SiCp增强2024铝基复合材料超塑性的研究

对搅拌铸造法制备的SiCp/2024Al复合材料超塑性的预处理、力学行为、微观结构及变形机制进行了研究,结果表明,合适的强烈塑性变形是改善复合材料组织进而提高超塑性的有效方法:经小挤压、热轧和冷轧后,在温度为823K、初始应变速率为 1.1×10-3 s-1的拉伸变形条件下,超塑延伸率为405%,超塑变形机制为晶粒的适度长大、动态连续再结晶和适当的微量液相共同协调的晶界滑动:液相不是该复合材料展现超塑性的必要条件。     

挤压铸造铝基复合材料的高应变速率超塑性

用挤压铸造、挤压比仅为１０∶１的挤压以及进一步的轧制成功地制备了具有高应变速率超塑性行为的βＳｉＣ晶须增强ＬＹ１２复合材料。该复合材料晶粒细小,约为２μｍ;在温度为８０３Ｋ和初始应变速率为１．１×１０－１ｓ－１时,延伸率达３５０％,应变速率敏感系数ｍ值约为０．３５;超塑性变形的主要机制是细小晶粒的晶界滑动,适当的微量液相有利于该复合材料的高应变速率超塑性。     

SUPERPLASTICITY OF A SiC_w/2024 Al COMPOSITE MADE BY PRESSURE INFILTRATION

The superplastic characteristics of the β-SiC whisker reinforced 2024 aluminum composite, fabricated by pressure infiltration and hot-rolling after extrusion, were investigated. The composite has a fine grain size of about 1μm, and exhibits a maximum tensile elongation of 370% in the initial strain rate of 3.3×10-3s-1 at 788K.The superplastic deformation mechanism of the composite is thought to be grain boundary (interface) sliding accommodated by grain boundary diffusion of aluminum atom and an appropriate amount of liquid phase.     

Study on high strain rate superplasticity of A 6061Al alloy composite reinforced with 30 Vol.% AlN particulate

An investigation on the superplastic behavior of 30 vol.% AlNp/6061Al composite prepared by powder metallurgy (PM) techniques was carried out. Superplastic tensile tests of the composite were performed at strain rates ranging from 10° to 10⁻³ s⁻¹ and at temperatures from 823 to 893 K. A fine-grained structure prior to superplastic testing was obtained by hot rolling after extrusion. The highest total elongation to failure of 438% was achieved at a temperature of 863 K and at an initial strain rate of 1.67×10⁻¹ s⁻¹ and the highest value of the strain rate sensitivity index (m) was 0.42 for the composite. Differential thermal analysis (DTA) was used to investigate the possibility of any partial melting in the vicinity of optimum superplastic temperatures. The formation of a liquid phase is attributed to the melting of the Al-Si eutectic phase at the surface of the AlN particulates at elevated temperatures, as determined by electron probe microanalysis (EPMA). The influence of the microstructure and the fracture behavior on the superplastic behavior of the composite was studied by transmission electronic microscopy (TEM) and scanning electron microscopy (SEM). A large number of matrix filaments were present at the fracture surfaces of the specimens when superplastic deformation of the composite was performed under the optimum superplastic test conditions. The presence of dislocations and fine recrystallized grains in the test specimens suggested that they play an important role in the high-strain-rate superplasticity for this composite.     

HIGH STRAIN RATE SUPERPLASTICITY IN A SiC_w/2024Al COMPOSITE MADE BY SQUEEZE CASTING

1.IntroductionHighStrainratesuperplasticity(HSRS)infineceramicwhiskerorparticulatereinforcedaluIninUIncompositesisveryattractipeforcommercialaPplicationsbecausetheHSRScompositesusuallyeallibitatotalelongation0f25M00%atahighstrainrate0f>10-2s-1Il-7]andoneofcurrentdrawbacksinsuperPlasticformingteclm0logyisaslowf0rIIilngratewhichistypically10-5-10-3s-1.Forindustrialfabricati0nofceramicwhiskerreinforcedaJumintuncomposites,squeezec88tingprocedureismorecost-ethetivethanpowdermetallurgy(P/M)m…     

Effect of partial melting on superplasticity ofAlNp/6061Al composite

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓａｒｅａｔｔｒａｃｔｉｖｅｆｏｒｍａｎｙｓｔｒｕｃｔｕｒａｌａｐｐｌｉｃａｔｉｏｎｓｂｅｃａｕｓｅｏｆｔｈｅｉｒｈｉｇｈｓｐｅｃｉｆｉｃｓｔｒｅｎｇｔｈａｎｄｔｈｅｉｒｍｏｄｕｌｕｓｏｆｅｌａｓｔｉｃｉｔｙ .Ｆｏｒｍｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓｃｏｎｔａｉｎｉｎｇｃｅｒａｍｉｃｒｅｉｎｆｏｒｃｅｍｅｎｔｓ ,ｓｔｒｅｓｓｃｏｎｃｅｎｔｒａｔｉｏｎｄｕｒｉｎｇｔｅｎｓｉｌｅｄｅｆｏｒｍａｔｉｏｎｏｃｃｕｒｓａｔｉｎｔｅ…     

HIGH STRAIN RATE SUPERPLASTICITY OF A AIN PARTICULATE REINFORCED 6061Al COMPOSITE

1. IntroductionHigh strain rate superplasticity (HSRS) in ceramic whisker or particulate reinforcedaluminum alloy composites is expected to offer an efficielltly near-net shape forming technique to the automobile, aerospace and even semiconductor industries, since the HSRScomposites usually exhibit a total elongation of 250%--600% at a high strain rate of about0.1--10s--ltl--171. The findings are significant not only for MMCs themselves but also forsuperplasticity itself since one of the m…     

SUPERPLASTICITY IN SiCw／ZK60 COMPOSITE

The superplastic deformation behavior of SiCw/ZK60 composite was investigated at temperatures ranging from 573K to 723K and at initial strain rates ranging from 8.3x10-4s-1 to 8.3x10-2s-1. A maximum elongation of 200% with a m-value of 0.35 was obtained at 613K and a initial strain rate of 1.67x 10-2s-1. The apparent activation energy (98kJ/mol) approximates that for grain boundary diffusion (92kJ/mol) in magnesium. It is proposed that the dominant mechanism of superplastic deformation in the present composite is grain boundary sliding accommodated by diffusional transport, besides, interfacial sliding plays an important role in the superplastic deformation.     

一种实现低合金超高强钢超塑变形的新思路

将Mn-Si-Cr系低合金高强钢在过冷奥氏体状态下进行适当预变形,水冷后的组织主要由铁素体、球状碳化物和马氏体组成。研究表明：700℃时的低速率小变形可使上述组织转变为（铁素体＋球状碳化物）复相组织,对超塑性变形有利;预变形后水冷的试样在700℃应变速率为10-4 s-1～2×10-4 s-1范围时的m值可达0.48,流变抗力为40～60 MPa,激活能约158 kJ/mol,属于晶界滑动变形机制,具有超塑性变形的特征。     

Superplastic deformation of SiCp/2024 Al composite fabricated by spray atomization and codeposition

In this paper, data are presented on the microstructure and superplastic deformation mechanics of an aluminum alloy, 2024, containing 10 vol% SiC particles. The material was fabricated by spray atomization and codeposition. The properties were studied after pretreatment by isothermal hot compression and isothermal hot forward extrusion (extrusion ratio 10.0). The experimental results show that the strain-rate sensitivity index (m-value) is 0.48 and the limit elongation (the elongation at fracture) is 345 % during superplastic uniaxial tension. The optimum conditions for superplastic behavior are 753 K of deformation temperature and 1.0 × 10⁻³ s⁻¹ of initial strain rate. Superplasticity may result from the fine grain size and the well-distributed SiC particles during superplastic uniaxial tension. Moreover, the simple and convenient pretreatment used in this paper is easily applied to industrial practice.     

氢对Ti-6Al-4V合金组织及超塑变形行为的影响

应用光学显微镜研究氢对Ti-6Al-4V显微组织的影响,并在温度800℃～860℃和应变速率10-3s-1的变形条件下进行超塑拉伸实验。结果表明,随着氢含量的增加,β相的比例提高,且由等轴组织转变为双态组织,随着氢含量的进一步增加,在α相中形成了氢化物;同时,适量的氢可以显著降低Ti-6Al-4V合金峰值应力,置氢0.32wt%H,其峰值流动应力降低了约55%;此外,适量置氢可以显著降低Ti-6Al-4V合金的超塑性变形温度,较原始合金最佳超塑变形温度可降低60℃～100℃,置氢0.11wt%H,在840℃获得了1190%的延伸率,较相同条件下的原始合金延伸率提高75%。文章研究结果可为超塑成形、超塑成形/扩散连接工艺及生产提供优化参考。     

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%...     

氮化硅陶瓷超塑性研究

以非晶氮化硅纳米陶瓷粉体为起始材料,以纳米氧化钇和氧化铝为添加剂液相烧结获得超塑性陶瓷块体材料,实现氮化硅陶瓷的超塑性拉伸和超塑性成形。氮化硅陶瓷的平均晶粒直径为280nm,在1550℃的较低温度,4.7×10-4/s的相对较高应变速率下,延伸率可达到110%,在成形速率0.2mm/min的条件下,可拉深成形出完好的球形和锥形零件。在室温断口上存在大量的细小的白色氮化硅晶粒;而高温断口上却几乎不存在这样的晶粒,这种不同可以用氮化硅陶瓷材料的超塑性变形机理来解释,也可以证明超塑性变形过程中晶界玻璃相的存在。     

Ti40阻燃合金粗晶超塑性变形行为及机理

借助OM、TEM研究了高温条件下Ti40阻燃合金的粗晶超塑性变形行为及机理。结果表明:在920℃下,应变速率为5×10-5～1×10-2s-1的Ti40合金表现出良好的超塑性行为,拉伸延伸率均超过250%,应变速率敏感指数m大于0.3。超塑变形后,粗大的等轴组织细化。TEM分析表明,在变形过程中,位错运动形成亚晶界,亚晶界通过吸收滑移位错形成小角度晶界甚至大角度晶界。Ti40合金的粗晶超塑性是由动态回复和再结晶共同作用的结果。     

Effects of Tool Rotation Rates on Superplastic Deformation Behavior of Friction Stir Processed Mg-Zn-Y-Zr AlloyEI北大核心CSCD

Compared to conventional Mg-Al and Mg-Zn system magnesium alloys, the Mg-Zn-Y-Zr heat-resistant alloy exhibits high thermal stability due to the addition of Y earth element, which is an ideal candidate for producing high strain rate superplasticity (HSRS, strain rate >= 1 x 10(-2) s(-1)). Recently, the HSRS of Mg-Zn-Y-Zr alloy was achieved by friction stir processing (FSP), because the FSP resulted in the generation of fine and equiaxed recrystallized grains and fine and homogeneous second phase particles. However, the study on superplastic deformation mechanism of FSP Mg-Zn-Y-Zr alloy at various parameters is limited relatively. Therefore, at the present work, six millimeters thick as-extruded Mg-Zn-Y-Zr plates were subjected to FSP at relatively wide heat input range of rotation rates of 800 r/min to 1600 r/min with a constant traverse speed of 100 mm/min, obtaining FSP samples consisting of homogeneous, fine and equiaxed dynamically recrystallized grains and fine and uniform Mg-Zn-Y ternary phase (W-phase) particles. With increasing rotation rate, within the FSP samples the W-phase particles were broken up and dispersed significantly and the recrystallized grains were refined slightly, while the fraction ratio of the high angle grain boundaries (grain boundaries misorientation angle >= 15 degrees) was increased obviously. Increasing rotation rate resulted in an increase in both optimum strain rate and superplastic elongation. For the FSP sample obtained at 1600 r/min, a maximum elongation of 1200% was achieved at a high-strain rate of 1x10(-2) s(-1) and 450 degrees C. Grain boundary sliding was identified to be the primary deformation mechanism in the FSP samples at various rotation rates by superplastic data analyses and surfacial morphology observations. Furthermore, the increase in rotation rate accelerated superplastic deformation kinetics remarkably. For the FSP sample at 1600 r/min, superplastic deformation kinetics is in good agreement with the prediction by the superplastic constitutive equation for fine-grained magnesium alloys governed by grain boundary sliding mechanism.     

Advances and applications in high strain rate superplasticity

High strain rate superplasticity (i.e., superplastic behavior at strain rates over 10^-2 s^-l) has been observed in many metallic materials such as aluminum alloys and their matrix composites and it is associated with an ultra-fine grained structure of less than about 3 pm. Its deformation mechanism appears to be different from that in conventional superplastic materials. A new model was considered from the viewpoint of the accommodation mechanism by an accommodation helper such as a liquid or glassy phase. The new mechanism was proposed in which superplasticity was critically controlled by the accommodation helper both to relax the stress concentration resulting from the sliding at grain boundaries and/or interfaces and to limit the build up of internal cavitation and subsequent failure. The possibility of the industrial applications was demonstrated for high-strain-rate superplasticity.     

High temperature tensile properties of hypereutectic Al-25Si based alloy

The high temperature tensile deformation of a hypereutectic Al-25Si based alloy fabricated by spray forming and subsequent hot extrusion was investigated. Tensile tests were conducted at various temperatures and strain rates. It was revealed that the ductility of the alloy is sensitive to both the test temperature and strain rate. At a given strain rate, the peak value of elongation was obtained at 500 °C. At 490 °C and above, the peak value of elongation was observed at a strain rate of 1.0 × 10^-2 s^-1, although the elongation increased with decreasing strain rate at 460 °C and below. The high elongation was exhibited when a high strain rate sensitivity index (m value) was attained and a liquid phase existed during deformation. The liquid phase appeared as a filament-like structure which is aligned with the tensile direction on the fracture surface of the tensile deformed specimen. A higher elongation (>35%) was obtained when the volume fraction of the liquid phase was 0.7%-1.7%. The maximum elongation of 75% was achieved when the volume fraction of the liquid phase was about 1%. The transition of the activation energy was observed at 430 °C when incipient melting occurred.     

SUPERPLASTICITY OF A WATER-QUENCHED AND TEMPERED 40Cr STEEL

1.IntroductionSuperplasticity possesses many good characteristics such as high elongation, low flow stress and high atom diffusion ability, which make it show good application in metal forming and diffusion bonding of complex shape structure. Up to now, the superplasticity of steel has been more investigated, however the pretreatment in order to obtain fine grain and then superplasticity was often carried out by circular quenchingof typically 3 times and subsequent high-temperature tempering, …     

Effect of current pulses on fracture morphology in superplastic deformation of 2091 Al Li alloy

１　ＩＮＴＲＯＤＵＣＴＩＯＮＧｅｎｅｒａｌｌｙ［１～４］，ｆｒａｃｔｕｒｅｉｎｓｕｐｅｒｐｌａｓｔｉｃｄｅｆｏｒｍａｔｉｏｎｉｓｉｎｔｅｒｇｒａｎｕｌａｒ．Ｂｕｔａｔａｃｅｒｔａｉｎｃｏｎｄｉｔｉｏｎ，ｉｔｃａｎｅｘｈｉｂｉｔａｌｏｃａｌｉｎｔｅｒｉｏｒｆｒａｃｔｕｒｅ．Ｒｅｆ．５ｒｅａｌｉｚｅｄｔｈａｔｓｕｃｈａｐａｒｔｉｃｕｌａｒｆｒａｃｔｕｒｅｗａｓｃｒｅａｔｅｄｂｙａｈｉｇｈｌｏｃａｌｓｔｒｅｓｓｃａｕｓｅｄｂｙｔｈｅｒｏｔａｔｉｏｎａｎｄｒｅａｒｒａｎｇｅｍｅｎｔｏｆｔｈｅｇｒａ…     

变形温度对碳化硅颗粒增强铝基复合材料超塑变形的影响

本文总结了变形温度对碳化硅增强铝基复合材料超塑性的影响规律。探讨了碳化硅颗粒对超塑变形的影响。讨论了碳化硅与铝基体之间的界面液相对超塑变形的影响。