Influence of pre-plastic deformation on thermal residual stress and yield st rength of SiCw/Al composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｅｔｏｔｈｅｄｉｆｆｅｒｅｎｃｅｏｆｃｏｅｆｆｉｃｉｅｎｔｓｏｆｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎｂｅｔｗｅｅｎｒｅｉｎｆｏｒｃｅｍｅｎｔａｎｄｔｈｅｍａｔｒｉｘｉｎＳｉＣｗ/Ａｌｃｏｍｐｏｓｉｔｅｓ,ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｉｓｎｏｔａｖｏｉｄｅｄｗｈｅｎｔｈｅｔｅｍｐｅｒａｔｕｒｅｉｓｃｈａｎｇｅｄ[1,2].Ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｃａｎｌａｒｇｅｌｙａｆｆｅｃｔｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｃｏｍｐｏｓｉｔｅｓ,ｓ…     

Effect of low temperature treatment on tensile yield strength of SiCw/6061 Al alloy composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎＳｉＣｗ/ 60 61ｃｏｍｐｏｓｉｔｅｓ,ｔｈｅｄｉｆｆｅｒｅｎｃｅｏｆｔｈｅｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎｃｏｅｆｆｉｃｉｅｎｔｂｅｔｗｅｅｎｒｅｉｎｆｏｒｃｅｍｅｎｔ(ＳｉＣｗ)ａｎｄｍａｔｒｉｘ(Ａｌａｌｌｏｙ)ｉｓｖｅｒｙｌａｒｇｅ.Ａｓａｃｏｎ ｓｅｑｕｅｎｃｅ,ｗｈｅｎｔｈｅｃｏｍｐｏｓｉｔｅｓｉｓｃｏｏｌｉｎｇｄｏｗｎｆｒｏｍｔｈｅｍａｎｕｆａｃｔｕｒｉｎｇｔｅｍｐｅｒａｔｕｒｅｔｏｒｏｏｍｔｅｍｐｅｒａｔｕｒｅ ,ａｌａｒｇｅｍｉｓｍａｔｃｈｔｅｎｓｉｌｅｓｔｒ…     

Elastic modulus of SiC_w/6061Al alloy composites as-squeeze-cast

1　ＩＮＴＲＯＤＵＣＴＩＯＮＣｏｍｐｏｓｉｔｅｏｆｓｉｌｉｃｏｎｃａｒｂｉｄｅｗｈｉｓｋｅｒｒｅｉｎｆｏｒｃｅｄａｌｕｍｉｎｕｍ (ＳｉＣｗ/Ａｌ)ａｓａｎｅｗｔｙｐｅｏｆｓｔｒｕｃｔｕｒａｌｍａ ｔｅｒｉａｌｎｏｔｏｎｌｙｈａｓｓｏｍｅａｄｖａｎｔａｇｅｓｓｕｃｈａｓｈｉｇｈｓｐｅ ｃｉｆｉｃｓｔｒｅｎｇｔｈ ,ｈｉｇｈｓｐｅｃｉｆｉｃｍｏｄｕｌｕｓ ,ｌｏｗｔｈｅｒｍａｌｃｏ ｅｆｆｉｃｉｅｎｔｏｆｅｘｐａｎｓｉｏｎａｎｄｓｏｏｎ[1,2 ] ,ｂｕｔａｌｓｏｃａｎｂｅｓｅｃｏｎｄａｒｉｌｙｓｈａｐｅｄｂｙｔｈ…     

SiC_w/Al复合材料的微观结构与性能

本文研究了17V.-％SiC_W/ZL109Al复合材料的微观结构和性能。透射电镜观察和能谱分析发现,在复合材料中Al扩散到SiC晶须内部,并且在晶须/基体界面处有位错存在,拉伸试验结果表明,在573和733K温度下热暴露和热循环都导致复合材料强度降低,在733K加热时间相同的条件下热暴露引起复合材料强度的降低比热循环引起强度的降低强烈。此外,SiC_W/Al复合材料还具有高的耐磨性,在所研究的晶须含量范围内(V_f=11-17％),晶须含量对复合材料的耐磨性几乎没有影响。     

低温循环过程中SiCw／6061Al复合材料残余应力的变化规律

研究了低温循环过程中压铸态ＳｉＣｗ／６０６１Ａｌ复合材料残余应力的变化零乱低温循环的降温阶段,复合材料基体经历错配拉伸塑性变形过程在升温阶段基体国卸载过程。经过一次低温循环后,残余应力有所降低。如果进行两次低循环自理只有当第二次循环下降温度低于第一次时,才能再次降低复合材料残余应力。     

Effects of crystal boundary gliding and dislocation on superplastic deformation of SiC_w/6061 Al composite

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｉｓａｎｅｗｋｉｎｄｏｆｍａｔｅｒｉａｌｄｅｖｅｌｏｐｅｄｉｎｒｅｃｅｎｔ 2 0ｔｏ 30 ｙｅａｒｓｃｏｍｐａｒｅｄｔｏｔｈｅｃｏｎｖｅｎｔｉｏｎａｌｍｅｔａｌｍａｔｅｒｉａｌｓ ,ｔｈｉｓｃｏｍｐｏｓｉｔｅｈａｓｍａｎｙｇｏｏｄｐｅｒｆｏｒｍａｎｃｅｓｏｎｏｎｅｈａｎｄ ;ｂｕｔｏｎｔｈｅｏｔｈｅｒｈａｎｄ,ｉｔｓａｃｔｕａｌａｐｐｌｉｃａｔｉｏｎｉｓｒｅｓｔｒａｉｎｅｄｄｕｅｔｏｉｔｓｐｏｏｒｐｌａｓｔｉｃｉｔｙｕｎｄｅｒｎｏｒｍａｌ…     

MICROSTRUCTURES AND PROPERTIES OF SiC_w/AL COMPOSITES

This paper presents an investigation on the microstructures and properties of the17v.-% SiCw/Al-12Si composites.TEM observations and EDAX analysis revealed that Aldiffuses into the SiC whiskers and that dislocations exist at the whisker/matrix interfaces.Tensile test results showed that the isothermal exposure and thermal cycle at both 573K and733 K caused the UTS reduction of the composites,and the reduction in UTS due to thermalexposure at 733 K was much more significant than that due to thermal cycle at the same tem-perature.The SiC_W/Al-12Si composites were also found to have exellent wear resistance,which does not seem to vary much with the volume content of whiskers in the ronge of 11—17%.     

C_f/SiC复合材料磨削表面的残余应力分析

应用X射线衍射法对C/SiC复合材料的磨削残余应力进行研究.结合抛光和热处理工艺,应用主应力之和的变化量确定磨削残余应力的分布.结果表明:SIC(422)晶面族比其它相和晶面更适用于复合材料残余应力的研究;熟塑性引入的残余拉应力作用于数微米的较浅表层深度内,但对磨削表面的残余应力起决定作用;冷塑性残余应力对应的作用深度较大;热塑性和冷塑性残余应力均可通过热处理方式得以消除.     

SiC_w/6061Al复合材料的组织与性能SCIEI

本文对SiC_w/6061Al复合材料的组织与性能进行了研究,结果表明,压铸法可以制备出高强度、高模量的各向同性复合材料,挤压使复合材料的强度由压铸态的582MPa提高到639MPa,并使材料变为各向异性,这可以由晶须的定向排列和基体的高密度位错得到解释。复合材料的抗高温性能要比基体高150℃,透射电镜观察还发现,层错是SiC晶须中常见的一种面缺陷。     

25SiC_w/LD2复合材料超塑变形过程中位错的分布规律

采用挤压铸造法制成复合材料并热挤压成板材 ,然后对其进行了超塑拉伸实验。当拉伸温度为5 70℃ ,应变速率为 2 .0× 10 -3s-1时获得了 2 80 %的延伸率 ,用TEM观察了超塑变形过程中位错的变化分布规律。结果表明 ,位错的密度及分布与变形温度及应变速率有一定关系。在最佳变形条件下 ,变形初期位错主要集中在晶界处分布 ,随着变形量的加大 ,位错向晶粒中间扩展 ,并发现有层错及孪晶出现 ,这对协调变形具有一定作用。     

Relaxation of residual stresses in 20%SiC_w/6061Al composite as-extruded at high temperature

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｌｕｍｉｎｕｍｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｒｅｉｎｆｏｒｃｅｄｗｉｔｈｓｉｌｉ ｃｏｎｃａｒｂｉｄｅｗｈｉｓｋｅｒ (ＳｉＣｗ/Ａｌ)ａｓａｎｅｗｔｙｐｅｏｆｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｎｏｔｏｎｌｙｈａｓｃｅｒｔａｉｎａｄｖａｎｔａｇｅｓｓｕｃｈａｓｈｉｇｈｓｐｅｃｉｆｉｃｓｔｒｅｎｇｔｈ ,ｈｉｇｈｓｐｅｃｉｆｉｃｍｏｄｕｌｕｓ ,ｌｏｗｃｏｅｆｆｉｃｉｅｎｔｏｆｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎ (ＣＴＥ)ａｎｄｓｏｏｎ ,ｂｕｔａｌｓｏｃａｎｂｅｓｅｃｏｎｄａｒｉ…     

屈服强度参数对10Ni5CrMoV钢焊接残余应力数值计算结果的影响

为了研究低合金高强钢在焊接过程中屈服强度参数变化对焊接数值计算结果的影响,测定了在稳态和冷却条件下10Ni5CrMoV钢在不同温度时的屈服强度和焊接接头的焊接残余应力,并采用有限元软件分别根据两种条件下所测屈服强度参数对10Ni5CrMoV钢焊接接头的焊接残余应力进行了数值计算.结果表明,冷却条件下不同温度的屈服强度测试值低于稳态条件下相应温度屈服强度测定值,根据冷却条件下测定的屈服强度曲线计算所得焊接残余应力分布与实测值具有更好的吻合度.     

高温屈服极限对高强钢焊接变形及残余应力影响的仿真研究

由于缺乏材料的高温数据,进行焊接仿真时所取的高温屈服极限通常有差异。采用双椭球热源模型,对某高强度结构钢的高温屈服极限设计了五种方案进行焊接仿真计算,研究了高温屈服极限对焊接变形和残余应力的影响规律。结果表明:高温屈服极限差异对焊接变形与焊接残余应力有不同的影响;高温屈服极限差异对变形影响较大,越靠近焊缝影响越明显;对残余应力影响较小,仅在近缝区的局部区域产生影响。焊接变形与残余应力均随高温屈服取值的增大而增大。     

Thermal residual stresses and stress distributions under tensile and compressive loadings of short fiber reinforced metal matrix composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｅｔｏｌａｒｇｅｒｄｉｆｆｅｒｅｎｃｅｉｎｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎｃｏ ｅｆｆｉｃｉｅｎｔｂｅｔｗｅｅｎｔｈｅｆｉｂｅｒａｎｄｔｈｅｍａｔｒｉｘａｎｄｓｐｅｃｉａｌｇｅｏｍｅｔｒｉｃａｌｓｈａｐｅｏｆｔｈｅｆｉｂｅｒ ,ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｅｓ (ＴＲＳ) ｇｅｎｅｒａｔｅｄｄｕｒｉｎｇｃｏｏｌｉｎｇｆｒｏｍｈｉｇｈ(ｐｒｏｃｅｓｓｉｎｇ)ｔｅｍｐｅｒａｔｕｒｅｔｏｒｏｏｍｔｅｍｐｅｒａｔｕｒｅｈａｖｅｉｍｐｏｒｔａｎｔｉｎｆｌｕｅｎｃｅ…     

Interfacial reaction in squeeze cast SiC_w/AZ91 composites with different binders

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｒｅｃｅｎｔｙｅａｒｓ,ｄｉｓｃｏｎｔｉｎｕｏｕｓｌｙｒｅｉｎｆｏｒｃｅｄｍａｇ ｎｅｓｉｕｍｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓａｒｅｏｆｇｒｅａｔｔｅｃｈｎｏｌｏｇｉｃａｌａｎｄｃｏｍｍｅｒｃｉａｌｉｎｔｅｒｅｓｔｓｆｏｒｕｓｅｉｎａｅｒｏｓｐａｃｅａｎｄａｕ ｔｏｍｏｔｉｖｅｉｎｄｕｓｔｒｉｅｓ.Ｔｈｉｓｉｓｄｕｅｔｏｔｈｅｉｒｌｏｗｄｅｎｓｉｔｙ ,ｈｉｇｈｓｐｅｃｉｆｉｃｓｔｒｅｎｇｔｈ ,ｈｉｇｈｓｐｅｃｉｆｉｃｓｔｉｆｆｎｅｓｓａｎｄｌｏｗｃｏｅｆｆｉｃｉｅｎｔ…     

电流脉冲对45碳钢试样位错密度和残余应力的影响

研究了电流脉冲对淬火45碳钢试样位错密度和表面残余应力的影响。根据XRD图谱,采用Modified Williamson-Hall(MWH)方法计算位错密度,进一步结合微观组织结构,分析了位错密度和残余应力的关系。结果表明,电流脉冲处理前后,位错密度由1.21×1015m-2变为0.80×1015m-2,表面残余应力σx由-250 MPa降低到-142 MPa,σy由-363 MPa降低到-172 MPa。与热处理相比,电流脉冲处理的试样位错密度和残余应力的降低率都比较大,表明电流脉冲除了产生热作用外,还产生了非热作用。位错密度和残余应力存在一定关系,符合Kocks-Mecking模型。电流脉冲处理过程中,位错激活运动,导致位错湮灭,位错密度降低,是残余应力降低的主要因素。     

降低冷轧取向硅钢残余应力和位错密度的磁-热耦合工艺

为了得到一种高效去除冷轧取向硅钢残余应力的工艺,制定了低温、低强度脉冲磁场的短时磁-热耦合处理试验方案,分别利用X射线残余应力仪和XRD测定了不同工艺处理前后取向硅钢的残余应力和位错密度。结果表明,采用低温、低强度脉冲磁场的短时磁-热耦合处理可以有效降低冷轧取向硅钢的残余应力和位错密度,当采用处理时间为3 min、处理温度为400 ℃、峰值电流为180 A的磁-热耦合工艺时,可取得最佳处理效果,残余应力降幅为55.5%,比单纯只施加低温热场或低强度脉冲磁场的处理效果优异。宏观残余应力的降低与位错密度具有紧密的联系,两者变化规律基本一致。短时、低温、低脉冲磁场强度磁-热耦合处理去除残余应力的微观机制是脉冲磁场和温度场耦合作用下进一步提高材料内部位错运动,实现了局部回复,达到位错密度和残余应力减小的目的。     

A numerical model to investigate the role of residual stresses on the mechanical behavior of Al/Al2O3 particulate composites

Research is presented about the mechanical behavior of a 6061 aluminum alloy reinforced with alumina particles. In particular, the role of thermal-induced residual stresses on the mechanical behavior of this composite is analyzed. Experimental tests were carried out to evaluate the mechanical characteristics of this type of material under static and fatigue loading. Fractographies on broken specimens evidenced the failure mechanisms under different load conditions. Also carried out were measurements using the x-ray diffractometric (XRD) technique to determine the residual stresses due to the thermal treatment both in the matrix and in the particles. A microscale finite-element model (FEM) of this material was developed to investigate the actual stress state caused by the thermal treatment and an applied load. A comparison of the numerical results and the experimental observations helped to explain the fracture modes under static and cyclic loading and to determine the role of the residual stresses under both monotone and cyclic loads. These results suggest some treatment to improve fatigue strength of the material.     

Effect of fiber distribution on residual thermal stress in titanium matrix composite

Residual thermal stresses (RTS) of SCS-6 SiC/Ti-24Al-11Nb composite were analyzed by using finite element method (FEM). Three models of fiber array in the composite and the effect of fiber distance on the RTS were discussed. In all the three models compressive stress was found in the radial direction and tensile stress in the tangential direction. It is pointed out that, in real composite system, hexagonal fiber geometry is superior because the distribution and the magnitude of the residual stress are similar to those in single fiber model. In square fiber geometry, it is easier to make the matrix crack due to the larger residual tangential stress. RTS becomes very large and changes violently when the fiber distance is less than 15μm or so, therefore too high fiber volume is apt to result in matrix crack.