制备工艺对铁基粉末冶金气门座圈致密性和性能的影响

采用烧结、熔渗、热处理制备了高性能铁基粉末冶金气门座圈。研究不同工艺对气门座圈的孔隙变化、致密性、显微组织和力学性能的影响,确定气门座圈致密性的最佳工艺条件。结果表明：采用熔渗或提高烧结温度,可使孔隙的形状趋于球化,大大减少孔隙的数量和大小,明显提高气门座圈的致密性。获得气门座圈理想致密性的最佳工艺条件：均匀压入14%~15%（质量分数）的熔渗薄铜片,在1150 ℃下熔渗烧结2 h,然后进行620 ℃高温回火;回火后可得到大量综合性能良好的回火索氏体,明显提高了气门座圈的综合性能     

粉末冶金钛合金致密化研究的进展

综述了粉末冶金钛合金致密化工艺及致密化机理研究的新进展。粉末冶金钛合金致密化工艺除采用传统的热等静压工艺外，注射成型、激光成型等新技术的应用可以得到相对密度达99％的烧结件，其拉伸性能达到甚至超过熔锻钛合金的水平；致密化理论方面的研究除扩散、蠕变及屈服机制外，钛合金中还有相变致密化机制与多组元合金元素的强化致密化机制。其中当粉末钛合金在理／口两相区温度下进行循环热压时，相变致密化起主要作用。当多组元粉末钛合金烧结时，促进液相形成或提供扩散通道的合金元素起强化致密化作用。这两种致密化机制在粉末钛合金烧结的实际应用中有重要意义。     

铜粉末化学镀银及其性能

论述铜粉化学镀银的原理及影响化学镀银的若干因素,观察其粉末的显微组织,测定镀银层厚度,并考察镀层的致密性。     

纳米Al2O3p化学镀铜复合粉末的烧结致密化

化学镀是制备纳米颗粒增强金属基复合材料的有效方法.对纳米Al2O3p化学镀铜粉末的烧结致密化特点进行了研究,分析了化学镀粉末的预处理、成型压力、烧结温度、保温时间、复压复烧工艺等对致密化的影响.在优化各影响因素的情况下,对Al2O3含量为10%的化学镀铜粉末采用常规粉末冶金工艺得到了相对致密度达94%的试样.     

Cu含量对Fe-Cu-C系粉末冶金轴承材料组织性能的影响

以还原铁粉、电解铜粉、鳞片状石墨粉制备成形的混合料为原料,经压制烧结得到了Fe-xCu-0.7C(x=10、15、20和25 mass%)粉末冶金轴承材料。采用扫描电镜、洛氏硬度计、万能材料试验机及摩擦磨损试验等研究了烧结体试样的显微组织、硬度、压溃强度及摩擦磨损性能,分析了Cu含量对烧结体试样的孔隙率、显微组织和力学性能的影响。结果表明：烧结体试样的显微组织主要由珠光体、铁素体、Cu相以及孔隙组成,随着Cu含量从10%增加到25%,烧结体的开孔隙率和硬度降低,压溃强度先升高后降低,摩擦系数以及体积磨损量先降低后升高。当Cu含量为15 mass%时,Fe-15Cu-0.7C烧结体试样的综合性能较好,其密度、硬度、压溃强度、摩擦系数以及体积磨损量分别为6.14 g/cm³、51.81 HRB、419.96 MPa、0.23和0.2145 mm³。     

铜、铬对灰铸铁强度及组织均匀性影响的研究

在实验室条件下考察了Cu、Cr对CE为3．85％和4．07％灰铸铁的强度(σb)、断面敏感性和显微组织均匀性的影响。结果发现：合金元素能有效提高强度，复合处理优于单独使用；对本试验阶梯试块而言，当碳当量高时，合金元素可改善铸件的断面敏感性，碳当量低时，则反之。合金化能显著改善微观组织的均匀性，从而改善铸件的加工性能。     

铁基粉末冶金摩擦焊接头分析

摩擦焊是一种固相连接方法，以其优质、离效、低耗环保的突出优点得到了广泛的应用。半个世纪的推广应用，证明了摩擦焊在简化结构和工艺、减少加工、提高质量、降低成本等方面具有独特的效果和显著的作用。摩擦焊不仅可焊接钢、铝、铜．还成功地焊接了高温强度级相差很大的异种金属。随着汽车、飞机及电气制造等部门大量采用粉末冶金材料，国外已采用摩擦焊方法成功地焊接了耪末冶金材料，但目前国内尚无这方面的报道。在此，通过优选工艺参数．成功地焊接了铁基粉末冶金材抖。     

铜对粉末冶金航空刹车材料物理力学性能的影响

研究了大范围铜含量对粉末冶金航空刹车材料物理力学性能的影响。结果表明 :铜通过对铁基组织的合金化和沉淀强化 ,影响刹车材料的密度、孔隙度、基体显微硬度、表观硬度以及抗压强度。Cu的含量为 30 %时航空刹车材料综合性能最佳。     

粉末冶金制备铁基复合材料致密化过程的研究

应用粉末冶金法,使(Fe-V合金+石墨)反应体系在真空状态下进行碳化反应和烧结致密化,制备了VC颗粒增强铁基复合材料,分析了该复合材料致密化过程的影响因素,应用扫描电镜分析了该复合材料的微观组织.     

铁基粉末温压过程中的致密化

采用自制电阻式粉末温压系统研究了铁基粉末的温压行为,对铁基粉末在温压过程中的加热温度与粉末流动性关系、加热方式与粉末冶金制品密度关系及模具温度与压坯硬度关系进行了研究。实验结果表明:粉末在合适的温度及压制力即粉末温度在(85±5)℃温度范围,模具外壁温度在135℃(内壁温度为115℃),压制力为700~750 MPa时,所得到的粉末压坯密度最大,且此时测出其脱模力亦较小,粉末压坯硬度值较大;润滑剂在压制过程中能够有效降低颗粒间以及粉末与模具间摩擦力,使实际作用在粉末上的作用力增大,有效提高了制品致密化程度。     

添加微量纳米铁粉对铁基粉末烧结温度的影响

将添加0.5%纳米铁粉的铁基粗粉末通过强烈球磨混合压制成的样品,在600、650、700、750、800、850、920℃温度下进行烧结,保温20 min,通过TEM、SEM等手段观察样品的形貌变化.结果表明,添加纳米铁粉后试样烧结温度可降低260℃.其原因是高活性低熔点的纳米铁粉在粗铁粉末颗粒界面上的快速吸附、溶解和扩散造成的.     

High density powder metallurgy design concepts for powder forging

The forging of powder metal compacted preforms to full density has evolved as an extension of the conventional powder metal process. Indentification and evaluation of the variables in the powder forging process is required to optimize each step of the process, from the powder to the product. Optimization leads to both maximum product quality and minimum process variation.     

A study on the development of a substitution process by powder metallurgy in automobile parts

Powder metallurgy processes using sintering are able to form net-shaped products and have been used widely in the production of automobile parts to improve productivity. However, the toughness of powder products is generally poor because they contain pores. Therefore, forged products are used in parts subjected to severe fatigue loads, but in the case of powder products having high toughness, they could substitute for forged products. In this study, the choice of powder materials and production processes, including mixing, compaction, sintering, and heat treatment are studied to produce the clutch disc spline hub of an automobile. For this, three types of materials are selected and processed and the mechanical properties and microstructure of the sample are investigated, along with the performance of a dynamic test carried out under real conditions.     

The influence of powder apparent density on the density in direct laser-sintered metallic parts

In direct laser sintering, the density is expected as high as possible for the industrial application. Since the density not only determines the industrial acceptance, but also limits the accuracy of the parts. This paper reports on the influence of the powder apparent density on final density of the sintered part's in direct laser sintering of Cu-based metal powder. The relative densities of the sintered parts with the different apparent densities using different process parameters have been investigated. The result shows that the apparent density has the most significant effect on final density of the sintered part. The final density increases with the increase of the apparent density. It is easy to get a higher final density in direct laser sintering process if a higher apparent density is used. However, the final density seems to have an upper limit for a given metal powder system.     

The effect of anisotropic dimensional change on the precision of steel parts produced by powder metallurgy

The dimensional characteristics of ring-shaped parts produced with an Fe–Cu–P alloy by a conventional powder metallurgy process were measured on both green and sintered parts. The dimensional change was investigated by dilatometry, and the work highlighted that the anisotropy observed is mainly due to the early sintering stage. In this study, where the alloy is characterised by a slight densification, the anisotropic behaviour has a negligible effect on the precision of the height and the internal diameter, while the effect on the precision of the external diameter may be relevant.The results have been generalised, considering larger volume variations and different anisotropy parameters, and some relations between the anisotropy parameters and the attainable ISO tolerance classes have been determined.     

粉末冶金工艺对4A11铝合金致密度的影响

采用粉末冶金法制备4A11铝合金,分析了压制力、烧结工艺以及挤压工艺对铝合金致密度的影响.研究表明:在一定压力范围内,铝合金的致密度随着压制力的增加而增加,当压制力到达一定值后,致密度趋于稳定.常规烧结过程不能使铝合金致密化,反而会使材料致密度有所下降.挤压使材料发生塑性变形,填补了材料中的孔洞,同时金属的流动划破了颗粒表面的氧化层,促进物质的扩散迁移,能够大幅度提高铝合金的致密度,其致密度最高达到97.8％.     

Influence of sintering temperature on the shrinkage and geometrical characteristics of steel parts produced by powder metallurgy

The dimensional and geometrical characteristics of Charpy bars produced with two different steels were investigated to evaluate the effect of increasing the sintering temperature from 1120 °C (conventional sintering temperature) up to 1350 °C. The problem was approached from the Geometric Dimensioning and Tolerancing (GD&T) point of view, referring to the standard ASME Y14.5 (2009). The dimensional and geometrical characteristics were evaluated using a Coordinate Measuring Machine (CMM), measuring the surfaces by scanning mode. The work highlights that the increase in the sintering temperature, aimed at improving the mechanical properties, does not prevent the main benefit of this technology, i.e., the possibility of producing parts with good dimensional and geometrical precision. Moreover, a methodology establishing the measurement procedures and data processing, to be used in future work for the characterisation of more complex shapes, was defined.     

Effect of heating mode on sintering of ferrous compacts through powder metallurgy route

Abstract

Microwave heating is recognised for its various advantages, such as time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved properties. The present paper focuses on preliminary work carried out with the use of microwave radiation applied to sintering of ferrous compacts. The ferrous alloy compacts were sintered in a multimode microwave furnace of 2·45 GHz and 6 kW nominal power at 1120°C for 60 min in forming gas. Results of densification, mechanical properties and microstructural evaluation of the microwave sintered samples are reported and compared with conventionally sintered ones. In general, it is observed that the microwave radiation generally enhances the properties of the sintered material when compared with conventionally sintered material.