高压扭转圈数对碳化硅颗粒铝基复合材料组织和性能的影响

采用高压扭转(high-pressure torsion,HPT)工艺,成功将8.75%体积分数SiC颗粒与Al的混合粉末制成金属基复合材料,并用金相显微镜、显微维氏硬度计、万能材料试验机和扫描电镜等,分析了扭转圈数对SiCp/Al复合材料的显微组织、显微硬度、拉伸性能和拉伸断口形貌的影响。结果显示,扭转圈数从0.5圈增加到4圈,基体的变形抗力降低,SiC颗粒在剪应力的作用下易于与基体协调变形,SiC颗粒分布均匀化程度显著提高;随着扭转圈数增加,试样所受到的剪切作用增大,极易引起位错的运动和增殖,基体晶粒得到细化,单位体积内的晶界增多,使试样显微硬度得到提高;扭转圈数越多,拉伸断口韧窝数量明显增多,且尺寸变小。     

高压扭转压力对SiC_p-Al复合材料组织性能的影响

采用高压扭转工艺将SiC和Al的混合粉末直接制备金属基复合材料。用金相显微镜、显微维氏硬度计、万能试验机和扫描电镜分析压力对SiCp-Al复合材料的显微组织和力学性能的影响。结果表明:压力越高,对SiCp-Al复合材料粉末成形的应变积累越有利;压力越高,扭转前粉末的致密程度越高,对SiCp-Al复合材料粉末成形的应变积累越有利,SiC颗粒在Al基体内的分布越均匀,显微硬度有所提高,但增幅不大;当压力从0.5 GPa增大至0.62 GPa,材料的屈服强度增加32.6%,但抗拉强度和伸长率均分别减小4%和25.5%。拉伸断口以大小不一的脱粘韧窝为主要特征。     

HPT法对SiCp/Al复合材料颗粒断裂的影响

采用高压扭转(HPT)法将SiC颗粒与纯Al粉的混合物固结成金属基复合材料。观察试样的显微组织,并对颗粒的数目、粒径及百分比进行测量,研究HPT法对SiCp/Al复合材料颗粒断裂的影响。结果表明,随着扭转半径增大,颗粒断裂现象严重,颗粒棱角钝化更加明显,颗粒数目增加,粒径减小;随着SiC颗粒体积分数的增加,这种趋势会强化;颗粒断裂现象是高压扭转法制备颗粒增强金属基复合材料的固有属性。     

SiC_p/Cu梯度复合材料热疲劳性能研究

采用粉末冶金方法制备了4种SiC颗粒呈渐变分布的梯度复合材料,应用扫描电子显微镜、X射线衍射仪、自动显微硬度计等,研究了梯度复合材料的显微组织、硬度分布和热疲劳性能。结果表明,SiCp/Cu梯度复合材料基体连续,梯度层过渡均匀,显微组织及硬度呈梯度分布;梯度复合材料的SiC颗粒渐变过渡越均匀,梯度复合材料抗热疲劳性能越好。     

脉冲磁场对SiC_P/AZ91D复合材料凝固组织的影响

研究了不同的脉冲电压、频率及模具预热温度对SiCP/AZ91D复合材料凝固组织的影响。结果表明,通过控制脉冲磁场参数和模具预热温度,可以有效改变SiC颗粒在合金凝固组织中的分布;在0~200V范围内,随着脉冲电压的增加,SiC颗粒逐渐分散均匀,但是当电压升高到250V时,SiC颗粒有团聚的趋势;在0~5Hz范围内,随着脉冲频率的增加,SiC颗粒分布逐渐均匀;在室温到600℃范围内,在磁场处理条件下,随着模具温度的升高,SiC颗粒分布逐渐均匀。     

碳化硅颗粒增强铜基复合材料的组织与性能分析

以添加0-20%体积分数的SiC颗粒增强铜基复合材料为研究对象,利用金相显微镜、扫描电镜、显微硬度和腐蚀试验等测试技术及实验手段,利用宏微观结合的方法进行组织与性能分析。结果表明,SiC颗粒随添加量的增加而明显增多且变密集,但总体分布较均匀,和基体结合较好。试样的显微硬度从21.1HV30逐渐增加到100.1 HV30。但随SiC颗粒的增加,材料密度下降,多孔率增加,导致抗腐蚀能力有所降低。     

多次搅拌下SiC颗粒增强铝基复合层组织与性能

采用搅拌摩擦加工制备SiC颗粒增强铝基复合材料,研究搅拌次数对复合层晶粒尺寸、硬度、拉伸及磨损性能的影响。结果表明,搅拌加工时添加SiC颗粒可提高复合层的硬度、耐磨性,但会降低其强度。随着搅拌次数的增加,复合材料硬度得到提高,添加SiC颗粒的试样经4道次搅拌后搅拌区平均硬度130 HV,而未添加颗粒时为118 HV。添加颗粒试样搅拌4次后,抗拉强度比搅拌1次试样强度明显提高,可达360.6 MPa,可达铝合金母材的68.5%。添加颗粒能够提高复合层的耐磨性,未添加颗粒时复合层摩擦系数为0.6,相比添加颗粒时仅为0.5。随着搅拌次数的增加,搅拌区晶粒细化程度得以提高,SiC颗粒分布更加均匀。     

Ni-SiC复合镀层组织和性能的研究

在A3钢板上制备了含有微米和纳米 SiC 的两种镍基复合镀层, 利用扫描电镜观察镀层表面显微组织, 利用X射线能谱分析SiC的分布情况, 通过纳米显微力学探针测量镀层微区硬度. 结果表明 : SiC 颗粒在镀层中分布均匀; SiC 颗粒附近复合镀层的硬度是纯镍镀层的 3 倍, 微米 SiC 复合镀层的弹性模量比纯镍镀层提高了近 5 倍, 而纳米 SiC 复合镀层则提高了 15 倍以上, 但随着远离 SiC 镀层硬度和弹性模量都有明显下降; SiC 颗粒的加入能够有效阻止镀层表面发生变形, 纳米 SiC 的作用更明显.     

电磁离心铸造B4C和SiC增强铝基复合材料的研究

研究了电磁离心铸造B4C颗粒和SiC颗粒同时增强Al基复合材料在不同励磁电压下两种颗粒的分布,以及颗粒分布对复合材料硬度的影响。试验结果表明,在电磁离心铸造过程中施加0V励磁电压时,在试样截面上B4C颗粒和SiC颗粒分别分布在内外两侧,施加50V励磁电压时,B4C趋于向外层均匀化分布;施加100V励磁电压时SiC趋于向内层均匀化分布。颗粒的分布决定了硬度值的分布变化。     

增强相含量对SiC_P/2024复合材料显微组织和力学性能的影响

采用热等静压的方法制备了不同比例SiC颗粒增强相增强铝基复合材料,研究了SiC质量分数在15wt%～20wt%条件下,增强相含量对SiC_P/2024复合材料微观组织、拉伸性能及硬度的影响。结果表明:SiC颗粒在铝基体中呈骨架连续分布,经固溶热处理和自然时效后,晶粒尺寸增大,整体均匀化,界面结合状态良好,SiC_P/2024复合材料的拉伸强度有明显的提高;当SiC质量分数在15wt%～20wt%时,随着增强相含量的增加,SiC_P/2024复合材料抗拉强度和硬度变化不大,但会提高材料的屈服强度。相比未添加SiC颗粒的铝基体,SiC颗粒作为硬质相加入到铝基体后,在界面结合状态良好的状态下,对材料的力学性能具有良好的改善作用。     

The evolution of homogeneity in processing by high-pressure torsion

Disks of high-purity aluminum were processed by high-pressure torsion (HPT) at room temperature under different conditions of imposed pressure and numbers of turns. Measurements were taken of the microhardness values both along diameters in each disk and following a rectilinear grid pattern to give color-coded maps of the hardness distributions. The results show the hardness increases by a factor of ∼2 in the first turn of HPT but the microhardness distribution is inhomogeneous because higher values of hardness are recorded in the central regions of the disks. This central region of inhomogeneity decreases with increasing numbers of turns so that the hardness distribution becomes essentially homogeneous after five turns. The results are different from earlier reports in HPT where the central regions of the disks have a lower hardness. The results are interpreted using a model in which the degree of hardness depends upon the rate of recovery in the material.     

快速凝固Al-In偏晶合金的显微结构

采用单辊法快速凝固工艺制备均质的Ａｌ－Ｉｎ偏晶合金,并对所获得的快速凝固组织和形貌进行了观察和研究。结果表明,细小的Ｉｎ颗料均匀分布在Ａｌ基体中：在甩带厚度方向上,随着与激冷面距离的增大,Ｉｎ颗粒尺寸逐渐增大;在同一辊速条件下（同一冷却速率）,随着Ｉｎ含量的增加,Ｉｎ颗粒的平均尺寸也不断增大;同一成分条件下,随着辊速的升高,Ｉｎ颗粒的平均尺寸不断减少;单辊法快速凝固过程中第二相液滴通过Ｂｒｏｗｎｉ     

TiC颗粒增强钢基表面复合材料的组织均匀性

为了优化自生TiC颗粒增强钢基表面复合材料的工艺参数,利用真空实型铸渗方法制备了自生TiC颗粒增强钢基表面复合材料,重点研究了自生TiC颗粒增强钢基表面复合材料的组织均匀性。结果表明,从基材和复合层间的界面到复合层表面,TiC颗粒尺寸逐渐增大,圆整度逐渐变差,其中Ti-C-20wt%Fe体系复合层中TiC颗粒的尺寸增长量(由1μm增长到2～3μm)明显小于Ti-C体系(由1～2μm增长到约10μm)。与Ti-C体系相比,Ti-C-20wt%Fe体系制备得到的复合层中元素分布、硬度和TiC颗粒的体积分数较均匀,在复合层相同位置上TiC颗粒较小,圆整度较好。     

INVESTIGATION ON THE DENSITY UNIFORMITY OF PRESSED PARTS BY LOW-VOLTAGE EI,RCTROMAGNETIC COMPACTION

Powder metallurgy is an efficient approach to fabricate varieties of high performance structure materials, function materials and special materials working under limited conditions. Research and development of new efficient technology to form high-density,high-performance and net shape parts is a key to widen application and development of powder materials. Recently, the low-voltage electromagnetic compaction (EMC) has been used by present authors to compacted copper, tin, aluminum powders and the products with 99% relative density have been acquired. In this work, the research has been extended to investigation on the density uniformity of pressed parts. The analysis results show that the density of the part compacted by low-voltage EMC decreases gradually in press direction as static compaction. But it is higher and more homogeneous. The densit3““ of the top part increases gradually from the center to the outer, which is just reversal of the bottom part. In some extent, the higher the discharging voltage is, the higher the densiO‘ is and the more homogeneous the distribution is. In addition, repetitive compaction can improve the density of powder parts and the distribution uniformity.     

INVESTIGATION ON THE DENSITY UNIFORMITY OF PRESSED PARTS BY LOW-VOLTAGE ELECTROMAGNETIC COMPACTION

1.IntroductionElectromagnetic compaction is a kind of high-energy and high-speed forming method. Magnetic forces have been used for more than two decades in powder compaction[1,2]. Powder Electromagnetic compaction refers to a new efficient forming technology, which uses the strong pulse electromagnetic power to compact powder to pressed density. The corresponding principle is as follows: by dint of magnetism pulse equipments, capacitor groups discharge electricity to generate the pulse m…     

Characterization of microstructure and local deformation in 316NG weld heat-affected zone and stress corrosion cracking in high temperature water

Microstructure and local deformation in 316NG weld heat-affected zones were measured by electron-back scattering diffraction and hardness measurements. With increasing the distance from the fusion line, kernel average misorientation decreases and the fraction of Σ3 boundaries increases. Stress corrosion cracking growth rates in high temperature water were measured at different locations in the heat-affected zones that correspond to different levels of strain-hardening represented by kernel average misorientation and hardness distribution. Intergranular cracking along random boundaries as well as extensive intergranular crack branching is observed in the heat-affected zone near the weld fusion line.     

Improved corrosion resistance through microstructural modifications induced by codepositing SiC-particles with electrolytic nickel

Micron and submicron-sized SiC-particles (5 and 0.3 μm respectively) were codeposited with nickel from a Watts electrolyte. The Ni-SiC composite coatings showed a better corrosion resistance in a 0.6 M NaCl solution than nickel electrodeposited under the same conditions. The corrosion rate of Ni-SiC decreases by two orders of magnitude with respect to pure Ni coatings. This improved corrosion resistance is quite independent of the size and amount of embedded particles, except for the smallest SiC-particles investigated. In that case, the pitting corrosion potential shifts to more noble values indicating a notable reduction of the localized corrosion susceptibility. This improved corrosion resistance of Ni-SiC coatings containing submicrometric SiC-particles is linked to a change in grain morphology and texture of the coatings. That morphology evolves from columnar grains to small and equiaxed grains.     

Characterization of Properties in Friction Welded Stainless Steel and Copper Materials

The aim of this study is to investigate the metallurgical and mechanical properties of friction welded stainless steel-copper joints. One of the manufacturing methods used to produce parts made from different materials is the friction welding method. Application of classical welding techniques to such materials is difficult because of they have different thermal properties. Stainless steel-copper joints are inevitable for certain applications due to unique performances such as higher electric conductivity, heat conductivity, corrosion resistance, and mechanical properties. In the present study, austenitic stainless steel and copper parts were joined by friction welding. Tensile, fatigue, and notch-impact tests were applied to friction welded specimens, and the results were compared with those for the original materials. Microstructure, energy dispersive x-ray, and x-ray diffraction (XRD) analysis and hardness variations were conducted on the joints. Results showed that various intermetallic phases such as FeCu₄ and Cu₂NiZn occurred at the interface. It was found from the microstructure and XRD analysis that intermetallic phases formed in the interface which further caused a decrease in the strength of the joints. However, hardness of the copper increased slightly, whereas the hardness of steel decreases slightly on the horizontal distance from the center.     

45钢电子束相变硬化温度场数值模拟与实验验证

建立了移动电子束高斯热源作用下的三维相变硬化过程中温度场的数学模型,分析过程中考虑了热源分布、热物性参数、热辐射等因素对温度场的影响,得到了电子束扫描相变硬化温度场的分布规律和硬化层的形态,并进行了实验验证;探讨了电子束工艺参数对硬化区深度和宽度的影响。结果表明:移动电子束高斯热源作用下的温度分布等值线呈勺状,表面最高温度滞后于束流中心,且处理后硬化层横截面呈月牙状;在固态相变条件下,硬化层的宽度和深度随着扫描功率的增加呈非线性增加,随着扫描速度的增加呈非线性减小。