变形工艺对TC11钛合金超塑性的影响

为了研究TC11(Ti-6.5Al-3.5Mo-1.5Zr-0.3Si)钛合金的超塑性变形行为,采用两种改锻工艺细化坯料原始组织,然后在电子拉伸试验机上分别以恒速、恒应变速率和最大m值法进行拉伸实验.结果表明,TC11钛合金在α+β区通过三维镦拔改锻工艺,可以获得晶粒度为6μm的细晶等轴组织,而在β区拔长改锻的组织为粗大的魏氏组织.在变形温度为900℃的条件下,TC11钛合金通过最大m值超塑变形方式获得了异常高的超塑性,最大伸长率达到2300%;而采用常规的恒应变速率和恒速超塑变形,伸长率分别为1147%和1100%.说明TC11钛合金在α+β区通过三维镦拔改锻细化晶粒后,以最大m值超塑变形是获得较好超塑性的有效方法.     

超塑成形工艺对TC21合金超塑性的影响

分析对比了一步与两步超塑成形法对未经特殊细化的TC21钛合金超塑性和显微组织的影响。研究结果表明:在变形温度为870~930℃范围内,两步超塑成形伸长率明显好于一步超塑成形。在变形温度为870℃,第1步和第2步应变速率均为3.3×10-4s-1,预应变量为50%,间隙保温时间为20 min时,两步超塑成形的伸长率达到最大值为438.60%,和恒应变速率的一步超塑成形相比,伸长率提高了74.72%。真应力-应变曲线表明:两步超塑成形时,第2步开始时的应力明显小于第1步结束时的应力,第1步变形对金属产生了一定的软化作用。显微组织显示:动态再结晶一直伴随着整个两步超塑性变形过程,再结晶行为的发生为塑性变形提供了细小等轴组织,有利于该合金超塑性的提高。     

分步变形条件对TC4-DT合金超塑性的影响

采用分步超塑成形法研究了未经特殊细化的TC4-DT钛合金的超塑性。结果表明,在温度为860~950℃,应变速率为3.3×10~(-4)～1.0×10~(-2) s~(-1),预应变量为20%～80%,间隙保温时间为5～30min条件下,TC4-DT合金均表现出良好的超塑性(305.93%～506.67%)。变形温度为890℃,预应变量为50%,间隙保温时间为10min,第1步和第2步应变速率均为3.3×10-4 s~(-1)时,TC4-DT合金表现出最佳超塑性,伸长率为506.67%。真应力-真应变曲线表明,第2步开始时的应力明显小于第1步结束时的应力,第1步变形对该合金产生一定的软化作用。TC4-DT显微组织显示,动态再结晶一直伴随着整个分步超塑性变形过程,静态再结晶发生在间隙保温时间。再结晶行为的发生,为塑性变形提供了细小等轴组织,有利于该合金超塑性的提高。     

分步拉伸变形对TA15合金超塑性的影响

采用分步变形法对TA15合金在10 kN高温电子拉伸试验机上进行了超塑性拉伸试验,研究了变形温度和预变形量对该合金超塑性性能及微观组织演变。结果表明:变形温度为850~950℃和预变形量为100%~200%时,TA15合金呈现出良好的超塑性;变形温度为900℃和预变形量为150%时,该合金的超塑性能最好,最大延伸率为1456%;变形温度为950℃时,该合金的超塑性能降低,延伸率仅为188%。TA15合金的微观组织状态显示:该合金在拉伸变形过程中微观组织保持等轴状,但是随着变形温度的升高,晶粒开始长大,变形温度越高,晶粒长大越显著。     

TC4-DT钛合金基于最大m值的超塑变形

采用最大m值法,在温度分别为850℃、870℃、900℃下,对改锻前及改锻后的TC4-DT钛合金棒材进行超塑性拉伸实验。实验结果表明,根据最大m值法拉伸试样TC4-DT在870℃的变形温度下,延伸率达到了最大值1240%,表明该类型TC4-DT钛合金的最佳超塑性变形温度在870℃左右;并且改锻后较细晶粒尺寸的TC4-DT棒材的超塑性明显高于改锻前的较粗晶粒组织,延伸率平均提高了一倍;分析显微组织可知,在超塑性拉伸变形中发生了动态再结晶。     

轧制镁合金超塑性和超塑胀形

对轧制态MB15镁合金进行了超塑性拉伸实验 ,结果表明 :晶粒尺寸为 5 .9μm的MB15镁合金板材 ,在温度为 5 73K、初始应变速率为 5 .5 6× 10 -4s-1的变形条件下 ,获得的最大延伸率为 30 9% ,应变速率敏感指数为0 .34;当真应变为 0 .3时 ,试样的晶粒尺寸为 4 .5 μm ,说明在拉伸初始阶段轧制镁合金可以获得细晶组织 ,同时发生了部分动态再结晶。利用扫描电镜观察断口发现典型的超塑性空洞形貌特征。通过胀形实验可以看出 ,该镁合金板材的超塑成形性能好 ,具有良好的超塑性成形应用潜力     

TC4钛合金设定m值超塑性拉伸方法

根据TC4钛合金的超塑性变形机理研究成果,结合设定m值超塑性拉伸方法的设计思路,在VISUAL BASIC环境下编写出了设定m值超塑性拉伸控制程序。在完成对该程序充分调试的基础上,对TC4钛合金进行设定m值超塑性高温拉伸试验,在TC4钛合金最佳变形温度850℃的条件下,将m值分别设定为0.3、0.35、0.4、0.45进行高温拉伸试验,获得TC4钛合金延伸率δ分别为704%、762%、819%、858%,再将应变速率敏感指数m值与延伸率δ对应后生成关系曲线并进行回归分析,最终得到TC4钛合金超塑性应变速率敏感指数m值与伸长率δ的关系式。     

应变速率循环法构建TC21钛合金超塑性本构方程

采用应变速率循环法在超塑拉伸机上对TC21钛合金进行5组高温超塑性拉伸实验,变形温度范围860℃~940℃,应变速率循环范围10-5s-1~10-3s-1。通过对拉伸实验数据分析,计算出TC21钛合金动态再结晶激活能Q,利用Arrhenius模型构建TC21钛合金高温条件下的超塑性本构方程,并通过1stOpt软件进行非线性回归拟合进行修正,得到了更为精准的超塑性本构方程。实验结果表明,当变形温度不变时,流动应力随着应变速率的增大而增大,且高应变速率时,流动应力对应变速率的敏感性要大于低应变速率时,可判定TC21钛合金属于正应变速率敏感材料。TC21钛合金在860℃附近时的超塑性较好,综合延伸率可达366.6%。     

变形温度对TC11钛合金超塑性的影响

通过高温拉伸试验研究TC11钛合金在应变速率0.001 s~(-1)、变形温度810～1050℃的超塑性变形行为,并用金相显微镜和透射电镜对变形试样的微观组织进行观察和分析.结果表明,在β单相区,TC11钛合金不能呈现超塑性;而在α+β两相区的810～980℃温度范围内,TC11钛合金呈现出超塑性,且最佳温度在900℃附近,其最大延伸率为595%,此时的超塑性变形过程中有晶内变形、界面滑动、动态再结晶或扩散蠕变的参与,且界面滑动出现在α/β相界面.α相和β相的相对含量对超塑性有较大的影响,初生α相含量在70%附近时对应着TC11钛合金的最佳超塑性.     

变形工艺对Inconel718合金超塑性的影响(英文)

Inconel 718合金经过热锻、δ相析出处理及再结晶热处理后,分别采用最大m值法和基于最大m值的应变诱发超塑性法进行高温拉伸试验,研究形变热处理及拉伸工艺对材料超塑性能的影响。结果表明,经过热变形、δ相析出及再结晶退火处理后,有效细化了Inconel 718合金的组织。析出的δ相可以在再结晶退火及热变形中起到控制晶界的作用。在950℃变形,采用上述两种方法拉伸变形得到的延伸率分别为566%和340%,说明基于最大m值的形变诱发超塑法可以进一步提高Inconel 718合金的延伸率。     

Superplastic Behaviour and Microstructural Evolution in Stepped Tensile Deformation of Titanium Alloy

The effect of stepped tensile deformation at 850, 900, 950 °C on the elongation, microstructure, and mechanical characteristics of titanium alloy has been investigated. The stepped uniaxial tension (stepped-UT) was composed of the following three steps in sequence: constant speed tension, clearance stage, and maximum m superplasticity tension (MaxmSPT). Results showed that the maximum elongation of TC6 alloy between 850 and 950 °C through the Stepped-UT was 2053%, in which the first engineering strain of constant speed tension was 2.0, the following clearance time was 15 min, and the MaxmSPT was finally carried on until failure. And the optimal elongations obtained by the MaxmSPT and constant speed tensile method were 1347 and 753.9% at 850 °C, respectively. The true stress-strain curves showed the strain rate sensitivity index m of the alloy in the stepped-UT was higher than the one in the single step of the MaxmSPT. Moreover, the microstructure of TC6 alloys in the stepped superplastic deformation was observed and the grain refinement was found. The grain refinement and true stress-strain curves of TC6 alloys were all affected by preplanned engineering strain and temperatures. The results also showed the joint action of the dynamic recrystallization and static or meta-dynamic recrystallization refined the grains, improved the structure property, and induced the plasticity enhancement.     

TC6钛合金基于m值的高效超塑变形研究

基于m值的高效超塑变形方法是一种全新的超塑性研究方法。采用该方法对TC6合金进行高温拉伸实验,研究其超塑性性能。实验结果表明,该合金具有较好的超塑性,采用该方法进行实验,能缩短拉伸实验的时间,并且可以获得良好的伸长率。其最佳变形温度为900℃,伸长率为1696%。     

Er、Zr微合金化5083铝合金的超塑性

针对5E83合金(Er、Zr微合金化5083合金),采用超塑性拉伸试验、扫描电镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM),探究了Er、Zr微合金元素、晶粒尺寸、变形温度、应变速率对合金超塑性的影响。通过再结晶退火、空冷和水冷的搅拌摩擦加工(FSP),分别获得了晶粒尺寸为7.4、5.2、3.4μm的完全再结晶组织,作为初始状态进行超塑性拉伸。结果表明,初始晶粒尺寸越细小,超塑性伸长率越高。当晶粒尺寸>5μm时,超塑性变形过程晶粒粗化缓慢,细化初始晶粒可显著提高超塑性;而当晶粒尺寸<5μm时,超塑性变形过程晶粒粗化严重,进一步细化初始晶粒对超塑性的提高有限。不同变形温度、应变速率的超塑性拉伸结果显示在变形温度为450～540℃、应变速率为1.67×10^-4～1.67×10^-1 s^-1,超塑性伸长率随变形温度和应变速率的提高呈现先上升后下降再上升的趋势;变形温度为520℃、应变速率为1.67×10^-3 s^-1条件下,水冷FSP态合金获得最大伸长率330%...     

喷丸工艺对TC4钛合金梯度纳米晶结构的作用规律

目的通过改变喷丸的压力或时间,在钛合金表面制备出剧烈塑性变形(SPD)层较厚、硬度较高的梯度纳米晶结构。方法改变喷丸压力(0.3~0.6 MPa)或喷丸时间(15~60 min),调控TC4钛合金表面梯度纳米晶结构的变形层厚度和纳米晶晶粒尺寸。利用金相显微镜观察塑性变形层截面的组织形貌,通过X射线衍射仪(XRD)和透射电子显微镜(TEM)确定喷丸表面纳米晶的晶粒尺寸,通过显微硬度计对塑性变形层的截面硬度进行研究。结果一定喷丸压力(0.6MPa)下,SPD层和总变形层厚度分别在喷丸25、30 min时达到饱和值78μm和143μm。一定喷丸时间(25 min)下,SPD层和总变形层的厚度随喷丸压力的增加而增厚,在0.4 MPa时达到饱和,分别为78μm和120μm。当SPD层厚度进入饱和阶段后,表层晶粒大小和硬度强化程度都趋于稳定;在0.6 MPa下,当表面α相细化至稳定阶段时,晶粒尺寸为30~90 nm,表面硬度提高约30%。结论喷丸SPD层及总变形层的厚度随喷丸时间的延长或喷丸压力的增大而增厚,当SPD层厚度趋于饱和后,表面晶粒尺寸和硬度强化程度都已饱和。     

钛合金激光焊缝的超塑性变形行为及显微组织

通过高温拉伸试验研究Ti-6Al-4V(TC4)合金激光焊缝的纵向超塑性变形行为,采用扫描电镜观察超塑性变形前后焊缝的显微组织.结果表明:TC4钛合金激光焊缝具有良好的超塑性变形能力,在900 ℃、10~(-3) s~(-1)工艺条件下伸长率达到最大值397%;在超塑性变形过程中,原始焊缝的针状马氏体首先转变为片层状的α+β组织,而后片层组织发生再结晶等轴化;随着变形温度升高或应变速率降低,等轴化程度增大.     

搅拌摩擦加工AZ31镁合金的超塑性

对搅拌摩擦加工AZ31镁合金的微观组织和拉伸力学行为进行了研究。结果表明,通过搅拌摩擦加工,热轧AZ31板材的平均晶粒尺寸由92.0μm细化到11.4μm。搅拌摩擦加工板材在高温下具有优异的塑性,伸长率在温度为723K和应变速率为5×10-4s-1的条件下达到1050%。该材料还具有高应变速率超塑性,在723K和1×10-2s-1的条件下伸长率达到268%。在相同实验条件下,母材由于晶粒尺寸粗大,没有显示出超塑性。     

Structure and properties of aluminum alloy 1421 after equal-channel angular pressing and isothermal rolling

Sheets from the aluminum alloy 1421 with an ultrafine-grained (UFG) structure and a weak crystallographic texture were prepared by the method of equal-channel angular pressing (ECAP) through a die with channels of a rectangular cross section and by subsequent isothermal rolling. Both operations were carried out at a temperature of 325°C. It is shown that severe plastic deformation (SPD) leads to the formation of a completely recrystallized uniform microstructure with an average grain size of 1.6 µm in the alloy. At room temperature the alloy 1421 demonstrates high static strength (σ_u = 545 MPa, σ_0.2 = 370 MPa) in the absence of a significant anisotropy. At temperatures of hot deformation, the alloy showed ultrahigh elongations under superplasticity (SP) conditions. At a temperature of 450°C and initial deformation rate of 1.4 × 10^?2 s^?1 the maximum elongation at fracture was ～2700%. At static annealing at a temperature of SP deformation, the UFG structure formed in the process of SPD remains stable. The SP deformation is accompanied by an insignificant grain growth and pore formation.     

Influence of hot isostatic pressing on microstructure,properties and deformability of selective laser melting TC4 alloy

The influence of different hot isostatic pressing regimes on microstructure, phase constitution, microhardness, tensile properties and deformability of TC4 alloy fabricated by selective laser melting (SLM) technology was studied. The results show that the microstructure of SLM TC4 alloy is composed of acicular martensite α' phase, and the sample exhibits high microhardness and strength, but low plasticity. After hot isostatic pressing, acicular martensite α' phase transforms into α+β phase, and with the increase of hot isostatic pressing temperature and duration, α phase with coarse lath is gradually refined, and the proportion of α phase is gradually reduced. Because of the change of phase constitution in SLM TC4 alloy after hot isostatic pressing, the grain refinement strengthening is weakened, the density of dislocation is reduced, so that both microhardness and tensile strength are decreased by around 20%, the elongation is increased by more than about 70%, even over 100%, compared with as-deposited TC4 alloy. When the hot isostatic pressing regime is 940℃/3 h/150 MPa, the tensile strength and the elongation achieve optimal match, which are about 890 MPa and around 14.0% in both directions. The fracture mechanism of alloy after 940℃/3 h/150 MPa HIP is dultile fracture. Hot isostatic pressing causes concave deformation of SLM TC4 alloy thin-walled frames, and the deformation degree increases with the increase of temperature.