Effect of galvanodynamic electrolysis conditions on the properties of a copper powder and the strength of compacts pressed from it

Conclusions Electrolysis under conditions of linear current application ensures that the loose deposit has a fine dendritic structure and enables the formation of particles larger than 220 m to be prevented almost completely. By varying the rate of current application and electrolyte concentration, it is possible to exercise control over certain processing properties of the powder.Translated from Poroshkovaya Metallurgiya, No. 11(287), pp. 4–7, November, 1986.     

Effect of compaction process sequence on axial density distribution of green compacts

Abstract

During powder compaction, frictional forces between the compact and the tool elements are developed. This causes pressure gradients in the compact, which produces, at the same time, undesirable density differences. This work presents a study about the effect of the compaction process sequence (CPS) and the ejection process on the axial density distribution during the uniaxial double ended pressing process of a high slenderness bushing. Different pressing processes were selected and carried out with a hydraulic press at laboratory and industrial levels (differences in the extraction method). Compacts were presintered and cut into thin discs in order to measure the local densities along the part, using the Archimedes' method. The obtained results show that the compaction process sequence has an important effect on the axial density distribution in a green compact, mainly in the case of compacts of high slenderness (>5). The ejection causes in the compact a post-compaction modification of the axial density distribution. Therefore, it is necessary to optimise the pressing process to obtain an adequate density distribution for each specific part.     

Effect of compaction density on foamability of Al–TiH2 powder compacts

Abstract

Al-TiH₂ powder mixtures have been cold compacted into precursors for foaming using single action, uniaxial pressing. After heat treatment, at 800°C for 5 min, foaming was only observed for precursors with a theoretical density above 94%. This density limit corresponds to the transition from interconnected to closed porosity, confirming that isolating porosity and enveloping the foaming agent in the matrix are vital to successful foaming. Although the variation in foam density for similar samples was small, the cell structures were different indicating that a low variation in foam density is not necessarily a good indication of achieving reproducible foam structures. The orientation of the sample had little effect on the foaming response for compacts with a length to diameter ratio below 1:2. For longer samples the foaming response was not uniform along the length of the sample indicating that in complex pressings the variation in local pressure must be understood in order to avoid regions being compacted below the critical density for foaming.     

热成形温度对高强钢方管组织及性能的影响

为了克服传统辊弯工艺和设备对室温下高强钢的影响,提出弯角局部感应加热辊压成形工艺制备高强钢方管,并通过单向拉伸试验、断口形貌观察、微观组织扫描电镜观察和X射线衍射分析研究热辊压成形温度对高强钢方管弯角处组织及力学性能的影响.结果表明,随着温度的升高,弯角力学性能得到明显的改善,断口形貌由室温下解理断裂逐渐过渡为韧性断裂,弯角处微观组织由板条状贝氏体向粒状贝氏体发展且多边形铁素体晶粒开始长大,方管外表面周向和纵向残余应力都明显降低且分布更加合理.综合实验分析,高强钢方管热辊压成形工艺的最佳温度为650℃.     

Influence of forming conditions on the mechanical properties of aluminum-lead powder metallurgy material

Translated from Poroshkovaya Metallurgiya, No. 6(306), pp. 45–49, June, 1988.     

Formation of properties and interparticular concrescence of hot-formed powder materials. III. Influence of technological factors of hot forming of powder compacts on concrescence and the mechanical properties of the obtained materials

Conclusions The technological conditions of obtaining powder materials exert a decisive influence on the course of the processes of concrescence, and consequently on the properties of the obtained specimens. If cooling and oxidation in the transfer of compacts from the furnace to the forging die are reduced to a minimum, then the optimal medium for sintering and hot repressing is a reducing medium, e.g., sharply dried hydrogen or DA. The accompanying removal of admixtures from the surfaces of open pores facilitates the processes of concrescence.In sintering in vacuum the admixtures are retained, and as a result of subsequent HP the role of nonmetallic inclusions as weakening factor increases, and the crack resistance of the material is impaired. Optimal is the procedure of hot repressing in which shear strain predominates, e.g., in extrusion which is accompanied by crumbling of the admixture layers and their redistribution, which promotes the processes of concrescence.Translated from Poroshkovaya Metallurgiya, No. 2, pp. 32–38, February, 1991.     

Effect of conditions of preparation of nickel fibers extruded from powders on their strength properties. Part II

Conclusions In the manufacture of extruded fibers the main process parameters determining their strength properties are sintering temperature and sintering time up to 1 h. Structural factors adversely affecting the strength of extruded nickel fibers are porosity, interfaces between blocks, and ash residue inclusions. Raising the sintering temperature from 1200 to 1280°C decreases the porosity and amount of ash residue inclusions and smoothens out the fiber surface profile. Under these conditions the strength of the fibers rises from 0.5–0.7 to 0.7–0.8 of the ultimate strength of the cast metal annealed at the same temperature.Translated from Poroshkovaya Metallurgiya, No. 7(211), pp. 41–44, July, 1980.     

干压成型工艺对石英基多孔材料的性能影响研究

本文以长江沿岸低品位石英砂为主要原料采用常压烧结研究干压成型工艺对石英基多孔材料性能的影响,为新型保温材料的开发提供参考。结果表明:随着成型压力的增加,石英基多孔材料气孔率降低。30 mm及50 mm多孔材料的气孔率均随保压时间的增加而降低,但是30 mm比50 mm降低速率慢。在成型压强及保压时间相同的条件下,50 mm多孔材料的气孔率均高于30 mm多孔材料的气孔率。通过条件优化,得到50 mm、5 MPa、5 min成型,烧结后的多孔材料性能较佳,气孔率为54.52%,孔结构较好。     

Influence of the forming process and sintering conditions on the structure and properties of powder ferrite materials

The effect of uniaxial and high isostatic pressing, and also sintering conditions, on the structure and properties of manganese—zinc, nickel—zinc, and barium ferrites was studied using x-ray, Mossbauer, magnetic, and gravimetric methods of analysis. Isostatic pressing was shown to have a positive effect on the crystallite-porosity structure and specified magnetic properties of the materials investigated.     

Mechanical properties of powder titanium at different production stages. I. Densification curves for titanium powder billets

The mechanical behavior of titanium powder billets at all production stages is examined. The dependence of how mechanical properties are formed on the structure is established. The compaction of a powder pressed in a rigid die mold, which is the initial stage of the production process, is analyzed. The experimental dependence of the compacting force on porosity is examined. The results are compared with theoretical data available.