WC_p/2024Al复合材料疲劳性能研究

利用粉末冶金法制备了WC颗粒体积分数分别为8.0%,11.8%,16.7%的WCp/2024Al复合材料,采用PQ1-6纯弯曲疲劳试验机对其进行高周疲劳性能测试,通过扫描电镜观察复合材料疲劳试验后的疲劳断口。结果表明:WCp/2024Al复合材料疲劳极限和疲劳寿命随着WC体积分数的增加而升高;复合材料的疲劳源产生于试样表面有缺陷或表面附近颗粒团聚的薄弱部位;随着WC体积分数的增加,WCp/2024Al复合材料的疲劳断口韧窝组织呈减少的趋势,脆性断裂特征逐渐明显;由空洞形核与长大造成的界面脱粘和基体相破坏是WCp/2024Al复合材料疲劳断裂的主要形式。     

热变形加工对WC_p/2024Al复合材料组织结构和力学性能的影响

本文采用真空热压方法制备了WCp/2024Al复合材料,研究了真空热压-热锻压-热轧制等热变形加工工艺对复合材料微观组织结构和力学性能的影响.结果表明,热锻压和热轧制加工显著细化了基体Al合金组织,改善了WC颗粒的分散性,促进了两相界面的冶金结合,材料强度得到大幅度提高;高变形速率的热锻压和热轧制工艺可降低复合材料界面WAl12中间相的生成温度,大量中间相的生成导致材料塑性下降.     

烧结工艺对Ti/Al2O3复合材料性能的影响

本文利用放电等离子烧结技术探讨了烧结温度和保温时间对40%Ti(体积分数)/Al2O3(体积分数)复合材料性能的影响.实验结果表明复合材料的性能受烧结温度的影响最为显著,过度的延长保温时间会使晶粒发生异常长大,使得复合材料性能降低.烧结温度1 300℃,保温8 min,制备的复合材料力学性能最佳,其弯曲强度、断裂韧性、显微硬度和相对密度分别为1002.22 MPa、19.73 MPa*m1/2、18.14 GPa和99.74%.     

Ti_3SiC_2/Al-Mg复合材料制备及界面反应研究

以Ti_3SiC_2作为外加增强相,Al-Mg合金为基体,通过放电等离子烧结法(SPS)制备了Ti_3SiC_2/Al-Mg复合材料,并研究了后续热处理对界面反应的影响。结果表明,SPS法能成功制得Ti_3SiC_2/Al-Mg复合材料,热处理过程中温度是影响界面反应是否发生的重要因素。当温度低于550℃时,未发生界面反应;温度达到600℃时,发生轻微的界面反应,主要产物是Al4C3和Mg2Si。界面反应的发生导致材料硬度增大,密度和导电率降低。此外,随着基体中Mg含量的增加,Ti_3SiC_2/Al-Mg复合材料的晶粒尺寸逐渐减小,硬度逐渐增大。     

发动机用石墨烯表面镀Cu增强钛基复合材料的制备及力学性能

通过微波烧结法制备石墨烯(GNPs)表面镀Cu增强钛基(Ti6Al4V)复合材料,探讨石墨烯表面镀Cu后对钛基复合材料显微组织和力学性能的影响。结果表明:石墨烯表面成功镀覆一层较均匀分布的Cu颗粒;石墨烯与基体Ti界面反应严重,容易生成粒径为2~5μm的TiC,石墨烯表面镀Cu后,界面反应产生的TiC含量更多,同时生成了Ti_2Cu相;相比于单纯外加石墨烯,石墨烯表面镀Cu后,提高了复合材料的力学性能,其相对密度、显微硬度、抗压强度分别达到95.48%、468 HV_(0.1)、1 406 MPa;室温磨损机制由基体(Ti6Al4V)的磨粒磨损转变为GNPs-Cu/Ti6Al4V复合材料的黏着磨损。     

工艺参数对Fe3Al/Al2O3复合材料力学性能的影响研究

以自制的亚微米Fe3Al为增强相、Al2O3为基体相,通过常压烧结制备出Fe3Al/Al2O3复合材料,研究了Fe3Al含量、烧结温度及保温时间对复合材料力学性能的影响.结果表明:增加Fe3Al含量、提高烧结温度及延长保温时间都可以不同程度的提高复合材料力学性能.最佳工艺参数为:Fe3Al含量(质量分数)为15%,成形压力为2488MPa,烧结温度为1380℃.此条件下制备的复合材料的各项力学性能较好:相对密度为93%,维氏硬度为9.3GPa,断裂韧度为7.51MPa·m1/2.烧结温度对提高复合材料力学性能的影响较大.     

高导热鳞片石墨/2024Al组织与性能研究

以2024铝合金为基体、平均粒径100μm的高导热鳞片石墨为增强体,并对鳞片石墨表面镀钛,通过放电等离子烧结(spark plasma sintering, SPS),制备石墨体积分数为60%的高导热鳞片石墨/2024Al复合材料。烧结温度是540℃,烧结压力是50 MPa,烧结时间5 min。通过金相显微镜(OM)、 X射线衍射仪(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对未镀钛和镀钛鳞片石墨/2024Al复合材料的显微组织和成分进行了分析和表征,结果显示,复合材料中都没有有害相Al_4C_3的生成,镀钛鳞片石墨/2024Al复合材料具有更好的界面结合。测试其热导率、热膨胀系数以及抗弯强度,未镀钛和镀钛鳞片石墨/2024Al复合材料在沿鳞片石墨片层方向的热导率分别为398和368 W·m~(-1)·K~(-1),变化不大;垂直于鳞片石墨片层方向的热导率分别为35和56 W·m~(-1)·K~(-1),有较大提高。镀钛后,复合材料的热膨胀系数降低,抗弯强度为96 MPa,和未镀钛鳞片石墨/2024Al的抗弯强度37 MPa相比,有较大提高。对鳞片石墨表面镀钛,能够改善碳与铝的界面结合,提高鳞片石墨/2024Al复合材料的热物理与力学性能。     

掺杂Nb2O5对RHP合成Al2O3-TiAl复合材料的影响

采用反应热压(RHP)工艺,利用Ti、Al、TiO2及Nb2O5之间的放热反应,在较低温度下制备了Nb2O5强化Al2O3/TiAl复合材料.借助XRD、OM及SEM等手段,考察了Nb2O5对Al2O3/TiAl复合材料的相分布及组织结构的影响.结果表明:材料产物由γ-TiAl、α2-Ti3Al、Al2O3和NbAl3相构成,Al2O3颗粒分布于基体交界处,存在一定的偏聚.Nb2O5的引入,使得γ-TiAl相含量减少,α2-Ti3Al相含量增大;基体晶粒有所细化,且分布逐渐趋于均匀.当Nb2O5的引入量(质量分数)为6%时,组织主要由α2-Ti3Al/γ-TiAl层片状晶团组成,出现了较完整的γ-TiAl晶粒,属于近片层(NL)组织结构,层片状晶团的尺寸小于50μm,γ晶粒尺寸小于5μm.力学性能测试表明,当Nb2O5的引入量(质量分数)为6%时,材料的抗弯强度达到最大值,约为593MPa,硬度为4.77 GPa;断裂韧度达到最大值,为8.93MPa·m1/2,具有可接受的力学性能.     

SiC/Ti_3Al复合材料原位合成及其界面反应动力学研究

利用TC4,Al廉价材料,通过磁控溅射物理气相沉积技术制备SiC先驱丝,利用热等静压工艺,在温度1423 K,压力170 MPa条件下进行复合,反应时间为1 h,通过原位反应生成Ti3Al基体,从而制备SiC纤维增强Ti3Al基复合材料。通过扫描电镜(SEM)和能谱分析(EDS)观察SiC纤维增强Ti3Al基复合材料基体与界面的微观组织形貌及界面元素分布,利用透射电镜(TEM)分析复合材料基体的物相结构,并对SiC纤维增强Ti3Al基复合材料的界面反应进行动力学分析。结果表明,利用TC4,Al制备的SiC先驱丝,通过原位反应可生成Ti3Al基体,属于六方晶系,组织为等轴晶,晶粒尺寸约为1μm。通过磁控溅射和热等静压工艺制备SiC纤维增强Ti3Al基复合材料,可缩短工艺流程,节约成本。根据SiC纤维增强Ti3Al基复合材料界面反应层生长动力学分析,得到界面反应层生长动力学方程:δ=2.73×10-6exp(-257.09×103/RT)t1/2,可准确预测连续碳化硅纤维增强Ti3Al基复合材料在制备和使用过程中界面反应层的生长规律,为其应用提供理论依据。     

B_(4)C-Al复合材料制备过程的化学反应北大核心

采用机械合金化和微波烧结法制备了B_(4)C-Al复合材料,采用DSC和XRD分析法,研究了B_(4)C和Al在20~1500℃温度区间内的化学反应和生成产物;采用扫描电子显微镜和透射电镜分析了B_(4)C-Al复合材料的相组成。结果表明:在625~690℃温度区间,B_(4)C和Al反应生成产物为Al_(3)BC和AlB_(2);在1150~1185℃温度区间内,B_(4)C和Al反应生成产物为Al_(4)C_(3)和AlB_(12)C_(2);在1320~1350℃温度区间,B_(4)C和Al反应生成产物为AlB_(12)C_(2)。     

元素粉末法制备SiC_p/2024Al复合材料扩散均匀化研究

利用元素粉末真空热压工艺制备SiCp/2024Al复合材料,采用光学显微镜(OM)、扫描电镜(SEM)和X射线衍射(XRD)对真空热压中各元素粉末的扩散均匀化过程及扩散均匀化温度和保温时间对颗粒增强Al基复合材料显微组织的影响进行了研究。结果表明,该复合材料热压态组织中有Cu的富集相存在;随着扩散均匀化处理过程中温度的升高和时间的延长,Al2CuMg相完全溶入Al基体中,Cu的扩散逐渐充分,各元素分布趋于均匀。该复合材料最佳扩散均匀化处理工艺参数为500℃保温3h。     

Microstructure evolution in metal-intermetallic laminate (MIL) composites synthesized by reactive foil sintering in air

Metal-intermetallic (aluminide) laminate (MIL) composites have been fabricated in air using dissimilar metal foils. Foils of varying Al thickness were reacted with foils of Ti-3Al-2.5V resulting in microstructures of well-bonded metal-intermetallic layered composites with either Ti or Al residual metal layers alternating with the Al₃Ti intermetallic layers. The MIL composites exhibit a very high degree of microstructural design and control. Microstructure characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractometry (XRD) has been performed, and basic physical properties of the Ti-Al composites have been determined. The Ti-Al reaction has been studied by interrupting the reaction processing, in steps, to observe the microstructural changes. An oxide layer between the Ti and Al foils initially controls the reaction kinetics. After breakdown of the oxide layer, a two-phase Al+Al₃Ti layer (∼10 μm thickness) is formed. After formation of the two-phase layer, liquid phases are continuously present, and Al₃Ti spherules (∼10 μm diameter) are formed through interfacial tension, solidify (in times of 2 to 4 μs), and are expelled into the liquid. This mechanism allows for a continuous reaction interface and higher reaction rates. Both reaction regimes, diffusion through the oxide, and, subsequently, the intermetallic phase reaction mechanism result in linear kinetics.     

Fabrication,microstructures and properties of 50 vol.-% SiCp/6061Al composites via a pressureless sintering technique

Commercial F500 SiC powder and 6061 Al powder were chosen to fabricate the 50?vol.-% SiCp/6061Al composites via pressureless sintering. Effects of pre-treatment of the SiC powder and sintering temperature on the microstructures and properties of the composites were studied. Densification mechanism and interfacial reaction of the composites were also investigated. The results show that the composites have a high sintering ability and a low interfacial reaction activity. The density, bending strength and thermal conductivity of the composites are all sensitive to the sintering temperature. The composites sintered at 680°C are nearly fully dense and have the following optimal properties: the relative density of 98.5%, the bending strength of 495?MPa, the TC of 153?W/(m?K) and the coefficient of thermal expansion of 8.1?×?10^?6/°C (50–100°C), which are superior to most of the SiCp/Al composites of the similar composition reported previously.     

粉末冶金法制备WC-Ni3Al复合材料的组织与性能

在WC粉末中直接添加Ni、Al元素粉末,通过在液相烧结过程中反应合成Ni3Al来制备WC-Ni3Al复合材料,对该材料进行组织结构观察及力学性能测定,分析铝含量对合金致密化和镍铝相形成种类的影响,并对材料的抗氧化性能进行测试。结果表明,制备的WC-Ni3Al复合材料具有圆钝的WC晶粒形貌,粘结相中除Ni3Al相外还有少量的NiAl和Ni相;铝含量对WC-Ni3Al材料致密度的影响主要与高熔点的NiAl的形成量有关。与普通WC-15Ni硬质合金的抗弯强度(1 900 MPa)和硬度(82.6 HRA)相比,WC-15Ni3Al复合材料具有低的室温抗弯强度和高的硬度,分别为1 170 MPa和86.5 HRA。随Ni3Al含量(质量分数)从15%增加到30%,WC-30Ni3Al复合材料的室温抗弯强度增加,而硬度降低,分别为1 660 MPa和81.7 HRA,其高温抗氧化性能比WC-30(Co-Ni-Cr)硬质合金提高1个数量级。     

Role of matrix alloy chemistry on the interfacial reaction and solidification of metal matrix composites

Equilibrium Si content required to suppress the interfacial reaction in 2124 Al/SiC and A356 Al/SiC has been thermodynamically predicted by combining Wilson equation with the Miedema model. In 2124 Al/SiC composites, good agreement between thermodynamically calculated and experimental result has been observed in the solid and semi solid state reaction. At higher temperature above 750°C, thermodynamically calculated results are much higher than that of experimental values. Strong influence of reinforcement size and volume fraction on the extent of interfacial reaction is also observed in 2124 Al/SiC composites. In these composites, formation of protective layer of Al₄C₃ crystals over SiC surface plays significant role in predicting the equilibrium Si content. The influence of reinforcement particle size and volume fraction on the extent of reaction has not been observed in A356 Al/SiC composites and irrespective of reaction temperature the thermodynamically calculated equilibrium Si contents for A356 Al/SiC composites agrees well with the experimental results.     

Mechanical Properties of Aluminium-Graphene Composite Synthesized by Powder Metallurgy and Hot Extrusion

The present work focuses on the development of multilayer graphene reinforced aluminium metal matrix composites by powder metallurgy followed by hot extrusion. Microstructure, grain size analysis and mechanical properties of hot extruded unreinforced aluminium and graphene reinforced aluminium composites are presented here. Microstructure shows uniform distribution of graphene throughout the matrix. Experimental results reveal significant increase in hardness as well as tensile strength of composite as compared to unreinforced aluminium. The improvements in properties are attributed to uniformly dispersed graphene sheets, an excellent interfacial bonding between graphene and aluminium matrix and grain refinement caused by the addition of graphene. Further, the strengthening mechanisms involved in the aluminum-graphene composite have been discussed. The fracture studies show the transition of ductile fracture in case of pure aluminium to brittle fracture in case of aluminium-graphene composites.     

Effects of Cerium on the Mechanical Properties of the ZA22／Al_2O_3 Composites

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镁锂基复合材料界面结构及热力学分析

制备了碳纤维及ＳｉＣ晶须增强的Ｍｇ８Ｌｉ１Ａｌ基复合材料。利用透射电镜,高分辨电子显微镜研究了Ｍｇ８Ｌｉ１Ａｌ／ＳｉＣｗ复合材料的界面结构,发现ＳｉＣ晶须与基体合金界面结合良好,没有明显的反应物。     

原位合成TiB2对B4C/2024Al合金复合材料组织与力学性能的影响

在B4C粉末中加入5%高纯TiO2,经过压制和烧结制备B4C-TiB2陶瓷预制体,然后在氩气气氛中1 200℃下浸渗2024铝合金制得B4C-TiB2/Al合金复合材料。对该复合材料进行力学性能测试、X射线衍射分析、显微组织观察和断口分析。结果表明:该复合材料主要由B4C,Al,Al3BC和AlB2相组成,原位合成的TiB2使B4C/Al合金复合材料的抗弯强度和断裂韧性显著提高,分别达到361 MPa和7.49 MPa m1/2,增幅分别为14.6%和11.5%,但密度变化很小。原位合成TiB2使B4C/Al合金复合材料的抗弯强度和断裂韧性提高主要来源于金属铝塑性变形的裂纹桥接机制、TiB2细化晶粒及微裂纹引起的主裂纹偏转分叉机制。     

Mg元素掺杂磷酸铈无机颜料的制备研究

用固态化学反应法以Mg为掺杂元素制备磷酸铈无机颜料,系统地研究了掺杂量、反应温度、反应时间三个因素对反应产物颜色的影响.反应物试样分别进行X射线衍射分析(XRD)、粒度测试和色度测试.试验结果表明,Mg元素的掺杂量起关键作用,当n(Mg)/n(Ce)为0.2～0.3时,可以得到直观上的草绿色试样.经XRD分析可知掺Mg后试样为磷酸铈单斜晶系粉末;经粒度检测可知,掺杂后磷酸铈颜料粉末的平均粒径在6.m～7 μm之间;最后色度测试得出的色度坐标为L*=68.2、a*=-9.3、b*=18.7,色度坐标表示的颜色为绿色.