Effect Of Low Temperature Aging Research Articles

Effect of Low-Temperature Aging on Thermally-Induced Phase Transformation of NiTi Wire with a Wide Range of Grain Sizes

Thermally-induced phase transformation (PT) is of significance and value to the application of NiTi alloy components. Low-temperature aging (LTA) treatment was used to alter PT characteristics of NiTi alloys avoiding undesirable grain growth. Effect of LTA on PT of NiTi wires with a wide range of grain sizes from 34 nm to 8021 nm was investigated in this study. As the average grain size varies from 34 to 217 nm, the temperature of the B2↔R transformation increase as a result of LTA, and the increasing effect is more obvious at a larger grain size. For NiTi alloys with average grain sizes ranging from 523 to 1106 nm, transformation sequence changes from B2↔B19' to B2↔R due to LTA. For the sample with an average grain size of 2190 nm, the B2↔B19' transformation is replaced by B2↔R←B19' after LTA. When the average grain size is larger than 2190 nm, transformation sequence changes from B2↔B19' to B2↔R↔B19' after LTA. Transmission emission microscope observations reveal that the above-mentioned PT behavior correlates with the coupled effect of grain size and precipitation. The precipitation of Ni4Ti3 in the grains with a size smaller than ~150 nm is inhibited after LTA, the temperature of B2→R of samples with average GS smaller than ~150 nm still is elevated due to the inhomogeneous grain size of NiTi wires.

Effect of low-temperature aging on the safety performance of lithium-ion pouch cells under mechanical abuse condition: A comprehensive experimental investigation

Understanding how aging affects the safety performance of lithium-ion batteries under mechanical abuse is of great importance. In this study, pouch cell batteries with four different aging levels (0%, 10%, 20% and 30% capacity fading), which respectively represent fresh, prior-scrapped, normally scrapped and over-scrapped batteries, are prepared at 0 °C and subjected to indentation loading. Mechanical-electrical-thermal responses of these batteries are compared. Results show that aged pouch cells have right-shifted force-displacement curves, higher inflection force and higher peak force. After short circuit, voltage dropping is faster and electric energy is released in a shorter duration for aged ones, leading to a higher temperature for the whole battery cell. For cells with 30% capacity fading, the voltage dropping and temperature increasing are in a steep behavior. And the generated heat after short circuit is concentrated in the indented area, resulting a localized peak temperature of 117∘C. To clarify the observations, mechanical tests in the component level are carried out. Results reveal that the response changes in cell tests are mainly from the anode. Compression test of aged anode electrode shows consistent mechanical response changes with cell test. The delay of anode fracture under compression loading lead to the enlargement of the shear fracture zone, together with the formation of sharp lithium dendrite, resulting in more severe short circuit.

Investigation of the effect of low temperature aging on the mechanical properties and susceptibility to sulfide stress corrosion cracking of 22%Cr duplex stainless steel

Duplex stainless steels (DSS) are corrosion resistant alloys largely used in the oil and gas production industry. Optimum properties are usually obtained with equal fractions of ferrite (δ) and austenite (γ) in the microstructure, which can be obtained by a proper solution heat treatment. However, work hardening can be used for applications where mechanical resistance must be increased, such as in casing and tubulars for oil and gas production. These pipes operate under high pressure in a harsh environment, composed by oil and high chloride water, low pH and high H2S and CO2 partial pressures. Additional strengthening can also be provided by low temperature aging which promotes the fine precipitation of a Cr-rich α’ phase by spinodal decomposition of ferrite. In this work, a DSS with 22%Cr (UNS S31803) received with an un-balanced microstructure (64% of ferrite), was aged at 475 °C for 8 h. For comparison, the material was correctly solution treated to obtain a balanced microstructure, and aged in the same way of the as received one. The effects on tensile mechanical properties, hardness and impact toughness were determined. The sulfide stress corrosion (SSC) susceptibility was evaluated by slow strain rate tensile (SSRT) tests in low pH and high pH2S chloride solution.

Effects of low temperature aging precipitates on damping and mechanical properties of ZK60 magnesium alloy

Effects of low temperature aging precipitates on damping and mechanical properties of ZK60 alloy are investigated by transmission electron microscopy, tensile testing and dynamic mechanical analysis. The results show that the mechanical properties of ZK60 alloy can be significantly improved by solution and ageing treatment, at the same time, the strain-amplitude-dependent damping capacity increased absolutely. The ZK60 alloy aged at 115 °C for 2 h exhibits higher mechanical properties (UTS of 232 MPa, YTS of 89 MPa, El of 11%) and better high strain-amplitude-dependent damping capacity than the as-cast and the solution-treated alloys, which is a promising damping magnesium alloy. The favourable damping capacity and its growth at medium high strain amplitude are closely connected with G.P.I zone, which is considered as a new energy-dissipation source. The damping capacity improvement can be explained by the self-modified Granato-Lücke model.

Effect of Low Temperature Aging on Hall-Petch Coefficient in Ferritic Steels Containing a Small Amount of Carbon and Nitrogen

Effect of Low Temperature Aging on Hall-Petch Coefficient in Ferritic Steels Containing a Small Amount of Carbon and Nitrogen

The Effect of Low Temperature Aging and the Evolution of R-Phase in Ni-Rich NiTi

This study investigates the thermal and mechanical properties that arise from aging Ni-rich Ni–Ti (Nitinol) at temperatures below 250 °C, well below those commonly used to fabricate medical devices. We demonstrate that the Ni50.8–Ti49.2 composition decomposes at temperatures as low as room temperature and discuss the unusual changes in thermal and mechanical behaviors compared to common aging treatments, such as separation of Martensite and R-phase transformations. Using such aging treatments, superelasticity can be achieved without the presence of austenite at body temperature (Af > 45 °C, well above the body temperature). Furthermore, the influence of R-phase on mechanical response and the disparity between thermal and mechanical behavior is discussed in detail.

The effect of low-temperature aging on the microstructure and deformation of uranium- 6 wt% niobium: An in-situ neutron diffraction study

The mechanical properties of uranium-niobium alloys evolve with aging at relatively low temperatures due to subtle microstructural changes. In-situ neutron diffraction measurements during aging of a monoclinic U-6Nb alloy at temperatures to 573 K were performed to monitor these changes. Further, in-situ neutron diffraction studies during deformation of U-6Nb in the as-quenched state and after aging for two and eight hours at 473 K were completed to assess the influence of microstructural evolution on mechanical properties. With heating, large anisotropic changes in lattice parameter were observed followed by relaxation with time at the aging temperature. The lattice parameters return to nearly their initial values with cooling. The active plastic deformation mechanisms including, in order of occurrence, shape-memory de-twinning, mechanical twinning, and slip-mediated deformation do not change with prior aging. However, the resistance to motion of the as-quenched martensitic twin boundaries increases following aging, resulting in the observed increase in initial yield strength.

221 The Effect of Low Temperature Aging in Double-Aged Maraging Steels

221 The Effect of Low Temperature Aging in Double-Aged Maraging Steels

A study on the pseudoelasticity of low temperature aged and thermomechanically treated Ti-51.5 at.% Ni shape memory alloy

Abstract The aim of the present work is to investigate the effects of low temperature aging and thermomechanical treatments on the transformation and deformation behavior of an Ni-rich NiTi alloy. One sample of solution treated Ti-51.5 at.% Ni shape memory alloy was aged at 300°C for 1 hr. The other solution annealed sample, was firstly cold rolled to a reduction of 20% and then aged at 300°C for 1 hr. Applying these treatments, samples showed R-phase transformations in the absence of B19′ phase formation according to differential scanning calorimetry curves. By applying 20% cold reduction in area prior to aging, almost complete recovery of strain was observed and pseudoelasticity improved significantly compared to the conventional aged sample. Results of thermal analysis and tensile tests suggest that the observed pseudoelasticity for the thermomechanically treated sample can be due to stress-induced formation of R-phase. It is proposed that if stress-induced transformation of B19′ phase does not take place, stress-induced transformation of R-phase can extend to higher than 1% strain. Hence, pseudoelastic behavior due to this transformation can be observed.

Effects of low temperature aging on the mechanical properties and corrosion resistance of duplex and lean duplex stainless steels UNS S32205 and UNS S32304

Duplex stainless steels (DSS) with austenite-ferrite microstructure are high strength and corrosion resistant steels frequently used as pipes and accessories in chemical/petrochemical on/and off-shore industries. Low temperature heat treatments (400-475ºC) may increase the hardness and wear resistance of duplex steels, due to a spinodal decomposition reaction of the ferrite, whose small particles α' precipitate in the matrix. In this work, several heat treatments at 400ºC and 475ºC with short duration (<24h) were performed on UNS S32304 and UNS S32205 grades. The kinetics of a' precipitation was studied by hardness measurements. Tensile tests were also carried out for some heat treatment conditions to evaluate the effect of the aging on the ductility of both grades. The hardening of duplex UNS S32205 was more intense than that of UNS S32304, although both steels have shown an interesting increase in tensile strength. Specimens of duplex steel heat treated at 475ºC for 4 h and 8 did not show any detectable decrease of corrosion resistance in anodic polarization and critical pitting temperature tests were carried out in NaCl media.

Effect of Low Temperature Aging on Internal Friction of AA2024

The anelastic behavior of AA2024 alloy is studied in the temperature range between room temperature and 325 °C. The internal friction technique is shown to be very sensitive to the microstructural changes that take place at these temperatures. Interrupted aging performed at low temperature induces increase in the peak height at ~230 °C indicating the slow release of vacancies aiding the aggregation of Mg and Cu which further transforms into semicoherent precipitates. Stretched specimens indicate increase in background which is attributed to anelastic or viscoelastic of dislocations. TDIF of T6I4 samples is strongly affected to the point of deformation, whilst TDIF of T6I6 samples is affected by the deformation but irrespective to the point of deformation.

The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

STATEMENT OF PROBLEMRecently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.PURPOSEThe objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM).MATERIAL AND METHODSY-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05).RESULTSThe mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa.CONCLUSIONThe monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

Effect of Low Temperature Aging of Type 316L Austenitic Stainless Weld Metal on Transformation of Ferrite Phase

The effect of low temperature aging of type 316L austenitic stainless weld metal on the transformation of ferrite phase was studied. Some specimens were aged at temperature 400oC at various holding times ranging from 100 to 5000 hrs. The ferrite content of the specimens was estimated before and after aging. It can be seen that the ferrite content decreased very slightly with increasing the aging time under low temperature aging when it was measured by Magne Gauge. Microstructure changes before and after aging were noticed. When observing the microstructure change of ferrite content being evaluated by optical metallography, it can be noted that the ferrite phase content reduced to 30% after aging for 500 hrs, while the reduced ferrites phase content reached at 60% after aging for 5000 hrs. Also, the microstructure evolution showed that the ferrite/austenite interface changed from smooth line into corrugated interface like saw-teeth after 5000 hrs aging. In the present study, the observed contradiction between the appearance of ferrite phase microstructure and the measured ferrite content using a Magne Gauge could be resolved by assuming that the dissolved ferrite content decomposed into α and ά, which kept the magnetic effect as a ferrite phase. It can be concluded that the ferrite number (FN) measurements were not sensitive to the decomposition of ferrite into α and ά, since they were a measure of the amount of presented ferromagnetic phase, and both α and ά were ferromagnetic constituents. These were significantly observed for early stage of aging till 1000 hrs, while at 5000 hrs aging, a slight change of FN could be attributed to G phase precipitate, which was a FCC phase.

Effect of low temperature aging on microstructure and mechanical properties of super-high strength aluminum alloy

The effects of heat treatment on the microstructure and mechanical properties of two alloys, namely Al-12.2% Zn-2.48% Cu-2.0% Mg-0.15% Zr-0.166% Ag (alloy 1), and Al-9.99% Zn-1.72% Cu-2.5% Mg-0.13% Zr (alloy 2) were investigated. The results show that low temperature aging after promotive solution treatment can increase elongation without the loss of strength for the studied alloys. The optimum aging treatment (T6) for alloy 1 and alloy 2 is 100 °C/80 h and 100 °C/48 h, respectively. Compared with other heat treatment alloys, alloy 1 and alloy 2 show super-high tensile strength up to 753 MPa and 788 MPa, remaining 9.3% and 9.7% elongation under T6 condition, respectively. During aging, trace addition of Ag enhances the formations of GP zone and metastable phase, and stabilizes GP zone and metastable phase to a higher temperature. Trace addition of Ag prolongs the aging time of reaching the peak strength and delays over-aging condition of the alloy. However, trace addition of Ag promotes the formation of coarse constituent in the alloy and consumes hardening alloying elements of Zn and Mg. Morecover, the addition of the transition element Zr in 7000 series super-high alloy forms incoherent Al3Zr dispersoid which can serve as nucleation sites for nonuniform precipitation of η phase during aging process. The higher the aging temperature, the greater the tendency for nonuniform precipitation of η phase.

Effects of Aging and Co Addition on Martensitic and Magnetic Transitions in Ni–Al–Fe β-based Shape Memory Alloys

Effects of low temperature aging and the addition of Co on the martensitic and magnetic transitions in the Ni–Al–Fe β (B2-type structure) alloy system were investigated using differential scanning calorimetry, transmission electron microscopy and vibrating sample magnetometry. The martensitic transition temperatures of a Ni57Al25Fe18 specimen homogenized at 1 473 K for 1 h were decreased by aging after homogenization, the maximum decrease by aging being observed at 573 K. On the other hand, the substitution of Co or Fe for Ni induced a decrease of the martensitic transition temperatures and an increase of the Curie temperature, while the substitution of Co for Fe resulted in an increase of the martensitic transition and Curie temperatures. Co was thus shown to be an effective element by which both the martensitic and magnetic transition temperatures can be controlled.

Effect of nano-scaled precipitates on shape memory behavior of Ti-50.9at.%Ni alloy

In order to clarify the effect of low temperature aging (<600K) on the shape memory behavior of a Ti-50.9at.%Ni alloy, the deformation behavior and microstructures were investigated using tensile tests, X-ray diffractometry and transmission electron microscopy (TEM). The specimens were solution-treated at 1073K for 3.6ks followed by aging at 373, 473 and 573K for various times ranging between 1.2 and 10,800ks. TEM observation revealed that after aging at low temperature (<600K) the size of Ti3Ni4 precipitates hardly increases, but their density increases with increasing aging time in the early stage of formation of Ti3Ni4 precipitates. The critical stress for slip deformation abruptly increases with increasing density of fine Ti3Ni4 precipitates (<10nm) in the specimens aged at the low temperature region. This is attributed to the increase in the number of pinning points to hinder the movement of dislocations. With increasing aging time and temperature the size of Ti3Ni4 precipitates increases, resulting in decreasing the critical stress for slip.

Static strain aging phenomena in cold-rolled dual-phase steels

The effect of low-temperature aging, with aging temperatures up to 170°C, on a cold-rolled CMn−CrMo dual-phase (DP) ferrite-martensite steel was investigated. This material was processed using three different intercritical annealing treatments, leading to DP structures with different microstructures and properties. It has been found that both the aging in the ferrite phase and the tempering in the martensite play an important role in the mechanical behavior of the material with regard to the strain aging phenomena. The yield stress increase accompanying the aging phenomenon revealed three separate aging stages. In the present study, those stages were determined to be the result of the pinning of dislocations in the ferrite, the C-cluster formation, or low-temperature carbide precipitation in the ferrite and the volume contraction of the martensite due to formation of low-temperature carbides, leading to the relief of residual stresses in the ferrite. In the absence of a clear yield point, a new method is proposed to measure the increase in yield stress due to aging only.

Ａｌ‐Ｍｇ‐Ｓｉ系合金のセレーションに及ぼす低温時効と復元処理の影響

In order to investigate effects of low temperature aging and reversion treatment on the serration of 6061 aluminum alloys, the reversion at from 423 to 853 K was conducted for the specimens in which the serration disappeared with the preliminary aging at 403 K. The measurements of electrical resistivity, DSC analysis and TEM micrographs showed that the solute atom concentration for the reversed specimens in which the serration generated again decreased remarkably due to formation of the precipitates, such as GP–zone, random-type, β″–phase, β′–phase and β–phase. Therefore, it was suggested that the disappearance of the serration was not affected by decrease of the solute atom concentration.

Transformation-toughened zirconia for dental inlays, crowns and bridges: chemical stability and effect of low-temperature aging on flexural strength and surface structure

Objectives. One concern, for transformation-toughened zirconia (Y-TZP) is their liability to low-temperature aging with accompanying alterations of properties such as strength. The loss in strength is attributed to the transformation of tetragonal grains to monoclinic. The transformation is related to loading of the dental inlays, crowns and bridges (reconstructions), temperature and time of exposure to surrounding media (aging) and the manufacturing process of Y-TZP. The purpose of this study was to determine chemical stability and effect of aging (4% acetic acid at 80 °C for 168 h) on flexural strength, surface and crystalline structures of two shades, P0 and P17, of a Y-TZP ceramic used for dental reconstructions. The hypotheses to be tested were that both shades of the dental Y-TZP ceramic have high flexural strength and chemical stability compared to other dental ceramics, and that the strength, surface and crystal structures of the ceramic were not affected by aging. Methods. Forty specimens of Y-TZP, 20 of the shade P0 and 20 of the shade P17 were ground and polished. Ten specimens of each shade were exposed to low-temperature aging. The flexural strength of all 40 specimens was registered. Surfaces of the specimens were evaluated by using scanning electron microscopy (SEM), X-ray diffractometry and roughness recorder. The chemical solubility in 4% acetic acid was recorded by weight loss, and SEM was used to evaluate the surfaces of Y-TZP and dental feldspathic porcelain samples immersed in 8% SnF. Wilcoxon Signed Rank test was used for statistical analysis. Results. As expected, the two shades, P0 and P17, of the studied dental Y-TZP had high strengths that were not affected by aging, and high chemical stability in the tested solutions. Contrary to what was assumed the crystal and surface structures of P0 and P17 were affected. Transformation from tetragonal to monoclinic structures occurred and small elevations on the ceramic surfaces were observed after aging. Significance. The transformed-toughened Y-TZP ceramic used for dental inlays, crowns and bridges has high flexural strength compared to other dental ceramics and is chemically stable. The chemical solubility is well below the limit values of ISO 6872:1995 for dental ceramics.

Low temperature aging embrittlement of CF-8 stainless steel

Abstract Cast stainless steels such as CF-8 are used for several components such as pump and valve casings, elbows, fittings and primary coolant pipes in nuclear power plants. CF-8 stainless steel has a duplex microstructure consisting of austenite and about 15–20% δ-ferrite. Long-term exposure at the reactor operating temperatures results in aging-induced embrittlement of the material due to spinodal decomposition of the ferrite phase. In this paper, we report the effects of low temperature aging (673 K) up to 18 months on the mechanical and fracture properties of cast CF-8 stainless steel in the range of 173–423 K. These studies have been carried out using non-destructive ball indentation tests. Standard Charpy and tensile tests were also carried out to complement the ball indentation data. Increase in strength and decrease in toughness have been observed following aging. These changes in the properties tend to saturate on aging for more than 12 months.