金属基粉末制备技术的研究进展及发展趋势

综述了机械粉碎法、物理法、化学法和电解法制备金属基粉末以及超微粉末制备的原理、技术特点、研究进展和局限性;认为机械粉碎法需细化粉末粒度、扩大材料范围;避免合金粉末的偏析、细化粉末粒度以及减少粉末的污染将是物理法未来研究的重点;化学法能制备纳米级别的粉末,但粉末表面能高,必须采取有效手段抑制粉末颗粒的长大;超微粉末制备需防止粉末吸湿和团聚,降低成本.     

金属合金粉末的研究与发展

叙述了制备金属合金粉末的方法及其应用现状,金属合金粉末的种类和性能,新开发的Fe-Ni-RE合金粉末材料与国内外同类合金粉末材料进行了比较,具有优良的耐磨性、耐蚀性和较高的硬度.分析合金粉末制粉及粉末处理工艺、成型工艺,总结了合金粉末的主要发展方向.     

激光同轴送粉增材制造粉末束流关键特征表征与分析

粉末束流焦距和焦点位置处的粉末颗粒的空间分布是粉末束流的两个关键特征,对激光同轴送粉增材制造工艺特性影响较大. 利用高速摄像拍摄粉末束流的宏观形貌,以图像灰度处理技术为基础,建立了粉末束流焦距和焦点位置处粉末颗粒空间浓度分布表征方法,提出利用有效粉斑直径定量分析粉末束流的汇聚性,系统研究了载气流量、同轴保护气流量、送粉速率等主要工艺参数对粉末束流关键特征的影响规律. 结果表明,工艺参数的改变几乎不影响粉末束流焦点位置处粉末颗粒呈高斯分布这一规律;载气流量增加,粉末束流焦距变小,有效粉斑直径变大,粉末束流汇聚性变差;同轴保护气流量增加,粉末束流焦距变长,有效粉斑直径基本不变;送粉速率提高,粉末束流的焦距和有效粉斑直径变化均不大.     

金刚石工具胎体预合金粉末制取与应用

预合金粉末是采用多种金属熔炼成低熔点合金后再喷制成的粉末,其制取可以用雾化法和湿法冶金等工艺生产.文中介绍了气体雾化法预合金粉末的工艺过程;描述了湿法冶金制取预合金粉末的工艺流程.分析了预合金粉末胎体金刚石工具的优点,说明了国外预合金粉末技术现状和发展趋势,剖析了国内预合金粉末及工具的研究情况,探讨了金刚石地质钻头胎体用预合金粉末的制取和实际应用情况,研究了切割花岗岩的预合金粉末胎体金刚石锯片.     

Research on Preheating of Titanium Alloy Powder in Electron Beam Melting Technology

研究了电子束熔化快速成形技术中的钛合金粉末预热工艺,并对粉末预热后的颗粒联接方式进行了分析.结果表明,当Ti6A14V粉末由电子束连续扫描快速预热升温至600℃以上,粉末颗粒中高比表面积的细小颗粒,由于高能量密度电子束作用将全部或部分熔化而充当粉末颗粒联接团聚的粘结剂,使得预热区域的粉末颗粒聚团结块.该粉末团聚体不仅能有效抵挡高速电子束流的冲击而使熔化成形的表面粉末不飞溅,而且也能避免成形表面粉末颗粒熔化时的球化效应.以Ti6Al4V粉末为原料并充分预热每层的成形粉末,制备了层间熔合良好并且力学性能优异的Ti6Al4V柱状试样.     

PREP法制备高温TiAl预合金粉末及其致密化坯体组织研究

采用等离子旋转电极雾化(PREP)法制备了高温Ti Al预合金粉末,该粉末粒度主要在46~150μm之间,其粒度呈现双峰分布。高温Ti Al预合金粉末的快速冷凝组织及相组成与粒度有关,一般大粒径粉末冷凝组织为枝状结构,小粒径粉末呈光滑状;该预合金粉末相主要由α2相组成,小于46μm粒径的粉末含有一定β相,大于200μm粒径的粉末出现γm相。不同粒度的粉末由于不同的相组织结构对热等静压致密化坯体组织具有一定遗传效应,粗粒度粉末在热等静压后坯体中易形成原始粉末颗粒边界或粗化的片层组织。     

FGH96粉末高温合金损伤行为与寿命预测

粉末高温合金中缺陷,尤其是非金属夹杂缺陷不可避免。为了对粉末高温合金的可靠应用,除需在工艺上进行控制以减少缺陷外,还必须研究缺陷对粉末高温合金的损伤行为,及根据粉末高温合金的疲劳特性研究粉末高温合金的寿命预测方法。针对我国先进航空发动机涡轮盘选材的第二代损伤容限型粉末高温合金FGH96,分析了国内外粉末高温合金的发展与应用状况,叙述了其缺陷特性以及缺陷对FGH96粉末高温合金的影响规律,介绍了FGH96粉末高温合金的断裂特征以及裂纹萌生与扩展特性,分析了粉末高温合金寿命预测研究的相关工作,并探索性阐述了基于原始疲劳质量的粉末高温合金寿命预测方法。     

两种3D打印用雾化Ti-6Al-4V粉末的对比研究

本研究分别利用水冷铜坩埚真空感应熔炼气雾化(VIGA-CC)和等离子旋转电极(PREP)两种技术制备出球形Ti-6Al-4V合金粉末,作者利用SEM、同步辐射CT扫描-三维重建和氩气含量测试等分析手段对不同粒径的Ti-6Al-4V合金粉末的孔洞缺陷和氩气含量、硬度值进行了表征。实验结果表明, VIGA-CC粉末粒度分布宽,细粉收得率较多,粉末粒度分布在40~180 μm之间, PREP粉末的粒度分布较窄,主要集中在110~180 μm之间；金属粉末内部的孔隙率、气体含量和孔尺寸随着粉末粒度的增大而增大,且同一粒径范围内VIGA-CC粉末的气孔概率多于PREP粉末；随着粉末粒径减小,粉末截面组织逐渐细化,其硬度值逐渐升高,整体上VIGA-CC粉末硬度值高于PREP粉末。     

溶胶-喷雾干燥W-Cu前驱体粉末煅烧过程中的相变

采用溶胶-喷雾干燥法制备不同铜含量的W-Cu前驱体粉末,前驱体粉末分别在400、600和800℃各煅烧90min,运用XRD和SEM等手段对煅烧前后复合粉末的相组成和显微形貌进行分析,研究前驱体粉末在煅烧过程中的相变行为。结果表明:前驱体粉末在煅烧过程中发生一系列的分解和化合反应,随着煅烧温度的升高,粉末的相组成、颗粒形貌和尺寸发生明显变化,对W-30%Cu(质量分数)合金,在400℃煅烧后,复合粉末由WO3、CuO和CuWO4组成,粉末颗粒大多呈立方结构,大小为200～400nm;在600℃煅烧后,复合粉末由CuO和CuWO4组成,粉末颗粒大多呈短棒状结构,大小为400～500nm;在800℃煅烧后,复合粉末由CuO、CuWO4和Cu3WO6组成,粉末颗粒大小为3～4μm;前驱体粉末中铜含量对煅烧后复合粉末的相组成也存在较大影响,铜含量越多,越容易生成复合氧化物。     

TiAl预合金粉末的表征和后续致密化显微组织特点

采用感应熔炼气体雾化法制备了TiAl预合金粉末.粉末粒度主要分布在100-250 μm,呈正态分布,粉末平均粒度为120.7 μm.TiAl预合金粉末的相组成与粒度分布有关,γ相所占比例越高,预合金粉末粒度越大.小粒度的预合金粉末主要由α2相组成;预合金粉末在温度高于500℃时效处理,发生α2→γ转变.TiAl预合金粉...     

Influence of Fe on Microstructure and Mechanical Properties in Pdoped Ni–Cr–Fe Alloys

The influence of Fe on the microstructure and mechanical properties of P-doped Ni–Cr–Fe alloys has been investigated.Results showed that increasing Fe content refined the dendrite microstructure and enhanced the solubility of P in as-cast alloys. The change of microhardness in different dendrite regions was attributed to the segregation of P atoms in solid solution state, which had strengthening effects. Increasing Fe contents from 15.2 to 60.7 wt% reduced the yield strength and tensile strength but had little influence on the elongation of alloys. The stress rupture life of alloys after heat treatment decreased with the increment of Fe contents, and the failure fracture modes transferred from transgranular to intergranular fracture mode. The change of fracture modes was due to the weakness of grain boundaries caused by the increment of Fe.In addition, the precipitation of M_(23)C_6 was believed to be related to the segregation of P toward grain boundaries, which led to the fluctuation of carbon and chromium atoms near the grain boundaries in alloys with low Fe contents. Consequently, the increment of Fe decreased the strength of matrix and changed the existence of P atoms and the precipitates at grain boundaries.     

The structure of molten zones in explosion welding (aluminium–tantalum,copper–titanium)

Investigations were carried out into the relief of the flat- and wave-shaped interfaces for explosion-welded aluminium–tantalum and copper–titanium welded joints. For these systems, characterized by a relatively high mutual solubility of the initial elements, the results show a typical set of the structures of the interfaces replacing each other with the intensification of the welding conditions. The unusual shape of the projections on the flat interfaces was found. They are similar to splashes, which form on the surface of the liquid, although they are solid-phase splashes. The vortex structure of the zones of local melting was also detected. The unusual shape of the waves was found: in the presence of mutual solubility they consist of the specially ordered set of projections. It may be assumed that this is caused by the formation of intermetallic compounds on the surface of the projections. The processes of self-organization, ensuring the evolution of the relief of the interface in the intensification of the welding conditions, have been investigated. The role of intermetallic compounds in these self-organization processes is clarified.     

德育的现代转型刍议

我国改革开放的迅猛发展,要求德育实现从传统向现代的转型。这种转型因其受到国情,民情,社情,世情的制约,会很艰难,但当前大学生“三德”匮乏的现实增强了转型的紧迫感。改革传统的德育体制应首先从注重人格教育,公民教育,精英教育入手。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The Coupled FEM Analysis of the Transient Temperature Field During Inertia Friction Welding of GH4169 Alloy

The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.     

极地海洋环境服役材料的摩擦学研究进展

随着北极航行的发展及极地资源开发的需要，如何提高极地海洋环境服役材料的摩擦学性能愈发重要。在极地海洋环境中，碎冰、冰层和海水中的腐蚀性物质会使材料受到摩擦磨损、腐蚀及其耦合的影响;低温潮湿环境会增加材料的脆性、使材料表面覆冰、改变材料的摩擦磨损机理;强紫外线会加速涂层老化;这些因素都会降低材料的耐磨性能，最终导致材料失效。因此，极地海洋环境服役材料的摩擦学与材料的性能、服役寿命息息相关。本文介绍了极地探索所面临的摩擦磨损问题;阐述了极地温度、极地海洋大气及海水成分、海冰运动和极地微生物等极地海洋环境特点及其对材料摩擦学性能的影响;重点介绍了金属材料、无机非金属材料、高分子材料在极地海洋环境下的摩擦学进展;探讨了提升材料在极地海洋环境下的耐磨防腐技术，如改性、表面修饰等;最后，结合极地海洋环境服役材料摩擦磨损研究中所面临的问题及发展趋势，对未来极地海洋服役材料的摩擦学研究工作进行展望。     

微米尺寸不锈钢的形变与疲劳行为的尺寸效应

采用聚焦离子束溅射蚀刻加工了微米尺寸304不锈钢悬臂梁试样．利用静态及动态弯曲加载研究了微米尺寸材料的形变与疲劳开裂行为．结果表明：随薄膜厚度的减小,材料的屈服强度升高,塑性下降．屈服强度随悬壁梁厚度的变化关系与Hall—Perch晶粒强化关系相似．微小悬壁梁屈服强度的升高来源于小尺度材料在非均匀变形下引起的应变梯度贡献的增加;而塑性下降则归因于较薄薄膜的晶粒内较少的可动位错．疲劳裂纹从尖缺口处萌生的门槛值接近块体材料．     

集装箱底侧梁开裂原因分析

集装箱底侧梁在操作过程中发生开裂。通过化学分析、力学测试、金相检验以及断口分析等手段,对开裂的集装箱底侧梁进行综合分析。结果表明,集装箱底侧梁裂纹对应 R角处的板厚度减薄了近 50%,严重降低了该位置的承载能力;同时材料本身塑性较差,并且室温折弯过程很可能 R角处已经产生了裂纹,随后再对其进行焊接操作,使得该区域韧性进一步降低,在集装箱作业过程中箱内载荷作用下, R角处作为应力集中部位受拉应力而发生瞬间断裂。     

Corrosion‐erosion damage of heat exchanger tubes by desalted crude oil flowing at shell side

Heat exchanger tubes were locally heavily damaged by desalted crude forming a shell side stream under the pressure of 2.6 MPa and at the temperature of 385–395 K. Boiler steel tube temperature was 97 K higher compared to that of the crude oil at its inlet to the exchanger. Two types of segmental baffles effected cross vortex type flow that was lowered nearly to a standstill at locations where the highest damage occurred. Close to the baffles where the damage was the highest the flow was completely different from that of the window flow. These were found from analyses of the flow and of locations of perforations. Most of the tube surface was with no damage and was covered with protective organic‐inorganic deposit. Electrochemical investigation proved a cathodic character of the deposited film against bare steel. Metallography examination of the steel showed typical structures that could not affect much the damage. The crude with low water content was not found aggressive when a corrosion test was performed at elevated temperature. The tests excluded the possibility for high rate of electrochemical corrosion at the surfaces with removed protective layers. The only reason of the damage may be cavitation corrosion at the ways of crude slow vortex flow at which temperature was high enough to allow explosions of low volatile components [1].     

Simulation of 3-D Deformation and Material Flow During Roll Forging Process Using System of Oval-Round Groove

Basing on the analysis of the traits of the roll forging process, a system-model of computer simulation has been established. Three-dimensional rigid-plastic FEM has been used for the simulation of the deformation process in the oval and round pass rolling, including the entering, rolling, and separating stages. The analysis was conducted using the Deform-3D ver.5.0 code. The important information concerned with the deformation area characteristic, material flow, and velocity field has been presented. Otherwise,the location of the neutral plane in the deformation area was shown clearly.