【作者】 肖丽；

【导师】 田素贵；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2014， 博士

【摘要】 本论文通过对热连轧Ti-6Al-4V合金进行不同工艺热处理、蠕变性能测试及组织形貌观察，研究制备工艺对合金组织结构和蠕变性能的影响；热处理对合金组织结构、力学性能和蠕变性能的影响，及长期时效对合金组织结构和蠕变性能的影响，通过EDS分析和XRD分析，研究了不同工艺制备合金的相组成，热处理对合金相组成的影响，通过SEM形貌观察及TEM衍衬分析，研究合金在蠕变期间的微观变形与断裂机制。得出如下结论：热连轧合金的微观组织结构由两相组成，相沿流变方向呈板条状分布，白色线条状β相沿相边界连续分布。与锻造态合金相比，板条状相的宽度较小。在400℃~420℃和550MPa~600MPa施加温度和应力范围内，测定出锻造和热连轧态合金稳态蠕变期间的蠕变激活能分别为102kJ/mol，108kJ/mol。锻造态合金在蠕变期间的变形机制是位错的双取向滑移，其中，近水平方向的<a+c>位错在(2110)柱面滑移，垂直的<a>位错在（1103）非基面滑移。热连轧态合金中相的变形机制是类直线的<a>位错和<a+c>位错在HCP结构的锥面和柱面发生双取向滑移。表明，热连轧态合金中易开动的滑移系较多，蠕变抗力较低，蠕变期间位错易于滑移是合金具有较高应变速率和较短蠕变寿命的主要原因。热连轧合金经两相区固溶及时效处理后，获双态组织，由高固溶度的等轴相和高体积分数的片层状组织组成，随着固溶温度提高，合金中等轴相的体积分数逐渐减少，且针状和羽毛状马氏体相存在于层片状组织中。热连轧合金经单相区固溶及时效处理后，组织结构为网篮组织，其中，片层状α相与β相呈多组平行束形式存在，各组平行束互成一定角度的。热连轧态合金经480℃时效150h，合金中相呈螺旋状形态，β相沿相界不连续分布，有粒状β相在相内析出，且弥散分布，并沿一定取向规则排列。经两相区和单相区固溶及长期时效处理后，合金仍获双态和网篮组织，并有大量粒状相在晶内和相内弥散析出。随着固溶温度的升高，合金中等轴相的体积分数减少，使其在室温、400℃~500℃的抗拉强度提高。经1000℃固溶及长期时效处理合金在室温的抗拉强度高于960℃和980℃固溶及时效处理合金，但该合金在400℃~500℃范围内的抗拉强度低于960℃和980℃固溶及时效处理合金，且该合金的断裂机制为韧性混晶断裂。在400℃~420℃和575MPa~625MPa施加温度和应力范围内，940℃和1000℃固溶及时效处理合金在稳态蠕变期间的激活能分别为185kJ/mol和249.8kJ/mol。在试验的温度和应力范围内，与双态组织合金相比，网篮组织合金具有较好的蠕变抗力。双态组织合金的蠕变机制是波浪状<a+c>位错在HCP结构的相中发生锥面滑移；而网篮组织合金的蠕变机制是(1/2)<111>位错在BCC结构的β相中发生多系滑移，其中，高体积分数富含元素V的β相是使合金具有较高蠕变抗力的主要原因。在400℃~420℃和550MPa~600MPa的温度和施加应力范围内，与热连轧合金、1000℃固溶及时效合金相比较，1000℃固溶及长期时效合金具有较好的蠕变抗力和较长的蠕变寿命。直接长期时效态合金在蠕变期间发生动态再结晶，并形成亚晶，随着蠕变进行，应变量增大，亚晶尺寸减小，并在亚晶中继续发生位错的滑移是直接长期时效态合金在蠕变期间的变形机制。直接长期时效态合金的蠕变机制是弯钩状<c>位错在HCP结构的相中发生柱面滑移。两相区及单相区固溶处理合金，经长期时效处理后，其组织结构仍为双态和网篮组织，其中，大量粒状相在晶内和相内析出，可阻碍位错运动，是使合金具有良好蠕变抗力和较长蠕变寿命的主要原因。更多还原

【Abstract】 By means of heat treatment, creep properties measurement and microstructureobservation, the influence of preparation technique and heat treatment on microstructure andcreep properties of hot rolled alloy are investigated. By means of SEM/EDS compositionanalysis and XRD analysis, and combined to the contrast analysis of dislocationconfiguration, the influences of heat treatment on the phases constitution and deformationmechanism of the alloy during creep are investigated. Some results are obtained given asfollows:The microstructure of hot rolled alloy consists of and phases, phase in the alloydisplays the strip-like configuration along the rolling direction, and the line-like phase isdistributed along the boundary of the stripe-like phase, but the width of the stripe-like phase is less than that of the forged alloy. In the range of the applied stress(550MPa~600MPa) and temperature (400℃~420℃), the creep activation energies of theforged and hot rolled alloy are measured to be102kJ/mol and108kJ/mol, respectively. Thedeformation mechanism of the forged alloy during creep is duplex slips of dislocations, the<a+c> dislocations with horizontal direction are activated on the (2110) prismatic planes,and the <a> dislocations with upright feature are activated on the (1103) non-basal planes.The deformation mechanism of the phase in hot rolled alloy during creep is duplexslips of the line-like <a+c> and <a> dislocations on the prismatic and pyramidal planes.Therefore, the lower creep resistance is thought to be the main reason of the alloy having thehigher creep strain rate and short creep life.After solution treatment at the temperature being lower than β phase transition point,the microstructure of hot rolled alloy consists of bimodal structure, including thatsuper-saturation equiaxed phase and lamellar structure. The quantity of the equiaxedphase decreases as solution temperature enhances, and the needle-like and feather-likemartensite are distributed in the lamellar structure. After solution treatment at thetemperature being higher than β phase transition point, the microstructure of hot rolled alloyconsists of basketweave structure, the lamellar structure of phases is arranged along thedirections at a certain angle. After aging at480℃for150h, phase in the alloy displays theconfiguration with spiral-like feature, the particle-like phase is distributed along theboundary of lamellar phase, and the particle-like β phase is dispersedly precipitated withinphase along the certain orientation. After aging for150h at480℃, the microstructures of the alloy solution treated in α/β phase and β phase region still consists of bimodal structureand basketweave structure, respectively, but significant amount of particle-like phase isdispersedly precipitated within the grains and phase.The quantity of the equiaxed phase in the alloy decreases as solution temperatureincreases, which enhances tensile strength of the alloy at room temperature and400℃~500℃range. Compared to the strength of the alloy solution treated at960℃and980℃, afteraging at480℃for150h, the alloy solution treated at1000℃displays a higher tensilestrength at room temperature, but the alloy displays a lower tensile strength at400℃~500℃ranges.In the applied stress of575MPa~625MPa and temperature of400℃~420℃ranges, thecreep activation energies of the alloy solution treated at940℃,1000℃are measured to be185kJ/mol and249.8kJ/mol, respectively. Compared to the alloy with bimodal structure, thealloy with basketweave structure has the better creep resistance under the conditions of theapplied stresses and temperatures. The deformation mechanism of the alloy with bimodalstructure during creep is the wavy-like <a+c> dislocations activated on the pyramidal planesin phase with HCP structure, while deformation mechanism of the alloy with basketweavestructure during creep is (1/2)<111> dislocations activated in slip systems in phase withBCC structure，and it is thought that the V-rich β phase with high volume fraction isresponsible for improving creep resistance of the alloy.In the range of the applied stress (550MPa~600MPa) and temperature (400℃~420℃),compared to hot rolled alloy and the alloy solution treated at1000℃, after aging for150h at480℃, the alloy solution treated at1000℃displays the better creep resistance and longercreep lifetime. The dynamic recrystallization of the alloy during creep occurs to form thesubgrains structure, and the size of the subgrains decreases as the creep goes on. Anddislocation slip in the subgrains is thought to be deformation mechanism of the alloy in thelater stage of creep. Moreover, deformation mechanism of the alloy during creep is thehook-like <c> dislocations activated on the prismatic planes in phase with HCP structure.After aging for150h at480℃, the alloy solution treated in α/β phase and β phase regionstill obtain bimodal structure and basketweave structure, respectively, thereinto, significantamount of particle-like phase precipitating within the grains and phases may hinderdislocation motion, which is thought to be the main reason of the alloy possessing bettercreep resistance and longer creep lifetime.更多还原