陶瓷微结构件的注射成形工艺及其微观组织

采用粉末微注射成形技术制作了ZrO2陶瓷微结构件,分析了其注射成形工艺,包括喂料配制、注射工艺及烧结工艺对微观组织的影响.实验结果表明,粉末体积分数为55%的生坯注射成形后在1 500℃下烧结2 h,采用排水法测得其微结构相对密度高达98.5%,采用纳米硬度分析法得到其微结构的显微硬度值为13.75 GPa.扫描电子显微镜(SEM)结果表明,提高模具温度和注射压力,有利于微结构的填充,进而改善微结构件的微观组织;高的烧结温度可以增加零件的致密度,但容易导致晶粒的过度长大和尺寸不均匀.激光共聚焦光学显微镜观察结果表明,使用亚微米级陶瓷超细粉得到的微结构具有良好的表面质量,其烧结前、后的表面粗糙度值分别为0.33μm和0.28μm.此外,提高粉末含量可以减小零件收缩率,从而有利于微结构的尺寸精度控制.     

超快扫描量热揭示铝基金属玻璃过冷液态:接近液体脆度的理论极限（英文）

铝基非晶合金具有密度低、强度高、耐腐蚀等诸多优异性能;然而,铝基非晶合金形成能力差,一般需要非常高的冷却速率,这限制了铝基非晶合金的应用.玻璃形成理论认为形成能力与过冷液体密切相关.但在一般升温测量时,铝基非晶合金不显示玻璃转变或过冷液体,而是直接变成晶态.目前为止,关于铝基非晶合金的玻璃转变和过冷液体属性仍然是未知的.本文采用超快速差热分析方法(Flash DSC)使得升温速度达到10000 K s^-1,测量了20余种常见铝基非晶合金的玻璃转变行为和过冷液体特征.发现铝基非晶合金普遍具有很高的液体脆度系数(m),其中某些成分m>160,已经接近理论上预测的脆度系数上限m^175.通过系统研究这些成分的形成能力,发现铝基非晶合金的玻璃形成能力与脆度系数成反相关,而且这种相关不是线性的.只有m<100时,降低m才会对玻璃形成能力有明显影响;相反, m>100的玻璃形成力普遍较弱,而且随m变化不显著.因此,过高的液体脆度系数可能是铝基非晶合金形成能力差的一个重要原因.     

Nanosecond Laser “Pulling” Patterning of Micro–Nano Structures on Zr-Based Metallic Glass

Flexible and controllable fabrication of micro–nano structures on metallic glasses (MGs) endow them with more functional applications, but it is still challenging due to the unique mechanical, physical, and chemical properties of MGs. In this study, inspired by a new physical phenomenon observed in the nanosecond laser–MG interaction (i.e., the surface structure is transformed from the normally observed microgroove into the micro–nano bulge at a critical peak laser power intensity), a nanosecond laser “pulling” method is proposed to pattern the MG surface. The formation mechanism and evolution of the micro–nano bulge are investigated in detail, and accordingly, various micro–nano structures including the unidirectional stripe, pillar, cross-hatch patterns, “JLU”, circle, triangle, and square, are derived and created on the MG surface, which affects the surface optical diffraction. Overall, this study provides a highly flexible and controllable method to fabricate micro–nano structures on MGs.     

Near‐Net Shape Forming of Advanced Ceramics

A combination of temperature‐induced forming (TIF) and rapid tooling is a successful new route for near‐net shape forming of advanced ceramics. This novel forming method has several advantages, such as rapidly produced complex‐shaped ceramic parts, a more homogeneous density distribution of the green body, and more reliable mechanical properties than conventional pressing technologies offer. This new technique offers the opportunity to largely shorten the time to market for the production of complex‐shaped prototypes with rapid tooling.     

微塑性成形技术的研究进展

介绍了塑性微成形技术的发展背景及其基本特点,综述了尺寸效应及其对微塑性成形工艺的影响、微型构件微塑性成形工艺以及微成形装置的研究现状,并对其发展趋势进行了预测.     

Micro‐and Nanoscale Metallic Glassy Fibers

When bulk materials are made into micro‐and nanoscale fibers, there will be attractive improvement of structural and functional properties, even unusual experimental phenomena [Ref. 3 ]. The main drawback of various applications of metallic fibers is poor ability of present fabrication methods for controlling their dimensions and surface properties [Ref. 4 ]. Metallic glassy fibers (MGFs) are desired because of unique mechanical and physical properties and glass‐like thermoplastic processability of metallic glasses (MGs). Here, we report a synthetic route for production of micro‐to nanoscale MGFs (the diameter ranges from 100 µm to 70 nm) by driving bulk metallic glass rods in their supercooled liquid region via superplastic deformation. Compared with existing metallic fibers, the MGFs have precisely designed and controlled properties and size, high structural uniformity and surface smoothness, and extremely flexibility. Remarkably, the method is simple, efficient, and low cost, and the MGFs can be continuous prepared by the method. Furthermore, the MGFs circumvent brittleness of MGs by size reduction. We proposed a parameter based on the thermal and rheological properties of MG‐forming alloys to control the preparation and size of the fibers. The MGFs with superior properties might attract intensive scientific interest and open wide engineering and functional applications of glassy alloys.     

工艺参数对聚甲醛微注塑制品力学性能的影响机理EI北大核心CSCD

基于单因素实验,研究工艺参数对不同厚度聚甲醛(POM)微注塑制品屈服应力、弹性模量、断裂强度和断裂伸长率等力学性能指标的影响,并基于制品形态结构分析工艺参数对制品力学性能的影响机理。实验结果表明,随着注射速度的增大,1.0mm厚微制品的皮层厚度减小,过渡层厚度增加,结晶度增大,综合效应使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小;0.2mm厚微制品的皮层厚度占主导地位,其力学性能是由皮层的力学性能决定,皮层厚度先增大后减小使得屈服应力、断裂强度和弹性模量先增大后减小,断裂伸长率先减小后增大。随着熔体温度的升高,1.0mm厚微制品的分子链取向度减小,皮层厚度减小,收缩量增大,使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大;而0.2mm厚微制品的皮层减小,但过渡层增加,结晶度增大,且补料更充分,综合作用使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小。随着模具温度的升高,1.0mm厚微制品的皮层比例减小,结晶度增大,结晶度影响占主导,使得屈服应力、断裂强度和弹性模量逐渐增大,断裂伸长率减小;而0.2mm厚微制品的皮层厚度占主导,皮层厚度明显减小使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大。     

利用界面设计制造巨型金属玻璃

开发具有优良性能的材料一直是人类不懈的追求.如果将尺寸放大到与传统金属相当的水平,金属玻璃将是一种理想的金属材料.为了应对这一挑战,在过去的几十年中,研究学者们已经尝试了多种方法,包括基于热力学的合金开发、3D打印以及基于人工智能学习的合金优化设计新理念.本文提出了一种简便、灵活的界面设计理念来制造直径大于100 mm的巨型金属玻璃(GMG),通过该方法制造的巨型金属玻璃性能几乎与铸态样品相同.此外,利用该方法可制造复杂三维结构.本文提出的方法为克服合金系统中长期存在的玻璃形成能力(GFA)限制的问题,制造大尺寸、复杂结构金属玻璃开辟了新的思路和途径.     

非接触红外测温技术在快速成形领域的应用研究

深入研究再制造成形过程中温度场分布及变化对实现零件的成形与组织性能一体化控制具有重要意义.分别阐述了非接触红外测温技术常用设备(包括亮度测温仪、比色测温仪和红外热像仪)的工作原理及在再制造成形领域中的应用进展,并展望了非接触红外测温技术的发展方向.     

Ultrafast gas chromatography on single-wall carbon nanotube stationary phases in microfabricated channels

The key to rapid temperature programmed separations with gas chromatography are a fast, low-volume injection and a short microbore separation column with fast resistive heating. One of the major problems with the reduction of column dimensions for micro gas chromatography is the availability of a stationary phase that provides good separation performance. In this report, we present the first integration of single-wall carbon nanotubes (SWNTs) as a stationary phase into 100 mum x 100 mum square and 50-cm-long microfabricated channels. The small size of this column with integrated resistive heater and the robustness of the SWNT phase allow for fast temperature programming of up to 60 degrees C/s. A combination of the fast temperature programming and the narrow peak width of small-volume injections that can be obtained from a high-speed, dual-valve injection system allows for rapid separations of gas mixtures. We demonstrate highly reproducible separations of four-compound test mixtures on these columns in less than 1 s using fast temperature programming.     

Rapid screening of potential metallic glasses for biomedical applications

This paper presents a rapid screening process to select potential titanium and zirconium based metallic glasses (MGs) for bio-material applications. Electrochemical activity of 7 MGs including 6 bulk metallic glasses and 1 thin-film deposited MG in simulation body and human serum is first inspected. A low-voltage potential state test is also developed to simulate the cell membrane potential that the implant MGs will suffer. Results show that the MGs composed of Ti₆₅Si₁₅Ta₁₀Zr₁₀ and Ta₅₇Zr₂₃Cu₁₂Ti₈ exhibit excellent electrochemical stability in both simulation body fluid and human serum. In addition, the copper content in the MGs plays an important role on the electrochemical activity. MGs with the copper content higher than 17.5% show significant electrochemical responses. The cytotoxicity of the solid MG samples and the corrosion released ions are also evaluated by an in-vitro MTT test utilizing the murine bone marrow stem cells. Results indicate that all the solid MG samples show no acute cytotoxicity yet the corrosion released ions show significant toxicity for murine bone marrow stem cells. The rapid screening process developed in the present study suggests that the Ti₆₅Si₁₅Ta₁₀Zr₁₀ metallic glass has high potential for biomedical applications due to its good electrochemical stability and very low cytotoxicity.     

超声振动辅助塑性成形及形性预测研究进展

随着微机电系统等领域的快速发展,对零件成形精度与性能的要求日益增加。超声振动辅助塑性成形是一种典型的能场辅助塑性成形工艺,相比于传统塑性成形工艺,具有流动应力低、材料成形能力高、界面摩擦少、成形质量较好等优势,被广泛应用于难成形材料加工、微成形、复杂构件成形等塑性成形过程。然而,由于不同塑性成形工艺中金属的变形行为特性存在较大差异,对塑性成形质量与成形性能进行预测有利于实现成形过程的形性协同控制。介绍了超声振动辅助塑性成形在体积成形工艺（镦粗、挤压、拉拔等）与板料成形工艺（拉伸、拉深、渐进成形、冲压等）中的应用及发展概况,讨论了超声振动对材料塑性变形过程中宏观表现与微观演化的影响。在已有研究基础上,重点分析了超声振动辅助塑性成形过程中成形能力预测（流动应力、成形极限等方面）和成形性能预测（表面性能、力学性能、微观组织等方面）的研究进展,为金属零部件成形高质量形性调控提供理论参考,并展望了超声辅助塑性成形工艺的发展趋势。     

A nanoinjector for microanalysis

We describe a simple miniature injection device that can be used for introduction of nanoliter sample volumes in microfluidic systems. The hybrid microstructure consists of two hydraulically connected parts, a pulse micropump, and a multilevel cross-flow injector. Sample injection is accomplished by creating a transient pressure pulse in the sample line by means of the solenoid-based micropump. The sample line is aligned at right angles to the main carrier flow line. The two flow channels are located in two different parallel planes. The cross section of the two channels is defined by a self-sealing aperture in an elastomer. During the pressure pulse, the sample is introduced through this aperture directly into the main flow stream. Fast impulse-based injection causes rapid mixing of the injected sample with the main flow stream. This permits simple single-line manifold micro flow injection (MFI) systems. The deformation/relaxation of the elastomer is fast and repeatable; as such, rapid serial actuations essentially result in a larger injected sample volume without significantly affecting the peak shape. In the present form, 2-40-nL samples are easily injected by single injection, and the injected volume can be chosen by system parameters. The injection repeatability as observed by a photometric detector is better than 1.2% (n = 100).     

Atomic-level structure and structure-property relationship in metallic glasses

The structure of metallic glasses (MGs) has been a long-standing mystery. On the one hand, MGs are amorphous materials with no long-range structural order; on the other hand, topological and chemical short-to-medium range order is expected to be pronounced in these alloys, due to their high atomic packing density and the varying chemical affinity between the constituent elements. The unique internal structure of MGs underlies their interesting properties, which render MGs potentially useful for various applications. While more and more glass-forming alloys have been developed in recent years, fundamental knowledge on the structural aspect of MGs remains seriously lacking. For example, how atoms pack on the short-to-medium range, how the structure differs in different MGs and changes with composition, temperature, and processing history, and more importantly, how the structure influences the properties of MGs, are still unresolved questions. In this paper, we review the tremendous efforts over the past 50 years devoted to unraveling the atomic-level structure of MGs and the structural origin of their unique behaviors. Emphasis will be placed on the progress made in recent years, including advances in structural characterization and analysis of prototypical MGs, general structural models and fundamental principles, and the correlations of thermodynamic, kinetic, and mechanical properties with the MG structures. Some widely observed property-property correlations in MGs are also examined from the structural perspective. The insights summarized are shown to shed light on many intriguing behaviors of the MG-forming alloys and expected to impact the development of MGs. Outstanding questions in this important research area will also be outlined.     

特种能场辅助微塑性成形技术研究及应用

特种能场辅助微塑性成形技术是利用声、光、电、磁等特殊能量源对微型零件变形过程进行调控的先进制造技术。特种能场已被证明在宏观尺度下对于降低零件加工难度、提高尺寸精度、改善材料微观组织、提升构件力学性能、提高表面质量等存在促进作用。然而,在微塑性成形过程中,材料的变形特性在尺寸效应的影响下与宏观情况存在一定差异。梳理了特种能场辅助微塑性成形技术的研究进展,总结了微型零件在特种能场辅助下的成形特点。其中,着重综述了超声场辅助微成形中体积效应和表面效应的宏观表现及微观机理,展示了多种微成形工艺中超声场对微型零件成形质量的提升效果。同时,重点概述了电场辅助微成形时材料力学性能及微观组织演变规律,剖析了电致塑性效应产生的本质原因。此外,列举了激光、电磁、高压流体等其他特种场辅助微成形的原理及作用效果。最后,对特种能场辅助微成形的发展趋势进行了展望。     

材料损伤HIP自愈合机理研究

目的研究金属注射成形烧结后内部缺陷自愈合方法。方法将热等静压(HIP)技术与金属注射成形(MIM)工艺结合,控制热等静压参数使得注射成形烧结后的内部缺陷产生自愈合。借助扫描电镜观察内部孔隙消除与缺陷的闭合情况,通过CAE仿真分析颗粒间应力变化,研究热等静压工艺(HIP)自愈合的机理,通过力学抗压试验测试HIP后力学性能。结果扫描电镜结果表明,内部孔隙与缺陷在HIP后完全消除,CAE结果表明,HIP自愈合过程主要是高温高压下的材料发生塑性变形流动机制与扩散蠕变机制起主导作用。力学性能结果表明,HIP后抗压强度提升21.47%,屈服强度提升28.91%,并且HIP后应变断裂点数值明显小于热等静压前。催化进度过程中,粉体内部聚甲醛气体分解挥发后,在零件的内部会形成多孔性结构,并且气体逃逸的通道形成了裂纹,造成烧结过程中厚壁件内部形成空隙与裂纹。结论热等静压后由金属注射成形烧结后形成的内部缺陷完全消除。随着研究的深入和完善,可为金属粉末成形零件的性能优化和广泛应用提供基础。     

An experimental and numerical investigation on micro rolling for ultra-thin strip

The demand for miniaturized parts and miniaturized semi-finished products is increasing nowadays, because microforming processes can improve production rate and minimize material waste due to less forming passes. However, traditional macro metal forming processes and modelling cannot be simply scaled down to produce miniaturized micro parts. In this study, a 2-Hi micro rolling mill has been successfully built. Experimental and numerical investigations on the micro rolling process for ultra-thin SUS 304 stainless steel strip have been conducted. The experimental results show that the micro rolling deformation of ultra-thin strip is influenced by size effect which results from the specimen size difference and this size effect is embodied in the flow stress and the friction coefficient. Analytical and finite element (FE) models in describing size effect related phenomena, such as flow stress, friction, rolling force and deformation behaviour, are proposed. The material surface constraint and the material deformation mode are critical in determination of material flow stress curve. The analysis of surface roughness evolution with rolling conditions has also been performed. The identified analysis on deformation mechanics provides a basis for further exploration of the material behaviour in plastic deformation of micro scale and the development of micro scale products via micro rolling.     

Rapid Prototyping of Ceramica via Temperature Induced Forming

Rapid tooling is the process of directly or indirectly employing rapid prototyping technologies in tool and mold fabrication. By combining rapid tooling and temperature induced forming (TIF) a novel near-net shape process for the rapid production of complex-shaped prototypes of advanced ceramics has been developed. Rapid tooling via stereolithography quickly produces complex-shaped molds with precise surface quality and the TIF technology enables the forming and consolidation of Al2O3 green bodies in nonporous molds. Thus Al2O3 green parts with high density and without any cracks are realized. This novel process shows excellent potential for near-net shape production of advanced ceramics with complex geometry, fine surface finish and reliable mechanical properties.     

Correlation between glass transition temperature and melting temperature in metallic glasses

We report that the glass transition temperature (T_g) of a variety of metallic glasses (MGs) correlates with the eutectic or peritectic temperature of two main components corresponding stoichiometric proportion in their binary phase diagram. The correlation suggests that the T_g of MGs is mainly determined by their solvent of two base components, which have composition close to the eutectic and peritectic points in the binary phase diagram and the weakest link in amorphous structure. The results have implications for understanding the structure and glass transition in MGs and for predicting and designing metallic glasses with a desirable T_g.     

中空吹塑成形技术探讨

吹塑加工成形也称中空吹塑,是一种发展迅速的塑料加工方法。它是将挤出的熔融塑料毛坯,置于模具内,借助压缩空气吹胀而贴于型腔壁上,经冷却硬化为塑件,此方法主要用于成型空心塑件。制品包装容器、工业制品将有较大增长,而且注射吹塑、多层吹塑会有快速的发展。针对中空吹塑加工技术的应用和发展,介绍了中空吹塑成型的加工方法,分析了中空吹塑成型基本性能的技术要求,研究了中空吹塑成型加工的塑料模具设备,同时指出了聚合物中空吹塑成型加工技术。