Friction Wear Property of Brake Materials by Copper-based Powder Metallurgy With Various Brake Speeds

The experiment is conducted on MM-1000 friction test machine, which tests friction wear property of copper-based brake materials by powder metallurgy at different brake speeds. It shows that the coefficient of friction and wear volume are greatly influenced by brake speed. When the brake speed is 4000 r/min, which is a bit higher, the material still has a higher coefficient of friction with 0.47. When the brake speed is over 4000r/min, the coefficient of friction decreased rapidly. When the brake speed is 3000r/min, the material’s wear is in its minimum. That is to say no matter how higher or lower the brake speed is the wear volume is bigger relatively. With the brake speed of the lower one it mainly refers to fatigue wear; while of higher one it mainly refers to abradant and oxidation wear.

Research on Silicon Carbide Dispersion-Reinforced Hypereutectic Aluminum-Silicon Electronic Packaging Materials

The objective of this study is to improve the mechanical properties and machining performance of high thermal conductivity and low expansion silicon carbide dispersion-strengthened hypereutectic aluminum-silicon electronic packaging materials to meet the needs of aviation,aerospace,and electronic packaging fields.We used the powder metallurgy method and high-temperature hot pressing technology to prepare SiC/Al-Si composite materials with different SiC contents(5vol%,10vol%,15vol%,and 20vol%).The results showed that as the SiC content increased,the tensile strength of the composite material first increased and then decreased.The tensile strength was the highest when the SiC content was 15%;the sintering temperature significantly affected the composite material’s structural density and mechanical properties.Findings indicated 700℃was the optimal sintering and the optimal SiC content of SiC/Al-Si composite materials was between 10%and 15%.Besides,the sintering temperature should be strictly controlled to improve the material’s structural density and mechanical properties.

Combined powder metallurgy routes to improve thermal and mechanical response of Al−Sn composite phase change materials

Powder metallurgy processes are suitable to produce form-stable solid−liquid phase change materials from miscibility gap alloys.They allow to obtain a composite metallic material with good dispersion of low-melting active phase particles in a high-melting passive matrix,preventing leakage of the particles during phase transition and,therefore,increasing the stability of thermal response.Also,the matrix provides structural properties.The aim of this work is to combine conventional powder mixing techniques(simple mixing and ball milling)to improve active phase isolation and mechanical properties of an Al−Sn alloy.As matter of fact,ball milling of Sn powder allows to reduce hardness difference with Al powder;moreover,ball milling of the two powders together results in fine microstructure with improved mechanical properties.In addition,different routes applied showed that thermal response depends on the microstructure and,in particular,on the particle size of the active phase.In more detail,coarse active phase particles provide a fast heat release with small undercooling,while small particles solidify more slowly in a wide range of temperature.On the other hand,melting and,consequently,heat storage are independent of the particle size of the active phase.This potentially allows to“tailor”the thermal response by producing alloys with suitable microstructure.

Worn surface characteristics of Cu-based powder metallurgy bake materials for aircraft

Cu-based powder metallurgy brake materials are used for aircraft widely and successfully.The characteristics of worn surface of Cu-based powder metallurgy brake materials for aircraft after working under service condition were studied,and two main wear mechanisms were discussed.The results show that the main components of worn surface are graphite,SiO2,Fe,Cu and oxide of Fe(Fe3O4 and FeO);the worn surface can be divided into three zones:severe wear zone,mild wear zone,and low wear zone; fatigue wear and grain wear are the main wear mechanisms of Cu-based materials.Some debris kept between brake discs reduce the wear rate to a certain extent by taking part in the regeneration of friction film.

Powder Metallurgical Fabrication and Microstructural Investigations of Aluminum/Steel Functionally Graded Material

Aluminum/steel electric transition joints (ETJs) are used in aluminum reduction cell for the purpose of welding aluminum rod and steel bracket components. Solid state welding process used for joining aluminum and steel at the electric transition joints have the drawbacks of cracking and separation at the interface surfaces. Cracking and separation at the electric transition joints are caused by the stress singularities that developed due to the mismatch in thermal and mechanical properties of each material. To overcome the drawback of electric transition joints, aluminum/steel functionally graded may be used as electric transition joints or proposed. Therefore manufacturing and investigation of aluminum/steel functionally graded materials fabricated by powder metallurgy process were carried out through the current work. Different samples with different layers of aluminum/steel functionally graded materials were compacted using steel die and punch at the same compacted pressure and sintered temperature. After investigating the different samples of aluminum/steel functionally graded materials under different fabrication conditions, the suitable fabrication regime was determined with the aid of microscopic observations.

Die wall lubricated warm compaction of iron-based powder metallurgy material

Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant. Iron based samples were prepared by die wall lubricated warm compaction at 175 ℃, using a compacting pressure of 550 MPa. Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant. Admixed lubricant concentration ranging from 0 to 0.5% was tested. Extremely low admixed lubricant contents were used. Results show that in addition to the decrease in ejection forces, the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubricant content, then decreases with the decrease of admixed lubricant content. The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant. No scoring was observed in all die wall lubricated experiments.

Damping capacity of high strength-damping aluminum alloys prepared by rapid solidification and powder metallurgy process

Two kinds of high strength-damping aluminum alloys （LZ7） were fabricated by rapid solidification and powder metallurgy （RS-PM） process. One material was extruded to profile aluminum directly and the other was extruded to bar and then rolled to sheet. The damping capacity over a temperature range of 25-300 ℃was studied with damping mechanical thermal analyzer （DMTA） and the microstructures were investigated by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that the damping capacity increases with the test temperature elevating. Internal friction value of rolled sheet aluminum is up to 11.5×10^-2 and that of profile aluminum is as high as 6.0×10^-2 and 7.5×10^-2 at 300 ℃, respectively. Microstructure analysis shows the shape of precipitation phase of rolled alloy is more regular and the distribution is more homogeneous than that of profile alloy. Meanwhile, the interface between particulate and matrix of rolled sheet alloy is looser than that of profile alloy. Maybe the differences at interface can explain why damping capacity of rolled sheet alloy is higher than that of profile alloys at high temperature （above 120 ℃）.

Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa.m^1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

Microstructural characterization and mechanical properties of functionally graded Al2024/SiC composites prepared by powder metallurgy techniques

Al2024/SiC functionally graded materials (FGMs) with different numbers of graded layers and different amounts of SiC were fabricated successfully by powder metallurgy method and hot pressing process. The effects of increasing SiC content and number of layers of Al2024/SiC FGMs on the microstructure and mechanical properties of the composite were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) analyses indicated that Al and SiC were dominant components as well as others such as Al4C3, CuAl2, and CuMgAl2

Preparation of FVS1212/FVS0812 materials and its mechanical properties

FVS1212/FVS0812 material was prepared by adding FVS1212 powder into FVS0812 powder. The structure and mechanical properties of materials were studied by means of X-Ray, tensile measurement, OM and SEM. The results show that adding proper content FVS1212 powders can improve the tensile strength of FVS0812 aluminum at room temperature and elevated temperature, and that the elongation of FVS1212/FVS0812 material is better than that of FVS1212 aluminum.

Development of Iron Based Brake Friction Material by Hot Powder Preform Forging Technique used for Medium to Heavy Duty Applications

A promising friction material, Iron -based friction material, was prepared by powder metallurgy (PM) processing utilizing hot powder preform forging (near net-shape).The preparation of the product and its characterization are presented in this paper. These products are useful in heavy duty Military Aircraft applications such as AN-32. In order to eliminate costly environmental control systems to protect products during their high temperature processing (as is conventionally practiced employing hydrogen gas), the present investigation relies on carbon (mixed in the brake pad formulation) as reducing agent and high temperature oxidation resistant glassy coating (separately developed) applied over the product’s surface after cold compacting. After conducting an initial characterization such as hardness, density and Pin-on Disc tests, the samples were tested in sub-scale dynamometer under Rejected Take Off conditions. It was observed that the obtained density in the present investigation is higher than the reported density obtained by sintering route, and wear is on the lower side of the range as per the Aeronautical Standards. Optical metallography was used to investigate the microstructure of friction, interface and backing layer. It was observed that the distribution of ingredients in matrix was homogeneous. The results also indicate that the coefficient of friction is more stable, and wear is lower with respect to temperature rise. .

Preparation and characterization of porous magnesium materials

The proper spacer material and the preparation technology for biological compatible porous magnesium materials were explored by the powder metallurgy method, and microstructures, porosity and mechanical properties of sintered porous magnesium were investigated. The results show that compared with spacer materials of NH4CO3, NH3Cl and carbamide, NH4CO3 is the best one for preparation of sintered porous magnesium,and the worst one is NH3Cl.The isolated blind pores are formed mainly by the particle interval of the magnesium powders. Adding spacer material favors the formation of open pores, while has little contribution to the formation of blind pores. The overall porosity and porosity of open pore of the sintered porous magnesium increase with the increase of added spacer material, while decrease with the increase of the molding stress. The mechanical properties of sintered porous magnesium increase with decreasing addition of spacer material and increasing molding stress.

超细晶/纳米晶钨材料制备技术的研究进展

晶粒细化可显著提高超细晶/纳米晶钨材料的性能,介绍了超细晶/纳米晶钨材料制备技术的最新研究进展,包括粉末冶金法和深度塑性变形法,粉末冶金法的烧结工艺主要包括热等静压烧结、超高压通电烧结、放电等离子体烧结、微波烧结等;深度塑性变形法包括高压扭转、等通道挤压、表面机械研磨处理和累积轧制等。由于超细晶/纳米晶钨材料存在大量的晶界可有效提高材料的力学性能和抗辐照性能,因此有望解决纯钨材料作为核聚变堆面向等离子体材料存在的问题,对超细晶/纳米晶钨材料的发展提出了建议。

铁铜基粉末冶金材料制动工况下的摩擦磨损性能

采用MM3000型摩擦磨损试验机,在7种连续制动工况下分别测试铁铜基粉末冶金摩擦材料的摩擦性能和耐热性能,利用扫描电镜和能谱仪分析研究两种转速(等效半径线速度)下摩擦材料的磨损机理。结果表明:在线速度为19.40 m·s^(-1)时,随着面压增加,摩擦材料的动摩擦系数略有降低。在0.44 MPa面压下,动摩擦系数为0.267~0.312;在0.80 MPa面压下,动摩擦系数为0.258~0.308。在线速度19.40 m·s^(-1)、面压0.44 MPa、单位面积制动能量268 J·cm^(-2)的连续制动工况条件下,动摩擦系数波动较大,在其他工况条件下,动摩擦系数波动较小。随着制动能量的增加,7种连续制动工况下平均动摩擦系数在0.300~0.334之间,动摩擦系数均在0.250以上,无明显衰退现象,表明铁铜基粉末冶金摩擦材料具有较好的耐热性能。在线速度为19.40 m·s^(-1)工况下,铁铜基摩擦材料的摩擦磨损机理主要为磨料磨损及氧化磨损;在线速度为30.00 m·s^(-1)工况下,铁铜基摩擦材料的摩擦磨损机理主要为疲劳磨损及氧化磨损。

苛刻制动能量密度下铜基粉末冶金摩擦材料摩擦学行为

基于国家标准中高速列车200、340和400 km/h紧急制动参数,利用MM−3000摩擦磨损试验机,设计基于等制动能量密度、等压强的等效放缩实验,研究铜基粉末冶金摩擦材料配对铸钢在不同苛刻制动能量密度(157、446和616 J/mm^(2))下的摩擦学行为。研究结果表明:在157和446 J/mm^(2)制动能量密度下,材料平均摩擦因数稳定在0.250左右,制动效果较好;在616 J/mm^(2)制动能量密度下,材料平均摩擦因数从0.260迅速衰退至0.210,制动效果减弱;随着制动能量密度增加,摩擦材料亚表面存在成分与性能不同的摩擦层结构,其厚度先增加再减小,纳米压痕硬度逐渐减小,材料磨损机制发生了由犁削、黏着磨损到氧化磨损、疲劳磨损再到严重氧化磨损与剥层磨损的转变。

粉末冶金法制备高熵合金黏结相硬质材料研究进展

传统硬质材料黏结相Co在高温下易软化是限制其应用的重要因素,高熵合金的开发弥补了这一缺陷。高熵合金是由多种金属元素形成的固溶体,与Co相比进一步改善了硬质材料的耐磨性、耐腐蚀性和抗氧化性能,在切削加工领域具有广阔的应用前景,逐渐成为金属材料的研究热点。本文对近年来粉末冶金法制备高熵合金黏结相硬质材料的研究进行综述,具体包括硬质材料基体、高熵合金粉末制备方法、高熵合金硬质材料的烧结方法和高熵合金对硬质材料的影响机制,并对存在的不足进行总结与展望。

铁基粉末冶金材料表面滚压致密化效果及组织演变

采用不同滚压压力对不同密度的Fe–2Cu–0.6C粉末冶金材料进行表面滚压加工,研究材料密度和滚压压力对致密化效果的影响。结果表明:滚压压力和材料密度是影响表面致密化效果的主要因素。随着滚压压力的增加,致密层厚度和表面硬度显著增加。材料密度对表面致密化效果的影响随着滚压压力的增加而减弱。当滚压压力较小时,致密层厚度和表面硬度随着材料密度的增加而增加;当滚压压力较大时,不同密度材料表面硬度和致密层厚度接近。滚压后表面层珠光体沿滚压方向弯曲,靠近表面的层片间距变小,部分区域层片发生扭折,出现波浪形,甚至部分渗碳体破碎断裂;铁素体细化,沿着滚压方向弯曲,在铁素体晶粒边界存在大量位错纠缠和位错墙。铁素体细化和珠光体变形为表面强化提供了有利的条件。

Mn含量对多孔Ti-Mo-Mn合金微观结构及力学性能的影响

以钛粉、钼粉和锰粉为原料,碳酸氢铵颗粒为造孔剂,采用粉末冶金工艺制备出医用多孔Ti-Mo-Mn合金,并研究了锰含量对多孔Ti-Mo-Mn合金微观结构和力学性能的影响。结果表明,随着锰含量从0wt%增加到10wt%,多孔Ti-Mo-Mn合金的孔隙率降低,大孔孔径少量减小,β-Ti相的比例相对增多,弹性模量和抗压强度相应增加。含7.5wt%Mo和5wt%~10wt%Mn的多孔Ti-Mo-Mn合金具有三维连通的多孔结构和良好的力学性能,有潜力用作皮质骨缺损修复材料。

国内粉末冶金闸片的发展现状与展望

粉末冶金闸片广泛应用于高铁、动车组列车、地铁等城市轨道交通中,是保证车辆安全行驶的核心零件。从学术、专利、产业化三个方向对粉末冶金闸片的国内研究现状进行了分析。在学术方面,系统分析了摩擦材料、摩擦性能、检修工艺的研究进展;在专利方面,对闸片的加工制造和结构展开了具体分析;在产业化方面,总结并分析了国内主要粉末冶金闸片生产公司的发展。从以上三个方面概述了国内在粉末冶金闸片领域的进展情况及目前所存在的问题,并针对相关问题提出可行的解决方法。最后,针对目前的研究现状,从新型闸片研究、极端条件产品开发、促进专利开发及产业化发展等方面对粉末冶金闸片的发展前景进行了展望。

近海风力发电用铜基粉末冶金摩擦材料研究进展

近海风力发电机组制动具有“三高”(高速、高力矩、高压力)和“一特殊”(海洋水雾、盐雾腐蚀环境)的特点,铜基粉末冶金材料因具有组织均匀、导热性好、耐磨性高、摩擦系数稳定等优点,可应用于近海风力发电的摩擦材料。本文综述了近年来铜基粉末冶金摩擦材料在成分组元、制备工艺以及仿真模拟等方面的研究进展,其中铜基粉末冶金材料的成分组元主要包括基体组元、润滑组元和摩擦组元,其制备工艺主要采用传统热压烧结和放电等离子烧结,同时概述了材料在制动过程中温度场和应力场的仿真模拟,最后展望了铜基粉末冶金摩擦材料的发展前景。