material is examined. Furthermore, the tensile strength as well as the gear-specific tooth root carrying capacity are studied. The results are compared to a conventionally processed material via continuous casting. It is shown that residual stress annealing widely compensates material anisotropy following the LPBF process. Material hardness in the as-built condition is increased up to 21 % compared to a conventional material. The case hardening behavior shows a difference in the resulting case hardening depth in comparison to conventional material. The residual stresses measured at the surface after the case hardening show compressive stresses. Pulsator tests deliver a stress-cycle (S-N) curve from which the tooth root carrying capacity can be derived.

Structural response of melt-spun poly(3-hydroxybutyrate) fibers to stress and temperature

We have investigated the structural response of melt-spun poly-3-hydroxybutyrate (P3HB) fibers to stress and temperature and its impact on the mechanical properties. Low-stress (≤1.6 MPa, 100–130 °C) annealed P3HB fibers showed a considerable viscoelastic behavior and remained ductile up to at least two months. Stress annealing with high weights (≥32 MPa), however, lead to fibers with a higher tensile strength (182 MPa) and with a lower elongation at break (22%). These significant differences in the tensile properties are closely related to structural changes, which we have studied with in-situ wide-angle x-ray diffraction (WAXD) and small-angle x-ray scattering (SAXS) experiments. A highly oriented non-crystalline mesophase (Pnc), which is located in-between orthorhombic α-crystals is growing during high-stress annealing but disappears during low-stress annealing. However, it is possible to restore the mesophase by post-drawing. The viscoelastic hysteresis behavior of low-stress annealed fibers is explained by a reversible transformation of α-crystals into mesophase and back.

Investigation of the Property Change in FINEMET Alloy After Conventional, Pulse and Mechanical Stress Annealing

Abstract In the present work the comparison of the effect of traditional, pulse and stress annealing is made by monitoring the important mechanical and magnetic properties of FINEMET type amorphous precursor alloy. The magnetic properties were determined from the shape of magnetization curve (coercive force, anisotropy) during various heat treatments and the mechanical properties were measured using brittleness test. The traditional heat treatments were performed in resistance furnace and the magnetic measurements were performed in astatic magnetometer. The pulse and stress annealing (as well as their combinations) were carried out inside in the magnetometer. The temperature of pulse heat treatments is regulated with the length of current pulse flowing through the sample. After each pulses the magnetization curves were measured in-situ, in the magnetometer.

Route of magnetoimpedance and domain walls dynamics optimization in Co-based microwires

The influence of post-processing (annealing and stress-annealing) on the magnetic softness, Giant magnetoimpedance (GMI) effect and domain wall dynamics of Fe3.6Co69.2Ni1B12.5Si11Mo1.5C1.2 glass-coated microwires is studied.As-prepared Co-rich glass-coated microwire presents linear hysteresis loops and rather higher magnetoimpedance ratio with double-peak magnetic field dependence, typical for materials with transverse magnetic anisotropy.Considerable magnetic hardening and transformation of linear hysteresis loop with low coercivity (Hc ≈ 4 A/m) into rectangular with Hc ≈ 90 A/m upon annealing without stress is observed. However, we observed remarkable MI effect improvement at certain annealing conditions.Stress-annealing of studied microwire allows considerable magnetoimpedance ratio and domain wall velocity increasing. Additionally, remanent magnetization growth and coercivity decrease are generally observed upon stress annealing. Frequency dependence of maximum GMI ratio for as-prepared and annealed samples is evaluated. The obtained frequency dependence of the maximum GMI ratio allows determination of the optimal GMI measurement conditions for each sample. The observed stress-induced anisotropy and related changes in magnetic properties are discussed considering the internal stresses relaxation and “back-stresses”.

Magnetic Properties in Finemet-Type Soft Magnetic Toroidal Cores Annealed under Radial Stresses

Applying tensile stresses on straight soft magnetic ribbons before core fabrication is a routine method of inducing magnetic anisotropy, while methods of stress annealing of ribbons after core winding are seldom explored. In this study, we utilize a novel approach to induce magnetic anisotropy by applying radial stresses on tape-wound cores of Fe73.5Si13.5B9Cu3Nb1 (at. %) ribbon during crystallization heat treatment. The results show that while stress annealing does not change the structural characteristics of annealed samples, the magnetic anisotropies induced can increase to values ~3–5 times larger than the sample annealed in the absence of external stress. This increase in magnetic anisotropy energy is associated with ~25–50% decrease of magnetic inductance in the treated cores. These results suggest that the magnetic properties of nanocrystalline soft magnetic alloys can be effectively tuned by applying radial stresses.

Softening and magnetic properties of ultrahigh Fe content FeSiBCuPC nanocrystalline alloy induced by low-pressure stress annealing

Due to the rapid growth of precipitated nanoparticles in ultrahigh Fe content nanocrystalline alloys, we propose a new method of low-pressure stress annealing (LPSa) to control crystallization behavior to achieve excellent magnetic properties and mechanical properties of Fe85.7Si0.5B9.3Cu0.7P3.5C0.3 nanocrystalline alloy. It demonstrates that LPSa promotes the precipitation of α-Fe phase and suppresses the growth of nanoparticles, which obtains a higher saturation magnetization of 202.1–206.6 emu/g and a lower coercivity of 6.7–8.2 A/m. Besides, the formation of fine and uniform nanocrystalline structure induced by LPSa achieves the lower value and uniform distribution of hardness and Young's modulus, resulting in softening.

Tailoring the magnetization linearity of Finemet type nanocrystalline cores by stress induced anisotropies

In this paper a theoretical and experimental investigation will be presented on the linearity of the flat hysteresis loop obtained by continuous stress annealing of Finemet type nanocrystalline ribbon. The stability of the effective permeability versus the magnetizing field depend on the residual random distribution of local magnetization and can be characterized by i) the coefficient a in the expression of magnetization approaching the saturation: M/Ms = 1 − a/H, valid in a restricted region, for Hlin < H < Hsat, where Hlin is the limit of linearity and by ii) the distribution of the anisotropy field ΔHK. The theoretical upper limit of linearity is given by the anisotropy field HK = Bs/µo.µeff. The linearity limit, Hlin, can be expressed as a difference between the value HK and the half width of the anisotropy field distribution, ΔHK. The linearity will be measured by the ratio R = Hlin/HK. The parameter R is almost constant (around 0.72) for large applied stresses and carefully selected annealing parameters (furnace geometry, temperature distribution along the furnace and pulling velocity). For small applied stresses (i.e. for effective permeability’s above 4000) however this linearity parameter is reduced to zero and a potbellied loop appears. A possible explanation will be given for the stress dependence of linearity parameter based on the back stress model of stress annealing.

Soft magnetic microwires for sensor applications

We provide an overview of the routes allowing the optimization of magnetic softness, giant magnetoimpedance (GMI) effect and domain wall dynamics in one of the families of magnetic microwires: glass –coated microwires prepared using Taylor-Ulitovsky method. The magnetic properties of as-prepared microwires are determined mostly by the magnetoelastic anisotropy. Conventional annealing allows a considerable improvement of the domain wall dynamics in Fe-rich microwires and a slight decrease of the coercivity, however, remarkable magnetic hardening is observed after conventional furnace annealing of Co-rich microwires. Stress annealing of Fe-rich microwires allows a considerable magnetic softening and GMI effect enhancement and even more remarkable improvement of the domain wall dynamics. In Co-rich microwires stress-annealing allows the improvement of GMI effect and even the induction of transverse magnetic anisotropy at high enough annealing temperature. However, the highest GMI effect is observed for stress-annealed Co-rich microwires which present rectangular hysteresis loops. Consequently, annealed Co-rich microwires can present both, fast domain wall propagation and GMI effect.Observed induced anisotropy and related changes of the magnetic properties are discussed considering the internal stresses relaxation, “back-stresses” and circumferential magnetic field during proposed post-processing.Consequently, correctly designed post-processing enabled us to design the magnetic anisotropy distribution beneficial for the optimization of the GMI effect and the domain wall dynamics in magnetic microwires.

Impact of Stress Annealing on the Magnetization Process of Amorphous and Nanocrystalline Co-Based Microwires.

The domain wall (DW) dynamics of amorphous and nanocrystalline Co-based glass-coated microwires are explored under the influence of stress annealing. Different annealing profiles have enabled remarkable changes in coercivity and magnetostriction values of Co-based amorphous microwires with initially negative magnitude, allowing induced magnetic bistability in stress-annealed samples and, consequently, high DW velocity has been observed. Similarly, Co-based nanocrystalline microwires with positive magnetostriction and spontaneous bistability have featured high DW velocity. Different values of tensile stresses applied during annealing have resulted in a redistribution of magnetoelastic anisotropy showing a decreasing trend in both DW velocities and coercivity of nanocrystalline samples. Observed results are discussed in terms of the stress dependence on magnetostriction and microstructural relaxation.

Effect of imprinting times and stress annealing on warm laser shock imprinting

The rapid development of mechanical systems’ miniaturization has expanded the demand for higher precision and performance micro formed parts. For improving the forming height and quality of formed parts, and studying the influences of the stress annealing and imprinting times on the forming as well as surface roughness (Sa) of the formed parts, this paper proposed a composite process of imprinting times and stress annealing on warm laser shock imprinting (WLSI) to realize the precision forming of the aluminium foil. In this research, the WLSI experiments were carried out with the imprinting temperature, imprinting times, and stress annealing treatment as variables. Subsequently, the forming height, surface roughness, and surface oxidation of the formed parts were measured, the loading–displacement curve were monitored, the transient deformation process induced by WLSI was divided four stages (deformation stage, rebound stage, vibration stage, and stable stage), and the residual stress distribution of the formed parts were simulated and analyzed by ABAQUS. Finally, the influences of the above three factors on the formed parts were discussed and explicated, and these results showed that the imprinting times and stress annealing can improve effectively the forming effect of WLSI.