High-temperature Tensile Deformation Research Articles

High-temperature tensile and creep deformation of cross-weld specimens of weld joint between T92 martensitic and Super304H austenitic steels

The high-temperature mechanical behavior of cross-weld specimens prepared from a dissimilar weld joint between T92 martensitic and Super304H austenitic heat-resistant steels incorporating Ni-based weld metal was evaluated at temperatures up to 650°C. For both high temperature tensile and creep tests, failure took place in T92 due to its faster degradation with temperature increase. The heat-affected zone of T92 played a critical role during creep deformation, resulting in type IV failure under the long-term creep condition. For the creep specimens, the location of failure shifted from the base metal region to the fine-grained heat-affected zone as the creep duration time increased from the short-term to the long-term condition. The massive precipitation of Laves phase on the grain boundaries of the fine-grained heat-affected zone during creep deformation was observed and found to be responsible for the accelerated void formation in the area leading to the premature failure.

High temperature tensile deformation behavior of Grade 92 steel

Candidate structural materials for advanced reactors need to have superior high temperature strength and creep-rupture properties among other characteristics. The ferritic–martensitic Grade 92 steel (Fe–9Cr–2W–0.5Mo, wt.%) is considered such a candidate structural material. Tensile tests were performed at temperatures of 600, 650 and 700°C in the strain rate range of 10−5–10−3s−1. After analyzing the tensile results using the Bird–Mukherjee–Dorn (BMD) equation, a stress exponent of about 9.5 and an activation energy of about 646kJ/mol were obtained. In the light of high values of the stress exponent and activation energy, the threshold stress concept was used to elucidate the operating high temperature deformation mechanism. As a result of this modification, the true activation energy and stress exponent of the high temperature deformation in Grade 92 steel were found to be about 245kJ/mol and 5, respectively. Thus, the dominant high temperature deformation mechanism was identified as the high temperature climb of edge dislocations and the appropriate constitutive equation was developed.

Constitutive modeling for high-temperature tensile deformation behavior of pure molybdenum considering strain effects

In order to get a reliable constitutive equation for the accurate simulation, high temperature flow behavior of molybdenum sheet was investigated by performing uniaxial hot tensile tests in the temperature range of 993–1143K at an interval of 50K with strain rates ranging from 0.0005 to 0.02s−1. The true stress–strain curves revealed the characteristics of strain hardening and followed by flow softening under lower strain rates at temperature over 1093K, and the dominant role of work hardening at higher strain rates and lower temperatures. Considering the effects of strain rates and temperature incorporating strain on the flow behavior, the Arrhenius-type constitutive equation with material constants expressed by the polynomial fitting of strain was established, and the flow stress values predicted by the constitutive equation agreed well with the experimental results.

Dynamic recovery and recrystallization during high-temperature tensile deformation of a free-standing Pt-aluminide bond coat

Free-standing Pt-aluminide (PtAl) bond coat, when subjected to tensile testing at high temperatures (T≥900°C), exhibits significant decrease in strength and increase in ductility during deformation at strains exceeding that corresponding to the ultimate tensile strength (UTS), i.e., in the post-UTS regime. The stress–strain curve is also marked by serrations in this regime. Electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM) studies suggest dynamic recovery and recrystallization (DRR) as the mechanisms for the observed tensile behavior in the coating. Activation energy values suggest vacancy diffusion assists DRR. The fine recrystallized grains formed after deformation had a strong 〈110〉 texture.

High-temperature deformation behaviors of W/Zr based amorphous interpenetrating composite

The high-temperature tensile deformation behaviors of porous tungsten/zirconium-base metallic glass interpenetrating composites were examined systematically spanning a wide range of temperature. The deformations of composite at around supercooled liquid region all presented similar characteristics, including initial linear elastic behavior, obvious stress overshoot followed clear “work hardening”, which is different from that of monolithic BMG at high temperature close to the initial crystallization. The sample after tensile test still exhibited excellent compressive properties. The deformation and strengthening mechanisms were discussed in details. The W substrate dominates the deformation processes of the composite. The amorphous phase is helpful to the deformation and formability of the composite due to its good plastic deformation under high temperature. The results promise that the interpenetrating composite can be employed to produce parts using high-temperature forming techniques.

In situ observation of high temperature tensile deformation and low cycle fatigue response in a nickel-base superalloy

High temperature tension and low cycle fatigue experiments of IN718 alloy have been performed in the electro-hydraulic servo system with scanning electron microscope at 455°C. Fatigue crack initiation and propagation process are investigated in situ. Results show that the carbide and twin grain are the crack source of the low cycle fatigue of IN718 alloy, and the low cycle fatigue life of the alloy increases with the decrease in grain size.

Recrystalization Behavior of Coldworked 14Cr-15Ni-2Mo Austenitic Stainless Steel Under Tensile Deformation

AbstractRecrystallization behavior of 20% coldworked alloy D9 (14Cr-15Ni-2Mo austenitic stainless steel) during high temperature tensile deformation has been assessed. The alloy was produced by vacuum induction melting followed either by vacuum arc refining (VAR) or electroslag refining (ESR). Tensile studies were carried out at various temperatures between ambient and 1073 K at an interval of 50 K and at strain rate of 1.2 × 10−3 s−1. The peak in the stress-strain curve was observed for the tensile tests conducted at 973–1073 K. This is attributed to dynamic recrystallization during tensile deformation. The values of the apparent activation energy were estimated as 384 kJ/mol for ESR grade alloy D9 and 372 kJ/mol for VAR grade alloy D9 by hyperbolic-sine Arrhenius equation, which agree well with that required for dynamic recrystallization in stainless steels. TEM studies confirmed extensive recovery and dynamic recrystalization in both the alloys.

Effect of Hf on carbides of FGH4096 superalloy produced by hot isostatic pressing

FGH4096 alloys with Hf contents of 0, 0.3 and 0.6wt% were studied to clarify the effect of Hf on the carbides in these alloys. The carbides in FGH4096 alloys produced on HIPing and during high temperature tensile deformation were analyzed by SEM, TEM and EDS. The results indicated that carbides in HIPed alloys were mainly blocky MC and the previous particle boundaries (PPB) in the alloys were decorated by the carbides. ZrO2 cores with a cubic lattice were observed in part of the MC distributed at the PPB (PPB MC), while part of PPB MC in Hf modified alloys had an orthorhombic HfO2 core. Volume fraction of MC increases with increasing Hf content of the alloys. The formation of PPB MC was suppressed in the alloy with 0.3wt% Hf, but more MC precipitated at the PPB when Hf content of the alloy was raised to 0.6wt%. The amount of M23C6 delineations that precipitated at grain boundaries during aging treatment decreased with increasing Hf content. Besides, the formation of a film-like M23C6 at grain boundaries during tensile deformations at 650°C and 750°C were suppressed in the Hf modified alloys, which contributed a lot to the improvement of the tensile properties of FGH4096 alloys at elevated temperatures.

Modeling high-temperature tensile deformation behavior of AZ31B magnesium alloy considering strain effects

The hot tensile deformation behaviors of AZ31B magnesium alloy are investigated over wide ranges of forming temperature and strain rate. Considering the effects of strain on material constants, a comprehensive constitutive model is applied to describe the relationships of flow stress, strain rate and forming temperature for AZ31B magnesium alloy. The results show that: (1) The effects of forming temperature and strain rate on the flow behaviors of AZ31B magnesium alloy are significant. The true stress–true strain curves exhibit a peak stress at small strains, after which the flow stress decreases until large strain, showing an obvious dynamic softening behavior. A considerable strain hardening stage with a uniform macroscopic deformation appears under the temperatures of 523 and 573K. The strain hardening exponent (n) increases with the increase of strain rate or the decrease of forming temperature. There are not obvious strain-hardening stages when the forming temperature is relatively high, which indicates that the dynamic recrystallization (DRX) occurs under the high forming temperature, and the balance of strain hardening and DRX softening is easy to obtain. (2) The predicted stress–strain values by the established model well agree with experimental results, which confirm that the established constitutive equation can give an accurate and precise estimate of the flow stress for AZ31B magnesium alloy.

High temperature deformation characteristics of equal channel angular pressed AA6082-T6

High temperature deformation behavior of 6082AA that was over aged and pressed to 6 passes in equal channel angular die via route C was investigated. High-temperature tensile deformation was conducted in the range of 753 to 823K at four strain rates in the range of 10−2–6×10−1s−1. Stress dependence of the strain rate revealed a stress exponent, n of 7 throughout the ranges of temperatures and strain rates tested. The apparent activation energy was calculated to be 223kJmole−1. These findings implied the presence of threshold and by incorporating the threshold stress in the analysis, the true activation energy was calculated to be about 139kJmol−1. A plot of normalized strain rate (ε̇kT/DGb) vs. normalized effective stress (σ–σo)/G, on a double logarithmic scale, gave an n value of 5. Ductility increased with strain rate for all the temperature ranges and maximum ductility value of 173% was achieved at 823K for 6×10−1s−1.

Microstructure Features during High Temperature Tensile Deformation of an AZ31 Alloy with Nd and La Additions

Microstructural features and tensile behaviors of an AZ31 alloy with Nd and La additions were investigated with elongation-to-failure tensile tests at constant temperatures of 300 °C, 350 °C, 400 °C, and 450 °C, and constant strain rates of 10-2s-1and 10-3s-1. Experimental data show that the material exhibits tensile ductilities of over 100% at 450 °C, featured by long steady state deformation. Microstructure studies show that annealed coarse grains were remained in the gauge region after the tensile tests, and the dominate deformation mechanism was dislocation creep, other than dynamic recrystallization or grain boundary sliding. Cavity evolution near fracture end caused premature failure of the material, although fine grains developed through dynamic recrystallization.

Mechanical Properties of B-Doped Ni3Al-Based Intermetallic Alloy

The mechanical behavior and microstructural evolution during high temperature tensile deformation of recrystallized Ni3Al polycrystals doped with boron were investigated as functions of initial grain size, tensile strain rate and temperature. In order to obtain more precise information on the deformation mechanism, tensile specimens were rapidly quenched immediately after deformation at a cooling rate of more than , and were then observed by transmission electron microscopy (TEM). Mechanical tests in the range of 923 K to 1012 K were carried out in a vacuum of less than Pa using an Instron-type machine with various but constant cross head speeds corresponding to the initial strain rates from to . After heating to deformation temperature, the specimen was kept for more than 1.8 ks before testing. The following results were obtained: (1) Flow behavior was affected by initial strain size; with decreasing initial grain size, the level of a stress peak in the true stress-true strain curve decreased, the steady state region was enlarged and elongation increased. (2) On the basis of TEM observation of rapidly quenched specimens, it was confirmed that dynamic recrystallization certainly occurred on deformation of fine-grained () and intermediate-grained () specimens at an initial strain rate of and at 973 K. (3) There were some dislocation-free grains among the new recrystallized grains. The obtained results suggest that both dynamic recrystallization and grain boundary sliding are operative during high temperature deformation.

Transition in Deformation Mechanism of AZ31 Magnesium Alloy during High-Temperature Tensile Deformation

Magnesium alloys can be used for reducing the weight of various structural products, because of their high specific strength. They have attracted considerable attention as materials with a reduced environmental load, since they help to save both resources and energy. In order to use Mg alloys for manufacturing vehicles, it is important to investigate the deformation mechanism and transition point for optimizing the material and vehicle design. In this study, we investigated the transition of the deformation mechanism during the high-temperature uniaxial tensile deformation of the AZ31 Mg alloy. At a test temperature of 523 K and an initial strain rate of 3×10−3 s-1, the AZ31 Mg alloy (mean grain size: ~5 μm) exhibited stable deformation behavior and the deformation mechanism changed to one dominated by grain boundary sliding.

Tensile properties of hot rolled Mg–3Sn–1Ca alloy sheets at elevated temperatures

Mechanical behavior of hot rolled Mg–3Sn–1Ca (TX31) magnesium alloy sheets were studied in the temperature range 25–350 °C. The microstructure of the alloy consisted of the eutectic structure of α-Mg + Mg 2Sn and a dispersion of needle-like CaMgSn. The highest room-temperature ductility of 18% was obtained by hot rolling of the cast slabs at 440 °C, followed by annealing at 420 °C. The high temperature tensile deformation of the material was characterized by a decrease in work hardening exponent ( n) and an increase in strain rate sensitivity index ( m). These variations resulted in respective drops of proof stress and tensile strength from 126.5 MPa and 220 MPa at room temperature to 23.5 MPa and 29 MPa at 350 °C. This was in contrast to the ductility of the alloy which increased from 18% at room temperature to 56% at 350 °C. The observed variations in strength and ductility were ascribed to the activity of non-basal slip systems and dynamic recovery at high temperatures. The TX31 alloy showed lower strength than AZ31 magnesium alloy at low temperatures, while it exhibited superior strength at temperatures higher than 200 °C, mainly due to the presence of thermally stable CaMgSn particles.

High Temperature Tensile Deformation Behavior of New Heat Resistant Aluminum Alloy

This study attempted to investigate the high temperature tensile deformation behaviour of new Al-1%Mg-1.1%Si0.8%CoNi heat resistant aluminium alloy. New aluminium alloy strengthened by Co-Ni based phase was manufactured by using powder ball milling and continuous casting, based on the alloy design & preliminary test. High temperature tensile tests were conducted at various temperatures from 25�� to 450�� . OM, SEM, EPMA, XRD, FIB and HR-TEM equipments were used to analyse microstructure, phases, and fracture surface. Microstructure of the new alloy mainly consisted of Al matrix and Co-Ni based phases (1~8 Πm). The Co-Ni based phase was analyzed and confirmed as (Ni, Co)3Al having incoherent interface with matrix. In high temperature tensile results, the new aluminium alloy didn’t show significant decrease (19.6%) of strength with increasing temperature (450�E ), suggesting totally different behaviour with conventional A319 alloy (87.0% decrease of T.S.). Fractography observation results of new alloy represented the ductile fracture mode with dimples. Voids were mainly initiated at Co-Ni based strengthening phases. It was apparently observed that the strengthening effect of the (Ni, Co)3Al could be still maintained at high temperature of 450�� . The deformation mechanism of this alloy was also discussed. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11

High Temperature Tensile Deformation Behavior of New Heat Resistant Aluminum Alloy

This study attempted to investigate the high temperature tensile deformation behaviour of new Al-1%Mg-1.1%Si-0.8%CoNi heat resistant aluminium alloy. New aluminium alloy strengthened by Co-Ni based phase was manufactured by using powder ball milling and continuous casting, based on the alloy design & preliminary test. High temperature tensile tests were conducted at various temperatures from 25°C to 450°C. OM, SEM, EPMA, XRD, FIB and HR-TEM equipments were used to analyse microstructure, phases, and fracture surface. Microstructure of the new alloy mainly consisted of Al matrix and Co-Ni based phases (1∼8μm). The Co-Ni based phase was analyzed and confirmed as (Ni, Co)3Al having incoherent interface with matrix. In high temperature tensile results, the new aluminium alloy didn’t show significant decrease (19.6%) of strength with increasing temperature (450°C), suggesting totally different behaviour with conventional A319 alloy (87.0% decrease of T.S.). Fractography observation results of new alloy represented the ductile fracture mode with dimples. Voids were mainly initiated at Co-Ni based strengthening phases. It was apparently observed that the strengthening effect of the (Ni, Co)3Al could be still maintained at high temperature of 450°C. The deformation mechanism of this alloy was also discussed.

High temperature tensile behaviors of extruded and rolled AZ31 Mg alloy

High temperature tensile ductilities and deformation mechanisms of an extruded and rolled AZ31 Mg alloy were investigated. Elongation-to-failure tests were conducted under constant T-head velocity and constant temperatures ranging from 300 °C to 450 °C. Strain-rate-change tests were conducted under varying strain rate from 5×10 −5 s −1 to 2×10 −2 s −1 and constant temperature from 300 °C to 450 °C. Experimental results show that the maximum elongation of the AZ31 alloy with an average grain size of about 19 μm is 117% at strain rate of 10 −3 s −1 and temperature of 450 °C. Stress exponent and activation energy were characterized to clarify the deformation mechanisms. The enhanced ductility is dominated by solute drag dislocation creep, and the major failure mechanism is cavity growth and interlinkage.

High temperature tensile behavior of a PH stainless steel

High temperature tensile deformation of 15-5 PH stainless steel in peak age and overaged conditions has been studied over the temperature range of 300 to 600°C and different strain rates. Dynamic recrystallization was the main softening mechanism when the alloy deformed at imposed temperature and strain rate region. The apparent activation energy was calculated as 284.8 and 323.1kJ/mol for peak age and overaged conditions, respectively.

Relation between local necking and cavitation during high-temperature tensile deformation of polycrystalline pure aluminum

For polycrystalline aluminum with grain size of 170 and 346μm, tensile deformation was carried out at a true strain rate of 1×10−2/s and a temperature of 553K (=0.59Tm, Tm: melting temperature in K). Onset and progress of local necking during the deformation were investigated by measurements of small-angle X-ray scattering (SAXS) from a viewpoint of cavity formation on grain boundaries. The cavitation was observed in the change of the SAXS intensities as a function of local strain along the gauge part of specimen. The intensities increase rather slowly during the beginning uniform deformation. However, it increases rapidly in the gauge part where the local necking has occurred. The degree of cavitation is found to be more remarkable for a specimen with smaller grain size. Cavity size and size distribution are evaluated from the SAXS profiles. The local necking phenomenon is discussed from a viewpoint of cavitation.

On the hot tensile deformation behavior of an AISI 316LN stainless steel

The hot deformation characteristics of AISI 316LN stainless steel were studied in the temperature range of 1123–1323 K and strain rate range of 10−4–10−1s−1 by carrying out tensile tests. The flow stress, ultimate tensile stress and percentage elongation were found to be strongly dependent on the temperature and strain rate. The critical strain required for the initiation of dynamic recrystallisation and peak strain were determined at each condition and their variation with temperature and strain rate studied. The deformation behavior was analyzed using a generic model for high temperature deformation and deformation parameters were computed. The variation of the true activation energy with strain for rate controlled high temperature tensile deformation was obtained. Microstructural studies were carried out on tested samples and the results of all the above studies are presented.