Partial Melting Method Research Articles

Tuning High and Low Temperature Foaming Behavior of Linear and Long-Chain Branched Polypropylene via Partial and Complete Melting.

While existing foam studies have identified processing parameters, such as high-pressure drop rate, and engineering measures, such as high melt strength, as key factors for improving foamability, there is a conspicuous absence of studies that directly relate foamability to material properties obtained from fundamental characterization. To bridge this gap, this work presents batch foaming studies on one linear and two long-chain branched polypropylene (PP) resins to investigate how foamability is affected by partial melting (Method 1) and complete melting followed by undercooling (Method 2). At temperatures above the melting point, similar expansion was obtained using both foaming procedures within each resin, while the PP with the highest strain hardening ratio (13) exhibited the highest expansion ratio (45 ± 3). At low temperatures, the foamability of all resins was dramatically improved using Method 2 compared to Method 1, due to access to lower foaming temperatures (<150 °C) near the crystallization onset. Furthermore, Method 2 resulted in a more uniform cellular structure over a wider temperature range (120–170 °C compared to 155–175 °C). Overall, strong extensional hardening and low onset of crystallization were shown to give rise to foamability at high and low temperatures, respectively, suggesting that both characteristics can be appropriately used to tune the foamability of PP in industrial foaming applications.

Anisotropic microstructure and thixo-compression deformation behavior of extruded 7075 aluminum alloy in semi-solid state

In order to examine the micro-mechanism behind the thixotropic behavior of semi-solid alloys, microstructural effects on the compression deformation of semi-solid 7075 aluminum alloy prepared by recrystallization and partial melting (RAP) method were investigated. The fibrous and deformed microstructure of as-extruded 7075 aluminum alloy can transform into elongated and globular grains via reheating to semi-solid states, and exhibiting dominated {100}<001> recrystallization texture and preferred crystal growth in extrusion direction. The anisotropic microstructure of semi-solid alloys depends on the remelting temperatures to a great degree. Correspondingly, the initial peak stress of compression stress-strain curves also demonstrated as anisotropic behavior. It was analyzed that the crystallographic texture caused orientation dependent Young's modulus and a corresponding elastic response, and the disagglometation of the saturated solid skeleton led to an increase of viscoplastic stress, which relates to the amount of bonds between solid grains.

Application of Radial Forging and Remelting Treatment to Prepare Semi-Solid Billet of AlMg0.7Si Alloy

Semi-solid AlMg0.7Si alloy was prepared by recrystallization and partial melting (RAP) method which including radial forging (RF) and remelting process. RF was carried out with different area reduction ratios (ARRs) to accumulate strains, effect of ARR and remelting time on microstructure was studied, mechanism of RAP preparing semi-solid AlMg0.7Si alloy was summarized. Results show that, compared with the large and irregular solid grains form remelting of starting material, solid grains of semi-solid alloy prepared by RAP are fine and globular, and the optimum microstructure can be obtained when alloy with 80% ARR is remelted at 630 °C for 10 min. With the increase of ARR, the solid grains are smaller and rounder. With the increase of remelting time, the average grain size is increased, and the spheroidization degree of solid grain is gradually improved. The main mechanism consists of pre-deformation, recovery and recrystallization, grains fragmentation, grains spheroidization and coarsening.

Thermoelectric materials for middle and high temperature ranges

Abstract

Interfacial strength and structure of joining between 2024 aluminum alloy and SiCp/2024 Al composite in semi-solid state

Semi-solid joining of 2024 aluminum alloy and SiCp/2024 Al composite was investigated based on the shear strength and microstructure of interface. An as-extruded 2024 aluminum alloy was chosen in this study for its fine crystal grain and higher strain energy, which was beneficial to the preparation of semi-solid billet. Then recrystallisation and partial melting method (RAP) was carried out to prepare semi-solid billet of 2024 aluminum alloy. Then the semi-solid 2024 aluminum alloy was joined with the SiCp/2024 Al composite, which was also in the semi-solid state, at/under different temperatures/pressures. Shear test was performed to measure the interfacial strength. Scanning electron microscope (SEM) was used to observe the microstructure of interface. The results showed that the shear strength of interface had reached to that of SiCp/2024 Al composite. The shear strength increased as the applied pressure increasing, and had a close relationship with temperature. The mechanism of semi-solid joining with pressure was that the mixture of two kinds of base materials, accompanying with the diffusion of atom at high temperatures. It should be pointed out that the microstructure of interface was much finer than that of the substrate, due to the nucleation promotion of SiC particle in the solidification process.

Characterization of Superconducting BSCCO/CaSiO&lt;sub&gt;3&lt;/sub&gt; and BSCCO/CaZrO&lt;sub&gt;3&lt;/sub&gt; Ag PIT Wires

The addition of two compounds, calcium silicate and calcium zirconate was tested, in the preparation of Bi: 2212 silver sheathed wires by powder-in-tube method, which were successfully tested previously in processing chips. The wires were treated in an atmosphere of O2/Ar using partial melting method. The characterizations were structural and on their electrical and magnetic properties. As the results, transition temperatures were higher than the expected for this stage, ranged from 105K (BSCCO880) to 116K (+Si883). The critical current densities encountered in transport and magnetization measurements were improved in comparison with the wires without addition.

Relationship between microstructure and thermoelectric properties of Bi2Sr2Co2Ox bulk materials

Abstract

Effect of Cooling Rate on Mechanical Properties of 7075 Aluminum Rods Extruded in Semisolid State

Semisolid extrusion of metals involves extrusion of metallic alloys with a microstructure consisting of spherical solids in a liquid matrix. In this research, the effect of cooling rate during forward semisolid extrusion on microstructure and mechanical properties of 7075 aluminum was investigated. Semisolid microstructure was prepared according to the recrystallization and partial melting (RAP) method. Optimum semisolid temperature and holding time which were resulted in a suitable microstructure for specimens were determined at 580 °C for 10 min. Different cooling rates were applied during semisolid extrusion and the resulted mechanical properties were studied. Tensile properties of semisolid extruded rods in T6 condition were also compared with those of conventionally extruded specimen. The results indicate that utilizing optimum values of semisolid extrusion parameters, namely, temperature and time of heating as well as cooling rate severity, brings both the possibility to obtain mechanical properties of conventionally extruded specimens and to get advantages of semisolid forming technique. Experimental results also show that increment of cooling rate and extrusion pressure improves the mechanical properties.

Refinement of Cast Cr-V-Mo Steel by Using Recrystallization and Partial Melting Method and Post Heat Treatments

The conventional route for tool steel manufacturing consumes large amounts of energy and time and results in a long process chain for the manufacture of products. Environmental consciousness is fuelling the development of an improved route with a shorter process chain and lower energy consumption that can replace the conventional one. An energy-efficient process route for manufacturing products with high quality was proposed based on recrystallization and partial melting (RAP) technology. To verify the feasibility of the RAP-based route, the effects of predeformation, partial melting, and post heat treatments on the microstructure characteristics and mechanical properties of cast Cr-V-Mo steel were studied experimentally. During the RAP process, plastic deformation, recrystallization, austenization, grain growth, and partial melting occurred. When the RAP processed specimen was quenched from 1050 oC after isothermal holding for 480 s and then tempered twice at 560 oC for 2h, microstructural evolution occurred in both former solid-phase and liquid-phase regions and caused a good combination of mechanical properties.

Effects of heat treatment on microstructure and mechanical properties of Cr–V–Mo steel processed by recrystallization and partial melting method

The phase segregation of semisolid processed products resulted in an inhomogeneous microstructure and poor mechanical properties of such products. Optimal subsequent heat treatments including quenching and tempering with various processing parameters were conducted to improve the quality of RAP (recrystallization and partial melting) processed Cr–V–Mo steel. The microstructure characteristics and mechanical properties, such as hardness, tensile strength, elongation, impact toughness, and resistance to high-temperature wear, of specimens subjected to various heat treatments were investigated. When the RAP-processed specimen was quenched from 1050°C after isothermal holding for 480s and then tempered twice at 560°C for 2h, microstructural evolution took placed in both former solid-phase and liquid-phase regions. The weakening of phase segregation, the redistribution of carbides, and the release of residual stress occurred during this heat treatment strategy caused a good combination of mechanical properties.

Electro-Physical Properties of Superconducting Ceramic Thick Film Prepared by Partial Melting Method

BiSrCaCuO superconductor thick films were prepared at several curing temperatures, and their electro-physical properties were determined to find an optimum fabrication conditions. Critical temperatures of the superconductors were decreased with increasing melting temperature, which was related to the amount of equilibrium phases of the superconducting materials with temperature. The critical temperature of BiSrCaCuO bulk and thick film superconductors were 107 K and 96 K, respectively. The variation of susceptibility of the superconductor thick film formed at 950 degrees C had multi-step-type curve for 70 G externally applied field, whereas, a superconductor thick film formed at 885 degrees C had a single step-type curve like a bulk BiSrCaCuO ceramic superconductor in the temperature-susceptibility curves. A partial melting at 865 degrees C is one of optimum conditions for making a superconductor thick film with a relatively homogeneous phase.

Effect of Recrystallization and Partial Melting Method on Microstructural Evolution of SKD61 Tool Steel in Semi-Solid State

The microstructural evolution and basic refinement mechanism of the semi-solid-state SKD61 tool steel fabricated by recrystallization and partial melting (RAP) method were investigated experimentally. The effects of different parameters in RAP processing were systematically clarified to achieve the grain refinement of cast SKD61 steel in the semi-solid state. Results showed that, the microstructure of RAP processed specimen were finer and more globular than the microstructure of starting material. The distribution of finer solid particles in the RAP processed specimen was affected by the distribution of strain during predeformation. Uniform and spherical solid particles inclined to locate in the regions suffered from larger strain. The specimens subjected to a plastic predeformation at a lower temperature have a more uniform and spherical semi-solid microstructure than those specimens undergoing predeformation with the same reduction at higher temperatures. In addition, the grain refinement mechanism of SKD61 tool steel processed by RAP method was discussed.

Effects of predeformation and semi-solid processing on microstructure and mechanical properties of Cr–V–Mo steel

An energy-efficient process route for manufacturing machine tools and dies of high quality was proposed based on recrystallization and partial melting (RAP) method and semi-solid forming technology. To verify its feasibility, the effects of parameters such as predeformation, heating rate, and holding time on the microstructure and mechanical properties of cast Cr–V–Mo steel were studied experimentally. Recrystallization, austenization, grain growth and partial melting occur during heating of predeformed cast billet. These behaviors refine the microstructure and improve the mechanical properties. The refinement of microstructure and improvement of mechanical properties become more significant, when RAP is conducted with larger predeformation (50%), higher heating rate (50°C/s) and shorter isothermal holding time (20s).

Electrical and superconducting properties of BiSrCaCuO ceramics superconductors

Electrical and superconducting properties of BiSrCaCuO superconductor prepared by partial melting method were determined to study its superconducting mechanism. Induced voltage of the BiSrCaCuO superconductor was not so significantly dependent upon on the shape and size of the superconductor. Anti-magnetism was less dependent upon the melting and the annealing temperatures. BiSrCaCuO film prepared at 1158K shows the maximum magnetic susceptibility in this study. Differential conductance behavior of the superconductor with magnetic flux was not well matched by a conventional flux flow model. It suggests that a superconducting mechanism for type II superconductor should be able to explain the fact that magnetic properties arise from the interaction between the trapped magnetic flux and weak link of the superconducting connectors forms in the superconducting material.

Critical Current Characteristics of Bi2212 Round Wires Prepared by Isothermal Partial Melting Method

We prepared Bi2212 round wires using the isothermal partial melting process, in which partial melting and solidification are carried out at the same temperature but in changing oxygen partial pressure. We found that the homogeneity of Bi2212 phase inside the wire was important for the J c performance of the wire and the homogeneity was improved by extending the heat treatment time. The J c value of 6.6times104 A/cm2 at 4.2 K and 10 T were obtained. We can expect further enhancement of J c property by optimizing the heat treatment conditions and improving the homogeneity of Bi2212 filaments of the wires.

Transfer of mass in the growth of Y1Ba2Cu3O7−δ+Y2BaCuO5 pseudo-crystals by a top-seeded growth process

Textured Y1Ba2Cu3O7−δ+Y2BaCuO5 pseudo-crystals were grown by the partial melting method. The thermocapillary effect on the deviation of the stoichiometry of Y1Ba2Cu3O7−δ+Y2BaCuO5 bar samples during the partial melting process is shown. The hydrodynamic equation describing the mechanism of transfer of the BaCuO2 and CuO phases in the pores of samples is proposed. The coefficient of Y2BaCuO5 diffusion into the liquid BaCuO2+CuO phases is determined.

Isotropic pinning in heavily Pb-doped Bi-2212/Ag tapes

Heavily Pb-doped Bi-2212/Ag tapes have been prepared using an isothermal partial melting (IPM) method. Under heavy Pb doping, irreversibility field ( H irr) for magnetic fields parallel to the c-axis ( H‖ c-axis) is elevated at temperatures higher than 20 K and is comparable to H irr for H‖ ab-plane. As a result, the original anisotropic pinning properties disappear in Pb-doped tape. At 30 K, the isotropic pinning force suppresses the anisotropy of transport critical current density ( J c) under magnetic field which is the most serious problem for power applications of Bi-2212 materials. Transmission electron microscopic (TEM) observation shows a disordered stripe structure and stacking faults along the c-axis in the bc-plane of Bi-2212 grains in Pb-doped tape. Such a stripe structure or stacking faults seem to be related to the production of strong pinning centers by heavy Pb doping.

Mechanism of Bi 2Sr 2CaCu 2O x crystallization and superconducting properties for Bi 2Sr 2CaCu 2O x/Ag tapes prepared using isothermal partial melting method

The mechanism of Bi 2Sr 2CaCu 2O x (Bi-2212) crystallization from a partially molten state has been studied by means of thermal analysis, X-ray diffraction (XRD) measurement, and microstructural observation in Bi-2212/Ag tapes. Tapes have been prepared using the isothermal partial melting (IPM) method, under which partial melting and solidification are carried out at the same temperature in an nitrogen atmosphere and 20% oxygen partial pressure ( p(O 2)), respectively. The Bi-2212 phase crystallizes by peritectic reaction between (Sr, Ca)CuO 2 (1:1 phase) and the liquid phase at processing temperatures ( T p)≥855°C. At the beginning of Bi-2212 crystallization, only the 1:1 and the liquid phases are present in tapes. The Bi-2212 nucleation occurs in the vicinity of 1:1 grains (homogeneous nucleation). This peritectic reaction progresses by recovery of oxygen in the liquid phase. In contrast, the nucleation of the Bi-2212 phase occurs heterogeneously at T p≤850°C. The Bi-2212 phase co-exists with four Bi-free phases ((Sr, Ca) 14Cu 24O 41 (14:24 phase), (Sr, Ca) 2CuO 3 (2:1 phase), (Sr, Ca)O (1:0 phase), and the 1:1 phase) and the liquid phase in the early stage of the Bi-2212 crystallization step. Since the precipitation temperature of the Bi-2212 phase is higher than 850°C, the Bi-2212 crystallization progresses by direct precipitation. The crystallization paths affect microstructure and transport critical current density ( J c) of Bi-2212 tapes.

Floating zone partial melting and solidification of SmBCO superconductor under low oxygen partial pressure

Microstructure control of SmBCO superconductor was carried out using the floating zone partial melting and solidification method under 0.01 atm oxygen partial pressure which is a preferable atmosphere to obtain a crystal with stoichiometric SmBCO. The growth rate, initial composition, and addition of small amount of platinum dependences on the microstructure formations of the (Sm211 + L) mixture during melting and the Sm123 or Sm123/211 during solidification were investigated. Furthermore, superconductive properties of the solidified Sm123/211 were measured by SQUID after appropriate oxygen annealing. Estimated critical current density of the single crystalline Sm123/211 was 3.6 × 104 A/cm at 77 K, 1 T.

Preparation parameters governing microstructure and grain coupling of Bi 2Sr 2CaCu 2O x/Ag tapes prepared by partial melting

Bi 2Sr 2CaCu 2O x (Bi-2212) tapes have been prepared using the isothermal partial melting (IPM) method, in which partial melting and solidification are carried out at the same temperature but in different atmospheres. Maximum critical current density ( J c) at 4.2 K under 0 T is 3.0×10 5 A/cm 2 and 1.9×10 5 A/cm 2 for the tapes prepared at 865°C and 830°C, respectively. This difference in J c is attributed to Bi-2212 grain size, which is larger in the former tape than the latter. Large grains and a rough distribution of solid phases (Bi-free and Cu-free phases) in a partially melted state lead to large Bi-2212 grains. Amount of impurities decreases and grain coupling becomes stronger with increasing solidification time ( t s). J c is saturated in tapes solidified for more than a certain time, the length in which is dependent on melt processing temperature. More time is needed to achieve saturated J c in tapes melted at higher temperature, because it takes longer for the large solid grains to react completely with a liquid phase in the partially melted state. It is clear that Bi-2212 grain size can be controlled by melt processing temperature, and that both amount of impurities and grain coupling strength can be controlled by solidification time.