钨对铸态Ti-45Al-8Cr-2Nb合金的高温性能影响

采用高温拉伸测试及显微组织观察,研究了微量钨对铸态Ti-45Al-8Cr-2Nb(原子百分比)合金的高温性能影响。结果表明,在基体合金中添加2%W,能使铸态合金的最大伸长率降低,而最大伸长率相应的温度向高温方向移动;高温变形过程中,晶粒滑动的协调过程由晶界扩散转化为体扩散;含钨的合金在800℃时的伸长率从0.62%提高到90%。     

Microstructure and mechanical properties of cast Ti-47Al-2Cr-2Nb alloy melted in various crucibles

The main factors limiting the mass production of TiAl-based components are the high reactivity of TiAl-based alloys with the crucible or mould at high temperature.In this work,various crucibles (e.g.CaO,Y2O3 ceramic crucibles and water-cooled copper crucible) were used to fabricate the Ti-47Al-2Cr-2Nb alloy in a vacuum induction furnace.The effects of crucible materials and melting parameters on the microstructure and mechanical properties of the alloy were analyzed by means of microstructure observation,chemical analysis,tensile test and fracture surface observation.The possibilities of melting TiAl alloys in crucibles made of CaO and Y2O3 refractory materials were also discussed.     

退火工艺对Ti-4Al-2V合金组织及耐蚀性能的影响

对挤压成形Ti-4Al-2V合金棒材进行普通退火、再结晶退火、双重退火处理,并通过X射线衍射仪、扫描电镜对退火前后的组织结构进行表征。同时,通过电化学工作站测试钛合金在3.5％NaCl溶液中的耐腐蚀性能,分析热处理工艺与合金腐蚀倾向间的相关性。结果表明,未处理合金棒材表面无明显宏微观缺陷,不同温度退火后钛合金主要组织为α相,960 ℃+570 ℃双重退火后,合金组织由粗晶粒状的α相和细针状的α相组成。未处理合金伴有网篮组织,经不同温度退火后获得少量魏氏组织和双态组织。通过分析不同温度退火后钛合金的极化曲线与交流阻抗谱可知,相比未处理合金,760 ℃退火后合金的自腐蚀电流密度较小,对应的极化电阻较大,腐蚀倾向较小,960 ℃+570 ℃双重退火后合金的Nyquist图显示最大的容抗弧,表明其耐蚀性能较好。     

溅射Ni-16Co-26Cr-10Al纳米晶涂层的熔盐热腐蚀性能

利用磁控溅射技术在铸造Ni-16Co-26Cr-10Al合金上溅射了相同成分的纳米晶涂层,并进行900℃热腐蚀实验,结果表明:溅射Ni-16Co-26Cr-10Al纳米晶涂层由于晶粒尺寸细小,促进了保护性氧化物形成元素Al沿原"短路扩散通道-晶界"向氧化前沿的扩散,从而促进了保护性Al2O3的快速形成,使得溅射Ni-16Co-26Cr-10Al纳米晶涂层表现出比M38合金更优异的抗热腐蚀性能。     

Ti-3.0Al-3.7Cr-2.0Fe低成本钛合金的热压缩变形行为

为研究钛合金的热压缩变形过程中流变应力、显微组织等随变形条件的变化,对自行研制的Ti-3.0Al-3.7Cr-2.0Fe低成本钛合金在Gleeble 1500D热模拟实验机上进行高温压缩变形实验。对d 8 mm×12 mm的试样进行等温压缩变形实验,研究该合金在变形量为30%、50%和70%(对应真应变为1.2)、变形温度为800~950℃、应变速率为0.01~10 s 1条件下的变形行为、流变应力的变化规律以及变形条件对显微组织的影响。结果表明:该合金流变应力受变形温度和应变速率影响显著,流变峰值应力随变形温度的升高和应变速率的降低而降低。采用Arrhenius双曲正弦模型确定该合金在本实验条件下的变形激活能Q=214.22 kJ/mol和应力指数n=3.81,并根据得到的参数建立相应的热变形本构关系为=6.91×108[sinh(0.011σ)]3.81exp[214 220/(RT)]。通过显微组织观察发现,在950℃、变形速率≥0.1 s 1时,发生再结晶现象,且随着变形速率的增加,再结晶现象越明显。     

Ti-3.0Al-3.7Cr-2.0Fe-0.1B钛合金的热压缩行为(英文)

利用Gleeble-1500D热模拟试验机对低成本钛合金Ti-3.0Al-3.7Cr-2.0Fe-0.1B的热压缩行为进行研究。采用的应变速率分别为0.01、0.1、1.0和10s1,选用的温度分别为800、850、900和950°C,试样的变形量最大为70%。结果表明:峰值流变应力随着温度的增加和应变速率的降低而降低;根据Arrhenius公式获得该合金在本实验条件下的本构方程为ε=6.1×1012[sinh(0.0113044σ)]3.35×exp(-261719.8/RT),并得到了该合金的加工图。当应变速率大于等于1.0s1时,合金内发生动态再结晶现象,且应变速率越大动态再结晶现象越明显。     

Hot Corrosion Behavior of SiO_2–Al_2O_3–Glass Composite Coating on Ti–47Al–2Cr–2Nb Alloy: Diffusion Barrier for S and Cl

Type Ⅰ hot corrosion behavior of SiO_2-Al_2O_3-glass composite coating based on Ti-47 Al-2 Cr-2 Nb substrate was investigated in the mixture salt of 25 wt%NaCl + 75 wt%Na_2SO_4 at 850 °C. The results showed that there was a bidirectional ion exchange between composite coating and the film of mixed salts, and the sodium ion in the molten salts penetrated into the glass matrix of composite coating, while the potassium ion in the glass matrix dissolved into the molten salts. A decrease in hot corrosion rate was achieved for the coated alloy in comparison with the bared substrate due to the composite coating acting as a diffusion barrier to sulfur and chlorine and preventing the molten salts from diffusing to the coating/alloy interface during the hot corrosion exposure. Additionally, the composite coating decreased the oxygen partial pressure at the coating/alloy interface and promoted the selective oxidation of Al to form a protective Al_2O_3 layer.     

Ti-22Al-24Nb合金热成形工艺参数优化研究

采用Gleeble-3500热模拟试验机研究Ti-22Al-24Nb合金在温度900～1110℃和应变速率0.01～10 s~(-1)条件下的热变形行为。分析了该合金的高温流变应力曲线特性和不同相区的热变形激活能及变形机制,并根据基于Prasad和Murty失稳判据下的加工图及相应的组织特征优化了该合金的热成形工艺参数。结果表明,Ti-22Al-24Nb合金的流变应力对热成形工艺参数敏感;其在(α_2+B2)两相区的主要变形机制为晶界滑移,对应的变形激活能为603.56 kJ/mol,而B2单相区的变形激活能为406.25kJ/mol,其变形主要以动态回复和动态再结晶的变形机制为主。根据这两种加工图的比较和组织观察可知,Ti-22Al-24Nb合金选择基于Prasad失稳判据下的加工图更为合理;其对应的主要失稳区为900～990℃、0.2～10 s~(-1)和1035～1095℃、1～10 s~(-1),且失稳区所预测的组织中主要存在绝热剪切带和局部流变失稳现象;而动态再结晶及胞状亚结构的组织易出现在η峰区,表明该合金较优的热力参数区间是990～1035℃、0.01～0.03 s~(-1),1040～1090℃、0.02～1 s~(-1)和1090～1110℃、0.01～0.18 s~(-1)。     

真空烧结温度对Ti-44Al-2Cr-4Nb-0.2W-0.2B合金显微组织及力学性能的影响

为获得细晶TiAl合金及有效减少传统铸造带来的内部缺陷,采用真空热压烧结工艺制备了Ti-44Al-2Cr-4Nb-0.2W-0.2B合金,研究了烧结温度对TiAl合金微观组织及力学性能的影响。结果表明:Ti、Al元素粉末反应合成后,经XRD检测,3种烧结温度(1150、1240、1300℃)烧结后的合金主要由γ-TiAl和α_2-Ti_3Al_2种基体相组成,随着烧结温度的增加,γ相含量增加,α_2相则减少;结合SEM观察发现,改变烧结温度可获得TiAl合金不同典型组织,其中1150℃烧结合金为近γ组织、1240℃烧结为双态组织、1300℃烧结为近片层组织,烧结温度的升高使得合金组织愈发均匀;配合EDS分析,烧结温度的升高有助于Nb元素在基体相中的扩散,同时合金密度随烧结温度的升高逐步增大,当烧结温度升至1300℃,合金的密度达到4.419g/cm~3;通过力学性能检测,在1240℃烧结制备的TiAl合金组织为细小的双态组织,显示出较好的综合力学性能,其显微硬度为5270 MPa,在高温压缩时展示出良好的抗压强度。     

Ti-6Al-4V合金渗氮层的生物腐蚀行为

采用真空感应快速渗氮技术对Ti-6Al-4V合金进行表面渗氮,将渗氮前后的试样置于SBF溶液中探究其耐蚀性。利用维氏硬度计、光学显微镜、电化学工作站、光学3D表面轮廓仪、扫描电镜(SEM)和X射线衍射(XRD)等技术对渗氮层进行测量和观察。试验结果表明:820 ℃下对Ti-6Al-4V钛合金进行真空感应渗氮处理后,渗氮层厚度达20 μm,其氮化物层硬度得到明显提高。同时,经过感应渗氮处理后样品的表面粗糙度增加。电化学试验表明经感应渗氮后Ti-6Al-4V钛合金的耐蚀性明显增强。     

定向凝固Ti-46Al-8Nb合金的微观组织演变与微观偏析(英文)

在3～70μm/s的生长速度范围内对Ti-46Al-8Nb(摩尔分数,%)合金进行定向凝固实验,研究其微观组织演变和微观偏析形式。在该生长速度范围内,固-液界面表现为规则的枝晶生长,一次枝晶间距随着生长速度的加快而逐渐减小。在定向凝固过程中观察到典型的L+β→α包晶反应,最终得到具有α2/γ层片和B2相的微观组织。在各个晶粒中,层片与β相枝晶初始生长方向呈0°或45°。包晶反应导致严重的成分偏析,在凝固过程中,铝富集在枝晶间,铌富集在枝晶心部。随着α相的形核和生长,铌的偏析程度逐渐增大,从而促进B2相的析出,而富集在枝晶间的铝在包晶反应发生后逐渐变得均匀、一致。     

Ti-6Al-4V在溴化锂溶液中的初期空化腐蚀研究

利用扫描电镜、粗糙度轮廓仪、三维视频显微镜和电化学测试技术研究了Ti-6Al-4V合金在溴化锂溶液中空化腐蚀的破坏过程及腐蚀和空化的协同作用。从粗糙度、平均空化腐蚀深度和微观形貌随时间的变化观察到Ti-6Al-4V合金空化腐蚀破坏的3个阶段:线性增长的初始阶段;增长速率降低的过渡阶段;粗糙度基本不变的稳定阶段。Ti-6Al-4V合金的低强度α相吸收空泡溃灭产生的冲击能优先发生塑性变形,材料表面变形不均匀,在空化作用下α相局部区域表面钝化膜破裂并暴露出钛合金基体,由于α相电位低于β相,形成小阳极大阴极,同时腐蚀物和腐蚀产物在空化的搅拌作用下能够及时扩散,加速了腐蚀溶解,产生的腐蚀坑又导致局部内应力更加集中而加强力学因素,表面凹凸程度增加。空化力学和电化学腐蚀的共同作用使腐蚀坑继续发展并促进了新腐蚀坑的生成,腐蚀坑周边的β相发生脱落,从而导致表面凹凸程度降低。初期阶段,电化学腐蚀促进了空化作用。     

Ti-48Al-2Nb-2Cr合金热变形行为及本构关系研究

采用Gleeble-1500热力模拟机对铸态Ti-48Al-2Nb-2Cr合金进行高温变形热压缩试验,变形温度范围为1050~1200℃,应变速率范围为0.001~0.1s^-1,压缩变形量为60%。研究该合金高温变形温度和应变速率与流变应力之间的关系,计算了合金激活能,并建立了Ti-48Al-2Nb-2Cr合金的Arrhenius本构模型和多元线性回归的本构模型。结果表明,该合金的激活能随温度升高和应变速率增大而增大;Arrhenius本构模型的相关系数为0.98228,平均相对误差为9.97%,相对误差在10%以内的点只占62.0%;而采用多元线性回归本构模型的相关系数为0.99566,平均相对误差为4.76%,相对误差在10%以内的点占92.6%,本构精度较高。     

Isothermal compression behavior and constitutive modeling of Ti-5Al-5Mo-5V-1Cr-1Fe alloy

Hot compression behavior of Ti-5Al-5Mo-5V-1Cr-1Fe alloy with an equiaxed (α+β) starting microstructure was investigated by isothermal compression test and optical microscopy. Based on the true strain–stress data with temperature correction, constitutive models with a high accuracy were developed and processing maps were established. Strain inhomogeneity at different locations in the compressed sample is reduced by raising temperature, leading to a uniform distribution of α phases. For the temperature range of 800–840 °C with a strain rate of 10 s^?1, the transformed volume fraction of α phase increases and the average grain size of α phase decreases slightly with increasing the temperature, indicating co-existence of dynamic recovery and dynamic recrystallization. Flow localization and faint β grain boundaries are observed at the strain rate of 10 s^?1 in the temperature range of 860–900 °C. The processing map analysis shows that hot working of Ti-5Al-5Mo-5V-1Cr-1Fe alloy should be conducted with the strain rate lower than 0.01 s^?1 to extend its workability.     

热连轧Ti-6Al-4V合金的蠕变行为及影响因素

采用热处理、蠕变性能测试及位错组态的衍衬分析,研究热连轧Ti-6Al-4V合金的蠕变行为及影响因素.结果表明:经低于β相变点的固溶处理,合金的组织结构由高固溶度的等轴α相和网篮组织组成;随着固溶温度提高,网篮组织数量增多;经1 000 ℃固溶处理后合金可获得完全网篮组织;与940 ℃固溶时效合金相比,经 1 000 ℃固溶时效合金在420 ℃、575 MPa条件下具有较低的应变速率和较长的蠕变寿命;在试验的温度和应力范围内,计算出该合金的蠕变激活能为249.8 kJ/mol;在蠕变期间,热连轧合金的变形机制是位错在具HCP结构的α相中发生双取向滑移,940 ℃固溶处理合金的蠕变机制是波浪状位错在α相中发生锥面滑移,而经1 000 ℃固溶处理合金的变形机制是<1/2>(111(位错在具BCC结构的β相中发生多系滑移;经1 000 ℃固溶处理合金中所含的高含量富V的β相可提高合金蠕变抗力,这是合金具有较低应变速率和较长蠕变寿命的主要原因.     

Corrosion resistance improvement of Ti-6Al-4V alloy by anodization in the presence of inhibitor ions

Colorful thin oxide films were synthesized by galvanostatic anodization on Ti-6Al-4V alloy. Three different aqueous solutions containing corrosion inorganic inhibitors (Na₂MoO₄, NaH₂PO₄ and NH₄VO₃) were employed for the anodization treatment. The effect of inhibitor anions on the corrosion behavior of the alloy in Ringer solution was studied. Open circuit potential (OCP), Tafel polarization, linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to evaluate the corrosion performance of the treated electrodes. The incorporation of the inhibitor ions was detected by the release of Mo, V and P through ICP-AES technique. The formed oxides were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that compact, amorphous oxides without pores or cracks were obtained independently of the solution used. The sample anodized in Na₂MoO₄ solution registered the lowest corrosion current density (0.11 μA/cm²), and it was able to protect the alloy even after 168 h of immersion in Ringer solution. No cracks or corrosion products were detected. The XPS analysis reveals the incorporation of molybdenum to the oxide film in the form of Mo⁶⁺ and Mo⁴⁺.     

双时效对Ti-4Al-5Mo-6Cr-5V-1Nb合金显微组织和力学性能的影响

研究了固溶、固溶后单时效以及固溶后双时效处理对Ti-4Al-5Mo-6Cr-5V-1Nb合金组织和力学性能的影响。结果表明,820℃下固溶0.5 h后,合金中的α相完全溶解;单/双时效合金的硬度均随时效时间增加先升高后降低;合金经300℃/8 h+500℃/8 h双时效处理后可达到4580 MPa的峰值硬度(HV),1462 MPa抗拉强度以及3.4%延伸率,其强度比原始合金高6%,也高于单时效合金。界面能计算结果表明ω相使α相形核的阻力降低50%,促进了α相的析出并细化α板条,从而提升合金的硬度,强度及塑性。     

Nitrogen ion implantation and in vitro corrosion behavior of as-cast Ti-6Al-7Nb alloy

In the present investigation, surface modification of Ti-6Al-7Nb alloy with nitrogen ions is considered as a method to improve its performance with respect to corrosion. Nitrogen ion was implanted on Ti-6Al-7Nb alloy at an energy of 70 and 100 keV using a 150 keV accelerator at different doses between 1×10¹⁶ and 3×10¹⁷ ions/cm². Gracing incidence X-ray diffraction was employed on the implanted specimens to understand the phases formed with increasing doses. The implanted samples were subjected to electrochemical study in Ringer's solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The OCP of the implanted specimens were found to shift in the noble direction in comparison with unimplanted specimen. The passive current density and area of the repassivation loop were found to decrease as the dose values increased. The electrochemical impedance spectroscopic results indicate that the polarization resistance was higher for the dose of 2.5×10¹⁷ ions/cm² implanted at both energy of 70 and 100 keV. Nitrogen ion implantation enhanced the passivability and reduces the corrosion kinetics of the alloy surface with increasing tendency for repassivation. Nature of the surface and reason for the variation and improvement in corrosion resistance are discussed in detail.