挤压Mg-Zn-Y合金的腐蚀行为

研究了大挤压比(81∶1)条件下Mg-Zn-Y合金在3.5%(质量分数)NaCl水溶液中的腐蚀行为。通过失重法和电化学法测试了合金的腐蚀性能,并对合金的微观腐蚀过程进行了分析。结果表明:随着Zn、Y含量的增加,准晶相含量逐渐增加,合金的耐蚀性能逐渐降低。准晶相和α-Mg基体界面处的α-Mg基体一侧优先发生腐蚀,随后一方面向基体扩宽延伸而形成腐蚀坑;另一方面逐渐沿I-phase与α-Mg基体界面扩展,直至界面结合处形成裂纹环路而导致I-phase颗粒脱落,进而在合金表面形成点蚀坑。     

准晶增强Mg-Zn-Y合金的ECAP变形组织及力学性能

镁及镁合金作为目前工业应用中最轻的结构材料之一,具有良好的应用前景,然而由于镁合金自身强度较低、抗氧化性能差以及高温抗蠕变性能差等问题,使其作为某些结构件的应用受到限制,为进一步扩大其应用,人们采用了多种方法来提高其综合力学性能.二十面体准晶相(简称Ⅰ-phase)由于其特殊的结构而具有优异的力学性能,如高强度、高硬度等,将Ⅰ-phase作为一种增强相引入到镁合金中可大大提高镁合金的力学性能,为新型镁合金的开发和实际应用提供了一种新途径.本文采用常规铸造法制备了含有粗大网状Ⅰ-phase和α-Mg两相组织的Mg-Zn-Y合金.研究了合金含量及Zn/Y比对Mg-Zn-Y合金显微组织和力学性能的影响,探讨了热处理工艺对合金中相析出行为及Ⅰ-phase热稳定性的影响.以时效处理后的Mg-Zn-Y合金为研究对象,研究了两种塑性变形工艺(常规热挤压和等径角挤压变形)对合金显微组织和力学性能的影响,并对合金的细化机制、断裂行为与强化机制进行了研究.研究结果表明,在Y含量为0.3%～2.0%(at),Zn含量为1.7%～6.0%(at)的富镁Mg-Zn-Y合金中,合金的铸态组织及相组成取决于Zn/Y比和Zn含量,Zn/Y比为6时,合金的铸态组织由α-Mg基体和晶界上富镁相与Ⅰ-phase两相共晶组织组成;在所研究的合金成分范围内,合金中Ⅰ-phase的形成及其体积分数与合金的凝固速度有关,采用快速凝固的方法得到的合金中,由于第二相的形核及长大受到抑制,形成的Ⅰ-phase的体积分数相对于常规铸造工艺下制备的合金中Ⅰ-phase的含量有所减少,同时发现,合金的极限抗拉强度和屈服强度随合金中Ⅰ-phase体积分数的增加而增加,但合金的延伸率略有降低;在400℃、24h的热处理工艺下,Mg95Zn4.3Y0.7合金基体上有球形Ⅰ-phase析出,且析出的Ⅰ-phase在随后的时效处理中表现出热稳定性;在190℃不同时效时间下合金基体中的析出相为密排六方结构的MgZn2相,其析出行为与Mg-Zn二元合金类似.Mg-Zn-Y合金的热挤压结果表明,通过挤压变形可以显著细化合金的晶粒组织,合金的晶粒大小可由变形前的40～60μm减小到8～15μm,在挤压过程中位于晶界的Ⅰ-phase被破碎并较均匀地分布在基体合金中,随着挤压比的增大和挤压温度的降低,晶粒进一步细化,Ⅰ-phase的弥散程度增加.挤压变形可以显著提高Mg-Zn-Y合金的强度、硬度和延伸率;随着挤压比的增大,合金的强度、硬度和延伸率均有所增加;在所研究的3种合金中,Mg95Zn4.3Y0.7合金在523K以25:1的挤压比挤压后,具有较高的力学性能,其极限抗拉强度为287MPa,屈服强度为203MPa,延伸率为14.1%.对于预挤压态Mg-Zn-Y合金的ECAP变形结果表明,ECAP对于预挤压态Mg-Zn-Y合金组织的细化是一个不断加强的过程,1道次ECAP变形后,在一些粗大晶粒之间分布着许多细小的晶粒,随变形道次的增加,原始粗大的晶粒消失,形成均匀细小的等轴晶粒,平均晶粒尺寸为1～3μm,同时在ECAP过程中Ⅰ-phase被破碎并呈弥散分布.ECAP变形1道次可以显著提高Mg-Zn-Y合金的抗拉强度、屈服强度和延伸率,Mg95Zn4.3Y0.7合金ECAP变形1道次后力学性能指标σb=331MPa,σ0.2=223MPa,δ=19.4%.Mg-Zn-Y合金以A、BA、Bc、C等4种不同工艺路线进行8道次ECAP变形后的显微组织差异不大,均形成细小的等轴晶粒;4种工艺路线在1～8道次的变形过程中,合金的力学性能变化不同,对于路径A和BA,随着变形道次的增加,合金的抗拉强度、屈服强度和延伸率变化幅度不大,对于路径BC和C,变形道次超过4次后,产生的变形织构的弱化作用导致合金的屈服强度迅速降低,但是合金仍保持较高的抗拉强度和延伸率.通过对ECAP变形过程中Mg-Zn-Y合金晶粒细化过程的分析,结合其力学性能的变化得出ECAP变形的细化机制和准晶相强化机制:ECAP对于准晶增强Mg-Zn-Y合金的细化机制主要是基体在不同变形路径下的连续剪切变形机制和准晶粒子对于基体的剪切及钉扎机制;准晶增强Mg-Zn-Y合金ECAP变形过程中存在3种强化机制:细晶强化、第二相粒子强化和位错强化,3种强化机制分别在ECAP变形的不同阶段起主导作用,在共同的强化作用下提高合金的强度.     

稀土元素Nd对Mg-Zn-Y合金组织结构和力学性能的影响

通过制备Mg-6Zn-1.5Y-0.8Zr-xNd(x=0、1、2、3、4)系列合金,研究了稀土元素Nd对Mg-6Zn-1.5Y-0.8Zr合金组织结构和力学性能的影响。通过金相显微镜、扫描电镜、EDS、XRD等手段,观察和分析了合金的微观形貌和组织结构,测量了合金抗拉强度、屈服强度和伸长率等力学性能。结果表明:合金中添加稀土元素Nd后晶粒明显细化,随着Nd元素含量的增加,晶粒细化效果更为明显;通过XRD分析可知,添加Nd元素后,合金中并没有出现新的含Nd的物相;扫描电镜和EDS分析表明,合金中加入的Nd置换了部分Y,形成了Mg3(NdY)2Zn3、Mg3-(NdY)Zn6的相结构,Nd元素对Y的置换主要出现在Mg3(NdY)2Zn3结构中,在Mg3(NdY)Zn6相结构中出现较少;力学性能测试结果表明,随着Nd含量增多,合金晶粒细化,细晶强化作用明显,合金屈服强度逐渐增大,而抗拉强度和伸长率在Nd含量为3%(质量分数)时达到最大,比未添加Nd元素时提高约25%以上。     

AlMn二十面体准晶的凝固形貌与固液界面稳定性

根据已经报导的实验结果对在典型的AlMn二元合金中二十面体准晶的凝固形貌及合金成分、冷速的关系进行了研究,对二十面体准晶与相应的晶体的凝固形貌进行了比较。实验结果与理论分析表明,在晶体凝固中适用的形貌稳定性理论也可以应用了二十面体准晶的凝固形貌予测及控制。     

挤压比对Mg-Zn-Y合金微观组织和力学性能的影响

研究了在350℃不同挤压比(16、32)下的Mg-6xZn-xY(x=0.5,0.75,1)合金微观组织和室温力学性能。结果表明,当挤压比为32时,合金中第二相体积百分含量较多,平均晶粒尺寸较小。其中,Mg-6Zn-1Y合金在挤压比为16时,α-Mg基体平均晶粒尺寸为14.6μm,抗拉强度及屈服强度分别为264MPa和169MPa;当挤压比为32时,α-Mg基体平均晶粒尺寸为5.9μm,抗拉强度和屈服强度达到337 MPa和237 MPa,分别提高了27.7%和40.3%。另外,所有合金经热挤压后都有良好的塑性,室温拉伸断口均呈韧性断裂特征。     

机械合金化制备的Fe1-xNix合金纳米晶粉末的形貌和微结构

利用机械合金化方法制备了Ｆｅ１－ｘＮｉｘ合金纳米晶粉末,Ｘ分别为０．１５、０．４５、０．８０,球磨时间为２、４、８、１６、４０ｈ。利用扫描电子显微交易和坶分析仪观察和分析了样品的形貌和微结构。发现整个球磨过程枳发为３个阶段。开始阶段,由于冷焊,Ｆｅ、Ｎｉ混合粉末凝聚成一些粒径较大的颗粒;在中间阶段,内应力达到最大值,原先形成的大颗粒破碎,粒径分布变窄;最后阶段,ＦｅＮｉ粉完全合金化,粒度再次增大,     

等离子喷涂-激光重熔制备AlCuFe准晶涂层的研究

报道了在氩气气氛下，利用固体YAG激光对等离子喷涂AlCuFe准晶涂层进行激光重熔制备包含二十面体准晶I相及β类似相涂层的研究。结果表明，在激光功率固定为300W的情况下，随着激光扫描速度的增加，低碳钢基体中Fe元素对涂层的稀释度减小，从而使不同扫描速度下所得离子喷涂-激光重熔涂层中I相和β相的含量比I/β依次增加。同时随着激光扫描速度的增加，激光熔化涂层的熔池深度变浅。当激光扫描速度大于某一定值时，涂层熔化深度达不到涂层与基体的结合界面从而无法使涂层与基体之间实现冶金结合，不利于涂层结合力的提高。     

一个与准晶相关的新Al－Cu相

本文报道一个新Ａｌ－Ｃｕ相具有正交结构，空间群Ｆｄｄｄ．点阵常数为：ａ＝０．８１６６ｎｍ，ｂ＝０．９９９５ｎｍ，ｃ＝１．４１４９ｎｍ，表达式为Ａｌ４３．２Ｃｕ５６．８．该相与Ａｌ－Ｃｕ－Ｆｅ准晶的价电子浓度相同，是一个由ＣｓＣｌ结构衍生的类似相．     

Al-Ni-Fe系铸态合金中的准晶相

系统研究了Al72.5Fe14.5Ni13和Al71Fe5Ni24铸态合金的相组成，发现其中分别存在D—Al72．6Fel4．6Nil2．8和D'—Al70．5Fe10Nil9．5两种十次准晶，它们各自与AlFe和AlNi二元十次准晶相关．实验结果与三元准晶相图的电子浓度特征吻合，说明三元准晶相图的电子浓度特征对确定三元准晶的理想成分和探索准晶新成分有一定的指导作用．     

晶化分数对钛基非晶复合材料热塑性成形能力的影响

目的 研究晶化分数对原位晶化钛基非晶复合材料热塑性成形能力的影响,优化Ti基非晶复合材料的制备和设计。方法 首先采用电弧熔炼和铜模铸造制备出成分为Ti45Zr20Be29Fe6和Ti45Zr20Be29Cu6的非晶合金,通过连续加热DSC及等温DSC研究其晶化动力学,然后根据得到的等温晶化规律制备不同晶化体积分数的非晶复合材料,并通过静态热机械分析(TMA)表征其热塑性成形能力。结果 Ti45Zr20Be29Fe6在406 ℃与411 ℃时,等温晶化过程为形核率随时间增大的形核长大过程;Ti45Zr20Be29Cu6在370,375,380,385 ℃时,等温晶化过程为形核率随时间减小的形核长大过程;XRD物相分析表明,等温处理后Ti45Zr20Be29Fe6和Ti45Zr20Be29Cu6的析出相分别为β-Ti和α-Ti2Zr;两种内生复合材料的热塑性成形能力均随晶化相体积分数的增大而降低,且Ti45Zr20Be29Fe6基体复合材料的热塑性成形能力比以Ti45Zr20Be29Cu6为基底的复合材料更好。结论 晶化分数增加会降低钛基非晶复合材料的热塑性成形性能,且其影响程度与复合材料的基体和晶体第二相的特性有关。     

Fiber volume fraction effects on fatigue crack growth in SiC/Ti-15-3 composite

The effects of fiber volume fraction (15, 37, and 41%) on fatigue crack growth in unidirectional SiC/Ti-15-3 composite were investigated at room temperature. The effect of fiber volume fraction on the fiber bridging mechanism was studied to support development of physically-based crack growth models. While each fiber volume fraction exhibits similar decreasing crack growth rates prior to fiber bridging induced crack arrest, post-arrest behavior (observed after incrementally increasing the applied stress level) is quite different. After crack arrest, the 15% (37 and 41%) material exhibited higher (lower) crack growth rates and lower (higher) toughness values than the unreinforced matrix. These different behaviors occur because of differences in the amount of fiber bridging during the post-arrest regime. Metallography of interrupted tests revealed the extent of fiber bridging in the crack wake and matrix plasticity ahead of the crack tip. Models for predicting the effective matrix stress intensities were evaluated and compared to experimental data. A fiber pressure model and finite element studies were used to estimate the condition of the bridged fiber zone and associated fiber stresses. Since the vast majority of useful life for these materials experiences fatigue crack growth, these results assist in discerning an optimum fiber volume fraction for structural applications.     

Ni体积分数对Ni-Al2O3太阳光谱选择性吸收薄膜光学性能的影响

借助计算机模拟剖析了Ni体积分数对Ni-Al2O3太阳光谱选择性吸收薄膜光学性能的影响规律,并依据这一规律指导了以水溶胶-凝胶法制备的Ni-Al2O3太阳光谱选择性吸收膜系的优化。模拟结果表明,以呈现类金属特征的基层Ni-Al2O3薄膜与Ni体积分数不超过基层0.5倍且呈非金属特征的中间层薄膜组合,在其上再沉积一减反射顶层,如此3层复合可获得高吸收率和低发射率的太阳光谱选择性吸收膜系。依据这一规律指导的以水溶胶-凝胶法制备的Ni-Al2O3膜系其吸收率高达0.93,发射率低至0.04,成为一个很好的太阳光选择性吸收表面。     

Calcium phosphate coating on magnesium alloy by biomimetic method: Investigation of morphology, composition and formation process

Magnesium alloy has similar mechanical properties with natural bone and can degrade via corrosion in the electrolytic environment of the human body. Calcium phosphate has been proven to possess bioactivity and bone inductivity. In order to integrate both advantages, calcium phosphate coating was fabricated on magnesium alloy by a biomimetic method. Supersaturated calcification solutions (SCSs) with different Ca/P ratio and Cl⁻ concentration were used as mimetic solutions. The morphology, composition and formation process of the coating were studied with scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results show that a uniform calcium phosphate coating was observed on magnesium alloy, the properties of which could be adjusted by the SCSs with different Ca/P ratio. The formation process of the coating was explored by immersing magnesium alloy in SCSs with different Cl⁻ concentration which could adjust the hydrogen production. According to SEM results, the hydrogen bubbles were associated with the formation of grass-like and flower-like coating morphologies. In conclusion, the biomimetic method was effective to form calcium phosphate coating on magnesium alloy and the morphology and composition of the coating could be accommodated by the Ca/P ratio and Cl⁻ concentration in SCSs.     

乙腈与水的体积比对SDBS掺杂PPY的微观形貌与导电性的影响研究

以FeCl3为氧化剂,SDBS为掺杂剂,乙腈和水为混合溶剂,通过化学氧化法合成了导电聚吡咯。FT-IR和XRD表征结果表明SDBS掺杂到了吡咯环上,所合成的PPY产物为非晶态结构。在此基础上,重点研究了腈水比对PPY产物的微观形貌、产量和导电性的影响。结果表明,PPY产物的微观形貌直接受腈水比的影响,可通过调控腈水比来调控PPY产物的微观形貌为絮状、颗粒状、片状等形态。在0∶10~6∶4的范围内,随着腈水比的增大,PPY的产量逐渐降低;在0∶10~2∶8的腈水比范围内,PPY的电导率随腈水比的增大而增大,在2∶8~6∶4的腈水比范围内,PPY的电导率随腈水比的增大而减小。     

等离子体清洗工艺对镁基金属表面形貌及膜／基结合强度的影响

采用不同等离子体清洗工艺对镁基金属样品进行清洗,随后磁控溅射沉积纯Cr镀层.利用SEM、划痕仪分析了不同等离子体清洗工艺下镁基金属的表面形貌与膜／基结合强度的变化.结果表明,过高的清洗偏压作用下,基体表面会产生深径比＞0.5的孔洞状结构缺陷;过长清洗时间后,离子轰击产生的能量积淀效应使基体表面温升显著,局部区域出现熔融...     

Interlaminar stress distribution of composite laminated plates with functionally graded fiber volume fraction

Various functionally graded design methods have been proposed recently for fiber reinforced composite plates. The laminates with variable fiber spacing along the thickness direction are focused on in this paper. Fiber volume ratio distribution functions are defined separately in each single layer. Classic state space method as well as differential quadrature state space method are utilized here for different boundary and plied conditions. For the latter method, a sub-layer based scheme, which has both high accuracy and less numerical capacity, is suggested for functionally graded plates. Numerical examples indicate that the non-uniform distribution of fibers rearranges the stress field, of which the in-plane stresses are sensitive to the fibers’ distribution, while the transverse stresses are not affected so much. In-plane stresses near interfaces would decrease if the fiber ratio reduces in this region, which provides a method to resolve the interfacial stress concentration problems.     

The effect of volume fraction of primary α phase on fracture toughness behaviour of Timetal 834 titanium alloy under mode I and mixed mode I/III loading

The effect of volume fraction of primary α phase on mode I and mixed mode I/III fracture toughness of Timetal 834 titanium alloy was investigated. The mode I and mixed mode I/III fracture toughness values for loading angle of 30° were found to initially decrease and subsequently increase with increase in volume fraction of primary α phase. On the other hand, mixed mode I/III fracture toughness for loading angle of 45° was found to monotonically decrease with increasing volume fraction of α phase. The fracture toughness was also found to marginally increase with increasing loading angle for the two lower primary α volume fractions, i.e. 6% and 15% whereas it marginally decreases with increasing loading angle for primary α volume fraction of 30%. The results were explained on the basis of the nature of stress field ahead of the crack tip under mixed mode I/III loading as well as the fracture mechanisms operative in this alloy for different α volume fractions.