注射成形钛合金粉末流变特性

以Ti?6Al?4V合金粉末为原料,选用60%(质量分数)石蜡、35%低密度聚乙烯和5%硬脂酸为粘结剂配方制备注射成型喂料。采用毛细管流变仪测定喂料的流变参数,分析不同球磨时间、粉末装载量、温度下喂料的流变学性能。结果表明：随着球磨时间的增加,喂料粘度增加,n 值减小;粉末装载量越高,喂料的粘度值越大,而且粘度与粉末装载量满足经验公式： mA ?=?=(1/)/ maxbr φφηηη,经计算,m的值为0.33。粘性流动激活能Ea值随剪切速率的增加而减小。     

表面活性剂添加对超细98W-1Ni-1Fe粉末注射成形喂料流变行为的影响(英文)

研究超细98W-1Ni-1Fe粉末的注射成形。系统研究球磨和硬脂酸(SA)添加对粉末特性以及喂料流变行为的影响。结果表明:球磨和SA添加均有效提高喂料的装载量。SA添加可以避免喂料制备过程中粉末与粘结剂间的表面反应,从而缩短混炼时间。SA添加可以降低喂料的粘度,但这种效果随温度升高而逐渐消失,在125℃以上时变为一种不利的效果。SA添加可以降低注射所需的温度。添加SA的粉末喂料在115℃时具有最低的粘度及剪切敏感性,而未加SA的粉末喂料在135℃时才具有最低的粘度及剪切敏感性。同时,添加SA的粉末喂料相比未添加SA的粉末喂料具有较低的温度敏感性及较佳的综合流变性能,因此,更适合于超细98W-1Ni-1Fe粉末的注射成形。     

粘结剂配比对316L不锈钢粉末注射成形喂料流变行为的影响

制备了58%粉末装载量、不同粘结剂配比的316L不锈钢粉末注射成形喂料,对比了各粘度模型的应用范围。采用Second Order模型回归了喂料的各项流变参数,分析了剪切速率和温度对喂料粘度的影响。结果表明,Second Order模型适合用于描述实验喂料的流变行为,剪切速率和温度对喂料粘度的影响规律:粘度随剪切速率和温度的升高而降低。该粘结剂体系的最佳配比为65%石蜡、30%低密度聚乙烯及5%硬脂酸,考虑了剪切速率和温度对粘度的影响,其流变行为公式为lnγ=2.1335-0.9717lnγ+0.107T-0.0511(lnγ)2+0.0066T lnγ-0.0005T2。     

Ti-6Al-4V金属粉末注射成形喂料的制备与性能表征

通过Ti-6Al-4V粉末制备金属粉末注射成形喂料。利用转矩流变仪确定喂料的临界粉末装载量,观察喂料粘度的变化,判断喂料的均匀性。采用旋转流变仪对喂料进行流变实验。通过改变烧结温度确定合适的烧结工艺。结果表明,喂料的临界粉末装载量为51%,混炼2次能使喂料更均匀密实。喂料的粘度随剪切速率的增加而减小,喂料呈假塑性流体行为。当烧结温度为1280℃时,烧结坯密度为4.32 g·cm~(-3)、抗拉强度为987 MPa,此时拉伸断面具有较少的孔洞结构和较好的结构完整性。     

球磨高氮不锈钢粉末特性及注射喂料流变性能

采用高能球磨技术制备了高氮节镍不锈钢近球形复合粉末,与石蜡基多聚合物组元黏结剂混炼制成金属注射成形喂料,研究了注射喂料的黏度、剪切速率以及温度等对黏度的影响。结果表明:高能球磨能够显著改善高氮不锈钢粉末的工艺特性,球磨60 h得到的粉末颗粒细小,球形度较好,振实密度高,适合用来制作高质量的金属注射成形喂料。其中,粉末装载量为58%的喂料应变敏感因子最小(n=0.45),粘流活化能最低(E=28.70 kJ/mol),综合流变学因子最大(αSTV=2.96),表明该喂料具有最好的综合流变性能,非常适宜进行后续注射成形工艺。     

316L不锈钢粗粉注射成形喂料的流变行为

制备了平均粒度为30μm的316L不锈钢粗粉注射成形喂料,研究了剪切速率、温度对喂料流变行为的影响,应用毛细管粘度计测量了3种喂料在不同温度下的粘度值,比较了3种不同成分喂料的应变敏感性因子的大小。结果表明:粉末装载量为58%、粘结剂成分为65%PW+30%LDPE+5%SA的喂料应变敏感性因子较小,较适合316L不锈钢粗粉的注射成形。     

注射成形97W—2Ni—1Fe重合金的研究

制备了几种不同粉末装载量的９７Ｗ－２Ｎｉ－１Ｆｅ重合金注射成形喂料,对这些喂料的流变学行为进行了研究,测量了烧结后产品的力学性能和烧结过程中的收缩。研究结果表明喂料的流变行为可用假塑性体来描述,注射成形所得合金的力学性能优于传统压制／烧结所得合金,当粉末装载量（体积分数,％）为４７时合金力学性能最好。成形坯在烧结过程中的收缩基本各向同性,产品的尺寸偏差小。     

水雾化Inconel713C喂料流变性能的研究

以水雾化法制备的Inconel713C合金粉末为原料,利用ZRZ1452型熔体流动速率仪,研究了三种塑基粘结剂体系和Inconel713C合金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n和τ_w-γ_w近似关系式。结果表明:在52%装载量下,三种组分喂料的粘度均随温度的升高以及剪切速率的增大而减小。粘结剂组成为85%POM+5%HDPE+10%其他助剂的喂料(D1)具有最好的充模性,呈假塑性流体。喂料D1的粘度与温度关系更好地符合Arrhenius定律,随剪切速率的增加,粘流活化能降低,而指前因子增大。     

YT5硬质合金注射成形喂料流变学行为研究

在金属注射成形(MIM)工艺中,喂料的流变性能直接决定注射坯的质量,进而决定最终制品的力学性能及尺寸精度。评价喂料流变性能的主要指标是粘度以及粘度对应变和温度的敏感性。本文比较研究了三种YT5硬质合金注射成形喂料的粘度与剪切速率、粘度与温度的关系。研究结果表明:复合粘结剂体系50～70%PW+20～30%EO+20～30%LLDPE+5～10%SA与YT5硬质合金粉末形成的注射成形喂料具有最佳的流变性能,其非牛顿指数n和粘流活化能△Eη分别为0.640,37.7 kJ·mol~(-1)·K~(-1)。     

金属粉末颗粒形貌对注射成形喂料粘度的影响

将气雾化球形不锈钢粉末与水雾化不规则形状不锈钢粉末按一定比例混合,利用毛细管流变仪测定喂料的流变性能,分析了粉末形貌、剪切速率和温度对喂料粘度的影响。结果表明:气雾化球形粉末制得的喂料对温度变化特别敏感,通过掺杂25%~75%的不规则形状粉末可降低喂料粘度对温度的敏感性,并降低喂料的流动指数,使喂料的流变稳定性能得到提高,更利于注射成形。     

RHEOLOGICAL PROPERTIES OF METAL INVECTION MOLDING BINDER AND FEEDSTOCK

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Effects of milling and active surfactants on rheological behavior of powder injection molding feedstock

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Metal injection molding of W-Cu powders prepared by low energy ball milling

Low energy ball milled W/Cu powders were used for metal injection molding (MIM) in order to overcome the low powder volume fraction of MIM parts after debinding as well as the inherently poor sinterability of the W-Cu powder compacts. Ball milling was carried out using commercial fine W and Cu powders to form a powder mixture suitable for injection molding. W powders showed no change in either size or shape during the milling process, but the ductile Cu powders were easily deformed to a three-dimensional equiaxed shape, having a particle size comparable to that of W powders. This modification of powder characteristics by ball milling resulted in an improvement of the solid loading of roughly 58%, maintaining a high and uniform powder packing density in the feedstock. The densification behavior of W-Cu MIM parts is also discussed on the basis of the relationship between Cu composition and W particle size.     

Thermo-physical characterization of binder and feedstock for single and multiphase flow of PIM 316L feedstock

A thorough knowledge of the material properties of the feedstock and binder system is essential for successful powder injection moulding (PIM) as well as for numerical simulation. In view of the above, characterization of a developed binder system and feedstock has been reported in this paper for processing of 316L stainless steel powder through PIM route. The binder system consists of paraffin wax, stearic acid and low-density polyethylene. The feedstock comprises of 316L stainless steel powder and the above binder system. The thermal, physical and rheological characteristics of the binder system and feedstock have been investigated separately along with binder removal technique from the injection-moulded green compact. The thermal characterization revealed the semi-crystalline nature having distinct melting and solidification range for both the binder and feedstock. Data from DSC and TGA show that injection of the feedstock should be carried out above 102 °C (i.e. the upper melting temperature) but below 154 °C as beyond which the binder components paraffin wax and stearic acid start degrading and mould temperature should be below 57 °C. The binder and feedstock are found as shear-thinning fluid as viscosity decreases with the increase in shear strain rate and temperature. However, the viscosity of the binder is more sensitive to shear strain rate and temperature compared to that of the feedstock.     

Rheological properties of metal injection molding feedstock

Viscosity of a polyethylene glycol-polymethyl methacrylate (PEG-PMMA) binder and PEG-PMMA/Fe-2Ni feedstock in powder injection molding was measured and calculated. A logarithmic additivity between viscosity of the binder and that of its constituents was found. Other factors, such as temperature, powder loads, content and type of surface-active agents and those of polymers, in relation to rheological properties of feedstock were discussed as well. The results showed that with increasing viscosity of surface-active agent, polymer melt index or temperature, the feedstock viscosity decreased while higher polymer content and powder loading would lead to additional feedstock viscosity. The relationship mentioned above is expressed and effectively explained why the change rate of feedstock viscosity will slow down with the increase of shear rate.     

金属注射成形与塑料注射成形的比较研究

从喂料性能和流变性方面对金属注射成形(MIM)和塑料注射成形(ABS)进行了比较。MIM喂料由质量分数为98%的铁粉和2%的镍粉和粘结剂混炼而成。粉末装载量的体积分数为58%。结果表明:MIM喂料与塑料相比具有密度和导热系数大,比热容小的特点。通过对流变性的比较发现:ABS和MIM喂料相比,后者对温度变化较为敏感,而对剪切速率的敏感性低于ABS。     

Cu-Cr-Zr复合粉末机械合金化研究

以Cu、Cr和Zr粉末为原料,采用机械合金化制备了Cu-90%Cr2Zr复合粉末。利用X射线衍射仪(XRD)和扫描电镜(SEM)研究了机械合金化过程中粉末的物相和微观形貌。结果表明:Cu-Cr-Zr粉末可通过机械合金化获得过饱和固溶体;在一定的球磨时间内,随球磨的进行,Cu-Cr-Zr粉末晶粒细化至纳米尺寸,晶格常数增加,晶格畸变降低,粉末形貌呈片状;但进一步球磨会导致铬的晶格常数降低,导致畸变增加,使得粉末变得不规则及颗粒大小不均。