Primary Crystallization Research Articles

Effect of Ge on soft magnetic properties at elevated temperature for Si-rich Finemet-type alloy

• The effect of Ge doping on the soft magnetic properties is investigated for Si-rich Finement-type alloy. • The Curie temperature is enhanced by doping Ge in Si-rich Finemet-type alloy. • The initial permeability μ i of 540°C-annealed Fe 72 Ge 2.5 Cu 1 Nb 3 Si 17.5 B 5 alloy possesses a relatively large value of 5000 until 600°C. The results obtained by partially substituting Ge for Fe in the Fe-based nanocrystalline alloy for improving the magnetic properties at high temperatures are presented in this work. These studies were performed on the Fe 74.5- x Ge x Cu 1 Nb 2 Si 17.5 B 5 ( x =2.5, 5, 7.5) alloys. The nanocrystallization and the Curie temperature are dependent on the Ge concentration. The onset temperature of primary crystallization decreases with the increase of Ge, indicating that the dual-phase nanocrystalline structure could be formed at a relatively lower temperature compared with the Ge-free alloy . For the alloy with x =2.5at%, the Curie temperature of the amorphous alloy is enhanced to 405°C. The initial permeability μ i of 540°C-annealed alloy possesses a relatively large value of 5000 until 600°C. Such a magnetic softness at elevated temperature is superior to that of Finemet-type Fe-based nanocrystalline alloys ever reported.

Temperature-Dependent Phase Evolution in FePt-Based Nanocomposite Multiple-Phased Magnetic Alloys

A quaternary Fe-Pt-Nb-B alloy has been fabricated by the melt spinning method with the purpose of the formation of crystallographically coherent multiple magnetic phases, emerging from the same metastable precursor, as well as to investigate the phase interactions and the influence of their coupling on magnetic performances. For this purpose, extended structural and magnetic investigations were undertaken by making use of X-ray diffraction, transmission electron microscopy, and 57Fe Mössbauer spectroscopy, as well as magnetic measurements using SQUID magnetometry. It was documented that intermediate metastable phases formed during primary crystallization, in intermediate stages of annealing, and a growth-dominated mode was encountered for the secondary crystallization stage upon annealing at 700 °C and 800 °C where fcc Fe3Pt and fct Fe2B polycrystalline were formed. The Mössbauer investigations have documented rigorously the hyperfine parameters of each of the observed phases. The fcc A1 FePt phase was shown to exhibit a peculiar ferromagnetic transition, and this transition has been proven to occur gradually between 300 K and 77 K. The magnetic measurements allowed us to identify the annealing at 700 °C as optimal for obtaining good magnetic features. Coercive field dependence shows similarities to the random anisotropy model for samples annealed at 500 °C to 700 °C which are nanocrystalline. These results show good perspectives for use in applications where different magnetic states are required at different operating temperatures.

Influence of composition and cooling rate of alumocalcium slag on its crumblability

The main components of metallurgical slags are iron compounds, which are extracted by reduction smelting. There are several types of this process with obtaining various products based on iron and slags of various compositions (aluminum-calcium self-disintegrating), etc. The mode of smelting and cooling of alumocalcium slag, formed during melting in the furnace, should ensure the most complete spontaneous crumbling of it, as well as high rates of extraction of REM from it. Synthetic slags similar in phase composition to industrial samples after smelting of iron-containing ores were selected for the experiments. The simulated samples correspond to the region of primary crystallization of bicalcium silicate on the triple state diagram of CaO – SiO2 – Al2O3 system. The slag after crumbling was subjected to a sieve analysis using a mechanical sieve. In the experiments, slags with a silicon module k = 2.0 were used, which actively crumbled during their cooling. With an increase in the silicon module, the crumbling deteriorates. It was established that it is impossible to precisely limit the areas of compositions of crumbling slags at certain cooling rates. The conducted studies showed that the crumblability of slags improves as it approaches the center of the bicalcium silicate region. The composition of slags close to composition of the intersection points of the lines 2CaO·SiO2 – 2CaO·Al2O3 and 2CaO·SiO2 – 12CaO·7Al2O3 with the lines of the permanent silicon module granulometric composition almost does not depend on the cooling rate. The temperature mode from smelting to cooling affects the slags crumblability. The most promising are slags with a silicon module in the range of 2.85 – 3.00, close to the phase triangle 12CaO·7Al2O3 – 2CaO·SiO2 – 2CaO·Al2O3 .

Microstructural evaluation and mechanical properties of bulk nanostructured Al86Cu6Y6La2 (at.%) alloy produced by hot consolidation of amorphous melt-spun flakes

Amorphous melt- spun Al86Cu6Y6La2 (at.%) alloy is hot consolidated at T = 723 K and P = 700 MPa. The glassy ribbons show three devitrification steps which fcc-Al phase is precipitated during the first crystallization stage, and formation of intermetallic compounds (Al3Y, AlCu, AlCu3 and Al3Y5) take place in the next steps. The calculated Avrami exponent (n ∼ 2.6) shows the first crystallization reaction is governed by the diffusional growth process and increasing nucleation rate. Moreover, the activation energy calculated with different methods show that Ea for the primary crystallization are in the range of about 254- 267 KJ.mol−1. Amorphous ribbons exhibit a remarkably tensile strength of 910 ± 7 MPa. Combined rapid solidification and hot consolidation produce a bulk sample with high hardness (345.1 ± 12.3 HV), compressive strength (460 ± 10 MPa) and 4 pct plastic strain. These high mechanical properties are due to ultrafine microstructure induced by the rapid solidification process.

Correlations between olivine composition and groundmass mineralogy in Sierra Leone kimberlites provide constraints on craton-specific melt-lithosphere interactions

Sierra Leone contains two Jurassic-aged diamondiferous kimberlite clusters, namely Koidu and Tongo-Tonguma (hereafter referred to as Tongo), consisting of eruptive pipes and NE-SW trending dikes. In this study, a combination of detailed petrography, and phlogopite, spinel, and olivine compositions in hypabyssal samples is presented to classify and constrain the petrogenesis of these kimberlites. Both the Koidu and Tongo rocks are predominantly macrocrystic and highly micaceous with phlogopite abundances, normalised to olivine-free, of 36–65 vol% in the groundmass. These phlogopite contents are comparable to those of some cratonic lamproites and significantly higher than any other kimberlites. Other groundmass minerals include spinel, perovskite, and apatite set in a base of carbonate and serpentine. Phlogopite and spinel have similar compositions in the Koidu and Tongo samples, displaying evolutionary trends consistent with those observed in worldwide kimberlites. Olivine macrocrysts and microcrysts display complex zoning with distinct cores, internal zones, and rims. The core compositions display a range in Mg# (81–95) and are interpreted to be derived from the disaggregation of lithospheric mantle xenoliths and proto-kimberlite related megacrysts. The Tongo olivine rims, interpreted to be primary magmatic crystallisation products, have similar compositions from various locations within the cluster whereas the Koidu samples display a range in rim compositions (Mg# 87–89) from different locations within the cluster. The average Koidu rim compositions display a strong positive correlation with the average core compositions, consistent with the trend formed by kimberlites worldwide and indicative of a strong control by melt-lithosphere interaction on melt compositions. Previously, it has been shown that the Mg# of olivine rim's negatively correlates with the abundance of groundmass phlogopite (± oxide minerals) in kimberlites. However, the Koidu and Tongo kimberlites are exceptionally phlogopite-rich given their olivine Mg#, fall outside of the worldwide kimberlite array and have olivine compositions and phlogopite abundances like some cratonic lamproites. This leads us to suggest that Koidu and Tongo represent a rare style of highly micaceous kimberlite magmatism, not previously reported in other cratonic regions, and are genetically linked to the assimilation of K 2 O-rich, metasomatic mantle lithologies. We further suggest that the K 2 O content, reflected by groundmass phlogopite abundances, of worldwide kimberlite and cratonic lamproite parent magmas ascending to the surface may be related to assimilation of craton-specific styles of metasomatic lithologies in the SCLM. • Unique highly micaceous kimberlites from Sierra Leone. • Olivine compositions constraining melt-SCLM interactions. • Craton-specific melt-SCLM assimilation and K2O enrichment.

Long-lived Nb-Ta mineralization in Mufushan, NE Hunan, South China: Geological, geochemical, and geochronological constraints

The Mufushan Complex (MFSC), located in northeastern Hunan, is a significant producer of Nb-Ta-Li-Be rare metals in South China. The present study examines the genetic relationship, material provenance, fluid evolution, and metallogeny of the co-developed ore-free pegmatite (OFP) and ore-bearing pegmatite (OBP) in granite-related pegmatite-type Nb-Ta rare-metal deposits in MFSC. Three minerals (columbite-tantalite (coltan), zircon, and monazite) were chosen for analysis. The coltan grains display both primary crystallization structures (crystal homogeneity, oscillatory zonings, and primary growth rims) resulting from equilibrium and disequilibrium reactions due to localized changes in the physicochemical conditions and environment, as well as later replacement structures (alteration rims, patches, irregular zonations, and complex zonations) from metasomatic replacement processes related to hydrothermal fluid activity. The coltan yielded two weighted mean 206Pb/238U ages of 138.1 ± 2.1 Ma and 125.3 ± 2.0 Ma corresponding to magmatic and hydrothermal Nb-Ta mineralization ages. For the OFP, zircons also yielded two weighted mean 206Pb/238U ages of 138.4 ± 0.8 Ma and 131.5 ± 0.7 Ma, whereas monazite gave a weighted mean U-Pb age 142.9 ± 1.2 Ma. The ages of 142–138 Ma and 131 Ma represent the early and late stages of OFP crystallization and barren pegmatites in the MFSC, respectively. Zircon Lu-Hf isotopic compositions link rare-metal metallogenesis to the Lengjiaxi Group, which was the source material to the Mufushan composite batholith. Calculated εHf(t) values and TDM2 ages from the OFP (−7.6 to −3.6 and 1676–1418 Ma, respectively) and the OBP (−14.1 to +4.9 and 2976–1548 Ma, respectively) are akin to those of schists and metasandstones of the metasedimentary Lengjiaxi Group. We propose a long-lived (ca. 13-Myr) event involving two metallogenic episodes of Nb-Ta mineralization in the Mufushan region. This study demonstrates the potential of zircon, coltan, and monazite for fingerprinting minerals and classifying the mineralization potential of pegmatite veins.

Crystallization studies on heterogeneous melts of polybutene-1

The heterogeneous melts of isotactic polybutene-1 (iPB-1) containing Form I or Form II seeds with uniform size and random distribution were prepared by selective melting of melt crystallized and transformed samples, respectively. Compared with a reference blank melt, the remnant Form I or II seeds are able to significantly reduce the half-time of crystallization under isothermal conditions. Besides, the nucleation efficiency of Form II seeds is much higher than that of Form I seeds because of the lower lateral surface energy and highly lattice match. Furthermore, a great number of tiny spherulites with submicrometer radius nucleate and grow simultaneously, offers an opportunity to follow the development of spherulites at the very early stage. The analysis of the differential scanning calorimetry (DSC) curves confirms that the mass fraction for faster primary crystallization of heterogeneous melts is lower than that of blank melt, which clearly indicates that growth rate of spherulites is decreasing before impingement. The radius of spherulites was not much larger than the diffusion length provides the foundation for the observed non-linear growth of spherulites. This quantitative comparison of the crystallization kinetics of blank melt and heterogeneous melts can therefore be applied as a method to improve our understanding of nucleation and the diffusion-controlled growth of polymer.

Improvement of soft magnetic properties of a Fe84Nb7B9 nanocrystalline alloy by synergistic substitution of P and Hf

A strategy of similar elements synergistic substitution was implemented to enhance the amorphous forming ability (AFA), thermal stability, and soft magnetic properties of Fe-Nb-B nanocrystalline alloys. Substitution of B by 2–6 at.% P in a Fe84Nb7B9 alloy increases the AFA and transforms the partially crystallized melt-spun ribbon into a fully amorphous structure. 2–4 at.% P lowers the grain size and enhances the size uniformity and volume fraction of the α-Fe phase in the annealed alloys, thus decreasing coercivity (Hc) from 20.0 to 12.8 A/m and increasing saturation magnetic flux density (Bs) from 1.50 to 1.57 T, whereas 6 at.% P coarsens the α-Fe grains and reduced the magnetic softness. Subsequent replacement of Nb by 2–3.5 at.% Hf increases the thermal stability of a Fe84Nb7B5P4 amorphous alloy, and further refines the α-Fe grains and improves the structural uniformity of the nanocrystalline alloys, thereby enhancing the soft magnetic properties and enlarging optimum annealing temperature window (ΔToa). The Fe84Nb3.5Hf3.5B5P4 nanocrystalline alloy with an average grain size of 9 nm exhibits a low Hc of 11.2 A/m, high Bs of 1.55 T, and wide ΔToa of 90 K. The mechanism of P and Hf substitutions affecting the structure and magnetic properties of the Fe84(Nb, Hf)7(B, P)9 nanocrystalline alloys was discussed in terms of primary crystallization behavior regulation.

Phase equilibria of the Sb2Te3+2BiI3↔Bi2Te3+2SbI3 reciprocal system: Synthesis and characterization of the cation-substituted Bi1−xSbxTeI solid solutions

The phase equilibria of the Sb2Te3+2BiI3↔Bi2Te3+2SbI3 reciprocal system have been investigated over the entire concentration range using differential thermal analysis (DTA), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) techniques. Liquidus surface projection, solid-phase equilibrium diagram at 300 K and a number of isopleths sections of phase diagram were constructed based on experimental results and literature data. The primary crystallization areas of all the existing phases, their homogeneity ranges, as well as, types and coordinates of non- and monovariant equilibria were revealed. It is determined that the BiTeI−SbTeI section of this reciprocal system is non-quasi-binary due to the incongruent melting of one of the initial ternary compound. However, it is stable at subsolidus and forms wide areas of solid solutions based on the initial compounds. Additionally, dielectric functions and Raman spectra of Bi1−xSbxTeI (x=0; 0.05 and 0.1) phases were studied. The nature of the dependence of the dielectric function on the photon energy was identified based on the obtained ellipsometric data, while Raman spectra show that no structural changes were observed with an increasing concentration of antimony in the solid solution.

Structure and properties of powder gas-plasma coatings based on nickel

Problem. The development of modern technology requires a constant increase in reliability and durability of products. Widely used in the practice of domestic and foreign engineering coatings from electrolytic chromium for several hundred hours are triggered, they are unsatisfactorily working on friction and wear at high temperatures. The subject of the study were powder materials based on nickel PG-SR 3 and PG-SR 4. The work is devoted to the study of the formation of gas-plasma coatings on parts of the cylinder-piston group of internal combustion engines using self-fluxing powders based on nickel, as well as the structure and properties change after coating sputtering, its reflow, subsequent hardening. Goal. The purpose of this work is to study powder materials applied to the working surfaces of piston rings by gas-thermal spraying. The object of the study are processes of formation of the structure and properties of coatings from powder materials. Methodology. Plasma sputtering modes were carried out with the following constant parameters: sample rotation speed - 45 rpm, linear speed of sample movement relative to the plasma jet - 18.4 m/min; the diameter of the charge line in the anode nozzle is 2 mm; the distance from the place of introduction of the powder to the cut of the nozzle is 4 mm; the axis of the plasma jet is perpendicular to the axis of rotation of the sample. Radiographically, a multiphase structure is registered in the initial powder. The most fully presented solid solution lines based on nickel and carbide phase Cr23С6 type. But many lines cannot be clearly identified. A match can be found with the main lines of chromium and nickel borides, chromium silicides. The X-ray pattern of the fused layer quite completely coincides with the X-ray pattern of the powder. Chromium carbide lines and the strongest lines of other phases are preserved on the radiograph of the unmelted layer. Preservation of phase lines in the deposited layer without reflow and the layer after quenching indicates that these phases are formed during primary crystallization. This is confirmed by the metallography of the original powder and the original layer. In the structure of the powder, crystals are visible, as well as a dispersed mixture of phases between them. Electron microscopic studies show that in the area of coarse mixtures, oriented areas are observed, in the area of fine mixtures - non-oriented, less dispersed. Results. The presence in the deposited layer of a solid solution based on nickel, carbide phase, borides of chromium and nickel, chromium silicides is established. The greatest macro- and microhardness is possessed by fused layers containing the greatest number of strengthening phases. Originality. Gas-thermal sputtering of powder materials applied to the working surfaces of piston rings is used, which significantly increases their operational properties in comparison with other methods. Practical value. The conducted researches and industrial tests allowed to introduce the coating into production. Conclusions. As a result of the conducted researches on surfacing and heat treatment of coatings made of PG-SR powders, it was confirmed that the best properties have fused coatings. For coatings made of PG-SR powders, heat treatment is undesirable, as it deteriorates the structure and properties of the coating.

Mechanical properties and microstructure of polychlorotrifluoroethylene toughened by polyamide 11 based on intermolecular interaction

AbstractPolychlorotrifluoroethylene (PCTFE) is a promising candidate for cryogenic storage and transportation materials in clean energy industry. But, how to improve its toughness without scarification other performance is still challenging. In this study, the immiscible PA11 is introduced into PCTFE matrix as toughening agent based on a strategy of enhanced interfacial effect. As the incorporation of PA11 increased from 0 to 20 wt%, the toughness of the PCTFE/PA11 shows a trend of first increasing and then decreasing, which reaches the optimal performance with 5 wt% PA11. The elongation at break and impact strength are respectively increased by ~3 and ~1.9 times without obvious reduction of other mechanical performance. Meanwhile, PA11 could enhance the primary nucleation and crystallization ability of PCTFE. With further detailed information of microstructures and Fourier infrared spectra, a multieffect synergistic toughening mechanism based on rigid particle and intermolecular interaction has been elucidated. Furthermore, the toughening of PA11 on PCTFE at ultra‐low temperature of −196°C is confirmed.

Aerosol Assisted Synthesis of Y/ZSM‐5 Composite Zeolite and Its Application in Cracking Reaction

AbstractY/ZSM‐5 composite zeolite was synthesized by an aerosol assisted hydrothermal method including a two‐step crystallization. The aerosol technique was used to prepare the precursor of Y/ZSM‐5 composite zeolite. This helped to fully utilize the amorphous silica‐alumina species left in the primary crystallization solution of NaY zeolite, and to bring the two zeolites close to each other during the second crystallization step. The optimal adding sequence and synthesis conditions were investigated to reduce the amount of template and accelerate the crystallization rate. The composite zeolites were analyzed using XRD, SEM, nitrogen physical adsorption, NH3‐TPD techniques. It was found that the acid properties can be adjusted by modulating the SiO2/Al2O3 molar ratio of the secondary crystallization feed. The BET specific surface area of the optimal Y/ZSM‐5(20) composite zeolite is 502 m2/g, the pyrolysis conversion rate of 1,3,5‐triisopropylbenzene reaches 95.1 %, and the selectivity to benzene reaches 53.4 %.

Long-range-diffusion-assisted but interface-controlled crystallization of a Mg-Ni-Mm glass below its glass-transition temperature

A metallic glass of nominal composition Mg75Ni20Mm5 (Mm: mischmetal) when heated shows primary crystallization to Mg2Ni. Transmission electron microscopy studies, including annealing experiments in-situ, supported by differential scanning calorimetry and X-ray diffraction, reveal the remarkable complexity of this crystallization. The crystals are lens-shaped and at constant temperature show linear (constant-rate) growth, despite marked partitioning of nickel from the glass to the crystal. The growth, constrained by atomic rearrangement at the glass-crystal interface, gives a crystalline phase that is partially disordered and has almost half of its magnesium sites vacant. The combination of solute partitioning and isothermal linear growth challenges usual assumptions about the characteristics of primary and polymorphic crystallization. This hybrid behavior is interpreted in terms of the widely differing diffusivities of the atomic species in this system.

An experimentally validated model for quiescent multiphase primary and secondary crystallization phenomena in PP with low content of ethylene comonomer

While crystallization behavior of isotactic polypropylene homopolymers had been subject to a wide range of experimental and modeling studies, this is not the case for propylene-ethylene random copolymers (PPR). This class of polymers offers up to now significant challenges, both from an experimental as well as a modeling perspective. The ethylene incorporation in the propylene chains, as well as the distribution of this comonomer, has a marked effect on the crystallization kinetics. Moreover, the presence of these defects causes a clear separation between primary crystallization (i.e. space filling) and subsequent secondary crystallization (increase of crystallinity in filled space) within the spherulitic skeletons, particularly subsequent at high primary crystallization temperatures. In this work, the underlying mechanism is first quantified by means of a combination of in-situ WAXD and SAXS experiments, as well as ex-situ WAXD experiments and calorimetric measurements. Based on these experiments an extended model framework is presented, capable of predicting multiphase non-isothermal crystallization kinetics as well as the final crystallinity as a function of the applied thermal conditions relevant for processing. The chemical composition distribution (CCD) of the ethylene comonomer serves as critical input to parameterize the model. Optical microscopy- and DSC experiments are used for parameterization of the primary crystallization model. The model developed in this study is, in principle, applicable to all polypropylenes, ranging from homo-polymers to random copolymers with variable comonomer content and/or CCD but, so far, only applied and validated on one PPR. To validate the model and the parameters for a given PPR, several non-isothermal and isothermal experiments (the latter followed by subsequent cooling) are conducted over a wide range of crystallization temperatures and cooling rates. The good match between experiments and model predictions demonstrates the power of the newly developed framework. The final crystallinity, the amount of α - and γ -phase, and the ratio between primary and secondary crystallization can be predicted as a function of the time-temperature history. To the best knowledge of the authors, it is the first time that such a direct connection with the CCD is incorporated in a crystallization model. Consequently, the model offers a new tool to bridge the gap between chemical structure and resulting product properties, which now has come one step closer for PPR systems. • Isothermal and cooling experiments reveal primary and secondary crystallization behavior of PPR. • Primary crystallization is modeled via formation of α-skeletons, in which γ-phase co-crystallizes. • Incorporated multi-phase secondary crystallization to predict final phase composition. • Final crystallinity from the introduction of a crystallizable fraction and kinetic maximum. • Direct link between chemical composition distribution and crystallization kinetics.

Role of Fe substitution for Co on thermal stability and glass-forming ability of soft magnetic Co-based Co-Fe-B-P-C metallic glasses

Soft magnetic Co-based bulk metallic glasses (BMGs) with large supercooled liquid region (ΔTx) of 47 K and high saturation magnetic flux density (Bs) up to 1.21 T have been developed in a new Co-Fe-B-P-C alloy system without early transition metal and rare earth elements. Substitution of Co by 10–35 at.% Fe in a Co75B10P7.5C7.5 alloy promotes the occurrence of glass transition and enhances the stability of supercooled liquid and glass-forming ability (GFA). The ΔTx of 37–47 K and a critical sample diameter up to 1.2 mm can be achieved for Co40–55Fe20–35B10P7.5C7.5 BMGs. The improved thermal stability and GFA are attributed to complicated primary crystallization phases and stabilized alloy melts, respectively. The addition of Fe enhances the Bs of the Co-based BMGs from 0.79 to 1.21 T, and increases coercivity from 1.1 to 7.2 A/m. The Co-based BMGs also exhibit high yield strength of 3243–3665 MPa with plastic strain up to 2.3% and low viscosity of around 3.0 × 109 Pa·s in the supercooled liquid state.

Radio‐Frequency Rapid Thermal Processing Enabling Spatial Phase Transformation and Nanocrystallization of Soft Magnetic Amorphous Alloys

Thermal processing of soft magnetic amorphous and nanocrystalline alloys is explored under the influence of radio‐frequency induction‐heating techniques. Direct induction‐heating concepts based on longitudinal and transverse flux heating are examined and the details of electromagnetic fields interaction with metallic strips are discussed by analytical calculations as well as finite element analysis. Initial experimental results confirming spatial control of phase transformations and nanocrystallization within a single strip of Finemet Fe‐based amorphous ribbons are reported. The degree to which primary and secondary crystallization temperature are achieved depends on the spacing between the ribbon relative to the induction coil as well as the coil design and configuration. For transverse coil configurations, the local temperature and therefore microstructural evolution is different across the lateral dimension of processed ribbons, with reduced gap sizes producing enhanced peak temperatures and larger temperature distributions with greater spatial variation in microstructure. In addition, indirect susceptor‐based induction heating under tension is performed and the impact of microstructure is demonstrated. Herein, potential for exploiting spatially optimized phase transformations is illustrated through electromagnetic field–assisted processing in a scalable manufacturing process with amorphous and nanocrystalline soft magnetic alloys.

Crystallisation behaviour and morphological studies of PEKK and carbon fibre/PEKK composites

The increased interest in carbon fibre/poly(etherketoneketone) (CF/PEKK) as an option for high-performance applications calls for a thorough understanding of the composite's crystallisation behaviour, due to the essential role that crystallinity plays in performance. In this study, differential scanning calorimetry was used with a variety of thermal cycles to evaluate the effect of thermal history on crystallinity development in unreinforced PEKK and CF/PEKK. Different isothermal holding temperatures during cooling affected the ratio between primary and secondary crystallisation, and non-isothermal cooling cycles influenced the extent of crystallisation. The inclusion of carbon fibres increased the proportion of secondary crystallisation in the matrix and slowed down crystallisation kinetics. A Velisaris-Seferis model was used to model crystallisation kinetics for the isothermal data, and adapted Nakamura models were used for the non-isothermal data. Based on this work, optimum isothermal hold temperatures during cooling for CF/PEKK are estimated to lie in the range of 220–260 °C.

Microstructure evolution, magnetic properties and frequency characteristics of Si-rich FeSiBCuNb soft magnetic alloy induced by annealing treatment

The influences of heat treatment on the microstructure, domain structure and magnetic characteristics of the Fe 73.5 Si 15.5 B 7 Cu 1 Nb 3 alloy were investigated. We demonstrated that the as-spun alloy exhibits high amorphous forming ability and good thermal stability with a large annealing interval between the primary and secondary crystallization peaks over 170 °C. Also, the interaction of chemical concentration fluctuations and heterogeneous nucleation is responsible for the nanocrystallization mechanism of alloy. Furthermore, the magnetic structures change from the narrow and zigzag-like branched domains to wide and regular striped domains with increasing annealing temperature, which leads to a decrease in pinning effects. Appropriate magnetic anisotropy introduced by heat-treatment process has effect on the magnetic mechanism and the shape of magnetic hysteresis loops, which adjusts the frequency characteristics. After the optimum annealing, the alloy exhibits the excellent magnetic properties including high Ms. of 135.4 emu/g and low Hc of 0.56 A/m, together with good low-frequency characteristics. • Nanocrystallization mechanism of the Si-rich Finemet amorphous alloy were studied roundly. • High volume fraction, fine, and uniformly distributed nanocrystalline structure was obtained. • Optimal Ta induced wide magnetic domains achieves high Ms., low Hc and high L. • High-temperature annealing introduced anisotropy improves high frequency characteristics.

Nanostructure evolution, thermal stability and hardness of amorphous Al–Cu-Y (Co, La) (at.%) alloys

Al alloys with nominal composition of Al86Cu6Y6Co2, Al86Cu6Y6La2 and Al84Cu6Co2Y6La2 (at.%) were studied in as- spun and annealed states using differential scanning calorimetry (DSC), field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and microhardness. The effect of La and Co atoms and annealing temperature on enhancement of glass forming ability, thermal stability and hardness of Al–Cu–Y based alloys were investigated. The results show the amorphous Al84Cu6Co2Y6La2 alloy with higher RE (Y, La) contents and more elements is thermally stable up to 618±2 K while primary crystallization occurs. It also indicates the highest hardness of 378.1 ± 15.3 HV which enhances even more to 394.2 ± 16.8 HV after primary crystallization due to nano-sized α-Al crystals formation. The hardness of the alloy decreases to 340.3 ± 16.4 HV after the second crystallization reaction, possibly because of the presence of some weak intermetallic compound, growth of the α-Al and crystallization of the amorphous matrix.

Bulk Enthalpy of Melting of Poly(l-lactic acid) (PLLA) Determined by Fast Scanning Chip Calorimetry.

The bulk enthalpy of melting of α-crystals of poly (L-lactic acid) (PLLA) is evaluated by fast scanning calorimetry (FSC), by correlating the melting enthalpy of samples of different crystallinity with the corresponding heat capacity at 90 °C, that is at a temperature higher than the glass transition temperature of the bulk amorphous phase and lower than the melting temperature. Extrapolation of this relationship for crystals formed at 140 °C towards the heat capacity of fully solid PLLA yields a value of 104.5±6 J g-1 when melting occurs at 180-200 °C. The analysis relies on a two-phase structure, that is, absence of a vitrified rigid amorphous fraction (RAF) at the temperature of analysis the solid fraction (90 °C). Formation and vitrification of an RAF are suppressed by avoiding continuation of primary crystallization and secondary crystallization during cooling the system from the crystallization temperature of 140 °C to 90 °C, making use of the high cooling capacity of FSC. Small-angle X-ray scattering (SAXS) confirmed thickening of initially grown lamellae which only is possible if these lamellae are not surrounded by a glassy RAF. Linear crystallinity values obtained by SAXS and calorimetrically determined enthalpy-based crystallinities agree close to each other.