Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

Improved continuous precipitation kinetics and tensile properties of extruded AZ80 alloy through {10-12} twin formation

This study investigates the effect of{10-12}deformation twins on the continuous precipitation behavior of an extruded Mg-8.0Al-0.5Zn-0.2Mn(AZ80)alloy during aging.The extruded AZ80 alloy is compressed along the transverse direction to introduce{10-12}twins,followed by an aging treatment at 300℃.The extruded material exhibits a twin-free microstructure with low internal strain energy,whereas the pre-twinned material possesses abundant{10-12}twins and has high internal strain energy.The aging results reveal that the peak-aging time of the pre-twinned material(1 h)is one-eighth of that of the extruded material(8 h).Although Mg_(17)Al_(12)continuous precipitates(CPs)are observed in both the peak-aged materials,these CPs are much smaller and more densely distributed in the pre-twinned material despite the significantly shorter aging time.The CPs size in the peak-aged materials increases in the following order:twinned region in the pre-twinned material(0.47μm)<residual matrix region in the pre-twinned material(1.71μm)<matrix region in the extruded material(2.55μm).Moreover,the CPs number density in the twinned region of the pre-twinned material is approximately 11 times higher than that in the matrix region of the extruded material.The peak-aged pre-twinned material exhibits significantly higher tensile strength and ductility than the peak-aged extruded material.These results demonstrate that the formation of{10-12}twins in the extruded AZ80 alloy substantially accelerates the static precipitation of CPs during aging at 300℃and improves the tensile properties of the peak-aged material.

Effect of Curing Age on Tensile Properties of Fly Ash Based Engineered Geopolymer Composites(FA-EGC)by Uniaxial Tensile Test and Ultrasonic Pulse Velocity Method

Tensile properties of fly ash based engineered geopolymer composites(FA-EGC)at different curing ages were studied by uniaxial tensile test and ultrasonic pulse velocity(UPV)methods,which included uniaxial tensile properties,the correlation between ultrasonic pulse velocity and tensile properties,and characteristic parameters of microcracks.The experimental results show that obvious strain hardening behavior can be found in FA-EGC at different curing ages.With the increase of curing age,the tensile strength increases,the tensile strain decreases and the toughness becomes worse.The UPV of FA-EGC increases with curing age,and a strong correlation can be found between tensile strength and UPV.With the increase of curing age,the average crack width of FA-EGC decreases and the total number of cracks increases.This is because the strength of geopolymer increases fast at early age,thus the later strength development of FA-EGC tend to be stable.At the same time,the bond strength between fiber and matrix,and the friction of fiber/matrix interface continue to increase with curing age,thus the bridging effect of fiber is gradually strengthened.In conclusion,the increase of curing age is beneficial to the development of tensile properties of FA-EGC.

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting(HPDC)technology has evolved in the past decades,enabling stronger and larger one-piece casting with significant part consolidation.It also offers a higher design freedom for more mass-efficient thin-walled body structures.For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance,shock towers and hinge pillars,etc.),a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

Multiscale tensegrity model for the tensile properties of DNA nanotubes

DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical properties of such DNTs.This paper aims at presenting a multiscale model to quantify the correlations among the pre-tension states,tensile properties,encapsulation structures of DNTs,and the surrounding factors.First,by combining a statistical worm-like-chain(WLC)model of single DNA deformation and Parsegian's mesoscopic model of DNA liquid crystal free energy,a multiscale tensegrity model is established,and the pre-tension state of DNTs is characterized theoretically for the first time.Then,by using the minimum potential energy principle,the force-extension curve and tensile rigidity of pre-tension DNTs are predicted.Finally,the effects of the encapsulation structure and surrounding factors on the tensile properties of DNTs are studied.The predictions for the tensile behaviors of DNTs can not only reproduce the existing experimental results,but also reveal that the competition of DNA intrachain and interchain interactions in the encapsulation structures determines the pre-tension states of DNTs and their tensile properties.The changes in the pre-tension states and environmental factors make the monotonic or non-monotonic changes in the tensile properties of DNTs under longitudinal loads.

Microstructure and tensile properties of AE42-based magnesium alloys with calcium addition

The as-cast microstructure of AE42 was of typical dendritic and composed of the a matrix and some needle-shaped interphases Al11RE3. A small mount of Ca addition results in significant microstructural refinement and formation of a Al2Ca phase, which showed two kinds of morphologies, lamellar and tiny granular. The former distributes on grain boundaries and the later is within the matrix grains. With the increase of Ca addition the volume fraction of Al-RE compound (Al11RE3) decreases, but Al2Ca increases. Addition of Ca causes a significant increase of yield strength of the alloy both at ambient and elevated temperatures, but a little decrease of the ductility. With calcium addition the ultimate strength decreases at ambient temperature and 150°t, but increases at 175°C and 200°C.

Molecular dynamics study on temperature and strain rate dependences of mechanical tensile properties of ultrathin nickel nanowires

Based on the EAM potential, a molecular dynamics study on the tensile properties of ultrathin nickel nanowires in the （100〉 orientation with diameters of 3.94, 4.95 and 5.99 nm was presented at different temperatures and strain rates. The temperature and strain rate dependences of tensile properties were investigated. The simulation results show that the elastic modulus and the yield strength are gradually decreasing with the increase of temperature, while with the increase of the strain rate, the stress--strain curves fluctuate more intensely and the ultrathin nickel nanowires rupture at one smaller and smaller strain. At an ideal temperature of 0.01 K, the yield strength of the nanowires drops rapidly with the increase of strain rate, and at other temperatures the strain rate has a little influence on the elastic modulus and the yield strength. Finally, the effects of size on the tensile properties of ultrathin nickel nanowires were briefly discussed.

Tensile properties and microstructure of Ti14 alloy after semi-solid forging

Tensile properties of a new α＋Ti2Cu alloy after solid forging at 950 °C and semi-solid forging at 1 000 °C and 1 050 °C were investigated over the temperature range of 20-600 °C. The results reveal that high strength and low ductility are obtained in all semi-solid forged alloys. Tensile properties decrease as the semi-solid forging temperature increases, and cleavage fractures are observed after semi-solid forging at 1 050 °C. The variations in tensile properties are attributed to the coarse microstructures obtained in the semi-solid alloys. It is found that the elevated semi-solid temperatures lead to more liquid precipitates along the prior grain boundaries, which increases the peritectic precipitation and formation of Ti2Cu precipitation zones during re-solidification. Recrystallization heat treatment leads to fine microstructure of semi-solid forged alloys, resulting in improvement of tensile properties.

Effect of heat treatment on microstructure and tensile properties of A356 alloys

Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted.T6 treatment is a long time treatment（solution at 535 ℃ for 4 h ＋ aging at 150 ℃ for 15 h）.The other treatment is a short time treatment（solution at 550 ℃ for 2 h ＋ aging at 170 ℃ for 2 h）.The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy,scanning electronic microscopy and tension test.It is found that a 2 h solution at 550 ℃ is sufficient to make homogenization and saturation of magnesium and silicon in α（Al） phase,spheroid of eutectic Si phase.Followed by solution,a 2 h artificial aging at 170 ℃ is almost enough to produce hardening precipitates.Those samples treated with T6 achieve the maximum tensile strength and fracture elongation.With short time treatment（ST）,samples can reach 90% of the maximum yield strength,95% of the maximum strength,and 80% of the maximum elongation.

Microstructure and tensile properties of containerless near-isothermally forged TiAl alloys

Ti-47Al-2Nb-2Cr-0.4（W, Mo） （mole fraction, %） alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile properties were investigated. The results show that the TiAl ingot exhibits good heat workability during containerless near-isothermally forging process, and there are not evident cracks on the surface of as-forged TiAl pancake with a total deformation degree of 60%. The microstructure of the TiAl ingot appears to be typical nearly-lamellar（NL）, comprising a great amount of lamellar colonies （α2＋γ） and a few equiaxed γ grains. After near-isothermally forging, the as-forged pancake shows primarily fine equiaxed γ grains with an average grain size of 20 μm and some broken lamellar pieces, and some bent lamellas still exist in the hard-deformation zone. Tensile tests at room temperature show that ultimate tensile strength increases from 433 MPa to 573 MPa after forging due to grain refinement effect.

Orientation dependence of transverse tensile properties of nickel-based third generation single crystal superalloy DD9 from 760 to 1100 ℃

At temperatures ranging from 760 to 1100 °C, the tensile properties of a nickel-based third generation single crystal superalloy DD9 with [100],[120] and [110] orientations were studied. The microstructures and fracture surfaces were observed by OM, SEM and TEM. Results show that the tensile strength of [100] specimen is higher than that of [120] and [110] specimens at 760 and 850 °C;while at the temperatures higher than 980 °C, the tensile strength of all specimens has little difference. The fracture mechanisms of [100],[120] and [110] specimens are the same at 760 and 980 °C. At 1100 °C, the fracture surfaces of [100] and [120] specimens are characterized by dimple features;while [110] specimen shows mixed quasi-cleavage and dimple featured fracture surfaces. At 760 °C, obvious superlattice stacking faults (SSFs) are observed only in [100] specimen;while at 1100 °C, the dislocation configurations of all specimens are similar. The difference in the number of potential active slip systems in [100],[120] and [110] specimens during the tensile deformation process is the main reason for the transverse tensile anisotropy.

Microstructures,tensile properties and serrated flow of Al_xCrMnFeCoNi high entropy alloys

Microstructures and mechanical properties of dual-phase AlxCrMnFeCoNi (x=0.4, 0.5, 0.6, at.%) alloys were investigated. Thermomechanical processing leads to a microstructural evolution from cast dendritic structures to equiaxed ones, consisting of face-centered cubic (fcc) and body-centered cubic (bcc) phases in the two states. The volume fraction of bcc phase increases and the size of fcc grain decreases with increasing Al content, resulting in remarkably improved tensile strength. Specifically, the serrated flow occurring at the medium temperatures varies from type A+B to B+C or C as the testing temperature increases. The average serration amplitude of these Al-containing alloys is larger than that of CoCrFeNiMn alloy due to the enhanced pinning effect. The early small strain produces low-density of dislocation arrays and bowed dislocations in fcc grains while the dislocation climb and shearing mechanism dominate inside bcc grains. The cross-slip and kinks of dislocations are frequently observed and high-density-tangled dislocations lead to dislocation cells after plastic deformation with a high strain.

Effect of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn alloys

The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron microscopy(SEM)and tensile test.It is found that,as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist ofα-Mg+β-Li duplex matrix,MgLiAl2 and Li2Mg Sn phases.Increasing Sn content leads to grain refinement ofα-Mg dendrites and increase in content of Li2MgSn phase.During hot extrusion,complete dynamic recrystallization(DRX)takes place inβ-Li phase while incomplete DRX takes place inα-Mg phase.As Sn content is increased,the volume fraction of DRXedα-Mg grains is increased and the average grain size of DRXedα-Mg grains is decreased.Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys.Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.

Tensile properties of as-deformed 2A50 aluminum alloy in semi-solid state

Tensile properties of as-deformed 2A50 aluminum alloy were investigated in the high temperature solid and semi-solid states. The results show that temperature has almost no effect on the maximum tensile stress between 500 ℃ and 530 ℃, and the maximum tensile stress decreases rapidly when the temperature is above 532 ℃. The ductility decreases with increasing temperature and has an obvious fall when the temperature is above solidus temperature. This alloy almost has no ductility above 537 ℃, and cannot sustain tensile stress above 550℃. A brittle temperature range in which this alloy is prone to form microcracks was derived. The relation between microstructure, fraction solid and tensile properties were also investigated by examining the metallograph and fracture surface morphology of tested specimens, which could provide reference for forecasting the microcracks in this alloy occurring in semi-solid processing.

Microstructure and tensile properties of low cost titanium alloys at different cooling rate

Titanium and titanium alloys have several advantages, but the cost of titanium alloys is very expensive compared with the traditional metal materials. This article introduces two new low-cost titanium alloys Ti-2.1Cr-1.3Fe (TCF alloy) and Ti-3Al-2.1Cr-1.3Fe (TACF alloy). In this study, we used Cr-Fe master alloy as one of the raw materials to develop the two new alloys. We introduce the microstructure and tensile properties of the two new alloys from β solution treated with different cooling methods. Optical microscopy (OM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM) were employed to analyze the phase constitution, and scanning electron microscopy (SEM) was used to observe the fracture surfaces. The results indicate that the microstructures consist of β grain boundary and α′ martensite after water quenching (WQ), β matrix and α phase after air cooling (AC) and furnace cooling (FC), respectively. Also, the microstructure is the typical basketweave structures after FC. Of course, athermal ω is also observed by TEM after WQ. The strength increases with decreasing cooling rates and the plasticity is reversed. Because of the athermal ω, the strength and ductility are highest and lowest when the cooling method is WQ. The strength of TACF alloy is higher than the TCF alloy, but the plasticity is lower. The fracture surfaces are almost entirely covered with dimples under the cooling methods of AC and FC. Also, we observe an intergranular fracture area that is generated by athermal ω, although some dimples are observed after WQ.

Phase precipitation behavior and tensile properties of as-cast Ni-based superalloy during heat treatment

The phase precipitation behavior and tensile properties of an as-cast Ni-based alloy,IN617B alloy,after solution heat treatment and long-term aging treatment were investigated.Ti(C,N),M6C and M23C6 are the primary precipitates in as-cast microstructure.After solution heat treatment,most of carbides dissolve into the matrix except a few fine Ti(C,N)within grains.During long-term aging at 700°C,the phase precipitation behaviors of the alloy are characterized as follows:(1)M23C6 carbides at grain boundaries(GBs)transform from film-like shape to cellular shape and gradually coarsen due to the decrease of the surface energy and element aggregation to GBs;(2)M23C6 carbides within grains have a bar-like morphology with a preferential growth direction[110]and have a cube-on-cube coherent orientation relationship with the matrixγ;(3)γ?particles inhibit the coarsening of M23C6 within grains by constraining the diffusion of formation elements.Furthermore,the tensile strength of the alloy obviously increases,but the ductility significantly decreases after the aging for 5000 h.The alloy has a relatively stable microstructure which guarantees the excellent tensile properties during long-term aging.

Modifying microstructures and tensile properties of Mg-Sm based alloy via extrusion ratio

Microstructure and tensile properties of a Mg-Sm-Zn-Zr alloy with various extrusion ratios(ERs)of 6.9,10.4 and 17.6 were systematically investigated.It was identified that,greater ER increased dynamic recrystallization(DRX)fraction and coarsened DRX grains,which further suggests weakened basal fiber texture for the studied alloy.This is mainly due to the rising temperature from massive deformation heat when hot-extrusion.As a result,greater ER corresponds to a decreased strength but improved ductility.Finally,transmission electron microscopy(TEM)observations reveal that the dominant intermetallic phase,Mg_(3)Sm,is metastable,and it will transform into Mg_(41)Sm_(5)during extrusion with high-ER.This transformation leads to the accumulation of surplus Sm and Zn atoms,which induces the precipitation of Sm Zn_(3)phase at the surface of Mg_(41)Sm_(5)matrix.

Effect of Bi modification treatment on microstructure,tensile properties,and fracture behavior of cast Al-Mg_2Si metal matrix composite

Bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process, the present study investigated the effects of different concentrations of Bi on the microstructure, tensile properties, and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite. The results show that the addition of the proper amount of Bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite. With an increase in Bi content from 0 to lwt.%, the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape; and its average particle size is significantly decreased from 70 to 6 μm. Moreover, the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like. When the Bi addition exceeds 4.0wt.%, the primary Mg2Si becomes coarse again. However, the eutectic Mg2Si still exhibits the modified morphology. Tensile tests reveal that the Bi addition can improve the tensile strength and ductility of the material. Compared with those of the unmodified composite, the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% Bi increase 51.2% and 100%, respectively. At the same time, the Bi addition changes the fracture behavior from brittle to ductile.

Effect of axial force on microstructure and tensile properties of friction stir welded AZ61A magnesium alloy

The influences of axial force on tensile properties of friction stir welded AZ61A magnesium alloy were studied. Five different values of axial forces ranging from 3 to 7 kN were used to fabricate the joints. Tensile properties of the joints were evaluated and correlated with the stir zone microstructure and hardness. From this investigation, it is found that the joint fabricated with an axial force of 5 kN exhibits superior tensile properties compared to other joints. The formation of finer grains in the stir zone and higher hardness of the stir zone are the main reasons for the superior tensile properties of these joints.

Effects of microstructure on tensile properties of AA2050-T84 Al−Li alloy

The effect of microstructure evolution on the tensile properties of 2050 Al-Li alloy thick plate aged at 150 ℃ with 80 mm in thickness(t) was studied from a microstructural perspective. Scanning electron microscope, optical microscope, transmission electron microscope and X-ray diffractometer were used to explore the surface(t/6), interlayer(t/3) and center(t/2) thickness layer of this alloy. Results show that the secondary phases on grain boundaries, precipitates and textures vary depending on the thickness location. The precipitation strengthening has a stronger influence on the alloy along the rolling direction than the transverse direction from the under-aged to the peak-aging condition;however, its effect on the anisotropy is insignificant. The higher Taylor factor(M) value caused by stronger β fiber rolling textures and the intergranular phases is the main reason that leads to the highest strength at the t/2 position along the rolling direction. The M-value has a limited change at different thickness layers along the transverse direction, which causes the same tensile strength.