钛基复合材料激光选区熔化增材制造成形技术研究进展

钛基复合材料相对于钛合金具有更高的硬度、强度和耐磨性,可以进一步扩大钛合金在航空航天、海洋、医疗等领域的应用范围.现阶段钛基复合材料的制备方法可以分为两大类:第一,传统方法(例如熔炼和铸造).该方法存在着能耗大、成本高的问题.第二,激光选区熔化技术.该技术具有加工时间短、成形精度高、不需要制备模具的优点,但在加工过程中还存在着容易球化、开裂、降低成形件塑性等缺点.本文综述了当前国内外钛基复合材料的研究进展,包括增强体以及工艺参数调控对显微组织、成形质量及性能的影响,并结合现阶段研究现状对后续发展方向进行一定的讨论和展望.     

SiCp颗粒增强铝基复合材料塑性变形中过程的强化机制与断裂机制研究

综述了SiCp颗粒增强铝基复合材料的强化机制与断裂机制.分析了影响SiCp颗粒增强铝基复合材料强化、断裂的因素及其低塑性的原因,在此基础上提出改善其塑性的几点设想.     

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.     

颗粒增强铝基复合材料强化机制的研究现状评述

颗粒强化机制研究对于复合材料的设计及性能预测具有极其重要的意义,一直是复合材料学领域的研究热点。但相关的系统报道甚少,本文就颗粒增强铝基复合材料的强化机制从直接强化、间接强化与混合强化三个方面展开综述,并指出这些强化机制所存在的不足及其发展趋势。     

碳纳米管增强镁基复合材料制备及界面研究进展

在碳纳米管增强镁基(CNTs/Mg)复合材料制备过程中,碳纳米管间极易因范德华力团聚,且碳和镁浸润性差,因此,研究碳纳米管的均匀分散和良好的界面结合对CNTs/Mg复合材料的应用具有重要意义。本文综述了碳纳米管增强镁基(CNTs/Mg)复合材料的制备工艺进展和近年来国内外学者在改善界面结合与碳纳米管化学镀层方面的研究成果,总结了镁基复合材料的界面增强机制,并展望了CNTs/Mg复合材料未来的界面研究发展方向。     

颗粒增强铝基复合材料界面性能的研究

颗粒增强铝基复合材料具有较好的比刚度、比强度、抗疲劳、耐热耐磨和辐射屏蔽等优点,广泛应用于航空航天、军工、电子和汽车等领域。在这类材料中,基体-增强体界面的结构与性能对复合材料宏观性能影响显著。综述了颗粒增强铝基复合材料主要的制备方法和应用现状,特别聚焦于界面的结构及其对复合材料宏观性能的影响方式与机制,同时指出了复合材料制备过程中各种因素对材料界面性质的影响。最后,展望了颗粒增强铝基复合材料界面性能研究的发展前景,指出可采用先进的微纳米尺度的测量技术,结合显微结构表征的方法,系统地研究界面性能与结构之间的关系。     

SiCw＋B4Cp／MB15镁基复合材料力学性能与微观结构

对真空反压浸渍方法制备的挤压态ＳｉＣＷ＋Ｂ４ＣＰ／ＭＢ１５镁基复合材料及基体合金进行了一系列的力学性能测试，并用ＳＥＭ观察增强剂分布与断口形貌，用ＴＥＭ和ＥＤＳ方法对复合材料的界面结构进行分析。研究结果表明，上述复合材料同基体相比有更高的强度、弹性模量和比强度、比弹性模量。深浸蚀ＳＥＭ相分析表明均匀排布的晶须、颗粒起到很好的增强效果。复合材料的断口有晶须露头与韧窝存在，该复合材料具有一定的韧性；并在ＳｉＣ／ＭＢ１５界面上发现Ｚｎ析出相。     

镍基高温合金增材制造研究进展

镍基高温合金因其优异的高温强度及耐腐蚀、抗氧化性能而备受关注,被广泛应用于航空航天等领域。本文对增材制造镍基高温合金的制备方法、常见牌号以及合金的组织与性能进行了综述,总结了当前存在的问题,提出了未来值得探索的研究领域。金属增材制造技术制备的镍基高温合金具有良好性能,能实现复杂构件精密成形,且制备过程中材料浪费少,有望成为未来航空航天等领域中镍基高温合金构件的重要制备工艺。常见的镍基高温合金增材制造方法有粉末床熔化、定向能量沉积和电弧增材制造等,粉末床熔化被广泛用于制造高精度和复杂零件,但制造速度相对较慢,且设备和材料成本较高。定向能量沉积自由度和灵活性更高,可用于制备功能性梯度材料,但精度较低。电弧增材制造具有较低的设备成本和材料成本,适用于大型零件的快速制造,但其制备的合金表面粗糙度较差,需要进行额外的加工或后处理。在增材制造过程中被广泛研究的镍基高温合金包含IN625,Hastelloy X等固溶强化型和IN718,CM247LC,IN738LC等沉淀强化型高温合金。与传统的铸造和锻造方法相比,增材制造独特的逐层成型、快冷快热的制备过程带来了粗大的柱状晶粒组织和大量细小晶粒的独特...     

SiC颗粒增强Al基复合材料中有害界面反应的控制

对有害界面化学反应的控制，是当前SiC颗粒增强Al基复合材料研究中的主要问题之一，本文对近年来国内外研究工作者，通过添加Si元素及对SiC颗粒进行表面处理来控制SiC/Al之间有害界面反应的研究进展进行了评述。     

CuZr-based bulk metallic glass and glass matrix composites fabricated by selective laser melting

Monolithic bulk metallic glass and glass matrix composites with a relative density above 98 ％ were produced by processing Cu46Zr46Al8 (at.％) via selective laser melting (SLM).Their microstructures and mechanical properties were systematically examined.B2 CuZr nanocrystals (30-100 nm in diameter) are uniformly dispersed in the glassy matrix when SLM is conducted at an intermediate energy input.These B2 CuZr nanocrystals nucleate the oxygen-stabilized big cube phase during a remelting step.The presence of these nanocrystals increases the structural heterogeneity as indirectly revealed by mircrohardness and nanoindentation measurements.The corresponding maps in combination with calorimetric data indicate that the glassy phase is altered by the processing conditions.Despite the formation of crystals and a high overall free volume content,all additively manufactured samples fail at lower stress than the as-cast glass and without any plastic strain.The inherent brittleness is attributed to the presence of relatively large pores and the increased oxygen content after selective laser melting.     

选区激光熔化石墨烯增强金属基复合材料研究进展

石墨烯拥有不同于传统材料的特殊性能,如优异的结构力学性能以及导热性能,自被发现以来即获得广泛的关注,其中一个重要应用是作为增强相来增强金属基材料,从而获得高性能的结构和功能复合材料。近年来为了满足复合材料性能优化及结构精密复杂的需求,对其制造方法提出了更高的要求。选区激光熔化(Selective Laser Melting, SLM)作为增材制造技术的一种,避免了传统制造技术成本高、周期长、精度低等问题,可更加灵活地实现功能-结构-材料一体化。本文总结了SLM制备石墨烯及其增强金属基(铝、镍、钛、铁、铜)复合材料的应用研究与发展现状,讨论了石墨烯增强金属基复合材料所面临的主要问题,并展望了石墨烯增强金属基复合材料的应用与发展前景。     

Anisotropic corrosion resistance of TiC reinforced Ni-based composites fabricated by selective laser melting

Electrochemical measurements on three planes of TiC/Inconel 718 composites fabricated by selective laser melting (SLM) were performed to study the corrosion property. The results showed that the YZ-plane with dense and fine columnar structures possessed high microhardness and superior corrosion resistance in 3.5 wt% NaCl solution. For the XZ-plane, a decreased anti-corrosion property was observed owing to its inhomogeneous microstructures. While the XY-plane with large irregular pores and clustered ring-like structures was more susceptible to corrosion compared with the other two planes. Comparative analysis suggested that the anisotropic corrosion behaviors were significantly dependent on the surface defects, microstructure characteristics and added reinforcements.     

激光选区熔化纳米SiC/AlSi7Mg复合材料微观组织及力学性能EI北大核心CSCD

采用机械混合法制备纳米SiC/AlSi7Mg混合粉末,利用激光选区熔化技术(selective laser melting,SLM)成形纳米SiC颗粒增强AlSi7Mg复合材料,观察和分析试样的相对密度、物相和微观组织,并测试材料的硬度和拉伸性能。结果表明:SLM成形纳米SiC/AlSi7Mg复合材料试样的相对密度随着扫描速度和扫描间距的增大均呈现先增加后减少的趋势,相对密度最高可达99.75%;试样微观组织与SLM成形铝合金相似,Si相呈网状结构均匀嵌入α-Al基体中,且在Al基体中存在与Si分布相似的纳米SiC团聚物及Mg_(2)Si相;与AlSi7Mg相比,复合材料微观组织由柱状晶转化为等轴晶,且晶粒明显细化(平均晶粒尺寸为1.36μm);由于SiC的加入,产生细晶强化和固溶强化,试样的硬度和强度均明显提高,硬度最高达到137.3HV,抗拉强度达到448.3 MPa,屈服强度达到334.7 MPa,但伸长率下降至3.9%,断裂模式主要为脆性断裂。     

Thermal behavior and densification mechanism during selective laser melting of copper matrix composites: Simulation and experiments

Simulation of temperature distribution and densification process of selective laser melting (SLM) WC/Cu composite powder system has been performed, using a finite volume method (FVM). The transition from powder to solid, the surface tension induced by temperature gradient, and the movement of laser beam power with a Gaussian energy distribution are taken into account in the physical model. The effect of the applied linear energy density (LED) on the temperature distribution, melt pool dimensions, behaviors of gaseous bubbles and resultant densification activity has been investigated. It shows that the temperature distribution is asymmetric with respect to the laser beam scanning area. The center of the melt pool does not locate at the center of the laser beam but slightly shifts towards the side of the decreasing X-axis. The dimensions of the melt pool are in sizes of hundreds of micrometers and increase with the applied LED. For an optimized LED of 17.5 kJ/m, an enhanced efficiency of gas removal from the melt pool is realized, and the maximum relative density of laser processed powder reaches 96%. As the applied LED surpasses 20 kJ/m, Marangoni flow tends to retain the entrapped gas bubbles. The flow pattern has a tendency to deposit the gas bubbles at the melt pool bottom or to agglomerate gas bubbles by the rotating flow in the melt pool, resulting in a higher porosity in laser processed powder. The relative density and corresponding pore size and morphology are experimentally acquired, which are in a good agreement with the results predicted by simulation.     

Tailored reinforcement/matrix interface and thermodynamic mechanism during selective laser melting composites

The simulation of thermodynamic behaviours of reinforcing particles and reinforcement/matrix interface during selective laser melting of particle reinforced metal matrix composites was presented. The transition from powder to solid phase, the surface tension and the density change were taken into account. It showed that the operating temperature and the resultant turbulent intensity increased with increasing the applied linear energy density, giving rise to the high instability of the molten pool. The gravity and capillary forces play a crucial role in the rearrangement and the attendant distribution state of the reinforcing particles. The particle morphology and distribution state in the as processed parts were experimentally studied, which were in good agreement with the results predicted by simulation.     

选区激光熔化AlSi10Mg合金不同温度原位拉伸变形行为及断裂机理研究

为了提高选区激光熔化AlSi10Mg合金在航空航天领域的应用,基于自主研发的原位SEM高温拉伸台,本文对比分析了原位拉伸非校准样品的选区激光熔化AlSi10Mg合金在室温、200、300 ℃条件下的力学性能与显微组织动态演化,并总结了断裂机理。结果表明,选区激光熔化AlSi10Mg合金的显微结构由α-Al基体、共晶Si和大量的气孔组成,且共晶Si呈连续网格状均匀分布在α-Al基体上。随着温度的升高,选区激光熔化AlSi10Mg合金的强度降低。屈服强度从室温的207 MPa降低到300 ℃时的52 MPa,极限抗拉强度从室温的304 MPa降低到300 ℃时的71 MPa,延伸率则随温度的升高而增大,从室温的7.4%增大到300 ℃时的59.5%。室温拉伸过程中试样并未出现明显的颈缩现象,而是随着温度的升高,试样的颈缩现象逐渐明显,表明试样经历了更加充分的塑性变形, 并且随着温度的升高,试样的断裂位置越来越偏离标距段中心。通过对试样变形行为的研究发现,200 ℃时,变形主要集中在晶内,发生晶内滑移;而300 ℃时滑移主要集中在晶界,导致晶界滑移。由于试样表面及内部存在大量缺陷,因此,室温下选区激光熔化AlSi10Mg合金的断裂机理为熔池边界的组织突变结合孔洞连通造成的准解理断裂。随着温度的升高,由于初始孔洞边缘的应力集中产生新的孔洞形核,新形核的孔洞与相邻孔洞相连通,导致试样的最终断裂。     

碳纳米管对激光选区熔化成形Al基复合材料的影响

基于激光选区熔化（SLM）方式,通过改变扫描速度,制备不同碳纳米管（CNTs,质量分数分别为0、0.5wt%、1.0wt%、1.5wt%、2.0wt%）含量的CNTs/Al复合材料试件,探究不同CNTs含量与激光扫描速度对试件性能的影响。结果表明,CNTs含量小于1.0wt%时,分散效果较好,大部分CNTs以单根状态黏附于Al粉表面;含量大于1.0wt%时,CNTs团聚尺寸增大、数量增多。相同SLM成形工艺下,低CNTs含量的CNTs/Al复合材料试件内部孔隙较少,致密度较高;高CNTs含量的CNTs/Al复合材料试件内部孔隙逐渐增多,致密度降低。激光扫描速度为1 300 mm/s工艺下,随着CNTs质量分数的增加,CNTs/Al复合材料试件硬度呈先上升后下降趋势,在CNTs含量为1.0wt%显微硬度达到最高。CNTs/Al复合材料试件平均晶粒尺寸相对于铝合金试件更加细化,在CNTs含量大于1.0wt%时,尽管晶粒依然细化,但试件致密度降低造成显微硬度下降明显。     

Plastic deformation of a Zr-based bulk metallic glass fabricated by selective laser melting

Fully amorphous Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa and a reproducible plastic strain of about 0.5% were obtained for cylindrical SLM samples.The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass.This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation.Despite these heterogeneities,the shear bands are straight and form in the plane of maximum shear stress.Additive manufacturing,hence,might not only allow for producing large BMG samples with complex geometries but also for manipulating their deformation behaviour through tailoring porosity and structural heterogeneity.     

Microstructural evolution and defect formation in a powder metallurgy nickel-based superalloy processed by selective laser melting

In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.