喷射沉积SiC_P/Al复合材料的塑性变形致密化与冶金缺陷消除研究进展

喷射沉积SiC_P/Al基复合材料具有优异的力学性能,但因孔隙、沉积颗粒边界、沉积颗粒表面的氧化皮等冶金缺陷无法完全消除而使其应用受限,消除冶金缺陷和改进致密化技术对于提高喷射沉积铝基复合材料的性能和扩大其应用尤为重要。本文论述了喷射沉积颗粒增强铝基复合材料的致密化技术,着重介绍了楔形压制工艺、陶粒轧制、旋球同步致密化等新型致密化技术;展望了喷射沉积铝基复合材料的发展趋势,认为热等静压、陶粒轧制的剪切作用小,不能完全消除孔洞和沉积颗粒边界等缺陷;提出颗粒增强铝基复合材料的喷射沉积制备与致密化同步进行有利于减少晶粒与弥散粒子的粗化,提高复合材料的力学性能和成形性能。采用旋球同步致密减少坯料孔隙,降低坯料沉积坯中的氧含量,再通过楔形压制实现沉积颗粒间的完全冶金结合。     

搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

Mechanical properties of hot pressed SiCp and B4Cp/Alumix 123 composites alloyed with minor Zr

In the present study, effect of Zr addition on the microstructure and wear behavior of aluminum alloy composites (AMCs) reinforced with B4Cp and SiCp particles fabricated via hot pressing were investigated. The samples for the study composed of unreinforced aluminum alloy (Alumix 123) and the composites reinforced with 10% B4Cp and % SiCp were prepared by hot isostatic pressing (HIP) method. Similarly, all the samples alloyed with 0.2% Zr were also produced in order to make a comparison. The produced samples were evaluated for microstructural properties and mechanical tests for hardness, tensile and bending strength were performed. Wear test was carried out at 5 mm/s sliding speed under 3.0 N load for the all kind of hot pressed produced samples. The hot pressed composite microstructures have a more uniform distribution of the reinforcements. After HIP process, the composites were successfully produced with high density (>99%). The addition of Zr increased the yield and tensile strength of the samples. The highest strength value was found for the sample Al 123 matrix alloy with Zr. Evaluation of microstructures showed that copper and zirconium dispersed equally within the matrix microstructure without agglomeration. For the composite samples, Al3Zr, appeared as white precipitate, were inspected around B4C and SiC particles. The composite containing SiC particles and Zr had wear resistance value superior to those of the other counterparts.     

热轧高含量B4C颗粒增强Al基复合材料的成形性能

高含量B₄C (B₄C≥30wt%)颗粒增强Al基(B₄C_P/Al)复合材料具有优异的结构和功能特性,尤其是具有优异的中子吸收性能,在核防护领域被用做屏蔽材料使用。但由于高含量B₄C颗粒的加入,使B₄C_P/Al复合材料变形困难。采用ABAQUS数值模拟方法对不同变形量下B₄C_P/Al复合材料的热轧过程进行数值模拟分析,在480℃温度下对热压烧结的B₄C_P/Al复合材料坯料进行轧制,并对其微观组织和力学性能进行分析。数值模拟结果表明,热轧变形量达到60%以上时,B₄C_P/Al复合材料板材表面中间区域应力较小,侧面应力较大,在板材边缘容易产生残余应力。研究结果表明,随轧制下压量的增加,B₄C_P/Al复合材料中B₄C颗粒分布明显均匀,位错密度增加。当轧制变形量达到70%时,B₄C_P/Al复合材料的屈服强度提高至249.46 MPa,极限抗拉强度提高至299.56 MPa。在拉伸过程中,B₄C颗粒优先断裂,但并未与基体界面脱黏,B₄C颗粒承受了主要载荷,Al基体发生塑性流动,从而提高了B₄C_P/Al复合材料的强度。      

SiCp／Al复合材料的微观结构与界面

对用压力铸造法制造的碳化硅颗粒增强铝合金（ＳｉＣｐ／Ａｌ）复合材料的微观结构和界面进行了研究。结果表明：碳化硅颗粒在复合材料中均匀分布，复合材料的基体中有较高的位错密度，碳化硅颗粒中有少量的层错。研究还发现ＳｉＣｐ／Ａｌ复合材料中界面结合良好，没有反应物生成，并且在界面处没有发现孔隙存在。在复合材料拉伸断口上没有发现裸露的碳化硅颗粒，说明在复合材料拉伸破坏时ＳｉＣｐ－Ａｌ界面没有开裂，反映了压铸ＳｉＣｐ／Ａｌ复合材料中良好的界面结合。     

Preparation and investigation of Al–4 wt % B<Subscript>4</Subscript>C nanocomposite powders using mechanical milling

Boron carbide nanoparticles were produced using commercially available boron carbide powder (0·8 μm). Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill under argon atmosphere up to 20 h. The same process was applied for Al–4 wt % B₄C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. Scanning electron microscopy (SEM) analysis as well as apparent density measurements were used to optimize the milling time needed for completion of the mechanical milling process. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. FE-SEM images show that distribution of boron carbide particles in aluminum matrix reaches a full homogeneity when steady state takes place. The better distribution of reinforcement throughout the matrix would increase hardness of the powder. To study the compressibility of milled powder, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B₄C particles. For better distribution of reinforcement throughout the matrix, r, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B₄C particles.     

Reinforcement in Al Matrix Composites: A Review of Strengthening Behavior of Nano‐Sized Particles

Aluminum matrix composites (AMCs) reinforced with the nano‐sized particles are very important materials for the applications in industrial fields. These aluminum matrix composites consist of an aluminum matrix and nano‐sized particles, which own very different physical and mechanical properties from those of the matrix. Nano‐sized particles show a more obvious strengthening effect on the matrix than the micro‐sized particles do, because of the high specific surface area which is positive for the pinning effect during the deformation process. Thus, the nano‐sized particle‐reinforced AMCs usually exhibit a good ductility. The main issues of the fabrication methods are the low wettability between the nano‐sized particles and the molten aluminum alloys, which is fatal to the conventional casting methods, and the agglomeration of nano‐sized particles which happened easier than the larger particles. Several alternative processes have been presented in literature for the production of the nano‐sized particle‐reinforced aluminum composites. This paper is aimed at reviewing the feasible manufacturing techniques used for the fabrication of nano‐sized particle‐reinforced aluminum composites. More importantly, the strengthening mechanisms and models which are responsible for the improvement of mechanical properties of the nano‐sized particle‐reinforced aluminum composites have been reviewed.

     

热轧工艺对20%B4C/Al复合材料显微组织及缺陷的影响

采用热等静压烧结与热轧相结合的方法制备了20%B_4C/Al(质量分数,下同)复合材料,采用排水法及SEM、EDS等手段研究了热轧工艺(道次变形量、总变形量)对复合材料缺陷及显微组织的影响。研究结果表明,热等静压制备的B_4C/Al复合材料坯体密度可达2.66g/cm3(相对密度100%),B_4C颗粒分布均匀且与Al界面处结合紧密;B_4C/Al复合材料轧制道次变形量应控制在10%以内,进一步增加道次变形量复合材料内出现宏观裂纹。复合材料经热轧后,B_4C颗粒仍分布较为均匀,且与Al基体结合紧密,复合材料内部未观察到明显的显微缺陷。     

SiCp/Al复合材料的磨损特性分析

本文研究了SiC颗粒增强铝基(ZL102)复合材料的磨损特性。结果表明,SiC颗粒的加入可提高材料的耐磨性,复合材料与基体合金相比,磨损速率相当低,而且其抗粘着磨损能力更强,磨损性能与增强相数量、分布及界面结合有关。      

界面改性对SiC_p/Cu复合材料热物理性能的影响

采用热压烧结法成功制备SiC_p/Cu复合材料。采用溶胶-凝胶工艺在SiC颗粒表面制备Mo涂层,研究Mo界面阻挡层对复合材料热物理性能的影响。结果表明:过氧钼酸溶胶-凝胶体系能够在SiC颗粒表面包覆连续性、均匀性较好的MoO_3涂层,最佳工艺配比为SiC∶MoO_3=5∶1(质量比)、过氧化氢∶乙醇=1∶1(体积比),SiC表面丙酮和氢氟酸预清洗处理有利于MoO_3涂层的沉积生长。MoO_3在540℃第一步氢气还原后转变为MoO_2,MoO_2在940℃第二步氢气还原后完全转变为Mo,Mo涂层包覆致密完整。热压烧结SiC_p/Cu复合材料微观组织致密均匀,且相比原始SiC颗粒增强的SiC_p/Cu,经溶胶-凝胶法界面改性处理的SiC_p/Cu复合材料热导率明显提高,SiC体积分数约为50%时,SiC_p/Cu复合材料热导率达到214.16W·m~(-1)·K~(-1)。     

Crack‐Tip Stress Field and Fatigue Crack Growth Monitoring Using Infrared Lock‐In Thermography in A359/SiCp Composites

Abstract: This paper deals with the study of fracture behaviour of silicon carbide particle‐ reinforced aluminium alloy matrix composites (A359/SiCp) using an innovative non‐destructive method based on lock‐in thermography. The heat wave, generated by the thermo‐mechanical coupling and the intrinsic energy dissipated during mechanical cyclic loading of the sample, was detected by an infrared camera. The coefficient of thermo‐elasticity allows for the transformation of the temperature profiles into stresses. A new procedure was developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermographic results on the crack growth rate of A359/SiCp composite samples with three different heat treatments were correlated with measurements obtained by the conventional compliance method. The results obtained by the two methods were found to be in agreement, demonstrating that lock‐in thermography is a powerful tool for fracture mechanics studies. The paper also investigates the effect of heat treatment processing of metal matrix composites on their fracture properties.     

Abrasive wear of Al‐SiC composites

The two‐ and three‐body abrasion of aluminium matrix composites, reinforced with silicon carbide particles, have been investigated. The metal matrix composites were fabricated by a powder metallurgy route involving a final hot extrusion step. Air atomised aluminium powder Al 1100 was used as matrix and α‐SiC_p as reinforcement with mean sizes of 10, 27 and 43 μm; in the proportions of 5, 10 and 20 vol.%. Using a pin‐on‐disc apparatus and a wet monolayer tester, two‐ and three‐body abrasion tests were carried out respectively against silicon carbide and alumina abrasives with four different grit sizes. The microstructural characterizations were performed using light microscopy. The dominant wear mechanisms were identified using scanning electron microscopy. The influence of type of the abrasive particles on wear resistance and dominating wear mechanisms was reported. Relationships between size and volume fraction of the SiC_p reinforcement and wear resistance were discussed. It was shown that SiC_p particles reinforcement increases the abrasion resistance against all the abrasives used. This increase was generally higher against alumina than against silicon carbide abrasives.     

基于Murty准则的SiCp/Al复合材料热加工图研究

采用热模拟压缩试验对15%(体积分数)SiCp/Al复合材料在温度为623~773K、应变速率为0.001~10s~(-1)的热变形行为进行了研究,基于Murty准则建立了该材料的热加工图,并在此基础上建立了SiCp/Al复合材料临界失稳应变分布图。结果表明,随变形温度升高,SiCp/Al复合材料中的强化机制逐渐减弱,软化机制逐渐增强。基于临界失稳应变图可以确定出适合SiCp/Al复合材料加工的两个区域,分别为变形温度700~773K、应变速率0.001~0.01s~(-1)和变形温度740~773K、应变速率0.02~0.14s~(-1)。     

Microstructure and strengthening mechanism of bimodal size particle reinforced magnesium matrix composite

One kind of (submicron + micron) bimodal size SiCp/AZ91 composite was fabricated by the stir casting technology. After hot deformation process, the influence of bimodal size particles on microstructures and mechanical properties of AZ91 matrix was investigated by comparing with monolithic A91 alloy, submicron SiCp/AZ91 and micron SiCp/AZ91 composites. The results show that micron particles can stimulate dynamic recrystallized nucleation, while submicron particles may pin grain boundaries during the hot deformation process, which results in a significant grain refinement of AZ91 matrix. Compared to submicron particles, micron particles are more conducive to grain refinement through stimulating the dynamic recrystallized nucleation. Besides, the yield strength of bimodal size SiCp/AZ91 composite is higher than that of single-size particle reinforced composites. Among the strengthening mechanisms of bimodal size particle reinforced composite, it is found that grain refinement and dislocation strengthening mechanism play a larger role on improving the yield strength.     

Finite element simulation of the micromachining of nanosized-silicon-carbide-particle reinforced composite materials based on the cohesive zone model

A finite element method based on the cohesive zone model was used to study the micromachining process of nanosized silicon-carbide-particle(SiCp) reinforced aluminum matrix composites. As a hierarchical multiscale simulation method, the parameters for the cohesive zone model were obtained from the stress-displacement curves of the molecular dynamics simulation. The model considers the random properties of the siliconcarbide-particle distribution and the interface of bonding between the silicon carbide particles and the matrix.The machining mechanics was analyzed according to the chip morphology, stress distribution, cutting temperature, and cutting force. The simulation results revealed that the random distribution of nanosized SiCp causes non-uniform interaction between the tool and the reinforcement particles. This deformation mechanics leads to inhomogeneous stress distribution and irregular cutting force variation.     

6061铝颗粒层增强7075铝基复合材料的微观结构及阻尼性能

采用热轧法制备出具有颗粒层状结构的6061p/7075铝基复合材料以改善7075铝合金的阻尼性能。通过OM、SEM、EDS和XRD分析6061p/7075层状铝基复合材料的微观组织,分别采用万能力学试验机和动态热机械分析仪分析其力学性能和阻尼行为。研究表明,6061铝颗粒层存在大量的颗粒间界面和微小孔隙,6061铝颗粒层与7075铝基体之间界面结合良好,没有发生界面反应;6061p/7075层状铝基复合材料最大抗拉强度为370.5 MPa,比7075铝基体提高了30%;6061p/7075层状铝基复合材料和基体材料的内耗值分别随着温度和应变量的升高而增大,复合材料的阻尼性能明显优于7075铝基体,在360℃时,复合材料的内耗值高达0.117,比7075铝基体提高了149%;6061p/7075层状铝基复合材料和基体材料的储能模量分别随着温度和应变量的升高而降低,在30℃时,复合材料的储能模量为38601 MPa,比7075铝基体高16%。      

无压浸渗法制备不同体积分数及梯度SiCp/Al复合材料

选用不同粒径大小的SiC颗粒,并通过对颗粒分布的有效控制,采用无压浸渗工艺制备了不同体积分数(15%～65%)的SiCp/Al复合材料,并在此基础上试制了梯度SiCp/Al复合材料.运用OM,XRD等手段对所制备的复合材料进行了显微组织观察与成分分析,并对选定体积分数的复合材料进行了密度以及力学测试.研究结果表明,无压浸渗工艺下不同体积分数的SiCp/Al复合材料组织均匀、致密,力学性能良好;具有梯度结构的SiCp/Al复合材料层间结合良好,没有层间剥离现象.     

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.     

In‐situ composite coating on powder metallurgy master alloy fabricated by vacuum hot‐pressing sintering technology

A material consisting of an in‐situ titanium carbide reinforced nickel‐aluminide (Ni₃Al) coating and a powder metallurgy master alloy was fabricated by vacuum hot‐pressing sintering technology. A metallurgical bonded, pores‐free interface between composite coating and powder metallurgy master alloy was formed at the sintering temperature of 1050 °C, pressure of 10^‐4 Pa and pressing pressure of 40 MPa. The phase, microstructure and wear behavior of composite coating were investigated. The results showed that polygonal titanium carbide particulates with various sizes were homogeneously distributed in nickel‐aluminide matrix. The sintering temperature, pressing pressure and heat from as‐reactions‐formed coating green compact facilitated the pore infiltration with transiently generated liquid phases and ensured the high‐intensity metallurgical bonding between composite coating and powder metallurgy master alloy. Due to the abnormal elevated‐temperature properties of nickel‐aluminide matrix, titanium carbide particulates reinforcement and the mechanically mixed layer protection, TiC/Ni₃Al‐coated parts demonstrated superior wear resistance and lower friction coefficient while compared with Ni₃Al‐coated parts and H13 steel.     

Achieving strength-ductility synergy in cold spray additively manufactured Al/B4C composites through a hybrid post-deposition treatment

Cold spray additive manufacturing (CSAM) provides a potential solid state manufacturing route to fabricate variety of aluminum matrix composites (AMCs) with reduced possibility of undesired chemical reactions and residual thermal stresses. This study presents a hybrid (i.e. hot compression + hot rolling) post-deposition treatment to reinvigorate the mechanical properties of cold spray additively manufactured Al/B₄C composites. The as-deposited samples were initially subjected to 30% thickness reduction via hot compression treatment at ∼500 °C followed by a hot rolling treatment with 40% thickness reduction in 2 passes. Electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) results revealed that after hybrid post-deposition treatment (involving 70% accumulative thickness reduction), the aluminum grains in the matrix were extensively refined due to simultaneous operation of continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX). Furthermore, interfacial defects were remarkably reduced while the nature of Al/Al and Al/B₄C interfacial bonding was changed from sheer mechanical interlocking to metallurgical bonding which facilitated efficient transference of applied load to uniformly dispersed bimodal B₄C particles. As a result, ultimate tensile strength (UTS) and elongation (EL) of the as-deposited sample were simultaneously improved from ∼37 to 185 MPa and ∼0.3% to 6.2%, respectively.