TiAl基合金片层结构粗化行为研究进展

片层结构是TiAl合金中最重要的微观结构形态。综述了当前TiAl合金片层结构粗化的研究进展,介绍了TiAl合金片层结构的连续粗化和不连续粗化类型,分析了粗化行为的热力学驱动力来源,包括化学体积自由能、界面能、弹性应变能和晶界能,简述了粗化的动力学特征,并讨论了影响粗化行为的各种因素,包括温度、时间、组织条件和合金元素等。在此基础上研究了Ti-4822合金片层结构的粗化行为,描述并分析了片层高温下连续粗化与不连续粗化行为的特征,及其随温度与时间的变化规律。发现在1160 ℃,两种粗化方式存在明显的竞争关系。在共析温度附近,不连续粗化占据优势地位,而在更高的温度（高于1200 ℃）,不连续粗化被抑制,连续粗化占据主导地位。     

Al-Zn-Cu系合金不连续析出组织变形后的结构与性能

采用扫描电镜、透射电镜、X射线衍射及硬度测试等手段研究了添加2at％Cu的AlZn对称成分合金在冷轧后重新加热过程中的组织结构变化。结果发现：该合金不连续析出组织在冷变形后重新加热时发生了再结晶，以连续粗化与不连续粗化2种机制进行，再结晶温度约为100℃：而且相组成物由Al相、Zn相和细小的ε相转变为Al相、Zn相和粗大的T'相。AlZn-2Cu合金不连续析出组织在冷变形后重新加热时，硬度的变化是由再结晶软化、T’相粗化以及Zn原子的固溶强化共同影响的结果。     

Al-Zn-Mg-Cu合金半固态等温组织粗化研究

采用半固态等温热处理方法,研究了Al-Zn-Mg-Cu合金在加热到两相区温度等温保温过程中的组织粗化规律。回归拟合结果表明,α(Al)晶粒平均直径与等温时间近似满足方程：,粗化速率系数K随等温温度升高而增大,其在610和620 ℃下对应的值分别为14811.4和17836.3 μm4/s。实验合金组织的多边化、球化和粗化现象是同时发生的,组织粗化以晶粒合并长大和Ostwald熟化的方式进行。等温前期粗化以合并为主,但随着晶间液相增多,合并变得困难,导致等温后期粗化速率下降     

冷坩埚定向凝固TiAl基合金热处理

针对冷坩埚定向凝固条件下获得的大尺寸TiAl基合金坯锭试样,采用不同热处理工艺参数,包括普通退火处理,温度循环热处理和快速加热循环热处理,并对坯锭热处理前后的组织和力学性能进行了比较。结果表明,合适的热处理工艺在不改变原始定向凝固钛铝基合金的晶粒状态的同时,可以使柱状晶内片层组织变得均匀和细小致密,并提高了其力学性能。定向凝固试样在1360℃温度以上出现再结晶和晶粒长大现象,而温度低于1150℃时则不然。温度循环热处理和快速加热循环热处理对细化定向凝固组织TiAl基合金的全片层组织都起到很好的促进作用。     

塑性变形对Cu—Ni—Fe合金失稳分解组织不连续粗化的影响

固溶处理后的塑性变形能促进Ｃｕ－Ｎｉ－Ｆｅ合金时效过程中失稳分解组织的不断连粗化,塑料变形程度对不连续粗化组织的最终形态有明显的影响。变形程度较小时,组织呈近片层状;     

快速加热循环热处理细化TiAl基合金的显微组织研究

在研究Ti－Al二元相图及合金元素的影响、TiAl基合金显微组织类型与连续冷却转变、热处理实践及效果的基础上，提出了快速加热循环热处理新工艺，该工艺的特点是：加热速度快，单相构保温，保温时间短，冷却速度相对较慢。分析了该工艺的优点和缺点。     

镍基非晶态合金晶化过程的研究

本文研究了非晶态Ni_(83)Cr_7Fe_3Si_4B_3合金在动态加热及等温热处理条件下的晶化过程。结果表明,对于动态加热及等温热处理两种情况,镍基非晶态合金的晶化过程相同,结晶相没有发生变化。但是,在动态加热条件下,初始晶化主要是成核结晶,而在等温热处理晶化过程中晶粒长大起主要作用。     

ON THE CRYSTALLIZATION OF AMORPHOUS Ni-BASE ALLOY

本文研究了非晶态Ni_(83)Cr_7Fe_3Si_4B_3合金在动态加热及等温热处理条件下的晶化过程。结果表明,对于动态加热及等温热处理两种情况,镍基非晶态合金的晶化过程相同,结晶相没有发生变化。但是,在动态加热条件下,初始晶化主要是成核结晶,而在等温热处理晶化过程中晶粒长大起主要作用。     

Ti-48Al合金全片层组织的稳定性

研究了Ti 48Al合金全片层组织在 115 0℃时效时的组织稳定性。结果表明 ,140 0℃ ,1h固溶处理后炉冷获得的粗片层组织的稳定性远远优于空冷获得的细片层组织。细片层组织首先在晶界处发生不连续粗化 ,而后粗化片层组织中的α2 相发生溶解并球化 ,从而转变为近γ组织 ;空冷组织中魏氏片层的存在降低了片层组织的稳定性 ,魏氏片层 /基体界面与晶界一同成为片层组织发生分解的起始部位。Ti 48Al 0 .8%B(摩尔分数 )合金的细片层组织因晶界TiB2 相的存在有效抑制了晶界不连续粗化 ,但γ相从TiB2 /基体界面和晶界重新形核生长使片层组织转变为均匀的细晶近γ组织     

等通道转角挤压AZ91D镁合金在半固态等温热处理过程中的组织演变

用金相显微镜观察了等通道转角挤压AZ91D镁合金在570℃等温热处理过程中的组织演变。结果表明,等通道转角挤压后半固态等温热处理是一种适于制备AZ91D镁合金半固态浆料的方法。该材料的微观组织在此过程中经历了四个阶段：初期的快速粗化阶段、组织分离阶段、晶粒球状化阶段和最后的粗化阶段。当挤压4道次后,加热时间为15 min时,组织球化效果最好,晶粒最细小;而后随着加热时间的延长,晶粒尺寸和形状系数逐渐增大;当加热时间一定时,随着挤压道次的增加,组织的晶粒尺寸和形状系数减小。     

全片层高Nb含量TiAl合金长期热循环后的显微组织不稳定性

对全片层Ti-45Al-8.5Nb-（W,B,Y）合金在900℃下进行长期热循环（500次和1000次）实验,采用扫描电镜（SEM）及透射电镜（TEM）研究该合金长期热循环后的显微组织不稳定性。结果表明：合金经热循环后主要产生两种类型的组织不稳定性：1）长期热循环特别是1000次热循环后,在Al偏析处易产生因晶界迁移引起的不连续粗化,随着循环次数的增加,元素扩散致使Al偏析逐渐减少;2）1000次热循环后,α2片层变细且发生断裂,这是由α2→γ相变导致的α2片层溶解所致。同时,γ晶粒在α2片层或（α2＋γ）片层内部以任意方向形核。     

Effects of discontinuour coarsening of lamellae on creep strength of fully lamellar TiAl alloys

High temperature creep of a binary Ti-42mol%Al alloy with fully lamellar structure was studied to examine effects of lamellar spacing on creep strength. Strain hardening is more significant in a finer lamellar material, resulting in higher creep strength at high stresses. Discontinuous coarsening of lamellae takes place during creep, and is more substantial in the finer lamellar material at low stresses. Because of the microstructural degradation, the strengthening by fine lamellae diminishes at low stresses. Some specimens were annealed at high temperatures to finish the discontinuous coarsening prior to creep testing. In these specimens, the strengthening by fine lamellae becomes effective even at low stresses.     

Precipitation kinetics of NZ30K-Mg alloys based on electrical resistivity measurement

The electrical resistivity of NZ30K-Mg alloy was measured at different heating rates during continuous heating to study the precipitation kinetics. Two kinds of metastable phases, β″ and β″, formed during the heating. Kissinger method and differential isoconversional method were employed to assess the precipitation kinetic parameters of NZ30K-Mg alloy, activation energy E_α and pre-exponential factor A′_α. The fraction of transformation (α) and the precipitation sequence in NZ30K-Mg alloy were determined. Continuous heating transformation (CHT) and isothermal heating transformation (IHT) diagrams were further obtained for guiding the aging of NZ30K-Mg alloy. The analysis shows that the precipitation kinetic parameters of NZ30K-Mg alloy can be obtained accurately using isoconversional method.     

Structural transformations activated during the formation of the lamellar microstructure of TiAl alloys

The structural transformations activated during the formation of the lamellar microstructure have been studied in a Ti₄₉Al₄₇Cr₂Nb₂ alloy. By performing statistical analysis of the microstructure, a special attention has been paid to the orientations of the lamellae and to the interface relationships. Experiments were conducted on specimens in an as-HIPed condition as well in an isothermal forged plus annealed condition. In the annealed alloy, three mechanisms of the lamellar formation were evidenced depending upon the nucleation temperature: a heterogeneous transformation occurring at grain boundaries, a homogeneous nucleation in the α₂ matrix and an interfacial nucleation of twin-related lamellae. The microstructural analysis of the as-HIPed alloy was aimed at determining the activated mechanisms among those evidenced in the annealed alloy.     

铸态Ti-46Al-6(Cr, Nb, Si, B)合金的高温流变行为及其组织演变

以3次真空自耗熔炼的Ti-46Al-6(Cr,Nb,Si,B)(at%)(以下简称G4合金)合金为对象,采用恒温等应变速率热模拟压缩试验研究G4合金在1050～1250℃及0.001～1s-1应变速率下的高温流变行为和组织演变。结果表明,在高温变形过程中,G4合金呈现先硬化后软化的流变行为特征,组织由粗大的铸态γ+γ/α2近片层组织演变为细小的近等轴γ+α2组织;造成G4合金流变软化和组织演变的主要原因是动态再结晶(DRX)。变形温度和应变速率是影响G4合金高温流变和组织演变的2个主要因素。铸态G4合金在高温下的变形机制以γ/α2层片晶团的扭折、弯曲、球化和DRX以及γ晶粒的拉长、破碎和DRX为主,孪生变形也起到了一定的辅助作用。其最佳高温塑性变形温度为1150℃,应变速率应不大于0.1s-1。     

Effects of thermal exposure on the microstructure and properties of a γ-TiAl based alloy containing 44Al–4Nb–4Zr–0.2Si–0.3B

The microstructural stability after long-term aging at 700°C of a TiAl-based alloy containing 44Al–4Nb–4Zr–0.2Si–0.3B (in at%) has been studied. The microstructural observations are consistent with those established previously, i.e. even as low as 700°C the microstructure is unstable in that after prolonged aging, decomposition of the α₂ lamellae and increased volume fraction of gamma phase have been observed. Despite this, it has been shown that, with a combination of slow cooling from the annealing temperature and a ‘stabilisation’ treatment at an intermediate temperature, the mechanical properties of this alloy can be retained. This increase in thermal stability has been attributed to the large α₂ lamellae which result from slow cooling and are less susceptible to complete dissolution during aging, and also to the formation of gamma grains which are embedded in and constrained by the ω phase between the lamellar colonies. ©     

Ti—48Al合金片层组织的连续粗化机制

研究了 115 0℃时效时Ti 48Al合金全片层组织的连续粗化机制。片层组织的连续粗化不仅能通过片层界面缺陷 (如台阶、端部、弯曲的界面等 )迁移来实现 ,而且可以通过γ/γ片层界面迁移或分解的方式来实现 ;在真孪晶、伪孪晶和 12 0°旋转有序型γ/γ界面当中 ,12 0°旋转有序界面的稳定性最低 ,最容易迁移或分解 ;γ片层内的 12 0°旋转有序畴界与片层界面的交汇处易形成热沟(thermalgroove) ,它往往成为片层界面发生分解的起始部位     

Thermal stability of Zr_(55)Al_(10)Ni_5Cu_(30)bulk amorphous alloy during continuous heating and isothermal annealing

1　INTRODUCTIONBulkamorphousalloyspossessalongrangedis orderbutshortrangeorderstructure ,whichresem blesthestructureofliquid .Andthereisasupercooledliquidregionbeforecrystallizationofabulkamor phousalloy .Thisuniquestructureresultsinexcellentpropertiessuchashightensilestrength ,highhard ness,highimpactfractureenergy ,highelasticener gy ,highcorrosionresistance ,highviscousflowabilityandgoodsoftmagnetism[13] .Thesynthesisofmetallicglassesinabulkform (withthickness >1mm )wassuccessfullyachi…     

Deformation of Zr41Ti14 Cu12. 5Ni10Be22.5 bulk amorphous alloy under isobaric pressure in super-cooled liquid region

The curve of crystallization transition during continuous heating for the Zr41Ti14 Cu12. 5Ni10Be22.5 bulk amorphous alloy was measured by means of dilatation(Fully automatic transformation recording/measuring instrument) and X-ray diffraction(XRD) method. The deformation behavior of the alloy at various heating rates in the supercooled liquid region was studied. The results show that the glass transition temperature of the alloy increases slightly and the supercooled liquid region(SLR) increases significantly with increasing heating rate. The deformation amount under isobaric pressure of 1 N for the alloy in the SLR increases with increasing heating rate. As the heating rate of the alloy increases from 5 to 100℃/rain, the amount of deformation of the alloy increases from 8.3% to 45%     

等径道角挤压预变形AZ61镁合金在半固态等温处理中的微观组织演变(英文)

利用金相显微镜和图像分析设备对等径道角挤压预变形AZ61镁合金在半固态等温处理中的微观组织演变进行研究。先利用等径道角挤压对AZ61镁合金铸坯在310℃进行应变诱导,然后将其在半固态进行不同时间的等温处理。研究结果表明:挤压道次、等温处理温度和变形路径影响预变形AZ61镁合金在半固态等温处理中的微观组织演变过程。在将等温处理温度从530℃升高至560℃的过程中,合金的平均晶粒尺寸从22μm增大到35μm。当等温处理温度为575℃时,平均晶粒尺寸减小。当等径道角挤压的变形路径为BC时,预变形AZ61镁合金在半固态等温处理中获得的微观组织晶粒尺寸最小。