金属粉浆浇注成型与烧结实验研究

金属粉浆浇注成型与烧结工艺,是基于快速原型的金属型腔模具快速制作中比较关键的工艺环节.文章以3种进口和国产树脂为粘结剂,分别使用平均粒径为44μm的较粗铁粉、平均粒径为4μm较细的羰基铁粉,以及两者按照一定比例组成的双形态混合铁粉为基体材料,分别在空气和真空下混浆、注浆,研究了粉浆浇注成型工艺中的若干关键技术问题.实验表明,采用真空下混浆、注浆,不但可以有效消除气泡,还可以同时提高浆体的流动性和密实性;另外,铁粉粒度的大小也直接影响着浆体的流动性.实验中同时发现,使用较细的羰基铁粉与相对较粗的铁粉,按照合理比例组成的双形态混合粉末,具有更好的流动性和充填性,而且从密度特征看,试样更具密实性.将注型坯试样在氢气保护下进行烧结,低温阶段将注型坯中的有机粘结剂成分进行脱除,高温阶段实现金属粉末烧结形成骨架状金属结构.实验结果表明,在合理的烧结规范下,选择合适的粘结剂,采用粗细两种铁粉组成的双形态混合粉浆,并且壁厚小于一定尺寸的试样,在烧结过程中更有利于试样形状的保持,且烧结后试样结构较为均匀.文章的实验研究为基于快速成型的金属基薄壁型腔模具的快速制作,提供了必要的工艺基础和技术支持.     

碳纤维／羰基铁粉吸波涂层

北京工业大学材料学院采用化学镀的方法在碳纤维表面镀覆了一层金属镍，将镀镍后的碳纤维与羰基铁粉混合制备吸波涂层。并对吸波涂层吸波性能进行测试。实验所用碳纤维是低温处理的聚丙烯腈基短切碳纤维，含碳量大于96％，平均直径为7μm，截面形状为近似圆形。长度为3mm，密度为1．74g／cm^3。短切碳纤维的所用羰基铁粉粉体Fe的含量≥97％，其平均粒度为4．5μm，粒径范围为1．5～7．0μm，分布不均匀，有效磁导率(μ)≥2．85。     

以107硅橡胶为基体的粘弹性磁性磨具制备及实验研究

目的为解决当前粘弹性磁性磨具制备工艺复杂、使用寿命短且加工过程易分解等问题,研制一种以107硅橡胶为基体的粘弹性磁性磨具,并通过加工实验研究了粘弹性磁性磨具流动性、自身配比和加工转速对工件光整加工效果的影响。方法选用新制备的粘弹性磁性磨具对铝合金管外圆表面进行光整加工实验,选取不同交联剂含量的新磨具对其进行加工实验,分析基体流动性对光整加工效果的影响;选取不同的工件转速进行加工实验,分析工转速对光整加工效果的影响;选取铁磁相和磨粒相比例不同的新磨具进行加工实验,分析铁磁相和磨粒相比例对粘弹性磁性磨具光整加工效果的影响;选取磨粒相粒径不同的新磨具进行加工实验,分析磨粒相粒径对光整加工效果的影响。结果当107硅橡胶为20 g、羰基铁粉为15 g、碳化硅为5 g、甲基硅油为1 g、软化剂为1 g、交联剂为0.14 g、工件转速为350 r/min、磨粒相粒径为600目时,可将工件表面粗糙度值Ra由0.299μm下降到0.113μm,Ra值相对下降率约为62.2%,加工效果最好。结论新制备的磨具有性能稳定、制备方便、可根据不同工况调整流动性等优点。     

多粒径颗粒对石墨烯/铝基复合材料组织及性能的影响

采用球磨和真空热压烧结结合的工艺制备石墨烯增强铝基(Gr/Al)复合材料，研究不同粒径铝粉混合对复合材料微观组织和力学性能的影响。结果表明，利用球体最密堆积原理设计的多粒径铝粉混合，M₁(1μm∶10μm按1∶1.5混合)和M₂(10μm与100μm按1∶1.5混合)的致密度均高于单一粒径的试样(S),M₂致密度达到96.2%。M₁试样抗拉强度和伸长率相较于S试样有所降低，M₂试样抗拉强度和伸长率均提高，其中伸长率提升31.8%。多粒径混合可促进分散小粒径铝粉和石墨烯，有效降低孔隙率，在减少原始颗粒界面的同时增加裂纹扩展路径，大尺寸粒径颗粒的加入使得复合材料的塑性大幅提升。     

直接喷墨打印喷头直径对铁磁软磁材料成形性能的影响

以羰基铁粉为原料,DISPER-Y220为分散剂,制备出粘度为0.55 Pa·s,流动性良好的料浆,以此料浆作为打印"墨水",利用直接喷墨打印成形技术制备出纯铁软磁材料制件。喷头直径分别0.5、0.8和1.0 mm,打印成形后通过脱脂和烧结制备出制件。结果表明:分散剂添加量为1%时(质量分数),料浆粘度最低,随着固含量的增大,料浆粘度变大,随着剪切速率的增大,料浆表现为剪切变稀特征;喷头直径为0.8 mm所打印的烧结体,表面粗糙度(R_a)最低,其R_a为0.8μm;在1300℃保温2 h烧结后,喷头直径为0.5 mm打印的烧结体致密度最高,为96.3%,其磁饱和感应强度Bs达到1.53 T,最大磁导率μmax达到2630。     

粉末粒径对高速压制Ti-6Al-4V合金性能的影响(英文)

采用高速压制(HVC)技术成形平均粒径分别为103、66和44μm的3种Ti6Al4V合金粉末,然后将合金粉末进行真空烧结,考察粉末粒径对成形效果和烧结体性能的影响。结果表明,细粉末比粗粉末更难压制,获得的压坯密度也更低。但是细粉末压坯的烧结密度明显高于粗粉末压坯的烧结密度。与粒径为103和66μm的粉末相比,粒径为44μm的粉末的压坯密度最低,在冲击能量为913J时其相对密度为85.1%。然而在1300°C烧结2.5h后,粒径为44μm的粉末压坯的烧结密度最高,其相对密度达到98.2%。而且,粒径为44μm的烧结试样具有最高的硬度和压缩强度,分别为HV354和1265MPa。     

添加碳、镍、钴粉对烧结Ti-12Mo合金密度和强度的影响

Ti-(10%~15%)Mo合金具有高强度、耐蚀的性能，期望作为高强度材料使用，但还需要进一步提高烧结合金的密度和力学性能，为此日本人选择了碳、镍、钴作为添加元素，并探讨了其添加效果。 原料粉末采用平均粒径为38m的钛粉和0.67m的钼粉，添加元素采用碳粉，平均粒径5m的镍粉及平均粒径1.4m的钴粉。钛粉和12mass%的钼粉与各添加量的碳、镍、钴粉混合，各元素的添加量为0.4mass%~ 1.0mass%，混合粉末在100MPa压力下压缩成形，在高真空(1~2×10-3Pa)，于1100℃、1200℃、1300℃各温度下烧结2h，测定烧结体的密度、力学性能及组织。 试验结果表…     

直流电弧等离子体法制备纳米铁粉

采用自行研制的高真空双枪直流电弧金属纳米粉连续制备系统，制备了纯度较高的纳米铁粉。采用L16（4^3）正交实验的方法研究了各工艺参数对粉体产率及平均粒径的影响。利用X射线衍射（XRD）、透射电子显微镜（TEM）和相应选区电子衍射（SAED）试手段对样品的成分、形貌、晶体结构等进行了表征。利用SimplePCI软件测定了样品的平均粒径。结果表明：制备的纳米铁颗粒具有明显的球状形态，在静磁力的作用下呈现出链状分布；纳米铁粉的尺寸分布较窄，平均粒径在29～86nm范围内；电流是影响产率的主要因素，而充气压力是影响粒度分布的主要因素。     

预氧化烧结高密度钨合金

选取平均粒度为２．０μm的W粉末，小于４８μm的羰基Ni粉末和小于７４μm的羰基Fe粉末，纯度大于９９％。按照９０W－７Ni－３Fe配成合金粉末。先期投入４９％Ni，２１％Fe以及３０％的W粉末（均质量分数）球磨８h后，再加入余量的W粉末球磨至２２h，球料比为４∶１，停机后在真空中干燥。利用冷等静压成型得到７mm×６０mm的试样棒。将试样棒埋在Al２O３粉中，置于空气烧结炉中加热至４５０℃，经过３０min的保温预氧化后，再经不同温度在氨分解的氢气氛（低于－２０℃的露点）中烧结，最后以５０℃／min的速率冷却到室温，为进一…     

电脉冲孕育处理Al-22Si合金衰退性的研究

研究了电脉冲孕育处理后不同静置时间对Al-22Si合金凝固组织中初生相形态、大小、分布的影响。结果表明，电脉冲处理后立刻浇注对Al-22Si合金有较明显的变质作用，初生Si相形态由粗大板条状变为块状，其平均尺寸由153．15μm降至77．35μm，分布也较均匀；但电脉冲处理也存在着较明显的衰退性，即随着熔体静置时间的延长孕育效果逐渐消失，当静置时间为80min时，其组织形态与未经电脉冲处理的组织相似，其平均尺寸由77．35μm升至143．67μm。     

Fabrication and electrical characterization of 15% yttrium-doped barium zirconate—nitrate freeze drying method combined with vacuum heating

We applied a nitrate freeze-drying method to obtain a fine synthesized powder of 15% yttrium-doped barium zirconate. Fine 15% yttrium-doped barium zirconate powder of particle size about 30 nm was obtained by synthesizing at 500 °C in vacuum from a powder mixed by the nitrate freeze-drying method. However, we could not obtain such fine powder by synthesizing in air. Using the powder synthesized in vacuum, large and homogeneous grains of 15% yttrium-doped barium zirconate were easily obtained after sintering. Then, the bulk and grain boundary resistance were evaluated by AC 2-terminal measurement of sample in the form of bar and pellet and DC 4-terminal measurement of bar-shape sample. The grain boundary resistance was not inversely proportional to the grain size as theoretically expected. We concluded that specific grain boundary conductivity varies with samples. Some impurities, evaporation loss of barium oxide and/or other unexpected reasons might affect the grain boundary resistance in 15% yttrium-doped barium zirconate.     

Flow analysis of semi solid processing for grey cast iron

Abstract

Fluidity tests for semi solid processed grey cast iron were conducted at different degrees of primary fraction solid using fluidity strips with 2·5, 5 and 14 mm wall thickness. The microstructure of the fluidity strip castings was examined. Fluidity parameters, such as slurry velocity, critical solid concentration and choking range were studied. It can be concluded that critical solid concentration increases with the increase of wall thickness. The slurry velocity drops suddenly at a certain fraction solid very near to the critical solid concentration. Choking range zone can be measured by observing microstructure. A solidification model for fluidity has been developed based on the literature and microstructure study of semi solid processed grey cast iron. A mathematical equation has been obtained from the solidification model by modifying Flemings' fluidity model in order to analyse cavity filling of semi solid grey cast iron.     

超细硬质合金中晶粒非均匀长大机理

采用市售的粒度为0.8μm的WC粉末和粒度为1.6μm的Co粉制备了WC-10%Co超细硬质合金,通过金相显微镜﹑扫描电子显微镜观察了不同烧结温度下制备的试样WC晶粒形貌,对超细晶粒硬质合金非均匀长大现象及机理进行了研究。结果表明:粉末湿磨后的粗大颗粒在烧结过程中起晶核作用,是引起晶粒非均匀长大的关键因素。固相烧结时,烧结体中细小颗粒受到张力的作用发生旋转,当其取向与邻近的大颗粒取向一致时,形成共格界面,以粗大晶粒为核心以并合的方式非均匀长大;液相烧结时,细小晶粒溶解并优先地在大晶粒的某些低能量晶面如(0001)和(1010)面析出,引起晶粒异常长大。本研究中,当烧结温度达到1 410℃时,WC晶粒可异常长大为接近20μm的粗大晶粒。     

2618铝合金支座等温成形锻件的粗晶问题

2618铝合金因其耐热性能良好、热状态下塑性好、塑性变形时工艺性能好,而被广泛应用于航空航天工业.然而,在塑性变形时,由于2618铝合金抑制晶粒长大的微量元素含量较少,致使锻件易出现粗晶问题,使得材料力学性能下降,影响锻件质量.分别使用了国内生产的Φ165 mm和国外进口的Φ160 mm两种2618铝合金原始棒料,采用...     

Erosion–corrosion behavior of Ti(C,N)-based cermets with different TiN contents

Ti(C,N)-based cermets are fabricated with diverse contents of TiN addition by traditional powder metallurgy technique. The microstructure and properties are investigated and discussed. The influence of TiN content on the erosion and erosion–corrosion resistance is researched under alkaline conditions. Results reveal that the grain size decreases along with the increase of TiN. However, too much TiN results in incompact material and residual porosities in cermets. The grain size plays an important role in wear behavior. The effect of TiN content on erosion–corrosion of Ti(C,N)-based cermets is the same as that on erosion. It is advantageous for the wear resistance to add a small amount of TiN. Excessive TiN makes the wear resistance decrease on the contrary. In alkaline slurry, the cermets with coarse grains deteriorate largely due to corrosion which decreases the mechanical properties and speeds up the total loss of material. Nevertheless, the mechanical erosion is responsible for the degradation of cermets with fine grains. Cermets with 7.5 wt.% TiN addition have the highest erosion and erosion–corrosion resistance.     

喷射沉积2195铝锂合金轧制板材晶粒组织及性能控制研究

研究了喷射沉积制备2195铝锂合金锭坯挤压板坯经不同终轧温度热轧至6mm厚度板材,以及经不同中间退火后再冷轧至6mm厚度板材固溶后的晶粒组织。结果表明,终轧温度290℃时,热轧板固溶后表层为粗大再结晶晶粒,而中心层为细长纤维状晶粒;终轧温度降低至220℃时,虽然表层再结晶晶粒尺寸减小,但中心层转变为尺寸粗大的长条状再结晶晶粒。板材中尺寸1μm以上的富Cu第二相粒子数量随中间退火(空冷)温度的增加(从330℃提高至450℃)而增加;冷轧固溶后表层等轴状再结晶晶粒尺寸增加,而中心层晶粒逐渐由粗大长条状再结晶晶粒转变为细小等轴状再结晶晶粒。适当温度中间退火、随炉冷却并冷轧、固溶后表层和中心层全部为细小等轴状再结晶晶粒。优化中间退火后的冷轧板材T8时效态强度最高,而终轧温度220℃的热轧板材T8时效态强度最低。     

Bimodally grained high-strength Fe fabricated by mechanical alloying and spark plasma sintering

Nanocrystalline iron containing a certain fraction of coarse grains with nanosized oxide dispersoids has been processed by mechanically milling Fe powder and subsequent spark plasma sintering. Sintered samples exhibited a high tensile strength of 2100 MPa with 5% ductility; by optimizing the sintering conditions, it was possible to tune the strength–ductility balance. The optimally sintered material showed a tensile strength of 1500 MPa and 15% elongation. The microstructure consists of nanograined (<100 nm) as well as coarse-grained regions (>1 μm) with uniform dispersion of nanosized chromium oxide particles (～10 nm). The strength and elongation show strong dependence on the volume fraction of the coarse grains, and the high strength can be attributed to the ultrafine grain size of the nanograined regions and precipitation hardening by the oxide dispersoids. The ductility is considered to be due to the presence of coarse grains.     

船用钛合金焊接接头精细组织表征

对12 mm厚Ti6321进行TIG焊,采用OM,TEM等方法对焊接接头显微组织进行了分析,划分了焊接接头的区域,并讨论了各区的精细组织变化规律.结果表明,焊缝从表面到中心晶粒逐渐由柱状晶过渡为等轴晶,随着高温停留时间的延长和温度梯度的降低,晶内α相有粗大的等轴化趋势,位错密度不断升高.热影响区根据焊接热循环所处最高温度的不同划分为过渡区、细晶区和粗晶区.过渡区为等轴α、棒状α和残留β,细晶区为棒状α和残留β,粗晶区为针状α和残留β,随着高温停留时间的降低,晶内α较为细小,位错密度不断降低.     

Formation Mechanism of Nanoparticles in Fe–Cr–Al ODS Alloy Fabricated by Direct Oxidation Method

This study presents the fabrication of 14CrFe-Cr-Al oxide dispersion strengthened(ODS) alloy by a direct oxidation process.In order to explain how oxide nanoparticles are formed in the consolidation process,the powders after oxidation are subjected to vacuum thermal treatment at high temperatures.Differential scanning calorimeter,X-ray photoelectron spectroscopy,scanning electron microscopy and transmission electron microscopy techniques are used to detect the generation,evolution of oxides on both the surface and interior of the powder,as well as the type of oxide nanoparticles in the fabricated ODS alloy.It is found that an iron oxide layer is formed on the surface of the powder during low temperature oxidation.And the iron oxide layer would be decomposed after thermal treatment at high temperature.In the consolidation process,the oxygen required by the reaction of alumina and yttrium oxide to produce nano scale Y-Al-O particles mainly derives from the decomposition of iron oxide layer at elevated temperature and the inward diffusion of oxygen.Using the direct oxidation process,YAlO_3 nanoparticles are dispersed in the grains and at the grain boundaries of Fe-Cr-Al ODS alloy.     

Effect of powder particle size on gradient formation and grain growth in ultrafine crystalline gradient cemented carbide

Sinter-HIP combining vacuum and pressure in one-step sintering process has been applied to prepare ultrafine crystalline cemented carbide with a surface gradient layer enriched in binder. The effect of powder particle size on gradient formation and grain growth has been examined. The results show that the gradient layer thickness increases with decreasing WC and Ti(C,N) powder particle size. The number of abnormal WC grains increases with decreasing WC powder particle size. The formational mechanism of the gradient cemented carbide with ultrafine grains is discussed through analyzing the decomposability of nanoscale Ti(C,N), atomic diffusion and grain growth during one-step Sinter-HIP process.