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(0.47 μm) < residual matrix region in the pre-twinned material(1.71 μm) < matrix region in the extruded material(2.55 μm).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.

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.

Effects of caliber rolling on microstructure and room temperature tensile properties of Mge3Ale1Zn alloy

Mge3Ale1Zn(AZ31)alloy was caliber rolled isothermally in the temperature range of 250e450
C to develop fine grains of 3.6e12.5 mm.The stressestrain curves obtained from tensile tests at room temperature were found to vary with the temperature employed in caliber rolling.Maximum tensile strength of 290 MPa and ductility of 13.5%were obtained upon caliber rolling at 300
C as compared to 188 MPa and 15.2%,respectively,in the mill-rolled condition.The variations in tensile properties are explained by the concomitant grain size,texture and twins obtained as a function of caliber rolling temperature.

Effects of La addition on the microstructure and tensile properties of Al-Si-Cu-Mg casting alloys

The effects of La addition on the microstructure and tensile properties of B-refmed and Sr-modified A1-1 1Si-1.5Cu-0.3Mg cast- ing alloys were investigated. With a trace addition of La （0.05wt%-0. lwt%）, the mutual poisoning effect between B and Sr can be neutral- ized by the formation of LaB6 rather than SrB6. By employing a La/B weight ratio of 2：1, uniform microstructures, which are characterized by well refined ct-A1 grains and adequately modified eutectic Si particles as well as the incorporation of precipitated strengthening intermetal- lics, are obtained and lead to appreciable tensile properties with an ultimate tensile strength of 270 MPa and elongation of 5.8%.

IMPROVEMENT IN TENSILE PROPERTIES OF α+β TYPE Ti ALLOYS BY HYDROGEN TREATMENT

A new process to refine the microstructure of α+βtvpe Ti alloys was developed by using hydrogen as a temporary alloying element.It involves hydrogenating the alloys below the hydrogenated β transus temperature about 0-40 K,air cooling to room temperature and then dehydrogenating at 948 K.Ti-6AI-4V and Ti-5AI-2.5Fe alloys treated hy this new process show much refined microstructures,and the yield strength,ultimate strength as well as the elongation increase 8—15,5—13 and 7—14% respectively

Microstructures and tensile properties of submerged friction stir processed AZ91 magnesium alloy

6 mm thick AZ91 casting alloy plates were subjected to normal friction stir processing(NFSP,in air)and submerged friction stir processing(SFSP,under water),and microstructures and tensile properties of the experimental materials were investigated.After FSP,the coarse microstructures in the as-cast condition are replaced by fine and equiaxed grains and the network-like eutecticβ-Mg_(17)Al_(12)phases disappear and are changed into particles pinned at the grain boundaries.SFSP results in further grain refinement in comparison with NFSP,and the average grain sizes of the NFSP and SFSP alloys are 8.4±1.3 and 2.8±0.8µm,respectively.XRD results reveal that the intensity ofβ-Mg_(17)Al_(12)diffraction peaks in the SFSP specimen decreases compared with NFSP.Due to significant grain refinement,the tensile strength and elongation of the SFSP AZ91 alloy are increased from 262 MPa and 18.9%for the NFSP material to 282 MPa and 25.4%,and the tensile strength(282 MPa)is nearly three times that of the BM(105 MPa).SFSP is an effective approach to refine the grain size and enhance the tensile properties of AZ91 casting alloy.

Tensile Properties of Surface-Treated Glass Fiber Reinforced PTFE Composite with Rare Earth Elements

The optimum amount of rare earth elements (RE) for treating glass fiber surface and its effect on the tensile properties of glass fiber reinforced polytetrafluoroethylene (GF/PTFE) composites were investigated. The tensile properties of GF/PTFE composites with different surface treatment conditions were measured. The fracture surface morphologies were observed and analyzed by SEM. The results indicate that rare earth elements can effectively promote the interfacial adhesion between the glass fiber and PTFE, owing to the effects of rare earth elements on the compatibility. The tensile properties of GF/PTFE composites can be improved considerably when the content of RE in surface modifier is 0.2%～0 4%, and the optimum performance of GF/PTFE composites is obtained at 0.3%RE content.

Texture development and tensile properties of Mg?Yb binary alloys during hot extrusion and subsequent annealing

Ytterbium(Yb)containing magnesium alloys have aroused extensive interest due to their excellent mechanical properties after thermomechanical processing and heat treatment.Unfortunately,the sole effect of Yb addition on the microstructure and mechanical properties of pure Mg matrix remains uncertain to date.In this work,the effects of Yb concentration on the texture development and tensile properties of pure Mg matrix during hot extrusion and the subsequent annealing were systematically investigated.The results revealed that the constitutional supercooling induced by Yb addition refined the as-cast microstructure but exerted a negligible effect on the original columnar grain morphology.When extruded at 300°C,the dynamic recrystallization(DRX)process was considerably retarded.The in-grain misorientation axes(IGMA)analysis combined with TEM observation indicated that non-basal slips operated with increasing Yb concentration.Specifically,the prismaticslip should be robustly activated in Mg-1.0 Yb extrudate,promoting the formation of the texture with{10?10}plane normal to the extrusion direction(ED),while for the Mg?2.0 Yb counterpart,the increased activity of pyramidal<c+a>slip and the relaxation of basal/<c+a>dislocations generated an ED-tilted texture component.The preferential grain growth dominated the subsequent annealing texture development at 400°C when a comparable grain size was achieved.An obvious ED-tilted texture intensity with the peak around<12 13>was observed in Mg-2.0 Yb alloy,which was primarily caused by grains with the basal orientation vanished and with the non-basal orientations intensified due to a higher concentration of Yb solute.Favored by the grain refinement,the Mg-2.0 Yb extrudate exhibited a high tensile yield strength of 304±3.5 MPa,while the subsequently annealed counterpart presented a favorable elongation to failure of 14.8±1.2%,which mainly due to the homogeneous grain structure,weak ED-tilted texture,and dissolution of coarse phases after high-temperature annealing.

Influence of rapid heating process on the microstructure and tensile properties of high-strength ferrite–martensite dual-phase steel

Three low-carbon dual-phase （DP） steels with almost constant martensite contents of 20vo1% were produced by intercritical annealing at different heating rates and soaking temperatures. Microstructures prepared at low temperature （1043 K, FH1） with fast-heating （300 K/s） show banded ferrite/martensite structure, whereas those soaked at high temperature （1103 K, FH2） with fast heating reveal blocky martensite uniformly distributed in the fine-grained ferrite matrix. Their mechanical properties were tested under tensile conditions and compared to a slow-heated （5 K/s） reference material （SH0）. The tensile tests indicate that for a given martensite volume fraction, the yield strength and total elongation values are noticeably affected by the refinement of ferrite grains and the martensite morphology. Metallographic observations reveal the formation of microvoids at the ferrite/martensite interface in the SH0 and FH2 samples, whereas microvoids nucleate via the fracture of banded martensite particles in the FH1 specimen. In addition, analyses of the work-hardening behaviors of the DP microstructures using the differential Crussard-Jaoul technique demonstrate two stages of work hardening for all samples.

Microstructure and tensile properties of thixo-diecast AZ91D magnesium alloy

The thixo-diecasting(TDC)process is the combination of semi-solid billet preparation technology and die casting technology.The TDC process not only keeps the characteristics of thixo-forming but also has high efficiency and low cost.In the present work,the microstructures and mechanical properties of an AZ91D magnesium alloy prepared by the thixo-diecasting(TDC)process were characterized in as-cast condition.The TDC alloy produced exhibits a unique microstructure containingα-Mg solid solution andβ-Mg17Al12intermetallic compound,and there are some small droplets and a small gray globule with eutectic structure in the primaryα-Mg grains.The ultimate tensile strength and elongation of the TDC alloy also increase in comparison with other processes,such as thixocasting.Fracture surface observation shows that a crack mainly originates from the brittle fracture of the eutectic phases.The deformation of ductileα-Mg phase provides the TDC alloy with the main strain.

Strain rate sensitivity of tensile properties in high Nb containing TiAl alloys

The effect of strain rate on the yield strength of high Nb containing TiAl alloy was studied. The results show that the strain rate sensitivity varies with the test temperature, and the yield strength is not sensitive to the strain rate at room temperature but significantly sensitive to the strain rate at high temperature. An increase of the strain rate or a decrease of the temperature results in an obvious change of fracture mode. It is found that the strain rate sensitivity of this alloy varying with temperature is due to the dislocation climb generated at high temperature.

Grain boundary characteristics and tensile properties of Ti14 alloy after semi-solid deformation

The microstructure and room-temperature tensile properties of Ti14,a new α＋Ti2Cu alloy,were investigated after conventional forging at 950°C and semi-solid forging at 1000 and 1050°C,respectively.Results show that coarse grains and grain boundaries are obtained in the semi-solid alloys.The coarse grain boundaries are attributed to Ti2Cu phase precipitations occurred on the grain boundaries during the solidification.It is found that more Ti2Cu phase precipitates on the grain boundaries at a higher semi-solid forging temperature,which forms precipitated zones and coarsens the grain boundaries.Tensile tests exhibit high strength and low ductility for the semi-solid forged alloys,especially after forging at 1000°C.Fracture analysis reveals the evidence of ductile failure mechanisms for the conventional forged alloy and cleavage fracture mechanisms for the alloy after semi-solid forging at 1050°C.

Influence of Homogenization on the Microstructure and Tensile Properties of Extruded Mg-Zn-Zr-RE Alloy

The microstructure and tensile properties of the extruded Mg-Zn-Zr-RE alloy bars are studied.The extruded bar without previous homogenization has the highest tensile strength,whereas the tensile strength of the extruded bar previously homogenized at 400℃ or 380℃ is lower.During long time homogenization,the trans- formation of rare earth compounds Mg_3REZn_6(Z phase)and Mg_3RE_2Zn_3(W phase)into Mg_(41)RE_5 and Mg Zn phases occurr and the MgZn phase grow up.In addition,the dynamic recrystallization takes place in sub- sequent extrusion that caused decrease of the tensile strength.

Influence of magnetically constricted arc traverse speed (MCATS) on tensile properties and microstructural characteristics of welded Inconel 718 alloy sheets

The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone.This paper reports the direct effect of magnetically constricted arc traverse speed(MCATS)on bead profile,tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding(GTCAW)process.The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing.It is correlated to the solidification conditions during welding.The relationship between MCATS and Arc Constriction Current(ACC)was derived.Its interaction effect on the magnetic arc constriction and joint performance was analysed.Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties(98.39% of base metal strength with 31.50% elongation).It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer,discrete laves phase in interdendritic areas.

Experimental Study on Tensile Properties of Steel Plate Bonded by CFRP

The tensile properties of five groups of composite specimens, which consist of steel plate bonded by CFRP,were experimentally researched. The failure types, performing characteristics and failure mechanism of the composite specimens were investigated in detail. The influence of different ratio of CFRP on bearing capacity, loading-strain curves, compound modulus, rigidity and ductility of the composite specimens was analyzed. The experimental results indicate that the composite specimen can work harmonically and the steel plate does not break in tension. Comparing with steel plate, the bearing capacity and the rigidity of the composite specimens increase and ductility decreases. The bearing capacity increases sharply with the increase in the number of layers of CFRP. With the increase in CFRP, the yield strength increases slightly and ductility decreases. The experimental researches can provide a theoretical basis for engineering application of combination strengthening.