40CrNi2Si2MoVA钢制零件磁痕显示分析

本文采用磁粉、X射线、CT和超声等无损检测和金相分析等方法对40CrNi2Si2MoVA钢制零件的磁痕显示进行了系统分析.研究认为,40CrNi2Si2MoVA钢制零件的磁痕显示为显微成分沿变形方向偏析导致的马氏体转变点Ms差异所致.显微成分偏析是钢锭结晶过程中不可避免的,但可通过优化熔炼工艺参数降低显微偏析的程度.本文还分析了四种磁痕显示的类型及其判别方法.     

车牌识别嵌入式系统的软硬件设计

作为交通信息服务系统的重要手段,车牌识别技术避免了人工操作存在的各种弊端。文中设计了车牌识别嵌入式系统的软硬件,该系统的整体框架主要包含3个模块,分别是OV7670摄像头、STM32单片机和TFT显示屏。为满足任务需求,设计了最小系统和电源模块等硬件;为解决传统投影法误差较大的问题,该系统在字符分割前会先对车牌区域进行识别,并采用上下投影的方式在有效区域内进行字符分割。实验表明,该系统可以实现车牌识别功能,且精确度较高。     

Progress in additive manufacturing on new materials: A review

Recent efforts and advances in additive manufacturing (AM) on different types of new materials are presented and reviewed. Special attention is paid to the material design of cladding layers, the choice of feedstock materials, the metallurgical behavior and synthesis principle during the AM process, and the resulted microstructures and properties, as well as the relationship between these factors. Thereafter, the trend of development in the future is forecasted, including: Effects of the particles size and size distribution of powders; Approaches for producing fine microstructures; Opportunities for creating new materials by AM; Wide applications in reconditioning of damaged components; Challenges for deep understanding and applications of the AMed new materials. The idea of “Develop Materials” or “Create Materials” by AM is highlighted, but a series of scientific, technological and engineering problems remain to be solved in future.     

天然橡胶的疲劳特性研究进展

叙述了天然橡胶的疲劳特性，着重归纳了天然橡胶的破坏机理及影响其疲劳破坏的主要因素。     

Effects of submicron diamonds on the growth of copper in Cu-diamond co-deposition

Submicron diamonds were co-deposited on aluminum substrates with copper from the acid copper sulfate electrolyte by electrolyte-suspension co-deposition.After submicron diamonds were added to the electrolyte,the shape of copper grains transformed from oval or round to polyhedron,the growth mode of copper grains transformed from columnar growth to gradual change in size,and the preferred orientation of copper grains transformed from (220) to (200).Analyzing the variation of cathodic overpotential,it was found that the cathodic overpotential tended to remain unchanged when copper plane (220) grew in the process of electrodepositing pure copper,while it tended to decrease with time when copper plane (200) grew m the process of co-deposition.It was inferred that copper plane (200) was propitious to the deposition of submicron diamonds.     

均匀化和均匀化后处理对GH742合金γ′相的影响

采用电子探针(EPMA)对GH742铸锭未经任何处理和均匀化后两种状态下的主要合金元素做了定量分析,并使用SEM扫描电镜对GH742铸锭三种不同状态下γ′相作了比较.结果表明:铸锭原始态存在偏析,γ′相在枝晶间和枝晶干处形状、尺寸差别较大,总体上尺寸较小;经均匀化后无粗大γ′相存在;均匀化后特殊处理部分γ′相尺寸增大,热加工塑性有明显提高.     

时效处理对粉末高温合金惯性摩擦焊接头室温拉伸行为的影响

对惯性摩擦焊扩散连接的FGH96合金试样经时效处理前后的室温拉伸行为进行了研究,并对其失效机制进行了评估.结果表明,对于焊接态(原状态)FGH96合金试样,由于焊缝区和热影响区的γ'相综合强化效果弱,晶界平直化,导致焊缝区和热影响区的强度低于基体,在室温拉伸过程中塑性应变量大:由于热影响区的晶粒尺寸大,晶界强化效果弱,...     

凝固模式对定向凝固TiAl-Nb合金组织和力学性能影响

目的 研究凝固模式对TiAl-Nb合金定向凝固组织和力学性能的影响。方法 利用Bridgman定向凝固方法制备了单一β、亚包晶、过包晶以及单一α相4种凝固模式的TiAl-Nb合金,对显微组织进行观察,并进行室、高温拉伸性能测试及断口形貌分析。结果 单一β凝固模式柱状晶明显倾斜,其他凝固模式合金的柱状晶挺直且宽度较均匀,除单一α凝固合金中片层方向近似与定向凝固方向平行外,其他模式凝固合金中大部分片层方向与定向凝固方向呈近45°夹角;拉伸性能结果显示,亚包晶合金室温和高温抗拉强度最高,分别为429和483 MPa,单一α相合金室温和高温抗拉强度最小,分别为281和204 MPa。结论 亚包晶合金其室温和高温拉伸性能均高于其他凝固模式的合金性能,但定向凝固试样制备过程中产生Y2O3颗粒夹杂,导致拉伸试验过程容易形成应力集中,致使定向凝固TiAl-Nb合金较早发生断裂。     

Ru对第四代镍基单晶高温合金DD22长期时效组织演化的影响EI北大核心CSCD

利用透射电镜和场发射扫描电镜研究了两种不同Ru含量(3%和5%,质量分数)的第四代镍基单晶高温合金DD22在1130℃长期时效过程中γ′相形貌演化、TCP相析出和界面位错网的演化情况。研究结果表明:在完全热处理后5Ru合金比3Ru合金的γ′相尺寸更小,形状更规则,γ/γ′相界面的错配度更大,高Ru含量使合金Re,Mo等元素出现反分配现象;5Ru合金在1130℃长期时效过程中γ′相粗化速率、溶解速率和形筏速率均低于3Ru合金;5Ru合金在长期时效1000 h后仍没有TCP相析出,而3Ru合金在时效50 h后便析出TCP相,随着长期时效时间延长,TCP相数量增多,尺寸增大;与3Ru合金相比,长期时效1000 h后5Ru合金γ′/γ界面位错网更加致密和规则;综上所述,Ru的元素反分配作用和低的扩散系数使5Ru合金比3Ru合金表现出更高的组织稳定性。