Duplex Aging Treatment Research Articles

Role of intermediate phases on microstructures, wear and corrosion resistance in new-developed (α + β) titanium alloy

A new (α + β) Ti alloy has been designed and prepared in this work, and the results show that three intermediate phases will be transformed including α′′ martensite, O′ and ω. Upon continuous heating, the α′′ martensite decomposes gradually and disappears before α precipitation. The ω and O′ domains are generated continuously upon aging, and such two intermediate phases co-exist when α phase nucleation occurs. It has been proved that the ω and O′ domains play a direct role in promoting α phase formation. Through the ω and O′ domains assisting α nucleation mechanism, a uniform distribution of fine α precipitates can be obtained after aging. Under the treatment of pre-aging at 300 °C plus aging at 600 °C, the α phase having smallest size and largest number density is obtained, resulting in highest wear resistance and corrosion resistance. For this sample, its average friction coefficient and wear ratio are 0.174 and 3.75×10−4 mm3/(N·m), respectively. During friction tests, the mixture of abrasive wear, adhesive wear and oxidation wear should be activated. Due to the formation of passivation films on the alloy surface, this alloy has exhibited better anti-corrosion properties than Ti-6Al-4 V alloy, and its corrosion current density in 3.5 wt% NaCl solution can be reduced to 1.79×10−8 A·cm−2. Compared with the samples under duplex aging treatments, the direct aged sample also presents outstanding anti-corrosion properties.

A novel strategy to regulate the precipitation-strengthened high-entropy alloy fabricated by laser directed energy deposition

The optimization of the aging process is an effective strategy for achieving excellent performance in the rapidly solidified CoCrFeNiTi0.7 high-entropy alloy (HEA). Current research has clearly demonstrated that the unique design of the high-low duplex aging (HLDA) strategy plays a crucial role in achieving outstanding wear resistance in additive manufacturing of the rapidly solidified CoCrFeNiTi0.7 HEA. The microhardness of the SA-750 and HLDA samples increased to approximately 678 HV and 729 HV, respectively, compared to the as-deposited sample (LDED) with a microhardness of approximately 506 HV. Additionally, the wear rates of the SA-750 and HLDA samples were reduced by approximately 17.1% and 24.7%, respectively, compared to the LDED sample. This remarkable improvement in wear resistance can be attributed to the introduction of high-density nanoscale core-shell microstructures formed by secondary η2 and L12-γ' phases. Furthermore, when compared to the grain size of SA-750 (65.63 μm), the HLDA sample exhibited the precipitation of cellular precipitates at the grain boundary, and the grain size (68.46 μm) did not show significant growth or coarsening. This demonstrates the precise control of the matrix grain size achieved in our study. Therefore, the high-low duplex aging treatment has been validated for developing high-performance rapidly solidified CoCrFeNiTi0.7 HEA. This strategy provides a targeted approach for tissue design to tap into the maximum potential of additive manufacturing precipitation-strengthened HEAs.

Effect of the duplex aging on the phase constitute and antibacterial properties of Ti-13 Nb-13Zr-7Ag

Biomedical titanium alloy Ti-13 Nb-13Zr-7Ag (TNZ-7Ag) has a low elastic modulus, but its antibacterial ability is still not satisfied. In this paper, a duplex aging treatment was applied to TNZ-7Ag alloy to improve the antibacterial properties, and the effects of the duplex aging on the microstructure, antibacterial properties and mechanical properties of TNZ-7Ag were studied, and the corrosion resistance and cytotoxicity were assessed. Microstructure observation indicated that the chemical component segregation appeared in the alloy matrix after the pre-aging at 350℃, and two types of martensite α" phases, namely primary α"M and secondary α"T, appeared in the solute-rich areas. During the subsequent aging at 600℃, α"T promoted the precipitation of Ti2Ag, which enhanced the antibacterial properties. In the solute-poor areas, the spherical α phase precipitated, which significantly improved the ratio of strength-to-modulus. Finally, TNZ-7Ag treated by a duplex aging treatment of 350 ℃/2 h+600 ℃/2 h exhibited an antibacterial rate of 99.9 % and the ratio of strength-to-modulus of 18.59.

Enhanced strength-ductility synergy in a new 2.2 GPa grade ultra-high strength stainless steel with balanced fracture toughness: Elucidating the role of duplex aging treatment

Tuning thermal treatment schedule has been confirmed as an effective technical route for achieving optimum properties of steels. In the present work, the role of a unique duplex aging process on the enhanced strength-ductility synergy in a newly designed 2.2 GPa grade martensitic ultra-high strength stainless steel (UHSSS) was fully elucidated utilizing multi-scale characterization methods and various mechanical tests. Compared with the first aging-treated steel, the strength and ductility are synergistically enhanced after the second aging treatment due to increased volume fractions of Laves phase and reversed austenite as well as intensification of spinodal decomposition. Specifically, nanoprecipitates not only act as “obstacles” for dislocation movements, but also delay the deformation localization and necking instability, resulting in the dramatic increase of both strength (359 MPa for yield strength) and ductility (17% for reduction of area). The second aging-treated steel exhibited an impressive combination of mechanical properties: yield strength ∼ 1876 MPa, ultimate tensile strength ∼ 2259 MPa, elongation to fracture ∼ 11.5%, reduction of area ∼ 52%, and fracture toughness ∼ 43 MPa·m0.5 at ambient temperature. As revealed by the microstructural characterization, the aged steel is primarily strengthened by three distinct types of nanoprecipitates, including M2C, Laves phase, and α’Cr domains. The strengthening contributions of these precipitates were quantitatively estimated in terms of Orowan dislocation looping or cutting mechanisms. It is found that Laves phase contributed the maximum strength increment induced by precipitation hardening. An accessible pathway consisting of duplex aging treatment and co-precipitation of multiple nanoprecipitates is thus validated to exploit high-performance UHSSSs.

Precipitation behaviour of single and duplex aged metastable β-Ti alloy, Ti–5Al–5Mo–5V–3Cr

This work presents the influence of single-aging and duplex-aging treatments on microstructure evolution and the associated properties of Ti-5553 β-Ti alloy. We found that single-aged samples with a slow heating rate and duplex-aged samples produced approximately the same microstructures and microhardness at all aging conditions. This can be attributed to the same precipitation mechanism in both cases as observed via in situ electrical resistivity measurements. The slowly heated and duplex-aged samples generally produced higher microhardness in comparison to fast-heated samples; however, the difference in the microhardness tended to decrease with aging time at higher temperatures. A correlation () between the microhardness values and the width of α-phase (d) was established for all the aged samples. Highlights Duplex aging and slow heating yield similar microstructure and microhardness. Duplex aging and slow heating showed similar precipitation mechanism. Duplex aging and slow heating generally produced higher hardness than fast heating. The gap in hardness for different aged conditions decreased at higher temperatures. The microhardness values showed a good correlation with the width of α-phase.

Effect of duplex aging on microstructural and mechanical behavior of a new β-Ti alloy for biomedical applications

The influence of duplex aging on the microstructural and mechanical behavior of Ti–25Nb–10Ta–1Zr-0.2Fe alloy was investigated. The first step of duplex aging (DA) treatments was carried out at 300 °C or 400 °C for 20min and 1 h, followed by the second step aged at 550 °C for 20min-24 h.A small amount of athermal ω (ωath) formed in the β matrix after solution treatment and water quenching. During single aging (SA) at 550 °C, upon slowly heating process, the ωath→isothermal ω (ωiso)→isothermal α" (α"iso) might occur. Subsequently, the α"iso dissolved rapidly and transformed into α phase at the early stage of aging, resulting in a fine distribution of α precipitates in the β matrix. During DA treatments, the fine ωiso and α"iso were observed in the first stage aging at 300 °C/400 °C, then the metastable ωiso and α"iso decomposed into α phase at higher temperature of 550 °C. Besides fine α laths, ladder-shaped α clusters with large size were observed after DA. There was a single-peak in the hardness curve of SA, and the peak hardness was associated with the uniform distribution of fine plate-like α phase. After DA treatments, the alloy showed stronger age-hardening and displayed obvious double-peak precipitation hardening. The first hardness peak was the result of the dense ωiso nano-particles formed in the first aging stage, while the second one could be mainly attributed to these large ladder-shaped α clusters in the second aging stage. Compared with SA, the balance between high strength and low modulus could be improved by an appropriate DA treatment.

Combined Effect of Cryogenic and Aging treatments on Wear Behavior of Ti-6Al-4V α/β Alloy for Biomedical Applications

Ti-6Al-4V α/β titanium alloy is used in biomedical applications to produce artificial joints due to its excellent osseointegration property, high corrosion resistance, low density, and low Elasticity modulus compatible with bone structure. Considering the usage area, Ti-6Al-4V alloy is expected to have high tensile properties and high wear resistance. In this study, aging treatment and a combination of aging and cryogenic treatment were applied to the alloy to obtain high tensile properties and wear resistance. Cryogenic treatment was conducted at deep (-196°C) and shallow (-140°C) cryogenic treatment temperatures. Also, aging treatment was conducted to the alloy with/without cryogenic treatment as a single-step or duplex. The effect of the heat treatment types on the alloy's mechanical and microstructural properties was determined by tensile test, hardness test, wear test, XRD phase analysis, and microstructural investigations. With the application of the duplex aging treatment amount of the β phases decreased, a good balance between tensile strength and the elongation was obtained, and the wear resistance of the alloy increased compared to the single-step aging. In addition, the decrease of the cryogenic treatment temperature slowed down the phase transformation kinetics and caused a decrease in precipitation of α phases at both single-step and duplex aged samples. Superior wear resistance was obtained with the reduction of β phases in the microstructure of the samples that were duplex aged after cryogenic treatment.

Cryogenic and Aging Treatment Effects on the Mechanical Properties of Ti-15V-3Al-3Cr-3Sn Titanium Alloy

Abstract In this study, single and duplex aging treatment was applied to the metastable beta titanium alloy of titanium-15 vanadium-3 aluminum-3 chromium-3 tin with cryogenic treatment. The single-step aging treatment was applied for 20 h at 450°C and 10 h at 550°C. The cryogenic treatment was carried out at −196°C for 24 h, followed by single-step or duplex aging treatment. The results obtained show that the cryogenic treatment causes the formation of martensitic alpha phases. Following the cryogenic treatment, martensitic alpha phases were observed in the sample, which was subjected to aging treatment at 450°C for 20 h, whereas these phases disappeared completely in the sample treated at 550°C for 10 h. Preaging treatment applied after cryogenic treatment prevented the formation of precipitate-free zones by providing a finer and uniform distribution of α phases. Cryogenic treatment followed by preaging treatment at 250°C for 24 h led to the formation of dense metastable prephases. This resulted in a 10% increase in tensile strength, 4% elongation, and 5% hardness compared to preaging at 300°C for 10 h after cryogenic treatment. The optimum mechanical properties in single-step sample groups were obtained in samples aged 20 h at 450°C. In duplex-aged samples, optimum mechanical properties were obtained in cryogenic treatment followed by 250°C/10 h + 450°C/20 h duplex aging treatment.

Effect of Heat Treatment Procedure on Mechanical Properties of Ti-15V-3Al-3Sn-3Cr Metastable β Titanium Alloy

In this study, the effects of various heat treatment procedures on the mechanical properties of the Ti-15V-3Al-3Sn-3Cr metastable β titanium alloy were investigated. Single-step and duplex aging treatments were applied to the alloy at low and high aging temperatures. Duplex aging treatments were carried out by selecting two different pre-aging times and temperatures: 10 h at 300 °C and 24 h at 250 °C. Thus, the effects of pre-aging on the mechanical properties of the alloy were examined. Optimum tensile properties were obtained in the duplex-aged samples, which was aged at 550 °C for 20 h after being pre-aged at 250 °C for 24 h. While fine, high volume fraction and uniformly dispersed α phases increased the tensile strength and % elongation of the alloy in the aging treatment, the fatigue crack propagation rate also increased. Also, it was observed that the threshold stress intensity factor range (ΔKth) increased with the aging treatment. While the lowest ΔKth value was obtained at the solution-treated sample, the highest ΔKth value was obtained in the sample to which duplex aging treatment was applied depending on precipitation of fine and high volume fraction of α phases.

Friction Stir Processing of Beta C and Ti-185: A Unique Pathway to Engineer Microstructures for Exceptional Properties in β Titanium Alloys

Metastable β titanium alloys offer a wide range of attractive property combinations. Conventional processing options have practical limitations in achieving maximum attainable properties and utilizing them to their fullest potential. In the current study, friction stir processing (FSP) of β alloys is explored as a unique path for microstructural engineering. Two metastable β titanium alloys, Ti-1Al-8V-5Fe (Ti-185) and Ti-3Al-8V-6Cr-4Mo-4Zr (Beta C), subjected to FSP with two different tool rotation rates at a constant traverse speed were analyzed in different microstructural conditions. Fully retained β grain structures with grain sizes in the range 4 to 7 µm in Ti-185 and 10 to 15 µm in Beta C were obtained in the as-FSP condition. Post-FSP duplex aging treatment of the low heat input condition resulted in better tensile properties compared to those of high heat input condition, attributable to high number density of nucleation sites generated during FSP. Transmission electron microscopy observations of high-strength Ti-185 sample revealed fine α platelets of length in the range 50 to 130 nm and an aspect ratio in the range 3 to 10, providing significant strengthening contribution. Approximate nose temperatures and nose time calculations of the continuous cooling transformation of β to α were made for various commercial Ti alloys to assess the potential of achieving ultra-high strength levels via FSP.

Effect of aging treatment on microstructures, tensile properties and intergranular corrosion behavior of Al–Cu–Li alloy

The influence of aging treatment on microstructures, tensile properties and corrosion properties of Al–Cu–Li alloy was investigated. The results show that the T8 duplex aging treatment was more effective than T6 and T8 single aging treatment in enhancing the tensile properties and improving the intergranular corrosion (IGC) resistance. Based on the microstructure observation, tensile test, electrochemical experiment and IGC measurement, the factors which affect the microstructures, tensile properties and IGC behavior changing of Al–Cu–Li alloy during aging treatments were discussed in detail.

Two-step Aging Treatment in Ultra-High-Strength Al-Zn-Mg-Cu Aluminum Alloy

The parameters of duplex aging treatment of pre-stretched plates including both the temperature and the holding time of two aging stages have been systematically investigated by using electric conductivity and tensile properties tests, exfoliation corrosion experiments and TEM observations. The results show that both the first and the second age have effect on properties of plates after having been performed by different duplex aging treatments and the effect of the second age is much greater. It is found that such a duplex aging treatment is appropriate in which the temperature of the second age is 155°C and the holding time of the first and the second age is 4-6 and 28-32 hours, respectively. The ultimate strength of specimens treated with the duplex aging treatment given above can achieve 540MPa while electric conductivity is 40.5-42 %IACS.

Effect of ω-assisted precipitation on β→α transformation and tensile properties of Ti–15Mo–2.7Nb–3Al–0.2Si alloy

Microstructure and tensile properties of Ti–15Mo–2.7Nb–3Al–0.2Si alloy subjected to single and duplex aging treatments were investigated. The single aging treatment was carried out at 500°C for 8h. The duplex aging treatments was performed at 320°C for 2h for the first step, and the second step was carried out as the single treatment. As for microstructure, researches indicated that the precipitation formed during aging treatments was affected by phase transformation courses. Different from the needle-like α precipitates of β matrix during the single aging treatment, the finer shuttle-like α precipitates during the duplex aging treatment was obtained due to the assistance of ω phase formed in the first step aging. EBSD analysis showed that the orientation of precipitation was similar no matter with the single aging or the duplex aging treatment. The higher ultimate tensile strength value of 1437MPa was obtained through strengthening of shuttle-like α phase with a length of 0.5μm in the duplex aging treatment, with an acceptable elongation of 10.6%. The tensile fracture of those aging treatments illustrated that deep dimples in the duplex aging sample were beneficial for the higher strength.

Influence of Rate of Heating to Aging Temperature on Precipitation Hardening in a Metastable β Titanium Alloy

A comparison between slow heating to aging temperature and direct charging at aging temperature on the microstructure and mechanical properties obtained after the aging was established for the metastable beta (β) titanium alloy Ti-15V-3Cr-3Al-3Sn. The alloy was subjected to two single aging (SA) and two duplex aging (DA) conditions, with two heating rates to aging temperature: (i) low heating rate of 5 oC/min (ii) direct charging into a furnace heated to aging temperature. The microstructure analysis was carried out using Field Emission Scanning Electron Microscopy. Mechanical Testing was carried to evaluate Ultimate Tensile Strength (UTS), 0.2% Yield Strength (YS), % Elongation (%El.), % Reduction in area (%RA) and hardness. In the case of SA samples aged at 500 °C for 8 h and 500 °C for 10 h, heating rate of 5 °C/min to aging temperature resulted in a finer microstructure but did not help in achieving better strength-ductility combination compared to direct charging. Lower rate of heating allows enough dwell time in the temperature range 250-300 oC for pre-precipitation reaction to occur which aids in fine scale precipitation of alpha phase during aging. In the case of DA samples aged at 250 oC for 24 h followed by 500 oC for 8 h and 300 oC for 10 h followed by 500 oC for 10 h, no tangible difference between lower rate of heating and direct charging was observed in mechanical properties or microstructure. This is believed to be due to the pre-aging steps 250 oC/24 h or 300 oC/10h in the two DA treatments, which create finely distributed precursors thereby leaving no scope for the heating rate to play a role.

Studies on single and duplex aging of metastable beta titanium alloy Ti–15V–3Cr–3Al–3Sn

This paper presents the age hardening behavior of metastable beta titanium alloy Ti–15V–3Cr–3Al–3Sn subjected to various single and duplex aging treatments. Single aging was carried out in the range 200–550°C for times up to 150h (h). For duplex aging first step was performed in two different ways: (i) 250°C for 24h (ii) 300°C for 10h; second step was carried in the range 350–500°C, for times up to 150h. The decomposition of alpha (α) phase during aging was monitored by hardness measurements, tensile testing, different microscopic techniques and X-ray diffraction. Duplex aging treatments resulted in higher hardness and strength compared to single aging. There was a good balance of tensile strength and ductility after two duplex aging treatments 300°C/10h+500°C/10h and 250°C/24h+500°C/8h. Precipitate free zones (PFZs) were observed when aged at ⩽450°C in the microstructure; aging at ⩾500°C gave freedom from such zones. Duplex aging resulted in a finer size and higher density of α precipitates compared to single aging. Duplex aging 250°C/24h+500°C/8h led to a four to five fold improvement in high cycle fatigue (HCF) life compared to single aging at 500°C/10h. The observed improvement in HCF life could thus be related to smaller size and larger density of α precipitates resulting from duplex aging. Optical microscopy and X-ray diffraction studies clearly revealed that preaging for 10h at 300°C accelerated the α-phase precipitation reaction during aging.

Enhanced mechanical properties in an Al–Cu–Mg–Ag alloy by duplex aging

Abstract A type of duplex aging heat treatment was developed to improve the mechanical properties at room temperature and elevated temperatures in a pre-strained Al–Cu–Mg–Ag alloy. In contrast to the conventional T8 temper at 165 °C and 200 °C, the hardening response of the alloy to aging was increased by duplex aging treatment, the ultimate tensile strength and yield strength of duplex aging temper were improved by approximately 3–7%, which was attributed to the fact that the recovery of dislocations occurred and the precipitation of θ′ phase was restrained effectively at high aging temperature, and more Ω precipitates were formed during secondary aging.

Influence of HIP processing on microstructure and mechanical properties of superalloy Udimet 720LI

Inert gas (high purity argon) atomised powder of composition conforming to that of the superalloy Udimet 720 of low interstitial grade was hipped at 1200°C/120 MPa/3 h. The hipped alloy has shown near theoretical density and consisted of equiaxed grains with an average diameter of ∼45 μm. While primary γ′-Ni3 (Ti, Al) precipitates with an acicular morphology were found at the grain boundaries, finer secondary γ′ precipitates with near cuboidal morphology were present in the austenite γ matrix. The yield strength (YS) of the as hipped alloy was found to be the same as that of the wrought alloy heat treated for creep applications (termed as creep resistant alloy) at room temperature (RT) as well as at 650°C. However, the ultimate tensile strength (UTS) and ductility were found to be higher than those of the wrought creep resistant alloy. On the other hand, the YS and UTS of the as hipped material were lower than those of the wrought alloy heat treated for high strength applications (termed as high strength alloy), although the ductility of the former was comparable to that of the latter. In order to improve the strength, the hipped alloy was subjected to a heat treatment consisting of solution treatment followed by two-step aging. Extensive precipitation of fine and coarse γ′ precipitates with cuboidal morphology during duplex aging treatment has led to a considerable improvement in YS and UTS of the alloy, although the corresponding ductility dropped moderately at RT and at 650°C. Fractography of the tensile tested specimens has shown ductile transgranular mode of fracture in the as hipped alloy at RT and at 650°C, while the hipped+heat treated alloy exhibited a mixed mode of fracture at those temperature. The stress rupture properties of the as hipped alloy compare well with those of the wrought alloy and have been found to improve significantly after heat treatment. The present investigation reveals that the hipped superalloy Udimet 720LI has substantial potential for use in the development of near net shaped components for aerospace applications.

Effect of Single and Duplex Aging on Precipitation Response, Microstructure, and Fatigue Crack Behavior in Al-Li-Cu Alloy AF/C-458

The interrelationships between precipitate characteristics and mechanical properties of Al-Li-Cu alloy AF/C-458 were quantified. The microstructure, precipitation response, and fatigue crack growth (FCG) rates in the Al-Li-Cu alloy AF/C-458 were studied following single and duplex aging treatments for varying aging times on specimens that were given a 6% stretch after solution heat treatment. The aging response was studied using hardness and compression yield strength measurements. Quantitative transmission electron microscopy methods were used to characterize average size, volume fraction, number density, and interparticle spacing of strengthening precipitates [i.e., δ’ (Al3Li) and T1 (Al2CuLi)]. Strength and FCG rates for select heat treatments were obtained and were related to the precipitate microstructure and yield strength data.

The Strengthening and Microstructure of Precipitation Hardened Al-Li-Cu Alloys

The interrelationships between precipitate characteristics and mechanical properties of an Al-Li-Cu alloy AF/C458 was quantified. The microstructure, precipitation response, and strength in the Al-Li-Cu alloy AF/C458 were studied following single and duplex aging treatments for varying aging times on specimens that were given a six percent stretch after solution heat treatment. Aging response was studied using hardness and compression yield strength measurements. Quantitative transmission electron microscopy methods were used to characterize average size, volume fraction, number density, and interparticle spacing of strengthening precipitates, {delta}'(Al{sub 3}Li) and T{sub 1} (Al{sub 2}CuLi). (orig.)

An Economical Heat Treatment Cycle for IMI Ti-230

IMI Ti-230 (Ti + 2.5% Cu) is a commercial age-hardening alloy which is capable of withstanding considerable cold deformation in the solution heat treated condition. Age-hardening is associated with the coherent Ti2Cu precipitates. IMI recommends a duplex aging treatment comprising of nucleation (first aging) at 400°C for 24 hours followed by growth (second aging) for 8 hours at 475°C. This investigation was aimed at designing a shorter and economical heat treatment cycle for achieving properties comparable to those obtained by the standard 32 hours duplex aging treatment as recommended by IMI. In addition, the effects of cold deformation at various stages in the aging cycle on the precipitation reaction were assessed by tensile property measurements.