Onset Crystallization Temperature Research Articles

Soft magnetic cobalt based amorphous alloys with low saturation induction

The influence of the concentration of alloying components on thermal stability, magnetic and electrical properties of amorphous alloys of Co73-66Fe4,6-3Cr0-9(B,Si)22-29 system was studied by methods of differential scanning calorimetry, XRD, resistometry and magnetometry. The crystallization of several alloys with advanced magnetic characteristics was studied. At continuous heating of the ribbons, either primary or eutectic crystallization was observed depending on the chemical composition of these alloys. Certain tendencies in the anomalous behavior of temperature dependence of electrical resistance of ribbons were revealed. By increasing chromium and metalloids concentrations, we obtained the alloys with relatively low saturation induction and large difference between the Curie temperature and the temperature of crystallization onset. The heat treatment regimes to obtain the best magnetic properties of these alloys were found. Prospective applications of Co73-66Fe4,6-3Cr0-9(B,Si)22-29 amorphous ribbons for fabrication of high sensitive sensors of magnetic field were discussed.

Analytical characterization of polyamide 11 used in the context of selective laser sintering: Physico-chemical correlations

Polyamide 11 is an attractive material for additive manufacturing, however, in the selective laser sintering process it is subject to significant thermally induced stress. Suitable analytical methods are necessary to indicate any changes in the material properties. In this work, thermally stressed powder samples and printed tensile bars were analyzed by size exclusion chromatography-multi angle laser light scattering and differential scanning calorimetry. Based on the molecular weight distribution, crystallization and melting temperatures, ageing states of the investigated powders can be defined and transferred to the particles of the printed components. As a result, thermal stress led to an increase in molar mass and polydispersity. Moreover, calorimetric measurements indicated a delayed nucleation process as well as a decrease in polymorphism. Additionally, polymeric material with lower polydispersity values across the tensile bars could lead to decreasing elongation at break (εB) values. For the crystallization onset temperature the opposite effect on εB was observed.

The Onset and Solidification Path of a Basaltic Melt by in situ Differential Scanning Calorimetry (DSC) and ex situ Investigations

The in-situ differential scanning calorimetry (DSC) technique has been applied to investigate the solidification paths of a basaltic liquid. The starting glass was heated up to 1300 °C, kept at this superliquidus temperature for 2 h and cooled at rates (∆T/∆t) of 7, 60, 180, 1000, and 1800 °C/h, down to 800 and 600 °C. Glass transition temperature (Tg), crystallization temperature (Tx_HR) and melting temperature (Tm) were measured by in-situ DSC spectra on heating. Tx measured along the cooling paths (Tx_CR) shows exothermic peaks that change from a single symmetric shape (7 and 60 °C/h) to multi-component patterns (180, 1000 and 1800 °C/h). The recovered products characterized by FE-SEM and EPMA-WDS show a phase assemblage of spinel (sp), clinopyroxene (cpx), melilite (mel), plagioclase (plg), and glass. Moreover, crystal size distributions (CSDs) and growth rates (Gmax and GCSD) were also determined. The crystal content slightly increases from 7 to 1800 °C/h. Faceted sp are present in all the run products with an amount always < 2 area%. Cpx increases from 7 to 1800 °C/h, changing its texture from almost faceted to dendritic between 60 and 180 °C/h. The area% of mel follows an asymmetric Gaussian trend, while plg nucleates only at 7 °C/h with a content < 2 area%. The coupling of DSC and SEM outcomes indicate that sp nucleate first, followed by cpx and mel (and/or plg). The increment of ∆T/∆t causes an increase of the CSD slope (m) and crystal population density per size (n0), as well as a decrease of the crystal size, for both cpx and sp. The log-linear CSD segments with different slopes at 7 and 60 °C/h suggest multiple nucleation events and crystal growth by coarsening. Gmax and GCSD for cpx and sp directly measured on the actual crystallization time by DSC spectra, both increase with the increasing of ∆T/∆t. The onset temperature of crystallization (Txi) decreases as ∆T/∆t increases, following an exponential trend that defines the uppermost portion of a time-transformation-temperature (TTT)-like curve. This analytical model allows us to quantitatively model the kinetic crystallization paths of dry basalts.

Monitoring the Crystallization Behavior of Hydrogenated Coconut Oil Using Ultrasonic Phase Velocity

AbstractFat crystals are known to affect the stability and applicability of fat‐containing foods, and changes in quality during low‐temperature preservation. Therefore, understanding fat crystallization behavior is important for product development and quality control. Ultrasonic measurement is a nondestructive, noncontact, and highly versatile on‐line measurement method. Herein, we aim to verify the applicability of the ultrasonic characteristics to monitor fat crystallization behavior of hydrogenated coconut oil (HCO) using ultrasonic phase velocity (UPV) at 1.98 MHz under different cooling rates and with different emulsifier additives. The UPV was found to increase with decreasing HCO temperature, and the UPV‐temperature relation had an inflection point at approximately 20–25 °C. The inflection point coincided with the crystallization onset temperature determined by differential scanning calorimetry. The density of HCO was found to increase with decreasing temperature, while the compressibility of HCO decreased with the temperature. From the Laplace equation established between the UPV (c) and the density (ρ), c = (ρβ)−0.5, the increase in the compressibility (β) of UPV indicates a decrease in ρβ. Consequently, since the density increases with cooling, the dominant factor that causes an increase in UPV is a reduction in compressibility. The UPV of the solid phase was highly correlated with the crystallization enthalpy (R2 = 0.99).

Effect of CeO2 and Eu2O3 on the calorimetric behavior of Si–Al–Zn–K–Ti oxide glass

Glasses and glass-ceramics based on SiO2 have attracted a large attention. In this work, the thermal properties and crystallization kinetics of Si–Al–Zn–K–Ti glasses are investigated. Based on the thermal parameters derived from the differential scanning calorimetry technique ran upon various heating rates, the characteristic glass transition temperature, onset crystallization temperature and crystallization temperature were extracted. The crystallization peaks are carefully investigated by Kissinger, Ozawa and modified-Kissinger methods. Avrami index and the dimensionality of the crystal growth vary from 2 to 4 at the same time that crystallization activation energy decrease from 177.80 kJ/mol to 145.40 kJ/mol in Ozawa method and the thermal stability reaches to 177.20 ΔC° by doping with 0.5 wt% of CeO2 and 0.5 wt% of Eu2O3, both in excess. Our results confirm the role of rare earth ions in the crystallization kinetics, as well as improvement in the glass thermal stability.

Effects of Nb Addition and Heat Treatment on the Crystallization Behavior, Thermal Stability and Soft Magnetic Properties of FeSiBPCuC Alloys

In this paper, the effect of the replacement of Fe by Nb on the glass forming ability (GFA), the thermal stability and the crystallization behavior of Fe84.5−xSi0.5B10.5P3.5C0.7C0.3Nbx (x = 0, 1, 2) alloys were investigated. The results show that the addition of Nb increases the GFA. Increasing Nb content can enhance the first onset crystallization temperature (Tx1), the second onset crystallization temperature (Tx2) and ΔTx (ΔTx = Tx2 − Tx1), which broadens the range of annealing temperatures. The coercivity (Hc) of ribbons decreases with increasing Nb content after annealing at a low heating rate and reach as a minimum of 24.5 A/m when the Nb content is 2 at.%. The process of annealing at a high heating rate distinctly decreases Hc, and all samples present excellent soft magnetic properties. The nanocrystalline alloy exhibits the lowest Hc of 6.4 A/m after annealing at 460 °C for 5 min.

Effect of loading rate on crystallization of metallic glass supercooled liquids

Metallic glasses exhibit unique thermoplastic processing capability, which is enabled by their metastable supercooled liquid state below the crystallization temperature. The thermoplastic processing critically depends on the crystallization time (processing time window), temperature (viscosity), applied load, and strain-rate. Among these parameters, the effects of crystallization time and processing temperature have been extensively studied. However, the effects of load and loading rate have not been thoroughly investigated. In this work, we performed a systematic study of load on the supercooled liquid state of three metallic glass formers: Pt-based, Zr-based, and Pd-based. The results show that the load-response of a metallic glass supercooled liquids is strongly composition dependent. The onset temperature of crystallization decreases with increasing load in Pt-based metallic glass whereas for Zr-based and Pd-based metallic glasses the onset temperature remains unchanged. The crystallization peak time is reduced for all three metallic glasses after thermoplastic forming. The results are discussed in terms of nucleation and growth of crystallites in metallic glasses.

Effect of bismuth incorporation on thermal properties of quaternary chalcogenide glass Se80Te15-xCd5Bix (x=0,5,10) alloys

Differential scanning calorimetry has been employed to investigate the thermal properties of Se80Te15-xCd5Bix (x = 0, 5, 10) glass system. The Variation of characteristic temperatures such as glass transition temperature (Tg), onset crystallization temperature (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) are studied as a function of composition and heating rate. A stepwise increase in values of characteristic temperatures has been observed with the increase in heating rate. Further, obtained values of characteristic temperatures display decreasing trend with increase in bismuth concentration. The compositional and heating rate dependence of Thermal parameters such as glass forming ability (ΔT), thermal stability (Hg), enthalpy (ΔH) and entropy (ΔS) has been investigated. It has been observed that ΔT and Hg have lowest and highest values for Se80Te5Cd5Bi10 and Se80Te15Cd5 compositions respectively. Avrami index (n) and activation energy for crystallization (Ec) have been calculated for all the samples. Values of n obtained for Se80Te15Cd5, Se80Te15Cd5 Bi5 and Se80Te5Cd5Bi10 compositions are found to be 1.44, 2.16 and 2.16 respectively. Based on the obtained values of n, the nucleation process in alloys is discussed. It is noteworthy to mention that least value of Ec is observed for the alloy Se80Te5Cd5Bi10 containing the highest amount of bismuth. Furthermore, calculated thermal parameters are used to anticipate the electrical switching behavior of the alloys.

Specifics of Crystallization of Amorphous TiNiCu Alloys with High Concentrations of Copper

Ribbons of alloys of the quasi-binary TiNi–TiCu system with 25, 30, 35, and 40 at % copper were fabricated by planar flow casting at a cooling rate of 106 K/s. The thickness of the ribbons was 30–50 μm, and their width was 10–20 mm. The structure and phase transformations of alloys were studied using electron microscopy, X-ray diffraction, and differential scanning calorimetry. It was found that the alloys with 25 and 30 at % Cu in the initial state have an amorphous-crystalline structure, which undergoes one-stage polymorphic crystallization of the amorphous state with the formation of austenitic phase B2 under heating in a calorimeter. When cooled to room temperature, phase B2 undergoes a martensitic transformation to orthorhombic phase B19. It was demonstrated that the alloys with 35 and 40 at % Cu become amorphous when quenched and undergo two-stage (primary and eutectic) crystallization under heating. The resulting structure is two-phase (tetragonal phase B11 (TiCu) with a small fraction of phase B2). An increase in the concentration of copper leads to a reduction in the onset temperature of crystallization.

Compositional dependence of crystallization temperatures and phase evolution in hafnia-zirconia (HfxZr1−x)O2 thin films

Polymorphic (HfxZr1−x)O2 (HZO) thin films exhibit ferroelectric, dielectric, and antiferroelectric properties across a wide compositional range due to the existence of orthorhombic, monoclinic, and tetragonal phases. To better understand the phase stability across the HfO2–ZrO2 compositional range, we investigate the structural evolution of HZO thin films in situ via high-temperature x-ray diffraction (HTXRD) for five different compositions [ZrO2, (Hf0.23Zr0.77)O2, (Hf0.43Zr0.57)O2, (Hf0.67Zr0.33)O2, and HfO2]. The real-time monitoring of HZO crystallization reveals a competing driving force between the tetragonal and monoclinic phase stabilities for HfO2-rich vs ZrO2-rich compositions. Additionally, we confirm an XRD peak shift toward lower 2θ with increasing temperature in ZrO2, (Hf0.23Zr0.77)O2, and (Hf0.43Zr0.57)O2 films, which we ascribe to the appearance of a metastable orthorhombic phase during heating. A monotonic trend for the onset crystallization temperature is reported for five compositions of HZO and reveals an increase in onset crystallization temperature for HfO2-rich compositions. Relative intensity fraction calculations suggest a higher fraction of monoclinic phase with increasing annealing temperature for (Hf0.67Zr0.33)O2. This study of phase stability and onset crystallization temperatures offers insight for managing the thermal budget for HZO thin films, especially for temperature-constrained processing.

Accelerated crystallization and phase formation in Fe40Ni40B20 by electric current assisted annealing technique

Abstract The effect of electric current assisted annealing was investigated in amorphous Fe40Ni40B20 melt spun ribbons in terms of manipulating the crystallization temperature and phase formation. A specific setup was developed, which allows to measure the sample temperature and the electrical resistance in-situ during the annealing process. By employing these simultaneous measurements, the shift of the crystallization temperature was evaluated by employing different electric current modes and current densities. It was found that the onset temperature for crystallization is shifted to lower temperatures when a certain threshold of electric current density is surpassed. Maximum temperature shifts up to 130°C were achieved using direct and alternate current modes, while in pulsed current mode the maximum shift was 100°C. Even though a noticeable change was observed in the crystallization temperature when an electric current is applied during annealing, the nucleated phases were found to be the same as in the samples annealed without current. The reasons for the observed behavior are discussed and compared to propositions found in the literature. It is concluded that the ‘‘hot spots’’ mechanism is in good agreement with the results obtained in this work.

Modified PLLA: effect of BPADD on properties

Poly(l-lactic acid) (PLLA) modified by a new organic nucleating agent, N,N′-dodecanedioic bis(piperonylic acid) dihydrazide (BPADD), was fabricated, and its crystallization, melting behavior, thermal stability, fluidity and mechanical properties were investigated. The melt-crystallization behavior proved that BPADD could bring about a fast nucleation rate to promote the crystallization of PLLA; 2 wt% BPADD exhibited the best crystallization accelerating effect due to having the highest crystallization onset temperature and the highest melt-crystallization temperature. However, PLLA/3% BPADD had the largest melt-crystallization enthalpy. In addition, the frontier orbital energy indicated that the nucleation effect of BPADD on PLLA might be attributed to intermolecular interaction. The melt crystallization also depended on two critical factors, the cooling rate and final melting temperature. An increase in BPADD content led to greater inhibition of crystal growth during cold crystallization. The differences in the melting behavior of PLLA/BPADD samples reflected the previous crystallization process, the heating rate and BPADD content. BPADD was harmful to maintaining the thermal stability of PLLA; however, the intermolecular interaction could prevent the decomposition onset temperature from continuously decreasing. The usage of BPADD resulted in better fluidity and higher tensile strength; the tensile modulus and elongation at break were associated with BPADD content.

Crystallization, sinterability, and dielectric properties of MgO–Al2O3–SiO2 glass-ceramics doped with TiO2

The effects of TiO2 on crystallization, microstructure, thermal, and dielectric properties of MgO–Al2O3–SiO2 (MAS) glass-ceramics were investigated. The results showed that with the TiO2 content increasing, the glass transition temperature (Tg) increased gradually, while the onset of crystallization temperature (Tx) and crystallization peak temperature (Tp) increased firstly and then decreased. The main crystalline phase for all the samples was μ-cordierite. β-Quartz and α-cordierite precipitated as the minor crystalline phases with TiO2 content ≥ 2 mol%. A small amount of TiO2 could promote the sintering process and improve the dielectric properties of MAS glass-ceramics. However, an excess of TiO2 addition could worsen the sintering and dielectric properties. The addition of TiO2 was beneficial to decrease the coefficient of thermal expansion (CTE). The MAS glass-ceramics doped with 2 mol% TiO2 heated at 925 °C showed excellent properties: high density (2.64 g/cm3), low CTE value (3.34 × 10–6/°C), low dielectric constant (5.44), and dielectric loss (2.17 × 10–3) at 1 MHz, which was a promising material for LTCC applications.

Er3+/Yb3+ co-doped TeO2–ZnO–ZnF2–La2O3 glass with a high fluorescence intensity ratio for an all-fiber temperature sensor

Er3+/Yb3+ co-doped TeO2–ZnO–ZnF2–La2O3 (TZZL) glasses with different concentrations of Er3+ ions were fabricated. Strong green upconversion emission bands centered at 523 and 545 nm induced by 980 nm excitation were observed. The maximum emission intensity of the TZZL glasses was obtained at the Er3+ ion concentration of 0.2 mol%. High-temperature difference (ΔT = 131.8 °C) between the transition and onset crystallization temperatures was confirmed by differential thermal analysis curve. The relationship between fluorescence intensity ratio value and temperature was examined within 303–560 K. The maximum absolute sensitivity (Sa) and the maximum relative sensitivity (Sr) was 0.006 K−1 at 560 K and 0.012 K−1 at 303 K, respectively. A prototype of an all-fiber temperature sensor was designed, and its temperature-sensing performance within 293–383 K was evaluated. Results showed that the absolute errors were within ±1 K, and the largest value of relative standard deviation was approximately 0.2%, suggesting that Er3+/Yb3+ co-doped TZZL glasses have potential applications in optical-fiber temperature sensors.

Crystallization and magnetic hardening behaviour of Fe-rich FeSiBNb(Cu) melt-spun alloys

The sequential, multi-stage crystallization and magnetic hardening behaviour of Fe82B14Si2Nb2, Fe83B13Si2Nb2, Fe83B12Si2Nb2Cu1 and Fe85B13Nb2 melt-spun alloys have been investigated. The microstructure-crystallization-magnetic property relationship was established using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), magnetometry, transmission electron microscopy (TEM) and magneto-optical Kerr effect microscopy (MOKE) techniques. The increase of Fe content (>82 at%) of as-quenched ribbons imparts microstructural heterogeneity across the ribbon cross–section; i.e., textured α-Fe crystals at the free surface to hetero-amorphous microstructure in the bulk matrix. The isochronal annealing of hetero-amorphous alloys depicts simultaneous surface and bulk crystallization process occurring before and after the crystallization onset temperature (Tx1) temperature. The annealing temperature range (Ta < Tx1) coinciding with the paramagnetic region of the thermo-magnetic plot, induces irreversible magnetic hardening due to simultaneous coarsening of pre-existing crystal nuclei and exchange de-coupling between nanocrystal and intergranular matrix. The onset of primary crystallization in the pre-crystallized ribbons results in bimodal nanocrystallite distribution having an average crystallite size exceeding the ferromagnetic exchange length of Fe-based alloys. The minor Cu addition alters the growth morphology of pre-existing nuclei from dendrite-like to equiaxed, assisting heterogeneous nucleation and improving intergranular amorphous stability by delaying boride precipitation. The soft-magnetic property deterioration of partially crystallized ribbons is discussed within the framework of Extended-Random Anisotropy models.

A new mathematical expression for the relation between characteristic temperature and glass-forming ability of metallic glasses

Based on the classical theory of nucleation, a new criterion ϖ, defined as (Tx−Tg)⋅Tg⋅Tx/(Tl−Tx)3 (where Tg, Tx and Tl are the glass transition temperature, the onset crystallization temperature and the liquidus temperature) and correlated to the critical casting diameter (Dmax), which has been proposed to evaluate the glass-forming ability (GFA) of bulk metallic glasses (BMGs). According to the linear fitting results of 667 reported BMGs, the relationship between Dmax and ϖ is expressed as Dmax=(1.08±0.26)+(10.22±0.45)ϖ. The interrelationship between the new criterion ϖ and Dmax exhibits better ability for evaluating GFA of the alloys than nine criteria reported in literature, and the values of Dmax of Fe-BMGs could be calculated by this ϖ parameter in an appreciable range. Therefore, the proposed ϖ parameter has certain significance for the development of new metallic glasses and the determination of their Dmax.

Non-isothermal crystallization kinetics investigation of different zones at the joining area of a bulk metallic glass welded by friction stir spot welding (FSSW)

The connection cross section of a Ti-based bulk metallic glass welded with friction stir spot welding method, was investigated using Vickers micro-hardness and SEM. Regarding the results, four zones were detected at the connection site. The crystallization kinetics of the four zones identified at the joining area, was studied using the DSC at heating rates of 10–50 K min−1. Apparent activation energy (Ec), frequency factor (A) at characteristic temperatures (Tg, Tx1, Tp1) and local activation energy (Ec(α)) variations of different zones during the first crystallization transformation were calculated by isokinetics and isoconversional models. The crystallization conversion function for each zone was determined using the Sestak-Berggren equation. Sub-tool tip stir zone (TSZ) showed the highest thermal stability. The thermo-mechanically affected zone (TMAZ) with the highest onset crystallization temperature (Tx1) has a higher thermal stability in comparison to sub-tool shoulder stir zone (SSZ) with the lowest thermal stability and base metal (BM).

Formation, thermal stability and mechanical properties of high-entropy (Fe0.25Co0.25Ni0.25Cr0.125Mo0.0625Nb0.0625)100‒xBx (x = 7–14) amorphous alloys

High-entropy (Fe0.25Co0.25Ni0.25Cr0.125Mo0.0625Nb0.0625)100‒xBx amorphous alloys are formed with low (8–14 at%) boron contents by melt spinning. With increasing boron, the broad halo in X-ray diffraction shifts to indicate a decreasing average spacing of nearest-neighbor atoms. The crystallization onset temperature and the Vickers hardness increase with boron content. The glass transition is observed even for a low-boron (13 at%) alloy. The 8–11 at% B alloys crystallize in stages: [am] → [am’ + bcc] → [am″ + bcc + fcc] → [bcc + fcc + borides]. The bcc precipitates, diameter ∼10 nm enriched in (Fe,Co) and the fcc precipitates, diameter ∼15 nm enriched in (Ni,Fe), are stable on annealing over a wide range (900–1060 K) below the temperature at which borides form. The bcc phase shows no internal defects, while the fcc phase has defects such as twin boundaries. The microhardness (Hv) of the [am″ + bcc + fcc] nanostructure reaches a high maximum of 1460–1560 kgf‧mm−2, before decreasing rapidly when the formation of borides marks the disappearance of the residual amorphous phase. The high thermal stability of the three-phase nanostructure is attributed to the residual amorphous phase enriched in B, Cr, Mo and Nb. These low-boron metastable alloys with novel three-phase nanostructures are attractive as potential amorphous coatings or ultrahard structural alloys with high thermal stability.

Crystallization and corrosion resistance of Zr–Ti–Y–Al–Cu–Ni–Co–Fe complex multi-component bulk metallic glasses

A series of Zr–Ti–Y–Al–Cu–Ni–Co–Fe complex multi-component bulk metallic glasses (CMBMGs) were designed using multi-substitution strategy in Zr55Cu35Al10, Zr60Cu30Al10 and Zr60Cu28Al12 BMGs, and their crystallization and corrosion behaviors were systematically investigated. It is found that, CMBMGs have higher complexity in crystallization compared to their ternary counterparts, and well-dispersed nano-crystals with diameters of 5–30 nm could be easily formed in CMBMGs in a wide range of annealing temperature, reflecting sluggish crystallization kinetics. Moreover, these CMBMGs exhibit considerable higher corrosion resistance than their ternary counterparts. Besides, both the glass transition temperature (Tg) and onset crystallization temperature (Tx) decrease compared to their ternary counterparts. In addition, it is interesting that the crystallization behavior and corrosion resistance of these Zr–Ti–Y–Al–Cu–Ni–Co–Fe CMBMGs are mainly influenced by the elements substituted in Zr–Cu–Al alloys, which provides a novel route for compositional optimization of CMBMGs. This work is beneficial to better understand the phase formation and properties of BMGs with complex compositions.

New FeNiCrMo(P, C, B) high-entropy bulk metallic glasses with unusual thermal stability and corrosion resistance

New Fe20–35Ni20Cr20–30Mo5–15(P0.6C0.2B0.2)20 bulk metallic glasses with excellent thermal stability, strength, and corrosion resistance have been developed through the high-entropy alloy design strategy. The high-entropy bulk metallic glasses (HE-BMGs) possess larger supercooled liquid regions of ∼69 K, higher crystallization onset temperatures of ∼852 K, larger undercoolings of ∼109 K, and more sluggish crystallization process upon heating than the conventional metallic glass benefited from the high mixing entropy effect. The HE-BMGs also exhibit ultrahigh strength of ∼3.4 GPa, Vickers hardness of ∼1107, and superior corrosion resistance in acids and NaCl solutions by formation of highly stable Cr- and Mo-enriched passive films. The new metal-metalloid HE-BMG system and exceptional properties give the alloys good promise for both scientific and engineering applications.