SiCp／LD2复合材料的微区力学性能

用ＵＭＨＴ３ 型超显微硬度仪测试ＳｉＣｐ／ＬＤ２ 复合材料界面附近基体中的硬度值, 结果表明,由于热膨胀系数差异, 复合材料中的热残余应力超过基体的屈服极限, 导致界面附近基体内存在热残余应变, 并使基体应变硬化, 因而超显微硬度值的变化可以反映热残余应变的分布状况。界面附近基体的超显微硬度随颗粒尺寸、距界面的距离和颗粒的尖锐程度而变化, 与有关复合材料中热残余应变分布的计算结果吻合。     

SiCp/Al复合材料热循环后尺寸稳定性

采用无压渗透法制备了SiCp/Al复合材料,经过不同预处理,以及含不同组元的SiCp/Al复合材料,在热机械分析仪中进行20～180℃热循环,测试复合材料热循环后的长度变化。以单位长度的变化,即残余应变来分析热循环后尺寸稳定性。结果表明,SiCp/Al复合材料在热循环后会产生残余应变,残余应变随热循环次数增加而减小,尺寸趋于稳定。预处理的不同,热循环后残余应变也不同,冷热循环预处理的热循环后残余应变最小。SiCp/Al复合材料中颗粒尺寸较大以及基体较硬,则复合材料热循环后尺寸稳定性也较高。     

界面改性对SiCf/Cu基复合材料热膨胀性能的影响

研究了SiCf/Cu基复合材料分别在有无Ti6Al4V界面改性涂层两种情况下的纵向热膨胀行为,并采用扫描电镜对热循环后的试样进行显微形貌观察。结果表明,界面结合强度对纤维增强金属基复合材料的纵向热膨胀行为有很大影响。对于没有Ti6Al4V涂层的复合材料,其热膨胀行为不稳定,在经历连续两次热循环后,其纵向均表现为正的残余应变,原因是基体发生了严重的界面脱粘、滑移和膨胀;而对于有Ti6Al4V涂层的复合材料,其纵向热膨胀系数明显减小,两次热循环后其尺寸保持稳定,纤维/基体界面结合也保持稳定。     

超声深滚作用力对Ti-6Al-4V合金微观组织及表面性能的影响

目的改善Ti-6Al-4V合金的微观组织及表面性能。方法用不同作用力(150、250、350、450 N)的超声深滚工艺对Ti-6Al-4V进行表面处理。通过金相显微镜观察、透射电镜分析、维氏硬度测试和残余应力测试,分别评价表面处理后材料的显微组织变化、显微硬度分布和残余应力分布。结果随着超声深滚作用力的增加,表面塑性变形层厚度增大,但增大趋势随作用力的增加而趋缓,450 N超声深滚作用后,塑性变形层厚度最大。超声深滚处理后,材料表面出现纳米晶,随作用力的增加,纳米晶会逐渐转为非晶态。350 N深滚后,距表面220μm处会出现少量的孪晶及大量位错堆积。随着塑性应变的加剧,孪晶逐渐消失,晶粒不断细化。材料近表面硬度提高明显,提高幅度同作用力呈正相关。材料基体的硬度为328 HV。在150 N力作用后,材料距表面50μm处的硬度能达到343 HV,而在450 N力作用后可以达到381 HV。随着超声深滚作用力的增加,材料近表面的残余压应力总体呈现增加趋势,最大残余应力可达到-875 MPa;残余应力的分布范围随力的增加,从0.40 mm增长到0.58 mm。另外,不同作用力作用后,材料最大残余压应力均出现在距表面20~40μm处。结论超声深滚作用可有效改变TC4合金的表面微观组织及性能,进而影响其结构完整性和服役寿命。     

2D Cf／Mg-2．0Re-0．2Zr复合材料的尺寸稳定性

采用压力浸渗法制备碳纤维织物(2D Cf)及单向碳纤维(1D Cf)增强镁合金复合材料,测试丁两种复合材料在50-350℃范围内的热膨胀行为.结果表明,2D Cf/镁合金复合材料(简称2D)平面内不同方向的平均热膨胀系数均随温度升高不断降低.从50到350℃,0°/90°方向的甲均热膨胀系数由4.03×10-6℃-1降至1.83×10-6℃-1;45°方向的平均热膨胀系数由4.53×10-6℃-1降至2.31×10-6℃-1.根据推导公式可以准确计算2D增强复合材料20-150℃范围内0°/90°方向的平均热膨胀系数.20～150℃热循环测试结果表明,2D复合材料具有较好的尺寸稳定性,在热循环过程中存在应变滞后现象,其残余塑性变形主要是基体合金在热应力作用下产生的塑性变形,并且从第2次热循环起,复合材料在热循环中产生的净应变不随热循环次数增加而变化.     

Cu-Nb复合线材在形变与退火过程中显微结构演变的研究

采用SEM和TEM,对不同形变量及退火温度下的Cu-Nb微观复合线材的显微组织结构进行了分析,并对形变和退火试样进行了硬度测试.结果表明:随着形变量增大,材料界面密度及其增加速率逐渐增大.当材料结构达到纳米尺寸时(应变=24.8),界面密度及其增加速率显著增加,使得硬度及其增加速率明显增大,同时伴随有纳米Cu基体内部层错和旋转晶界的产生.退火过程中Cu基体的显微组织变化表现出明显的多尺度效应,其变化可分为3个阶段:微米及亚微米Cu基体先发生回复再结晶,而纳米Cu基体回复再结晶受到抑制;纳米Cu基体回复再结晶;Nb丝球化及长大.     

SiCP/Al复合材料温度变化引致尺寸不稳定性的研究

研究了ＳｉＣｐ／Ａｌ系复合材料经不同热处理后在温度反复变化时的尺寸稳定性，结果表明，在温度反复循环后会产生累积残余应变εｅｒ，随循环次数的增多，εｃｒ减小，尺寸趋于稳定，预处理对热循环累积残余应变有影响，退火态εｃｒ最大，时效态次之，而预循环态最小。复合材料中颗粒尺寸越大，颗粒体积分数越高以及基体越硬均对抵抗环境温度变化尺寸稳定性有利。与均质的纯铝相比较，复合材料的热循环累积残余应变较大，抵抗温度     

钴磷合金镀层在热循环中组织和性能的变化

选用3Cr2W8V为基体材料,对其进行钴磷化学镀,研究了该镀层在680～20℃热循环试验中组织和性能的变化。结果表明,Co-P合金镀层经过一定的循环次数后析出Co2P及CoP2等磷化物;粗大的磷化物与镀层的相界面为热裂纹形成及优先扩展的区域;镀层的表面硬度随热循环次数的增多而下降;镀层的厚度影响材料的热疲劳寿命;镀层随热循环次数的增多而破坏加剧,最终与基体分离,使基体受损。     

应变过程中Cu-6%Ag合金的组织纤维化及导电特性

通过冷拉拔应变制备了纤维相强化的Cu-6%Ag(质量分数,下同)合金,研究了不同应变条件下合金的显微组织和电阻率变化规律,讨论了应变对Cu-6%Ag合金导电性能的影响机制.随应变程度的增加,原始组织中的Cu基体晶粒、不平衡共晶体及次生相粒子最终演变成细密的纤维结构,合金电阻率上升.次生相界面、共晶体与Cu基体界面及位错对电子散射作用程度的变化导致了合金电阻率在不同变形程度范围内有不同的变化规律.当变形超过一定程度后,电阻率升高规律与来自较高Ag含量合金中纤维相尺度进入纳米数量级的界面散射模型相符.     

应变过程中Cu-6%Ag合金的组织纤维化及导电特性

通过冷拉拔应变制备了纤维相强化的Cu-6%Ag(质量分数,下同)合金,研究了不同应变条件下合金的显微组织和电阻率变化规律,讨论了应变对Cu-6%Ag合金导电性能的影响机制.随应变程度的增加,原始组织中的Cu基体晶粒、不平衡共晶体及次生相粒子最终演变成细密的纤维结构,合金电阻率上升.次生相界面、共晶体与Cu基体界面及位错对电子散射作用程度的变化导致了合金电阻率在不同变形程度范围内有不同的变化规律.当变形超过一定程度后,电阻率升高规律与来自较高Ag含量合金中纤维相尺度进入纳米数量级的界面散射模型相符.     

Particle shape effects on ductility of SiC particle reinforced LD2 matrix composites investigated by AFM based nanoindentation

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Thermal stresses in metal matrix composites studied by internal friction

Thermal stresses in metal matrix composites (MMC) can induce plastic deformation and damage accumulation in the region close to the reinforcements. In this connection, Al-4% Cu-based MMC reinforced with 10, 20 and 30% Al₂O₃ short fibres were characterized by internal friction (IF) measurements. As a function of the temperature, a maximum of damping has been observed in the composites at ca 150 K during cooling. This maximum is absent in the corresponding unreinforced AlCu alloy. The maximum is attributed to the generation and motion of dislocations produced by high thermal stresses at metal-fibre interfaces. The height of the maximum is found to be an index of the extent of relaxation of thermal stresses by the plastic deformation of the metal matrix. IF measurements have allowed us to identify whether plastic flow in the matrix or damage accumulation at matrix-fibre interfaces take place for different composites.     

低温循环过程中SiCw／6061Al复合材料残余应力的变化规律

研究了低温循环过程中压铸态ＳｉＣｗ／６０６１Ａｌ复合材料残余应力的变化零乱低温循环的降温阶段,复合材料基体经历错配拉伸塑性变形过程在升温阶段基体国卸载过程。经过一次低温循环后,残余应力有所降低。如果进行两次低循环自理只有当第二次循环下降温度低于第一次时,才能再次降低复合材料残余应力。     

Influence of pre-plastic deformation on thermal residual stress and yield st rength of SiCw/Al composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｅｔｏｔｈｅｄｉｆｆｅｒｅｎｃｅｏｆｃｏｅｆｆｉｃｉｅｎｔｓｏｆｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎｂｅｔｗｅｅｎｒｅｉｎｆｏｒｃｅｍｅｎｔａｎｄｔｈｅｍａｔｒｉｘｉｎＳｉＣｗ/Ａｌｃｏｍｐｏｓｉｔｅｓ,ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｉｓｎｏｔａｖｏｉｄｅｄｗｈｅｎｔｈｅｔｅｍｐｅｒａｔｕｒｅｉｓｃｈａｎｇｅｄ[1,2].Ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｃａｎｌａｒｇｅｌｙａｆｆｅｃｔｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｃｏｍｐｏｓｉｔｅｓ,ｓ…     

Thermal expansion and dimensional stability of unidirectional and orthogonal fabric M40/AZ91D composites

Unidirectional (60%, volume fraction) and orthogonal (50%, volume fraction) M40 graphite fibre reinforced AZ91D magnesium alloy matrix composites were fabricated by pressure infiltration method. The coefficients of thermal expansion (in the temperature range of 20-350 ℃) and dimensional stability (in the temperature range of 20-150 ℃) of the composites and the corresponding AZ91D magnesium alloy matrix were measured. The results show that coefficients of thermal expansion of the composites in longitudinal direction decrease with elevating temperature. The coefficients of thermal expansion (CTE) for unidirectional M40/AZ91D composites and orthogonal M40/AZ91D composites are 1.24×10-6 ℃-1 and 5.71×10-6 ℃-1 at 20 ℃, and 0.85×10-6 ℃-1 and 2.75×10-6 ℃-1 at 350 ℃, respectively, much lower than those of the AZ91D alloy matrix. Thermal cycling testing demonstrates that the thermal stress plays an important role on residual deformation. Thus, a better dimensional stability is obtained for the AZ91D magnesium alloy matrix composites. More extreme strain hysteresis and residual plastic deformation are observed in orthogonally fabric M40 reinforced AZ91D composite, but its net residual strain after each cycle is similar to that of the unidirectional M40/AZ91D composite.     

Role of interfacial and matrix creep during thermal cycling of continuous fiber reinforced metal–matrix composites

A uni-dimensional micro-mechanical model for thermal cycling of continuous fiber reinforced metal–matrix composites is developed. The model treats the fiber and matrix as thermo-elastic and thermo-elasto-plastic-creeping solids, respectively, and allows the operation of multiple matrix creep mechanisms at various stages of deformation through the use of unified creep laws. It also incorporates the effect of interfacial sliding by an interface-diffusion-controlled diffusional creep mechanism proposed earlier (Funn and Dutta, Acta mater., 1999, 47, 149). The results of thermal cycling simulations based on a graphite fiber reinforced pure aluminum–matrix composite were compared with experimental data on a P100 graphite–6061 Al composite. The model successfully captured all the important features of the observed strain responses of the composite for different experimental conditions, such as the observed heating/cooling rate dependence, strain hysteresis, residual permanent strain at the end of a cycle, as well as both intrusion and protrusion of the fiber-ends relative to the matrix at the completion of cycling. The analysis showed that the dominant deformation mechanism operative in the matrix changes continually during thermal cycling due to continuous stress and temperature revision. Based on these results, a framework for the construction of a transient deformation mechanism map for thermal excursions of continuous fiber composites is proposed.     

Mechanical spectroscopy of thermal stress relaxation at metal–ceramic interfaces in Aluminium-based composites

The micromechanisms of thermal stress relaxation in aluminum-based metal-matrix composites (MMCs) have been investigated by mechanical loss and dynamic shear modulus measurements during thermal cycling between 100 and 500 K. A transient mechanical loss maximum, which is absent in the monolithic material, appears during cooling. This damping maximum is strongly dependent on the measurement parameters: oscillation frequency, oscillation amplitude and cooling rate. In addition, it increases with the volumetric reinforcement content and decreases if the matrix strength is improved. The shear modulus evolution during thermal cycling shows that no detectable interfacial debonding occurs. Compared with alloyed MMCs, Al4N-based MMCs show the highest damping maximum simultaneously with a plateau in the elastic shear modulus. The mechanical loss maximum is attributed to dislocation generation and motion near the interfaces, resulting from the differential thermal contraction of matrix and reinforcement. A new model is proposed which describes this specific mechanical behavior of MMCs in terms of the development of microplastic zones in the matrix near the metal–ceramic interfaces.     

原位生成Al2O3、TiB2和Al3Ti/Al复合材料的热循环行为

本文研究了Al-TiO2-B系原位生成Al2O3、TiB2和Al3Ti/Al颗粒增强铝基复合材料的热循环行为，研究结果表明了纯铝及B／TiO2摩尔比分别为0、1和2的颗粒增强铝基复合材料的热循环行为具有以下结果，纯铝和复合材料热循环后均产生了残余应变和滞后环；Al-TiO2-B系列复合材料热循环应变的各项指标均比纯铝基体大大降低，且具有较小的内耗功和较好的热稳定性，可以预测其具有较高的热疲劳寿命，热循环曲线能很好的评估复合材料在温度循环变化的环境中工作时的热稳定性和热疲劳。     

Effects of particle size on residual stresses of metal matrix composites

A finite element analysis was carried out on the development of residual stresses during the cooling process from the fabrication temperature in the SiCp reinforced AI matrix composites. In the simulation, the two-dimensional and random distribution multi-particle unit cell model and plane strain conditions were used. By incorporating the Taylor-based nonlocal plasticity theory, the effect of particle size on the nature, magnitude and distribution of residual stresses of the composites was studied. The magnitude thermal-stress-induced plastic deformation during cooling was also calculated. The results show similarities in the patterns of thermal residual stress and strain distributions for all ranges of particle size. However, they show differences in magnitude of thermal residual stress as a result of strain gradient effect. The average thermal residual stress increases with decreasing particle size, and the residual plastic strain decreases with decreasing particle size.     

Effect of thermal stresses on the thermal expansion and damping behavior of ZA-27/aluminite metal matrix composites

When the fabrication of a metal matrix composite (MMC) involves its cooling from a high temperature, plastic-elastic residual deformation fields can be generated within and around the particle due to the differential thermal expansion between the particle and matrix metal. The present investigation is concerned with the effect of thermal residual stresses on the thermal expansion and damping behavior of aluminite particulate-reinforced ZA-27 alloy MMCs. Composites were prepared by the compocasting technique with 1, 2, 3, and 4 wt.% of aluminite reinforcement. Thermal expansion and damping properties have been studied experimentally as a function of temperature over a temperature range 30 to 300 °C both in the heating and cooling cycle. The thermal expansion studies exhibited some residual strain, which increased with the increase in the weight percent of the reinforcement. The damping capacity of both the composites and matrix alloy is found to increase with the increase in temperature during the heating cycle, whereas in the cooling cycle, damping behavior exhibits a maximum, which becomes more pronounced with the increase in the weight percentage of the reinforcement. The appearance of the maximum may be linked with dislocation generation and motion as a result of plastic deformation of the matrix at the metal/reinforcement interface. This phenomenon is attributed to the thermal stresses generated as a result of coefficient of thermal expansion (CTE) mismatch between the composite constituent phases. The thermal stresses have been estimated in both the cases using simple models.