Microstructural adjustments and mechanical properties of a cold-rolled biomedical near β-Ti alloy sheet

In this study, microstructural adjustments and mechanical properties of a cold-rolled nearβ-type alloy Ti-25Nb-3Zr-3Mo-2Sn (wt%) sheet were investigated.Microstructures and phase transformation products strongly depended on aging temperatures. Solution treatments within singleβ-phase field removed the stress-inducedα″martensites and produced a few new lath-shaped ones, but metastableβphase still dominated. This is exactly the reason why current alloy exhibits the lowest modulus (54 GPa) and best elongation to fracture (39%),but the worst yield strength of only 340 MPa, at solutiontreated state. A fairly large number of ellipsoidalωphase nanoparticles precipitated throughout parentβphase during aging at 380℃. Theseωnanoparticles possess remarkable strengthening effect, but deteriorate ductility seriously. A novel post-aging process was proposed to remove brittleωphase. By contrast, aging at 450℃resulted in sufficient precipitation of fine needle-like a phase. This brought about the best combination of high yield strength (770 MPa) and moderate elastic modulus(75 GPa) and good elongation (15%) for biomedical implants.     

Effect of Aging on the Microstructure and Mechanical Properties of 1460 Alloy

Effects of the aging temperature on the hardening response,the tensile properties and the precipitate microstructure evolution of 1460 alloy were studied in this work.It was found that Al3(Sc,Zr) and d0(Al3Li) phases were precipitated from the matrix at the very early aging stage,while the precipitation of T1(Al2Cu Li) and h0(Al2Cu) was much slower than that of the d0 phase.When aging at higher temperature(160 and 190 °C),the d0,T1 and h0 phases tended to form simultaneously and grow up very quickly.Conversely,the d0 and h00(Al2Cu) phases were precipitated separately and more dispersive at lower aging temperature(130 °C).Taken together,the alloy aged at 160 °C exhibited improved mechanical properties owing to the uniform dispersion of the fine T1 precipitates.     

Evolution of Microstructures and Mechanical Properties of Zr-Containing Y-CLAM During Thermal Aging

The thermal stability and mechanical properties of China low activation martensitic steel with Zr and Y were investigated via thermal aging at 550 °C for 8000 h. The Laves phase content monotonically increased with thermal aging, and the volume fraction of the Laves phases stabilized in the alloy after 3000 h of thermal aging. The observed degradation in mechanical properties was because of the coarsening of M_(23)C_6 carbides and matrix grains during the earlier stages of thermal aging. The precipitation of Laves phases and V_3Zr_3C particles increased the strength and hardness of the alloy. Grain coarsening was the primary reason for the decrease in impact properties, and the ductile-to-brittle transition temperature increased from-71 to -48 °C after 8000 h of thermal aging.     

Relationship between microstructure and tensile properties on a near-β titanium alloy after multidirectional forging and heat treatment

In this study, a new near-beta titanium alloy, Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr, was prepared by induction skull melting(ISM) and multidirectional forging. The effect of aging heat treatment on microstructure and tensile properties of the alloy after solution treatment in the twophase(α + β) region was investigated. The micros tructure results show that the globular primary α phase(α_p) and the needle-like secondary α phase(α_s) are precipitated in the β matrix. The size of α_s increases with the increase in aging temperature,while the content of α_s goes up to a peak value and then decreases. The tensile testing results show that the strength increases first and then decreases with the increase in temperature. The variation of ductility presents the opposite way compared with the trend of strength level.When aged at 500 ℃, the alloy exhibits an excellent balance of tensile strength(1529 MPa) and elongation(9.22%). And the relative mechanism of strengthening and toughening was analyzed and discussed.     

Effect of second phase precipitation behavior on mechanical properties of casting Al-Cu alloys

The effect of the second phase precipitation behavior on the mechanical properties and fracture behavior of the modified casting Al-Cu alloys was investigated. The tensile strength of the alloys increases firstly and then decreases due to the appearance of θ＇ precipitation phases, which increases firstly and then become coarser with the aging time increasing from 10 h to 20 h at 155 ℃. The strength of the alloys reaches the peak, resulting from ,Ω and θ＇ precipitation phases, and decreases due to ,Ω phases becoming coarser and θ＇ precipitation decreasing with the aging time increasing from 10 h to 20 h at 165 ℃. ,θ phase becoming coarser and θ＇ precipitation decreasing result in the strength of the alloys drastically decreasing after aging at 175 ℃ for 20 h. The ductility remains high level with increasing aging time at 155 ℃. The ductility irregularly changes as aging time prolongs at 165 ℃. The ductility is very low and at the same time gradually decreases with increasing aging time at 175 ℃. The Al-Cu alloy with a promising combination of tensile strength and ductility of about 474 MPa and 12.0% after aging at 165℃ for 10 h is due to a dense, uniform distribution of,Ω precipitation phases together with a heterogeneous distribution of θ＇ precipitations.     

Effect of mold temperature and casting dimension on microstructure and tensile properties of counter-gravity casting Ti-6Al-4V alloys

The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 °C and 650 °C, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. β grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties' comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing(HIP). The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.     

EFFECTS OF AGING TEMPERATURE AND TIME ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AN Fe-BASE SUPERALLOY

The mechanical properties and microstructure of an Fe-base superalloy GH35A have been examined after aging at 650—750℃ for 100—10000 h.The tensile strength of the alloy changes no more with aging temperature and the time at room temperature,but the ductility and impact toughness at room temperature,as well as the stress-rupture life up to 700℃ de- crease slowly during aging up to 10000 h The initiation time to worsen its properties becomes shorter as the aging temperature rises.The variation of the mechanical properties of the alloy was found mainly depending on the formation,morphology,distribution and characteristic of the σ-phase precipitation.     

Microstructure and mechanical properties of a new Ti_2AlNbbased alloy after aging treatment

A new Ti_2AlNb-based alloy with the composition of Ti-22Al-25Nb-1Mo-1V-1Zr-0.2Si(at%) was fabricated in the sequence of arc melting, forging, solid solution and aging. Present paper focuses on the effects of aging temperatures(700, 750, 800, 850 and 900 ℃) on microstructure, room-temperature tensile properties as well as tensile properties at 650 ℃ and creep properties at650 ℃/150 MPa. It is obvious that the aging treatment promotes the precipitation of O lathes from B2 matrix.With aging temperature increasing, the content of O phase decreases and its size increases gradually, which leads to the decrease in tensile strengths both at room temperature and 650 ℃ and a little increase in ductility. For creep properties, the sample aged at 700 ℃ shows the best creep resistance due to its extremely high O phase content. Aging at 800 ℃ leads to the decrease in the content of O phase and softening of the alloy significantly. However, with aging temperature further increasing from 800 to 900 ℃,the precipitated O phase will be coarsened gradually, which strengthens the alloy again.     

Inluence of heat treatment on microstructure and tensile properties of a cast Al-Cu-Si-Mn alloy简

Solution and aging treatments are important approaches to improve mechanical properties and microstructure of aluminum-base alloys. In this research, a new type high strength AI-Cu-Si-Mn cast alloy was prepared. The effect of different solution and aging treatment temperatures on microstructure and mechanical properties of the AI-Cu-Si-Mn cast alloy were studied by means of microstructure observation and mechanical properties testing. Results showed that after solution treated at different temperatures for 12 h and aged at 175 ℃ for 12 h, with the increase of the solution temperature, both the tensile strength and the elongation of the alloy firstly increase and then decrease, and reach their peak values at 530 ℃. When the solution temperature is below 530 ℃, the microstructure of the alloy consists of a phase, undissolved e phase and T phase; while when it exceeds 530 ℃, the microstructure only consists of cr phase and T phase. After solution treated at 530 ℃ for 12 h and aged at different temperatures for 12 h, both the tensile strength and the elongation of the alloy firstly increase and then decrease with the increasing of temperature, and reach their peak values at 175 ℃. Therefore, the optimal heat treatment process for the alloy in this study is 12 h solution at 530 ℃ and 12 h aging at 175 ℃, and the corresponding tensile strength is 417 MPa, elongation is 4.0%.     

Effect of heat treatment on microstructure and high temperature tensile properties of cast nickel-base superalloy with high W, Mo and Nb contents

The microstructural features and high temperature tensile properties of M963 superaUoy at as-cast, as-solutioned and as-aged conditions were investigated in detail. The results show that the solution treatment at 1220℃ for 4 h,AC causes an increase in high temperature yield strength but a drastic drop in high temperature ductility due to the precipitation of both the secondary carbide M6C along grain boundaries and at the interdendritic regions and very fine γ‘ particles in the dendrite cores. Aging treatment following the solution treatment can improve the high temperature tensile properties of M963 superalloy due to the coaraing of the γ’ precipitate. One stage aging at 850℃ for 16 h following the solution treatment causes an increase in both strength and ductility d alloy M963, and two-stage aging of 1089 ℃/2 h, AC plus 850℃/16 h, AC following the solution treatment further increases the ductility d alloy M963 but slightly decreases its strength.     

Effect of heat treatment and exposure on microstructure and mechanical properties of Ti–25V–15Cr–2Al–0.2C (wt%)

The effect of heat treatment and exposure on the microstructure and mechanical properties of extruded, burn-resistant β titanium alloy Ti–25V–15Cr–2Al–0.2C (wt%) has been studied. It has been found that pre-exposure annealing at 600, 700 and 800°C affected the distribution of α phase that precipitated following subsequent exposure at temperatures between 450 and 550°C. Samples annealed at 600°C and subsequently exposed at 450°C showed excellent microstructural and property stability. Although the room-temperature ductility of the alloy decreased and the strength increased slightly with increasing exposure time at 500°C, no further drop in ductility was observed after 500 h. However, a gradual degradation of properties with exposure time was observed in samples exposed at 550°C. The significance of the observations is discussed in terms of the effect of pre-exposure annealing and exposure on α precipitation and tensile properties.     

Enhanced Strength in Cu-Ag-Zr Alloy by Combination of Cold Working and Aging

In this investigation, the effect of different degree of cold rolling and post-aging treatment on the microstructure and mechanical properties of a Cu-3wt.%Ag-0.5wt.%Zr alloy was studied by means of hardness measurement, tensile tests, optical and electron microscopy. The alloy was subjected to cold rolling up to 80% followed by aging in the temperature range of 400-500 °C. The yield strength, ultimate tensile strength and hardness were found to increase as degree of cold rolling increased, but at the expense of ductility. Aging of cold rolled samples in the studied temperature range has resulted in different combinations of strength and ductility. However, aging of cold rolled samples at 400 °C for 1 h has resulted in a combination of high strength and moderate ductility. A yield strength and ultimate tensile strength of 511 and 560 MPa, respectively with a ductility of 12% were achieved for 80% cold rolled and aged (400 °C for 1 h) sample. The high strength achieved after 80% cold rolling and aging is mainly attributed to precipitation of fine silver precipitates.     

Effect of Aging Treatment on the Formation of α Precipitates in β-Type Ti–6Mo–6V–5Cr–3Sn–2.5Zr Alloys

The microstructural evolution of a novel β-type Ti–6Mo–6V–5Cr–3Sn–2.5Zr (wt%) alloy subjected to different aging treatments was investigated. The normalized intensity of the α precipitates reached a peak value at 450 °C. A nanoscale orthorhombic phase was observed to coexist with α precipitates in the β matrix, which followed the Burgers orientation relation of 〈\(1120\)〉_α//〈111〉_β and {0001}_α//{110}_β. Fine α precipitates were formed with metastable O and β′ phases, and the β phase was spinodally decomposed to β and β′ phases. The maximum hardness value of the specimen was obtained after aging at 450 °C. Compositional partitioning of Mo, V, and Cr elements occurred with the depletion of fine acicular α precipitates upon aging 450 °C.     

Microstructure control in two-phase Al–21Ti–23Cr alloy

To improve the mechanical properties of the Al–21Ti–23Cr two-phase alloy consisting of L1₂ matrix and 20 vol% Cr₂Al as a second phase, microstructure control was conducted through the aging treatment as a thermal process and the addition of V and Zr as conventional alloying. It was found that TiAlCr was precipitated as a third phase in the L1₂ matrix by the aging treatment at 800 and 1000°C, and its size was smaller at 800°C than at 1000°C. The yield strength of the aged alloy increased rapidly only at 800°C although the third phase was precipitated at both 800 and 1000°C. In the V-added two-phase alloys, the yield strength and the strain increased simultaneously when V was added up to 3 at%, which is attributable to the improvement in the ductility of Cr₂Al. Microstructure control conducted in this study suggests the possibility of improving the mechanical properties of L1₂ (Al,Cr)₃Ti-based two-phase alloy by precipitating the fine third phase in the L1₂ matrix and enhancing the ductility of the second phase.     

Effect of aging and cold rolling on the microstructure and mechanical properties of a new Fe-Mn-Al-Cr-C duplex alloy

The microstructural changes that occur during aging and cold rolling of a new Fe-Mn-Al-Cr-C duplex alloy have been investigated. Two treatments were developed to produce either a good combination of tensile strength and ductility (σ _u =800 MPa, σ _y =525 MPa, and A=46%) or a high strength (σ _u =1340 MPa, σ _y =1200 MPa, and A=15%) with a ductile type of fracture after aging at 320 °C. Aging between 550 °C and 700 °C led to a significant decrease in strength and ductility due to the precipitation of the brittle βMn phase. However, aging above 750 °C showed a considerable increase in strength and ductility due to the precipitation of very fine grains of ferrite within the austenite phase.     

Effect of Microstructure on the Electrochemical Behavior of Ti-10 Mass% Mn Alloys in High Chloride Solution

The effect of microstructure on the corrosion of heat-treated Ti-10 mass% Mn alloys was investigated by electrochemical impedance spectroscopy (EIS) in 10% NaCl solution of pH 0.5 at 97 °C. Sample of solution heat treatment (ST) had a single β phase, and samples subjected to the aging heat treatment at 600 °C had α phase precipitation in β phases. The EIS measurements showed that the corrosion resistance of the aging heat-treated samples showed lower values than ST sample, however, much higher values than pure Ti. Thus, Mn was effective to increase the corrosion resistance of Ti alloys. Laser micrographs of heat-treated samples indicated that α phase was selectively corroded and made the pit after the corrosion test. The transmission electron microscope (TEM)-energy dispersive x-ray spectrometry (EDXS) analyses showed that the Mn content was 9 mass% in the β phase and 0.7 mass% in α phase. Hence, it was understood that less-Mn α phase was selectively corroded in the corrosion test. However, as compared with pure Ti, the aging heat-treated samples showed much higher resistance against the corrosion by the 0.7 mass% Mn in α phase. Finally, it was concluded that it was possible to keep the high corrosion resistance for heat-treated Ti-10 mass% Mn alloy by controlling the microstructure of α phase.     

热处理工艺对紧固件用高强钛合金棒材的组织和性能的影响

研究了紧固件用Ti-26合金棒材经80%变形后同溶态与时效态的显微组织和力学性能的变化规律.结果发现:不同的同溶温度决定Ti-26合金中β品粒的大小,时效温度决定析出α相的形态与尺寸.时效后的组织中只有β相与针状α,其中析出相α处于中间湿润状态.同溶后合金的强度较低,但塑性最好;时效后的强度高,塑性相对较低.时效过程中随温度的升高,强度降低,塑性提高.断口分析说明,析出的α相降低了合金的塑性,其中伸长率受到的影响最大.     

Thermal stability and creep behavior of Ti–V–Cr burn-resistant alloys

The thermal stability and creep behavior of Ti–35V–15Cr (35V alloy) and Ti–25V–15Cr (25V alloy) burn-resistant titanium alloys are researched. The results show that post-exposure tensile properties deteriorated with the increase in exposure temperature (450–600 °C). The decrease in tensile properties of the 35V alloy results from the combination of surface oxidation and microstructural changes and the decrease in tensile properties of the 25V alloy results from surface oxidation. The main change of the microstructure during thermal exposure is the heterogeneous precipitation of α phase on β grain boundaries. Increased vanadium content in the alloy shows an adverse effect on alloys’ thermal stability. The creep resistance of the 35V alloy is little better that that of the 25V alloy. During creep exposure at 540 °C for 100 h, the heterogeneous precipitation of α phase on β grain boundaries in 35V alloy strengthens the grain boundary, leading to increases in the creep resistance, while the heterogeneous precipitation of α phase in grains and grain boundaries in the 25V alloy is rod-like, leading to decreases in the creep resistance.     

Precipitation Hardening of Cu-3Ti-1Cd Alloy

Precipitation strengthening of Cu-3Ti-1Cd alloy has been studied using hardness and tensile tests, electrical resistivity measurements, and transmission electron microscopy. The alloy exhibited a hardness of 117 Hv in solution-treated (ST) condition and attained a peak hardness of 288 Hv after aging at 450 °C for 72 h. Electrical conductivity increased from 7%IACS (International Annealed Copper Standard) in ST condition to 13%IACS on aging at 450 °C for 16 h. The alloy exhibited yield strength (YS) of 643 MPa and ultimate tensile strength (UTS) of 785 MPa in peak-aged (PA) condition. Strengthening in Cu-3Ti-1Cd alloy in PA condition is attributed to solid solution strengthening effect of cadmium (Cd) as well as fine scale precipitation of metastable and coherent β′-Cu₄Ti phase. On overaging at 450 or 500 °C, the alloy showed a decrease in hardness as a result of formation of equilibrium precipitate β-Cu₃Ti as continuous precipitation within the matrix and as discontinuous precipitation at the grain boundaries. While the tensile properties are better, the electrical conductivity of Cu-3Ti-1Cd alloy is less than that of binary Cu-2.7Ti alloy. The strengthening mechanism is the same in both binary and ternary alloys of Cu-Ti, i.e., precipitation of metastable and coherent β′-Cu₄Ti phase.     

热处理对激光立体成形TB18钛合金组织和力学性能的影响

采用BLT-C1000型激光立体成形设备制备了沉积态的TB18钛合金,然后采用OM、SEM和拉伸试验机等方法研究了不同热处理工艺对TB18钛合金显微组织和力学性能的影响。结果表明,沉积态试验合金的宏观组织以长条形β晶粒为主,晶内由亚稳β相和针状次生α相组成,且存在贯穿β晶粒的沉积层线。随着直接时效温度的升高,原始β晶粒形状变化不大,内部次生α相厚度增加,在形貌上次生α相从针状向片状转变。直接时效温度高于550 ℃时,沉积层线消失,直接固溶温度高于830 ℃时显微组织以全β晶粒组成。固溶+时效处理后,微观组织以纵横交错的细层片状α相为主。随着直接时效温度的升高,抗拉强度和屈服强度降低,伸长率增加。固溶+时效后析出次生α相,抗拉强度和屈服强度显著增加,同时伸长率下降。综合考虑,实际生产中沉积态的TB18钛合金的最佳热处理工艺为直接时效500 ℃×4 h,此时强度和伸长率均高于指标要求。