RESEARCH ON THE STRUCTURE AND PROPERTIES OF THE WELDED METAL FROM HIGH-CHROME STEELS AND THE INFLUENCE OF RAPID HEATING DURING HEAT TREATMENT

In this paper, a simple 24-filament structure Nb3Al superconducting wire has been firstly prepared by using the jelly-roll Nb/Al composite wire, the reel-to-reel rapid heating and quenching (RHQ), and phase transformation heat treatment. In order to obtain the Nb3Al long wire with good superconducting properties, various heating current (HC) and wire moving speed (WMS) were used to produce high-quality Nb(Al)ss supersaturated solid solution during RHQ process; thereafter, the Nb(Al)ss wire was put into the Cu tube and drawn for preparing the Cu-cladded Nb3Al wire. The results suggest that for the Nb3Al wire with the HC 262 A and WMS of 300 mm/s, its onset Tc and layer Jc at 4.2 K and 12 T measured by the transport way reach 17.7 K and 1.58 × 105 A/cm2, respectively. The magnetization measurement (M-H) of Nb3Al wires indicate that the diameter reduction of Nb(Al)ss solid solution wires after RHQ will significantly improve their grain connectivity and thus Jc properties at the optimal heat treatment conditions. The work suggests the simple-structured Nb3Al superconducting wire is promising to the practical high-field magnet application.

Four new compositions of titanium alloys of Ti–Al–Mo–Fe and Ti–Al–Mo–Cr systems with content of β-phase stabilizing elements in a range of 3.8–9.8 wt.% (in terms of “molybdenum equivalent” CMo) were studied. The alloys were melted by single-melt electron-beam cold hearth technique, thermomechanically processed, and subjected to conventional (in furnace) or continuous rapid (resistant heating by electric current) heat treatments with different regimes. The microstructure, phase composition, and mechanical properties both in as-deformed state and after heat treatments were studied in detail. It is found that the proposed thermomechanical processing allows to obtain a transformed microstructure characterized by nearly equiaxed α-phase particles with relatively small aspect ratio and weak crystallographic texture of a basal type. Subsequent annealing in the α + β field led to completion of the α + β microstructure transformation; a microstructure of globular type was obtained in the low-alloyed (CMo = 3.8%) material. The phase transformations at various stages of strengthening heat treatments and their influence on the final microstructure and properties were studied, depending on the content of β-stabilizing elements and processing route. Particular attention was paid to the influence of the content of β-stabilizing element on the mechanical properties, as well as to the difference between the alloying systems with iron or chromium. It is shown that the alloys of proposed compositions provide high strength and reliability; they are competitive with conventional commercial alloys in terms of the balance of mechanical properties in hot deformed, annealed, and thermally strengthened states. Strengthening treatment based on rapid heating allows to achieve strength above 1500 MPa with sufficient ductility.

The effect of subjecting mild steel to several cycles of rapid heat treatment on its mechanical properties and microstructure was investigated. Mild steel of 0.213 wt % carbon was subjected to transformation heat treatment from austenite to pearlite and quenched in running water. Rapid heating was achieved by preheating an electric muffle furnace to 840 °C before charging the samples into it. Each cyclic heat treatment was for a period of 200 seconds held at 840 °C and cooled to 700 °C which was repeated four times. The effects of cycle numbers were evaluated by testing for impact, hardness, ultimate tensile strength and microstructural properties. The results showed that after 4th cycle of rapid heating the samples had impact energy 64.6 J, Brinell hardness number 563 and ultimate tensile strength 1257.78 N/mm2. The samples after one cycle had ultimate tensile strength 1027.45 N/mm2, % elongation 10.396% and impact energy 286.174 N.m before failure. Through cyclic heating, grain refinement was achieved by the fast simultaneous nucleation at the grain boundaries and the fast martensite to austenite transformation due to the fast heating rate which prevented austenite grain growth. Mechanical properties of the studied steel sample were improved with the rapid heat treatment cycles given.

As shown by Koistinen,1,2 rapid induction heating and quenching can be used to eliminate the yield point and stretcher strains that appear during forming operations on low-carbon steel sheets. Here it is pointed out that such rapid temperature change can produce inhomogeneous plastic deformation, and is then the thermal equivalent of temper rolling or flex-leveling. Theoretical heating (cooling) requirements for eliminating discontinuous yielding on this basis are derived from existing thermoelastic solutions, and experimental results on aged temper-rolled sheet specimens are presented in support of the calculations. The necessary rate of temperature change is more easily reached by quenching than by rapid heating, but rapid heating is essential to control the carbon and nitrogen taken into solution and for high product output. The required rate of temperature change is easily obtainable for sheets of 14 gage (0.19 cm) and heavier, but as sheets become thinner the minimum rate increases rapidly. Because of an increased rate of aging after rapid heating and cooling, the process is of little interest to steel producers as a substitute for temper rolling, but may be attractive to industries which consume large quantities of rimmed steel sheet.

Depletion kinetics of perfluoropolyether films with functional end groups using molecular dynamics simulation

The earliest stages of annealing of graphitizable anthracene coke and non-graphitizable sucrose char were observed by rapid heating with a CO2 laser. Structural transformations were observed with transmission electron microscopy. Anthracene coke and sucrose char were laser heated to 1200 °C and 2600 °C for 0.25–300 s. The transformations are compared to traditional furnace heating at matching temperatures for a 1 h duration. Traditional furnace and CO2 laser annealing followed the same pathway, based upon equivalent end structures. Graphitizable anthracene coke annealed faster than non-graphitizable sucrose char. Sucrose char passed through a structural state of completely closed shell nanoparticles that opened upon additional heat treatment and gave rise to the irregular pore structure found in the end product. The observed curvature in sucrose char annealed at 2600 °C results from shell opening. The initial presence of curvature and loss by heat treatment argues that odd membered rings are present initially and not formed upon heat treatment. Thus, odd membered rings are not manufactured during the annealing process due to impinging growth of stacks, but are likely present in the starting structure. The observed unraveling of the closed shell structure was simulated with ReaxFF.

Understanding the kinetics of lubricant depletion under rapid and isothermal heat treatment is of fundamental importance in maintaining the stability and reliability of lubricated surfaces. In this paper, molecular dynamics simulation coupled with a coarse-grained bead-spring polymer model is employed to study lubricant depletion instability. During rapid heating, the lubricant decomposes at an increasing rate with temperature. However, a maximum rate is observed during desorption due to the influence of lubricant-to-substrate interaction. During the isothermal stage, the rates of desorption (rdes) and decomposition (rdec) decrease over time, showing an exponential depletion process. It is found that rdes or rdec increases with both the temperature and lubricant mass or bond coverage. Moreover, the rate constants for desorption (kdes) and decomposition (kdec) are calculated based on a first-order kinetics-controlled reaction. For a given lubricant mass coverage, ln(kdes) exhibits a non-linear relation with 1/T, indicating non-Arrhenius-like behavior of lubricant desorption. However, for a given lubricant bond coverage, ln(kdec) versus 1/T yields a straight line, signifying Arrhenius-like behavior of lubricant decomposition. The kinetics of lubricant depletion also shows that lubricant desorption is favored over decomposition under heat treatment to high temperatures and is the major cause of lubricant degradation and failure on the surface.

It is well established that microwaves can heat ceramics for processing applications, but considerably less attention has been given to the use of high frequency radiation for the processing of silicon wafers. There are many aspects of semiconductor processing that require heating, including dopant or ohmic contact interdiffusion, implantation damage annealing, and wafer bonding. Conventionally, the wafers are heated in furnaces or halogen lamp Rapid Thermal Processing (RTP) chambers. An alternative, electromagnetic induction heating (EMIH), uses radio (RF) and microwave radiation to rapidly (125C/s) and volumetrically heat silicon wafers to temperatures in excess of 1000C. In contrast to conventional (heat lamp) RTP, which heats through surface absorption, EMIH has the advantage of heating throughout the material. The presence of insulating layers, most notably thick oxides (several hundred nanometers) on the surface of the wafer, do not inhibit rapid heating since the wave transmits through the insulator and directly into the silicon. Conventional RTP, due to its dependence on surface absorption, may have trouble rapidly heating through this insulating layer. Furthermore, the volumetric nature of the heating makes it attractive for low thermal budget microelectromechanical systems (MEMS) applications [1] which may require rapid heating well below the wafer surface. Because of this, EMIH has found applications in ultra shallow junction formation [2], direct silicon bonding for MEMS applications [1], and direct silicon bonding for silicon on insulator technology [1].

In compression molding of polymer optical components with micro/nanoscale surface features, rapid heating of the mold surface is critical for the implementation of this technology for large-scale applications. In this Letter, a novel method of a localized rapid heating process is reported. This process is based on induction heating of a thin conductive coating deposited on a silicon mold. Since the graphene coating is very thin (∼45 nm), a high heating rate of 10∼20°C/s can be achieved by employing a 1200 W 30 kHz electrical power unit. Under this condition, the graphene-coated surface and the polymer substrate can be heated above the polymer's glass transition temperature within 30 s and subsequently cooled down to room temperature within several tens of seconds after molding, resulting in an overall thermal cycle of about 3 min or shorter. The feasibility of this process was validated by fabrication of optical gratings, micropillar matrices, and microlens arrays on polymethylmethacrylate (PMMA) substrates with very high precision. The uniformity and surface geometries of the replicated optical elements are evaluated using an optical profilometer, a diffraction test setup, and a Shack-Hartmann wavefront sensor built with a molded PMMA microlens array. Compared with the conventional bulk heating molding process, this novel rapid localized induction heating process could improve replication efficiency with better geometrical fidelity.

Load partitioning behavior in a metastable austenitic stainless steel subjected to pre-deformation below and above Md temperature: Experimental and modeling studies

Evolution of microstructure, phase composition, and tensile properties of severely cold deformed titanium metastable β alloy in rapid continuous heating

A bioluminescent adenosine triphosphate (ATP) assay using a luciferin-luciferase reagent was conducted as a viability test for Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) eggs treated with low or high temperatures to evaluate the potential into use for quarantine operations. ATP concentrations in B. dorsalis eggs treated with different temperatures, including freezing, cold treatment, and rapid and slow heating, simulating a hot water immersion treatment and vapor heat treatment, respectively, were measured. Mean ATP concentrations in untreated eggs decreased as egg age increased. For freezing and rapid heating, the mean ATP concentrations in treated eggs significantly decreased 24 h after the treatments, and the maximum ATP concentrations were lower than the minimum ones for untreated eggs. Most ATP concentrations in the cold treatment group exceeded the minimum ones in untreated eggs. Mean ATP concentrations in eggs treated with slow heating decreased less than those in eggs treated with rapid heating. There is potential to use ATP assays in plant quarantine operations for the rapid determination of the viability of fruit fly eggs treated with hot water immersion, although more validation research is first required. Verification tests should be performed by applying ATP assays during quarantine, by using flies and host fruit subjected to different temperature treatments.

Rapid mold heating has been recent issue to enable the injection molding of thin-walled parts or micro/nano structures. Induction heating is an efficient way to heat a conductive workpiece by means of high-frequency electric current caused by electromagnetic induction. Because the induction heating is a convenient and efficient way of indirect heating, it has various applications such as heat treatment, brazing, welding, melting, and mold heating. The present study covers an experimental investigation on the rapid heating using the induction heating and rapid cooling using a vortex tube in order to eliminate an excessive cycle time increase. Experiments are performed in the case of a steel cup mold core with various heating and cooling conditions. Temperature is measured during heating and cooling time, from which appropriate mold heating and cooling conditions can be obtained.

Structure and mechanical properties of high-temperature titanium alloys after rapid heat treatment

ABSTRACTChange in the light-induced minority carrier effective lifetime τeff of crystalline silicon caused by rapid laser heating is reported. The top surface of n- and p-type silicon substrates with thicknesses of 520 μm coated with thermally grown SiO2 layers were heated by a 940 nm semiconductor laser for 4 ms. τeff was measured by a method of microwave absorption caused by carriers induced by 620 nm light illumination at 1.5 mW/cm2. τeff for light illumination of the top surfaces was decreased to 1.0x10-5 and 4.8x10-6 s by laser heating at 5.0x104 W/cm2 for n- and ptype 520-μm-thick silicon substrates, respectively. The decrease in τeff resulted from the generation of defect states associated with the carrier recombination velocity at the top surface region, Stop. Laser heating increased Stop to 6000 and 10000 cm/s for n- and p-type silicon samples, respectively. Heat treatment at 400oC for 4h markedly decreased Stop to 21 and 120 cm/s, respectively, for n- and p-type silicon samples heated at 5.0x104 W/cm2. Laser heating at 4.0x104 W/cm2 for 4 ms was also applied to samples treated with Ar plasma irradiation at 50 W for 60 s, which decreased τeff (top) to 2.0x10-5 s and 3.9x10-6 s for n- and p-type silicon samples, respectively. Laser heating successfully increased τeff (top) to 2.8x10-3 and 4.1x10-4 s for n- and p-type samples, respectively. Laser irradiation at 4x104 W/cm2played a role of curing recombination defect sites.