大型复杂薄壁Ti-6Al-4V合金熔模精密铸造工艺研究

根据复杂薄壁铸件的熔模铸造理论,对Ti-6Al-4V合金滑轨铸件结构及难点进行了全面的研究分析,针对型壳的制造、合金的熔炼和浇注以及铸件的热等静压三个方面开展了相关工艺研究.结果表明:采用氧化钇耐火材料和三醋酸锆粘结剂进行面层造型,料浆涂挂性好,有较好的润湿性和良好的工艺性能;采用真空自耗凝壳炉熔炼合金以及离心浇注,可保证钛合金熔液的质量和充填性能;采用热等静压工艺处理铸件,可提高铸件的质量和性能.最终确定熔模精密铸造最佳工艺参数,并据此生产出了合格的铸件.     

新型高强韧钛合金的粉末热等静压规律研究

采用无坩埚感应熔炼超声气体雾化法(EIGA)制备出一种钛基预合金粉末,然后用粉末冶金热等静压技术(PM-HIP)进行成形,研究了热等静压温度对该粉末冶金钛合金性能的影响。结果表明,采用气体雾化制粉工艺能够制备出满足要求的洁净预合金粉末,其相变点为883℃。热等静压温度在β相变点以下,制备的高强韧钛合金呈α+β双态组织,拉伸强度和冲击性能与热等静压温度成正相关。热等静压温度高于β相变点,组织中形成大尺寸的晶粒,α相衍射峰增强,为针状分布,合金性能略有下降。采用粉末热等静压技术制备的新型α+β两相钛合金具有高强高韧的特点,热处理能够提高合金的冲击性能。     

热等静压对铸件致密化及组织演变机理的影响研究

研究了铸件制品的热等静压致密化机理,分析了铸件制品热等静压的致密化模型,综合应用合金的蠕变理论和粉末冶金的烧结理论,利用现有的物理和数学模型对铸件在热等静压过程中的内部孔洞类缺陷闭合过程机理进行了阐述。确认了热等静压过程中起主要致密化作用的孔洞形变机制,为选择制定合适的热等静压工艺参数提供了理论参考。     

低成本制备Ti-3Al-2V合金精密铸件的可行性研究

用精密铸造方法制备的形状复杂的Ti-3Al-2V合金零部件综合性能良好。为进一步降低Ti-3Al-2V合金精密铸件成本,采用3种不同的原料(1海绵钛、铝钒中间合金、纯铝丝和铝箔,2回收的Ti-3Al-2V合金料,3回收的Ti-6Al-4V合金、纯钛料),分别经真空自耗电弧炉熔炼、真空凝壳炉重熔、离心浇注等工序得到Ti-3Al-2V合金精密铸件,并分析了铸件的化学成分,测试了铸件的室温拉伸性能。结果表明,3种不同原料制备的精密铸件,其化学成分和退火后的室温拉伸性能均能满足客户要求;如果控制好回收料的处理工序,合理地使用回收料,可进一步降低Ti-3Al-2V合金精密铸件的成本,有望在汽车、高铁等许多民用领域替代钢材而得到广泛应用。     

热等静压处理对K4169合金的改善作用

热等静压处理不仅能够闭合K4169合金铸件的显微疏松,还能闭合宏观孔洞.但是,实际生产中发现,有时热等静压处理不仅不能消除铸件的疏松和孔洞,而且铸件表面还出现荧光缺陷增多的现象.这是铸造工艺参数和铸型组合方式不合理造成的.另外,K4169合金铸件热等静压处理后进行标准热处理会使力学性能下降.为此,作者研究了一种改型热处理制度,这种改型热处理制度能明显提高铸件的力学性能.     

超高强度β21S合金铸锭成分均匀性的控制

针对超高强度β21S合金（Ti-3al-15Mo-2.7Nb-0.2Si)熔炼上的技术难点,采用真空自耗电弧熔炼和真空凝壳浇铸的方法,研究了Mo,Nb合金元素的添加式以及熔炼工艺参数对该合金铸锭成分均匀性的影响,结果表明：以Ti-Nb,Ti-Mo中间合金为配料,采用合理的熔炼工艺,可获得性能良好,成分均匀的β21S合金铸锭。     

真空脱气对粉末冶金Ti2AlNb合金力学性能的影响

采用无坩埚感应熔炼超声气体雾化法制备了成分为Ti-22Al-24Nb-0. 5Mo(原子分数,x/%)的预合金粉末,并对预合金粉末的化学成分、表面状态及流动性等进行了表征。通过包套热等静压工艺制备了粉末冶金Ti2AlNb合金,研究了真空脱气对粉末冶金Ti2AlNb合金力学性能的影响。结果表明,超声气体雾化法制备的Ti2AlNb合金粉末化学成分批次稳定性好;从粉末填充的工艺性能方面考虑,热等静压成形应选取粒度小于250μm以下的全粒度分布预合金粉末;真空脱气处理可减少粉末冶金Ti2AlNb合金的孔隙缺陷,提升合金拉伸性能的稳定性和高温持久寿命。     

粉末冶金Ti-5Al-2.5Sn ELI合金稳定性分析

采用无坩埚感应熔炼超声气体雾化法制备了洁净Ti-5Al-2. 5Sn ELI预合金粉末,并利用包套热等静压工艺制备了全致密的Ti-5Al-2. 5Sn ELI合金叶轮。测试了6个不同批次Ti-5Al-2. 5Sn ELI合金的化学成分和力学性能,统计了不同批次粉末合金的性能及成分变化规律。研究结果表明,采用包套热等静压工艺可获得全致密的Ti-5Al-2. 5Sn ELI合金,合金成分稳定均匀,力学性能接近锻造合金的水平且稳定性好。采用该工艺制备的Ti-5Al-2. 5Sn ELI合金叶轮与包套界面反应小,且组织中晶粒细小均匀,无孔隙缺陷。     

FGH96镍基粉末高温合金氧化物夹杂的计算机断层扫描研究

利用计算机断层扫描技术（computed tomography,CT）研究了FGH96镍基粉末高温合金内部Al₂O₃、SiO₂及莫来石三种氧化物夹杂对不同工艺（热等静压工艺、热等静压+热挤压+等温锻造工艺及热等静压+等温锻造工艺）的敏感程度。结果表明:热等静压+等温锻造工艺能显著减小Al₂O₃夹杂物的尺寸和其在合金中的含量,采用热等静压+热挤压+等温锻造工艺最能有效减少SiO₂夹杂物在合金中的含量,而莫来石夹杂对热等静压+热挤压+等温锻造工艺和热等静压+等温锻造工艺均较为敏感,且两种工艺对莫来石夹杂的作用效果类似。夹杂物在实际盘件中呈油饼状,极大地恶化了合金低周疲劳性能,且夹杂物越接近试样表面,试样的低周疲劳性能恶化越显著。热等静压+等温锻造工艺对减小三种夹杂的尺寸均有良好效果,这为人们选取合适工艺消除合金中氧化物夹杂提供了重要参考。     

热等静压及其加锻造和热挤压粉末高温合金FGH95的组织和性能

本工作的目的在于研究不同成型工艺对粉末高温合金FGH95组织和性能的影响,以确定合适的成型工艺。采用了氩气雾化的FGH95合金粉,用热等静压(HIP)、及其加锻造和热挤压三种工艺使之致密化。对各种压坯的显微组织和机械性能进行了研究。扫描电镜和透射电镜的研究结果说明,经过锻造或挤压的合金,其显微组织有明显的改善。热等静压合金的断口是沿粉末颗粒间断裂的,这是由于显微组织中存在着原始颗粒边界(PPB),降低了合金的力学性能。在热等静压加锻造或热挤压的合金中,由于消除了原始颗粒边界,断口是穿晶断裂的,因而改善了合金的强度和塑性。采用热挤压或热等静压加锻造成型工艺比较有效。     

The effect of silica-containing binders on the titanium/face coat reaction

The interactions of CP-Ti and Ti-6Al-4V with investment molds containing alumina/silica and yttria/silica face coat systems were studied. “Containerless” melting in argon was employed and small test samples were made by drop casting into the molds. The effects of the face coat material and mold preheat temperatures on the thickness of the alpha case in the drop castings were evaluated with microhardness and microprobe measurements. It was found that the thickness of the alpha case was the same, whether a yttria/silica or alumina/silica face coat was used, indicating that the silica binder can reduce the apparent inertness of a more stable refractory, such as yttria. It was also found that the alloyed titanium castings had a thinner alpha case than those produced from CP-Ti, which suggests that the thickness of the alpha case depends on the crystal structure of the alloy during cooling from high temperatures. Furthermore, the small drop castings made in small yttria crucibles used as molds exhibited little or no alpha case.     

外科植入物用Ti-6A1—7Nb合金板棒丝材制备及性能表征

在工业生产条件下,通过熔炼、锻造和轧制工艺制备出不同规格的外科植入物用的Ti-6A1-7Nb合金板、棒、丝材,表征了不同规格材料的组织与性能,进行了Ti-6A1—7Nb合金材料体外细胞毒性试验、刺激与迟发型超敏反应试验、污染物致突变性检测和骨植入试验。研究结果表明：板、棒、丝材组织与性能均满足GB23102-2008、GB／T13810-2007和ASTMF1295标准要求;Ti-6A1—7Nb合金材料不含毒性组元,生物相容性好,是一种比Ti-6A1-4V合金更理想的外科植入物材料;多种形式植入件的近百例临床使用效果良好,适合临床应用。     

Enhanced superplasticity and strength in modified Ti-6AI-4V alloys

Although Ti-6A1-4V displays extensive superplasticity at 1200 K, lower superplastic forming temperatures are desirable. A study was conducted with the goal of modifying the composition of the Ti-6A1-4V alloy to lower the optimum superplastic forming temperature. Computer modeling results and previous experimental data suggested that additions to Ti-6A1-4V of beta-stabilizing elements which have high diffusivity in the beta-phase would permit lower superplastic forming temperatures. A series of modified alloys with 2 wt pct additions of Fe, Co, and Ni was prepared for experimental evaluation. The modified alloys achieved desirable microstructures for superplasticity at 1088 K,i.e., the grain size was approximately 5 μm and roughly equal volume fractions of the alpha- and beta-phases were present at the deformation temperature. The superplastic properties of the modified alloys were measured at 1088 K and 1144 K. The modified alloys produced values of flow stress, strain rate sensitivity, and total elongation at 1088 K approaching those of the base Ti-6A1-4V alloy at its standard superplastic forming temperature of 1200 K. In addition to lowering the superplastic forming temperature, the β-stabilizing additions also increased room temperature strength levels above those normally found for Ti-6A1-4V. Based on the room temperature and elevated temperature tensile properties, addition of selected beta-stabilizing elements to Ti-6A1-4V simultaneously raises resistance to deformation at room temperature and lowers resistance to deformation at elevated temperatures. This reversal in behavior is explained by considering the effect of beta-stabilizer additions on the deformation mechanisms at room temperature and at elevated temperatures.     

Ti－6A1－4V合金的腐蚀与磨蚀行为的研究

本文采用多种试验方法，研究了Ｔｉ与Ｔｉ－６Ａ１－４Ｖ的腐蚀与磨蚀行为。试验结果表明，Ｔｉ－６Ａ１－４Ｖ合金具有优良的均匀腐蚀、点蚀、晶间腐蚀与磨蚀性能。     

Creep fracture characteristics of weld-repaired cast Ti-6Al-4V

Constant load creep tests were conducted with cast Ti-6Al-4 V bars in air and vacuum at 315† and 650†C. Some of the bars were notched in their gauge section and heliarc-welded to simulate a weld repair in a casting. Results indicate that the welding has little influence on the time to rupture of the bars. Fractographic analysis of the bars indicates minor differences in the welded and unwelded fracture surfaces. However, these differences do not affect the microstructural influence on the creep and fracture processes. The prior beta grain, size and the alpha platelet size are shown to control the creep fracture of this alloy. These data show that weld repair of titanium castings for creep applications should be acceptable.     

Effect of activity differences on hydrogen migration in dissimilar titanium alloy welds

The effect of alloy composition on hydrogen activity was measured for seven titanium alloys as a means to determine the tendency for hydrogen migration within dissimilar metal welds. The alloys were: Ti-CP, Ti-3A1-2.5V, Ti-3Al-2.5V-3Zr, Ti-3Al-2Nb-lTa, Ti-6A1, Ti-6A1-4V, and Ti-6Al-2Nb-lTa-0.8Mo. Hydrogen pressure—hydrogen concentration relationships were determined for temperatures from 600 °C to 800 °C and hydrogen concentrations up to approximately 3.5 at. pct (750 wppm). Fusion welds were made between Ti-CP and Ti-CP and between Ti-CP and Ti-6A1-4V to observe directly the hydrogen redistribution in similar and dissimilar metal couples. Hydrogen activity was found to be significantly affected by alloying elements, particularly Al in solid solution. At a constant Al content and temperature, an increase in the volume fraction of β reduced the activity of hydrogen in α-β alloys. Activity was also found to be strongly affected by temperature. The effect of temperature differences on hydrogen activity was much greater than the effects resulting from alloy composition differences at a given temperature. Thus, hydrogen redistribution should be expected within similar metal couples subjected to extreme temperature gradients, such as those peculiar to fusion welding. Significant hydrogen redistribution in dissimilar alloy weldments also can be expected for many of the compositions in this study. Hydride formation stemming from these driving forces was observed in the dissimilar couple fusion welds. In addition, a basis for estimating hydrogen migration in titanium welds, based on hydrogen activity data, is described.     

Effect of activity differences on hydrogen migration in dissimilar titanium alloy welds

The effect of alloy composition on hydrogen activity was measured for seven titanium alloys as a means to determine the tendency for hydrogen migration within dissimilar metal welds. The alloys were: Ti-CP, Ti-3A1-2.5V, Ti-3Al-2.5V-3Zr, Ti-3Al-2Nb-lTa, Ti-6A1, Ti-6A1-4V, and Ti-6Al-2Nb-lTa-0.8Mo. Hydrogen pressure-hydrogen concentration relationships were determined for temperatures from 600 ‡C to 800 ‡C and hydrogen concentrations up to approximately 3.5 at. pct (750 wppm). Fusion welds were made between Ti-CP and Ti-CP and between Ti-CP and Ti-6A1-4V to observe directly the hydrogen redistribution in similar and dissimilar metal couples. Hydrogen activity was found to be significantly affected by alloying elements, particularly Al in solid solution. At a constant Al content and temperature, an increase in the volume fraction ofΒ reduced the activity of hydrogen in α-@#@ Β alloys. Activity was also found to be strongly affected by temperature. The effect of temperature differences on hydrogen activity was much greater than the effects resulting from alloy composition differences at a given temperature. Thus, hydrogen redistribution should be expected within similar metal couples subjected to extreme temperature gradients, such as those peculiar to fusion welding. Significant hydrogen redistribution in dissimilar alloy weldments also can be expected for many of the compositions in this study. Hydride formation stemming from these driving forces was observed in the dissimilar couple fusion welds. In addition, a basis for estimating hydrogen migration in titanium welds, based on hydrogen activity data, is described.     

Void formation,void growth and tensile fracture in Ti-6AI-4V

Metallurgical and Materials Transactions A - The influence of microstructure on void formation, void growth and tensile fracture was investigated for the Ti-6A1-4V alloy, aged to yield strengths of...     

Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements

The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al₂O₃-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (α = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (α = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy (p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.