Oxidation characteristics of Ti-25Al-10Nb-3V-1Mo

Static oxidation kinetics of Ti-25Al-10Nb-3V-1Mo (atomic percent) were investigated in air over the temperature range of 650–1000°C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to two distinct stages of parabolic oxidation. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using x-ray diffraction techniques, electron microprobe analysis, and energy dispersive x-ray analysis. Oxide scale morphology was examined using scanning electron microscopy of the surfaces and cross-sections of oxidation specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO₂ doped with Nb, a top layer of Al₂O₃ and a thin bottom layer of TiN. The transition between the first and second parabolic stage is linked to the formation of a TiAl layer at the oxide-metal interface. Porosity also formed in the TiO₂ layer during the second stage, causing degradation of the oxide and breakaway oxidation.     

High-Temperature Oxidation of Ti-48Al-2Nb-2Cr and Ti-25Al-10Nb-3V-1Mo

The short-term oxidation behavior of a-TiAl alloy (Ti-48Al-2Nb-2Cr) was compared andcontrasted to that of an₂-Ti₃Al base(Ti-25Al-19Nb-3V 1Mo) alloy. Oxidation ofTi-25Al-10Nb-3V-1Mo was found to occur at a moderate rate at 800°C, in aN₂ + 20% O₂ environment. A largeincrease in the oxidation rate occurred above thistemperature. This large weight increase was attributedto a breakdown in the protective oxide scale on the surface of the₂ intermetallic alloy, therebypermitting rapid diffusion of oxygen and nitrogen to thesurface of the intermetallic. The oxidation rate of thisalloy at 1200°C was not significantly higher thanthe oxidation rate at 1000°C. In contrast, theoxidation rate of Ti-48Al-2Nb-2Cr remained low up to1200°C. At this temperature, a significant increasein oxidation was observed and was attributed to acceleratedoxygen diffusion through the ₂ phaseand increased solubility of oxygen in the gamma phase ofthe intermetallic microstructure. This weight increaseoccurred despite the fact that at 1200°C, theintegrity of the oxide layer formed on the surface ofthis alloy was maintained. The results of this studyillustrate the need for developing protectiveenvironmental coatings tailored to the individualintermetallic alloy.     

Strength and modulus of a molybdenum-coated Ti-25Al-10Nb-3V-1 Mo intermetallic

The three- point bend strength, Young’s modulus, and vibrational damping of a plasma- sprayed molybdenum-coated Ti- 25Al- 10Nb- 3V- lMo intermetallic were measured. The bend strength of the intermetallic samples was significantly reduced as a result of the molybdenum coating. This decrease in the strength was attributed to cracks formed in the molybdenum coating during the plasma spraying process. Experimental measurements done using the piezoelectric ultrasonic composite technique (PUCOT) indicated that the modulus and vibrational damping of the coated samples were significantly higher than for the uncoated substrates. Thermal cycling of the molybdenum- coated intermetallic between 600 °C and room temperature revealed a saturation increase in the modulus with a corresponding decrease in the mechanical damping. This behavior was attributed to crack healing occurring in the molybdenum coating during the thermal cycling process.     

NiAl-25%Cr合金的高温蠕变行为

研究挤压NiAl-25Cr合金在1073~1123K温度区间的蠕变行为。结果表明:在实验温度区域内,挤压NiAl-25Cr合金表现出两种明显不同的蠕变机制;在低温区域中,由位错的滑移和攀移控制蠕变变形过程;而在高温区域中,位错粘滞滑移控制蠕变变形过程。在研究蠕变的温度范围内,合金的蠕变表观激活能高于Ni的晶格自扩散能,这可以解释为在蠕变瞬时变形过程中,第二相粒子沿着基体相运动的结果,第二相粒子可能是γ'-Ni3Al相或α-Cr相。     

Ti-25Al-14Nb-2Mo-1Fe合金的热变形行为及本构方程的建立

通过热模拟压缩试验研究了Ti-25Al-14Nb-2Mo-1Fe合金在变形温度950~1100 ℃,变形速率0.001~1 s^-1,最大变形程度50%条件下的热变形行为。结果表明：Ti-25Al-14Nb-2Mo-1Fe合金的流变应力对热变形工艺参数（变形温度和变形速率）的敏感性较高,其真应力-真应变曲线具有峰值应力、应变软化和稳态流动特征。采用Arrhenius双曲正弦函数和多元回归处理法确定了合金在试验条件下的应力指数n、变形激活能Q等材料参数,建立了Ti-25Al-14Nb-2Mo-1Fe合金高温变形本构关系模型。     

Ti-6Al-3Nb-2Zr-1Mo合金片层组织热加工行为

利用Gleeble-1500热模拟试验机对Ti-6Al-3Nb-2Zr-1Mo合金片层组织进行热压缩实验,实验温度为850～1050℃,应变速率为0. 01～1 s~(-1),变形量为60%。实验结果表明,热加工温度一定时,流变应力随变形量和应变速率的增加而急剧增加直至达到峰值,然后下降,最后趋于平缓,这是由加工硬化和动态再结晶所致。应变速率恒定时,随着变形温度的上升,流变应力随之降低。绘制应力-应变曲线,计算其热变形激活能Q为748. 845 k J·mol~(-1),构建本构方程,并在动态材料模型的基础上建立了热加工图。并通过加工图确定3个失稳区,变形温度为980～1030℃、应变速率为0. 3～1 s~(-1)时合金发生剪切,形成绝热剪切带。结合加工图,确定了适合的加工区域,即加工温度为970～1010℃,应变速率为0. 03～0. 07 s~(-1)。     

组织对医用Ti-3Zr-2Sn-3Mo-25Nb钛合金低周疲劳行为及变形机制的影响

研究了具有2种不同组织（固溶态、时效态）的Ti-3Zr-2Sn-3Mo-25Nb(TLM)合金在室温应变控制的低周疲劳循环变形行为及微观变形机制。结果表明：TLM合金的循环硬化/软化行为与应变幅和组织密切相关。固溶态合金的低周疲劳寿命更高,且弹性模量均随循环周次和总应变幅的增大,从保持不变到急剧增加,时效态的弹性模量则在循环变形过程中基本保持不变。微观组织特征表明,固溶态合金的循环变形机制主要依赖位错滑移、变形诱发的α″马氏体和独特的“Z”型β孪晶协同作用,而时效态合金则只是以位错滑移为主。     

FEATURES OF ANNEALING MICROSTRUCTURE AND TEXTURE IN Ti－25Al－10Nb－3V－1Mo SHEET

ＦＥＡＴＵＲＥＳＯＦＡＮＮＥＡＬＩＮＧＭＩＣＲＯＳＴＲＵＣＴＵＲＥＡＮＤＴＥＸＴＵＲＥＩＮＴｉ－２５Ａｌ－１０Ｎｂ－３Ｖ－１ＭｏＳＨＥＥＴＭａｏＷｅｉｍｉｎ；ＹｕＹｏｎｇｎｉｎｇ；ＹａｎｇＨｏｎｇ；ＳｏｎｇＢｏ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａ...     

SiC和Al2O3颗粒对Ti-25Nb-3Mo-3Zr-2Sn合金微磨损行为的影响

本文研究了SiC和Al₂O₃颗粒对生物医用植入材料Ti-25Nb-3Mo-3Zr-2Sn合金的微磨损行为的影响。在文中研究了合金的比磨损率、摩擦系数、磨损机制以及微磨损与腐蚀之间的协同作用。研究结果显示,合金的比磨损率随磨粒尺寸的增加而增加。由于SiC磨粒的硬度和切削性均优于Al₂O₃磨粒,由此在同尺寸磨粒下SiC磨粒所造成的材料的损失比Al₂O₃磨粒造成的要大。摩擦系数的结果显示,在同一种磨粒作用下,Hank’s溶液中所获得的摩擦系数的平均值大于蒸馏水中所获得的摩擦系数平均值,且由于Hank’s溶液的腐蚀性所致在Hank’s溶液中获得的摩擦系数的稳定性要比在蒸馏水中的稳定性差;在同尺寸磨粒下,Al₂O₃磨粒所造成的摩擦系数要大于SiC磨粒所造成的。随磨粒尺寸的减小,磨损机制由三体磨损转变为混合磨损之后再转变为二体磨损。从磨损机制图中可以看出腐蚀对材料损失的贡献是不容小视的,磨损机制为以磨损为主的磨损腐蚀。     

Ti-6Al-3Nb-2Zr-1Mo钛合金热变形行为及加工图

利用Gleeble-3800热模拟试验机,在变形温度为820-1060℃及应变速率为0.001-1s_-1参数范围内对Ti-6Al-3Nb-2Zr-1Mo钛合金进行等温恒应变速率压缩试验。建立了该合金的高温变形本构方程,得到两相区和单相区的表面激活能分别为764.714 和126.936 kJ/mol。基于DMM和Prasad失稳准则建立了应变为0.4和0.7时的热加工图。分析加工图发现: Ti-6Al-3Nb-2Zr-1Mo钛合金在840–1060 ℃,应变速率为0.001–0.1 s_-1,之间主要发生DRV/DRX,此区间变形时耗散率峰值51%分别出现在940℃/0.001s_-1和880℃/1s_-1,其变形后微观组织演变机制与热加工图匹配较好,当变形发生在820℃,较高应变速率(≥1s_-1)下该合金加工时易发生流变失稳现象。     

热处理对Ti-18Nb-10Zr合金微观组织和超弹性的影响

研究了固溶、固溶时效、短时退火对Ti-18Nb-10Zr(at%)合金微观组织和超弹性的影响。采用室温拉伸测试了合金超弹性;借助X射线衍射（XRD）、电子背散射衍射（EBSD）、透射电子显微镜（TEM）对微观组织、相变行为进行了观察与分析。结果表明,冷轧态Ti-18Nb-10Zr合金,800 ℃固溶后,发生了完全再结晶,由β相和细小的无热ω相组成,回复应变约为2.65%;再在350 ℃时效后,由于等温ω相尺寸和体积分数显著增加,急剧降低了合金Ms,应力-应变曲线未呈现超弹性;650 ℃短时退火后,合金基本完成再结晶,由单一的β相组成,平均晶粒尺寸约为10 μm,晶粒细化改善了合金超弹性,回复应变约为2.86%。     

Aging effects on the creep behavior of the near-alpha titanium alloy Ti-1100

During aging of the silicon-bearing, near-alpha titanium alloy Ti-1100 at the service temperature of 593 °C, the precipitation of Ti₃AI and silicide particles has been observed. The objective of this article is to determine the influence of these precipitates on creep behavior. Stress relaxation tests, with the advantage of needing only a short time to produce a complete creep curve, were used to determine the creep behavior of Ti-1100. These accelerated creep tests reduce the chance of metallurgical changes that could occur in the long time required to perform conventional creep tests. The creep results obtained from the stress relaxation tests were verified with those obtained from conventional monotonic creep tests. Aging of the material for 500 h at 593 °C, where full precipitation of Ti₃AI is assumed to be incomplete, resulted in a small decrease in creep resistance compared to the unaged condition. Specimens aged for 1000 h, which corresponds to the averaged condition in which the precipitation of Ti₃AI is expected to be completed, were also examined. It was observed that these specimens yielded creep resistance similar to that of the unaged condition. Material aging for 1000 h followed by a special heat treatment, which results in the dissolution of Ti₃AI particles, although not affecting the silicide precipitates, resulted in the poorest creep resistance of the aging conditions investigated. The major conclusion of this study is that the presence of Ti₃AI has a beneficial influence on the creep resistance of Ti-1100 alloy.     

热处理对Nb-35Ti-4C合金微观组织和力学行为的影响

采用XRD、SEM和XRD对Nb-35Ti-4C合金热处理前后的相组成、界面结构、组织演变及力学行为进行研究。结果表明:热处理前后合金均由Nbss和(Nb,Ti)C构成。热处理过程中Nbss内部析出长条状的二次(Nb,Ti)C;(Nb,Ti)C内则析出长条状的二次Nbss。二次Nbss依附于fcc(Nb,Ti)C的密排面(111)面形核,与母相(Nb,Ti)C满足(N-W)位相关系:[011]_((Nb,Ti)C)//[001]_(Nbss), (111)_((Nb,Ti)C)//(110)_(Nbss)。碳化物与Nbss具有洁净良好的界面结合。热处理后单相(Nb,Ti)C变为(Nb,Ti)C+二次Nbss的共析组织。纳米压痕测试表明共析组织转变降低了碳化物的脆性,提高了合金的韧性。     

Influence of microstructure and alloying elements on corrosion behavior of Ti-13Nb-13Zr alloy

This work reports the effect of heat treatment on the corrosion behavior of Ti-13Nb-13Zr alloy in Ringer’s solution. The microstructural evolution of various phases after beta solution treatment (βST) and alpha + beta solution treatment (α+β ST), is studied using optical microscope, electron probe microanalysis and XRD techniques. Corrosion behavior of the solution treated samples is studied in Ringer’s solution using open circuit potential-time measurements and cyclic polarization. Corrosion studies reveal that, the heat-treated samples with depletion of Nb to very high levels in alpha phase exhibit inferior corrosion behavior. Amongst all the heat-treated samples investigated, the water quenched α+β ST specimen exhibit superior corrosion resistance due to the even distribution of the alloying elements in the three phases, namely α,α″ and β.     

新型β钛合金Ti-25Nb-10Ta-1Zr-0.2Fe的固溶时效行为

设计一种新型生物医用亚稳定β钛合金,合金成分为Ti-25Nb-10Ta-1Zr-0.2Fe(质量分数),采用真空自耗电弧熔炼制备合金锭坯,研究合金的固溶时效行为。通过X射线衍射(XRD)仪,透射电子显微镜(TEM),扫描电子显微镜(SEM)研究合金的相组成及微观组织。测量合金时效后的抗拉强度和不同时效时间的硬度。结果表明:800℃,1h固溶后合金得到马氏体α″相,400℃下时效,短时间即得到ω相和β相。ω相为脆性相,大量ω相的产生使合金的硬度值提高很多,但是强度值相比较冷轧态下降明显,使得材料断裂方式变为脆性断裂。合金在72h时效后ω相仍然保持较多量。     

氢对锻态Ti－25Al－10Nb－3V－1Mo合金热压缩行为的影响

利用等温压缩方法研究了氢对Ｔｉ_３Ａｌ基的Ｔｉ－２５Ａｌ－１０Ｎｂ－３Ｖ－１Ｍｏ锻态合金热变形行为的影响。在９００～１０００℃范围内，氢含量为０．２％的试样可使峰值流变应力比未氢化试样降低２５％～３１％，即相当于降低热压缩温度将近５０℃。相同温度变形的试样中氢含量增加所产生的组织变化与在更高温度压缩后所产生的组织变化相当。     

Tensile and creep properties of Ti-600 alloy

Ti-600 is one of the high performance titanium alloys used at 600℃, which was developed in Northwest Institute for Nonferrous Metal Research （NIN） in China. The tensile and creep properties of Ti-600 alloy with different thermal treatment conditions were investigated. The results indicate that Ti-600 alloy possesses favorite comprehensive properties solution-treated at 1020℃ for l h, then air-cool, and aged at 650℃ for 8 h, finally air-cooling, especially possesses quite good creep resistance. The residual deformation is less than 0.1% for the alloy exposed at 600℃ for 100 h with the stress of 150 MPa, and the bimodal microstructures of the alloy are almost the same as that of the alloy treated by duplex thermal treatment, only needle primary α phases became relatively thicker and coarsened. The ultimate strength and the elongation of the alloy tested at ambient temperature are l 080 MPa and 12%, respectively; while at 600℃, they are 690 MPa and 16%, respectively. The ductility of the alloy tested at room temperature is no less than 5% after thermal exposing at 600℃ for 100 h.     

Ti-10V-2Fe-3Al合金的高温流变行为及热加工图

利用Gleeble-3800热模拟试验机对Ti-10V-2Fe-3Al合金进行了变形温度为850~1150 ℃,应变速率为0.01~10 s-1的等温热压缩实验。引入Zener-Hollomon参数,建立了该合金的热塑性变形双曲正弦本构方程。基于动态材料模型理论构建了该合金在不同应变下的热加工图。结果表明：Ti-10V-2Fe-3Al合金的流变失稳区主要发生在高应变速率下,热变形时适宜的变形安全区温度为1100~1150 ℃,应变速率为0.01~0.07 s-1。     

Substructure of recovered Ti-23Nb-0.7Ta-2Zr-O alloy

Ti-23Nb-0.7Ta-2Zr-O （TNTZO, molar fraction, %） alloy is a newly developed multifunctional r-type titanium alloy. This alloy was reported to deform via a unique dislocation-free deformation mechanism, and thus its recovery and recrystallization behavior should be further studied and compared with traditional BCC metals. The substructures of the cold-swaged and the annealed TNTZO alloy were investigated by transmission electron microscopy（TEM） to study the recovery of the cold-swaged TNTZO alloy. The results show that no dislocation can be distinguished from the cold-swaged TNTZO alloy due to the heavily-accumulated strains, whereas high density dislocations were observed in the cold-swaged TNTZO alloy after annealing at 800 ℃ for 5 min. During annealing, recovery proceeds through the redistribution and annihilation of the dislocations, which are considered to result from the plastic deformation and the recovery process of the cold-swaged TNTZO alloy is similar to that of ordinary BCC metals.