超声辅助激光沉积原位TiC-TiB2/Al-12Si铝基复合材料微观组织及摩擦磨损行为研究

以Ti、B₄C和Al-12Si粉末为原材料,通过超声辅助激光沉积制备了原位TiC-TiB₂/Al-12Si铝基复合材料。采用XRD、EDS分析了复合材料的物相组成,通过OM、SEM观察了复合材料的微观组织,利用摩擦磨损试验机和三维轮廓仪测试了复合材料的磨损性能。结果表明,随Ti+B₄C含量的增加,ɑ-Al晶粒细化,原位生成的TiB₂呈棒状,且可成为ɑ-Al的异质形核核心;原位生成的TiC为150nm多边形形貌。随Ti+B₄C含量的增加,原位TiC-TiB₂/Al-12Si铝基复合材料的耐磨性提高;未加入Ti+B₄C的Al-12Si合金磨损机制为粘着磨损;当Ti+B₄C的加入量为8wt.%时,磨损机制为磨粒磨损;当Ti+B₄C的加入量为10wt.%时,其磨损机制转变为粘着磨损。     

原位颗粒对近液相线铸造6063铝合金微观组织和耐磨性的影响机理

以CuO-Al作为反应体系,在6063铝合金中原位反应生成Al₂O₃颗粒,采用近液线相铸造的方法制备6063Al-XAl₂O₃(X=0,2,4,6)复合材料。研究原位反应颗粒Al₂O₃与6063铝合金自带的原位结晶颗粒Mg₂Si的形状、尺寸、数量、分布、界面特征等对合金微观组织和耐磨性的影响机理。结果表明,在6063铝合金中原位反应生成尺寸在亚微米级的近球形θ-Al₂O₃颗粒;其(311)晶面与6063铝合金基体(111)晶面成共格界面;6063铝合金中Mg₂Si尺寸大约为100nm,呈条带状,其(02-2)与Al基体(111)晶面属于共格界面。随着Al₂O₃颗粒含量的增加,6063铝基复合材料的晶粒组织形貌由蔷薇状逐渐向等轴晶转变,晶粒尺寸逐渐减小。当Al₂O₃的质量分数为6%时,复合材料组织由等轴晶和细小的柱状晶组成。载荷为50N时,6063铝合金的磨损量为6.72mg,6063-6Al₂O₃复合材料的磨损量为1.63mg,相对于6063铝合金降低75.7%。原位颗粒(Al₂O₃+Mg₂Si)与铝基体都成共格界面,界面之间无污染,界面结合强度高,在磨损过程中,不易从基体中脱落,承当磨损过程中的大部分载荷。原位生成高硬度的Al₂O₃颗粒与原位结晶颗粒Mg₂Si协同作用共同提高复合材料的耐磨性。外加载荷为40N时,随着增强相质量分数的增加,复合材料的磨损机制由粘着磨损转变为磨粒磨损。6063铝合金磨损机制以严重的粘着磨损为主。6063-2Al₂O₃复合材料磨损机制主要以粘着磨损为主,6063-4 Al₂O₃和6063-6Al₂O₃复合材料主要表现为磨粒磨损。     

Ti 元素对B4C/Al复合材料力学性能的改善作用研究

B₄C/Al复合材料是目前最理想的中子吸收材料,广泛用于乏燃料储存。本文利用液态搅拌法制备B₄C/Al复合材料,通过添加Ti元素,探讨了界面反应对材料的界面结构和力学性能的影响。研究发现,Ti元素通过参与界面反应,改变了界面结构,在B₄C颗粒表面形成了紧密结合的纳米TiB₂界面层;Ti的添加消除了界面微裂纹、微孔、分离等缺陷。随着界面反应程度的加强,材料强度提高,尤其反应脱落的纳米TiB₂颗粒作为原位第二强化相进一步增强基体。B₄C/Al复合材料断裂过程表现为韧窝延性断裂;TiB₂界面层增强了B₄C颗粒与基体的结合,断裂行为从B₄C-Al界面脱落转变为B₄C颗粒断裂;但过渡的界面反应会形成微韧窝,引起材料延伸率下降。     

含微纳B4C/Ti颗粒铜基复合材料的微观组织与力学性能

采用高能球磨(HEBM)和放电等离子烧结(SPS)工艺成功制备出微纳B₄C/Ti颗粒增强铜基复合材料(CTBCs),通过X射线衍射(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)以及能谱(EDS)等测试手段对其微观组织形貌进行表征。结果表明,(B₄C+Ti)颗粒在基体中均匀分布,增强体与铜基体界面结合良好,且其结合形式为冶金结合和机械结合并存。采用阿基米德排水法测定出烧结态试样的致密度。复合材料的显微硬度、拉伸屈服强度、抗拉强度和延伸率等力学性能相较于纯铜试样得到显著提高,这主要归因于载荷传递、细化晶粒与热错配等强化机制。复合材料的拉伸断口表现出明显的韧性断裂特征。     

纳米CeO2掺杂对烧结钕铁硼磁体表面Zn-Al涂层性能的影响

采用喷涂工艺在烧结钕铁硼磁体表面制备了不同纳米 CeO₂ 掺杂量的 CeO₂ / Zn-Al 复合涂层。 利用扫描电子显微镜、显微硬度仪、盐雾试验箱和电化学工作站对 CeO₂ / Zn-Al 复合涂层的微观结构、力学性能及耐腐蚀性能进行表征分析。 结果表明:CeO₂ 纳米颗粒较均匀弥散分布于 Zn-Al 涂层中,不仅能够增加 Zn-Al 涂层的硬度,而且可以提高 Zn-Al 涂层的屏蔽性能,CeO₂ / Zn-Al 复合涂层耐中性盐雾试验能力高达 720 h。 添加的 CeO₂ 颗粒能够隔绝 Zn-Al 涂层中的锌铝薄片之间的直接接触,起到绝缘作用,延长了腐蚀介质渗入钕铁硼基体的腐蚀通道。     

Ti3AlC2掺杂SPS法制备Ti2AlC/TiAl复合材料的研究

通过2TiC-Ti-1.2Al体系的原位热压反应制备了Ti₃AlC₂陶瓷,然后以59.2Ti-30.8Al-10Ti₃AlC₂(wt%)为反应体系,采用放电等离子烧结技术制备出Ti₂AlC/TiAl基复合材料。借助XRD、SEM分析了产物的相组成和微观结构,并测量了其室温力学性能。结果表明：原位热压烧结产物由Ti₃AlC₂和TiC相组成,Ti₃AlC₂呈典型的层状结构,TiC颗粒分布在其间。SPS法制备的Ti₂AlC/TiAl基复合材料主要由TiAl、Ti₃Al和Ti₂AlC相组成,Ti₂AlC增强相主要分布于基体晶界处,表现为晶界/晶内强化作用。力学性能测试表明：Ti₂AlC/TiAl基复合材料的密度、维氏硬度、断裂韧性和抗弯强度分别为3.85 g/cm₃、5.37 GPa、7.17 MPa?m_1/2和494.85 MPa。     

(Ca0.96D0.04)MnO3(D=Ca, Sr, Rb, Sm)氧化物的制备和热电性能研究

利用溶胶凝胶法制备出(Ca_0.96D_0.04)MnO₃(D=Ca, Sr, Rb, Sm)氧化物粉末后,先分别采用氩气气氛的放电等离子烧结和空气气氛的常压烧结制备出CaMnO₃(CMO)块体,并对其相组成进行分析,选择出更为优异的CaMnO₃块体制备方法。再进一步制备出(Ca_0.96D_0.04)MnO₃(D=Sr, Rb, Sm)氧化物块体,最后对(Ca_0.96D_0.04)MnO₃(D=Ca, Sr, Rb, Sm)块体的物相组成、显微组织和热电性能进行测试分析。实验结果表明：氩气气氛放电等离子烧结制备的CaMnO₃块体发生物相分解,原因是放电等离子烧结的烧结环境贫氧;空气气氛的常压烧结可以得到物相较纯净的(Ca_0.96D_0.04)MnO₃(D=Ca, Sr, Rb, Sm)块体;在整个测试温度范围内,(Ca_0.96D_0.04)MnO₃(D= Sr, Rb, Sm)的ZT值在873K时达到最大,分别为0.11、0.08和0.07,相比于未掺杂试样提高了约1.3~2.2倍。     

压力烧结制备二氧化钛包覆的石墨烯增强铝基复合材料

使用压力烧结方法制备了石墨烯纳米片（GNP）增强的7075铝基纳米复合材料,提出了一种通过在GNP的表面涂覆二氧化钛（TiO₂）来优化界面结合的新工艺,并比对了原石墨烯及具有包覆层石墨烯对铝基纳米复合材料的力学性能和微观结构的影响。结果表明,与添加纯GNP相比,添加具有TiO₂涂层的GNP的纳米复合材料的力学性能提高。相比于基体,TiO₂包覆GNP增强的纳米复合材料的屈服强度、抗拉强度和显微硬度分别增加了38.9%、34.4%和20.1%。性能的进一步改善是由于TiO₂涂层优化了增强相与基体之间的界面结合,从而提高了载荷传递的有效性。     

微量元素Nb、C强化W-Lu2O3复合材料的组织及性能研究

采用机械球磨和放电等离子体烧结制备了W-Lu₂O₃和W-Nb-C-Lu₂O₃合金,通过场发射扫描电子显微镜(FE-SEM)、能谱(EDS)和透射电子显微镜(TEM)研究分析了合金复合粉末的形貌、合金烧结体表面形貌和断口形貌;测定了合金的致密度、热导率、硬度和强度。实验结果表明：在W-Lu₂O₃的基础上添加微量Nb和C对钨合金晶粒细化、致密化和强度提高有着明显的效果,W-Nb-C-Lu₂O₃合金的致密度比W-Lu₂O₃提高了5.75%,达到了95.12%,晶粒尺寸由8~13 μm细化到2~5 μm,W-Nb-C-Lu₂O₃合金比W-Lu₂O₃合金的显微硬度和强度得到明显改善。     

纳米Mg2Sn增强镁基复合材料组织与性能

利用纳米Sn粉高的表面活性,通过微米Mg粉与纳米Sn粉的机械合金化高效合成了含原位纳米Mg₂Sn相的复合粉末,将所得复合粉末热压烧结,获得高性能纳米Mg₂Sn增强镁基复合材料。对比研究了不同机械合金化时间对镁基复合材料组织、性能的影响,结果表明：随着机械合金化时间的延长,由纳米Mg₂Sn相组成的团簇尺寸不断减小,分布更加均匀,烧结态Mg₂Sn/Mg复合材料的各项力学性能也得到不断提高。     

Mechanical properties and fracture of Al–15 vol.-%B4C based metal matrix composites

The present work was performed on three aluminium metal matrix composites (MMCs) containing 15 vol.-%B₄C particles. The matrix in two of these materials is pure aluminium, whereas the matrix of the third material was an experimental 6063 aluminium alloy. All composites were homogenised at elevated temperatures for 48 h before being quenched in warm water. The quenched samples were aged in the range of 25–400°C for 10 h, at each temperature. Hardness and tensile tests performed on the aged MMCs show that the presence of Zr (with or without Ti) resulted in a noticeable hardening due to the precipitation of a Zr rich phase. Maximum strengthening was obtained from the 6063 based MMC due to the precipitation of Mg₂Si phase particles. The present technique used to produce the MMCs examined proved capable of manufacturing composites with a uniform distribution of B₄C in the matrix with a strong degree of matrix/particle bonding. When the MMC samples were deformed to failure, the B₄C was fractured transgranularly without debonding from the matrix. The addition of Zr and Ti resulted in the formation of protective layers around the B₄C particles that were retained after fracture; these protective layers were not affected by the B₄C particle size (0·15–20 μm). Stacking faults were commonly observed in fractured Al 6063/B₄C/15p samples. The precipitation of zirconium–titanium compounds during aging contributed to the composite strength.     

Comparison of wear behaviour of LM13 Al−Si alloy based composites reinforced with synthetic (B4C) and natural (ilmenite) ceramic particles

Dry sliding wear behaviour of stir-cast aluminium matrix composites (AMCs) containing LM13 alloy as matrix and ceramic particles as reinforcement was investigated. Two different ceramic particle reinforcements were used separately: synthetic ceramic particles (B₄C), and natural ceramic particles (ilmenite). Optical micrographs showed uniform dispersion of reinforced particles in the matrix material. Reinforced particles refined the grain size of eutectic silicon and changed its morphology to globular type. B₄C reinforced composites (BRCs) showed maximum improvement in hardness of AMCs. Ilmenite reinforced composites (IRCs) showed maximum reduction in coefficient of friction values due to strong matrix−reinforcement interfacial bonding caused by the formation of interfacial compounds. Dry sliding wear behaviour of composites was significantly improved as compared to base alloy. The low density and high hardness of B₄C particles resulted in high dislocation density around filler particles in BRCs. On the other hand, the low thermal conductivity of ilmenite particles resulted in early oxidation and formation of a tribo-layer on surface of IRCs. So, both types of reinforcements led to the improvement in wear properties of AMCs, though the mechanisms involved were very different. Thus, the low-cost ilmenite particles can be used as alternative fillers to the high-cost B₄C particles for processing of wear resistant composites.     

Mechanical Properties of Squeeze-Cast A356 Composites Reinforced With B4C Particulates

In this study, different volume fractions of B₄C particles were incorporated into the aluminum alloy by a mechanical stirrer, and squeeze-cast A356 matrix composites reinforced with B₄C particles were fabricated. Microstructural characterization revealed that the B₄C particles were distributed among the dendrite branches, leaving the dendrite branches as particle-free regions in the material. It also showed that the grain size of aluminum composite is smaller than that of monolithic aluminum. X-ray diffraction studies also confirmed the existence of boron carbide and some other reaction products such as AlB₂ and Al₃BC in the composite samples. It was observed that the amount of porosity increases with increasing volume fraction of composites. The porosity level increased, since the contact surface area was increased. Tensile behavior and the hardness values of the unreinforced alloy and composites were evaluated. The strain-hardening behavior and elongation to fracture of the composite materials appeared very different from those of the unreinforced Al alloy. It was noted that the elastic constant, strain-hardening and the ultimate tensile strength (UTS) of the MMCs are higher than those of the unreinforced Al alloy and increase with increasing B₄C content. The elongation to fracture of the composite materials was found very low, and no necking phenomenon was observed before fracture. The tensile fracture surface of the composite samples was indicative of particle cracking, interface debonding, and deformation constraint in the matrix and revealed the brittle mode of fracture.     

Spark plasma sintering of B4C ceramics: The effects of milling medium and TiB2 addition

Boron carbide (B₄C) ceramics, with a relative density up to 98.4% and limited grain growth, were prepared at 1600-1800 °C by spark plasma sintering (SPS) technique. The effects of powder milling medium (water and 2-propanol) on the powders' surface characteristics and TiB₂ addition on the sintering densification were investigated. The ball milling processing of B₄C powders in water can promote the sintering of B₄C ceramics. A B₂O₃ layer on B₄C particle surface is concluded to promote the densification of the B₄C ceramics at an early sintering stage. This B₂O₃ layer, which normally inhibits the densification process at the final stage of the sintering, can be reduced through reaction with TiB₂ particles, resulting in further densification of the B₄C ceramics.     

Effect of limited matrix–reinforcement interfacial reaction on enhancing the mechanical properties of aluminium–silicon carbide composites

An unconventional approach to strengthening Al/SiC composites through controlled matrix–reinforcement interfacial reactions was studied. Composites with two distinct interfacial microstructures were prepared by varying the contact time between the SiC particles and molten aluminium during processing. The formation of a thin Al₄C₃ reaction layer along the particle–matrix interface was found to increase the composite yield strength, ultimate tensile strength, work-hardening rate and work-to-fracture, and change the fracture pattern from one involving interfacial decohesion to one where particle breakage was dominant. These changes were attributed to a stronger interface bond, which is thought to result from the tendency for the Al₄C₃ reaction layer to form semicoherent interfaces and orientation relationships with the aluminium matrix and SiC particles and for it to be mechanically “keyed-in” to both these phases. The stronger interface bond also enhanced the levels of plastic constraint which, when coupled with the greater work hardening, promoted local matrix failure, thereby reducing the composite ductility.     

Shape change of liquid particles embedded in a solid matrix caused by plastic deformation of a Cu-B2O3 alloy

A copper alloy containing amorphous B₂O₃ dispersed particles is made by internal oxidation of a dilute Cu-B solid-solution alloy. Although the B₂O₃ particles behave as plastically non-deformable particles at room temperature, these become liquid particles in the solid Cu matrix at high temperatures. Cu single crystals containing the B₂O₃ particles are tensile tested at high temperatures. The shape change of the liquid particles due to the plastic deformation of the Cu matrix is observed with electron imcroscopy. The occurrence of relaxation by the diffusion of the Cu atoms along the Cu/B₂O₃ interface affects the shape change. The kinetics of the diffusional relaxation is discussed on the basis of the results of observations of the particle shape. This article is based on a presentation made in the symposium “The l^st Korea-Japan Structural Dynamic Symposium”, held at Sunchon National University, Sunchon, Korea, August 5-8, 1999 under the auspices of The Korean Institute of Metals and Materials and the Research and Development Center for Automobile Parts and Materials.     

Tailoring Microstructure and Properties of Hierarchical Aluminum Metal Matrix Composites Through Friction Stir Processing

The fabrication of hierarchical aluminum metal matrix composites (MMCs) begins with the cryomilling of inert gas-atomized AA5083 Al powders with B₄C particles, which yields agglomerates of nanocrystalline (NC) Al grains containing a uniform dispersion of solidly bonded, submicron B₄C particles. The cryomilled agglomerates are size classified, blended with coarse-grain Al (CG-Al) powders, vacuum degassed at an elevated temperature, and consolidated to form the bulk composite. This hierarchical Al MMCs have low weight and high strength/stiffness attributable to the (A) Hall–Petch strengthening from NC-Al (5083) grains, (B) Zener pinning effects from B₄C particulate reinforcement and dispersoids in both the NC-Al and CG-Al, (C) the interface characteristics between the three constituents, and (D) a high dislocation density. The hierarchical Al MMCs exhibit good thermal stability and microstructural characteristics that deflect or blunt crack propagation. A significant change in the microstructure of the composite was observed after friction stir processing (FSP) in the thermomechanically affected zone (TMAZ) due to the mechanical mixing, particularly in the advancing side of the stir zone (SZ). The NC-Al grains in the TMAZ grew during FSP. Evidence of CG-Al size reduction was also documented since CG-Al domain was absent by optical observation. Given the proper control of the microstructure, FSP has demonstrated its potential to increase both strength and ductility, and to create functionally tailored hierarchical MMCs through surface modification, graded structures, and other hybrid microstructural design.     

Densification and compressive strength ofin-situ processed Ti/TiB composites by powder metallurgy

In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB₂, B₄C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB₂ or B₄C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100, 1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB₂ compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of the composite made from TiB₂ reactant powder was higher than that of the composite made from B₄C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between matrix and reinforcement made from TiB₂ reactant powder was better than that made from B₄C.