High-temperature Tensile Deformation Research Articles

Influence of Overaging on the Superplastic Behavior of an Al-Zn-Mg-Cu-Zr-Sc Alloy

This study examines the influence of overaging on the superplastic behavior of an Al-8.55Zn-2.65Mg-2.48Cu-0.1Zr-0.06Sc alloy (in mass%). Results show that the M-phase particles formed during overaging play the most crucial role during the high-temperature tensile deformation of the Al-Zn-Mg-Cu-Zr-Sc alloy. Even though specimens without overaging maintain their small grain structure due to the existence of fine coherent Al 3 (Sc x Zr 1―x ) particles, overaged specimens exhibit better superplasticity. The presence of liquid-like viscous flow may be the main factor contributing to the superior superplasticity of overaged specimens.

Hot deformation of AA6082-T4 aluminum alloy

High-temperature tensile deformation of 6082-T4 Al alloy was conducted in the range of 623–773 K at various strain rates in the range of 5 × 10−5 to 2 × 10−2 s−1. Stress dependence of the strain rate revealed a stress exponent, n of 7 throughout the ranges of temperatures and strain rates tested. This stress exponent is higher than what is usually observed in Al–Mg alloys under similar experimental conditions, which implies the presence of threshold stress. This behavior results from dislocation interaction with second phase particles (Mg2Si). The experimental threshold stress values were calculated, based on the finding that creep rate is viscous glide controlled, based on creep tests conducted on binary Al–1Mg at 673 K, that gave n a value of 3. The threshold stress (σo) values were seen to decrease exponentially with temperature. The apparent activation energy for 6082-T4 was calculated to be about 245 kJ mol−1, which is higher than the activation energy for self-diffusion in Al (Qd = 143 kJ mol−1) and for the diffusion of Mg in Al (115–130 kJ mol−1). By incorporating the threshold stress in the analysis, the true activation energy was calculated to be about 107 kJ mol−1. Analysis of strain rate dependence in terms of the effective stress (σ − σo) using normalized parameters, revealed a single type of deformation behavior. A plot of normalized strain rate (\( \dot{\varepsilon }kT/DGb \)) versus normalized effective stress (σ − σo)/G, on a double logarithmic scale, gave an n value of 3.

Mechanical properties of dual multi-phase single-crystal intermetallic alloy composed of geometrically close packed Ni 3X (X: Al and V) type structures

Dual multi-phase intermetallic alloy, which is composed of Ni 3Al(L1 2) and Ni solid solution (A1) phases at high-temperature annealing and is additionally refined by a eutectoid reaction at low temperature aging, according to which the Al phase is transformed into the Ni 3Al(L1 2) + Ni 3V(DO 22) phases, was prepared based on the pseudo-ternary system Ni 3Al–Ni 3Ti–Ni 3V. The high-temperature tensile deformation, fracture behavior and tensile creep were investigated using single crystalline material. The alloy with such a novel microstructure shows extremely high yield and tensile strength with good temperature retention, when compared not only with conventional Ni-based superalloys but also with polycrystalline materials reported previously. Over a broad temperature range fracture occurred along octahedral plane in the major component L1 2 phase, accompanied with high tensile elongation and ductile fracture mode. The tensile creep test conducted at 1173 K and 1223 K showed the presence of threshold stress, and also extremely low creep rate and long creep rupture time when compared with conventional Ni-based superalloys. The obtained results are promising for the development of a new-type of high-temperature structural material.

Microstructural design and high temperature tensile deformation behaviour of 8 mol% yttria stabilized cubic zirconia (8YCSZ) with SiO 2 additions

In the present study, the microstructural evolution and high temperature deformation behaviours of 8 mol% Y 2O 3 stabilized cubic zirconia (8YCSZ) containing up to 10 wt% SiO 2 is investigated. The experimental results show that the SiO 2 doped specimens sintered at 1400 °C contain only the cubic crystalline phase and SiO 2 has the very limited solubility of 0.3 wt% in cubic zirconia. This suggests that only small part of the SiO 2 dissolves in the cubic zirconia and the rest of SiO 2 segregates at grain boundaries and multiple junctions as amorphous (glassy) phase. This glassy phase prevents the grain growth by minimizing grain boundary energy and mobility, which results from solute segregation at the grain boundary and its drag. The deformation of the undoped 8YCSZ is characterized by large strain hardening with limited elongation. This is mainly due to severe grain growth during high temperature deformation. The addition of the SiO 2 results in a decrease in strain hardening and enhanced tensile elongation. These effects have been further improved with the increase of the SiO 2 addition reaching the elongation to failure of 152% for 10 wt% SiO 2 doped specimen in tension at a temperature of 1400 °C and strain rate of 1.3 × 10 −4 s −1. The decreased strain hardening and increased ductility in the SiO 2 doped specimens are due to the segregation of amorphous glassy phase to the grain boundaries, thus hindering grain growth and facilitating grain boundary sliding, which is the primary mechanism of deformation in fine grained materials at high temperatures.

Development of Dual Multi-Phase Intermetallic Alloys Composed of Geometrically Close Packed Ni3X(X:Al and V) Structures

AbstractDual multi-phase intermetallic alloys composed of Ni3Al (L12)+Ni3V (D022) phases were developed, based on the Ni3Al-Ni3Ti-Ni3V pseudo-ternary alloy system. High-temperature tensile deformation, fracture behavior, and compression and tension creep were investigated using polycrystalline and single crystalline materials. The alloys with such a novel microstructure show extremely high yield and tensile strength with good temperature retention, and also reasonable tensile ductility. Also, creep test conducted at high temperature showed extremely low creep rate and long creep rupture time. The obtained results are promising for the development of a new-type of high-temperature structural material exceeding conventional superalloys.

Effect of Microstructural Change on High-Temperature Deformation in Pre-Annealed Zr<SUB>65</SUB>Al<SUB>10</SUB>Ni<SUB>10</SUB>Cu<SUB>15</SUB> Bulk Metallic Glass

The effect of the microstructural change on the high-temperature tensile deformation behavior in the supercooled liquid region is investigated in the pre-annealed Zr 65 Al 10 Ni 10 Cu 15 bulk metallic glass. The microstructure before the tensile test on the specimen annealed at 673 K for 1.8ks shows that a small amount of icosahedral phase precipitates and a large amount of amorphous phase still remains. On the contrary, the specimen annealed at 673 K for 2.7 ks shows that a large amount of icosahedral phase precipitates and the presence of amorphous phase is hardly noticeable. From the fact that flow stress of the specimen annealed at 673 K for 2.7 ks increases in comparison with that of asreceived specimen as well as the specimen annealed at 673 K for 1.8 ks in the tensile test, it seems that the deformation behavior in the tension tests is greatly influenced by the difference in the degree of the precipitation of icosahedral phase. Since the m value is about 0.5 and many grain boundaries of icosahedral phase are formed in the specimen annealed at 673 K for 2.7 ks, the interaction between the icosahedral phase particles must be the cause of increase in initial stress. Accordingly, the microstructure of the gage section after tensile test in the specimen annealed at 673 K for 1.8 ks shows that the large amount of icosahedaral phase precipitates in the amorphous matrix. The strain hardening must be caused by the interaction between the icosahedral phase particles whose precipitation and growth are enhanced by deformation.

Microstructures and Mechanical Properties in Ni3Si-Ni3Ti-Ni3Nb-Based Multi-Intermetallic Alloys

ABSTRACTMicrostructure, high-temperature tensile deformation and oxidation property of Ni3Si-Ni3Ti-Ni3Nb multi-phase intermetallic alloys with a microstructure consisting of L12, D024 and D0a phases were investigated. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L12 phase in the wide range of test temperatures. 50-ppm boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. The multi-phase intermetallic alloy with a high Si content had good oxidation resistance, and also the boron addition to this alloy resulted in enhanced oxidation resistance. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy, which has a high Si content and is composed of L12 matrix dispersed by D024 and D0a phases, had the most favorable properties as high-temperature mechanical and chemical materials.

The Effect of Silicon Addition on High-Temperature Tensile Deformation of Superplastic Yttrium Aluminum Garnet (YAG) Ceramics.

The effect of doping Silicon on the high-temperature deformation of superplastic Yttrium Aluminum Garnet (YS-YAG) was studied under conditions of uniaxial tension. In the preceding paper, the elongation and strain rate of YAG ceramics was described as having decreased by the addition of Si as a sintering aid. This was one of the reasons that the grain size of Si-doped YAG ceramics greatly increased compared with that of non-doped YAG ceramics during deformation. Creep deformation of Y2O3-excess YAG, with an average grain size of 1.6μm, was shown to have an elongation of over 210% (=en) at 1773 K. Accordingly, we prepared Si-doped Y2O3-excess YAG ceramics (YS-YAG) having the above two chemical composition, and developed YAG materials having two characteristics; remarkable grain growth and elongation. The deformation of YS-YAG reached 200% (=en) at 1773 K under a constant stress creep tensile test, in spite of the grain size of YS-YAG changed from 1.5 μm to 6μm during deformation.

116 非弾性有限要素法によるセラミックス切欠材の高温引張変形解析(OS12-2 非弾性解析)(OS12 材料の塑性挙動の構成式のモデル化とシミュレーション)

116 非弾性有限要素法によるセラミックス切欠材の高温引張変形解析(OS12-2 非弾性解析)(OS12 材料の塑性挙動の構成式のモデル化とシミュレーション)

Ultrahigh-temperature deformation of high-purity HIPed Si3N4

High-temperature tensile deformation behavior of high-purity HIPed silicon nitride material was investigated in the temperature range between 1600°C and 1750°C. Recoverable anelastic and non-recoverable deformation was observed in high-purity HIPed silicon nitride. A power-law deformation model analogous to rheological models was used to distinguish the different deformation components. A stress exponent n = 1.64 and an activation energy Q 1 = 708 kJ/mol was determined for the non-recoverable deformation. For the anelastic deformation a stress exponent p = 4 and an activation energy Q 3 = 619 kJ/mol was observed. Diffusional creep and grain boundary sliding with the accomodation process responsible for the anelastic component are discussed as deformation mechanisms.

The high temperature tensile and compressive deformation characteristics of magnesia doped alumina

The mechanical characteristics of alumina have not yet been characterized completely in tension due in part to strain hardening accompanying grain growth and premature cavitation failure. Tensile tests were conducted on fine grained magnesia doped alumina over a range of strain rates, grain sizes and temperatures to evaluate the stress exponent, inverse grain size exponent and activation energy. Constant stress compression creep tests were also carried out under a similar range of experimental conditions. Extensive microstructural characterization after deformation indicated that there was considerable grain growth during deformation; however, the grains retained their initially equiaxed structure after significant deformation. Although a standard plot of strain rate versus stress indicated a stress exponent of ∼2, a complete analysis including the compensation of data for concurrent grain growth revealed that true stress exponent was ∼1, consistent with diffusion creep. It is argued that grain rearrangement processes accompanying grain growth will tend to mask the development of an elongated grain structure predicted by diffusion creep processes. In contrast to several ceramics with a significant amount of glassy phase, there is no significant difference between the elevated temperature tensile and compressive behavior of alumina.

Dynamic Internal Friction during High-Temperature Deformation in Aluminum Single Crystals with Different Orientations

Following the investigation of dynamic internal friction (DIF) in pure aluminum single crystals with [331] orientation reported before, the DIF in pure aluminum single crystals with two other orientations ([001], [111]) during high-temperature creep and tensile deformation has been studied. It is found that there also appears a peak of DIF at the early stage of deformation for [001] and [111] orientations, the dependence of DIF on measuring frequency and applied stress (or strain rate) is also similar to that observed for [331]. But owing to the differences in the orientation factor and the number of favourable slip systems, there are some differences in the peak height and the level of DIF among different orientations at the same test condition. As an example of the application of DIF, the generation rates of dislocations during creep and tensile deformation are evaluated from the data of DIF in aluminum single crystals with different orientations.

Cavitation damage during high temperature tensile deformation in fine-grained alumina doped with magnesia or zirconia

The high temperature tensile ductility of alumina doped with MgO or ZrO{sub 2} is limited around 70--110% for initial grain sizes of about 1 {micro}m. Such limitation may be correlated with strain hardening due to insufficiently suppressed grain growth in MgO-doped alumina or the level of flow stress heightened owing to second phase pinning and/or the intergranular segregation of Zr{sup 4+} ions in ZrO{sub 2}-doped one. This is because higher flow stresses can be assumed to accelerate damage process and thereby to limit tensile ductility. In comparison between these materials, however, such an approach based simply on flow rather similar tensile ductilities as above, irrespective of noticeable differences both in strain hardening behavior and in the level of flow stress between them. Although information on intergranular cavitation damage will give an additional basis for explanation, there has been little quantitative work on cavitation in there martials. The present study, therefore, examined the evolution of cavitation damage in a 0.2-wt%-MgO-doped alumina and a 10-vol%-ZrO{sub 2}-doped alumina with the same initial grain size of 1.0 {micro}m. An emphasis was placed on characterizing the difference in cavitation behavior between the materials.

Microstructure of INCOLOY MA956 after low and high temperature deformation

The ferritic FeCrAl alloy INCOLOY MA956 strengthened by oxide dispersoids is considered for applications at temperatures around 1000 °C. The oxide particles act as obstacles for moving dislocations. The results of tensile and compression tests showed that there are two different mechanisms of strengthening depending on the deformation temperature of the alloy. The microstructural investigations revealed the different dislocation substructure, especially dislocation-dispersoid interaction in the specimens deformed in low and high temperatures. At temperatures in the range 20–400 °C, dislocation loops around the dispersoid particles were observed, indicating an Orowan type of strengthening effect. During high temperature tensile and compression deformation, the shape of dislocations pinned at the departure side of particles indicated an attractive dislocation-particle interaction as described by the Rosler-Arzt model of dispersion strengthening.

High-temperature tensile ductility in WC-Co cemented carbides

High-temperature tensile deformation in WC-Co was investigated at temperatures between 1150 °C and 1250 °C. The flow stress is sensitive to temperature, strain rate, volume fraction of binder, and the addition of other carbides. The stress-strain rate relationship is divided into three regions at each temperature as in superplastic metals. A large tensile elongation over 100 pct was first obtained in WC-6Co and WC-13Co (wt pct) at temperatures of 1200 °C. Contrary to superplastic metals, the largest tensile elongation is not obtained in region II but on the border of regions I and II. The failure mode changes from necking in region I to sharp cracking in region II.

Microstructure and high-temperature tensile deformation of tiai(si) alloys made from elemental powders

Two ternary TiAl-based alloys with chemical compositions of Ti-46.4 at. pct Al-1.4 at. pct Si (Si poor) and Ti-45 at. pct Al-2.7 at. pct Si (Si rich), which were prepared by reaction powder processing, have been investigated. Both alloys consist of the intermetallic compounds y-TiAl, α2-Ti3Al, and ξ-Ti5(Si, Al)3. The microstructure can be described as a duplex structure(i.e., lamellar γ/α2 regions distributed in γ matrix) containing ξ precipitates. The higher Si content leads to a larger amount of ξ precipitates and a finer y grain size in the Si-rich alloy. The tensile properties of both alloys depend on test temperature. At room temperature and 700 °C, the tensile properties of the Si-poor alloy are better than those of the Si-rich alloy. At 900 °C, the opposite is true. Examinations of tensile deformed specimens reveal ξ-Ti5(Si, Al)3 particle debonding and particle cracking at lower test temperatures. At 900 °C, nucleation of voids and microcracks along lamellar grain boundaries and evidence for recovery and dynamic recrystallization were observed. Due to these processes, the alloys can tolerate ξ-Ti5(Si, Al)3 particles at high temperature, where the positive effect of grain refinement on both strength and ductility can be utilized.

Comment on “refutation of the relationship between denuded zones and diffusional creep”

In a recent paper Wolfenstine, Ruano, Wadsworth and Sherby [1] suggested that denuded zones observed after high-temperature tensile deformation of particle-containing materials are not related to diffusional creep. Among their arguments are that (a) denuded zones are found on only one side of a transverse boundary, 0o) denuded zones are evident on boundaries that are oriented far from the transverse direction, (c) there is a discrepancy between the measured creep rate and the creep rate calculated from the width of the denuded zones. In 1988 Bilde-Sarensen and Smith [2] considered the structural developments to be expected in diffusional creep of particle-containing materials on the basis of the dislocation model for grain boundary structures and properties. All three phenomena mentioned above were predicted from this analysis. Even so, we concur with Wolfenstine et al. in the suggestion that denuded zones may be formed by mechanisms other than diffusional creep, but at the same time we wish to point out that the structures mentioned under (a) and (b) are not inconsistent with deformation by diffusional creep. Therefore the observation of these structures cannot be considered a conclusive argument against the occurrence of diffusional creep.

High temperature tensile deformation of a nitrided Fe-1%V alloy

High temperature tensile deformation of a nitrided Fe-1%V alloy

オーステナイトステンレス鋼の高温変形挙動のコンピューターシミュレーション

A computer simulation system which calculates the high-temperature tensile deformation of austenitic stainless steel has been developed on the basis of a dislocation modeling. Plastic deformation by the external force is expressed by the flow of dislocations, and the load-deformation curves are computed as the reaction of material to a tensile testing machine. The formation of internal stress by work hardening and its recovery is represented by a cell structure model in which the framework is constructed by edge dislocation dipoles. The model also accounts for the temperature dependence of the effective stress by three types of dislocation motion ; free, pinning and dragging. The simulation system outputs computed curves of load-elongation and creep strain-time relation for the conventional tensile and creep tests. By selectiong suitable parameters in the model, the system is designed to allow us to predict the stress-strain and creep-rupture behavior of austenitic stainless steel. The model is so flexible that we can obtain good curve fitting to the experimental data of NRIM Creep Data Sheet.

High temperature tensile deformation behavior of β-Ti alloys

The high temperature tensile deformation behavior of β-Ti alloys has been investigated as function of strain rate, temperature and type of alloying elements. It was found that the magnitude of the flow stress drop increases with strain rate and solute concentration and decreases with temperature. For a given temperature and strain rate the extent of the drop decreased with a decrease in the relative atomic size between the solvent (titanium) and solute (manganese and vanadium) and a decrease in the diffusivity of the alloying element in the β phase. In addition, it was found that prestraining to a stress below the peak stress significantly reduces the peak stress and the magnitude of the flow stress drop. On the basis of these results it is suggested that the initial flow stress drop is due to the rapid multiplication of dislocations. The steady state behavior after the initial flow stress drop was attributed to dynamic recovery leading to the formation of subgrains.