Furnace Cooled Research Articles

An ANN Approach in Prediction of Microhardness in a Furnace Cooled Sintered P/M 6061 Aluminium Compacts

In this paper the effect of particle size of aluminium powder and furnace controlled cooling after sintering on porosity level and micro hardness of an elemental 6061 aluminium alloy has been investigated experimentally and the micro hardness value is compared with the Neural network algorithm using matlab. The algorithm used here are Gradient Descent Back propagation with Adaptive Learning Rate. Aluminium particle sizes of 20µm and 150µm were used. The elemental 6061 aluminium powders are warm compacted at 175MPa. After sintering for about one hour at 600°C, the aluminium compacts were furnace cooled at the rate of 1°C/min to different temperatures of 500°C, 400°C, 300°C and 200°C. When the cooling temperature after sintering inside the furnace is effected at various temperatures from 600°C to 200°C, for a precipitate hardened aluminium compacts with aluminium particle size of 20µm, the porosity level reduced by 26% and that for aluminium particle size of 150µm, the porosity level reduced by 23%. Marked improvement in micro hardness value is also observed correspondingly. Then the Neural Network was trained using the prepared training set which was recorded by the experimental values. At the end of the training process, the test data were used to check the accuracy result. As a result the Neural Network was found successful improvement in prediction of microhardness in a slow cooled sintered powder metallurgical 6061 Aluminium alloy.

Dynamic Electropulsing Induced Phase Transformations in a Furnace Cooled Zn-Al Based Alloy (ZA22)

Multi-phase identification and phase transformations in a dynamic electropulsing treated Zn-Al based alloy (ZA22) were studied by using backscattered scanning electron microscopy (BSEM) and electron back-scattered diffraction techniques (EBSD). By using EBSD, two hcp phases η' S and η' T with a small difference of about 1% in lattice parameters (c/a) were discriminated. Two stages of phase transformations: (a) η' S → η' T + e' T + α' T and e + α→ T' + η (in a way of quenching), and (b) T' + η → e + α and η' T + e' T + α' T → η' S (in a way of up-quenching), were detected. It was found that dynamic electropulsing was less effective in accelerating phase transformations than static electropusling. The mechanism of dynamic electropulsing induced phase transformations is discussed from the point view of Gibbs free energy and electropulsing kinetics.

Influence of Immersion Period on the Corrosion Behavior of Heat Treated Biomedical Alloy Ti -5Al - 2.5Fe

Heat treatment by solid solution method in the ?+? phase region was used at 970°C for Ti-5Al-2.5Fe alloy. The specimens cooled under different cooling media [water quenched (WQ), air cooled (AC) and furnace cooled (FC)], and subsequently aged at 550°C for 4 hours. Five specimens from each treatment were immersed in simulated body fluid SBF for a period of time (3 months). The dependence of corrosion rate on compositional variation in the phases resulted from various type of cooling rates are discussed based on immersion tests. The EDXA results show the precipitation of phosphate and calcium compounds on the alloy after 3 months of immersion in blood plasma solution forming a bone-like apatite, which enhanced the alloy biocompatibility making it more suitable to use as biomedical implant.

Influence of Immersion Period on the Corrosion Behavior of Heat Treated Biomedical Alloy Ti -5Al - 2.5Fe

Heat treatment by solid solution method in the ?+? phase region was used at 970°C for Ti-5Al-2.5Fe alloy. The specimens cooled under different cooling media [water quenched (WQ), air cooled (AC) and furnace cooled (FC)], and subsequently aged at 550°C for 4 hours. Five specimens from each treatment were immersed in simulated body fluid SBF for a period of time (3 months). The dependence of corrosion rate on compositional variation in the phases resulted from various type of cooling rates are discussed based on immersion tests. The EDXA results show the precipitation of phosphate and calcium compounds on the alloy after 3 months of immersion in blood plasma solution forming a bone-like apatite, which enhanced the alloy biocompatibility making it more suitable to use as biomedical implant.

Electropulsing-induced phase transformations in a Zn–Al-based alloy

Microstructural changes and phase transformations of an electropulsing-treated (EPT) ZA22 alloy wire were studied using scanning electron microscopy and transmission electron-microscopy techniques. Two stages of phase transformation were detected in the EPT alloy: (i) quenching from the as furnace-cooled (FC) state to the final stable state and (ii) up-quenching from the final stable state back to the as FC state through two reverse phase transformations: T′ + η → α + ε and η′T + ε + α → η′FC. Electropulsing accelerated phase transformation tremendously. It was at least 1200 times faster than the aging process. The mechanism of the electropulsing-induced phase transformations is discussed from the point of view of Gibbs free energy and electropulsing kinetics.

An Experimental Assessment of the Effects of Heat Treatment on the Microstructure of Ti-47Al-2Cr-2Nb Powder Compacts

A detailed and systematic microstructural characterization has been carried out on a Ti-47Al-2Cr-2Nb (at. pct) intermetallic alloy processed by powder metallurgy (PM). Heat-treatment parameters such as isothermal temperature, holding time, and cooling rate were varied in order to produce a series of near-γ, duplex, and fully lamellar microstructures. These were then quantitatively analyzed in terms of grain size, surface fraction, lamellar spacing, second-phase spatial distribution, and serrated grain boundary morphology. Owing to these extensive quantitative image analyses, several unusual microstructural features occurring in this well-known TiAl-based alloy were identified and assessed. First, a dissolution of the smallest γ grains was emphasized in subtransus conditions as the isothermal temperature or holding time was increased. Second, the competition that occurs between the α ⇒ α + γ transformation and the direct-ordering α ⇒ α2 reaction upon cooling from above the α-transus temperature is mainly governed by the reduction in chemical free energy. Third, new grains were found to nucleate upon cooling, which is presumably induced by a minimization of interfacial energy at prior α grain boundaries. Finally, new γ grains were formed as a result of the coarsening of primary γ lamellae under furnace-cooled (FC) conditions.

Enhanced Ductility due to Grain Refinement by Equal Channel Angular Extrusion in Automotive Aluminium Alloy 6016

Equal Channel Angular Extrusion (ECAE) with varying levels of applied backpressure was used to refine the microstructure of commercial automotive aluminium alloy 6016 at room temperature using route BC and a 90° die. Before processing, the alloy was solution heat treated at 560°C for 1 hour to produce an initial average grain size of ~190μm (in the furnace cooled condition) and ~200μm (in the water quenched condition). Two needle-like secondary phase precipitates were observed predominantly at grain boundaries and identified as α-Fe Al12Fe3Si2 and β-Fe Al5FeSi. The ability of Al 6016 to accumulate strain by simple shear was found to be dependent upon both the heat treatment condition and level of applied backpressure. The furnace cooled (FC) condition was found to accumulate higher strains than the cold water quenched (WQ) condition (under the same applied backpressure) with higher levels of backpressure allowing both conditions to accumulate greater equivalent plastic strains. A series of static annealing experiments were performed on as-processed material to investigate the grain stability of the ultrafine grained structure obtained after ECAE. Grain growth was observed to occur at 250°C in the FC condition of Al 6016 after 12 passes of ECAE where the average grain size approached 1μm. The engineering strain to failure in elevated temperature tensile testing was found to be dependent upon the number of passes of ECAE, test temperature, strain rate and level of applied backpressure. Increasing the number of passes and level of applied backpressure during ECAE and decreasing the strain rate during testing was found to produce the greatest tensile ductilities at 200°C (FC condition) and 300°C (WQ condition).

Magnetic force microscopy investigation of domain structures in Fe–xat.% Ga single crystals (12<x<25)

The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe–xat.% Ga (x=12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe–12at.% Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe–20at.% Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions—in the PA condition, clear dendritic domains were observed. For both FC and PA Fe–25at.% Ga, a much reduced [100] preferred domain orientation was found, the domain size was notably reduced, and dendrite formation was not observed.

Influence of microstructural changes on corrosion behaviour of thermally aged Ti‐6Al‐7Nb alloy

AbstractSolution treatment and ageing (STA) is an effective strengthening method for α + β titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti‐6Al‐7Nb alloy in a simulated body fluid (Ringer's solution). Ti‐6Al‐7Nb alloy is hot rolled in the α + β field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air‐cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 μA/cm2) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air‐cooled, and aged, in comparison with that for as‐rolled specimen (1.5 μA/cm2). The corrosion aspects resulting from various heat treatments are discussed in detail.

Use of EBSD to study stress induced microstructural changes in Zn–Al based alloy

Tensile stress induced microstructural changes in an eutectoid Zn–Al based alloy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) techniques. Both Zn-rich η′ T and ε phases were identified by EBSD using predetermined lattice parameters of the phases. It was found that tensile deformation resulted in decomposition of the Zn-rich η′ T and ε phases in the furnace cooled (FC) eutectoid Zn–Al based alloy. With increasing strain, the decomposition of the η′ T and ε phases developed in the high stress concentrated neck zone and the rupture part of the FC-tensile deformed specimen. The measured preferred crystal orientations of the Zn-rich phases in the FC-tensile deformed Zn–Al alloy were in a good agreement with previous XRD investigation.

Vacancy migration and long-range ordering due to ageing in AuCd shape memory alloys

Vacancy concentrations in the martensite phases ζ′ 2 and γ′ 2 of Au 1− c Cd c alloys (0.475≤ c≤0.500) are measured for samples furnace-cooled (FC) and water-quenched (WQ) from 763 K. There is a tendency for c V to increase with composition. It shows a much higher concentration in WQ samples than in FC samples, indicating the existence of large amount of quenched-in vacancies. Furthermore, the vacancy migration and the long-range ordering during ageing in martensite and parent B2 phases for FC and WQ samples of c=0.495 and 0.475 are examined by measuring the lattice constants and the integrated intensities by the X-ray diffraction method. In both samples, the martensite ageing does not bring about an effective vacancy migration and a detectable change in long-range order (LRO). For the B2 phase of the WQ sample, the quenched-in vacancies are drastically annealed-out by ageing, which accompanies a promotion of the LRO. The difference in ease of the vacancy migration between the martensite and the parent phases is due to the difference in the crystal structure.

Ultra-precision machining induced surface structural changes of Zn–Al alloy

Ultra-precision machining was carried out on a furnace cooled (FC) eutectoid Zn–Al alloy specimen using a new technology of single point diamond turning (SPDT). Microstructural changes and phase decomposition at the surface of the ultra-precision machined alloy specimen were investigated. It was found that the ultra-precision machining induced external stress resulted in decomposition of the ε phase and crystal orientation changes of the Zn-rich phases: η and ε, at the surface of the machined FC Zn–Al alloy specimen, which were in agreement with the tensile stress induced phase transformations and crystal orientation changes in the FC Zn–Al alloy specimen.

Soft Magnetic Properties of Co-Based Amorphous Alloy by Two-Step Cooling Method

The soft magnetic properties of Co-based amorphous Co 66 Fe 4 Ni 1 Si 15 B 14 alloy in terms of various annealing conditions have been investigated by magnetoimpedance (MI) effect and permeability ratio (PR). In order to enhance the soft magnetic properties by co-reducing internal thermal stress and magnetic ordering, we applied the furnace cooling to Curie temperature and subsequent water quenching (F&W) method, which considerably increased the initial permeability - to values 60% or 100% higher than in the only furnace-cooled (FC) or water-quenched samples, respectively. However, the MI and PR results show that the FC sample is softer than the F&W sample at high frequencies.

Microstructural and corrosion studies of Ti alloy (IMI 834) in acidic solutions

The electrochemical polarization behaviour of a titanium alloy (IMI 834) was studied in different concentrations of aqueous and ethylene glycolic solutions of hydrochloric and phosphoric acid at 30 °C. The influence of furnace cooled (FC), air cooled (AC) and water quenched (WQ) heat treatments and microstructure on polarization behaviour was also studied. An active passive transition and a large range of passivity potential were observed in aqueous and glycolic solutions of the acids. The magnitudes of the critical current density (ic) and passive current density (ip) were higher for hydrochloric acid in comparison to phosphoric acid. Values of ic and ip were lower in ethylene glycol–hydrochloric acid up to 7 M and were higher above 7 M hydrochloric acid–ethylene glycol solutions as compared to the corresponding hydrochloric acid concentrations. However, these values were always lower in ethylene glycol–phosphoric acid than in phosphoric acid solutions. The microstructure of the alloy after solution treatment (1080 °C, 30 min; FC, AC and WQ) showed single phase transformed β structure. The increase in the cooling rate enhances the fineness of the β laths. The working electrode surface was examined by scanning electron microscopy (SEM) and scanning tunnelling microscopy (STM).

Effects of thermal processing on thermal expansion coefficient of a 50 vol.% SiCp/Al composite

Abstract The thermal expansion coefficients (CTE) of a 50 vol.% SiCp/Al composite prepared by a squeeze casting route were measured and examined from room temperature to 600°C using thermomechanical analysis (TMA) method, under the conditions of as-cast (AS), water-quenched (WQ), furnace-cooled (FC) and air-cooled (AC). The influence of thermal processing on CTE of the SiCp/Al composite was studied in terms of thermal residual stresses generated upon cooling from the processing temperature. It is found that the introduction of high volume fraction of SiC particles to Al matrix could notably reduce the CTE of matrix, leading to the low CTE values of the composite either at room temperature or at high temperature. The CTEs of both the composite and the unreinforced Al matrix increase with increasing of temperature, while the composite shows a much slower increasing rate than the unreinforced Al matrix resulting from the restriction of SiC particles on Al matrix during thermal expanding process. The thermal expansion behavior of the SiCp/Al composite is influenced by the previous thermal processing history. The WQ and AS specimens present lower CTEs compared to the FC and AC ones, which is thought to be due to the difference in original thermal residual stresses within these specimens and their releasing behavior during subsequent heating.

Tensile deformation and phase transformation of furnace-cooled Zn–Al based alloy

Phase transformation and microstructural changes of the furnace-cooled (FC) eutectoid Zn–Al based alloy were studied during thermal ageing and tensile deformation using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Two types of decomposition of Zn-rich phases η FC′ and ε were detected in both the aged and the tensile deformed alloy specimens. Precipitates of α and T′ phases were distinctly observed inside the light contrast η FC′ and ε phases, respectively, using back-scattered electron imaging. Under tensile deformation at 150°C, the coarse lamellar structure was deformed into fine particulate structure, whilst the fine lamellar structure remained unchanged. The mechanism of tensile fracture of the alloy is discussed in relation to the stress-induced phase transformation and microstructural change. An intrinsic co-relationship of phase transformation between the aged and tensile deformed alloy specimens is also discussed.

The influence of synthesis conditions on superconductors

The resistivities and the critical temperatures of quenched and furnace-cooled (FC) samples of are found to be different. The influence of the cooling rate on Bi-2212 is studied with the help of x-ray diffraction, scanning electron microscopy and energy dispersive x-ray analysis of pellet and powder samples. There are several factors which influence the resistivity and the critical temperatures in polycrystalline samples. The granular compaction becomes better in the quenched sample whereas the FC sample has higher porosity. The compositional disorder induced by the cooling rate affects the resistivity and the critical temperature to a certain extent. The Cu stoichiometry is closer to two in the FC sample but the critical temperature is found to be smaller than that of the quenched sample.

Mechanical Milling Induced Preferred Orientation in a Zn-Al Based Alloy

Mechanical milling resulted in the preferred orientation of the Zn-rich metastable hep εη′FC and η′γ phases in the furnace cooled (FC) eutectoid Zn-Al based alloy filings, after hot rolling or elevated temperature tensile-creep. The milling induced preferred orientation for the Zn-rich ε phase, and theεη′FC and η′γ phases in the eutectoid alloy were at (0002) and 10&lmacr;0 crystal planes respectively, which reverted the original, 0 h milling state orientation as the directional external stress was destroyed during further milling.

Biocorrosion study of titanium‐cobalt alloys

The present work provides experimental results of corrosion behaviour in Hank's physiological solution and some other properties of in-house fabricated titanium-cobalt alloys with cobalt ranging from 25-30% in weight. X-ray diffraction (XRD) shows that, in water-quenched (WQ) alloys, beta-titanium is largely retained, whereas in furnace-cooled (FC) alloys, little beta-titanium is found. Hardness of the alloys increases with increasing cobalt content, ranging from 455 VHN for WQ Ti-25 wt% Co to 525 VHN for WQ Ti-30 wt% Co. Differential thermal analysis (DTA) indicates that melting temperatures of the alloys are lower than that of pure titanium by about 600 degrees C. Potentiodynamic polarization results show that all measured break-down potentials in Hank's solution at 37 degrees C are higher than 800 mV. The breakdown potential for the FC Ti-25 Wt% Co alloy is even as high as nearly 1200 mV.

Stability of lamellar structure in a Ti-47.8at%Al alloy

The stability of the lamellar structure is known to be highly structure sensitive. Although some reports have investigated the stability of lamellae in lower aluminum content alloys, few reports have studied the stability of lamellae in near gamma titanium aluminide alloys. The purpose of this paper is to investigate the stability of lamellar structure with different features in Ti-47.8at%Al alloy. The following conclusions were reached: (1) A lamellar structure was obtained in furnace cooled (FC), air cooled (AC) and oil quenched (OQ) samples. As the cooling rate increased, the interlamellar spacing decreased. Thus, the stability of lamellae decreased. The coarsening rate increased with increasing temperature. (2) An {alpha}{sup 2} single phase was obtained in the water quenched (WQ) samples. The lamellae transformed from the {alpha}{sub 2} phase are less stable, and hence have a faster coarsening rate and finer coarse structure compared with the lamellar formed during cooling. (3) Since coarse lamellae nucleate in the {alpha}{sub 2} and {gamma} matrices, more than one habit plane exists, so that the alignment of coarse lamellae is complex. Parallel coarse lamellae with same close-packed plane index form a packet.