Effect Of Isothermal Heat Treatment Research Articles

Strong and tough semi-crystalline poly(aryl ether nitrile) with low coefficient of thermal expansion

The crystallization of poly (aryl ether nitrile) (PEN) has an essential impact on improving heat resistance, mechanical properties, chemical resistance, and dielectric properties. However, during the synthesis process, high crystallinity PEN is prone to precipitate out, which makes it difficult to carry out the synthesis reaction, which poses a significant challenge to synthesizing high crystallinity and high molecular weight PEN. In this work, hydroquinone (HQ) as the main phenolic monomer and 4,4′-biphenol (BP) as the second phenolic monomer were used to solve the technical difficulties in synthesis by copolymerization. The crystalline PEN with high molecular weight and significant crystallinity was obtained by regulating the molar ratio of BP to HQ. The effects of isothermal heat treatment on its crystalline, mechanical, and thermal properties were investigated. The influence laws of molecular chain structure and heat treatment process on the properties of PEN films were revealed. Among them, when the isothermal treatment temperature was 270 °C and the HQ: BP was 85:15, the mechanical strength reached 130 MPa, and the elongation at break could be up to an astonishing 50 %. Besides, the CTE value from 50 °C–150 °C is 40.84 ppm/°C, which is lower than most thermoplastics. Therefore, PEN with the HQ to BP molar ratio of 85:15 is suitable for large-scale production, providing new crystalline plastic specifications for high-performance special engineering plastics. A crystal bridge-tie chain model is summarized by the properties of HQ/BP-PEN films under different crystallization conditions, which provides an idea for preparing stiff and tough films.

Effect of isothermal heat treatment on microstructure and wear behavior of pearlitic rail steel

Effect of isothermal heat treatment on microstructure and wear behavior of pearlitic rail steel

Effect of isothermal heat treatments under Ms temperature on the microstructures and mechanical properties of commercial high-silicon spring steel

Abstract The effect of isothermal heat treatment temperatures under martensite start (Ms) temperature on the microstructure and mechanical properties of high-silicon commercial spring steel has been investigated. For this purpose, tensile specimens are prepared from AISI 9254 steel isothermally heat-treated under Ms temperatures (225 °C, 250 °C, and 275 °C) for 168 h after austenitizing at 870 °C for 30 min. Optical microscopy, scanning electron microscopy and X-ray diffraction analysis were used to characterize the microstructures of the specimens. Mechanical properties were determined by the tensile and hardness tests. Experimental results revealed that microstructure consists of carbide-free bainite, carbon enriched retained austenite, and martensite in high-silicon spring steel by the isothermal treatment under Ms temperature. The yield and tensile strength were increased by decreasing the isothermal temperature. However, uniform elongation and breaking energy were decreased by decreasing the isothermal temperature. The specimen which was isothermally heat-treated at 250 °C under Ms temperature showed a very good combination of tensile strength and total elongation as 2046 MPa and 8.5%, respectively. Dimples along with cap and cone formation which are evidence of a ductile fracture were observed in fractured surfaces of all isothermally heat-treated specimens.

Effect of isothermal heat treatment on crystallinity, tensile strength and failure mode of CF/PPS laminate

The present work concentrates on the crystallinity, tensile strength and failure mode of CF/PPS laminate subjected to isothermal heat treatment of different temperatures and time periods. Results show that in the range of 100–210°C and 1–3 hours, with the increase of heat treatment temperature and time, both crystallinity and tensile strength of CF/PPS laminate increase firstly then decrease. Under the condition of 150°C-2 hours treatment, the CF/PPS has the optimal crystallinity level of 65.3% and the optimal tensile strength with a value of 718.2 MPa. Compared with the as-received specimen without heat treatment, the crystallinity and tensile strength have been increased by 46.4% and 15.3%, respectively. A laser confocal microscope has been used to observe and analyze the fracture morphologies of the specimens, results show that the failure modes of the specimens under conditions of 100°C and 150°C isothermal heat treatment are fiber extraction and fiber breakage, respectively, and both are AGM, while that of 210°C is debonding and delamination, which is DGM.

Effect of Isothermal Heat Treatment at 760 °C on the Oxidation Behavior of Ti-Al-Zr Alloy

This study reports the oxidation behavior of an alpha titanium alloy, Ti-Al-Zr. The alloy was isothermally heat-treated in the air at 760 °C for durations up to 700 hours. Heat treatment led to the formation of an oxide layer on the surface and an alpha case beneath the oxide layer. The oxide and the alpha case were characterized by optical microscopy, micro-hardness measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES). The oxide was predominantly rutile; however, other metal oxides were also present. An oxide growth mechanism has been proposed. An alpha case of a maximum depth of 646 μm was measured for the specimen exposed for 700 hours. The diffusion coefficient of oxygen in the metal matrix was calculated to be 8.83 × 10−14 m2/s. The alpha case formation led to straining of the matrix because of oxygen dissolution. Micro-strain was calculated from XRD measurements using the “Modified Williamson–Hall (Modified W–H)” method. A maximum micro-strain of 0.37 pct was calculated for the prismatic plane (110) for a 72 hours exposed specimen. A decreasing trend in the micro-strain value with increasing exposure time has been reported and explained.

Investigation of the effect of isothermal heat treatments on mechanical properties of thermo-mechanically rolled S700MC steel grade

The effect of isothermal heat treatments (1 hour at 200, 400, 600 and 800°C) on mechanical properties of thermo-mechanically rolled S700MC steel has been investigated by extensive mechanical characterizations. Treatments at 600°C increase yield and tensile strength and decrease impact energy. Below 600°C the steel retains its bainitic structure. Precipitation kinetics simulations indicate that this secondary hardening effect arises from the nucleation of fine (Nb,Ti)C particles, indicating that the bainitic structure is unstable above 600°C due to its high supersaturation with respect to C, Nb and Ti. These results can help to optimize the operating practices for post-weld heat treatments.

Texture of Rotary-Friction-Welded from Dissimilar Medium Carbon Steels

The purpose of the present study was to investigate the texture in dissimilar medium carbon steels welded by rotary friction technique. The Electron Backscatter Diffraction (EBSD) technique was the main technique used to investigate the effect of welding on grain size and grain crystallographic orientation in the welded joint. Moreover, the effect of isothermal heat treatment at 600°C on welded joint has been studied knowing that this annealing allows to decrease the residual stresses. EBSD results revealed different subzones in welded joint. The texture in the weld is essentially composed of three components: Goss {110} , Rotated Cube {100} , and Rotated Goss {110} orientation. The heat treatments applied on welded material had a slight effect on texture and grain size.

Microstructural modification and ageing behaviour of the Al–17Si–5Cu alloy using a novel approach

ABSTRACTA novel short duration heat treatment schedule is proposed in the present investigation for the Al-17 wt-% Si-5 wt-% Cu alloy (AR alloy). The existing heat treatment uses long duration (4–24 h) holding at solutionising temperature prior to ageing treatment. In the present investigation, the AR alloy is subjected to isothermal holding at 590°C for 15 min followed by warm water quenching prior to the normal ageing schedule. Detailed microstructural investigations involving size and shape of primary as well as eutectic Si particles, porosity measurements along with hardness and tensile property characterisation are carried out to find the effect of isothermal heat treatment. The study reveals considerable improvement in microstructure and mechanical properties after this isothermal heat treatment.

The effect of isothermal heat treatment on hydrogen environment-assisted cracking susceptibility in Monel K-500

The effect of isothermal heat treatment on hydrogen environment-assisted cracking (HEAC) susceptibility in a single heat of Monel K-500 was evaluated via slow-rising stress intensity (K) testing while immersed in 0.6 M NaCl solution and exposed to applied potentials ranging from −1000 to −1200 mVSCE (vs. saturated calomel electrode). Four heat treatments, corresponding to the non-aged, under-aged, peak-aged, and over-aged conditions, conducted at a constant aging temperature of 923 K, were examined in this study. Crack growth kinetics and fractography demonstrate that alloys heat-treated to the under-aged and peak-aged conditions exhibit increased susceptibility to HEAC relative to alloys treated to the non-aged and over-aged conditions, respectively. Microstructural variables that are expected to vary under this isothermal heat treatment protocol are grain size, grain boundary character, grain boundary impurity concentration, yield strength, strain hardening, and precipitate morphology. A detailed assessment of grain size, grain boundary character, and grain boundary impurity concentration evolution with aging time suggests these variables do not explain the observed variation in HEAC susceptibility of Monel K-500. Differences in the crack tip hydrostatic stress field induced by differences in yield strength and strain hardening were directionally consistent with the observed HEAC susceptibility, but do not capture the enhanced susceptibility of the under-aged heat treatment relative to the peak-aged condition. However, transmission electron microscopy of each heat treatment revealed the presence of planar slip in the under-aged and peak-aged specimens, as compared to wavy slip in the non-aged and over-aged specimens, suggesting that the propensity for strain localization correlates well with HEAC susceptibility.

Investigation of semi-solid microstructures of an A356 alloy containing rare-earth Gd during isothermal heat treatment

AbstractThe effects of isothermal heat treatment on microstructures of an A356 alloy containing rare-earth gadolinium (Gd) were investigated to obtain an optimum semi-solid structure. Our results revealed that the primary α-Al phase of the semi-solid A356 alloy containing Gd was significantly refined and that its morphology was spherical or near-spherical. Increases in holding temperature and prolongation of holding time led to an initial decrease in size during the primary α-Al phase, followed by a gradual increase. Solid–liquid interfacial tension resulted in the spheroidization of the primary α-Al phase.

Effect of Isothermal Heat Treatment on the Microstructure and Mechanical Properties of Medium-Carbon Bainitic Steels

Effect of Isothermal Heat Treatment on the Microstructure and Mechanical Properties of Medium-Carbon Bainitic Steels

Effect of Isothermal Heat Treatment on Cyclic Life of Yitria Stabilized Zirconia and Gadolinium Zirconate Thermal Barrier Coating

The effect of isothermal heat treatment on the thermal cyclic life of yttria stabilized zirconia (YSZ) and gadolinium zirconate (GZ) thermal barrier coatings (TBCs) have been investigated. The purpose of the isothermal heat treatment is to simulate thermal exposure on the TBC in the gas turbine. Duplex YSZ TBC with YSZ as a topcoat and NiCrAly as a bondcoat and five-layered GZ TBC with GZ as the topcoat (GZ / 50 wt.%GZ+50 wt.%YSZ / YSZ / 50 wt.%YSZ+50 wt.% NiCrAly / NiCrAlY) were plasma sprayed onto Nimonic 263 substrates to a total thickness of 900µm using F4-MB gun. The isothermal heat treatment was performed at a temperature of 1100°C for 100 hours with a heating rate of 250°C/hour in an air furnace. The thermal cyclic tests were performed with the following cycle in an air furnace: heat up from 1000°C to 1200°C within 1 hour, dwell at 1200°C for 5 minutes, water quench and oven dry. The cycle is repeated until 20% spallation of the coating. Result indicates that the isothermally heat treated five-layered GZ TBC has a better cyclic life than the duplex YSZ TBC and as-sprayed GZ TBC.

THE MICROSTRUCTURE DEVELOPMENT DURING ISOTHERMAL HEAT TREATMENT STUDY OF AN Al-Mg-Si ALUMINIUM ALLOY

The effects of isothermal heat treatment on the microstructure development of an Al-Mg-Si aluminum alloy have been investigated by means of transmission electron microscopy. From micrographs illustrating the micro structural change of the alloy during isothermal heat treatment; we can observe in the water quenched alloy sample aged for 50 and 75 hours at 350C, dispersoid particles that were aligned along <100> matrix direction losing their distribution at their early stage of precipitation with an increase in holding times. For the microstructure of the alloy ramp heated and aged at 450C for different holding times, we can clearly see dispersoid particles in their early stages of formation heterogeneously distributed with different shapes after an increase in holding times. These dispersoid particles exhibited strain field contrast when they are heated at low temperatures, that indicating they are coherent or semi-coherent with the matrix. A loss of coherency was observed for most of the dispersoid particles when they were aged with high holding times.

Effects of isothermal heat treatment on nanostructured bainite morphology and microstructures in laser cladded coatings

Laser cladding and subsequent isothermal heat treatments have been used to fabricate nanostructured bainitic coatings. XRD has been used to determine the kinetics of bainitic transformation process. OM, SEM and TEM have been used to characterize the morphology and microstructures at different stages of transformation. The results showed that at the initial stage of bainitic transformation, the bainite sheaves are short and thin at a relatively low transformation temperature. The fully transformed bainitic microstructure obtained at a relatively high temperature present a textured morphology. The chaotic growth orientations of the sheaves and the island like of the retained austenite have been observed at the low transformation temperature. A simple model has been established to describe the microstructures and the bainite sheaves growth evolutions during the isothermal holding at the different transformed temperatures. The morphology and distribution of the bainite in the coatings were analyzed by using the nucleation and growth rate of bainitic transformation theories, which is consisted with the experiment results.

Effect of Isothermal Heat Treatment on Dynamic Properties of a High Strength Steel

The high strength steel which was subjected with isothermal heat treatment at three different temperatures, namely 330°C, 350°Cand 380°C after different quenching temperature namely 880°C and 900°C,was investigated in this paper. The quasi-static and dynamic mechanical properties of new high strength steel was tested by universal material testing machine and Split Hopkinson Pressure Bar (SHPB). Experimental results have showed that the yield strength and tensile strength of the steel reach 1100MPa and 1400MPa respectively. Hardness, yield strength and toughness are found to decrease with the consequently increasing of isothermal temperature under the same quenching temperature. The compression properties of the steel under quenching temperature of 880°C are higher than that of 900°C with the same isothermal temperature. It can be found that the steel which is subjected with isothermal heat treatment show strain rate sensitivity under high velocity impact. When isothermal temperature is set 380°C, the steel exhibits the most obvious strain rate hardening effect.

Response of the solidification microstructure of a high Nb containing TiAl alloy to an isothermal high-temperature heat treatment

Vacuum induction melting device combined with temperature control system was employed to investigate the effect of isothermal heat treatment (IHT) during solidification process on the microstructure evolution of a high Nb containing TiAl alloy. The microstructures of the alloy in as-cast condition and after IHT were studied. The results show that the as-cast microstructures exhibit a significant microstructural inhomogeneity with fine grains in dendrite core and coarse grains in interdendritic region. A new treatment approach by means of a short-term IHT within the β phase field during solidification process is proposed to obtain a uniform and refined microstructure. Compared with the as-cast alloy, IHT can reduce the tendency for crack. This phenomenon is attributed to the improvement of microstructural homogeneity by the elimination of peritectic α phase and the microstructure refinement by β → α transformation.

Microstructure Evolution of Semi-Solid AZ91D Alloy During Isothermal Heat Treatment Process

The effect of isothermal heat treatment on the microstructure evolution of semi- solid AZ91 D magnesium alloy was investigated. The results show that the roundness of the primary α- Mg phase increases with the increasing temperature and time. The microstructure evolution of the semi-solid AZ91 D experiences three stages during isothermal heat treatment process, i.e. the structure separation,spheroidization and final coarsening. The liquid phase of semi- solid alloy has three types, namely, the molten pool, the"entrapped liquid"pool and the liner liquid film which separates two neighbor particles.The solid phase has two types, namely, the primary α-Mg particles and the α-Mg phase formed in the second solidification.

Effect of Isothermal Heat Treatment on Mechanical Properties of WC-17Co Coatings

Abstract WC-17Co cermet coatings were deposited on Ni718 alloys using the high-velocity oxygen fuel (HVOF) technique. These coatings were then heat treated by different processes (150 °C, 10 h; 300 °C, 10 h; 450 °C, 10 h). The effects of heat treatment on microhardness, elasticity modulus, and fracture toughness were studied by an indentation method. The residual stresses of the coated specimens were evaluated by the Almen strip method. The results show that the phase constitution and the structure of the WC-17Co coatings exhibit no obvious change in 150, 300, and 450 °C heat-treatment. The microhardness, elasticity modulus, and fracture toughness of the WC-17Co coatings decrease with the increase of heat treatment temperature. The descent tendency of the mechanical properties is attributed to the decline in compressive residual stresses after isothermal heat treatment.

Texture in Welded Industrial Aluminum

In this investigation, grain orientation has been studied in an industrial aluminium Al99.5 which has been welded by TIG process. The optical microscopy and EBSD (Electron Back Scattered Diffraction) were the main techniques used to illustrate the effect of welding on grain orientation in fusion zone and in heat affected zone. Epitaxial growth has been observed in weld joint and texture of each zone has been determined. On the other hand, the effect of isothermal heat treatment at 400 °C on homogenization of welded joint has been also studied. It was shown that the cube orientation {001}<100> is the dominant texture component in welded joint before or after heat treatments.

Effect of Heat Treatments on Microstructure and Mechanical Properties of Low Carbon Steel Pipes Welded by Induction Process

In this work, the effect of isothermal heat treatments on microstructure evolution and mechanical properties after welding by induction of A37 pipeline steel have been studied by scanning electron microscopy, hardness measurements, and tensile tests. Microstructural evolution in welded joint was identified after isothermal annealing from 200 until 900 °C.