纳米晶Al-Cu-Mg合金的微观组织与力学性能研究

以工程实际中应用较广的Al-Cu-Mg铝合金作为研究对象, 用Al-Cu-Mg铝合金气体雾化粉末作为原材料, 通过低温液氮球磨获得纳米晶后, 再经真空热压和热挤压制备了致密的大块体纳米材料. 通过力学性能测试, 挤压态的纳米晶Al-Cu-Mg块体材料抗拉强度达470 MPa, 经过T4处理后, 抗拉强度达到590 MPa, 远远超过常规方法制备的Al-Cu-Mg铝合金抗拉强度. 对纳米晶Al-Cu-Mg块体材料进行微观组织观察, 分析了材料强度提高的原因.     

Mechanical behavior of ultrafine-grained cryomilled Al 5083 at elevated temperature

The mechanical behavior of cryomilled and consolidated Al 5083 with a duplex ultrafine-grained microstructure is described for compression testing at different temperatures and strain rates. The relationship among flow stress, strain rate, and testing temperature provides an initial hotworking guide for finegrained cryomilled aluminum alloys. The ultrafine-grained material exhibits similar deformation characteristics, such as strain-rate sensitivity, which would be expected in a conventional aluminum alloy. These findings are discussed in the context of recent empirical and theoretical models for the deformation of materials with grain sizes between 100 and 1000 nm.     

Polymer Powder Processing of Cryomilled Polycaprolactone for Solvent‐Free Generation of Homogeneous Bioactive Tissue Engineering Scaffolds

Synthetic polymers used in tissue engineering require functionalization with bioactive molecules to elicit specific physiological reactions. These additives must be homogeneously dispersed in order to achieve enhanced composite mechanical performance and uniform cellular response. This work demonstrates the use of a solvent‐free powder processing technique to form osteoinductive scaffolds from cryomilled polycaprolactone (PCL) and tricalcium phosphate (TCP). Cryomilling is performed to achieve micrometer‐sized distribution of PCL and reduce melt viscosity, thus improving TCP distribution and improving structural integrity. A breakthrough is achieved in the successful fabrication of 70 weight percentage of TCP into a continuous film structure. Following compaction and melting, PCL/TCP composite scaffolds are found to display uniform distribution of TCP throughout the PCL matrix regardless of composition. Homogeneous spatial distribution is also achieved in fabricated 3D scaffolds. When seeded onto powder‐processed PCL/TCP films, mesenchymal stem cells are found to undergo robust and uniform osteogenic differentiation, indicating the potential application of this approach to biofunctionalize scaffolds for tissue engineering applications.     

低温球磨制备镁基储氢材料及其性能研究

用液氮低温球磨技术制备Mg-8 mol%LaNi0.5储氢材料.采用XRD和SEM研究材料的相结构和表面形貌,采用激光法测定粒度分布,采用PCT设备研究材料的储氢性能.结果表明:经过10 h球磨后,该材料有少量合金相生成:材料平均粒度为10um左右;材料具有平坦的吸放氢平台,吸氢量在573 K时为2.33%(质量分数);在4.0 MPa氢压和523～653 K条件下,3～5 min内完成饱和吸氢量的80%以上.低温球磨制备的材料活化性能好,不需活化,平台性能好,动力学性能得到改善.     

液氮球磨过程中钛粉的形貌和组织演变

采用液氮球磨技术制备出纳米晶钛粉。运用SEM、XRD和TEM研究了液氮球磨过程中钛粉的形貌和组织的演变。结果表明:钛粉颗粒在液氮球磨过程中以脆性开裂的方式细化,经8h液氮球磨后钛粉颗粒从球磨前的45μm减小到5μm左右,颗粒表面出现大量裂纹;采用液氮球磨方法制备纳米晶Ti粉仅需8h。     

低温机械合金化研究进展

介绍了2种经传统的球磨机改进而成的低温球磨机，对目前国内外低温机械合金化的研究现状，特别是对具有高温稳定性的纳米材料制备的应用进行了简要的概括总结，讨论了低温机械合金化的反应机制和能提高纳米材料高温稳定性的机理，对今后的发展趋势进行了展望。     

低温球磨制备块体纳米晶7050铝合金的组织和性能研究

采用低温球磨、热等静压和挤压等工艺制备了块体纳米晶7050铝合金。分别利用透射电镜(TEM)和扫描电镜(SEM)对制备铝合金的微观组织和断口形貌进行了观察,并对该铝合金的化学成分、密度、硬度和拉伸性能进行了测定。结果表明,制备的块体纳米晶7050铝合金的平均晶粒尺寸为100~200 nm,密度为2.76 g/cm3,HV显微硬度为1184 MPa。抗拉强度和延伸率分别为412 MPa和5.2%。经时效处理后,材料的拉伸性能虽有所提高,但仍低于传统7050铝合金。分析认为,由于雾化参数和球磨参数的选取欠合理,导致了薄片状粉体的产生。而薄片状的形貌又使得粉体不能有效充填包套,最终得到的块体材料致密度低,内部缺陷较多。这些缺陷使得块体材料内部的晶粒(或颗粒)之间形成弱界面连接,降低了材料的拉伸性能。     

低温球磨纳米晶Al-Zn-Mg-CU合金组织的演变

利用液氮低温球磨技术制备了纳米晶Al-Zn—Mg—Cu合金粉体,分析了材料在球磨过程中微观组织变化．结果表明,气雾化Al—Zn—Mg—Cu合金粉体随着球磨过程的进行晶粒尺寸逐渐减小,球磨15h后晶粒尺寸约为35nm;MgZn2相逐步分解,并最终过饱和固溶于α—Al中．制备的纳米晶Al—Zn—Mg—Cu合金粉体低于709K（0．77Tm,Tm为熔点）加热时,晶粒长大速度缓慢;709K加热1h晶粒尺寸仅为71nm．研究表明,液氮低温球磨过程中形成的Al2O3颗粒对晶粒的钉扎有效地提高了纳米晶Al-Zn—Mg—Cu合金粉体的热稳定性．     

Deformation twins and twinning at ambient temperature in cryomilled A1-Zn-Mg-Cu alloy powders

The nanocrystalline Al-Zn-Mg-Cu alloy powders were synthesized using cryomilling. Deformation twins and twinning at ambient temperature were observed in Al-Zn-Mg-Cu powders. Experimental results indicate that high strain rate at low temperature during cryomilling induces the formation of deformation twins by the climbing of the restricted dislocations in nano-scale grains, and the cryomilled powders at high energies and nonequilibrium state reduce the grain boundary energies by twinning.