含铌、钼TiAl合金热变形及氧化行为研究

发布时间：2018-01-19 16:15

本文关键词： TiAl合金热变形行为热加工图包套轧制氧化行为　出处：《北京科技大学》2016年博士论文　论文类型：学位论文

【摘要】：TiAl合金具有低密度、高强度、优异的阻燃能力以及优良的抗蠕变性能和抗疲劳性能等优点,成为航空航天领域最具竞争力的轻质结构材料之一。但TiAl合金热变形能力差,室温塑性低以及750℃以上的抗氧化性能不足等制约了该合金的实际工程化应用。本文通过添加p相稳定元素(Nb和Mo)制备出高温时含一定量具有BCC结构的p相TiAl合金,提高了其热变形能力,同时改善了抗氧化性能。目前,有关添加Nb和Mo元素的含p/B2相TiAl合金的板材轧制及氧化行为方面的研究报道较少,也是该合金在工业试制过程中急需解决的关键性问题,对该合金最终实现商业化生产具有现实意义。本文对该合金的热变形行为、板材制备和氧化行为系统地开展了相关基础研究,主要工作和结果如下：(1)采用真空悬浮熔炉制备了尺寸为φ110mm × 190mm的Ti-44.45A1-3.80Nb-1.01Mo-0.29Si-0.14B合金(简称TNM合金)铸锭。经热等静压和均匀化处理后的TNM合金无明显成分偏析和微观裂纹,组织由γ/α2片层团、β/B2相和γ相组成,并确立了该合金的凝固过程和相变规律。(2)通过Gleeble3500模拟压缩铸态TNM合金实验证明含β/B2相的TNM合金具有较好的热加工性,可在1200～1250℃及0.01～0.5s-1区内进行变形,该合金属负温度敏感材料和正应变速率敏感材料,其流变应力曲线的升高、降低及平稳过程对应了加工硬化和应变软化的交替控制和动态平衡过程。利用摩擦修正后的热压缩实验数据求解了不同应变条件下的材料常数,构建了TNM合金的本构模型,并验证了此模型能很好的预测该合金的热变形流变规律。随变形温度升高和应变速率减小,TNM合金的动态再结晶的临界应变减小。TNM合金低温和高温变形机制分别以Y相位错滑移和β、α和γ相的位错滑移为主,变形软化机制为丫相的动态再结晶。在高温变形过程中β相起到协调或“润滑”作用,提高合金的变形能力。(3)基于动态材料模型(DMM),建立了铸态TNM合金的热加工图,研究了在热加工图不同区域中材料组织的演变规律,按能量耗散效率η将热加工图分为安全区域和流变失稳区域。从未经锻造TNM合金铸锭上取料包套,成功地在加热温度为1250℃和道次轧制速度递减(112/75/55mm/s)的条件下轧制出尺寸为510mm × 105mm×1.40mm的板材。轧态TNM合金的显微组织为细小的近γ组织,通过热处理其力学性能得到改善。(4)在TNM合金升温阶段的氧化过程,氧化物首先在γ相上生长,774℃是氧化物明显迅速长大的开始温度点。TNM合金在800℃的氧化实验表明：等温氧化500h后氧化膜保持完整,循环氧化710次时氧化膜开始剥落,而外加拉应力则提高了合金的氧化速率;该合金抗氧化性能明显好于传统的Ti-48Al-2Cr-2Nb合金。Nb和Mo的协同作用改变了合金的氧化膜形成机制,形成连续致密的A1203氧化膜,可阻碍氧原子向内扩散降低了氧化速率,提高了TNM合金的长期抗氧化性。
[Abstract]:The TiAl alloy has low density, high strength, excellent flame retardant ability and excellent creep resistance and anti fatigue performance has become one of the most competitive lightweight structural materials in the aerospace industry. But the TiAl alloy hot deformation ability, ductility and low oxidation resistance of 750 DEG C for lack of practical constraints the engineering application of the alloy in this paper. By adding P elements (Nb and Mo) stable prepared at high temperature with a certain amount of BCC structure with P phase TiAl alloy, improve the deformation capacity of the heat, while improving the antioxidant properties. At present, with adding Nb and Mo elements with p/B2 phase TiAl alloy the Research Report of the rolling and oxidation behavior of less, and is also the key issue of the alloy in the industrial development process needs to be solved, the alloy eventually achieve commercial production. This paper has practical significance on the alloy heat The deformation behavior of sheet, preparation and oxidation system to carry out the basic research, the main work and results are as follows: (1) preparing the size of Ti-44.45A1-3.80Nb-1.01Mo-0.29Si-0.14B alloy with 110mm * 190mm vacuum furnace for suspension (TNM alloy) ingots. By hot isostatic pressing and homogenization obvious composition segregation and micro crack free TNM alloy treatment, organized by the gamma / alpha 2 lamellar, /B2 and beta gamma phase composition, and established the solidification process and the phase transformation of the alloy. (2) through the Gleeble3500 compression simulation of cast TNM alloys containing TNM experiments show that the B2 alloy has good thermal / beta processing, can be in 1200 to 1250 DEG C and 0.01 ~ 0.5s-1 in the area of deformation of this alloy is a negative temperature sensitive material and positive strain rate sensitive material, the rheological curves should be increased, and the lower stationary process corresponds to alternate work hardening and strain softening Control and dynamic balance process. Using friction modified hot compress test data for material constants under different strain condition, constructed the constitutive model of TNM alloy, and proves that the model can well predict the thermal deformation of the alloy rheological law. With the increase of deformation temperature and decreasing strain rate, critical strain the dynamic recrystallization of TNM alloy decreases.TNM alloy at low temperature and high temperature deformation mechanism with Y phase fault slip and beta, alpha and gamma phase dislocation slip and deformation softening mechanism for y phase dynamic recrystallization. During the process of high temperature deformation phase to coordinate or "lubricating" effect, improve the ability of deformation of alloy. (3) based on the dynamic material model (DMM), established the thermal processing map of TNM cast alloy, studied the microstructure evolution of materials in the hot processing map in different regions, according to the energy dissipation efficiency in the hot processing map can be divided into safety zone Domain and flow instability regions. Never forged TNM alloy ingot material package, successfully in the heating temperature is 1250 DEG C and rolling speed decreasing (112/75/55mm/s) under the condition of rolling plate size is 510mm * 105mm * 1.40mm. The microstructure of rolled TNM alloy is finer near gamma. Through heat treatment the mechanical properties were improved. (4) at the stage of heating and oxidation process of TNM alloy, oxide growth in the first phase, 774 C is obviously shows that the oxide grew rapidly start temperature of.TNM alloy in the oxidation experiments of 800 DEG C: 500h after isothermal oxidation film remains intact, 710 times of cyclic oxidation oxide film to start off, then increase the oxidation rate of stress and Gallas; synergistic effect of antioxidant properties of this alloy is obviously better than the traditional Ti-48Al-2Cr-2Nb alloy.Nb and Mo alloy changed the oxide film formation mechanism, shape As a continuous and compact A1203 oxide film, the oxidation rate of oxygen atoms can be hindered by the inward diffusion of oxygen atoms, and the long-term oxidation resistance of TNM alloy is improved.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.2

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