【作者】 刘斌；

【导师】 黄泽文；

【作者基本信息】 西南交通大学 ， 材料科学与工程， 2012， 硕士

【摘要】 对Ti-45A1-8.5Nb-(WBY)合金在700℃大气环境下分别进行了1000、1700、3000、10000小时的热暴露处理。通过扫描电镜、透射电镜的手段研究了系列高温热暴露对该合金组织稳定性的影响,并进行了室温拉伸测试。研究发现,Ti-45A1-8.5Nb-(WBY)合金在室温下为双态细晶组织。在热暴露1000小时后,在α2+Y层片晶团内α2层片通过α：→Y相变发生了平行分解,导致层片细化,这有利于提高该合金的拉伸强度,屈服强度和塑性。在热暴露1700小时后,合金开始通过α2+Υ→B2(ω)相变生成B2(ω)等轴晶粒。在3000小时热暴露后,从α2+Υ层片晶团形成的B2(ω)等轴晶粒达到18vo1.%,而且其上有针状相广泛析出。值得注意的是,经历10000小时热暴露形成的B2(ω)等轴晶粒和经历3000小时形成的接近,导致该合金的强度和塑性均出现了一定程度的降低,但在10000小时热暴露后,这种力学性能的降低不高于10%。对全层片组织的该合金分别在700°C和800°C大气条件下开展了长达500小时的氧化实验。结果显示,合金Ti-45A1-8.5Nb-(WBY)在700°C和800°C条件下的初始氧化速度较快,但大约在100小时后氧化进入一种稳定状态。700°C的氧化样品表层并没有形成典型金红石结构,形成了以A1203和TiO2为外层的不均匀氧化膜多层结构,厚度为20um左右。而800°C的氧化样品表面拥有典型的金红石结构,形成了外层以Ti02逐步占据主要地位的双层结构,厚度也为20um左右。800°C氧化样品整体增重比700°C样品上升了25%左右,但整体水平都不高,没有超过0.4mg/cm3,显示出合金Ti-45Al-8.5Nb-(WBY)在700°C和800°C大气氛围条件下有较好的抗氧化能力。更多还原

【Abstract】 Thermal exposure at700℃in air was carried out on isothermally forged alloy Ti-45Al-8.5Nb-(WBY) for up to10000hours. The changes in microstructure and phase structure were characterized using optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The corresponding changes in mechanical properties were examined by tensile testing at room temperature. It was found that the a2lamellae in the duplex microstructure decomposed to some degree after1000h exposure, which is assumed to be responsible for the increase of tensile properties. After1700h exposure, equiaxed B2(ω) grains formed by consuming a2+γ lamellar colonies, which can be represented by a2+γ→B2(ω) phase transformation. And after exposure for3000h, the volume fraction of the B2(ω) grains formed approach to18%. Moreover, need-shaped phase precipitated extensively in the B2(ω) grains. It was important to note that the amount of the B2(ω) grains formed after10000h exposure is quite similar to that after3000h exposure. As a result, the strength and ductility were reduced slightly after10000h thermal exposure, no more than10%for both.Oxidation resistance of the alloy was examined at700℃and800℃for up to500hours, respectively. It shows that a relatively fast oxidation occurred at the initial stage for the two temperatures but a stabilized condition was reached roughly after100hours. There is no typical rutile structure in the700℃-oxidized surface. An uneven multilayer oxidation layer with A12O3and TiO2(-20μm in thickness) formed as the outer layer in stead. For800℃-oxidized surface, however, typical rutile structure was produced and outer oxidation layer was formed with a higher percentage of TiO2. The weight gain at800℃is25%more than that at700℃oxidation but both remained at a relatively low level so that the weight gain is less than0.4mg/cm3throughout the500hour-long oxidation. This alloy therefore demonstrates a relatively good oxidation resistance both at700℃and at800℃.更多还原