Elevated-temperature Yield Strength Research Articles

Effect of Al content on microstructure and mechanical properties of Alx(Nb3TaTi3Zr)100-x refractory high-entropy alloys

In this study, seven refractory high-entropy alloys of Al x (Nb3TaTi3Zr)100-x (x = 0, 5, 10, 15, 20, 25, 30) were synthesized by vacuum arc melting and characterized by various techniques, including XRD, SEM, EDS, compression tests at both 1200 °C and room temperature, as well as hardness tests. The analysis revealed that the alloys exhibit a single BCC structure when the Al content is between 0 and 15%, while the B2 phase appears at 20% and a mixed structure of BCC + B2 + σ phase at 30%. As the Al content increases, the hardness, stiffness, and room temperature yield strength of the alloy increases, while the plasticity decreases. Notably, the alloy with 25% Al content displayed the highest yield strength of 1400 MPa and Young’s modulus of 75.94 GPa at room temperature. Moreover, the hardness of the seven alloys increased from 247 HV to 490 HV with Al content from 0 to 30%. Furthermore, the alloy containing 30% Al exhibited a notable elevated-temperature yield strength of 143 MPa at 1200 °C.

Manufacturing and processing of sheets using a Mg–Al–Ca–Zn–Y alloy for automotive applications

As the transportation industry evolves, so do its needs, creating opportunities for the use of non-standard materials. While electrically powered vehicles (EVs) generally operate at lower temperatures than those with internal combustion engines, operation at elevated temperature is still important for battery cases and motor housings. There, Mg alloy sheets could be used, as they have great potential for lightweighting. Mg–Al–Ca-alloys are particularly suitable, as they form temperature-stable phases, providing advantages compared to classical Mg–Al–Zn alloys.In this work, sheets made of an Mg–Al–Zn–Ca–Y alloy (AZXW3120) were manufactured via hot-rolling. The microstructure and texture in various conditions were analyzed and the mechanical properties were investigated at RT and 150 °C. The Ca additions led to a reduced texture after rolling and allowed for an increase in tensile strength of 15–20 MPa by age hardening. The age-hardenable AZXW3120 sheets showed better formability during cup-drawing (31.4 vs. 27.5 mm) and higher elevated temperature yield strength, of up to 25 MPa, compared to industrially produced AZ31 Mg sheet.

Effects of Nb on Elevated-Temperature Properties of Fire-Resistant Steel

Objective: Two kinds of fire-resistant steel with different Nb content (Nb-free and 0.03 wt.%) were prepared for studying the effects of Nb addition on the elevated-temperature strength of fire-resistant steel. Methods: Two stages of heat treatment were carried out on the steels to obtain different microstructures. Typical microstructures, dislocation, and precipitates morphology of steels were observed by SEM and TEM. The dislocation density was calculated by the X-ray data from the microstructures. High temperature and room temperature mechanical properties of steels were determined by tensile testing. Results: The results showed that the YS of N2-HR steel (addition of 0.03 wt.% Nb) at RT and 600 °C was higher than N1-HR steel (Nb-free) by about 81 and 30 MPa, respectively. This indicates that Nb is an alloying element as effective as Mo in increasing the elevated-temperature strength of fire-resistant steel. The dominant strengthening mechanisms of Nb addition on elevated-temperature yield strength are precipitation strengthening and bainite strengthening. Conclusions: Theoretical analysis shows that there are two precipitation strengthening stages in fire-resistant steel: (1) increasing dislocation density during hot rolling, and (2) blocking dislocation movement and recovery in tensile testing. The results also show that the effect of fine grain strengthening is not obvious at high temperature, but is obvious at room temperature.

Effects of Al(MnFe)Si dispersoids with different sizes and number densities on microstructure and ambient/elevated-temperature mechanical properties of extruded Al–Mg–Si AA6082 alloys with varying Mn content

The effects of Al(MnFe)Si dispersoids, with different sizes and number densities, on the evolution of microstructure and ambient/elevated-temperature mechanical properties of extruded AA6082 alloys, with varying Mn content, under T5 conditions, were investigated. Compared to the low density of coarse dispersoids formed during conventional homogenization, the high density of fine dispersoids formed during a new low-temperature homogenization was more effective in increasing the material’s resistance to plastic deformation during extrusion, resulting in the dissolution of more constituent Mg2Si particles into the α-Al matrix. A large amount of β", some β′ precipitates and fine dispersoids co-existed in the α-Al matrix of 0.5% Mn containing alloy, which afforded this alloy a substantial increase in ambient-temperature yield strength of 65–75 MPa under T5 conditions compared to the base alloy without dispersoids. A further increase in the Mn content decreased the number density of the β" precipitates, resulting in a decline in the mechanical properties. Upon thermal exposure at 300 °C for 100 h, β"/β′ fully transformed into an undesirable equilibrium β phase and lost their strengthening effect, while fine and dense dispersoids became the dominant strengthener, leading to a 55–70% increase in the elevated-temperature yield strength relative to the alloys either without dispersoids or with coarse dispersoids. Dispersoid strengthening was more pronounced at 0.7% Mn addition as further increasing the Mn content mainly contributed to the fraction of insoluble Mn-containing intermetallics.

The superior elevated-temperature mechanical properties of Al-Cu-Mg-Si composites reinforced with in situ hybrid-sized TiCx-TiB2 particles

The Al-Cu-Mg-Si matrix composites reinforced with in situ hybrid-sized TiCx-TiB2 particles with sizes ranging from 20 nm to 1.3 µm were successfully synthesized using the Al-Ti-B4C reaction system via a method that combined the combustion synthesis and the hot press assisted with hot extrusion. The sizes of the fabricated TiCx and TiB2 particles increased with increasing TiCx-TiB2 content. The hybrid-sized TiCx-TiB2 particles improved the elevated-temperature yield strength (σ.2), the tensile strength (σUTS), and the fracture ductility (εf) of the composites at both 493 K and 573 K. The 40 wt% (TiCx-TiB2)/Al-Cu-Mg-Si composite exhibited superior σ.2 (141 MPa), σUTS (164 MPa), and εf (31.2%) at 573 K, with enhancements of 60.2%, 72.6%, and 22.4% compared to the Al-Cu-Mg-Si matrix alloy (88 MPa, 95 MPa, and 25.5%). The improvement of the elevated-temperature mechanical properties for the in situ (TiCx-TiB2)/Al-Cu-Mg-Si composites was attributed primarily to the strengthening effects induced by the hybrid-sized TiCx-TiB2 particles and the θ′ precipitation strengthening.

Microstructure, elevated-temperature mechanical properties and creep resistance of dispersoid-strengthened Al-Mn-Mg 3xxx alloys with varying Mg and Si contents

In the present work, the effects of magnesium and silicon addition on microstructure, elevated-temperature yield strength and creep resistance of Al-Mn-Mg 3xxx alloys were investigated. The microstructure evolution under as-cast and heat-treated conditions was quantitatively evaluated by optical and electron microscopy. Results revealed that both magnesium and silicon had an important influence on the distribution and volume fraction of precipitated dispersoids in 3xxx alloys. Without Mg or Si addition, dispersoids could hardly form during the precipitation heat treatment; hence, the alloys free of Mg or Si possessed low yield strength and creep resistance at elevated temperature. A significant improvement in elevated-temperature yield strength and creep resistance was obtained over a wide range of Mg (0.5–1.5wt%) and Si (0.25–1wt%) content studied due to the precipitation of a large number of dispersoids. The best combination of yield strength and creep resistance at 300 ℃ was obtained by the alloy containing 1.0wt% Mg and 0.25wt% Si with the maximum volume fraction of dispersoids and the minimum volume fraction of dispersoid free zone. The effects of dispersoid strengthening, solid solution strengthening and grain size on yield strength and creep resistance were discussed based on experimental results.

Modeling elevated-temperature mechanical behavior of high and ultra-high strength steels in structural fire design

High and ultra-high strength steels are increasingly used in structures of tall and super-tall buildings, where fire safety has a substantial impact on the structural design. However, more widespread employment in engineering practice is substantially impeded by the lack of suitable design models for the constitutive mechanical behavior of such steels at elevated temperatures; and respective available experimental research is limited to investigations of unusually thin plate material with respect to structural applications. The present study completes the current database with an extensive series of strain-rate controlled tensile tests at different strain-rates with coupon specimens from high and ultra-high strength steel plates of varying thickness, and approves on the basis of this novel most comprehensive and consistent database that existing constitutive fire design models for mild carbon steels are only restrictedly adoptable for high strength steels. Analysis of the impact of the revealed model shortcomings at the material level on structural fire designs shows that the model's overestimation of the elevated-temperature yield strength leads to unsafe fire designs of structural applications with strength-induced failure modes, whereas in contrast the model's underestimation of the elevated-temperature Young's modulus leads to occasionally highly overconservative fire designs of structural applications with stability-induced failure modes.

Effect of Carbon and Titanium Additions on Mechanical Properties of B2 FeAl

Iron aluminides based on Fe3Al and FeAl are highly oxidation and corrosion resistant and have potential for elevated temperature structural applications. Carbon is an important alloying element in Fe3Al as it increases strength and creep resistance as well as resistance to environmental embrittlement. However, addition of carbon to FeAl has not been successful as it leads to precipitation of graphite which causes decrease in strength. Graphite formation can be prevented by the addition of titanium (Ti) which forms TiC in the FeAl matrix. Ti addition imparts strength to FeAl alloys containing carbon without loss of room temperature ductility. Observed mechanical properties have been related with the microstructure. Up to 75 % increase in elevated temperature yield strength is obtained at target service temperature (923 K). This can lead to successful development of carbon containing FeAl based alloys for elevated temperature structural applications.

Microstructure evolution and mechanical properties of Inconel 740H during aging at 750 °C

The microstructure evolution of Inconel 740H during aging at 750°C for up to 3000h was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), three-dimensional atom probe (3DAP) analysis and micro-phase analysis. The mechanical properties of samples after aging were also studied. The grain size increased substantially during the whole aging period. Two different types of grain boundary carbides were observed; block-shaped and needle-shaped. Both were identified to be M23C6 by selected area diffraction measurements. The grain boundary carbides did not coarsen significantly during aging, with the weight fraction increasing only from 0.20% to 0.28%. In contrast, a much higher coarsening rate of γ′ precipitates was observed, as evidenced from both TEM observations and SAXS analysis. 3DAP was used to study the elemental partitioning behavior between γ′ precipitates and γ matrix as well as the evolution in width of the γ/γ′ interface. A large increase in the width of γ/γ′ interfaces was seen between 1000h and 3000h aging. In addition, for the sample aged at 750°C for 3000h, Cr enrichment on the γ matrix side of the γ/γ′ interface was found. Tensile tests at 750°C of the aged samples showed a gradual decrease in elevated-temperature yield strength after 500h, when this alloy was over-aged. The critical precipitate size for the transition from precipitate cutting by weakly coupled dislocations to strongly coupled dislocations for Inconel 740H was calculated to be approximately 50nm, which agrees well with the experiment measurements of elevated-temperature yield strength. The room temperature impact toughness of all samples decreased during aging as the grain size kept growing.

Effects of Zinc and Aluminum Concentration on the Microstructure and Properties of ZA Series Mg Alloys

The microstructures of a series of high Zn magnesium alloys Mg-(7-11) Zn-(2-6) Al alloys were clarified, and effects of Zn and Al concentration about the ZA system alloys on the microstructure and properties were also investigated. For Mg-(7-11)Zn-4Al alloys with the Zn content increase, improved creep resistance is obtained due to block τ-Mg32(Al, Zn)49phase, with severe reduction in ultimate strength and ductility, and the best creep property is obtained with 11wt.% Zn concentration. However, a bit increasing Al content of Mg-9Zn-(2-6)Al alloys contributes to the improvement in the ambient and elevated-temperature yield strength, but seriously deteriorates the creep properties for the formation of lamellar φ-Al2Mg5Zn2eutectics or Mg51Zn20phase.

4040 革新的耐熱マグネシウム合金 : 長周期積層構造型Mg-Zn-RE合金(S19-1 高機能マグネシウム合金の創成と変形,S19 高機能マグネシウム合金の材料強度特性)

Recently, new magnesium alloys with high mechanical strength and heat-resistance have been developed in Mg-RE-Zn (RE: Y, Dy, Ho, Er, Gd, Tb, Tm) system, and are widely noticed in industrial circles. These Mg-RE-Zn alloys are characterized by a long period ordered (LPO) structure. The mechanical properties of these LPO Mg-RE-Zn alloys are drastically improved by plastic deformation. Extruded LPO Mg-RE-Zn alloys exhibit high yield strengths greater than 350MPa and elongations of 4% or higher at ambient temperature, and high elevated-temperature yield strength greater than 300MPa at 473K. The LPO Mg-RE-Zn alloys are promising candidates for lightweight structural materials.

Effects of Fe additions on the mechanical properties and oxidation behavior of CrTa Laves phase reinforced Cr

The addition of Fe to Cr–Cr2Ta eutectic alloys increased ambient fracture toughness from a maximum of 12–14 to 18–21 MPa m1/2. The elevated-temperature yield strength was depressed, but still reached >250 MPa at 1000 °C. The Fe additions also resulted in a potentially beneficial change in oxidation mechanism from Cr2N subscale formation to internal oxidation.

Structure and properties of Fe–Al–Ti intermetallic alloys

Structure and mechanical properties of Fe–Al–Ti alloys in the composition range Fe–(10–27.5) at.%Al–(10–30) at.%Ti have been studied. The alloys exhibited a wide range of microstructure comprising α-Fe, Fe 2Ti (Laves phase) and/or Fe 2AlTi (Heusler phase) depending on the composition. Their room temperature hardness, Young's modulus, ratio of plastic to elastic work and yield strength were determined. Elevated temperature yield strength and creep properties of these alloys were also studied. It was observed that significant increase in strength and hardness may be achieved in alloys containing two or more phases. The compressive creep behaviour of these alloys followed the power law in creep in the temperature range 873–1073 K. Creep stress exponents in the range 3–6 were observed, suggesting dislocation creep to be the operative mechanism. Apparent activation energy for creep was found to be in the range of 400 to 600 KJ/mol.

Rapidly Solidified Powder Metallurgy Mg<SUB>97</SUB>Zn<SUB>1</SUB>Y<SUB>2</SUB>Alloys with Excellent Tensile Yield Strength above 600 MPa

Nanocrystalline magnesium alloys having high tensile strength, high elevated-temperature tensile strength, high-strain-rate superplasticity and high thermal stability have been developed in Mg 97 Zn 1 Y 2 (at% I alloy by rapidly solidified powder metallurgy (RS P/M) processing. The tensile yield strength and elongation that were dependent on the consolidation temperature were in the ranges of 480 to 610MPa and 5 to 16%, respectively. Young's modulus of the RS P/M alloy was 45 GPa. The specific tensile yield strength was four times as high as that of a commercial AZ91-T6 alloy, and was higher than those of conventional titanium (Ti-6Al-4V) and aluminum (7075-T6) alloys. The RS P/M alloys exhibited excellent elevated-temperature yield strength that was 510 MPa at 423 K. The RS P/M alloy also exhibited high-strain-rate superplasticity at a wide strain-rate range from I × 10 - to I × 10 0 s -1 and at a low temperature of 623 K. It is expected that the Mg 97 Zn 1 Y 2 RS P/M alloy can he applied in some fields that requires simultaneously the high specific strength at ambient and elevated temperatures and high workability.

High Strength Nanocrystalline Mg-Al-Ca Alloys Produced by Rapidly Solidified Powder Metallurgy Processing

Nanocrystalline magnesium alloy having high specific tensile strength, high Young's modulus, high elevated-temperature tensile strength, high-strain-rate superplasticity and high corrosion resistance has been developed by rapidly solidified powder metallurgy (RS P/M) processing in amorphous forming Mg 70 Al 20 Ca 10 alloy. The density of the nanocrystalline RS P/M alloy was 1.80 g/cm 3 . The compressive yield strength and plastic strain that were dependent on the consolidation temperature were in the ranges of 570 to 930 MPa and 0.5 to 9.2 %, respectively. The tensile yield strength, plastic elongation and Young's modulus of the RS P/M alloy extruded at 673 K were 600 MPa. 1.0% and 50 GPa, respectively, The specific tensile yield strength was four times as high as that of a commercial AZ91-T6 alloy. The RS P/M alloy exhibited excellent elevated-temperature yield strength that was 360 MPa at 473 K. The RS P/M alloy also exhibited superplasticity at a high strain rate of 1. 1x10 0 S -1 and at 723 K. It is expected that the Mg 70 Al 20 Ca 10 RS P/M alloy is applied in some fields that requires simultaneously the high specific strength at ambient and elevated temperatures, high workability and high corrosion resistance.

Thermal stability and elevated temperature mechanical properties of electroslag remelted Fe-16wt.%Al-(0.14–0.5)wt.%C intermetallic alloys

Addition of carbon in the range of 0,14–0.5 wt.% to the Fe 3Al-based intermetallic Fe-16wt.%Al (Fe-28at.%Al) alloy results in the formation of a thermally stable dispersion of Fe,AIC carbide phase. The volume fraction of these precipitates increases with increase in carbon content. Processing of these alloys through a combination of air induction melting and electroslag remelting leads to enhanced elevated temperature mechanical properties compared to those reported for the low (< 0.01 wt.%) carbon alloys with similar Al contents. Enhancement of up to 30% in elevated temperature yield strength was observed at the test temperatures (600, 700 and 800°C) used. The improvement in mechanical properties may be attributed to the presence of strengthening Fe 3AlC phase as well as the interstitial carbon present in the alloy matrix. The addition of carbon also leads to improved room temperature mechanical properties in contrast with other alloying additions (such as Mo, Ti and Si) used for enhancing elevated temperature properties of Fe 3Al-based intermetallic alloys. It is suggested that carbon may be an important alloying addition to these alloys.

Microstructure, excess solid solubility, and elevated-temperature mechanical behavior of spray-atomized and codeposited Al-Ti-SiCP

In the present study, the microstructure, thermal stability, and elevated temperature mechanical behavior of Al-Ti-SiCP metal matrix composites (MMCs) processed by spray atomization and codeposition were investigated. The evolution of the microstructure of the spray-deposited material before and after thermal annealing was studied using X-ray diffractometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical microscopy. The thermal stability of the spray-deposited materials was determined by monitoring the changes in hardness after isochronal thermal anneals at various temperatures. The results of X-ray and microanalysis studies revealed the presence of a supersaturated solid solution of Ti in α Al in the spray-atomized and codeposited material, with Ti concentrations in the 0.8 to 1.1 wt pet range. The formation of an extended solid solution was discussed in light of the cooling rates present during atomization and, subsequently, during deposition. Regarding mechanical behavior, the present results suggest that the as-spray deposited and hot extruded Al-Ti matrix is thermally stable up to a temperature of 400 °C and that the excess solid solubility of Ti in a Al, resulting from the rapid quench during processing, is maintained up to a temperature of 300 °C. The elevated-temperature mechanical properties of the hot extruded spray-deposited materials were studied following a 100-hour exposure at 250 °C, 350 °C, and 450 °C; the roomtemperature mechanical properties were also determined. Results show that the elevated-temperature yield strength of the spray-deposited and extruded materials compared favorably to those of an equivalent alloy made by powder metallurgical materials, were superior to those of the ingot material, but were inferior to those of mechanically alloyed Al-Ti materials. In addition, TEM studies showed no evidence of interfacial reactions at the Al-Ti/SiCP interface.

The effect of grain size on the elevated temperature yield strength of polycrystalline aluminum

The effect of grain size on the elevated temperature yield strength of polycrystalline aluminum

The separate roles of subgrains and forest dislocations in the isotropic hardening of type 304 stainless steel

Tests on 304 stainless steel were conducted involving first warm working in torsion, then cold working in torsion, and finally measurement of the elevated-temperature yield strength in compression. These tests permitted separation of the effects of subgrain size and forest dislocation density on the isotropic part of the flow stress. Forest dislocation strengthening appears to dominate in this material. The results are best fitted by a root-mean-square summation of strength terms representing the contributions of solutes, forest dislocations, and subgrain boundaries. The same equation successfully predicts the flow stress during elevated-temperature transient deformation (under both constant strain rate and variable strain rate) from the transient dislocation substructure.

Dispersion-strengthened zirconium alloys

Inert particle strengthening concepts were extended to zirconium-base alloys. By using powder metallurgy techniques inert particles of Y 2O 3 were mechanically dispersed in a Zircaloy-2 matrix. Hot-hardness, elevated-temperature tensile, 343°C creep, and 400°C steam corrosion data for the resulting materials were obtained and interpreted. The elevated temperature yield strength of Zircaloy-2 was increased. Much of the increase was related to oxygen contamination. However, significant strengthening, in excess of that caused by oxygen, was shown to have been caused by inert particle dispersion. The 343°C, steady-state creep rates of dispersion-strengthened Zircaloy-2 were markedly lower than those for wrought Zircaloy-2. Yttria dispersants were noted to have some adverse effect on corosion resistance in 400°C steam. Oxygen contamination is the major technological problem with regard to the development of dispersion-strengthened zirconium powder metallurgy materials. Alloy additions of Be are suggested as a means of minimizing both the corrosion and oxygen contamination problems.