Effect Of High Temperature Deformation Research Articles

The Effect of High-Temperature Deformation on the Mechanical Properties and Corrosion Resistance of the 2024 Aluminum Alloy Joint after Friction Stir Welding.

The 2024 aluminum alloy is one of the high-quality lightweight materials. Friction stir welding (FSW) has shown advantages in reducing welding defects and improving welding quality in 2024 aluminum alloys. Currently, the research regarding FSW joint corrosion performance is mainly about the joint without plastic deformation. However, FSW joints often need to be formed into complex shapes by plastic deformation. The influence of plastic deformation on the corrosion performance of FSW joints is the focus of scientific research. To address this problem, the effect of high-temperature deformation on the mechanical properties and corrosion behavior of 2024 aluminum alloy joints was researched. The exfoliation corrosion test, scanning electron microscopy, energy-dispersive spectroscopy, and transmission electron microscopy were employed to analyze the corrosion mechanism and microstructure. The results show that high-temperature deformation of the weld nugget zone greatly affects the mechanical properties and corrosion behavior of the FSW joint. Compared with the 0% deformation specimen, the hardness and tensile strength of the 20% deformation FSW joint increased by 32% and 21%, respectively. The FSW joint with 20% deformation shows the best mechanical properties and corrosion resistance. The number of precipitated S' phases of the FSW joint increases when the deformation increases to 20%, and the shape of the S' phase is a regular round particle shape. The dislocation density of the FSW joint increases continuously during deformation, which provides a favorable nucleation location for the S' phase.

Effect of high temperature deformation on the behavior of FeO eutectoid transformation

Eutectoid transformation behavior of FeO at different temperatures after high temperature deformation was investigated through simulation experiments and compared with undeformed specimens. The results show that the deformation behavior caused a significant effect on both the morphology and the formation process of the oxide scale. After deformation, the outer side of the deformed FeO, which produces a large number of micropores, provides the nucleation plasmas for the proeutectoid, which directly affects the concentration of Fe in the FeO. Fe supersaturation in FeO boundary which caused by “Fe-vacancy” makes the eutectoid transformation occurs rapidly, and Fe-cluster formed in FeO grain boundary.

Structural evolutionary behavior of Zr-based bulk metallic glasses under thermoplastic deformation

Zr55·7Cu22·4Al14.7Ni7.2 alloy rods with a diameter of 3 mm were prepared by copper mold suction casting. The microstructure, thermomechanical properties and high temperature plastic deformation behavior of the alloy specimens before and after uniaxial compression in supercooled liquid region (SLR) were investigated by X-ray diffractometer, scanning electron microscope, differential scanning calorimeter and microcomputer-controlled electronic universal testing machine. And the effects of different deformation conditions on the thermomechanical properties and microhardness of the specimens after high temperature deformation were analyzed. The results show that during plastic deformation in SLR, this alloy exhibits stress overshoot in the low temperature region - high strain rate conditions, exhibiting non-Newtonian fluid properties, while alloy softening occurs in the high temperature region - medium to high strain rate, showing the deformation behavior of a Newtonian fluid. The alloy crystallizes after deformation at high temperature and low strain rate (750 K, 2 × 10−4 s−1 and 760 K, 2 × 10−4 s−1∼5 × 10−4 s−1), generating dendritic τ3 phase (Zr51Cu28Al21), while still maintaining an amorphous structure in the low and medium temperature region, but this structure has part of the amorphous matrix that has been transformed into ordered clusters of atoms, and the degree of transformation increases sharply with decreasing strain rate, which in turn causes a sharp reduction in the crystallization incubation period and the exothermic enthalpy of crystallization. And the effect of high temperature deformation on the Vickers microhardness of metallic glass was analyzed.

Effect of high temperature deformation on the deformation behavior and thermodynamic properties of a Zr-based bulk amorphous alloy

Zr 55.7 Cu 22.4 Ni 7.2 Al 14.7 alloy rods with a diameter of 3 mm were prepared by copper mold suction casting. The structure, thermodynamic properties and plastic deformation behavior of the specimens before and after compression in supercooled liquid region were studied by X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and uniaxial compression machine (equipped with a high-temperature oven). The range of thermal forming process parameters was also discussed. The results show that the alloys have obvious glass transition and crystallization kinetics, and the crystallization activation energies obtained by the Kissinger and Ozawa equations are 297.1 kJ/mol and 294.9 kJ/mol, respectively. The amorphous alloys exhibit stress overshoot in low temperature region at high strain rates and deformation behavior of alloy softening in high temperature region at medium to high strain rates. Meanwhile, the viscosity of the alloy remains approximately constant at 740 K and 750 K, showing Newtonian fluid characteristic. It can be concluded that the optimal thermoplastic forming process ranges from 740 K to 750 K, 5 × 10 −4 s −1 to 5 × 10 −3 s −1 . The crystallization activation energies of the specimens after deformation are slightly higher than before, and they increase with the increase of strain rate. • Zr-based bulk amorphous alloy has a good thermodynamic stability, which facilitates thermoplastic forming. • The amorphous alloy shows superplastic deformability at high temperatures and strain rates. • The crystallization activation energies of the deformed specimens are higher than that of the undeformed. • The crystallization activation energies of the alloys after deformation increase with increasing strain rate.

Effect of High-Temperature Deformation on the Physical and Mechanical Properties of In Situ Titanium Composites with Silicide–Boride Reinforcement

The efficiency of thermomechanical processing was studied to optimize the mechanical properties of cast ternary and multicomponent hypoeutectic titanium-based alloys with silicide–boride reinforcement, produced by electron-beam crucible-skull melting. All the alloys studied exhibit low plasticity in cast state. High-temperature deformation, such as forging of samples heated to 1050°C in air, can significantly enhance the properties of the alloys: the plasticity of ternary Ti–Si–B alloys increases by four to six times (from 0.5 to 2–3%) and their fracture toughness increases by three times (from 11 to 36 MPa ∙ m0.5). The plasticity of the alloys with Zr, Al, and Sn additions increases by one order of magnitude (to 0.2–0.3%) and their fracture toughness by almost twice. The greatest high-temperature creep-rupture resistance at a fracture toughness of 26 MPa ∙ m0.5 is shown by the Ti80Zr1.2Al5.5Sn2.1Si8.7B2.5 alloy: 1038, 887, and 572 MPa at 600, 700, and 800°C, respectively.

Evaluation of Carbon Partitioning in New Generation of Quench and Partitioning (Q&P) Steels

Quenching and partitioning (Q&P) and a novel combined process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble®3S50 thermomechanical simulator. The heat treatments involved intercritical annealing at 800 °C and a two-step Q&P heat treatment with a partitioning time of 100 seconds at 400 °C. The “optimum” quench temperature of 318 °C was selected according to the constrained carbon equilibrium (CCE) criterion. The effects of high-temperature deformation (isothermal and non-isothermal) on the carbon enrichment of austenite, carbide formation, and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT) and scanning transmission electron microscopy (STEM). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples, it was significantly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the deformation-induced austenite-to-ferrite transformation (DIFT) phenomenon. By APT, the carbon accumulation at austenite/martensite interfaces was observed, with higher values for HSQ&P deformed isothermally (≈ 11 at. pct), when compared with non-isothermal HSQ&P (≈ 9.45 at. pct) and Q&P (≈ 7.6 at. pct). Moreover, a local Mn enrichment was observed in a ferrite/austenite interface, indicating ferrite growth under local equilibrium with negligible partitioning (LENP).

Effect of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement of 2.25Cr–1Mo-0.25 V steel

In this paper, the effects of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement (HE) of the 2.25Cr–1Mo-0.25 V steel was investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and tensile tests. The SEM and TEM images demonstrated that high temperature plastic deformation (HTPD) led to the coarsening of carbides and the dislocation density increase. The tensile tests displayed that the HTPD resulted in the cracking susceptibility increase, as indicated by the increased numbers and sizes of cracks at the fractured surface. This was attributed to the coarsening of carbides during high temperature deformation. In contrast, the HTPD highly decreased the loss of ductility compared to the un-deformed specimens, although the amount of ductility losses (elongation or reduction of area) did not change significantly as the HTPD increased. The correlations among carbides, hydrogen and cracks were discussed.

The Effect of High-Temperature Deformation on the Structure of Iron Aluminides

The iron aluminides are very perspective materials with many advantages – for example excellent corrosion resistance and/or good strength up to 600 °C. Due to these benefits they appear as suitable materials for use in high temperature applications. But some negative properties (sharp drop in strength above 600 °C or limited ductility at room temperature) are the major obstacles for their use. One way, how to improve mechanical properties of iron aluminides, is doping of binary alloy by alloying elements, which can form strengthening precipitates. Depending on their size the precipitates of secondary phases can block dislocation movement or act as strengthening phase as known in composite materials.One from many properties, which is important to know before a new type of material is used in structural applications, is its deformation behaviour. In present paper there was studied the structure of Fe-25Al-5Zr (in at. %) sample in as cast state and in states after high-temperature deformation at 600 and 800 °C in detail. A high resolution SEM equipped with EDX and EBSD was used for the study of structure. It was measured that huge grains are presented in the structure of as cast state. After deformation at 600 °C there were still observed huge Fe3Al-matrix grains, but strongly deformed. Also formation of sub-grains due to deformation is obvious. Deformation at 800°C led to formation of small grains due to recrystallization. Higher deformation degree in non-eutectic areas led to preferential recrystallization while Fe3Al phase in eutectic regions remained deformed (nonrecrystallized).

Effects of high-temperature deformation and cooling process on the microstructure and mechanical properties of an ultrahigh-strength pearlite steel

In this study, a new type of pearlite steel, 80CrSiV, is designed and the effects of the cooling rate, final cooling temperature, deformation temperature and level of deformation on the microstructures and mechanical properties of the steel are determined through thermal simulation, scanning electron microscopy, transmission electron microscopy, hardness and tensile tests. Results show that the microstructures and mechanical properties of the steel are significantly affected by the cooling rate after deformation and the final cooling temperature but are only slightly affected by the deformation temperature and level of deformation. A full pearlite microstructure with a hardness of HRC50.3, a tensile strength of 1715MPa and an elongation not less than 17.9% can be obtained under the condition of a cooling rate of 120°C·min−1 and a final cooling temperature of 550°C.

The Effects of High Temperature Deformation on Bainite Transformation

The effects of high temperature deformation on transformed microstructure and transformation amount in a high strength bainitic steel were investigated. It indicates that isothermal bainitic transformation is promoted by high temperature deformation. The transformed bainite microstructure is also affected by high temperature deformation, i.e. deformation retards the growth of bainite sheaves, leading to shorter banitie plates. The present study is useful to further understand the effects of ausforming on bainitic transformation.

Effects of High Temperature Deformation and Thermal Exposure on Microstructure and Mechanical Properties of Co-Based Superalloy

The gas turbine components operated in hot combustion gas undergo material degradation due to the thermal cycles. The failure mechanism of the hot gas components would be accompanied by material degradation in the properties of high temperature strength and creep rupture time. Many stationary parts in gas turbine are made of Co-based superalloy because of their high temperature performance. In this work, we survey the time and temperature dependent degradation of Co-based superalloy. We prepared the specimens of Co-based superalloy ECY768 that are exposed at 871 and 982 oC in 1000 ~ 5000 hours. We carried out the mechanical test and microstructural observation.

Recrystallisation of austenite grain when non-isotherm steel working: Effects of thermal kinetics and deformation-based mechanisms

The effects of high temperature deformation on the recrystallisation of austenite grains and hardening occurring during hot forging of steels were studied. Three commercial steels containing various carbon weight percentages were heated beyond the austenitising temperature and free forged up to desired deformation ratios. The specimens were then air-, or oil-cooled. Two zones were distinguished according to the grain-size: a zone with fine grains, associated with highest plastic deformation and, a zone with coarse grains located within the subsurface layers. Unexpectedly, the highest values of microindentation hardness were obtained in the coarse-grain zone. Consequently, the interaction between the grain-size gradient induced by thermal kinetics of cooling and the local hardening governed by dislocation kinetics was studied by means of microindentation hardness inspections. Analysis of stress–strain curves confirmed that while forging enhances mechanical strength, it has a detrimental effect on ductility of steel.

Effect of high temperature deformation and different cooling rates on microstructure and mechanical properties of Fe–Al alloys

Although iron and aluminum alloy forms several intermetallic phases, the iron-rich iron aluminide compositions appear to have the most potential for structural applications. A 100 kg of steel containing 0.88 wt.% C, 1.88 wt.% Mn, 0.44 wt.% Si, 0.081 wt.% Cu, 6.9 wt.% Al and 2.00 wt.% Cr was prepared using vacuum induction furnace. The dilatation was carried out to determine the critical phase transformation. Hot forging process was carried out after heating at 1200 °C with a high reduction ratio in cross-section 85%. The transformation temperatures Ac 1 and Ac 3 are 897.7 and 964.2 °C respectively. The density of Fe–Al after hot forging was measured using Archimedes method and it is approximately 6.804 gm/cm 3. The as-cast grain size is more than 3000 μm. Hot forging process refines the grain size down to 423 μm. The non-metallic inclusions (after severe hot forging) are very fine and well distributed. The material is so sensitive to the final cooling rate after hot forging. After introducing different cooling rates, the material exhibits different tensile characteristics, of sand cooling (slow cooling) the tensile strength is 729.5 MPa and elongation is 3.4%. After air cooling (moderate cooling rate), the strength is 62.1 MPa and elongation is 2.9% while of water quenching (drastic cooling), the strength is 559.3 MPa and the elongation is 1.4%.

EFFECT OF HIGH TEMPERATURE DEFORMATION ON THE LOW THERMAL EXPANSION BEHAVIOR OFFE-29%NI-17%COALLOY

The effect of high temperature deformation on the low thermal expansion property of Fe -29 Ni -17 Co alloy was investigated in the compressive temperature range of 900~1300°C at a strain rate range of 25 ~ 0.01 sec.-1. The thermal expansion coefficient (α30~400) generally increased with increasing compressive temperature. In particular, α30~400increased remarkably as the strain rate decreased at temperatures above 1100°C. Note, however, that α30~400at low compressive temperatures (900°C and 1000°C) increased abnormally at high strain rates. Based on the investigation of various possibilities of change in low thermal expansion behavior, the experimental results indicated that both the appearance of the α phase and evolution of grain size due to hot compression clearly influenced the low thermal expansion behavior of this invar-type alloy. The correlation between the microstructural cause and invar phenomena and theoretical explanation for the low thermal expansion behavior of Fe -29% Ni -17% Co were also suggested.

Effect of High Temperature Deformation on the Hot Ductility of Nb Microalloyed Steel

Low hot ductility of steel at the straightening stage of the continuous casting process is a problem found in steels containing microalloying and/or certain alloying additions. The thermal schedule undergone by the billet surface in the mill has a significant effect on the hot ductility. In this work, thermomechanical processing was employed to alleviate the problem of hot ductility in the Nb-microalloyed steel. Specimens were melted in situ and subjected to the billet surface thermal schedule in order to generate a microstructure similar to that present at the straightening stage of the continuous casting process. Some deformation schedules were incorporated with the thermal schedule at very high temperatures, specifically during solidification, within the d-ferrite region, and during the d®g transformation, and the hot ductility was subsequently evaluated at the end of the thermal schedule where the straightening operation is performed. After the thermal schedule alone, the steel exhibited a very low hot ductility at the straightening stage. It was found that deformation at very high temperatures prior to the straightening stage had a considerable effect on the hot ductility, either detrimental or beneficial, depending on the region in which the deformation has been executed. The mechanisms leading to loss and improvement of hot ductility are explained in this paper.

Development of Deformation and Recrystallization Orientations during Hot Rolling of Al-4.5Mg Alloy

Controlling the metallurgical structure during hot rolling of high magnesium-aluminum alloys is of essential importance in the production of sheet products, because hot rolling parameters significantly affect alloy recrystallization behavior. Developing the proper microstructure and grain texture in the hot band is necessary to ensure good mechanical properties and formability in the final product. In order to study the effects of high temperature deformation on the recrystallization behavior of Al-4.5 Mg, a designed laboratory hot rolling experiment was performed to investigate the interactions between hot rolling reduction, speed, and temperature. The evolution of microstructure and texture during hot rolling was examined using transmission electron microscopy (TEM) and orientation distribution functions (ODFs). The recrystallization behavior observed is explained in terms of the development of grain orientation during deformation in order to propose a recrystallization mechanism for this alloy system.

Microstructural Development in a Metal Matrix Composite During Thermomechanical Processing

Although a considerable amount of research on particulate reinforced metal matrix composites (MMCs) has concentrated either on their primary processing, or on their failure while in service, little attention has been given to their mechanical and/or physical behavior during secondary processing. Hence, there is only limited information available to facilitate the design of suitable thermomechanical processing schedules for these alloys. However, in order to design an appropriate processing route, it is necessary to develop an understanding of the microstructural development of both the matrix alloy and reinforcing particles during hot deformation. This research investigated the effect of high temperature deformation on the microstructural development of the aluminum alloy 2618 reinforced with 17% SiC particles by volume. Particular attention was directed towards the fracture behavior of the reinforcing particles deformed under conditions of plane strain. Results from extensive quantitative metallography show that SiC particles can be significantly refined during thermomechanical processing. Additionally, at these elevated deformation temperatures, particles redistribute themselves within the matrix, resulting in a more homogeneous distribution. This behavior has been characterized using Dirichlet tessellations. Finally, it is shown how the refinement and redistribution of the SiC particles can lead to the enhancement of the fracture-related properties.

Effect of high-temperature deformation on the texture of a two-phase titanium alloy

Changes in the texture of both the α- and β-phases of the two-phase alloy Ti-6AI-4V have been determined in order to clarify the mechanisms of high-temperature deformation. A strain of ∼ 1.5 was applied to the alloy at 928 °C, at strain rates representative of superplastic and nonsuperplastic conditions. The α-phase texture changed very little with strain rate whereas that for the β-phase was much more sensitive. The β-phase texture was weakened at superplastic strain rates but developed a fibre texture at non-superplastic rates. It is postulated that under superplastic conditions the alloy deforms predominantly by grain boundary sliding of the soft β-phase grains, with the hard primary α-phase grains remaining in their original orientations and the measured loss in texture intensity being attributed to the loss in texture of the secondary α-phase only. Under non-superplastic conditions there is a greater contribution from plastic deformation in the β-phase which, in turn, can enhance the secondary α-phase texture.

Effect of creep deformation on precipitation hardening

The effect of high-temperature deformation on the kinetics of precipitation for several commercial aluminium alloys has been investigated. It has been found that mobile dislocations introduced during high-temperature deformation are efficient sinks for vacancies and retard the ageing process in spite of the additional vacancies produced through deformation. The plentiful supply of dislocations accelerates the loss of coherency of intermediate precipitates. Cold deformation after the quench, but before ageing, refines the precipitate size, which retards loss of coherency and results in improved creep strength.

The influence of high temperature plastic deformation on the kinetics of graphitization of pyrolytic carbons

T he effects of high temperature deformation on the isothermal graphitization vs. time characteristics of a substrate- nucleated pyrolytic carbon have been investigated by comparing the x-ray structures of deformed and undeformed samples which had identical heat treatment histories. The deformation was performed in tension parallel to the substrate and in compression parallel or perpendicular to the substrate. In all cases graphitization was enhanced by plastic deformation. The effect appeared to have two components: (1) An immediate and direct influence of the deformation process, and (2) a residual effect due to deformation-induced microstructural changes. Possible mechanisms are discussed and it is concluded that the phenomena result primarily from stress-assisted bond-breaking.