SiCw／MB15镁基复合材料挤压板材的力学性能和断口分析

研究了SiCw/MB15镁基复合材料板材的力学性能和拉伸断口,研究结果表明,SeCw/MB15镁基复合材料板材中晶须轴向平行于挤压方向排布,分布均匀,与基体合金的结合良好,晶须排布的方向性对SiCw/MB15镁基复合材料板材的弹性模量及延伸率几乎没有影响,但是SiCw/MB15镁基复合材料板材的抗拉强度表现出明显的方向性。     

粉末冶金法制备SiC晶须增强MB15镁基复合材料

采用粉末冶金法制备了SiC晶须增强镁基复合材料(SiCW／MB15)试样。通过检测基体显微硬度探讨了SiCW对镁合金时效规律的影响，并借助扫描电镜(SEM)、透射电镜(TEM)和拉伸试验，研究了混粉方式对复合材料室温力学性能、SiCW分布及显微结构的影响。结果表明，MB15及其复合材料的时效硬化曲线上均存在双峰现象；SiCW的加入既提高了MB5的硬度，又加快了其时效速度：混粉方式对晶须分布及SiCW／MB15复合材料的室温力学性能影响很大。     

挤压态SiC2／1050A复合材料的强度预测

为了考察挤压态复合材料的性能，挤压铸造SiCw/1050A复合材料被热挤压，对复合材料中的组织结构参数进行了测定和分析，并采用混合法则对挤压态SiCw/1050A复合材料的强度进行了预测，结果表明，挤压导致复合材料中组织参数发生变化（包括晶须和基体），进而影响复合材料的性能，用修正的混合定律预测挤压态SiCw/1050A复合材料纵向强度时必须增大表征基体贡献的系数c到6左右才能得到满意的结果，表明基体强度是影响SiCw/1050A复合材料强度的一个重要因素。     

粉末冶金法制备15镁基复合材料组织及性能的研究

采用粉末冶金法制备了SiC颗粒及晶须增强MB15镁基复合材料的试样，借助扫描电镜对其显微结构及拉伸断口进行了观察分析。同时，比较了SiC颗粒和晶须对MB15镁合金室温力学性能的影响。结果表明，SiC颗粒和晶须能显著提高MB15镁合金的室温强度和弹性模量，且SiC晶须的作用比SiC颗粒更明显。     

挤压态SiCw/1050A复合材料的强度预测

为了考察挤压态复合材料的性能,挤压铸造SiCw/1050A复合材料被热挤压。对复合材料中的组织结构参数进行了测定和分析,并采用混合法则对挤压态SiCw/1050A复合材料的强度进行了预测。结果表明,挤压导致复合材料中组织参数发生变化(包括晶须和基体),进而影响复合材料的性能。用修正的混合定律预测挤压态SiCw/1050A复合材料纵向强度时必须增大表征基体贡献的系数c到6左右才能得到满意的结果,表明基体强度是影响SiCw/1050A复合材料强度的一个重要因素。     

预制块制备对挤压铸造SiCW／ZM5复合材料性能的影响

制备了含不同粘结剂的ＳｉＣ晶须预制块,并采用挤压铸造法制备出含不同粘结剂的ＳｉＣｗ／ＺＭ５镁基复合材料,对其组织结构和力学性能进行了研究。结果表明,采用含酸性磷酸铝粘结剂制备的ＳｉＣｗ／ＺＭ５镁基复合材料的性能最佳,这可能和粘结剂与晶须以及基体合金的界面反应有关     

粉末冶金法制备MB15镁基复合材料组织及性能的研究

采用粉末冶金法制备了 Si C颗粒及晶须增强 MB15镁基复合材料的试样 ,借助扫描电镜对其显微结构及拉伸断口进行了观察和分析。同时 ,比较了 Si C颗粒和晶须对 MB15镁合金室温力学性能的影响。结果表明 ,Si C颗粒和晶须能显著提高 MB15镁合金的室温强度和弹性模量 ,且 Si C晶须的作用比 Si C颗粒更明显     

挤压变形对SiCw/ZK51A镁基复合材料组织和性能的影响

利用透射电镜、扫描电镜和拉伸试验等实验方法,研究了铸态和挤压态ＳｉＣｗ／ＺＫ５１Ａ镁基复合材料的组织与力学性能。结果表明,挤压铸造ＳｉＣｗ／ＺＫ５１Ａ复合材料经等温热挤压后,其力学性能有很大提高。主要原因是：挤压变形能消除铸造缺陷,增强ＳｉＣ晶须与ＺＫ５１Ａ镁合金基体的界面结合,使复合材料中ＳｉＣ晶须发生定向分布,沿挤压方向呈准一维分布特征,晶须的增强承载能力得到充分发挥。     

SiCw/AZ91复合材料的制备与力学性能研究

采用粉末冶金法制备了不同配比的Si Cw/AZ91镁基复合材料,并研究了其显微组织和力学性能。结果表明,加入适量的SiCw后,SiCw弥散分布在晶界上,有效提高了镁基复合材料的强度和硬度。     

低体积分数SiCW/Al复合材料的制备

提出了一种低体积分数SiCw／Al复合材料的制备方法，将SiCw与铝粉混合制成预制件，再将其与铝基体用挤压铸造法制成复合材料，通过微观组织观察发现，用该方法制备的低体积分数复合材料中晶须分布均匀。经挤压后可使铝粉颗粒和铝基体充分融合。断口观察发现，复合材料中晶须与基体间的结合非常好。     

热挤压对不同搅拌时间制备的纳米SiCp/Mg-9Al-1Zn复合材料组织和性能的影响

通过半固态搅拌铸造和热挤压变形复合工艺制备出了质量分数为1%的纳米SiCp/Mg-9Al-1Zn镁基复合材料。研究了搅拌时间分别为10min和30min时对纳米SiCp/Mg-9Al-1Zn镁基复合材料的显微组织和力学性能的影响。结果表明,对于铸态的纳米SiCp/Mg-9Al-1Zn镁基复合材料来说,搅拌时间为30min时,基体的晶粒细化,但在晶界处析出的Mg17Al12相数量增多,网状化严重且SiC团聚增加,使得复合材料的力学性能下降。而通过热挤压后,复合材料形成了粗晶与细晶交替的组织结构。特别是对于搅拌时间为30min的复合材料,细晶区增多且纳米SiC颗粒分布更加均匀, 这就使得力学性能高于搅拌10min的挤压态的SiCp/Mg-9Al-1Zn复合材料。     

热挤压变形对搅拌铸造SiCp/2024复合材料显微组织与力学性能的影响

利用搅拌铸造?热挤压工艺制备SiCp/2024复合材料板材。通过金相观察(OM)、扫描电镜(SEM)及力学性能测试等手段研究了该复合材料热挤压变形前后的显微组织与力学性能。结果表明,复合材料铸坯主要由大小为80μm~100μm的等轴晶组成,晶界第二相粗大呈非连续状分布,SiC颗粒较均匀地分布于基体合金,大部分SiC颗粒沿晶界分布,少数颗粒分布于晶内;热挤压变形后,显微孔洞等铸造缺陷和SiC颗粒团聚现象明显消除,SiC颗粒及破碎的第二相沿热挤压方向呈流线分布,复合材料的强度和塑性显著提高;拉伸断口表明,热挤压变形有利于改善SiC颗粒与基体合金的界面结合;SiCp/2024复合材料主要的断裂方式为SiC颗粒断裂和SiC/Al的界面脱粘。     

FORMING PROCESS OF HOT-EXTRUDED SiCw/6061Al COMPOSITES(Ⅰ)

１ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｒｅｃｅｎｔｙｅａｒｓ，ｍｏｒｅａｎｄｍｏｒｅｃｏｎｔｉｎｕｏｕｓｌｙｏｒｄｉｓｃｏｎｔｉｎｕｏｕｓｌｙｒｅｉｎｆｏｒｃｅｄｍｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓ（ＭＭＣｓ）ｈａｖｅｂｅｅｎｕｓｅｄｔｏｍａｋｅｓｔ...     

反复塑性变形对SiC_p/AZ31镁基复合材料组织和性能的影响

采用反复塑性变形(RPW)技术,结合挤压工艺制备出SiC颗粒增强AZ31镁基复合材料,研究了循环次数(RPW次数)对SiC_p/AZ31镁基复合材料显微组织和性能的影响.结果表明,反复塑性变形具有明显的AZ31基体晶粒细化、SiC_p细化和分散作用,能显著提高SiC_p/AZ31复合材料的抗拉强度和硬度,并改善其塑性.在SiC_p的体积分数为4%时,经RPW为300次的热挤压后,AZ31基体晶粒粒径达到最小值20 μm,SiC_p被粉碎成3 μm以下的微粒,且弥散分布于合金基体中,复合材料的室温抗拉强度和硬度(HV)达到或接近最大值,分别为359 MPa和107.     

Microstructures and mechanical properties of Al 2519 matrix composites reinforced with Ti-coated SiC particles

Ti-coated SiC_p particles were developed by vacuum evaporation with Ti to improve the interfacial bonding of SiC_p/Al composites. Ti-coated SiC particles and uncoated SiC particles reinforced Al 2519 matrix composites were prepared by hot pressing, hot extrusion and heat treatment. The influence of Ti coating on microstructure and mechanical properties of the composites was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the densely deposited Ti coating reacts with SiC particles to form TiC and Ti₅Si₃ phases at the interface. Ti-coated SiC particle reinforced composite exhibits uniformity and compactness compared to the composite reinforced with uncoated SiC particles. The microstructure, relative density and mechanical properties of the composite are significantly improved. When the volume fraction is 15%, the hardness, fracture strain and tensile strength of the SiC_p reinforced Al 2519 composite after Ti plating are optimized, which are HB 138.5, 4.02% and 455 MPa, respectively.     

Characterization of hot pressed SiC whisker reinforced TiB2 based composites

TiB₂–SiC ceramic composites, with different contents of SiC whiskers (SiC_w), as a ceramic sinter-additive, were prepared by the hot pressing process at 1850 °C for 2 h under a pressure of 20 MPa. For comparison, a monolithic TiB₂ ceramic was also fabricated under the identical temperature, pressure, atmosphere, and holding time by the hot pressing process. The effects of fabrication process and SiC whiskers on microstructural features, phase evolution and mechanical properties were investigated. Hardness measurements revealed an initial increase in hardness for TiB₂–SiC compared to TiB₂. Also the improvement of the fracture toughness was attributed to the toughening and strengthening effects of SiC whiskers such as crack deflection. The results showed that promoted densification of TiB₂–SiC ceramic composites is due to addition of SiC whiskers and reduction of oxide impurities by reacting with SiC whiskers and removing them from the surface layer of TiB₂ particles. The reaction between TiB₂ particles and SiC whiskers led to in-situ formation of TiC phase in the matrix as well. In general, it is concluded that the sinterability of TiB₂-based composites was remarkably improved by introducing SiC whiskers compared to the single phase TiB₂ ceramic.     

MICROSTRUCTURE AND PROPERTIES OF SiC_w/6061Al COMPOSITE The Author is now with Institute of Metal Research,Academia Sinica,China

The SiC_w/Al composite prepared by squeeze casting has a combination of superior roomtemperature specific strength and modulus together with excellent thermal properties.Theextrusion can make an improvement on the strength and ductility of the composite from 582MPa as squeeze casted up to 639 MPa,and on the transformation from isotropic to theanisotropic structure.This seems to be explained by the orientation of whiskers and thedensification of dislocations in matrix.TEM observation indicates that the stacking fault isthe usual planar defect on the SiC_w surface.     

Processing and response of aluminum-lithium alloy composites reinforced with copper-coated silicon carbide particulates

Lithium-containing aluminum alloys have shown promise for demanding aerospace applications because of their light weight, high strength, and good damage tolerance characteristics. Additions of ceramic reinforcements to an aluminum-lithium alloy can significantly enhance specific strength, and specific modulus while concurrently offering acceptable performance at elevated temperatures. The processing and fabrication of aluminum-lithium alloy-based composites are hampered by particulate agglomeration or clustering and the existence of poor interfacial relationships between the reinforcing phase and the matrix. The problem of distribution of the reinforcing phase in the metal matrix can be alleviated by mechanical alloying. This article presents the results of a study aimed at addressing and improving the interfacial relationship between the host matrix and the reinforcing phase. Copper-coated silicon carbide particulates are introduced as the particulate reinforcing phase, and the resultant composite mixture is processed by conventional milling followed by hot pressing and hot extrusion. The influence of extrusion ratio and extrusion temperature on microstructure and mechanical properties was established. Post extrusion processing by hot isostatic pressing was also examined. Results reveal the increase in elastic modulus of the aluminum-lithium alloy matrix reinforced with copper-coated SiC to be significantly more than the mechanically alloyed Al-Li/SiC counterpart. This suggests the possible contributions of interfacial strengthening on mechanical response in direct comparison with a uniform distribution of the reinforcing ceramic particulates.     

Effect of SiC whiskers on the oxidation protective properties of SiC coatings for carbon/carbon composites

In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.