双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。      

颗粒粒径对碳化钨/高强钢复合材料界面微观组织和元素扩散的影响

利用"冷压成型-真空烧结法"制备了碳化钨/高强钢复合材料。结合光学显微镜、扫描电镜、超高温激光共聚焦显微镜和显微硬度计等分析测试手段对不同碳化钨(WC)颗粒粒径下获得的复合材料以及界面的显微组织和硬度进行了分析。实验结果表明,WC粉末颗粒粒径越小,WC平均晶粒尺寸越小;同时,WC致密度越高,当WC粉末颗粒粒径为100 nm,致密度达到91.22%;WC粉末颗粒粒径越小,复合材料中WC一侧的硬度越高。当WC粉末颗粒粒径为100 nm,烧结温度为1 320℃时,WC最高硬度值达1 680HV_(0.1)左右;且在靠近结合界面处WC硬度较其他位置更高;芯部的高速钢材料随WC颗粒粒径的变化不大,都在500HV_(0.1)左右。当WC粉末颗粒粒径为200 nm时,碳化钨与高强钢在界面处形成了一定宽度的过渡层,复合材料的结合为冶金结合;高强钢基体中的铁元素扩散到接触的碳化钨组织中,产生了一定宽度的熔合层,复合材料界面结合相对较好。在过渡区域内,W、Fe和Co元素在界面处都发生了明显的扩散;随着碳化钨颗粒粒径的增大,元素扩散趋势减弱。当WC粉末颗粒粒径为500 nm时,在复合材料界面处Fe元素和W元素未发生明显扩散现象,只有Co元素发生了一定程度的扩散。     

颗粒增强金属基复合材料中界面附近位移场测量的探索

本文采用数字散斑相关法对高能超声法制备的颗粒增强金属基复合材料在拉伸变形过程中颗粒与基体的界面处的位移进行了测量与分析，。实验结果表明，界面处所发生的位移变化要大于颗粒和基体内部所发生的位移，说明在颗粒与基体合金的界面处存在着导致应变集中的缺陷，从而导致了颗粒增强金属基复合材料失效过程中常常出现颗粒与基体在界面处脱粘的损伤形式。     

不同粒度SiCP增强铜基复合材料拉伸性能及断裂机制的研究

以不同粒度SiCP和电解铜粉为原料,采用粉末冶金工艺制备了SiCP增强Cu基复合材料.研究了SiCP和基体铜粉粒度的变化对材料拉伸性能和断裂机制的影响.结果表明,在基体铜粉粒度为44μm时,10μm的SiCP增强复合材料的抗拉强度达到最大值,为265.7MPa,其断裂机制是以Cu-SiC界面处基体撕裂为主,而当SiCP粒度为2μm时,由于分散不均匀、团聚等原因使得材料强度降低.大粒度SiCP(＞10μm)增强复合材料由于界面面积有限和增强颗粒间距过大,使得增强效果有限,其断裂机制是以Cu-SiC界面脱粘和SiCP解理开裂为主.实验证实了在SiCP增强铜基复合材料中基体和增强颗粒粒度存在着最佳配比关系可使复合材料达到最佳增强效果.     

增强颗粒尺寸对B4C/Al-Zn-Mg-Cu复合材料微观组织及力学性能的影响

用真空热压法制备不同B₄C颗粒尺寸(7μm、14μm、20μm)的15%B₄C/Al-6.5Zn-2.8Mg-1.7Cu复合材料，研究了增强颗粒尺寸对其微观组织和力学性能的影响。结果表明，在这三种复合材料中B₄C颗粒均匀分布，B₄C-Al界面反应较为轻微，未见明显的界面反应产物。三种复合材料基体中沉淀相的尺寸基本相同(约为5.5 nm)。B₄C颗粒的尺寸对复合材料力学性能有较大的影响。B₄C颗粒尺寸为7μm的复合材料性能最佳，屈服强度为648 MPa，抗拉强度为713 MPa，延伸率为3.3%。随着颗粒尺寸的增大复合材料的强度和延伸率均降低。对三种复合材料的强化机制和断裂机制的分析结果表明：小尺寸B₄C颗粒增强的复合材料强度较高，颗粒在变形过程中不易断裂，因此其塑性较好。     

碳化硅增强铝基复合材料的力学性能和断裂机制

研究了碳化硅颗粒(SiCp)尺寸对用粉末冶金法制备体积分数为15%的SiCp/2009铝基复合材料力学性能和断裂机制的影响.结果表明,复合材料的强度随着SiCp尺寸的增大而减小,塑性则随着颗粒的增大而增大.当SiCp尺寸为1.5μm时,SiCp/2009A1复合材料的断裂主要以界面处撕裂和基体材料的开裂为主;当SiCp尺寸为20 μm时,复合材料的断裂主要以SiCp断裂为主;当SiCp尺寸处于两者之间时,SiCp/2009A1复合材料界面处撕裂和SiCp断裂的共同作用决定复合材料的断裂.     

界面过渡层对SiC/Al双连续相复合材料性能的影响

研究了界面过渡层对SiC/Al双连续相复合材料性能的影响.结果表明,界面过渡层降低了复合材料中的残余应力,改善了界面的结合,提高了复合材料的压缩性能.当界面过渡层中SiC的体积分数接近50%时,复合材料的压缩强度最高,塑性最好,但弹性模量较低.界面过渡层的存在改变了复合材料的弯曲断裂机制.SiC原始泡沫增强的复合材料在断裂时,增强体SiC泡沫先断裂,基体后破坏,断裂表面凹凸不平;含界面过渡层的复合材料断裂时,过渡层的外侧界面先被撕开,内侧界面结合良好,基体与增强体同时断裂,断口平整.     

WC/铁基表面复合材料的热疲劳裂纹形成过程

为了对高热疲劳性能的表面复合材料的设计提供理论依据 , 采用热震试验方法对通过真空实型铸渗(V2 EPC) 方法制备的 WC/铁基表面复合材料的热疲劳性能进行了研究 , 重点讨论了热疲劳裂纹的形成机制。研究结果表明 , 随着 WC颗粒体积分数的增加 , 表面复合材料的热疲劳性能有所改善 , 当 WC体积分数达到 52 %时 , 复合层表面在经过 10次热循环后能保持完好。热疲劳裂纹扩展机制研究表明 , 陶瓷 WC颗粒增强铁基表面复合材料的热疲劳裂纹的产生和扩展是由 WC和基体本身的热应力和二者界面交变循环应力共同交互作用的结果 , 可以通过选用高热导率的陶瓷颗粒作为增强体、 改善陶瓷颗粒本身的微观质量和采用与陶瓷颗粒热膨胀系数相接近的基体等方法提高复合材料的热疲劳性能。      

SiC颗粒增强铝合金基复合材料断裂与强化机理

对SiC颗粒增强铝合金基复合材料的室温拉伸断裂与强化机理进行了研究。结果表明:该类材料的断裂包括基体韧断、界面脱开和增强体颗粒断裂三种方式,均属于MNG模式;该类复合材料的强化效果取决于基体强度与界面强度的匹配关系,当基体的屈服强度达到某一临界值时,通过添加增强体颗粒来强化材料是非常困难的。      

YAl 2P / Mg -Li -Al复合材料动态拉伸断裂过程原位观察

通过 SEM中静载动态拉伸 , 原位观察和研究了搅拌铸造法制备的 YAl _2P/ Mg-Li-Al 基复合材料裂纹的萌生及扩展机制。结果表明 , 微裂纹萌生位置主要为复合材料的铸造缺陷处、 复合材料的基体中以及颗粒/基体界面处 , 并以在复合材料基体中萌生为主。微裂纹的扩展主要在基体和 YAl ₂颗粒/基体界面处进行。主裂纹的长大方向具有选择性 , 裂纹主要沿颗粒贫化区与颗粒富集区的交界处开裂 , 主裂纹扩展到一定程度后 , 试样全面失稳而迅速断裂。基体的断裂失效在 YAl 2P/ Mg2Li2Al复合材料拉伸断裂过程中起很大作用。     

A Multiscale Understanding of the Thermodynamic and Kinetic Mechanisms of Laser Additive Manufacturing

Selective laser melting (SLM) additive manufacturing (AM) technology has become an important option for the precise manufacturing of complex-shaped metallic parts with high performance. The SLM AM process involves complicated physicochemical phenomena, thermodynamic behavior, and phase transformation as a high-energy laser beam melts loose powder particles. This paper provides multiscale modeling and coordinated control for the SLM of metallic materials including an aluminum (Al)-based alloy (AlSi10Mg), a nickel (Ni)-based super-alloy (Inconel 718), and ceramic particle-reinforced Al-based and Ni-based composites. The migration and distribution mechanisms of aluminium nitride (AlN) particles in SLM-processed Al-based nanocomposites and the in situ formation of a gradient interface between the reinforcement and the matrix in SLM-processed tungsten carbide (WC)/Inconel 718 composites were studied in the microscale. The laser absorption and melting/densification behaviors of AlSi10Mg and Inconel 718 alloy powder were disclosed in the mesoscale. Finally, the stress development during line-by-line localized laser scanning and the parameter-dependent control methods for the deformation of SLM-processed composites were proposed in the macroscale. Multiscale numerical simulation and experimental verification methods are beneficial in monitoring the complicated powder-laser interaction, heat and mass transfer behavior, and microstructural and mechanical properties development during the SLM AM process.     

Investigation of the mechanical behaviour of magnesium composites

Stress/strain and fracture toughness behaviour of a commercial heat-treatable magnesium alloy reinforced with up to 20 volume% short alumina fibres was studied at room and elevated temperatures. Microscopic examination of the composites, which were prepared by conventional squeeze casting, revealed damage of a small portion of the fibres during the infiltration process. Sufficient chemical reaction between the matrix alloy and alumina reinforcement tends to produce a good bond at the fibre/matrix interface. The tensile-related properties of the composites increased at room and elevated temperatures with increasing content of the reinforcement. The ductility and fracture toughness of the composites decreased at room temperature with increasing reinforcement content. While failure strains of the composites were slightly improved at higher testing temperatures, the fracture toughness decreased significantly as the testing temperature exceeded 100°C. Examination of the fracture surfaces of specimens tested at room temperature showed a mixed mode fracture appearance with predominantly brittle cleavage fracture. The fracture surfaces of specimens tested at temperatures above 100°C revealed increasing fibre/matrix interface debonding and fibre pull-out with increasing testing temperature. Micromechanism examinations of crack initiation and propagation indicated that the fracture process of the composites may be matrix controlled.     

WCP/Fe-C 复合材料的界面反应和基体合金化研究

利用离心铸造成型碳化钨颗粒(WCP ) 增强Fe-C 基体合金的复合结构空心圆柱体, 采用宏观测量、X 射线衍射分析和扫描电镜(SEM ) 与能谱(EDS) 的微观分析, 对WCP/Fe-C 界面反应和基体合金化研究。结果表明, 在转速800～ 1200 r/m in离心铸造机上获得了外径167mm , 内径87mm , 高67mm 的空心圆柱体, 其表面层为16～ 20mm 大断面WCP/Fe-C 复合材料, 芯部为Fe-C 基体合金。铸造碳化钨颗粒(CTCP ) 的表面被高温Fe-C 基体合金熔融体部分溶解, 甚至解体; 原位( in2situ) 自生成细小短棒状WC 和W₂C 先共晶析出相; 远离CTCP , 分布游离的细小颗粒状和网状WC、W ₂C、Fe₃W ₃C₂Fe₄W ₂C、Cr₇C₃ 和Fe₃₂C 碳化物。由于CTC_P 部分溶解和扩散作用, 复合结构空心圆柱体的Fe-C合金基体被不同程度合金化。      

Microstructure of alumina reinforced with tungsten carbide

Carbides and nitrides reinforced alumina based ceramic composites are generally accepted as a competitive technological alternative to cemented carbide (WC-Co). The aim of this work was to investigate the effect of dispersed tungsten carbide (WC) on the microstructure and mechanical properties of alumina (Al₂O₃). Micron size alumina and tungsten carbide powders were mixed in a ball mill and uniaxially pressed at 1600°C under 20 MPa in an inert atmosphere. The hardness of WC reinforced alumina was 19 GPa and fracture toughness attained up to 7 MPa m^1/2. It was demonstrated by TEM analysis that coarse, micrometersized tungsten carbide grains were located at grain boundaries of the alumina matrix grains. Additionally, sub-micrometer tungsten carbide spheres were found inside the alumina particles. Crack deflection triggered by the tungsten carbide at the grain boundaries of the alumina matrix is supposed to increase fracture toughness whereas the presence of intergranular and intragranular hard tungsten carbide particles are responsible for the increase of the hardness values of the investigated composite materials.     

WC在WC/灰铸铁复合材料基体中的溶解

为了对WC/Fe复合材料的界面设计和控制提供理论指导, 论文分析了WC在WC/灰铸铁复合材料基体中的溶解热力学, 通过差热分析、 光学显微镜、 扫描电镜和X衍射等测试方法研究了WC与灰铸铁基体之间的界面, 对WC颗粒在基体中的溶解过程进行了探讨。研究结果表明: WC颗粒与HT300基体润湿良好, 当系统最高温度为1450℃时, WC颗粒的表面有明显被溶解的痕迹, WC颗粒在HT300基体溶液中发生明显溶解的开始温度约为1281℃; 当系统温度升高到某一温度时, WC发生分解反应(2WCW₂C＋C), 元素扩散将促进WC颗粒的溶解。      

WCCo/cBN composites produced by pulse plasma sintering method

WCCo/cBN composites have been considered as a next-generation material for use in cutting-tool edges, being characterized by an optimal combination of hardness and toughness. They can be used instead of WCCo/diamond composites in machining of iron-based materials. The major challenge in sintering these composites is to produce a well-bonded interface between the WCCo matrix and cBN particles. In this study, WCCo/cBN composites were fabricated by the pulse plasma sintering technique. The aim of this work is to obtain sintered parts with density near the theoretical value and with very good contact between the cBN particles and WCCo matrix. cBN/cemented carbide containing 30 vol.% of cBN particles was produced using a mixture of 6 and 12 wt.% Co-added WC powder, with WC grain size of 0.4 μm and cBN powder with grain size ranging from 4 to 40 μm. Scanning electron microscopy (SEM) observations of the microstructure and diffraction phase examinations did not show the presence of hBN phase. The specific heating conditions used to consolidate the material using high-current pulses hamper the transformation of cBN into hBN and ensure a strong bond between the cBN particles and the cemented carbide matrix. Fractures through the WCCo/cBN composite showed that only few cBN particles were torn out from the cemented carbide matrix, with most of them having been cleaved along the fracture plane. This provides evidence that the bond at the WCCo/cBN interface is mechanically strong. Composites sintered at temperature of 1,200 °C under pressure of 100 MPa for 5 min had density near the theoretical value. Increase of the sintering temperature to 1,200 °C resulted in an increase of the hardness to 2,330 HK1 for the WC6Co/cBN(1/3) composite and to 2,160 HK1 for the WC6Co/cBN(37/44) composite.     

Mechanical properties of aluminium-based particulate metal-matrix composites

A study has been made on a range of particulate-reinforced metal-matrix composites, all based on the aluminium alloy 7075, in underaged, peak aged and overaged conditions. Heat treatments were designed such that equivalent underaged and overaged matrix strengths were achieved. The reinforcement used was silicon carbide, in a range of particle sizes. All composites were produced by the co-spray deposition process. The tensile properties and fracture toughness of these materials were investigated at room temperature. Material reinforced with coarse particulate was observed to have poor yield strength, poor fracture stress and poor ductility compared with materials reinforced with finer particulate. Materials reinforced with the finest particulate had the greatest ductility. However, the coarse particulate-reinforced material exhibited reasonable toughness, similar to that of material containing the finest particles. A model to predict fracture toughness from tensile ductility and nominal interparticle spacing is proposed which offers an explanation for the observed experimental results.     

搅拌摩擦加工制备颗粒增强铝基复合材料的研究现状及展望

铝合金作为现代工程和高新技术领域发展的关键材料之一,具有密度小、比强度和比刚度高、耐蚀性好等特点。通过在铝基体中添加增强相颗粒,制备得到的颗粒增强铝基复合材料既有铝合金良好的强度、韧性、易成形性等特点,又有颗粒的高强、高模等优点,是近年来应用最广的一类金属基复合材料。 目前,制备铝基复合材料的方法主要有粉末冶金法、铸造以及超声波法等,但这些方法在制备过程中需要较高的温度,颗粒与金属基体容易发生不良的界面反应,从而影响界面结合效果,降低复合材料的性能。搅拌摩擦加工(FSP)作为一种新型的固相加工技术,可同时实现材料微观组织的细化、致密化和均匀化。目前,FSP直接法已在铝基复合材料制备方面取得应用,主要是将增强相颗粒通过打盲孔或开槽的方式预置在金属基体内再进行FSP,进而制备出高致密度的颗粒增强铝基复合材料。因为FSP过程的温度低,颗粒与铝基体不会发生界面反应,所以该方法也被用于制备具有形状记忆效应(SME)的铝基功能复合材料。 近年研究结果表明,颗粒相对FSP制备的铝基复合材料晶粒细化起到显著作用,这有助于提高复合材料的拉伸强度、显微硬度及疲劳强度等力学性能。随着颗粒含量的增加和颗粒尺寸的减小,复合材料的力学性能得以增强。再者,减小颗粒尺寸有利于改善颗粒与基体之间的结合。另外,通过优化搅拌头的结构、形状和尺寸,以及FSP工艺参数,已经可以实现加工后颗粒相在基体中的均匀分布。 鉴于搅拌摩擦加工(FSP)直接法在制备颗粒增强铝基复合材料方面所具备的短流程、高效能以及基体与增强相颗粒界面无杂质等优势,本文对目前FSP直接法制备颗粒增强铝基复合材料的最新研究现状进行了总结。主要综述了FSP制备颗粒增强铝基复合材料过程中颗粒的含量、类型及尺寸对复合材料组织与力学性能的影响,并对颗粒分布均匀性以及颗粒与铝基体的界面问题做了阐述。文章最后深入分析了当前研究中的不足之处并展望了未来的研究方向。     

Mechanical and tribological behaviour of tungsten carbide reinforced aluminum LM4 matrix composites

Aluminum-based metal matrix composites (AMCs) play a vital role for potential applications in aerospace and automotive industries. This paper explores the experimental analysis of a composite with aluminum LM4 alloy as the matrix and tungsten carbide (WC) as the reinforcement material. The composite specimens were fabricated by the stir casting process. The reinforced ratios of 5, 10 and 15?wt.% of WC particulates were stirred in molten aluminum LM4 alloy (AALM4). Once the composite is solidified, the specimens are prepared to the required ASTM dimensions and tested for various mechanical properties such as tensile strength, impact strength and hardness. Moreover, the tribological behavior of the composite was studied using the pin-on-disc wear test apparatus. X-ray diffraction (XRD) analysis was conducted to analyze the various elements present in the composites. Finally, the scanning electron microscope (SEM) analysis reveals the uniform distribution of WC particles in Aluminum LM4 alloy matrix. The improvement in mechanical properties – hardness, impact strength and tensile strength – was achieved for the increase in the addition of wt.% of WC particles in the LM4 matrix. The decrease in mass loss was observed for the composite containing 15?wt.% of WC during the wear test among the various composites tested.     

45钢表面Ni/WC复合熔覆层的形成机制

采用真空熔覆技术在45钢表面制备Ni +WC复合熔覆层并进行阶段性取样,研究镍基复合涂层的形成机制。结果表明：在45钢表面生成与基体冶金熔合、WC硬质颗粒分布均匀的Ni基复合熔覆层。整个熔覆层由4 mm厚的复合层、1 mm厚的过渡层、20 μm厚的扩散熔合区以及250 μm厚的扩散影响区组成。复合层区由WC和分解形成的富W复相碳化物包围在Ni颗粒周围组成;复合熔覆层的主要组成相有γ-Ni固溶体、Cr₇C₃、Ni_2.9Cr_0.7Fe_0.36、Cr₂₃C₆、Ni₃Fe、Ni₃Si、Ni₃B、W₂C以及C等;真空熔覆过程包括：镍基合金颗粒达到熔点(900℃)前升温阶段颗粒间微烧结颈的形成、升温达到熔点(1020℃)开始的镍基合金颗粒熔融以及保温阶段(1060℃)的熔合扩散与WC颗粒微区位置的调整。