不同Al2O3含量的Al2O3/Cu复合材料的热变形行为

为探究Al₂O₃含量对Al₂O₃/Cu复合材料热变形行为的影响，采用内氧化法制备了3种Al₂O₃含量(0.28、0.66和1.13 mass%)的Al₂O₃/Cu复合材料，通过热模拟实验对其热变形行为进行了研究。结果表明：在823、923和1223 K时，随着Al₂O₃/Cu复合材料中Al₂O₃含量的增加，复合材料的峰值应力逐渐增大；显微组织观察发现，由于1.13 Al₂O₃/Cu复合材料内动态软化积累程度最大，导致其在1023和1123 K下出现了峰值应力下降现象。经热挤压后，在热变形过程中Al₂O₃/Cu复合材料的软化效果以动态回复为主。同时，发现0.28 Al₂O₃/Cu和0.66 Al     

Al2O3颗粒直径对1 vol%的Al2O3/Cu基复合材料组织和性能的影响

采用粉末冶金法+热压工艺制备了不同Al₂O₃颗粒直径的1 vol%Al₂O₃/Cu基复合材料，使用光学显微镜和扫描电镜(SEM)观察了复合材料的显微组织，利用电子拉伸试验机测试了复合材料的力学性能。基于弹/塑性理论推导出了复合材料中颗粒周边的弹性区宽度的表达式。结果表明：Al₂O₃颗粒直径对Al₂O₃/Cu基复合材料强度及基体晶粒尺寸有着较大的影响；Al₂O₃颗粒直径越大，Al₂O₃/Cu基复合材料的抗拉强度、屈服强度越小；当Al₂O₃颗粒直径为5μm时，Al₂O₃/Cu基复合材料的抗拉强度和屈服强度分别为207和90 MPa,是铜试样的95.8%和95.7%。     

Al2O3/Cu多孔复合材料的微观形貌和压缩性能

采用高能球磨-粉末冶金法制备了Al₂O₃/Cu多孔复合材料(A-C-M)。首先利用高能球磨法将Cu粉和Al₂O₃粉末均匀细化，然后将Al₂O₃/Cu复合粉末与造孔剂尿素均匀混合后，再将混合粉末冷压成型，最后通过溶脱-烧结工艺制得A-C-M。采用X射线衍射(XRD)和扫描电镜(SEM)对粉末原料和A-C-M的微观形貌进行表征分析，使用万能试验机对A-C-M进行压缩性能测试，探讨了尿素和Al₂O₃含量对A-C-M性能的影响。结果表明：高能球磨使Al₂O₃/Cu复合粉末的形貌由球状变为片状，复合粉末尺寸先减小后增大，在球磨4 h时获得最小平均粒径为25μm; A-C-M含有两种特征孔，100～300μm的大孔和1～10μm的微孔；随尿素含量的增加，孔的连通程度及复合材料的孔隙率逐渐增加，其压缩强度逐渐降低；随Al₂O₃含量的增加，A...     

Al2O3/TiB2/Al复合材料的微观结构和高温力学性能

以细雾化铝粉和TiB₂颗粒为原料,通过粉末冶金和热轧制制备微米TiB₂和纳米Al₂O₃颗粒增强铝基复合材料。室温时,由于TiB₂和Al₂O₃的综合强化作用,Al₂O₃/TiB₂/Al复合材料的屈服强度和抗拉强度分别为258.7 MPa和279.3 MPa,测试温度升至350℃时,TiB₂颗粒的增强效果显著减弱,原位纳米Al₂O₃颗粒与位错的交互作用使得复合材料的屈服强度和抗拉强度达到98.2MPa和122.5 MPa。经350℃退火1000 h后,由于纳米Al₂O₃对晶界的钉扎作用抑制晶粒长大,强度和硬度未发生显著的降低。     

不同基体对连续Al2O3f/Al复合材料纤维损伤的影响

采用真空气压浸渗法制备了增强体为Al₂O₃纤维,基体合金分别为1A99、ZL210A、ZL301及7075铝合金的连续Al₂O_3f/Al复合材料,并用NaOH溶液提取出Al₂O₃纤维,研究了不同基体对Al₂O_3f/Al复合材料纤维损伤的影响。结果表明,在同样的制备工艺下,不同的基体对Al₂O₃纤维的损伤程度不同。Al₂O₃纤维与纯铝及ZL210A基体界面反应程度微弱,纤维表面光滑,未发现界面反应产物,纤维剩余强度分别为1 746 MPa和1 658 MPa; Al₂O₃纤维与ZL301发生界面反应生成了MgAl₂O₄(镁铝尖晶石),纤维表面较为粗糙,剩余强度为1 584 MPa; Al₂O₃纤维与...     

0.5Y2O3/Al2O3-Cu/20Mo3SiC复合材料的热变形行为及热加工图

采用真空快速热压烧结法制备了0.5Y₂O₃/Al₂O₃-Cu/20Mo3SiC复合材料，在650～950℃温度范围和0.001～10 s^-1应变速率条件下，利用Gleeble-1500D数控动态-力学模拟试验机对0.5Y₂O₃/Al₂O₃-Cu/20Mo3SiC复合材料进行热变形试验，根据试验结果绘制了其真应力-真应变曲线。根据动态材料学模型，构建了复合材料的热加工图，确定其适宜的热加工参数。结果表明：0.5Y₂O₃/Al₂O₃-Cu/20Mo3SiC复合材料的真应力-真应变曲线存在典型的动态再结晶特征，其热激活能为211.109 kJ/mol,并构建了本构方程；基于动态材料模型构造的热加工图，确定了复合材料最佳的热加工工艺参数为：变形温度为725～950℃,应变速率为0.006～0.223 s^...     

Al2O3掺杂对烧结钕铁硼磁体电阻率和磁性能的影响

采用晶间掺杂法在钕铁硼合金粉体中掺入Al₂O₃,制备了Al₂O₃掺杂的烧结钕铁硼磁体,研究了Al₂O₃掺杂对钕铁硼磁体的电阻率、磁性能和微观结构的影响。结果表明：磁体电阻率随着Al₂O₃掺杂量的增加逐步提高,由未掺杂时的125.2μΩ·cm提高到Al₂O₃掺杂量为0.5 mass%时的144.4μΩ·cm,提高了15.3%;磁体矫顽力随着Al₂O₃掺杂量的增加呈先增大后减小的趋势,未掺杂磁体的矫顽力为13.28 kOe,当Al₂O₃掺杂量为0.3 mass%时,矫顽力达到最大值14.97 kOe,继续增加Al₂O₃掺杂量,磁体矫顽力开始下降;剩磁随着Al₂O₃掺杂量的增加逐步降低,由未掺杂时的13...     

层厚比对Cu-TiB2/Cu层状复合材料微观组织和力学性能的影响

铜基复合材料由于优异的综合性能在电子封装、电接触等领域具有重要应用价值。然而,克服材料的强-塑性倒置关系一直面临着极大的挑战,层状构型设计被认为是解决该倒置难题的有效策略。本文采用粉末冶金并结合原位反应法,通过控制铺粉工艺,制备出Cu层与TiB₂/Cu复合层交叠分布的Cu-TiB₂/Cu层状复合材料。研究了Cu-TiB₂/Cu层状复合材料的力学性能及断裂特征,并讨论了层状结构参数对材料综合性能的影响。当Cu层与TiB₂/Cu复合层的层厚比为1∶3时,Cu-TiB₂/Cu层状复合材料的极限抗拉强度(UTS)为315 MPa,断裂伸长率为18%,实现了良好的强塑性匹配。基于复合材料裂纹扩展路径表征与分析,揭示了层状构型设计在抑制裂纹扩展、促使裂纹偏转等方面的作用机制,为高强韧铜基复合材料的构型设计和性能优化提供新思路。     

Al2O3对铝熔体中杂质Fe扩散行为影响的分子动力学模拟

采用分子动力学模拟方法从均方位移、自扩散系数、径向分布函数、配位数等方面分析研究了Al₂O₃对铝熔体中杂质Fe扩散行为的影响规律。结果表明：Al₂O₃是影响铝熔体中杂质Fe扩散和富集的关键因素，随着Al₂O₃含量的增加，杂质Fe的均方位移随之下降，且随着时间的延长，均方位移的增加幅度减小，扩散系数从0.173×10^-8 m²/s下降到0.037×10^-8 m²/s，即Al₂O₃含量的增加阻碍了杂质Fe的扩散，且Al₂O₃含量阻碍杂质Fe扩散行为的倾向随着时间的延长而加剧。同时，随Al₂O₃含量的增加，径向分布函数曲线发生明显变化，曲线第一峰的高度逐渐变高，即Fe原子配位数逐渐增加，杂质Fe的聚集程度增加。分析认为Al₂...     

NbMoWTa-Al2O3固体润滑复合材料的宽温域摩擦磨损性能

通过高能球磨和放电等离子烧结方法制备了新型NbMoWTa难熔高熵合金基固体润滑复合材料。系统研究了纳米Al₂O₃作为固体润滑剂对NbMoWTa难熔高熵合金宽温域摩擦学性能的影响。结果表明：纳米Al₂O₃颗粒在具有BCC结构的NbMoWTa难熔高熵合金基体相晶界和晶内均匀分散,强烈的弥散强化显著提升了NbMoWTa的显微硬度。纳米Al₂O₃颗粒在室温至800℃范围内降低摩擦因数和磨损方面有显著作用。室温下,由于复合材料的显微硬度显著提升,添加足量的纳米Al₂O₃实现了复合材料耐磨性的提升。在中高温下,复合材料表面形成的连续致密氧化摩擦层对提升摩擦学性能起着关键作用。纳米Al₂O₃颗粒协助氧化摩擦层承载更大的载荷,提高其致密性及稳定性,从而更有效地保护基体。此外,在800℃下纳米Al₂O₃颗粒的存在能够抑制MoO3的过度挥发。     

Aging behavior of Al2O3 short fiber reinforced Al-Cu alloy composites

Al2O3 short fiber reinforced AI-Cu composites containing 1%, 3%, 5% and 7% Cu were fabricated by a squeeze casting technique. The as-cast Al2O3/Al-Cu composites were solution treated at 535 ℃ and then aged at 170, 190 and 210 ℃, respectively. Age hardening behavior of the Al2O3/Al-Cu composites was analyzed by measuring the hardness of the samples at different aging temperatures and aging time. Microstructures of the composites were observed by transmission electron microscope（TEM）. The results indicate that the hardness of the Al2O3/Al-Cu composites containing 7% Cu is much higher than that containing 1%-5% Cu because of the large amount of CuAl2 precipitant in the Al2O3/Al-Cu composite. With the increase of Cu content from 1% to 7%, the time needed for the appearance of peak hardness shortened, indicating that the addition of Cu can accelerate the kinetic of CuAl2 precipitation in the Al2O3/Al-Cu composites. The Al2O3/Al-Cu composite containing 7% Cu shows the highest increment of hardness by aging treatment. Therefore, in order to get a higher peak hardness, the Al2O3/Al-Cu composites need more Cu addition as compared with the un-reinforced Al-Cu alloys.     

Reactive mechanism and mechanical properties of in situ composites fabricated from an Al–TiO2 system by friction stir processing

In situ (Al₃Ti + Al₂O₃)/Al composites were fabricated from powder mixtures of Al and TiO₂ using hot pressing, forging and subsequent multiple-pass friction stir processing (FSP). The reactive mechanism and mechanical properties of the FSPed composites were investigated. Four-pass FSP with 100% overlapping induced the Al–TiO₂ reaction, as a result of the enhanced solid diffusion and mechanical activation effect caused by the severe deformation of FSP. Decreasing the size of TiO₂ from 450 to 150 nm resulted in the formation of more Al₃Ti and Al₂O₃ particles. The formation mechanisms of Al₂O₃ and Al₃Ti during FSP are understood to be a deformation-assisted interfacial reaction and deformation-assisted solution-precipitation, respectively, based on detailed microstructural observations. The microhardness, Young’s modulus and tensile strength of the FSPed composites were substantially enhanced compared with those of FSPed pure Al with the same processing history, and increased as the TiO₂ size decreased from 450 to 150 nm. The strengthening mechanisms of the FSPed composites included load transferring, grain refinement and Orowan strengthening, among which Orowan strengthening contributed the most to the yield strength of the composites.     

The Case for Whisker Reinforced Metals

The strength of Al₂O₃ whisker-metal composites calculated from available data are greatly superior to those of other high-temperature materials above 1200°F. To obtain the calculated composite strengths, it is necessary that adequate bonding be attained without deleterious whisker-matrix interactions. The effect of bonding on the mechanical properties of the whiskers should be clarified before composite fabrication is considered.     

Microstructure and mechanical properties of 7075 Al alloy based composites with Al2O3 nanoparticles

A new method was used to fabricate 7075 Al alloy based composites with Al₂O₃ nanoparticles to improve the distribution of particles. In this study, nano-sized particles were fed into the molten alloy through the flow of argon gas, then the Al₂O₃/7075 composites were prepared by solid-liquid mixed casting. The results indicated that the composite samples showed fine microstructure and achieved a homogeneous distribution of particles. Also, it was found that relative to the as-cast 7075 alloy, the Al₂O₃/7075 composites exhibited higher mechanical properties, which is due to the effect of uniform distributed Al₂O₃ nanoparticles reinforcement.     

Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al₂O₃ composites were studied. The effect of TiC and Al₂O₃ starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al₂O₃ composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al₂O₃ composites is due to a “true” cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.     

Effects of SiC interfacial coating on mechanical properties of carbon fiber needled felt reinforced sol-derived Al2O3 composites

3D carbon fiber needled felt and polycarbosilane-derived SiC coating were selected as reinforcement and interfacial coating, respectively, and the sol−impregnation−drying−heating (SIDH) route was used to fabricate C/Al₂O₃ composites. The effects of SiC interfacial coating on the mechanical properties, oxidation resistance and thermal shock resistance of C/Al₂O₃ composites were investigated. It is found that the fracture toughness of C/Al₂O₃ composites was remarkably superior to that of monolithic Al₂O₃ ceramics. The introduction of SiC interfacial coating obviously improved the strengths of C/Al₂O₃ composites although the fracture work diminished to some extent. Owing to the tight bonding between SiC coating and carbon fiber, the C/SiC/Al₂O₃ composites showed much better oxidation and thermal shock resistance over C/Al₂O₃ composites under static air.     

Investigation of the effect of Al2O3–Y2O3–CaO (AYC) additives on sinterability,microstructure and mechanical properties of SiC matrix composites: A review

Appropriate properties of SiC ceramic such as high hardness, low density, high melting point and high elastic modulus make this material as a favorite candidate for different industrial applications. Although some disadvantages including high sintering temperature, low sinterability, and low fracture toughness have restricted the use of this material, previous studies showed that using Al₂O₃-Y₂O₃ additives plays an effective role in the improvement of sinterability as well as the enhancement of the properties of these composites. Moreover, the addition of CaO results in the acceleration of the formation of molten phase and the improvement of sinterability. In addition, the use of these additives cause the formation of the intermetallic phases of Al₅Y₃O₁₂ (YAG) and CaY₂O₄ and by activating the mechanisms of crack deflection, crack bridging, phase transformation, strengthening the grain boundary and changing the fracture mode from intergranular to transgranular results in improved mechanical properties. This paper attempts to investigate the effect of using Al₂O₃–Y₂O₃–CaO (AYC) additives on sinterability, microstructure, and mechanical properties of SiC matrix composites including the composites reinforced with SiC fibers and SiC matrix nano-composites. Finally, the effect of the post-sintering annealing process under two conditions i.e., with and without applying pressure (pressureless sintering) on microstructure and mechanical properties has been studied.     

Thermal reliabilities of Sn-0.5Ag-0.7Cu-0.1Al2O3/Cu solder joint

The effects of trace addition of Al₂O₃ nanoparticles (NPs) on thermal reliabilities of Sn-0.5Ag-0.7Cu/Cu solder joints were investigated. Experimental results showed that trace addition of Al₂O₃ NPs could increase the isotheraml aging (IA) and thermal cyclic (TC) lifetimes of Sn-0.5Ag-0.7Cu/Cu joint from 662 to 787 h, and from 1597 to 1824 cycles, respectively. Also, trace addition of Al₂O₃ NPs could slow down the shear force reduction of solder joint during thermal services, which was attributed to the pinning effect of Al₂O₃ NPs on hindering the growth of grains and interfacial intermetallic compounds (IMCs). Theoretically, the growth coefficients of interfacial IMCs in IA process were calculated to be decreased from 1.61×10^-10 to 0.79×10^-10 cm²/h in IA process, and from 0.92×10^-10 to 0.53×10^-10 cm²/h in TC process. This indicated that trace addition of Al₂O₃ NPs can improve both IA and TC reliabilities of Sn-0.5Ag- 0.7Cu/Cu joint, and a little more obvious in IA reliability.     

The Microstructures and Mechanical Properties of V2O5-Doped Al2O3/TiAl In-Situ Composites by Reactive Hot Pressing Process

Al₂O₃/TiAl composites are successfully fabricated by the in-situ hot pressing method from the elemental powders of Ti, Al, TiO₂, and V₂O₅. The effect of V₂O₅ addition on the microstructure and mechanical properties of the Al₂O₃/TiAl in-situ composites is investigated in detail. It is found that the as-synthesized composites mainly consist of V-dissolved γ-TiAl, α₂-Ti₃Al, and Al₂O₃ particles along with a small amount of V₃Al phase, and the in-situ-formed fine Al₂O₃ particles tend to disperse on the grain boundaries of TiAl matrix. With increasing V₂O₅ content, the density and Vickers hardness of the resulting composites gradually increase, whereas the fracture toughness and flexural strength first increase and then decrease with the increase of V₂O₅ content. The composite with 3.5 wt.% V₂O₅ has the maximum value of 9.35 MPa m^1/2 and 713.36 MPa for the fracture toughness and flexural strength, respectively. The toughening mechanism is also discussed in detail.     

Preparation and characterization of Mo/Al2O3 composites

In order to improve the performance of molybdenum, the Mo/Al₂O₃ composites were prepared by using a hydrothermal method for the synthesis of the precursor powders and subsequent powder metallurgical processing. The morphologies of the composite powders and the microstructures and properties of the composites were investigated. Compared with the pure Mo powder, the grains of composite powders are smaller because of the existence of the fine Al₂O₃ particles. The results from the sintered composites show that the fine Al₂O₃ particles are evenly distributed in the Mo matrix and well bonded with the Mo matrix. With increasing Al₂O₃ content, all the values of the micro-hardness, compressive strength and flow stress at 0.08 strain are increased. The strengthening effect is more remarkable at elevated temperatures. At room temperature, the compressive strength and the flow stress at 0.08 strain of the composite with 40 vol.% Al₂O₃ are 1.67 and 2.01 times greater than those of pure molybdenum, respectively, while the values are up to 2.02 and 2.52 at 1100 °C.