Effect of cyclic heat treatment on microstructures and mechanical properties of directionally solidified Ti-46Al-6Nb alloy

The Ti-46A1-6Nb （mole fraction, %） ingots that were directionally solidified by cold crucible were cyclic heat treated at 1330 ℃ in the a phase region. The microstructures and mechanical properties of the ingots before and after heat treatment were investigated. The results show that the large columnar grains are changed into equiaxed grains after heat treatment. The grain size decreases with increasing the cyclic times, which is caused by the recrystallization and the transition from the large grain of small lamellae to the small grain of large lamellae. Four times of cyclic heat treatment refines the grain size from 1.33 mm to 0.59 turn, nevertheless the lamellar spacing increases from 0.71 ~tm to 1.38 lim. Extending the holding time and increasing the cyclic times of heat treatment eliminate the fl-segregation at the grain boundary and the interlamellar. The compression testing shows that the compressive strength of the directionally solidified ingot in the parallel and perpendicular directions are 1385.09 MPa and 1267.79 MPa, respectively, which are improved to 1449.75 MPa and 1527.76 MPa after two and four times of cyclic heat treatment, respectively, while that is 1180.64 MPa for the as-cast sample. The fracture mode of the sample after cyclic heat treatment is quasi-cleavage fracture.

Formation of fine fully-lamellar microstructure of TiAl-based alloy in rapid heating cyclic heat treatment process

The optical observation results of neocrystallization nucleation and growth of fine fully lamellar (FFL) α 2/ γ microstructure of a TiAl based alloy in rapid heating cyclic heat treatment process were reported. The characteristics of α+γ→α transformation under rapid heating conditions were analysed. A model for explaining the nucleation and growth mechanism of FFL α 2/ γ microstructure was proposed.

Effect of cyclic heat treatment on microstructure and mechanical properties of 50CrV4 steel

An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 °C(below Ac1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.

Microstructural Evolution of Cast Hyper-Eutectic Al-18% Si Alloy during Cyclic Semi-Solid Heat Treatment

The cyclic semi-solid heat treatment represents a promising technique for improving microstructure and mechanical properties of a wide range of metallic alloys. In the current research the influence of cyclic semi-solid heat treatment on microstructure of Al-18% Si alloy containing 0.8% Fe has been studied. All specimens were heated in an electrically heated resistance furnace with heating rate of 10°C·min-1 to 585°C. For a complete one cycle heat treatment (5 min heating time), samples after 5 min holding at 585°C were cooled to a temperature of 550°C in still air cooling and the samples were taken out immediately for water quenching. It was found that heat treatment cycles should be limited to 3 cycles or less in order to maintain fine grain size and globular structure without agglomeration and coalescence. Cyclic semi-solid heat treatment changes morphology of iron-rich intermetallics phases to be plate-like and fine plate iron-rich intermetallics phases, in stead of needle-like iron-rich intermetallics phases that are observed in as-cast samples. Cyclic heating shows a relatively higher hardness for all heating cycles compared with as-cast one due to its finer and globular structure. Cyclic semi-solid heat treatment technique results in lower coarsening rate constant compared with isothermal heat treatment one due to coarsening discontinuous effect.

Constitutive Model of Saturated Soft Clay with Cyclic Loads under Unconsolidated Undrained Condition

An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established.

Study on the Characteristics of Gut Microbiota in Chronic Hepatitis B(CHB)Patients with Damp Heat Syndrome and Liver Depression and Spleen Deficiency Syndrome

Objective:This study was designed to explore the characteristics of gut microbiota in CHB patients with two most common traditional Chinese medicine(TCM)Syndromes—damp heat syndrome and liver depression and spleen deficiency syndrome.Methods:According to the diagnostic criteria of Western medicine,TCM and screening exclusion criteria,65 cases of CHB with damp heat syndrome and 28 cases of CHB with liver depression and spleen deficiency syndrome were finally included in the study.All the basic information was gathered and the fresh fecal samples were collected for 16S rDNA sequencing.16S rDNA of gut microbiota was sequenced using Illumina hiseq 2,500 high-throughput sequencing platform.Based on the optimized sequence,Operational Taxonomic Units(OTU)clustering analysis and taxonomic annotation were carried out.Results:The difference in relative abundance of gut microbiota was significant between damp heat syndrome and liver depression and spleen deficiency syndrome in CHB patients.Cyanobacteria was only found in damp heat syndrome.The relative abundance of Erysipelotrichia and Subdoligranulum were higher in liver depression and spleen deficiency syndrome,while the relative abundance of Rhodospirillales,Alphaproteobacteria and Lachnospira were higher in the damp heat syndrome.LDA Effect Size(LEfSe)analysis showed that Lachnospira,Olsenella and Subdoligranulum had significant difference in species among the two TCM syndromes.Conclusion:The different characteristics of gut microbiota in the two TCM syndromes of CHB patients may play an important role in syndrome formation of TCM,which provides a new field of vision for the accurate diagnosis and treatment of TCM.

Performance and Optimization of Air Source Heat Pump Water Heater with Cyclic Heating

A new type of microchannel condenser applied in the air source heat pump water heater(ASHPWH)with cyclic heating was proposed in this study.The operating performance of the ASHPWH was frst tested.Then,the structure of the microchannel condenser was optimized with the implement of vortex generators.Finally,a numerical model of the ASHPWH was established and the optimized microchannel condenser was studied.The experimental results showed that the average coefficient of performance(COP)of the 1HP(735 W)ASHPWH reached 3.48.In addition,the optimized microchannel condenser could be matched with a 3 HP(2430W)ASHPWH with an average heating capacity of 10.30 kW,and achieving an average COP of 4.24,14.6%higher than the limit value in the national standard.

Modeling and cyclic behavior of segmental bridge column connected with shape memory alloy bars

This paper examines the quasi-static cyclic behavior, lateral strength and equivalent damping capacities of a system of post-tensioned segmental bridge columns tied with large diameter martensitic Shape Memory Alloy （SMA） link-bars. Moment-curvature constitutive relationships are formulated and analysis tools are developed for the PT column, including a modified four-spring model prepared for the SMA bars. The suggested system is exemplified using a column with an aspect ratio of 7.5 and twelve 36.5 mm diameter NiTi martensitic SMA bars. A post-tensioning force of 40% to 60% of the tendon yield strength is applied in order to obtain a self re-centering system, considering the residual stress of the martensitie SMA bars. The cyclic response results show that the lateral strength remains consistently around 10% of the total vertical load and the equivalent viscous damping ratios reach 10%-12% of critical. When large diameter NiTi superelastic SMA bars are incorporated into the column system, the cyclic response varies substantially. The creep behavior of the superelastic SMA bar is accounted for since it affects the re-centering capability of the column. Two examples are presented to emphasize the modeling sensitivities for these special bars and quantify their cyclic behavior effects within the column assembly.

Preparation and Characterization of Phenolic Prepolymer Impregnated Chinese Fir by Cyclic Increasing-Pressure Method with Green and Efficient

The Chinese fir wood was impregnated using a cyclic increasingpressure method(CIPM)with phenolic prepolymers as the impregnating modifier.Unmodified Chinese fir and progressive increasing-pressure method(PIPM)impregnated Chinese fir were used as reference samples and were compared and analyzed.The product’s chemical structure,internal morphology,crystal structure,and heat resistance were characterized.The transversal and longitudinal sections showed better filling effects,so that it bore greater external loading and reduced the water storage space.CIPM infused more phenolic prepolymer into the Chinese fir.Not only producing more physical filling but also forming more hydrogen bond associations and chemical bond combinations.Compared with PIPM and unmodi-fied Chinese fir,the CIPM impregnated Chinese fir had better mechanical strength and water resistance.The cellulose chains in CIPM impregnated Chinese fir were more closely linked and their crystallinity were clearly improved.Changes in internal morphology and crystal structure explained the reason why the mechanical properties and water resistance of CIPM impregnated Chinese fir were improved significantly.This Chinese fir had lower thermal decomposition rates,higher decomposition residual rates,and smaller combustion flames,which confirmed that it possessed improved heat and fire resistance.

Cyclic behavior of reinforced sand under principal stress rotation

Although the cyclic rotation of the principal stress direction is important,its effect on the deformation behavior and dynamic properties of the reinforced soil has not been reported to date.Tests carried out on large-scale hollow cylinder samples reveal that the cyclic rotation of the principal stress direction results in significant variations of strain components(ε,ε,εand γ) with periodic characteristics despite the deviatoric stress being constant during tests.This oscillation can be related to the corresponding variations in the stress components and the anisotropic fabric that rotate continuously along the principal stress direction.Sand under rotation appears to develop a plastic strain.Similar trends are observed for reinforced sand,but the shear interaction,the interlocking between particles and reinforcement layer,and the confinement result in significant reductions in the induced strains and associated irrecoverable plastic strains.Most of the strains occur in the first cycle,and as the number of cycles increases,the presence of strains becomes very small,which is almost insignificant.This indicates that the soil has reached anisotropic critical state(ACS),where a stable structure is formed after continuous orientation,realignment and rearrangement of the particles accompanied with increasing cyclic rotation.Rotation in the range of 60°-135° produces more induced strains even in the presence of the reinforcement,when compared with other ranges.This relates to the extension mode of the test in this range in which σ>σand to the relative approach between the mobilized plane and the weakest horizontal plane.Reinforcement results in an increase in shear modulus while it appears to have no effect on the damping ratio.Continuous cycles of rotation result in an increase in shear modulus and lower damping ratio due to the densification that causes a decrease in shear strain and less dissipation of energy.

PSI-driven cyclic electron fl ow partially alleviates the peroxidation of red alga Gelidium amansii(Gelidiaceae)caused by temporary high temperature

PSI-driven cyclic electron fl ow(CEF-I)helps higher plants avoid severe heat damage.Gelidium amansii,a red seaweed used in the production of agar,inhabits subtidal rocks but can be found in the intertidal zone.The biological role of CEF-I is still unclear in this organism.Wild G.amansii was exposed to 30℃heat stress for 12 h with continuous lighting.The results showed that treatment at 30℃gradually decreased maximal PSII photochemical effi ciency(F_(v)/F_(m)),linear electron transfer rate,and activity of photosynthetic reaction center.Both the maximal photochemical effi ciency under light(F_(v)'/F_(m)')and maximum quantum yield of light-adapted PSII(Φ_(PSII))were maintained at a relatively stable level during the initial 6 h and then signifi cantly decreased at 12 h.The up-regulated CEF-I helps to enhance proton gradient transfer across thylakoid membrane to protect oxygen-evolving complex against heat damage.Following the addition of a CEF-I inhibitor to plants,the F_(v)/F m greatly decreased,suggesting that the CEF-I alleviates degree of photoinhibition caused by strong light.The results of measurement of antioxidant enzymes,including superoxide dismutase(SOD),ascorbate peroxidase(APX)and catalase(CAT),and the contents of H_(2)O_(2)and malonaldehyde(MDA)provided additional evidence that CEF-I plays a protective role to a certain extent for G.amansii to manage stress at 30℃.Therefore,it can be concluded that CEF-I enables G.amansii to survive in intertidal zones by protecting it from the heat damage caused by high temperature stress.

Properties of Surface Cyclic Oligomers Present on Polyester Fiber

The effects of different treatments, such as dry heat,wet heat, solvent vapor and ultrasonic, on propertiesof the cyclic oligomers on the surface of polyester fiberare studied. The components of surface oligomers areanalyzed through Thin-Layer Chromatograph. Theresult shows that: all of the treatment, especially solvent vapor treatment,call significantly increase the content of surface cyclic oligomers.The content of cyclic triIner is increased more considerably than other oligomers. Moreover,the morphology and thedistribution of surface cyclic oligomers are also different from different treatments:Dry heat and wet heat cause larger polygonal solids distributed evenly on the surface of fiber;solvent vapor nlakes fiber surface exhibit irregular rodlike crystal shapes randomly;ultrasonic treatment induces some obscureand smaller deposi^on the surface of fiber.

Effect of cyclic heat treatment on microstructure and mechanical properties of laser aided additive manufacturing Ti-6Al-2Sn-4Zr-2Mo alloy

Globularαphases can significantly improve the ductility of titanium alloys.Cyclic heat treatment(CHT)has been proved to be an effective way to induce the formation of globularαphases inα+βtitanium alloy Ti-6Al-4V fabricated by laser aided additive manufacturing(LAAM).However,there is no prior research reporting methods for obtaining globularαphases in LAAM-built near-αtitanium alloys.This work investigated the cyclic heat treatment(CHT)procedures suitable for the LAAM-built near-αtitanium alloy Ti-6Al-2Sn-4Zr-2Mo(Ti6242)to attain the globularαphases.The results show that 980​℃ is the most suitable upper temperature limit for CHT.However,it is difficult to achieve a high volume fraction of the globularαphases in the LAAM-built Ti6242 alloys through CHT,which is ascribed to the low composition gradient caused by moreα-stabilizing elements and fewerβ-stabilizing elements.The as-built sample demonstrated elongation of 6.3%,which is lower than the AMS 4919J standard(elongation≥10%).After 980​℃ CHT and 980​℃ CHT with solution heat-treatment,the formation of the globularαphases significantly increased the elongation to 13.5%and 12.9%,respectively.Although the mechanical strength is reduced after heat-treatment,the room-temperature tensile properties still exceed the AMS 4919J standard.Fractography examination showed that the as-built sample exhibited a mixed brittle and ductile fracture behavior,while the 980​℃ CHT and 980​℃ CHT with solution heat-treated samples displayed ductile fracture.

Strength-toughness improvement of 13Cr4NiMo martensitic stainless steel with thermal cyclic heat treatment

To improve the strength-toughness of 13Cr4NiMo martensitic stainless steel(13-4MSS),a thermal cyclic heat treatment(TCHT)combined with the advantage of tempering was proposed.The microstructures were characterized by scanning electron microscopy,X-ray diffraction and electron backscattered diffraction,and the mechanical behaviors in terms of tensile properties and impact toughness were analyzed in correlation with microstructural evolution.It was found that grains and the martensitic matrix were refined by TCHT through the cyclic quenching transformation and austenite recrystallization,which was conducive to more nucleation quantity of reversed austenite during tempering.Two-sphericalcap nucleation model was used to explain the effect of refined grains of TCHT on the nucleation of reversed austenite.Grain refinement by TCHT improved the brittle fracture stress to reduce the ductile-brittle transition temperature and thus improved the cryogenic impact toughness of 13-4MSS.Reversed austenite distributed at the martensitic lath boundary enhances the crack arrest performance and increases the britle fracture stress.It is concluded that reasonable TCHT plus tempering process significantly improves the strength-toughness of 13-4MSS,reflecting the comprehensive effect of grain refinement and reversed austenite.

Effect of cyclic heat treatment on abnormal grain growth in Fe-Mn-Al-based shape memory alloys with different Ni contents

Cyclic heat treatment that can continuously promote abnormal grain growth is widely used for the prepa-ration of single-crystal Fe-Mn-Al-based shape memory alloys.However,it takes a long time to prepare large-size Fe-Mn-Al-based alloy single crystals via the reported cyclic heat treatments.Meanwhile,the long-time cyclic heat treatment at high temperatures leads to the development of defects including oxidation and a decrease in Mn,which would deteriorate superelasticity in the Fe-Mn-Al-based shape memory alloys.To shorten the fabrication time of single crystals,the effect of the cyclic heat treatment process on the abnormal grain growth in the Fe-Mn-Al-based alloys with different Ni contents was systematically investigated.It is found that the abnormal grain growth of Fe-Mn-Al-based alloys was not significantly affected by the Ni contents(within 2.1 at.%-6.2 at.%).In addition,the abnormal grain growth could be promoted by 1-2℃ min^(-1) cooling rate,high solution temperature,and multiple cycles,while it was insensitive to other processes including heating rate,dual-phase time as well as long-time solution treat-ment.These findings can guide optimizing the fabrication process of single crystals by cyclic heat treat-ment.Finally,the Fe_(41.9)Mn_(37.8)Al_(14.1) Ni_(6.2) single crystal prepared by the optimized cyclic heat treatment showed a recoverable strain of about 4%.

Microstructure and damping properties of LPSO phase dominant Mg-Ni-Y and Mg-Zn-Ni-Y alloys

This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.

Experimental Study on Transient Natural Convection in a Cube Enclosure with an Isolated Vertical Cyclically Heated Plate

The low frequency cyclical transient natural convection in a cube enclosure with an internal isolated vertical heated plate was investigated experimentally. A computer-aided experimental system was designed to generate the cyclical heating power input and also used for data reduction. The effects of the cyclic heating power input amplitude (from 0 to 8 W) and frequency (from 1/5400 s-1 to 1/600 s-1)as well as the per-cycle time-average power input (from 8 to 24 W) on the transient and time-average Nusselt number were parametrically studied. It was found that for such cyclical transient natural convection with low frequency, the plate heating power input amplitude and frequency have little effects on the time-average Nusselt number as long as the cyclical time-average heating power input remains the same, although the transient Nusselt number may be significantly affected. Therefore, the modified Grashof number based on the plate average heat flux can be used to characterize the time-average heat transfer process. The plate time-average Nusselt number is about 15% less than the infinite-space Nusselt number. The location of the isolated plate in enclosure does not appreciably influence the time-average heat transfer characteristics of the plate.

Heat Transfer,Knock Modeling and Cyclic Variability in a “Downsized”Spark-Ignition Turbocharged Engine

In the present paper a combined procedure for the quasi-dimensional modelling of heat transfer,combustion and knock phenomena in a “downsized”Spark Ignition two-cylinder turbocharged engine is presented.The procedure is extended to also include the effects consequent the Cyclic Variability.Heat transfer is modelled by means of a Finite Elements model.Combustion simulation is based on a fractal description of the flame front area.Cyclic Variability(CV)is characterized through the introduction of a random variation on a number of parameters controlling the rate of heat release(air/fuel ratio,initial flame kernel duration and radius,laminar flame speed,turbulence intensity).The intensity of the random variation is specified in order to realize a Coefficient Of Variation(COV)of the Indicated Mean Effective Pressure(IMEP)similar to the one measured during an experimental campaign.Moreover,the relative importance of the various concurring effects is established on the overall COV.A kinetic scheme is then solved within the unburned gas zone,characterized by different thermodynamic conditions occurring cycle-by-cycle.In this way,an optimal choice of the “knock-limited”spark advance is effected and compared with experimental data.Finally,the CV effects on the occurrence of individual knocking cycles are assessed and discussed.

Laboratory investigation on damping characteristics of homogeneous and stratified soil-ash system

In this study,the damping responses of uniform soil,equi-proportional fly ash,and local soil as a single unit were investigated.The large-strain cyclic triaxial tests were performed for the specimen compacted at the desired density(95%e99%of maximum dry density).The compacted specimens were tested under the loading frequency of 0.3e1 Hz with medium confinement of 70e100 kPa.Also,the unsymmetrical behavior of the hysteresis loop was analyzed using three different damping estimation approaches,i.e.symmetric hysteresis loop(SHL),asymmetric hysteresis loop(ASHL),and the modified American Society for Testing and Materials(ASTM)method.The outcome of the study shows for fly ash,local soil,and layered soil-ash,the ASHL technique has the highest damping value,followed by ASTM and then the SHL approach.The specimens prepared under high density and subjected to high confinement show low damping values.However,the specimens tested at high frequency exhibits high damping behavior.Similarly,the damping value of fly ash determined using the SHL and ASHL methods has a similar profile and reaches a maximum at 1%shear strain value before decreasing.The composite stratified deposit exhibits more dependency on relative compaction,confining pressure,and less on loading frequency.Based on the results,it is highly recommended to use the ASHL approach,especially under large strain conditions irrespective of soil type.The maximum damping ratio of stratified deposits is always in between the damping ratio of local soil and fly ash.The damping ratio of stratified soil and local soil is slightly larger than that of the other soils,although the damping ratio of fly ash is equivalent to that of the sand and clayey soil.These results may be helpful in the accurate determination of the damping properties of the layered soil-ash system that is required in the seismic response analysis.

Experimental study on cyclic deformation properties of saturated Fujian sand at different loading frequencies

In this study,a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction(shearing contractive(SC)period and initial shearing dilative(ISD)period)and post-liquefaction(late shearing dilative(LSD)period)deformation properties of saturated Fujian sand.The secant shear modulus G and damping ratioλin the entire cyclic loading process,and the unloading tangent shear modulus G_(L1)and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude ca.The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent.However,all the G-γ_(a),G_(L1)-γ_(a),and GL2-ca curves in the ISD and LSD periods showed a downward trend with an increase in f.This study also proposes a modified method for calculatingλto compensate for the analytical error caused by the non-closure of hysteresis loop.Compared with the classical curves that mainly applied in geotechnical engineering,theλfirst increases and then decreases with the increase ofγa.Furthermore,theλevaluated by the modified method is approximately 10%–15%more than theλevaluated by the traditional method when theλreaches its peak value.