Effect of pulsed current on reactively synthesised TiB2 consolidated by plasma pressure compaction

Abstract

The effect of pulsed current on TiB₂ formed by reactive consolidation between titanium and boron is reported in this paper. This consolidation was performed using the plasma pressure compaction (P²C) technique. A comparison between the pulsed and control samples reveals that pulsed current reduces grain growth (pulsed samples had an average grain size of 2·79 μm compared to 5·99 μm) while increasing sintering rates (pulsed samples were on average 15·5% more dense). The reduced grain growth and increased densification is due to the removal of adsorbed oxygen from the surface of the powder.     

超细粉末的高压软模成形方法

以近纳米粉体WC—Ni—Fe和W-Cu为原料，采用软模成形的方法，重点研究软模成形工艺参数对压坯密度和压坯强度的影响；对钢模压制和软模压制两种成形方法进行比较。结果表明：高压软模成形工艺能有效提高分层压力，使压坯相对密度大幅度提高，由33％提高到60％；压坯横向断裂强度超过17N／mm^2；所得压坯能够进行机械加工。     

粉末冶金高速压制技术及其应用

高速压制技术(HVC)是2001年瑞典提出的一种先进的成形技术,兼有动态压制的高冲击能量和传统压制的高速平稳性等多重特征,可广泛用于金属、陶瓷和聚合物等材料的成形.介绍了HVC技术的原理.论述了该技术与其它成形技术相比具有成本低、压坯密度高且分布均匀、低弹性后效和高精度、模具使用寿命长等特点.讨论了HVC技术对所用模具和原料粉的要求.介绍了HVC技术的研究进展,并对实际生产应用前景进行了展望.     

纯钛粉高速压制行为及其烧结性能研究

采用自主研发的机械蓄能式高速压机成形纯钛粉,研究纯钛粉高速压制成形行为及烧结坯的组织和性能。结果表明:经高速压制工艺成形的生坯密度随着冲击能量增加而增加。冲击能量为1805 J时获得的最高压坯密度为4.37 g/cm~3,相对密度达到96.9%。生坯的径向弹性后效随着冲击能量的增加而增加。在1200℃真空烧结后发现,随着冲击能量的增加和烧结时间的延长,烧结密度增加。烧结2.5 h后,获得的最高密度达到4.50 g/cm~3,相对密度为99.8%,最大硬度达到298 HV。当冲击能量为1805J烧结时间为1.5 h时,最高的抗拉强度达到638 MPa。径向烧结收缩率随着冲击能量增加而减少,而轴向烧结收缩率与冲击能量的关系不存在明显的规律。     

高密度铁基粉末冶金零部件制造原料的研究

温压粉末原料是采用温压成形技术制造高密度粉末冶金零件的基础和温压工艺的技术核心。高价格的进口温压粉末制约了我国高密度铁基粉末冶金零件的开发与应用,因此,必须开发出符合我国国情的温压粉末原料体系。作者根据我国资源特点,采用鞍钢产水雾化铁粉、水雾化低合金钢粉和攀枝花钢铁公司产转炉烟尘铁粉为原料,进行了制备相应体系的温压粉末原料和温压工艺参数优化的研究。以水雾化铁粉为原料设计制造的Fe-1.5Ni-0.5Mo-0.5Cu-0.6C粉末经637MPa压制,温压密度为7.46g/cm~3;压坯的回弹率为0.03％.在1150℃烧结40 min后,收缩率为0.025％。而以转炉烟尘铁粉设计制造的Fe-1.5Ni-0.5Mo-0.5Cu-0.6C粉末经686 MPa压制,压坯密度达7.35g/cm~3;以Fe-1.5Ni-0.5Mo水雾化合金钢粉为原料制造的Fe-1.5Ni-0.5Mo-1.5Cu-0.8C粉末在686 MPa时压制密度为7.35g/cm~3。这些粉末原料的设计为我国高强度铁基粉末冶金零部件的制造创造了条件。     

粉体的新压制方程研究

本文研究了由Al2O3粉和Cu粉组成的混合粉末体系的室温压制性能。测定了压坯密度与外加压力和混合粉末中陶瓷含量的关系。然后将试验数据代入由本文作者推导的含有三个参数的粉体的新压制方程之中，采用MATLAB软件求解超限定方程组，计算出方程中所含的三个参数的值。定量研究了这三个参数与体系中陶瓷含量的关系，然后把这三个参数与材料的特性联系起来，以此展示了这三个参数的物理意义，并确定了占主导地位的成形机制，进一步验证了该方程的科学性和适用性。     

Effect of compaction pressure and powder grade on microstructure and hardness of steam oxidised sintered iron

Abstract

Steam oxidation has proven to be an effective process to improve the properties of sintered iron components. The oxide formed on the surface and in the interconnected porosity strongly influences both the tribological and mechanical properties of these materials, for example through the extent of pore closure and the nature and morphology of the oxide produced. In this paper, the influences of compaction pressure and powder size on the microstructure, oxide content, hardness, and surface topography of steam treated sintered iron are analysed. Specimens prepared from atomised iron powders of different sizes (<65, 65–90, 90–125, and >125 µm) were compacted at four different pressures (300, 400, 500, and 600 MPa), sintered for 30 min at 1120°C and then subjected to a continuous steam treatment at 540°C for 2 h. A clear influence of the processing parameters on porosity was highlighted. Low porosity was always associated with high compaction pressure and greater powder size. Pore size was affected in the same way by compaction pressure, even though the effect of powder size acted in the opposite sense. Changes in compaction pressure and powder size had no significant effect on pore shape. Decreasing powder size always led to high hardness. The effect of compaction pressure on hardness is clear evidence of a compromise between porosity and blockage of the pore network by oxide. Samples produced with smaller powder sizes showed a continuous decrease in hardness as the compaction pressure increased, although for the large powder size there was a slight increase to a constant value of ultimate hardness. For the intermediate powder size a maximum hardness was obtained as the compaction pressure increased. X-ray diffraction showed that the oxide layer is composed of magnetite and haematite.     

Numerical simulation of powder compaction for two multilevel ferrous parts,including powder characterisation and experimental validation

Abstract

The paper presents a summary of two case studies that were carried out by the scientific team in the Thematic Network PM Modnet. During the life of this project, the compaction of complex multilevel ferrous components was investigated. These formed a vehicle to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results. Density comparisons were made with results from Archimedes, quantitative metallography, and computerised tomography and force levels were compared with recordings from the pressing trials. The results highlight differences between equipment and experimental techniques used in characterising powders. They also show that hardness, metallographic analysis, and computerised tomography may be used to measure density variations throughout the compact. The prediction of density variation was reasonably consistent when using different simulations, whereas punch force prediction showed good consistency. It was found that predicted and measured density distributions agree within 0·05 to 0·5 g cm^-3 and that punch force levels may be predicted within 10 to 30%. The study effectively establishes a benchmark with which to compare and improve future simulations.     

温压致密化机理及其在温压粉末设计中的应用

温压是一项以较低的成本制造高性能铁基粉末冶金零部件的新型成形技术.实验发现,颗粒重排是温压过程的主导致密化机理,而为颗粒重排提供协调性的塑性变形是另一重要的致密化机理.作者分析了影响这2个致密化机理的主要因素.在此基础上,提出了温压粉末原料的设计原则,并成功设计了高性能。低成本合金钢粉末的3大体系温压粉末原料.     

用作温压基粉原料的Fe-Ni-Mo合金钢粉温压与烧结行为研究

与通常采用纯雾化铁粉和部分合金化铁粉作为温压基粉不同,作者对水雾化Fe-Ni-Mo合金钢粉作基粉的Fe-1.5Ni-0.5Mo-1.0Cu-xC(x=0.6,0.8,1.0)粉末进行了温压与烧结行为的研究.结果表明,通过设计新型聚合物润滑剂,高硬度的合金钢粉仍适用于温压工艺.当粉末和模具的加热温度分别为125和145℃时,Fe-1.5Ni-0.5Mo-1.0Cu-0.8C的温压密度较高,在735MPa的压力下进行压制,压坯密度达到7.35g/cm~3,比室温压制提高了0.19g/cm~3左右.并且,温压压坯的弹性后效比室温压制降低了40％,在1120℃烧结1h后的烧结密度为7.32g/cm~3.     

Three-dimensional finite element analysis of powder compaction process for forming cylinder block of hydraulic pump

Abstract

A three-dimensional finite element analysis of a powder compaction process was undertaken to determine the optimum manufacturing conditions for the complex cylinder block found in the hydraulic pump of an excavator. A porous material model was used to ascertain the material behaviour. The finite element predictions for both the density distribution and compaction load were in good agreement with experimental results.     

New method for measuring and characterisation of friction coefficient at wide range of densities in metal powder compaction

Abstract

In order to investigate the friction behaviour of powder during compaction, a new method has been developed. Compaction is a complicated process and direct and continuous measurement of the coefficient of friction is not easy, because the coefficient of friction varies due to changes in such process parameters as pressure distributions, powder surface deformation etc. In this paper, a new device for measuring the coefficient of friction between metal powder particles in contact with the die wall during compaction is presented. Using the conventional methods for direct measurement of the radial pressure during compaction is very difficult. The new device offers the possibility of investigating the normal pressure on the powder particles directly and continuously by keeping the green density constant. The measurements are performed using strain gauges mounted on the upper punch. The upper punch surface in the new device corresponds to the die wall in a conventional press. The sliding velocity, compaction velocity, normal load and temperature can be monitored and controlled. Measurement of the coefficient of friction at low densities is one of the advantages and possible applications of this apparatus. The investigation shows that the powder compaction is controlled by a combination of powder rearrangement and elastic and plastic deformation of particles. At densities below 4g cm^-3 the dominant process is particle rearrangement. No plastic deformation occurs at such low values of density. At densities above 4·5g cm^-3 the plastic deformation of the powder surface in contact with the die wall seems to be completed and the coefficient of friction is more or less constant.     

硅粉常压直接氮化过程的非催化气固反应模型

以平均粒径2.2μm、纯度99.99%的硅粉为原料,采用纯度99.993%的高纯氮气作为反应气体,在1350和1400℃下进行了氮化时间为10~30 min的氮化实验,得出了不同温度下硅粉转化率随反应时间的变化关系.将硅氮反应看成非催化气固反应,建立了硅颗粒氮化动力学模型.通过对实验数据的拟合,得出两个模型参数:硅氮反应速率常数和氮气在产物层中的扩散系数.假定反应速率常数和扩散系数均满足阿伦尼乌斯公式,求得化学反应激活能和指前因子分别为2.71×10⁴J·mol^-1和3.07×10^-5m·s^-1,扩散激活能和指前因子分别为1.06×10⁵J·mol^-1和1.12×10^-9m²·s^-1.利用本文得出的氮化动力学模型对各温度下不同粒径硅粉的转化曲线进行了预测,预测曲线与文献中的实验数据在趋势上吻合较好.     

12Cr2MoWVTiB高压锅炉圆管坯的生产

叙述了衡阳钢管(集团)有限公司采用电弧炉→钢包精炼炉→水平连铸工艺生产12Cr2MoWVTiB高压锅炉圆管坯的情况,介绍了该钢种的化学成分设计、质量要求、生产工艺和实物质量水平。     

宝钢2050mm热轧精轧机组CVC液压系统的高压冲洗

本文介绍了宝钢２０５Ｏｍｍ热轧机精轧机组ＣＶＣ液压系统利用系统本身设备采用高压大流量冲洗新工艺，在提高冲洗精度、缩短冲洗时间和降低劳动强度等方面都取得了较好的效果。