Solute cluster size effect on the fatigue crack propagation resistance of an underaged Al–Cu–Mg alloy

The effect of Cu–Mg cluster size and number density on the fatigue fracture behavior of Al–Cu–Mg alloy with various aging conditions was investigated by means of transmission electron microscopy (TEM), atom probe tomography (APT), scanning electron microscopy (SEM) and fatigue testing. Results showed that the fatigue crack propagation (FCP) resistances of 170 °C/1 h and 170 °C/8 h samples were higher than that of 170 °C/0.5 h sample due to increased number density of great size Cu–Mg co-clusters (>50 atoms). These large clusters were harder to dissolve during cycle deformation, thus reduced the cyclic softening effect and enhanced the FCP resistance. Moreover, as aging prolonged, the critical shear stress (τ_m) of co-clusters by modulus hardening increased from 10.2 (MPa) in 170 °C/0.5 h sample to 12.4 in 170 °C/1 h sample and 12.1 in 170 °C/8 h sample. Thus the force required for the movement of dislocations impeded by co-clusters, as well as the resistance of FCP caused by co-clusters, in 170 °C/1 h and 170 °C/8 h sample was higher than that in 170 °C/0.5 h sample. The 170 °C/8 h sample possessed the lower FCP resistance than 170 °C/1 h sample because of the existence of S′ phase. S′ phase was a kind of semi-coherent unshearable precipitate and hence reduced the planar-reversible slip.     

Research on heat treatment of TiBw/Ti6Al4V composites tubes

Heat treatment with different parameters were performed on the hot-hydrostatically extruded and swaged 3.5 vol.% TiBw/Ti6Al4V composites tubes. The results indicate that the primary α phase volume fraction decreases and transformed β phase correspondingly increases with increasing solution temperatures. The α + β phases will grow into coarse α phases when the aging temperature is higher than 600 °C. The hardness and ultimate tensile strength of the as-swaged TiBw/Ti6Al4V composite tubes increase with increasing quenching temperatures from 900 to 990 °C, while they decrease with increasing aging temperatures from 550 to 650 °C. A superior combination of ultimate tensile strength (1388 MPa) and elongation (6.1%) has been obtained by quenching at 960 °C and aging at 550 °C for 6 h. High temperature tensile tests at 400–600 °C show that the dominant failure modes at high temperatures also differ from those at room temperature.     

Synthesis and optical properties of photochromic perinaphthothioindigo

(1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel–Crafts route and its photochemical properties in toluene and polymethylmethacrylate (PMMA) have been characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form (cis-PNT, λ_max = 484 nm) and a purple form (trans-PNT, λ_max = 595 nm). The stable purple form converts to the yellow form with a trans-PNT to cis-PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis-PNT to trans-PNT quantum efficiency of conversion of 0.27–0.85 in toluene and 0.17–0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its λ_max of 484 nm. trans-PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis-PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 h in toluene (25 °C) and even slower, 168 h, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage.     

Microstructure and tribological characteristics of aged Co–28Cr–5Mo–0.3C alloy

In this study, an attempt to investigate the role of isothermal aging on the microstructure and tribological characteristics of Co–28Cr–5Mo–0.3C alloy was made. Regarding the results, isothermal aging at 850 °C and 950 °C for at least 16 h contributed to the formation of lamellar-type carbides at the grain boundary regions. Moreover, at higher aging times (over 16 h), the amount of lamellar-type carbides decreased. The wear properties of as-cast and heat treated samples were determined at 0.5 ms⁻¹ speed several under normal applied loads such as 50, 80, and 110 N. At the lowest applied load (50 N), the samples were isothermally aged at 850 °C for 8 and 16 h and also the ones were aged at 950 °C for 16 h had higher wear resistance probably due to more volume fraction of lamellar-type carbides when compared to as-cast and the other aged samples, but, at higher applied loads (80 and 110 N) due to the formation of adhesive oxide layer on the as-cast sample surface, the wear rate of as-cast samples is lower compared with all heat treated ones.     

The influence of chemical composition and thermo-mechanical treatment on Ti–Nb–Ta–Zr alloys

Ti–Nb–Ta–Zr quaternary alloying system is very promising for biomedical alloys. It is due to good mechanical properties and corrosion resistance of titanium alloys. Moreover no potentially harmful elements are contained in this system.Mechanical properties were influenced by changing the chemical composition and by various heat-treatment operations. The alloys were prepared by arc melting and then they were hot forged (900–1000 °C). After solution treatment 850 °C/0.5 h/water quenched, cold swaging was carried out with section reduction about 85%. As final heat treatment aging at 450 °C/8 h/furnace cooling was used.Mechanical properties were measured from tensile tests results at cold swaged and aged specimens. The microstructure was observed by using light microscopy and transmission electron microscopy (TEM)-thin foils method. X-ray diffraction analysis reveals the phase composition. By using these techniques the changes in microstructure caused by precipitation during aging treatment were clarified. After aging, the presence of ω or α phases may occur. Influence of changing Zr and Ta contents on mechanical properties and also on precipitation of secondary phases during aging treatment was observed.     

The thermal stability performances of the color rendering index of white light emitting diodes with the red quantum dots encapsulation

Red phosphors are the traditional material used to improve the color rendering index (CRI) of white light emitting diode (WLEDs). In this paper, red quantum dots (QDs) were fabricated and coated on the blue LED chip to replace the red phosphors. By comparing the thermal performances of the CRI for the two WLEDs, we found that WLEDs with the encapsulation of yellow phosphors and red QDs exhibited higher CRI and lower sensitivity to temperature than those with the encapsulation of yellow and red phosphors. The CRI of WLEDs with yellow phosphors and red QDs was 90.9, and its range ability was only 0.3 when the environment temperature changed from 25 °C to 100 °C, while the CRI of WLEDs with yellow and red phosphors was as low as 81.8, and the change of CRI was 2.2 during the same temperature variation.     

Thermal aging effect on the ratcheting-fatigue behavior of Z2CND18.12N stainless steel

The uniaxial tensile and ratcheting-fatigue behaviors of the Z2CND18.12N austenitic stainless steel at room temperature were studied with different thermal aging periods (from 1 h to 500 h) at different thermal aging temperatures (500 °C and 700 °C). The thermal aging process resulted in apparent changes in the ratcheting behavior and the ratcheting-fatigue life. The precipitates under different thermal aging conditions were identified by SEM observation. Considering the deterioration of the material induced by thermal aging process, aging damage factor was introduced to predict the ratcheting-fatigue life, which resulted in good prediction for all the thermal aging conditions.     

Cavitation erosion resistance of heat-treated NiTi

NiTi (Ti–50.8 at.% Ni) specimens were solution-treated at 1000 °C, followed by aging between 200 and 600 °C. The cavitation erosion resistance of all the aged specimens in deionized water was improved relative to the solution-treated specimen, with a maximum increase of about 8.7 times, which was achieved by aging at 500 °C. The results also indicate that both austenite and martensite contribute to the high cavitation erosion resistance of NiTi. It is also shown that a simple macro-indentation test employing a Rockwell indenter may be used for preliminary screening of heat-treated NiTi with respect to cavitation erosion resistance.     

Effect of heat treatment on microstructure and mechanical properties of a new β high strength titanium alloy

Microstructure and mechanical properties of a new β high strength Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe titanium alloy were investigated in this paper. Both the α/β and β solution treatment and subsequent aging at temperatures ranging from 440 °C to 560 °C for 8 h were introduced to investigate the relationship between microstructures and properties. Microstructure observation of α/β solution treatment plus aging condition shows that the grain size is only few microns due to the pinning effect of primary α phase. The β solution treatment leads to coarser β grain size and the least stable matrix. The size and volume fraction of secondary α are very sensitive to temperature and strongly affected the strength of the alloy. When solution treated at 775 °C plus aged at 440 °C, the smallest size (0.028 μm in width) of secondary α and greatest volume fraction (61%) of α resulted in the highest yield strength (1624 MPa). And the yield strength decreased by an average of 103 MPa with every increase of 40 °C due to the increase of volume fraction and decrease of the size of secondary α. In β solution treatment plus aging condition, tensile results shows that the strength if the alloy dramatically decreased by an average of 143 MPa for every increase of 40 °C because of larger size of secondary α phase than α/β solution treated plus aged condition.     

Effect of post weld heat treatment on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel weldments

The effect of postweld heat treatment (PWHT) on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel joints with ER316LMn filler material was investigated. PWHT aging was performed for 1 h at four different temperatures of 600 °C, 760 °C, 870 °C and 920 °C, respectively. The microstructure revealed the sigma phase precipitation occurred in the weld metals heat-treated at the temperature of 870 °C and 920 °C. The PWHT temperatures have the less effect on the tensile strength, and the maximum tensile strength of the joints is about 630 MPa, reaching the 95% of the base metal, whereas the elongation is enhanced with the rise of PWHT temperatures. Meanwhile, the sigma phase precipitation in the weld metals reduces the impact toughness.     

Evaluation of hardness and surface quality of different wood species as function of heat treatment

The objective of this study was to evaluate the effect of heat treatment on surface roughness and hardness of four wood species, namely black alder (Alnus glutinosa L.), red oak (Quercus falcata Michx.), Southern pine (Pinus taeda L.) and yellow poplar (Liriodendron tulipifera). Samples were exposed to heat treatment schedules having two temperature and exposure levels of 120 °C and 190 °C for 3 and 6 h, respectively. Average hardness value of red oak samples exposed to a temperature of 190 °C for 6 h was 41.7% lower than that recorded before the heat treatment. Temperature of 190 °C produced 7.9% lower hardness values for black alder with the increased exposure time from 3 h to 6 h. No significant differences were found between same type of Southern pine and yellow poplar specimens before and after the heat treatment in terms of their hardness values. Among the four species considered in this study red oak having the most porous anatomical structure showed the roughest surface. An improvement in surface quality (R_a) with 7.46% with extending exposure time from 3 h to 6 h at the temperature level of 190 °C was noticed. However all four types of wood species kept in the oven at 190° for 6 h presented smoother surface quality. It was found that increased temperature from 120 °C to 190 °C for both exposure times showed significant differences from the surface quality of nontreated samples at 95% confidence level. The anatomical structure of samples was also observed by scanning electron microscope (SEM) and some damage of the cell wall was determined due to heat treatment. The findings of this study demonstrated that heat treatment resulted in adverse effect on hardness characteristics of the samples. It appears that strength losses can be limited through alternative modified heat treatment techniques. On the other hand, surface quality of the samples from all species was enhanced as a result of heat treatment. Therefore such heat treatment would be considered to improve surface quality of the sample for furniture applications where smooth surfaces are ideal adding potential value on wood material to be used more effectively in furniture manufacturing.     

Effect of (α + β) heat treatment on microstructure and mechanical properties of (TiB + TiC)/Ti–B20 matrix composite

For the first stage, a metastable β titanium alloy, Ti–3.5Al–5Mo–4V–2Cr–2Sn–2Zr–1Fe reinforced with trace amounts of TiB whiskers and TiC particles was fabricated by vacuum arc melting process and hot forging followed by heat treatment at 780 °C/740 °C, then by aging at 500 °C, 550 °C, 570 °C and 600 °C. For the second stage, the unreinforced titanium alloy was also fabricated by the same process. The microstructural characteristics were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Traces of TiB whiskers and TiC particles (2.2 vol.%) with a volume ratio of 2:3 synthesized in situ exerted a hybrid reinforcing effect on the β titanium alloy. The reinforcements were uniformly distributed in the matrix and the elastic modulus was improved about 25 GPa. Ultimate tensile strength and yield strength achieves about 1625 MPa and 1500MPa respectively, with ductility at 7% when the aging temperature is 500 °C. The ductility of (TiB + TiC)/(Ti–3.5Al–5Mo–4 V–2Cr–2Sn–2Zr–1Fe) matrix composite could be enhanced by increasing the aging temperatures. After 780 °C followed by aging at 570 °C, excellent strength and plasticity properties were obtained (ultimate tensile strength of matrix alloy is 1350 MPa with elongation of 18% and ultimate tensile strength of composite is 1500 MPa with elongation of 13%).     

Synthesis and characterization of Yb3+,Tm3+:Ba2YF7 nanocrystalline with efficient upconversion fluorescence

A novel upconversion luminescence nanocrystals Yb³⁺,Tm³⁺:Ba₂YF₇ were synthesized via the hydrothermal method. They have uniform morphology with a mean size of 30 nm even if annealed at 600 °C. Pumped by 980 nm laser diode the as-synthesized powers emit ultraviolet/blue light, which is in the range of the specific upconversion luminescent spectra of Tm³⁺ ions. After post-annealing at 600 °C in an argon atmosphere for 2 h, their upconversion luminescence intensity is 5 multiple improved and the ultraviolet/blue light can even be seen by the naked eyes under a low excitation power of 20 mW. This indicates that Ba₂YF₇ is a very effective luminescent host material. Excitation power dependences of individual upconversion emission intensity are plotted, which partly uncover the upconversion luminescence mechanism of Tm³⁺ ions.     

The paint–bake response of three Al–Mg–Zn alloys

The aging behaviors of three Al–Mg–Zn alloys have been investigated under conditions similar to the paint–bake cycle currently used in automotive manufacturing. The three alloys contain Mg in atomic concentrations from one to two times those of Zn. Natural aging at 25 °C after solutionizing is found to produce a linear increase in hardness with logarithmic time for times of up to 1 year. Hardnesses in naturally and artificially aged conditions are found to increase with Mg content. Artificial aging at 175 °C for 30 min, which simulates the automotive paint–bake cycle, produces increases in hardness of 15–36% over the solution-treated conditions. Peak hardness from artificial aging at 175 °C is produced in all alloys after approximately 8 h. Natural aging for 10 days prior to artificial aging at 175 °C does not produce significant changes in hardness compared with artificial aging alone. Natural aging for 1 year after simulated paint–bake aging increases hardnesses by 41–78% over those after simulated paint–bake aging alone. The precipitation strengthening mechanism in these alloys is consistent with η′ formation. Increases in hardness and strength with increasing Mg content are consistent with increased solid–solution strengthening, which is retained even after artificial aging.     

Photoluminescence and thermoanalytical studies of complexes based on 5-Cl-8-hydroxyquinoline and calix[4]arene ligands

A innovative 5-Cl-8-oxyquinolinepropoxycalix[4]arene ligand (2) have been prepared, exhibiting, at room temperature, blue fluorescent light emission and resulting in shift band to green fluorescent light (fluorescence mode) in the presence of coordinated Eu(III) and Tb(III) ions. Terbium complex presented phosphorescence emission as noted by typical bands at 490 nm, 545 nm and 585 nm. TG/DTG data exhibited typical thermal behavior for these compounds, however DSC curves showed the melting temperature near 300 °C for the samples, demonstrating an unusual thermal stability when quinoline derivatives are attached to calix[4]arene matrix. This fact strongly suggests an effective approach to preparing the photoluminescent compound associating high chemical and thermal stability.     

Synthesis of nanocrystalline MMoO4 (M = Ni,Zn) phosphors via a citrate complex route assisted by microwave irradiation and their photoluminescence

Nanocrystalline MMoO₄ (M = Ni, Zn) phosphors, which have wolframite-type structure, were successfully synthesized at low temperatures via a modified citrate complex route assisted by microwave irradiation. The citrate complex precursors were heat-treated from 300 to 600 °C for 3 h. Crystallization of the MMoO₄ (M = Ni, Zn) nanocrystallites were detected at 500 °C, and entirely completed at a temperature of 600 °C. The nanoparticles presented primarily dispersed and homogeneous morphology with particle size of 20–40 nm. The nanocrystalline MMoO₄ (M = Ni, Zn) phosphors prepared at 600 °C exhibited broad luminescence in green and blue wavelength region, respectively.     

Aging of a polymer core composite conductor: Mechanical properties and residual stresses

Polymer core composite conductor specimens were aged in atmospheric conditions at 140 and 180 °C and then tested under four point bending. When aged up to a year at a temperature of 140 °C no detrimental effect on flexural performance of the composite was observed, as opposed to aging at 180 °C, which had a very negative effect on the properties. A finite element model was developed to characterize the residual stress in the composite on a micro scale using representative volume elements (RVE). The residual stresses developed after aging at 140 °C for a year were minimal. However, at temperatures higher than 160 °C significant increases in the stresses were observed. The effect of chemical aging on the failure process of the rods was not considered but could result in the rapid reduction in the loads at failure for the rods tested at 180 °C for up to a year.     

Effect of aging on the tensile properties and microstructures of a near-alpha titanium alloy

The effect of aging temperature between 650 °C and 750 °C for different aging times on the tensile properties and microstructures of Ti60 alloy were studied. The results show that the strength of the alloy increases first and then decreases with the aging temperature increases from 650 °C to 750 °C. The reduction of area of the alloy is more sensitive to the aging time than elongation. With increasing aging temperature and time, the volume fracture and grain size of silicides and α₂ phase increase gradually. The silicides have the strengthen effect on the Ti60 alloy, but the effect weakens when the silicides grow up. The loss of ductility is mainly attributed to the precipitation of α₂ phase after aging treatment.     

Pore pressure and consolidation of saturated silty clay induced by progressively heating/cooling

The thermal pore pressure and consolidation of a saturated silty clay are experimentally studied. The specimen was heated progressively from the room temperature of 25 °C to 85 °C (T = 25 °C → 35 °C → 45 °C … → 85 °C), and then cooled from 85 °C to 25 °C (T = 85 °C → 75 °C → 65 °C … → 25 °C), with (case 1) or without (case 2) drainage between temperature stages at four confining pressures (50, 100, 150 and 200 kPa, respectively). It shows that during the undrained heating/cooling, the pore pressure reaches a peak at the time when the specimen is heated to the required temperature and then decreases slightly, and it declines to a minimum at the time when the specimen is cooled to the required temperature and then increases slightly. Such phenomenon can be attributed to the adjustment of soil structure induced by the interaction of solid grains with pore water. On the other hand, during the drained heating/cooling, the maximum pore pressure increases with the increase of temperature stages, and the normalized negative pore pressures show a decreasing trend with the decrease of temperature stages. This appears to be especially obvious as the applied confining pressures decrease. It is also observed that consolidation volumetric strains during the isothermal drainage increase significantly with the increase of temperature stage, and the reduction in the volumetric strains due to absorption after cooling shows a decreasing trend with the decrease of temperature stage.     

Heating aging behavior of Al–8.35Zn–2.5Mg–2.25Cu alloy

In the present work, the influence of heating aging treatment (HAT) on the microstructure and mechanical properties of Al–Zn–Mg–Cu alloy was investigated. When the final aging temperature (FAT) was lower than 180 °C, the hardness increased with the decreasing of heating rate, however, in the case of the FAT was higher than 180 °C, the variation of hardness was opposite. The electrical conductivity of Al–Zn–Mg–Cu alloy increased with the decrease of heating rate regardless of FAT. The tensile strength, yield strength and conductivity of the Al alloy after (100–180 °C, 20 °C/h) HAT increased by 1.6%, 4.5% and 14.1% than that after T6 treatment, respectively. The precipitates sequence of HAT was coincident with that of isothermal aging, which is SSS → GP zone → η′ → η. With the increase of FAT and the decrease of heating rate, the fine precipitates became larger and the continuous η phase at grain boundary grew to be individual large precipitates. The HAT time was decreased about 80% than that for T6 treatment, indicating HAT could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.