金属基复合材料微屈服强度影响因素的理论与实验分析

针对短纤维增强金属基复合材料(MMCs)的微屈服行为,应用细观力学计算和实验,定量分析了热处理状态、短纤维尺寸、体积比和分布状态对MMCs微屈服强度的影响.结果表明,短纤维的尺寸、分布状态、体积比对MMCs宏观和微屈服强度的影响趋势相反;时效处理可增加MMCs的宏观和微屈服强度;不同状态的MMCs微屈服行为符合Brown-lukens关系.     

冷热循环对颗粒增强铝基复合材料微屈服行为的影响

采用微屈服强度测试、透射电镜和高分辨透射电镜分析,对经过不同冷热循环工艺处理后的颗粒增强铝基复合材料的微屈服行为进行了研究。结果表明,冷热循环次数虽然对颗粒增强铝基复合材料微屈服行为的宏观规律没有本质的影响,但是仍然影响颗粒增强铝基复合材料的微屈服行为。对球形颗粒而言,小应变量下的微屈服强度随冷热循环次数的增加而增高;但对棱形颗粒而言,循环次数的影响较为复杂。研究还表明,冷热循环次数影响颗粒增强铝基复合材料微屈服行为的主要原因是其位错组态和残余应力在不同的循环次数下有明显的不同。     

SiCp／2024Al复合材料及2024Al合金的微屈服行为

对ＳｉＣｐ／２０２４Ａｌ复合材料及其基体２０２４Ａｌ合金的微了行为和热处理的影响进行了详细的比较研究。结果表明,由于ＳｉＣ颗粒的作用,复合材料在微屈服前即已产生明显的应变弛豫,并且其微屈服行为也与铝合金不同。在时效处理中,两种材料的微屈服强度均受时效强化相析出规律的控制。表明出“峰时效”现象;而冷热循环处理能改善２０２４Ａｌ的微屈服性能,但却对ＳｉＣｐ／２０２４Ａｌ的微屈服强度不利。     

金属铍的微屈服行为及机理

为研究金属铍的微屈服行为,通过透射电镜观察了1×10-5、50×10-6和200×10-6 3种不同微屈服阶段材料位错的变化,初探了铍的微屈服机理.通过130多个铍试样的微屈服强度与屈服强度的比较试验证明,用常规简单的屈服强度试验代替冗长的微屈服强度试验是可能的.     

SiCp/2024A1复合材料及2024A1合金的微屈服行为

对SiCp／2024A1复合材料及其基体2024A1合金的微屈眼行为和热处理的影响进行了详细的比较研究结果表明,由于SiC颗粒的作用,复合材料在微屈服前即已产生明显的应变弛豫,并且其微屈服行为也与铝合金不同在时效处理中,两种材料的微屈服强度均受时效强化相析出规律的控制,表现出“峰时效”现象;而冷热循环处理能改善2024A1的微屈服性能,但却对SiCp／2024A1的微屈服强度不利     

双剪统一屈服准则中的材料屈服极限和滑移面方向分析

对双剪统一屈服准则所表征的材料屈服极限和滑移面方向特性作了分析。结果表明,在描述材料的屈服极限方面,双剪统一屈服准则能够较好地反映中间主应力的影响,如中间主应力可提高材料的屈服极限,且屈服极限的提高具有区间性。但在描述材料屈服时的滑移面方向方面,虽然双剪统一屈服准则也能反映中间主应力的影响,但由于该准则是由两个表达式及相应的应力状态限制条件组成,当材料的实际应力状态同时满足这两个表达式的边界限制条件时,存在双重滑移角现象,并且滑移面的方向在该应力状态下会产生突变。由此可见,双剪统一屈服准则尚不能很好地描述材料屈服时的滑移特性。     

低温下奥氏体钢的不连续屈服

本文研究了应变速率和冷却剂状态对4K时许多奥氏体钢不连续屈服特性的影响,发现在4K的液氦中,作为应变速率的函数的不连续屈服起始应力和起始应变的变化;在4K的气态氦中比起在液态氦中,出现不连续屈服时的应力和应变要低得多.这些结果可以用宏观的热平衡和由运动位错引起的局部发热原理来解释.     

短碳纤维增强2024铝基复合材料微屈服行为研究

采用液态搅拌铸造制出了纤维长度分别为2mm和3mm、含量为2%的短碳纤维增强的含Sc的2024铝基复合材料。用加载-卸载法研究了两种材料不同时效态的微屈服性能。结果表明,短碳纤维增强2024铝基复合材料的微屈服强度具有宏观强度时效强化规律特征。峰值时效的材料具有最高的微屈服强度;微屈服阶段硬化率先增大后减小,均远高于宏观屈服初期硬化率。相比于2mm碳纤维,3mm碳纤维增强的含Sc的2024铝基复合材料具有更高的微屈服强度。     

退火及冷却方式对5182铝合金屈服平台的影响

利用力学性能测试及显微组织观察研究了退火及冷却方式对5182铝合金板材屈服平台的影响。结果表明:在相同温度退火时,水冷合金板材的屈服强度比空冷合金板材的低;提高退火温度后,无论是水冷还是空冷都可以在一定程度上缩短合金的屈服平台,相比于退火温度影响,冷却方式对屈服平台的影响更大,水冷可以明显缩短甚至消除屈服平台;板材在420℃退火保温1～3 min时晶粒尺寸约16μm,当退火温度升高到480℃时,其晶粒尺寸在3 min内由21. 6μm长到了28. 0μm,其中有部分晶粒发生了异常长大;随着晶粒尺寸的增大,合金的屈服平台也略有减小;通过高温退火和水冷的方式可以消除合金的屈服平台。     

屈服准则对DP600钢板各向异性行为的预测能力

采用Barlat89和Hill48屈服准则的两种参数求解方法,即应力各向异性数据求解法和变形各向异性数据求解法,分别推导与轧制方向成不同角度的单向拉伸加载下的屈服应力值和各向异性指数,并与NUMISHEET2014提供的DP600材料的实验数据进行比较。结果表明,在两种求解方法中,应力各向异性数据求解法在预测不同加载方向上的屈服应力时较为准确;变形各向异性数据求解法在预测不同加载方向上的塑性应变比时较为准确;Barlat89屈服准则对DP600材料各向异性的预测比Hill48屈服准则更准确。     

Micro-yield behaviors of Al2O3-SiO2（sf）/Al-Si metal matrix composites

Effects of the volume fraction and the size of crystallized alumina silicate short fibers as well as heat treatment processes on micro-yield strength（MYS） of Al2O3-SiO2（sf）/Al-Si metal matrix composite（MMC） that was fabricated by squeezing cast, were investigated by using continuous loading method on an Instron 5569 tester with a special extensometer with an accuracy of 10^-7. The results show that MYS of MMC decreases with the increase of volume fraction and length of the alumina silicate short fibers in the metal matrix composite, respectively. MYS of quenched Al2O3-SiO2（sf）/Al -Si MMC is the lowest, MYS of the MMC through peak-aging treatment is higher than that through other heat treatment methods. And before the peak-aging, MYS of MMC aging treated gradually increases with the increase of the aging time. Aging treatment after solution treatment is a preferred way that enhances micro and macro-yield strength of Al2O3-SiO2（sf）/Al-Si MMC.     

热处理工艺对Al2O3-SiO2/Al-Si复合材料微屈服行为的影响

以Al2O3-SiO2／Al-Si复合材料为研究对象，采用连续加载法，详细研究了热处理工艺对Al—Si基复合材料微屈服行为的影响规律及其原因。结果表明，复合材料经淬火处理后的微屈服强度最低，而经时效处理后的微屈服强度则好于其他热处理工艺的效果。时效处理是提高Al-Si基复合材料微屈服强度的有效途径之一。     

A STUDY ON MICRO-PLASTIC DEFORMATION BEHAVIOR OF 2024 A1 ALLOY

1.~hon2024Alalloyusedincomponentsofaprecisiondeviceishighlyrearredfordimensionalstability.althoughdimensionalstabilityhadbeenstudiedinseverallit.rat~.[l--3),therelationshipsbetweenndcrostructureanddimensionalstabilitypropertiesandAnsotmpofmicro--plasticdeformationresistanceforhotextruded2024Alalloybarwerenotinvestigatedindetails.SOInanyengineeringproblemsPertinentto2024hialloyremaininsuspense.Additionallytheconventionalevaluationfordimensionalstabilityinunloadingconditionisobtainedbyend--len…     

Microstructure and mechanical properties of high strength Mg−15Gd−1Zn−0.4Zr alloy additive-manufactured by selective laser melting process

In order to verify the feasibility of producing Mg−rare earth (RE) alloy by selective laser melting (SLM) process, the microstructure and mechanical properties of Mg−15Gd−1Zn−0.4Zr (wt.%) (GZ151K) alloy were investigated. The results show that fine grains (~2 μm), fine secondary phases and weak texture, were observed in the as-fabricated (SLMed) GZ151K Mg alloy. At room temperature, the SLMed GZ151K alloy has a yield strength (YS) of 345 MPa, ultimate tensile strength (UTS) of 368 MPa and elongation of 3.0%. After subsequent aging (200 °C, 64 h, T5 treatment), the YS, UTS and elongation of the SLMed-T5 alloy are 410 MPa, 428 MPa and 3.4%, respectively, which are higher than those of the conventional cast-T6 alloy, especially with the YS increased by 122 MPa. The main strengthening mechanisms of the SLMed GZ151K alloy are fine grains, fine secondary phases and residual stress, while after T5 treatment, the YS of the alloy is further enhanced by precipitates.     

Effects of heat treatment on microstructure evolution and mechanical properties of Mg-6Zn-1.4Y-0.6Zr alloy

To investigate the effects of solution temperature and the decomposition of I-phase on the microstructure, phase composition and mechanical properties of as-cast Mg-6Zn-1.4Y-0.6Zr alloy, solution treatment at 440 oC, 460 oC and 480 oC and further aging treatment were conducted on the alloy. The results indicate that the net-like intermetallic compounds(mainly I-phase) dissolve into the α-Mg matrix gradually with the increase of solution temperature from 440 oC to 480 oC. Besides, the I-phase decomposes completely at 480 oC, with the formation of fine W-phase(thermal stable phase) and Mg_7Zn_3 phase. In addition, a great number of fine and dispersive Mg-Zn binary phases precipitate in the α-Mg matrix during the aging treatment. Due to the increase of solute atoms and the precipitation of strengthening phases, such as W-phase and Mg-Zn phases, the optimal strength is obtained after solution treatment at 460 oC for 8 h and aged at 200 oC for 16 h. The yield strength(YS), ultimate tensile strength(UTS) and elongation are 208 MPa, 257 MPa and 3.8%, respectively. Compared with the as-cast alloy, the increments of YS and UTS are 117% and 58%, respectively, while the decrement of elongation is 46%.     

低温时效对两种牙科氧化锆陶瓷力学性能的影响

将牙科KAVO、TZ-3YS两种氧化锆在134 ℃, 0.2 MPa压力下进行时效处理,研究时效对材料的相结构、弯曲强度和断裂韧性的影响.结果表明,KAVO和TZ-3YS氧化锆的m相含量随时效时间的延长而增加.时效前后KAVO氧化锆的抗弯曲强度和断裂韧性没有明显变化,而TZ-3YS氧化锆的抗弯曲强度略有下降,断裂韧性略有增大.与TZ-3YS氧化锆相比,KAVO氧化锆抗弯曲强度较高,断裂韧性较低,抗时效能力强.临床应用宜采用抗时效、力学性能稳定的氧化锆陶瓷.     

Microstructure and Mechanical Properties of Cu-Ag-Zr Alloy

The Cu-3Ag-0.5Zr alloy was produced by vacuum induction melting and subsequently processed through hot forging and rolling. Detailed microstructural characterization of solution-treated (ST) specimen shows three types of phases: Cu matrix, zirconium-rich phase, and Cu-Ag-Zr intermetallic phase. Transmission electron microscopy studies together with energy-dispersive x-ray spectroscopy analysis established the presence of Zr-rich large particles in the ST condition. Aging at 450 °C for 4.5 h after solution treatment resulted in the formation of uniformly distributed fine spherical silver precipitates with an average diameter of 9.0 ± 2.0 nm. Consequently, room temperature yield strength (YS) and ultimate tensile strength (UTS) of the aged specimen increased by 110% and 15%, respectively, compared to those of 120 and 290 MPa of the ST specimen. At elevated temperature, the YS decreased to 146 and 100 MPa at 540 and 640 °C, respectively, for the aged sample. On the contrary, the YS increased to 140 MPa at 540 °C, and thereafter a decrease was observed with a value of 105 MPa at 640 °C for the ST sample. This decrease in YS at higher temperatures is attributed to coarsening of precipitates and dissolution of the precipitates, whereas an increase in YS is attributed to in-situ aging of the samples.     

Effects of under-aging treatment on microstructure and mechanical properties of squeeze-cast Al-Zn-Mg-Cu alloy

The effects of under-aging treatment on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy produced by squeeze casting were investigated using optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness and tensile testing. The results showed that most of secondary phases were dissolved into α(Al) matrix while no significant grain growth happened under the condition of solution treatment at 470 °C for 4 h. Due to the strengthening effect of GP zones, for alloys treated by under-aging process, the increase of aging time and aging temperature improved the ultimate tensile strength (UTS) and yield strength (YS), but decreased the elongation (δ) to some extent. By utilizing appropriate aging time and temperature, the best combination of strength and ductility could be obtained to fulfill the design requirements of automobile components.     

Microstructure and properties characteristic during interrupted multi-step aging in Al-Cu-Mg-Ag-Zr alloy

The effects of interrupted multi-step aging on the microstructure and properties of Al-Cu-Mg-Ag-Zr alloy were studied by tensile,hardness,electrical conductivity tests and transmission electron microscopy(TEM).Interrupted multi-step aging delayed the peak aging time compared to one-step aging and kept the same levels of hardness,electrical conductivity,ultimate tensile strength(UTS),yield strength(YS) and elongation as those of the T6 temper alloy while increased the fracture toughness notably.Ω phase and a little θ’ phase precipitated and grew simultaneously in the process of one-step aging at 160℃.During the second-step aging at 65℃ of interrupted multi-step aging,no TEM characteristic of Ω precipitates could be found.During the third step of interrupted multi-step aging,Ω began to dominate the microstructure like what happened in the process of one-step aging.The difference of properties between the T6 temper and the interrupted multi-step aged alloys might be related to the different precipitation sequences in the process of the two heat treatment technologies.     

预变形对挤压态Mg-6%Zn-1%Mn镁合金时效硬化效应和力学性能的影响(英文)

采用显微硬度测试、拉伸试验、金相观察和TEM观察,研究冷塑性变形对Mg-6%Zn-1%Mn(ZM61)合金时效硬化和力学性能的影响。在420℃固溶处理1h后,对ZM61挤压棒材试样进行室温拉伸变形,塑性应变有3种:0、5%和10%,预变形后再进行人工时效。时效硬化曲线表明:预变形可以显著加快硬化速率且提高峰值硬度;然而,当应变量由5%增加到10%后,峰值硬度并未增加。室温拉伸性能表明:预变形量增加,屈服强度和抗拉强度增加,伸长率略有降低,且屈服强度的增加幅度大于抗拉强度的。金相组织观察表明:当预变形应变量为5%时,金相组织中未观察到孪晶;预变形10%的组织中出现了大量的孪晶。TEM观察表明:预变形可以增加峰时效态组织中β1′杆状相的数量。