316L不锈钢粉末注射成形喂料流变性能的研究

简介了金属粉末注射成形的工艺过程,制备了不同粉末装载量的喂料,并分析了粉末装载量、剪切速率和温度对喂料流变性能的影响.结果表明:随着粉末装载量的增加,喂料的表观粘度增大;随着剪切速率的增大和温度的升高,喂料的表观粘度减小;在高的剪切速率下,喂料的粘流活化能较小,喂料对温度不敏感.     

粉末注射成形钨合金球制备工艺的研究

采用粉末注射成形方法制备一种军工用钨合金球,通过调节注射参数来消除其注射缺陷,通过调节烧结工艺来提高其综合性能.结果表明:钨合金球在注射过程中成形坯内的融合线随注射速率、注射压力、注射温度的升高而减少,且调节注射速率、注射温度的效果较调节注射压力更为显著;产品的密度、压溃压力、压缩率在1530℃前都随烧结温度的升高而增加,超过1530℃后都随烧结温度的升高而减小,产品的球直径变化量随温度的升高而变大;在1510℃下烧结的钨合金球综合性能较好,其密度为18.17 g/cm3,球直径变化量为0.12 mm,压溃压力为54 kN,压缩率为30.6%.     

新型催化脱脂型喂料的流变性能研究

利用XNR-400熔体流速仪,研究了催化脱脂型粘结剂体系和17-4PH不锈钢粉末混合制备的喂料的流变性能.通过线性回归分析,计算出非牛顿指数和粘流活化能.结果表明:喂料的粘度随着温度的升高以及剪切速率的增大而减小,具有较好的充模性,呈假塑性流体.在三种组份的喂料中,F3喂料的综合流变性能最好,在185℃和500 s-1剪切速率条件下,其非牛顿指数n和粘流活化能E分别为0.26864和34.96785kJ·mol-1.     

微晶蜡基WC–10Co注射成形喂料的流变性能及溶剂脱脂行为

以微晶蜡为粘结剂主要组元,与WC–10Co（YG10）粉末密炼混合,得到注射成形喂料。通过线性拟合计算出喂料的非牛顿指数、粘流活化能和综合流变学因子,考察不同温度与剪切速率下喂料的流变性能。对成形坯体在不同温度下于不同脱脂溶剂中的失重进行分析,考察坯体的溶剂脱脂动力学行为。结果表明,微晶蜡基喂料呈现假塑性流体的剪切稀化特征,对剪切速率和温度的敏感性较为稳定,综合流变性能良好。可溶性粘结剂组元的脱除主要发生在脱脂前期,由扩散所控制,且随着坯体厚度和体积的减小及脱脂温度的升高,扩散系数增大。     

TB2钛合金热压缩变形流变应力

在Gleeble-1500D热/力模拟试验机上,采用高温等温压缩试验,对TB2钛合金在高温压缩变形中流变应力行为进行了研究;应变速率为0.01-10 s^-1,变形温度为600-1200℃。结果表明：应变速率和变形温度的变化显著地影响合金流变应力的大小,流变应力随变形温度的升高而降低,随应变速率的提高而增大;可用Zener-Hollomon参数的双曲正弦函数形式来描述合金的流变应力行为。     

Ti-6Al-4V粉末注射成形喂料流变主曲线的生成

从流变学基本理论出发,讨论剪切速率、温度与Ti-6Al-4V粉末注射成形喂料的剪切粘度的关系。结果表明:随剪切速率增加,喂料的粘度降低;随温度升高,喂料的粘度下降;且喂料在不同温度下的粘度曲线形状相似,只是位置因温度不同而发生相对位移。在此基础上应用由"时温等效原理"发展而来的(0/??~???0)主曲线生成方法获得Ti-6Al-4V合金粉末喂料的流动主曲线。借助该主曲线,对于进一步研究金属粉末注射成形(MIM)喂料的其它特性以及生产实践大有益处。     

介质黏度对PCC分散体系流变行为的影响

在AR2000ex型流变仪上对沉淀碳酸钙(Precipitated calcium carbonate,PCC)在PEG(聚乙二醇)悬浮体系进行稳态剪切流变实验。通过2种方法来改变分散体系黏度:1)以PEG200(相对分子质量为200)为连续相,分散体系以10℃为间隔从10℃上升至50℃;2)在30℃用相同的聚合物3种不同相对分子质量的PEG(PEG200、PEG400和PEG600)。结果表明随着温度升高,PCC/PEG200分散体系的临界剪切速率越来越大。在剪切增稠区内流动指数N随温度升高而降低,稠度系数K随着温度升高而升高。临界剪切速率以及临界剪切黏度与温度严格满足Arrhenius关系:η=A exp[Ea/(RT)]。研究发现随温度的变化临界剪切应力不变。随着PEG的相对分子质量增加,分散体系的黏度增加,临界剪切增稠速率减小。PCC粉末的分形结构以及聚集体的形貌使得体系的相对黏度远大于硬球体系的相对黏度。     

初始晶粒尺寸对2024铝合金热变形行为和组织的影响

利用永磁搅拌近液相线铸造和普通铸造方法制备不同晶粒尺寸的2024铝合金铸锭,利用Gleeble-1500热模拟试验机研究初始晶粒尺寸对不同压缩变形条件下2024铝合金的热变形行为和变形后显微组织的影响。研究表明:2024铝合金的热变形行为依赖于变形条件和初始组织。初始晶粒尺寸对流变应力的影响是:当应变速率小于0.1 s~(-1)时,流变应力随晶粒尺寸减小而减少;当应变速率为10 s~(-1)时,流变应力随晶粒尺寸减小而增大。降低变形温度会弱化晶粒尺寸对流变应力的影响。热压缩流变应力随应变速率增大而增大,随变形温度升高而减小。应变速率为10 s~(-1)时,热压缩应力应变曲线呈现周期性波动;只在粗晶2024铝合金中发现变形剪切带。     

玻璃铝基复合材料高温压缩变形行为研究

利用Gleeble-1500对玻璃铝基复合材料在温度为573～723K、应变速率为0．01s^-1～10s^-1的条件下进行高温压缩变形行为的研究。结果表明：应变速率和变形温度的变化强烈影响复合材料的流变应力,流变应力随变形速率的提高而增大,随变形温度的升高而降低;玻璃铝基复合材料高温塑性变形时的流变行为可用Zener-Hollomon参数的双曲正弦函数来描述。     

纳米晶W-Ni-Fe粉的流变行为和烧结特性

研究了W-Ni-Fe纳米晶粉在注射成形中喂料的流变行为,纳米晶W-Ni-Fe粉采用机械合金化(MA)的方法制备,并将此粉末与蜡基粘结剂混合以形成一种喂料,讨论了MA球磨时间,纳米晶粉末体积和温度对喂料流变性的影响,随球磨时间增加,喂料的粘度以及粘度对剪切速率的敏感性降低,因此,在较长的球磨时间下,这种粉末喂料的流动性和成形性变好,随粉末体积增加,喂料的粘度遵循公式呈非线性增加,此时n=0.68.MA粉末喂料的粘度随温度和剪切速率的变化较小,所以注射温度和注射速度的变化对这种MIM注射坯的质量影响较小,本文也讨论了采用MA制备的W-Ni-Fe纳米粉末的烧结特性,实验结果表明球磨可以导致在液相烧结温度以下合金达到很高的密度,大的晶格畸变、晶粒细化和超饱和固溶体的形成,强化了烧结工艺。     

MIM注射料粘度与流变行为研究

对相同粉末装载量的４种粘结剂体系的Ｆｅ－ＮｉＭＩＭ注射料的粘度和流变行为研究了研究，采用毛细管流变仪，获得ＭＩＭ注射料对不同显度，不同剪切速率下的粘度值，分析了ＭＩＭ注射料的流动性能，粘度对应变速率的敏感性，粘度对温度的敏感性，比较了各粘结剂的粘度和注射料的流动性指数的差异。     

粉末注射成形中喂料充模过程的一维流动分析

通过对宾汉体和假塑性体的流变行为与实际喂料流变行为的比较,建立了能较好地与实际喂料符合的流变模型。对喂料的一维流动作了分析,建立了求解模内温度场、压力场、速度场及剪切速率的控制方程,并给出了其求解过程。     

曲轴用非调质钢C38N2的静态再结晶行为

通过热模拟实验、光学金相及透射电镜分析观察,研究了奥氏体化条件、变形温度、变形速率、变形量以及道次间隔时间对曲轴用非调质钢C38N2轧制道次间的静态再结晶体积分数和残余应变率的影响规律.实验结果表明:随着变形温度的升高、变形速率的增大、变形量的增大或道次间间隔时间的增长,静态再结晶的体积分数逐渐升高,道次的残余应变率逐渐降低;原始奥氏体晶粒尺寸增大,静态再结晶体积分数降低,但变化不大;在1250℃以下,随着奥氏体化温度的升高,静态再结晶体积分数降低不明显,但在1250℃以上,奥氏体化温度的升高明显降低了静态再结晶体积分数.通过线性拟合以及最小二乘法,得到静态再结晶体积分数与不同变形工艺参数之间关系的数学模型;对已有残余应变率数学模型进行修正,得到含有应变速率项的残余应变率数学模型,拟合度较好.      

喷吹煤与废塑料时矿石的还原粉化性能

以首钢炼铁原料为基础,对高炉喷吹煤与废塑料条件下的矿石还原粉化性能进行研究。结果表明:温度是影响炉料低温还原粉化的主要因素,500℃时粉化最为严重,900℃时炉料的低温还原粉化基本结束,在500~900℃,炉料粉化率随温度的升高而降低;相同温度条件下,炉料的低温还原粉化率随H2含量的增加而增加,随CO2含量的增加而减少;喷吹煤与废塑料后,炉料的低温还原粉化性能不会影响高炉的顺行;烧结矿的低温还原粉化率较大,球团矿、块矿较小。     

Variability of feedstock viscosity and its correlation with dimensional variability of green powder injection moulded components

Abstract

In this study, a correlation between green part dimensional variation and feedstock viscosity variation is presented for the powder injection moulding (PIM) manufacturing process. A correlation of an increase in green part dimensional variation as feedstock viscosity variation increases has been found and the correlation was independent of powder type (316L gas atomised and water atomised) and mixing technique (batch and continuous). The variation of feedstock viscosity was lowest over the greatest temperature range for high shear continuous compounding with a broad distribution of irregularly shaped powder. Thus, this feedstock material would have the greatest process window for injection moulding with the least variation.     

Influence of Procedure Parameters on Rheological Property of Semi-Solid AZ91D Magnesium Alloy

Semi-solid AZ91D magnesium alloy was investigated in isothermal steady-state condition. The influence of stirring technological parameters such as stirring temperature and shear rate to apparent viscosity of semi-solid alloy slurry was discussed. Apparent viscosity increases with stirring temperature decreases at the same shear rate. At the same stirring temperature, apparent viscosity decreases rapidly at first with shear rate increases, and then apparent viscosity decreases slowly with shear rate increases, when shear rate reaches a certain value, apparent viscosity appears tiny increase. According to the experimental data, the relation between solid volume fraction and apparent viscosity of semi-solid AZ9l D alloy at shear rate 238 s- 1 is fitted by regression method, it supplies useful data to the numerical simulation of semi-solid AZ91D alloy die casting process.     

Localized vs homogeneous deformation in Fe82B15Si3 amorphous alloy

Amorphous alloys are known to deform plastically either by a localized shear mode or in a homogeneous manner. Conditions that favor homogeneous deformation in an amorphous alloy consisting of 82Fe, 15B and 3Si in at. pct have been established by a free-bend test over a range of temperatures. These results are in turn related to the stress-strain rate-temperature relationship obtained by a load relaxation testing method. The intense, localized shear deformation is shown to occur at relatively high strain rate and low temperature regions where the rate sensitivity of flow stress,m, is small. With increasingm, plastic flow tends to take place homogeneously provided that the mode of deformation remains stable. The strain rate sensitivity of flow stress increases with decreasing strain rate and increasing temperature; the computed diffuse shear transformation zone also changes in the same manner. However, the general trend changes above the glass transition temperature, i.e., the diffuse shear transformation zone decreases and the flow strength increases with increasing temperature.     

Optimisation of process conditions in powder injection moulding of microsystem components using robust design method Part 2 – Secondary design parameters

Abstract

Powder injection moulding (PIM) is a proper fabrication method for microsystem technology components. This paper studies the process control of PIM to create thin walled, high aspect ratio geometries, which can be easily found in microtechnology based electro chemical, mechanical and biological systems (MECS). The powder used in this study is gas atomised 316L stainless steel with a median particle size of 10 μm. The effects of reducing the thickness of high aspect ratio geometries on the secondary design parameters including the maximum wall shear stress, cooling time and standard deviations of the melt front velocity and areas are studied. The study shows process parameters including fill time, feedstock injection temperature, mould wall temperature and switchover position can be optimised using the Taguchi robust design method.     

The characterization of the A1-12 Wt Pct Si flake powder produced by a double-disk process

A double-disk (DD) process was developed in this study for producing highly elongated flakes which are very promising for application as a filler for conductive composites with a plastic matrix. The Al-12Si alloy was selected as the experimental alloy in view of its high stiffness, strength, and integrity which are beneficial for retaining its high aspect ratio during the fabrication of the composites. Various operational parameters,i.e., pouring temperature and the rotational speeds of upper disk and quenching disk, were monitored in the powder production to reveal their effects on the size distribution and morphology of flakes. The flake formation mechanism was also investigated. Experimental results indicate that the broad size distribution of the flakes produced by the double-disk process rises from the splat-quenching effect and the formation of interlinked flakes and whisker-shaped flakes. The mean particle size (or mean flake width) increases with a decreasing rotational speed of centrifugal disk or quenching disk speed, but is little influenced by pouring temperature. The length-to-width ratio of flakes varies with the rotational speed of quenching disk but inversely with pouring temperature, centrifugal disk speed, and flake width. The thickness varies inversely with all of these variables. The aspect ratio varies with pouring temperature, rotational speed of quenching disk, and flake width, but varies inversely with centrifugal disk speed. All of these variations might be accounted for by considering the solidification rate and dragging rate. Based on these two rates, theoretical relationships for length-to-width ratio, thickness, and aspect ratio as a function of various metallurgical factors are derived and correlate sufficiently with the trends of experimental data.