【作者】 景然；

【导师】 刘日平； 马明臻；

【作者基本信息】 燕山大学 ， 材料学， 2013， 博士

【摘要】 钛及钛合金由于具有高比强度、优异的抗腐蚀性，低密度（密度仅为钢和镍基超合金的一半）等优点，在早期就被广泛应用于航空工业和化学工业中；而锆及锆合金具有中子吸收截面积小、抗辐照、抗氧化、耐腐蚀、热膨胀系数小以及密度小等优异的理化性能，目前被广泛应用于核工业和化学工业中。随着科技的迅猛发展，钛合金及锆合金在航天领域的应用正在逐渐增多。但由于现有钛合金的抗辐照性能差、膨胀系数大，而锆合金的强度比较低，两者均不适合作为航天飞行器的结构材料来使用。基于上述现状，本文以发展新型空间结构材料为目标，通过对合金成分的设计和优化和对锻造和热处理工艺参数的探索，设计具有优异力学性能的TiZr基合金体系，并系统研究TiZr基合金体系的相变、组织演化和强化机制。本文以Ti-6Al-4V为基体，以各元素对合金的相组成以及力学性能的影响作为依据，设计出新型TiZr基合金体系中各元素的含量，并且对TiZrAlV合金的成分进行了优化。使用非自耗电弧炉制备了一系列成分的TiZrAlV合金，其力学性能测试结果表明：Zr含量在15wt.%~20wt.%的范围内时，合金的强度得到较大的提升，并且密度控制在4.6g/cm~3左右；传统Ti合金中最主要的强化元素Al的含量控制在4.5wt.%~6.9wt.%的范围内时，可有效的提高合金的强度；β相稳定元素V元素的含量则控制在3.5wt.%~4.5wt.%的范围内；其余为Ti。TiZrAlV合金体系的β相转变温度随着Zr含量的增加而降低，其综合力学性能随Zr含量的增加而升高。根据成分优化的结果，使用水冷铜坩埚电磁感应悬浮熔炼以及工业自耗电弧炉熔炼制备了成分为Ti-15Zr-6Al-4V（T15Z合金）、Ti-20Zr-6.5Al-4V（T20Z合金）以及Ti-51Zr-4.5Al-4V（T51Z合金）高强度合金。通过开坯锻造、精锻和后续的热处理，合金的性能得到进一步的改善。主要的力学性能指标如下：T15Z合金经过退火后具有较好的塑性（大于13%）；T51Z合金在不同温度淬火后，其延伸率在15%左右；固溶时效态T20Z合金的最大抗拉强度可达1740MPa，延伸率为2.3%；T20Z合金700℃时效后的强度为1437MPa，延伸率为6.69%；退火态的T20Z合金的强度在1300MPa左右，延伸率大于10%。利用XRD、OM、FE-SEM以及TEM研究T20Z合金在不同热处理制度下的相变以及组织演化规律。结果如下：950℃固溶处理后的样品中出现了面心立方结构相，其晶格参数a=0.4385nm，而700℃时效后该fcc相转变成为α相。550℃~850℃保温120min退火后合金主要是由α相和β相组成，并且在650℃和750℃退火后出现面心立方结构相；在750℃以下退火后合金中残余β相的含量随着退火温度的升高而有所降低；在退火温度达到750℃以上时残余β相的含量则随着退火温度的升高而增加。T20Z合金在800℃~1050℃保温30min退火后合金由α相和β相组成；在950℃以下即双相区退火时，合金中残余β相的含量随退火温度的升高先增加后降低；在950℃以上退火时，合金中残余β相的含量随着退火温度的升高而增加。此外，在相同退火温度下，保温时间越长，T20Z合金中β相的含量也越高。退火态下的α相板条的厚度对退火温度很敏感。随着退火温度的升高，α相的形貌趋向于等轴状（1050℃除外）。T20Z合金在经过1000℃退火处理后，α相板条厚度达到了最大值4.22μm。更多还原

【Abstract】 Titanium and its alloys have been widely used in aviation and chemical industry todate, due to the exceptional strength-to-weight ratio, good corrosion resistance and theirdensity being only half of the steel and Ni-based super alloys. Meanwhile, zirconium andits alloys have been mainly used in nuclear and chemical industries because of theirunique physic-chemical properties, such as a small capture cross-section for thermalneutron, good anti-irradiation, favourable oxidation resistance and corrosion resistance,small expansion coefficient, and low density. The application of Ti and Zr alloys in spaceis also gradually increasing with the development of science and technology. At present,Ti alloys, which do not possess good irradiation resistance and have large expansioncoefficient, are not suitable to use in the extreme space environment as structural materials.Furthemore, besides the good anti-irradiation, low density and a small expansioncoefficient are also the desired properties of structural materials for space crafts, the lowstrength of Zr alloys restricts their applications as structural materials. Therefore, thisdissertation is aiming to develop new type aerospace materials by means of the alloycomposition design and optimization, forging and heat treatment process to design a seriesof TiZr-based alloys with exceptional mechanical properties. And the dissertation alsosystematically studys phase transition, microstructural evolution and strengtheningmechanism of the TiZr-based alloy.A series of TiZrAlV alloys designed are melted by utilizing a vaccumnon-consumable electro-arc furnce. Based on Ti-6Al-4V alloy, the composition of theTiZrAlV alloys are optimized according to the influence of various elements on phasecontents and mechanical properties. The strength and hardness of TiZrAlV alloysobviously increase and the densities of the alloys are around4.6g/cm~3, when the contentsof Zr is15wt.%~20wt.%. Al is the most major strengthening element in Ti alloys, andthe strength of alloys will increase distinctly when Al content is about4.5wt.%~6.9wt.%.The content of V, as a β-stabilized element, is about3.5%~4.5%. The β transustemperatures are decreased with Zr, and mechanical properties also increase. Based on the results of the composition optimization, the high-strength alloys, i.e.Ti-15Zr-6Al-4V (T15Z alloy), Ti-20Zr-6.5Al-4V (T20Z alloy) and Ti-51Zr-4.5Al-4V(T51Z alloy), are prepared by electro-magnetic induction melting and vaccum consumableelectro-arc furnace. After the break-down forging and subsequent heat treatment, themechanical properties of the alloys are obviously changed. After annealing, T15Z alloyhas good ductility (about13%). The ductility of T51Z alloy undergone water quenching atdifferent temperatures is about15%. The ultimate strength of T20Z alloy undergonesolution treatment and aging treatment reaches1740MPa with the low plasticity. Afteraging at700oC, the strength and ductility of alloy are1437MPa and6.69%respectively.The strength of the annealing T20Z alloy is about1300MPa and the ductility is greaterthan10%.Phase transition and microstructural evolution of T20Z alloy undergone different heattreating regime are investigated by means of XRD, OM, FE-SEM and TEM. FCC phasewas found after solution treatment at950oC and the lattice parameter was determined tobe a=0.4385nm. The FCC phase disappeared after aging at700oC. Annealing between550and850oC for120min, all TiZr-based alloys are mainly composed of α and β phase,and the FCC phase appeared between650and750oC. The volume fraction of β phasedecreases with anneraling temperatures below750oC, whereas the volume fraction of βphase increases with the annealing temperature over750oC. Annealing between800oCand1050oC for30min, all TiZr-based alloys are composed of α and β phase. The volumefraction of β phase is sensitive to the annealing temperature. Furthermore, at the sameannealing temperature (eg. annealing at850oC), the longer the holding time is, the higherthe volume fraction of β phase. Under the high temperatures annealing for short timeconditions, the thickness of lamellar α phase of T20Z alloy is sensitive to the annealingtemperatures. With the annealing temperature increasing, the morphology of α phase tendsto equiaxed grain, except alloy annealed at1050oC.更多还原