Ti2448合金高温变形行为及组织演变机制的转变

研究了多功能亚稳β型Ti2448（Ti 24Nb-4zr-8Sn,质量分数,%）合金在β单相区的高温变形行为.结果表明.在低应变速率(≤0.1 s^-1和高应变速率(≥1 s^-1)条件下,真应力和应变速率的双对数关系可以通过2个线性关系分别表征,平均应变速率敏感值（mavg）分别为0.265和0.032,这不同于常规β钛合金随着应变速率的增大而逐渐降低的应变硬化规律,即Sigmoidal曲线特征.微观组织演化和动力学分析显示,这种特殊的双线性关系与高应变速率导致的局域化非均匀塑性变形行为和动态再结晶（DRX）相关联.尽管动态回复（DRV）是该合金高温塑性变形的主要组织演变机制,高应变速率使得组织演变从DRV向DRX转变,并在交错的变形带内形成小于3μm的细晶组织.因此,高应变速率条件下的DRX是实现Ti2448合金高温变形过程中细化组织的主要机制.     

大晶粒单相Ni-50Al金属间化合物高温塑性

研究了原始晶粒尺寸为220 (m的正化学计量比单相Ni-50Al金属间化合物的高温变形行为及组织演变规律.结果表明,该合金在温度1000～1100 ℃,应变速率7.5×10~(-4)～1×10~(-3) s~(-1)范围内具有良好的高温塑性变形能力;在1075 ℃,应变速率为8.75×10~(-4) s~(-1)时,最大延伸率可达139%.金相显微分析表明,原始大晶粒组织经高温塑性变形后显著细化;EBSD与 TEM分析表明,变形过程中小角度晶界持续产生,较小角度晶界向较大角度晶界不断演变,最终导致晶粒显著细化.显微结构综合分析表明,大晶粒Ni-50Al合金的高温塑性变形是由位错的交滑移与攀移等交互作用产生的连续动态回复和再结晶导致的.     

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。     

Effect of equal channel angular extrusion on the microstructure and superplasticity of an Al-Li alloy

This research investigates the use of equal channel angular extrusion (ECAE) processing to produce a superplastic form of the aluminum alloy 2098. The starting material was a hot-rolled and precipitation-hardened plate with elongated grains of width 67–92 μm, and a composition in weight percent of 2.2% Li, 1.3% Cu, 0.73% Mg, 0.05% Zr, balance Al. Microstructural evolution was investigated with optical and transmission electron microscopy (TEM) and microhardness measurements after each step of a multipass ECAE process. ECAE produced a submicron grain structure with an average size of about 0.5 μm. The sub-grain microstructure size was a function of the magnitude of the input strain and the extrusion temperature. Misorientation angles of the developed submicron structure increase with increasing number of passes at warm working temperatures. Superplastic behavior of the ECAE-processed alloy was achieved. However, the low zirconium content of the 2098 alloy resulted in grain growth of the refined structure at the superplastic processing temperatures, placing a lower limit on the deformation rates that can be used.     

累积叠轧焊法制备超细晶纯铝的研究

采用累积叠轧焊方法在室温下对1060纯铝进行剧烈塑性变形，并分析1060纯铝变形前后内部微观组织结构的演变和力学性能的变化。实验结果表明，随着累积叠轧道次的增加，层界面复合越来越紧密，5道次后出现母材基体的相互渗透；材料的抗拉强度和硬度得到大幅度提高，伸长率在1道次时急剧下降，然后基本保持不变；晶粒尺寸急剧细化，等效真应变为6．4的条件下得到了平均晶粒尺寸为400nm的超细晶组织。     

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%...     

Effect of second phase particles on grain refinement during equal-channel angular pressing of an Al-Mg-Mn alloy

The process of grain refinement under severe plastic deformation was examined in an Al-5.4% Mg-0.5% Mn-0.1% Zr alloy, which was subjected to equal-channel angular pressing (ECAP) in the strain interval from 1 to 12 at a temperature of ∼300 °C. It was shown that the size and distribution of the second phase particles precipitated under homogenization annealing strongly affect grain refinement. Extensive grain refinement under ECAP was provided by a dispersion of Al₆Mn particles with an average size of ∼25 nm that precipitated during the homogenization annealing at an intermediate temperature. The fully recrystallized structure with an average crystallite size of ∼0.55 μm evolves through continuous dynamic recrystallization. In contrast, homogenization annealing at a high temperature leads to the formation of coarse Al₆Mn particles with a plate-like shape. Under further ECAP, the formation of coarse recrystallized grains takes place in this material due to the discontinuous growth of recrystallized grains during the inter-pass annealing between the ECAP passes. The role of second phases in grain refinement is discussed in terms of pinning and driving forces for recrystallization.     

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通过对传统孔型的讨论和模拟的结果分析,基于大塑性变形原理的晶粒超微细化方法,提出了均匀大应变棒材轧制的新型孔型设计思想,建立了以多向大塑性变形加工为特点的扁椭圆系列孔型.采用非线性有限元法,建立了孔型棒材温轧过程数值分析模型,对比分析了新型孔型系列与传统孔型系列轧件断面内塑性应变分布规律,得出了在满足形状尺寸精确的条件下新型扁椭孔型能更好地将大塑性应变引入到断面中心,并使断面塑性应变趋于均匀,其中心处最大累积应变超过5.0,达到产生超微细晶粒的大塑性变形制备条件.     

35CrMo钢动态再结晶过程数值模拟与试验研究

以热物理模拟试验研究为基础,得出35CrMo钢发生动态再结晶时的数学模型。采用热一力耦合的弹塑性有限元法对35CrMo结构钢在热变形过程进行了数值模拟。变形的不均匀性导致动态再结晶进行的不等时性,动态再结晶的发生初始于大变形区,随着应变的增加,逐渐向粘着区和自由变形区延伸。同时预测热变形过程的形变量、形变速率和形变温度对再结晶微观组织演变的影响。在一定温度下,再结晶晶粒尺寸的大小与应变速率呈反方向变化,随着变形的进行,试样内的晶粒尺寸趋于细化和均匀化。在一定应变速率下,随着形变温度的降低,再结晶晶粒尺寸趋于细化,导致了锻件的综合性能提高。为了观察显微组织演化过程,对模拟结果进行了金相法验证,模拟结果与实验结果比较吻合,模拟的结果是合理的。     

Changes in the grain structure of metallic materials upon plastic treatment

Experimental data on structural changes in the process of plastic deformation of polycrystalline copper and stainless steel have been reviewed. It has been shown that the mechanisms of the formation of a new grain structure, i.e., dynamic recrystallization, depend on the conditions of treatment or flow stresses at the steady-state stage, which are determined unambiguously by the temperature and strain rate. Upon hot deformation (low flow stresses), it is local migration (bulging) of grain boundaries and subsequent growth of these bulgings that seem to be the main mechanism of formation of new grains. Since the nucleation of new grains in this case is of a heterogeneous character, the microstructure evolution can be classified as a discontinuous dynamic recrystallization. Upon worm or cold deformation (high flow stresses), we deal with a dynamically recrystallized structure only after very high degrees of deformation. The new grain structure is formed due to the growth of angular misorientation between subgrains with an increase in the total degree of deformation, which can be considered as a continuous dynamic recrystallization. Changes in the mechanisms of dynamic recrystallization with changes in the conditions of treatment lead to a bimodal dependence of the size of dynamically recrystallized grains on the flow stresses.     

Deformation characteristics during Y-shaped tube hydroforming of 6061 aluminum alloy

To manufacture lightweight tube components for aerospace oil circuit systems, an experiment was run to investigate the deformation characteristics on Y-shaped tube hydroforming of 6061 aluminum alloy. Both strain state and metallurgical structure indicate that there are four kinds of prevailing defects during Y-shaped tube hydroforming: bursting, lack of cylindricity, wrinkling, and thinning due to the poor plastic property of 6061 aluminum alloy. The danger of bursting prevails at the early stage of the operation as a result of excessively high internal pressure. In contrast, wrinkling prevails after the middle stage of the operation as a result of excessively axial feeding and cannot be eliminated during subsequent deformation. Lack of cylindricity is mainly because of insufficient axial feeding and internal pressure but can be eliminated by increasing internal pressure. Elongation and compression deformations are originated on protrusion and main pipe of Y-shape tube respectively all the way through the bulging process. Consequently, minimum and maximum thicknesses are at the top of protrusion and the bottom of Y-shape tube respectively, which induces a V-shape borderline of thickness distribution. According to the excessive plastic deformation, microstructure evolution is originated. Crystal grain of protrusion is elongated and its grain size is about 150 μm. In contrast, crystal grain of the middle zone of main tube is refined greatly, which grain size is 50 μm, decreased by 75%. These are useful to improve the component.     

不同沉积温度下CrCN涂层的力学性能

使用磁控溅射技术在304不锈钢表面制备CrCN涂层,研究了沉积温度(200、250、300、350和400 ℃)对涂层结构及力学性能的影响。研究表明,沉积温度为250 ℃时,涂层的晶粒尺寸及表面粗糙度最大,但随着沉积温度的进一步升高,涂层的晶粒逐渐细化,表面粗糙度明显下降;同时涂层硬度伴随沉积温度的升高出现先增大后减少的趋势,沉积温度为350 ℃时,薄膜具有最高的硬度(22.85 GPa),抗弹性形变和抗塑性形变能力最好,体现出优异的力学性能。     

On the principles of the deformation methods of grain refinement in aluminum alloys to ultrafine size: II. Ultrafine-grained alloys

The applicability and efficiency of the principles of optimum structural heterogeneity and stage-by-stage grain refinement in relation to the formation of an ultrafine-grained (UFG) structure (with a grain size smaller than 1 μm) in bulk billets during severe plastic deformation are analyzed. The evolution of the criteria of these principles is considered when going from a fine-grained structure to a UFG structure and from conventional deformation treatment to severe deformation treatment. The dependence of the intrinsic mechanisms of grain refinement to ultrafine size on the initial structure of an alloy, including the heterogeneity of the initial structure, is analyzed.     

Effect of Various SPD Techniques on Structure and Superplastic Deformation of Two Phase MgLiAl Alloy

MgLiAl alloy containing 9 wt% Li and 1.5% Al composed of hexagonal α and bcc β phases was cast under protecting atmosphere and hot extruded. Various methods of severe plastic deformation were applied to study their effect on structure and grain refinement. Rods were subjected to 1–3 passes of Twist Channel Angular Pressing TCAP (with helical component), cyclic compression to total strain ε?=?5 using MAXStrain Gleeble equipment, both performed at temperature interval 160–200 °C and, as third SPD method, KOBO type extrusion at RT. The TCAP pass resulted in grain refinement of α phase from 30 μm down to about 2 μm and that of β phase from 12 to 5 μm. Maxstrain cycling 10?× up to ε?=?5 led to much finer grain size of 300 nm. KOBO method performed at RT caused average grain size refinement of α and β phases down to about 1 μm. Hardness of alloy decreased slightly with increasing number of TCAP passes due to increase of small void density. It was higher after MAXStrain cycling and after KOBO extrusion. TEM studies after TCAP passes showed higher dislocation density in the β region than in the α phase. Crystallographic relationship (001) α|| (110) β indicated parallel positioning of slip planes of both phases. Electron diffraction technique confirmed increase of grain misorientation with number of TCAP passes. Stress/strain curves recorded at temperature 200 °C showed superplastic forming after 1st and 3rd TCAP passes with better superplastic properties due to higher elongation with increasing number of passes. Values of strain rate sensitivity coefficient m were calculated at 0.29 after 3rd TCAP pass for strain rate range 10^?5 to 5?×?10^?3 s^?1. Deformation by MAXStrain cycling caused much more effective grain refinement with fine microtwins in α phase. Superplastic deformation was also observed in alloy deformed by KOBO method, however the value of m?=?0.21 was obtained at lower temperature of deformation equal to 160 °C and deformation rate in the range 10^?5 to 5?×?10^?3. Tensile samples deformed superplastically showed grain growth and void formation caused by grain boundary slip. Summarizing, all methods applied resulted in sufficient grain refinement to obtain the effect of superplastic deformation for alloys of two phase α?+?β structure.     

Deformation behavior of thin copper films on deformable substrates

The role of strain hardening for the deformation of thin Cu films was investigated quantitatively by conducting specialized tensile testing allowing the simultaneous characterization of the film stress and the dislocation density as a function of plastic strain. The stress–strain behavior was studied as a function of microstructural parameters of the films, such as film thickness (0.4–3.2 μm), grain size and texture. It was found that the stress–strain behavior can be divided into three regimes, i.e. elastic, plastic with strong strain hardening and plastic with weak hardening. The flow stresses and the hardening rate increase with decreasing film thickness and/or grain size, and are about two times higher in (111)-grains compared to the (100)-grains. These effects will be discussed in the light of existing models for plastic deformation of thin films or fine grained metals.     

Dynamic Recrystallization Kinetics and Microstructural Evolution for LZ50 Steel During Hot Deformation

The dynamic recrystallization (DRX) behavior of LZ50 steel was investigated using hot compression tests at a deformation temperature of 870-1170 °C and a strain rate of 0.05-3 s^?1. The effects of deformation temperature, strain, strain rate, and initial austenite grain size on the microstructural evolution during DRX were studied in detail. The austenite grain size of DRX was refined with increasing strain rate and decreasing temperature, whereas the initial grain size had no influence on DRX grain size. A model based on the Avrami equation was proposed to estimate the kinetics of the DRX under different deformation conditions. A DRX map, which was derived from the DRX kinetics, the recrystallized microstructure, and the flow stress analysis, can be used to identify optimal deformation conditions. The initiation of DRX was lower than Z _c (critical Zener-Hollomon parameter) and higher than ε_c (critical strain). The relationship between the DRX microstructure and the Z parameter was analyzed. Fine DRX grain sizes can be achieved with a moderate Z value, which can be used to identify suitable deformation parameters.     

Ultrafine-grained microstructures evolving during severe plastic deformation

The microstructures of ultrafine-grained nanostructured materials developed by severe plastic deformation are widely varied in their grain size and grain-size distribution; grain boundaries and their structures; lattice defects, especially dislocations; point defects; and impurities. All of these features can be influenced by the way severe plastic deformation is applied, and thereby have decisive effects on the physical and mechanical properties of the material. Probably, the most important factors determining microstructure are the imposed stress tensor, the degree and rate of strain, the temperature of deformation, the chemical composition of the deformed material, and the type of crystal lattice, showing that in order to develop specific properties, it is crucial to understand and optimize the microstructure.     

Effect of hot plastic deformation on microstructure and mechanical property of Mg-Mn-Ce magnesium alloy

Hot plastic deformation was conducted using a new solid die on a Mg-Mn-Ce magnesium alloy. The results of microstructural examination through OM and TEM show that the grain size is greatly refined from 45 μ to 1.1 μm with uniform distribution due to the occurrence of dynamic recrystallization. The grain refinement and high angle grain boundary formation improve the mechanical properties through tensile testing with the strain rate of 1.0× 10^-4 S^-1 at room temperature and Vickers microhardness testing. The maximum values of tensile strength, elongation and Vickers microhardness are increased to 256.37 MPa, 17.69% and HV57.60, which are 21.36%, 133.80% and 20.50% more than those of the as-received Mg-Mn-Ce magnesium alloy, respectively. The SEM morphologies of tensile fractured surface indicate that the density and size of ductile dimples rise with accumulative strain increasing. The mechanism of microstructural evolution and the relationship between microstructure and mechanical property of Mg-Mn-Ce magnesium alloy processed by this solid die were also analyzed.     

渗碳20CrMnTi温变形超细晶粒的形成机制

研究了渗碳 2 0CrMnTi钢温变形过程中微观组织演化规律 ,结果表明 :通过温变形 ,渗碳 2 0CrMnTi钢的晶粒由 16 μm～ 2 0 μm超细化到 2 μm～ 3μm ,甚至 1μm以下 ;晶界区域局部变形和晶界滑动控制晶粒的细化 ;而变形参数 ,尤其是应变速率控制晶界区域局部变形和晶界滑动     

DEVELOPMENT OF NEW GENERATION THERMOMECHANICAL SIMULATOR-MULTI-AXIS RESTRAINT COMPRESSION(MARC - STRAIN~(TM)) SYSTEM

1.BackgroundUltwhnefetrite(UFF)ndcrostructuredevelopmentinsteels,especiallyinstrUcturalsteels,hasincreasedintherecentyearsallovertheworldfromJapan{"'3,Ko..L3,4)Chi..[53tOAn.trali.L6),toCanada[7),tOEurope{"'j,etc..Japanese...~h..,[lo,ll,12)underaconsortiumofthegoVernment,nationalresearchinstitute,steelindustries,anduniversitieshavestartedsince1997a10yearcoOPerativeresearchprojectfordevelopingultrastrongandlonglifecycleSteelswithoutusingalloyingelements.Theyhavesucceededinnearlydoublingth…