12MnNb钢的ECAP变形及组织性能研究

室温下对12MnNb钢进行ECAP变形,累积等效应变达到4.通过光学显微镜、电子拉伸机等试验仪器设备,分析研究ECAP变形试样的显微组织特征及其演变规律,以及力学性能的变化规律.结果表明,C方式ECAP变形时,1道次的组织细化和强化效果最为显著,随后道次主要增加晶粒的取向差.经ECAP变形后,强度随变形道次的增加而增加,4道次后的抗拉强度达到895 MPa,并保持了较好的塑性,伸长率达到12.4%.     

等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

奥氏体不锈钢316L在ECAP过程中的组织演化及力学性能

对奥氏体不锈钢316L进行等效应变为1.02的6道次室温等通道挤压(ECAP)试验。结果表明,在ECAP挤压过程中316L发生了剪切滑移变形和孪生变形及晶粒碎化,经过4和6道次挤压后分别得到平均晶粒尺寸约80 nm和约61 nm的均匀分布的等轴晶粒。在1道次ECAP挤压后316L的抗拉强度由674 MPa增加到984 MPa, 规定塑性延伸强度则由594 MPa增加到922 MPa,维氏显微硬度由116.33 HV增加到328.31 HV,但是塑性下降严重,可以通过600 ℃后续退火处理进行改善。     

Mechanical properties at room temperature of an Al-Zn-Mg-Cu alloy processed by equal channel angular pressing

Tensile tests were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the mechanical properties at room temperature of overaged Al 7075-O alloy. ECAP processing was performed using route B_C at different temperatures and number of passes, i.e. different processing severity conditions. The maximum load (F_max) recorded during the last pass of each ECAP path considered in this study is a very good estimation of the processing severity. The mechanical properties were studied in terms of the balance between tensile strength and ductility. In the processed Al 7075-O alloy, the grain size was reduced down to ∼150 nm. Consequently, tensile testing at room temperature revealed a significant increase in the maximum tensile strength after ECAP with respect to the as start material. In the present study, as the processing severity increases with the number of ECAP passes or with the decrease in processing temperature, there is a consistent trend of increment in ultimate tensile strength with minor decrease in uniform plastic elongation respect to the first ECAP pass at room temperature. This is in contrast to the behaviour after more severe plastic deformation conditions, where an increase in strength together with a strong decrease in elongation would be expected.     

Damping behavior and mechanical properties of Mg-Cu-Mn alloy processed by equal channel angular pressing

Equal channel angular pressing(ECAP) was conducted at 250℃for 4 passes to the as-extruded Mg-3%Cu-1%Mn alloy with high strength and high damping capacity.After ECAP processing,the grain of as-extruded alloy is significantly refined to about 4μm,both yield strength and tensile strength of the as-extruded Mg-Cu-Mn alloy are decreased,but the ductility is improved.After the ECAP processing,the damping capacity of Mg-Cu-Mn alloy is decreased at room temperature,while is substantially increased at elevated te...     

等通道转角挤压变形Mg-1.5Mn-0.3Ce镁合金的组织、织构与力学性能

采用等通道转角挤压(ECAP)工艺以Bc路径在623K温度下对Mg-1.5Mn-0.3Ce镁合金进行变形,观察显微组织与织构,测试了力学性能。显微组织分析表明,镁合金经ECAP变形晶粒尺寸明显得到细化,经6道次ECAP变形后晶粒尺寸由原轧制态的约26.1μm细化至约1.2μm,且细小的第二相粒子Mg12Ce弥散分布于晶内及晶界处;同时经ECAP变形后,原始轧制织构随变形道次的增加不断减小,并开始转变为ECAP织构,织构强度不断增强;力学性能结果表明,由于晶粒细化作用大于织构软化作用,前3道次ECAP变形镁合金强度随道次的增加不断提高,与Hall?Petch关系相符,在第3道次时其抗拉强度和屈服强度达到最大值,分别为272.2和263.7MPa;在4道次之后形成较强的非基面织构,镁合金强度下降,与Hall?Petch呈相悖关系。断口分析表明,轧制态与ECAP变形镁合金的断裂方式都是沿晶断裂,由于6道次变形镁合金晶粒细化,存在更多的韧窝并获得16.8%最大室温伸长率。     

退火温度对ECAP变形高氮奥氏体不锈钢力学性能的影响

为研究等通道转角挤压(ECAP)+退火对高氮钢力学行为的影响,室温条件下对高氮钢进行1道次ECAP变形,之后分别在700、800、850、900 ℃下对不同N含量的试验钢进行退火处理,分析其力学性能变化规律。结果表明:高氮钢随着退火温度的升高,屈服强度和抗拉强度整体上呈下降的趋势,塑性随退火温度的升高而上升;不同状态高氮钢的抗拉强度与均匀延伸率之间都呈现了传统的强塑性之间的矛盾关系,随N含量的增加,呈现强度和均匀延伸率同步提高的趋势;高氮钢ECAP+低温退火后的拉伸断口呈现沿晶断裂形貌,随N含量的升高,沿晶断裂倾向更加明显。     

大塑性变形6013铝合金的时效特性与力学性能

利用X射线衍射分析（XRD）、差示扫描量热法（DSC）和拉伸试验,研究不同温度等通道转角挤压（ECAP）和常规静态时效处理后6013 Al-Mg-Si铝合金的微观结构、时效行为、析出动力学以及力学性能。XRD测得的ECAP变形后合金的平均晶粒尺寸在66-112 nm范围内,平均位错密度在1.20×10^14-1.70×10^14 m^-2范围内。DSC分析表明,由于ECAP后试样比常规时效处理试样拥有更细小的晶粒和更高的位错密度,因此,ECAP变形后合金的析出动力学更快。与未变形合金相比,ECAP后试样的屈服强度和抗拉强度都得到了显著提高。室温ECAP后试样的强度达到最大,其屈服强度是静态峰时效屈服强度的1.6倍。细晶强化、位错强化以及由于ECAP过程中的动态析出而产生的析出相强化,是ECAP合金获得高强度的几种主要强化机制。     

工业纯钛在120°模具中的多道次ECAP室温变形组织与性能

在室温,采用通道夹角为120°的变形模具对工业纯钛(Commemial Pure Titanium,CP-Ti)以Bc方式实施四道次ECAP(EqualChannel Angular Pressing)挤压变形,成功获得表面光滑无裂纹的变形试样.文中主要研究了工业纯钛在室温下进行ECAP多道次变形的组织结构演变,并测试了变形试样的力学性能.微观结构显示工业纯钛在室温下进行多道次ECAP变形时,只在前两道次产生了大量的变形孪晶,且随道次增加变形孪晶逐渐消失.最终获得的试样晶粒平均尺寸由最初的约28μm细化到约250 nm,试样断裂强度和显微硬度分别提高到773和2486 MPa,而试样仍保持较好的延伸率(可达16.8%).     

等通道转角挤压Al-10Mg-4Si合金的组织与性能研究

在250℃下以Bc路径对Al-10Mg-4Si合金进行4道次和8道次的等通道转角挤压,以求达到改善合金组织和提高合金力学性能的目的.扫描电子显微镜(SEM)和透射电子显微镜(TEM)对挤压前后的微观组织分析表明:铸态合金基体晶粒比较粗大,第二相Mg_2Si以粗大的汉字状或骨骼状分布于基体晶界处;经ECAP挤压后,基体晶粒得到细化,原粗大的汉字状Mg_2Si被碎化为短棒状或多边形状颗粒,并呈一定的弥散分布.室温拉伸测试结果表明:ECAP4道次挤压后,合金的抗拉强度和伸长率由铸态的166MPa、1.64%提高为322MPa、21.7%;ECAP8道次挤压后,合金的伸长率继续提高为24.7%.但抗拉强度下降到293MPa.     

Structure and mechanical behaviour of interstitial-free steel processed by equal-channel angular pressing

The influence of the number of passes in equal channel angular pressing (ECAP) following route B_C on microstructure and mechanical properties of interstitial-free steel was investigated by means of tensile tests and X-ray texture and diffraction profile analysis. A significant improvement of the mechanical properties was found with increasing the number of ECAP passes. After 8 passes, beside the high strength considerable ductility was observed and at 300 °C the ductility was the same as for the initial sample but with a two-times larger strength. The high strength measured at room temperature was only slightly reduced during annealing at temperatures up to 500 °C.     

Strong and ductile Al–Zn–Mg–Zr alloy obtained by equal angular pressing and subsequent aging

An ultrafine-grained Al–Zn–Mg–Zr alloy with superior mechanical performance was obtained by high passes of equal angular pressing (ECAP) and subsequent aging. After 8 ECAP passes and aging, the yield strength (YS) and ultimate tensile strength (UTS) of the solid-solutioned alloy are significantly improved from (98±10) and (226±7) MPa to (405±9) and (427±9) MPa, respectively. A large elongation is also maintained ((17.4±2.5)%). The microstructure features including grain refinement, morphology of precipitates, and dislocation density, were revealed with multiscale characterizations, including transmission electron microscopy, electron backscattered diffraction, and X-ray diffraction. After 8 passes of ECAP, the original coarse elongated grains are refined to a unique bimodal grain structure consisting of ultrafine equiaxed and lath-like grains. Additionally, the effects of ECAP and subsequent aging on the strengthening contribution of a variety of strengthening mechanisms, such as dislocation strengthening and precipitation strengthening, were discussed in detail.     

Evolution of the structure and mechanical properties of sheets of the Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy due to deformation accumulated upon rolling

The mechanical properties and microstructure of sheets of an Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy deformed and annealed after rolling have been investigated. The total accumulated true strain was ε_f = 3.33–5.63, and the true strain at room temperature and at 200 °C was ε_с = 0.25–2.3. The strength properties of the sheets (yield stress σ_0.2 = 495 MPa and ultimate tensile strength σ_u = 525 MPa) in the deformed state were greater than those after equal-channel angular pressing (ECAP) deformation. The mechanical properties of the deformed sheets after annealing depended on the size of subgrains inside the deformed grains bands with high-angle grain boundaries (HABs). With the increase in the annealing temperature from 150 to 300°С, the subgrain size increased from 80 to 300 nm. The relative elongation δ in the as-cast state and after annealing at 200–250°C (δ = 40–50%) was higher than that after annealing at 300–370°C (δ = 24–29%).     

基于Incoloy800H钨极氩弧焊接头组织及其性能分析

在2 mm厚800H合金钨极氩弧焊试验的基础上,研究焊接接头的微观组织和析出相成分,并分析焊接接头的力学性能和抗晶间腐蚀性能,观察拉伸断口和晶间腐蚀试样的形貌。结果表明:焊缝组织为柱状晶和等轴晶,热影响区晶粒明显长大,焊接接头中有少量的TiN和富Cr相(Fe,Cr)_(23)C_6析出相存在;母材、热影响区和焊缝的HV硬度分别为1730、1526和1590 MPa;室温抗拉强度和延伸率分别为565.0 MPa、31.8%,均超过ASME标准关于800H合金规定值(450.0 MPa和30.0%),拉伸断裂为韧性断裂;焊接接头高温(650℃)抗拉强度和延伸率分别为394.5 MPa、15.5%,其断口是混合型断口;较接头组织,母材腐蚀更为严重,表面晶界开裂并伴有少量且尺寸较小的腐蚀坑,基体中TiN缺陷处易引起点蚀。     

Predicting the critical pre-aging time in ECAP processing of age-hardenable aluminum alloys

Age-hardenable Al alloys may be successfully processed by equal channel angular pressing (ECAP) at room temperature, if the processing is carried out immediately after water quenching from the solution treatment temperature. It is important to estimate the critical time for any age-hardenable alloys, since after this time, ECAP processing will cause catastrophic cracking or segmentation at room temperature. In this study, ECAP processing was carried out on two age-hardenable Al alloys (2014 and 7075) at room temperature. The results demonstrated that the critical time could be predicted successfully by using tensile test curves related to different times after quenching. It is also shown that room temperature ECAP processing of these materials for more than a single pass is not possible and causes damage. However, a single pass will have significant effects on the strength of the material.     

不完全再结晶Fe40Mn10Cr25Ni25高熵合金的室温及低温力学性能

采用冷轧和退火热处理工艺制备了不完全再结晶结构的Fe₄₀Mn₁₀Cr₂₅Ni₂₅高熵合金,分析了合金的室温(298 K)及低温(77 K)拉伸时的力学性能。结果表明,合金具有优良的室温及低温力学性能,合金在低温拉伸时强度和塑性均得到了提高,其室温强度和断后伸长率分别为880 MPa和18%,低温强度和断后伸长率分别为1360 MPa和36%。合金在室温变形以位错滑移为主,低温变形以位错滑移和孪生为主。室温拉伸时,粗晶晶粒先于细晶晶粒变形,导致试样内部产生了应变梯度,提高了合金的加工硬化率,使合金在室温下具有良好的强塑性。低温拉伸时,粗晶晶粒中形成了大量的变形孪晶,从而提高了合金的低温力学性能。     

热轧温度对低密度Nb-Ti-Al-V-Zr-C合金性能的影响

对经挤压开坯的一种低密度铌合金分别在1000,1100,1200℃下进行了热轧,并利用光学显微镜、扫描电镜和场发射透射显微镜对试样的组织形貌进行了表征;对合金的室温和高温拉伸强度、延伸率进行了测试。结果表明:在1200和1100℃温度下热轧时,合金均具有优良的室温和高温性能,室温强度在600MPa以上,室温塑性大于12%,高温下的强度在80MPa以上,高温塑性大于30%,且随轧制温度升高,抗拉强度降低,塑性增大;而在1000℃下热轧时,室温和高温力学性能均较低,且室温拉伸断口表现为脆性断裂。     

等通道转角挤压Mg-3.52Sn-3.32Al合金的组织与力学性能

采用等通道转角挤压（ECAP）Bc路径对固溶态Mg-3.52Sn-3.32Al合金分别挤压1、4和8道次。利用光学显微镜、扫描电子显微镜、透射电子显微镜和X射线衍射仪分析合金的组织和相组成,并测试了其室温拉伸力学性能。结果表明,经ECAP挤压后,固溶态合金组织中析出大量细小的Mg2Sn相和极少量的Mg17Al12相。随挤压道次增加,合金的综合力学性能先提高后降低。经4道次挤压后,合金的综合拉伸力学性能相对较佳,抗拉强度、伸长率和硬度分别达到250 MPa、20.5%和61.3 HV9.8,较未ECAP时分别提高43.7%、105%和26.9%。经ECAP挤压的合金室温拉伸断口均呈韧性断裂。等通道转角挤压Mg-3.52Sn-3.32Al合金的力学性能受晶粒尺寸、析出相以及组织织构的共同影响。     

Continuous high strength aluminum bolt manufacturing by the spring-loaded ECAP system

Aluminum alloy 6061-T6 was used to produce an ultrafine-grained specimen by spring-loaded equal channel angular pressing (ECAP), which was continuously applied to a commercial multi-stage former at a production rate of 30 rpm at room temperature to manufacture high strength aluminum bolts. In order to increase the mechanical strength of the manufactured bolt, the bolt-forming process was introduced based on extrusion process in the present work. With the specimens processed by a single pass ECAP, underfilling at the bolt head and surface cracking at the flange of the produced bolts were observed due to the geometry of the ECAPed specimen and friction at the die interface, respectively. To remove these defects, modified route C for the second pass ECAP and aluminum fluoride coating with metal soap for the initial specimen were applied. Finally, the ultrafine-grained aluminum bolts were successfully manufactured in a continuous sequence. Both the ultimate tensile strength (UTS) and elongation to fracture of the manufactured bolts increased compared to the conventionally made bolts. According to the present investigation, an innovative approach utilizing the ECAP to develop high strength bolts without modifying conventional material is demonstrated.     

Effect of two-step severe plastic deformation on the microstructure and mechanical properties of commercial purity titanium

The present work investigates the microstructural and mechanical properties of commercial purity titanium after processing by a two-step severe plastic deformation procedure entailing warm equal channel angular pressing (ECAP) followed by cold rolling at liquid nitrogen temperature (LNT). The effect of subsequent cold rolling at room temperature is also investigated for comparison. After 10 passes of ECAP, an ultrafine-grained structure with average grain size of 213 nm was achieved. Subsequent cold rolling at LNT led to further refinement and decreased the grain size to 114 nm. Under these conditions, the material displayed high tensile strength of 995 MPa and high elongation to failure of 23%. These promising mechanical properties were interpreted in terms of characteristics of the microstructure: grain refinement, increased dislocation density, and a high fraction of high angle grain boundaries.