难变形材料热静液挤压复合精密塑性成形工艺

目的 研究热静液挤压及其复合塑性变形工艺在高密度钨合金、钨铜合金、钛基复合材料及镁合金薄壁细管等难变形材料方面的制备。方法 通过对高密度钨合金难变形材料进行热静液挤压及旋转锻造等塑性成形,分析了材料在成形过程中的微观组织及性能变化规律和强化机制,制备出大长径比穿甲弹弹芯材料。在此基础上,将该复合塑性变形技术拓展至两相不互溶材料钨铜合金、钛基复合材料及大长径比镁合金毛细管等难变形材料方面的制备。结果 热静液挤压及其复合塑性变形工艺在粉末冶金难变形材料的致密化方面具有显著优势,获得材料不仅致密度高,而且有效实现了控形控性;对于镁合金薄壁细管成形而言,也可以实现组织与性能的有效调配,同时材料的精度较高。结论 热静液挤压及其复合塑性变形工艺在难变形材料的制备与成形方面具有独特的优势与广阔的应用前景。     

机械球磨Cu-15%Cr复合粉末的致密化工艺研究

探讨机械球磨Cu—15％Cr复合粉末经真空烧结后采用热静液挤压致密化的可能性．研究了机械球磨时间、烧结温度、保温时间和挤压温度等工艺参数对材料致密化的影响．结果表明，热静液挤压工艺可以有效的促进机械球磨复合粉末的致密，所获得的材料具有优异的组织性能．     

粉末短流程成形固结技术的研究及展望

针对粉末冶金行业最新发展的几种短流程成形固结新技术,结合华南理工大学近十多年来在粉末材料-工艺-装备-零件一体化方面开展的研究,重点阐述了粉末冶金温压成形、高速压制成形、喷射成形、多场作用下粉末成形与烧结一体化技术的研究进展及应用情况。指出在粉末冶金成形固结研究领域,合理拓展现有粉末冶金技术规范的空间,有望给传统粉末冶金成形固结技术注入新的活力。粉末冶金成形固结新技术的不断出现,必将促进先进制造业和高技术产业的快速发展,也必将给材料工程和制造业带来更加光明的前景。     

TiAl合金气雾化制粉及热等静压成形研究进展

概述了TiAl合金气雾化制粉及热等静压成形的主要研究成果。在TiAl合金粉末制备方面,重点介绍了气雾化制粉工艺、粉末粒度控制、粉末氧含量控制和粉末组织特征。针对热等静压技术,介绍了TiAl合金粉末热等静压致密化过程及机理,总结了采用热等静压近净成形工艺制备TiAl合金转捩片的研究成果。结合粉末冶金TiAl合金研究进展,提出了未来TiAl合金粉末制备及成形技术的发展方向。     

喷射成形多孔材料的致密化工艺综述

介绍了6种常用的喷射成形多孔材料致密化工艺,即热挤压、轧制、锻造、热等静压、楔形压制和陶粒压制工艺,重点介绍了各种工艺的原理、特点、优缺点以及针对某些缺点而采取的一些改进措施.发现热挤压、轧制、锻造、热等静压和陶粒压制工艺能单次使喷射成形多孔材料整体成形致密化,而楔形压制是一种通过局部小变形累积以实现整体成形致密化的工艺;楔形压制在致密化喷射成形大尺寸材料方面具有独到的优势.最后,探讨和展望了今后的发展方向.     

运动器件中的粉末冶金零件

美国每年用于运动器具的花费高达170.64亿美元,无论是专业的还是业余的运动器材均要求降低成本,因此粉末冶金制造技术有着很大的吸引力,此文主要介绍重量轻的钛合金和高比重钨的粉末冶金运动器件.钛粉末冶金工艺有两种:一是元素粉末混合法,二是预合金法.现在这两种工艺都可通过金属注射成形(MIM)和激光成形来实现.元素粉末混合法成本低,但多数情况下材料性能较差;预合金法成本较高,但材料的机械性能相当于铸锻件.此外,粉末成形工艺还有冷、热等静压、粉末轧制和挤压、喷射成形和气相沉积等.     

喷射成形技术及其在钢铁材料上的应用

喷射成形是近年来发展非常迅速的一种近终成形先进冶金工艺技术。与传统铸造工艺及粉末冶金工艺相比,喷射成形设备、工艺简单,能生产偏析小、晶粒细、致密度高的材料。喷射成形技术在铝基合金、铁基合金、高温合金、铜合金及复合材料等方面都得到了广泛的应用。主要介绍该技术的原理及其在钢铁材料方面的应用情况,并讨论了它在钢铁领域的发展趋势,指出喷射成形工艺是一种有望替代粉末冶金工艺生产高合金钢材及一些特殊钢材的崭新工艺。     

喷射共沉积颗粒增强金属基复合材料的研究现状与进展

作为一种综合了铸造与粉末冶金优点制备近成形颗粒增强金属基复合材料的方法,喷射共沉积技术及其应用受到了广泛的关注。本文综述了喷射沉积颗粒增强金属基复合材料的发展现状;介绍了喷射共沉积技术的原理;讨论了喷射共沉积过程中金属液体对增强相的捕获机理和凝固前沿对颗粒的捕获问题;介绍了喷射沉积颗粒增强金属基复合材料的装置及工艺参数的控制;着重介绍了喷射沉积材料的组织性能及致密化工艺,提出通过旋球同步预致密后再分别进行往复镦-挤和等径角挤压实现沉积坯的大塑性变形达到完全致密与冶金结合;指出了喷射沉积金属基复合材料将向组织均匀化、韧性化、完全致密化方向发展。     

准晶合金粉末的固结成形

本文介绍了几种重要的准晶粉末固结成形方法,并简要说明了其固结原理。根据研究结果说明,亚稳态准晶合金粉末可以采用爆炸固结,超高压固结得到致密的大块准晶材料,稳定准晶合金粉末可采用多种动态热加工工艺进行致密化。另外还可以利用准晶相变规律来制备大块准晶材料。     

新型超高温结构材料MoSi_2的制备技术

综述了粉末冶金新工艺在制备超高温结构材料MoSi_2及MoSi_2基复合材料中的应用。这些新工艺包括:放热弥散法、反应烧结法、自蔓延高温合成、机械合金化、等离子喷射沉积、粉末注射成形、热等静压法和陶瓷颗粒固结法。还讨论了这些工艺在制备MoSi_2材料中的优势与劣势。     

Hot Hydrostatic Extrusion of Mechanically Alloyed Al-4.9Fe-4.9Ni Powders

Al-4.9 Fe-4.9 Ni alloy powders have been synthesized by mechanical alloying. The rnechanically alloyed powders are consolidated by hot hydrostatic extrusion. The results show that extrusion tempereture. extrusion ratio and lubricant have great effects on the quality of extruded rods and their mechanical properties, The mixture of graphite and glass powders as lubricant can prevent the oxidization of cold compacted billet by cladding the billet with this lubricant before heating. This technique greatly simplifies the conventional densification process of powders     

Mo-8wt%Cu纳米复合粉末的烧结与加工

用机械合金化法制取Mo-8%Cu(质量分数)纳米复合粉末,采用液相烧结和致密化后处理工艺制备了Mo-8%Cu(质量分数)合金。通过扫描电镜对Mo-Cu液相烧结和变形加工后合金显微组织进行了分析,研究了各种工艺参数对Mo-Cu合金致密性、拉伸强度、延伸率和晶粒尺寸的影响。结果表明,高能球磨的Mo-8%Cu(质量分数)纳米复合粉末坯体,经液相烧结后,其烧结态为Mo、Cu复合网状组织,可获得相对密度高达98.6%的Mo-Cu合金,再经静液挤压变形加工处理后,可获得全致密的Mo-8%Cu(质量分数)合金,在室温静液挤压40%形变率的条件下,拉伸强度可达到576MPa,延伸率5.8%。     

热挤压工艺对AZ31镁合金晶粒大小及性能的影响

对商用AZ31镁合金挤压棒材进行了不同工艺参数的挤压变形,系统研究了挤压工艺参数对AZ31镁合金晶粒大小以及性能的影响,并对镁合金组织的微晶尺寸进行了金相定量分析.研究结果表明,热变形可有效细化晶粒,但对AZ31镁合金晶粒细化是有限度的;对已通过热挤压变形晶粒细化的AZ31镁合金进一步进行大的塑性变形,其晶粒不但没有进一步的细化反而比挤压前略有长大.     

Processing of materials—monolithic to composites

A multimillion rupee 500-ton hydraulic extrusion/forging facility established at NPL, New Delhi, has been used to undertake extensive studies in forming, the process of plastically deforming, which is the most important way of shaping materials. Wrought materials are used extensively for making useful products employing extrusion and forging, the two important secondary processing techniques used to convert materials into useful shapes and sizes and also to improve the mechanical and metallurgical properties. The success of these processes depends on the proper control and eventual optimization of different process variables. Different ferrous and non-ferrous materials including 316 and 321 stainless steels (using glass lubrication), aluminium brass, admiralty brass and 70/30 and 90/10 cupro nickels have been extruded at a lab-scale production level to determine the influence of different extrusion variables such as temperature, strain rate, extrusion ratio, different die design and several different compositions of lubricants on pressure requirement and surface quality of the products. In the case of ferrous extrusions, the choice of billet-container lubricant has a marked effect on the shape of pressure-distance curves by influencing the effective coefficient of friction and heat transfer coefficient. Temperature, extrusion ratio and strain rate mainly influence the level of pressure-distance curves. Significance of specially designed dish shaped dies, avoiding the dead metal zone and the importance of extrusion limit diagrams for different materials on the available press capacity has also been highlighted. Deformation behaviour of the hi-tech materials; discontinuously reinforced metal matrix composites (MMCs) and aluminium-lithium alloys using hot extrusion and closed die forging, have been carried out. Parameters have been optimized to extrude rods and thin walled circular MMC tubes of aluminium alloy (2124/6061)-SiCp MMCs having varying volume fractions of SiCp. This developmental work has been carried out using powder metallurgy, liquid metallurgy and spray atomization and deposition routes, in joint collaboration with several R & D organizations. Hot extrusion being an important production technique, results of these experiments can be directly transferred to industries. Similar deformation studies either by closed die or by isothermal forging have been made to develop components. The pilot plant level facility is available for any industry for carrying out developmental R & D work. NPL welcomes such collaboration.     

Study of the properties of low-cost powder metallurgy titanium alloys by 430 stainless steel addition

Titanium is a lightweight metal with an outstanding combination of properties which make it the material of choice for many different applications. Nonetheless, its employment at industrial level is not widespread due to higher production costs with respect to competitor metals like steel and aluminium. In this work the production of low-cost titanium alloys is attempted by combining the utilisation of a powder metallurgy process and cheap alloying elements (i.e. commercial 430 stainless steel powder optimised for the powder metallurgy industry). Low-cost titanium alloys are fabricated by blending elemental titanium with stainless steel. The behaviour of the powders as well as that of the sintered materials are analysed and compared to that of a master alloy addition Ti6Al4V alloy. The produced low-cost titanium alloys show comparable properties to both wrought and powder metallurgy titanium alloys and, therefore, they are proposed as an alternative to obtain structural component made out of titanium alloys.     

Lubrication in Hot Tube Extrusion of Superalloys and Ti Alloys

Tubular products made of superalloys and titanium alloys usually work in high temperature environment and applied heavy loading. Hot extrusion is the best technology to form tubular billets with fine microstructures and good mechanical properties. Lubrication is one of the key techniques in hot extrusion, glass lubricants are most suitable for hot extrusion. Lubrication technique in hot extrusion is dealt with in this paper, the lubrication principle of hot tube extrusion is presented. Experiments of glass lubricated backward tube extrusion of titanium alloys and forward tube extrusion of superalloys are also discussed.     

Microstructural and mechanical characterisation of 7075 aluminium alloy consolidated from a premixed powder by cold compaction and hot extrusion

The present work concerns the processing of 7075 Al alloy by cold compaction and hot extrusion of a premixed powder. To this end, a premixed Al–Zn–Mg–Cu powder, Alumix 431D, was uniaxially cold pressed at 600 MPa into cylindrical compacts 25 mm in diameter and 15 mm thick. Subsequently, selected green compacts were subjected to either a delubrication or presintering heat treatment. Extrusion of the powder compacts was performed at 425 °C using an extrusion ratio of 25:1. No porosity was present in the microstructures of the extruded alloys. Heat treatment prior to extrusion had a great effect on the degree of alloy development in powder compacts and, as a direct consequence, remarkably affected the extrusion process and the as-extruded microstructures and mechanical properties of the processed materials. Hot extrusion caused banded structures for the alloys consolidated from the green and delubricated powder compacts. The alloy extruded from the presintered powder compact showed a fine, recrystallized microstructure which resulted in a superior combination of mechanical properties for the consolidated material.     

Application of superplasticity in commercial magnesium alloy for fabrication of structural components

Abstract

An investigation of the superplastic characteristics of magnesium alloys with several grain sizes revealed that grain boundary sliding took place more easily with grain refinement. The required grain size for high strain rate superplastic forming was estimated to be ～2 µm. The required grain structure could be obtained by several procedures, hot extrusion with a high extrusion ratio, severe plastic deformation via equal channel angular extrusion, consolidation of machined chip, and/or powder metallurgy processing of rapidly solidified powders, on a laboratory scale. The processing route of hot extrusion was selected in this study. An experimental study of superplastic press forming was conducted for a commercially extruded ZK60 alloy. The fabricated product did not essentially contain macroscopic defects, i.e. cracks or cavities. From an examination of tensile characteristics, it was found that the post-formed alloy exhibited higher strength and higher ductility compared with some conventional cast magnesium alloys, aluminium alloys, and steels. The experimental results support the possibility of using superplastically formed magnesium to produce structural components.     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.