Peak Aging Time Research Articles

Change in Fatigue Strength of Biomedical β-Type Titanium Alloy through Heat Treatment Processes

Relationships between fatigue properties and microstructures of hot-forged Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) in under aged, peak aged, and over aged conditions at aging temperatures of 673K and 723K are investigated. The changes in the fatigue properties of TNTZ subjected to thermomechanical treatments, which includes an aging treatment at 673K or 723K for 259.2ks after a severe deformation process by cold rolling, are also investigated.At an aging temperature of 673K, ω phase precipitates at the early stage of aging, but α phase precipitates at relatively longer aging time. The precipitation site of α phase changes from intra-grain to grain boundary at around peak aging time when TNTZ is aged at 673K and 723K. The elastic modulus of TNTZ increases simply with increasing aging time at both 673K and 723K. The fatigue strength of TNTZ increases considerably when α phase precipitates compared with when ω + α phases co-exist. The fatigue strength of TNTZ decreases slightly due to the coarsening of α phase precipitated in β grain and its grain boundary. TNTZ aged at 723K for 259.2ks after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Furthermore, the fatigue limitof about 770MPa (fatigue raito : 0.71) is nearly equal to that of hot-forged Ti-6Al-4V ELI alloy subjected to aging after solution treatment with equiaxed α structure.

Age hardening analysis of a hot rolled copper-alloyed interstitial free steel

Age hardening behaviour has been studied in a hot rolled copper-alloyed high strength interstitial free steel. The steel can be hardened to the peak-ageing strength employing low temperature coiling without any additional processing step. The age hardening data has been analysed with the available models for age hardening. The validity of the models has been tested and discussed to understand the effect of temperature on the peak-ageing time and the shape of the age hardening curves.

Effect of SiCp addition on age-hardening of aluminium composite and closed cell aluminium composite foam

The age hardening behavior of solid Al-alloy–SiCp composite and closed cell Al-alloy–SiCp composite cellular materials has been examined and compared. The peak aging period of these materials were also compared with that of the solid unreinforced alloy. The effect of SiCp content on the peak aging time has been examined. It was found that the composite aged faster than the alloy irrespective of SiCp content, wherein peak aging time was invariant to SiCp content. On the other hand, while the closed cell composite foam reached a peak aged condition faster than the alloy when SiCp content was less than 10 wt%, further increases in SiCp content delayed the age-hardening kinetics.

Age-hardening characteristic of an Al-Zn-Mg-Cu alloy produced by spray deposition

Abstract Al-10.8Zn-2.8Mg-1.9Cu alloy was synthesized by spray atomization and deposition technique. GP zones and age-hardening process in the alloy were investigated using high-resolution electron microscopy (HREM), selected area diffraction (SAD), and differential scanning calorimetry (DSC) analysis. The results indicated that spray deposition process accelerated the aging kinetics of the alloy at an aging temperature of 120°C, thereby reducing the peak aging time to 16 h. GPI and GPII are the two types of zones that are major precipitates for the alloy under peak-aged condition. The precipitation sequence for the alloy is also discussed.

Aging Characteristics of Al P/M Composites with Variation of Ceramic Contents

The aging behavior of sintered Al composites with various ceramic contents was investigated. 2xxx series blended powder was used as the starting powder. Ceramic contents were 0 wt.% and 5 wt.%. The blended powders were compacted at 250 MPa. The sintering process was performed at 620oC for 60 min in a N2 atmosphere. After sintering, each part was solution-treated at 518oC for 60 min and aged at 180oC. The Rockwell hardness value at the peak aging time increased with increased ceramic contents. However, the peak aging time at maximum hardness was reduced with increased ceramic contents. The changes in aging behavior may have been caused by the acceleration of diffusion due to the strain induced by differences in the thermal expansion coefficients of the matrix and the ceramic phases.

Processing and properties of Al–Li–SiCp composites

Al–Li–SiCp composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 mm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macroand microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ' (Al3Li) and S' (Al2CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.

Al2O3첨가에 따른 7xxx계 알루미늄 소결체의 시효특성 변화

Aging characteristics and mechanical properties of commercial 7xxx series Al composites were investigated from viewpoint of ceramic contents. After sintering process, sintered densities of blended and composite powder were 95 and 97%, respectively. Each part was solution-treated at <TEX>$475^{\circ}C$</TEX> for 60 min and aged <TEX>$175^{\circ}C$</TEX>. And two-step aging was also performed form <TEX>$120^{\circ}C$</TEX> to <TEX>$175^{\circ}C$</TEX>. The aging behavior of the sintered composite pow-der was different from that of sintered blended powder. The peak aging time of the composite was rapid as well due to strain. Before aging, mechanical properties of sintered composite powder was significantly higher than that of sintered blended powder. These increments of properties were directly affected by ceramic particles. However, after aging, incremental rate of mechanical properties was slowed in the composite.

Effect of prior cold work on age hardening of Cu–3Ti–1Cr alloy

The influence of 50%, 75% and 90% cold work on the age hardening behavior of Cu–3Ti–1Cr alloy has been investigated by hardness and tensile tests, and light optical and transmission electron microscopy. Hardness increased from 118 Hv in the solution-treated condition to 373 Hv after 90% cold work and peak aging. Cold deformation reduced the peak aging time and temperature of the alloy. The yield strength and ultimate tensile strength reached a maximum of 1090 and 1110 MPa, respectively, following 90% deformation and peak aging. The microstructure of the deformed alloy exhibited elongated grains and deformation twins. The maximum strength on peak aging was obtained due to precipitation of the ordered, metastable and coherent β′-Cu 4Ti phase, in addition to high dislocation density and deformation twins. Over-aging resulted in decreases in hardness and strength due to the formation of incoherent and equilibrium β-Cu 3Ti phase in the form of a cellular structure. However, the morphology of the discontinuous precipitation changed to a globular form on high deformation. The mechanical properties of Cu–3Ti–1Cr alloy are superior to those of Cu–2.7Ti, Cu–3Ti–1Cd and the commercial Cu–0.5Be–2.5Co alloys in the cold-worked and peak-aged condition.

Effect of aging treatment on mechanical properties of (SiC w+SiC p)/2024Al hybrid nanocomposites

2024Al based composites reinforced by a hybrid of SiC whisker and SiC nanoparticle were fabricated by a squeeze casting route. In the (SiC w+SiC p)/Al composites, the volume fraction of SiC whisker is 20% and that of SiC nanoparticle is 2%, 5% and 7%, respectively. The as cast composites were solution treated followed by aging treatment. The experimental results show that the SiC nanoparticles are more effective in improving the hardness and tensile strength of the composites than SiC whiskers. The hardening kinetics of the composites is enhanced by reinforcements addition and the peak aging time is 4-5 h. The hardness of all the hybrid composite decreases at the initial aging stage, suggesting that dislocation recovery softening process coexists with precipitation hardening. DSC study shows that the GP zone formation of the hybrid composites is suppressed.

Effects of Ag on microstructure and mechanical properties of 2519 aluminum alloy

The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3% (mass fraction) Ag accelerates 2519 aluminum alloy’s age-hardening, increases its peak hardness and reduces 4 h of peak aged time at 180 °C. The addition of 0.3% (mass fraction) Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200 °C is 24 MPa and 78 MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.

Effect of Scandium Addition on Aging Behavior of 6061 Aluminum Alloy

It has been reported that scandium addition improved various properties of aluminum alloys. However, present authors can not find any reports about the addition of Sc to 6000 series alloys. In this study, Sc was added to 6061 alloy and various effects of the Sc addition on aging behavior were examined, comparing with Al-Sc binary alloy. In the STQ state, resistivity at 77K, ρD77, of 0.2%Sc added alloy (6061+Sc) was about 2.0n-m higher than the alloy of no addition (6061). The ρD77 increased in initial stage of isothermal aging up to 473K, then decreased. Though ρD77 of binary Al-0.176%Sc alloy began to decrease from 1.8Ms at 448K and 18ks at 523K, excess decrease in ρD77 of 6061+Sc corresponding to precipitation of Sc compounds was not clear. Peak value of the HV0.1 was decreased and peak aging time delayed by the Sc addition in aging up to 498K. However, softening by overaging was retarded by the Sc addition. These effects of the Sc addition are considered to come from vacancy trap by solute Sc atoms or interface between particles of Sc compound and matrix acting as vacancy sinks.

生体用Ti-29Nb-13Ta-4.6Zr合金の力学的特性に及ぼす時効処理の影響

The relationships between mechanical properties and microstructure of Ti-29Nb-13Ta-4.6Zr in under aged, peak aged and over aged conditions at various aging temperatures were investigated. The maximum Vickers hardness values of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K are obtained at aging times of around 2419.2 ks, 3024 ks and 1209.6 ks, respectively. ω phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively low aging temperature, 573 K, while α phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively higher aging temperature, 723 K. At an aging temperature of 673 K that lies between aging temperatures of 573 K and 723 K, ω phase precipitates at the early stage of aging, but α phase precipitates at relatively longer aging time. The precipitation site of α phase changes from intragrain to grain boundary at around peak aging time when Ti-29Nb-13Ta-4.6Zr is aged at 673 K and 723 K. The tensile strength of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K increases up to a peak aging time with increasing aging time, but under over aging conditions, the tensile strength decreases. While the elongation decreases with increasing aging time at every aging temperature. The fatigue strength of Ti-29Nb-13Ta-4.6Zr increases greater when α phase precipitates than when ω phase precipitates. The fatigue strength of Ti-29Nb-13Ta-4.6Zr decreases a little due to the coarsening of α phase precipitated in β grain.

Al-Mg-Si合金における準安定相の析出形態と熱安定性におよぼす過剰Si濃度の影響

The influence of excess Si on the precipitation behaviour in an Al-Mg-Si alloy was studied by means of Vickers microhardness tests, high-resolution transmission electron microscopy (HRTEM) and differential scanning calorimetry (DSC). The metastable-phase precipitates formed during isothermal ageing up to the time to peak hardness were investigated from the viewpoints of the morphology, the density of precipitates and the change in the exothermic heat caused by the formation of precipitates in the DSC measurements. The changes in the density of precipitates and the exothermic heat with excess Si at peak ageing time showed a similar tendency to that of the peak hardness curves. Before the formation of the β′, three exothermic peaks of the metastable-phase precipitates appeared in the DSC curves of the alloy specimens isothermally aged for a short time. It was revealed that the formation of precipitates, which were named as Type-1, -2 and -3 in this work, corresponded to the three exothermic peaks.

Effect of Cold Work on the Precipitation Process in Aluminum Alloy 6063

Aluminum alloys can be strengthened by cold or hot working due to interaction between precipitates and dislocations. The alloy 6063 was deformed (2, 5, 10, 15 and 20) % after water quenching, and artificially aged at different aging temperatures (1605 180 and 200) oc for various periods of time (0.5, 5, 10, 50 and 100) hours. The results showed a considerable improvement in yield and tensile strength with an increasing level of prestrain. Generally aging temperature of 160 oc gave the best increase of yield and tensile strength, but these were decreased with increasing aging temperature i.e. (180 and 200) oc at a given level of prestrain.The peak aging time that improves the mechanical properties decreased with an increasing aging temperature. The alloy of 20 % deformation and aged at 160 oc for 10 hours developed maximum (yield, tensile strength and hardness) values compared with all other conditions involved, because the density of dislocation tangles which improved (yield and tensile) strength increased with increasing degree of prestrain.The 6xxx aluminum alloys are readily welded by most types of welding processes, but with severe local softening in the heat-affected zone (HAZ) where the hardness reduces to about half that of the parent metal.

Influence of prior cold work on age hardening of Cu–Ti–Zr alloys

The influence of prior cold work on age hardening behaviour of solution treated (ST) Cu–3Ti–0·1Zr and Cu–4Ti–0·1Zr alloys subjected to cold deformations of 50, 75 and 90% has been investigated by hardness and tensile tests and optical as well as transmission electron microscopy. Hardness of Cu–3Ti–0·1Zr and Cu–4Ti–0·1Zr alloys increased from 120 and 217 HV respectively in the ST condition to 365 and 433 HV respectively on 90% cold work and peak aging. Prior cold work reduced the peak aging time of the alloys while maintaining the same temperature, i.e. 450°C. Yield strength and tensile strength of Cu–3Ti–0·1Zr alloy reached maximum values of 940 and 1029 MPa respectively on 90% deformation and peak aging, while those of Cu–4Ti–0·1Zr alloy were 1258 and 1335 MPa respectively. The microstructure of the ST and deformed alloy exhibited elongated grains and deformation bands. The maximum strength on peak aging was obtained as a result of precipitation of ordered, metastable and coherent β′, Cu4Ti phase in addition to high dislocation density and deformation twins. These alloys were overaged as a result of the formation of incoherent and equilibrium β, Cu3Ti phase in the form of cellular structure. However, the morphology of the equilibrium β precipitate changed to globular form on high deformations.

Effect of copper content on mechanical properties and fracture behaviors of Al-Li-Cu alloy

A series of Al-Li-Cu alloys with copper content of 0 to 6 wt pct and lithium content of 2.5 wt pct were studied. The results showed that copper plays an important role in grain refining, homogenization, and aging, and significantly influences the mechanical properties and fracture behaviors of the alloys. With the addition of copper, the hardness and peak-aging time increase, and the tensile strength gradually increases to a maximum value with copper content of about 3 wt pct and decreases after that. However, elongation decreases constantly, and the crack roots increase and lead to early crack. The mechanism of mechanical properties and fracture behaviors of Al-Li-Cu alloy is also discussed.

Effect of Be Addition on the Precipitation Behaviors and Mechanical Properties in Al-Cu-Li-Mg-Zr-(Ag) Alloys

The effect of beryllium (Be) on the precipitation behaviors and mechanical properties of Al–Cu–Li–Mg–Zr–(Ag) alloys was investigated. The results show that adding 0.02%Be to Al–Cu–Li–Mg–Zr–(Ag) alloys, the elongation of the alloy increased without significant decrease in strength and the aging response was accelerated. In a Al–Cu–Li–Mg–Zr–(Ag) alloy, G.P. zone was formed at early aging time (2 h) and T1 and q′ phases were formed at peak-aging and over-aging times, while in Al–Cu–Li–Mg–Zr–(Ag)–Be alloys T1 and q′ phases were formed at early aging time (2 h) and the density of q′ phase was very low and fine T1 phases were homogeneously distributed at peak-aging and over-aging times.

Influence of Excess Si on the Morphology and Thermal Stability of Metastable Precipitates Formed in an Al&amp;ndash;Mg&amp;ndash;Si Alloy

The influence of excess Si on the precipitation behaviour in an Al-Mg-Si alloy was studied by means of Vickers microhardness tests, high-resolution transmission electron microscopy (HRTEM) and differential scanning calorimetry (DSC). The metastable-phase precipitates formed during isothermal ageing up to the time to peak hardness were investigated from the viewpoints of the morphology, the density of precipitates and the change of the exothermic heat caused by the formation of precipitates in the DSC measurements. The changes in the density of precipitates and the exothermic heat with excess Si at peak ageing time showed a similar tendency to that of the peak hardness curves. Four exothermic peaks of meatastable-phase precipitates appeared in the DSC curves of the alloy specimens isothermally aged for a short time. It was revealed that the precipitates named type-1, -2 and -3 in this work, correspond to the exothermic peaks (1), (2) and (3), respectively.

Mechanical Properties and Fracture Behavior of the Cu and Cu6Sn5–Dispersed Sn-Pb Solder Bumps Processed by Screen Printing

ABSTRACTThe mechanical properties of the 1-9 vol % Cu and Cu6Sn5-dispersed 63Sn-37Pb solder alloys were characterized with tensile test. Also, the Cu and Cu6Sn5-dispersed 63Sn-37Pb solder bumps of 760 μm size were fabricated on the Au(5 μm)/Ni(5 μm)/Cu(27 μm) BGA substrates by screen printing process, and their shear strength were characterized with variations of the dwell time at the reflow peak temperature(220°C) and aging time at 150°C. The yield strength and ultimate tensile strength of the 63Sn-37Pb solder alloy increased with dispersion of 1-9 vol % Cu and Cu6Sn5. In general, however, the Cu and Cu6Sn5-dispersed solder bumps exhibited lower shear strengths than those of the 63Sn-37Pb solder bumps The failure surface of the solder bumps after ball shear test could be divided into two regions of slow crack propagation and critical crack propagation, and the shear strength of solder bumps was inversely proportional to the slow crack propagation length.

Heat treatment of spray deposition SiCp/6066 aluminum matrix composites

Heat treatment of spray deposition 10% SiCp/6066 (ϕ(SiCp) = 10%) composites was investigated by means of hardness measurement. The results show that heat treatment technology is influenced by the presence of SiC particles. Compared with the base alloy 6066, the composites have lower burning temperature and is burnt at 540 °C due to the enrichment of Mg and Cu atoms in the SiCp/6066 interfaces. As a result, solution treatment of the composites should be carried out at lower temperature. The aging parameter values such as the aging temperature, the precipitation temperature of β′ and β phases, as well as the peak aging time, become lower. The optimum heat treatment process conditions are that the composites are solution-treated at 515 °C and aged at 165 °C for 5 h.