多粒径TiB2颗粒增强铜基复合材料的制备与载流摩擦磨损性能

采用粉末冶金工艺分别制备了单一粒径TiB₂颗粒和多粒径TiB₂颗粒增强铜基复合材料,对比研究了非载流和载流条件下多粒径（2 μm+50 μm）TiB₂/Cu复合材料的摩擦磨损行为。微观组织观察表明:不同粒径的TiB₂颗粒在Cu基体中分布均匀。与单一粒径TiB₂/Cu复合材料相比,多粒径TiB₂/Cu复合材料具有更高的相对密度、硬度和导电率。摩擦磨损实验结果表明:多粒径TiB₂/Cu复合材料抗摩擦磨损性能明显高于单一粒径TiB₂/Cu复合材料,当2 μm与50 μmTiB₂颗粒配比为1:2时,多粒径TiB₂/Cu复合材料的抗摩擦磨损性能最佳。相对于2 μm单一粒径TiB₂/Cu复合材料,电流为0 A时,（2 μm+50 μm）TiB₂/Cu复合材料的摩擦系数和磨损率分别降低了17.3%和62.5%;电流为25 A时,（2 μm+50 μm）TiB₂/Cu复合材料的摩擦系数和磨损率分别降低了6%和45.8%,同时载流效率和载流稳定性得到明显提高,磨损表面更加平整。磨损机制分析表明:多粒径TiB₂颗粒合理配比有利于提高复合材料载流质量,同时摩擦过程中大粒径的TiB₂颗粒起到支撑作用,小粒径的TiB₂颗粒弥散强化Cu基体,二者的协同作用使TiB₂/Cu复合材料具有更好的抗载流摩擦磨损性能。      

High-speed turning experiments on metal matrix composites

The hard abrasive ceramic component which increases the mechanical characteristics of metal matrix composites (MMC) causes quick wear and premature tool failure in the machining operations. The aim of the paper is to compare the behaviour of high rake angle carbide tools with their diamond coated versions in high-speed machining of an Al₂O₃Al 6061 MMC. The influence of the cutting parameters, in particular cutting feed and speed, on tool wear and surface finish has been investigated. The higher abrasion resistance of the coatings results in increased tool life performances and different chip formation mechanisms.     

原位合成TiB2/Fe复合材料的高温氧化行为

采用微波烧结技术原位生成TiB₂/Fe复合材料,研究其在500℃、600℃与700℃空气中的恒温氧化行为,并对氧化膜的表面、截面形貌及相组成进行了分析。结果表明:TiB₂/Fe复合材料由TiB₂、Fe₂B和α-Fe三种物相组成。随着氧化温度的升高,TiB₂/Fe复合材料的氧化增重明显增大,均呈现抛物线型规律,在500℃时,其氧化产物主要为Fe₂O₃和Fe₃O₄,而700℃时,其氧化物为Fe₂O₃、TiO₂、Fe₉TiO₁₅及少量Fe₃BO₆组成。相同温度下,随着TiB₂含量增加,TiB₂/Fe复合材料氧化物粒径、氧化增重和氧化层厚度均减小,氧化激活能增大,其抗氧化性能也越好。      

Erosive wear behaviour of aluminium based composites

Al-MMCs reinforced with short fibres or particles of ceramics such as alumina, titanium diboride and silicon carbide result in composites of high specific strength and stiffness, suitable for advanced engineering applications such as in the aerospace and automotive industries. This paper studies the erosion wear behaviour of Al-based composites reinforced with alumina-fibre and in-situ TiB₂ particles using a water/SiC particles slurry jet. From the results of our experiment, the erosion resistance of reinforced Al-MMCs depends on that of the Al-alloy and the reinforcing ceramics, as well as on the bonding strength between the matrix and ceramic fibres or particles. Some design strategies to enhance the erosion resistance of Al-MMCs reinforced with short fibres and particles have been discussed.     

不同冷却润滑方式对切削SiCP/Al复合材料刀具磨损的影响

为探究不同冷却润滑方式对切削SiC_P/Al复合材料刀具磨损的影响,进行了干切削（Dry）、微量润滑（MQL）、液氮（LN₂）、切削油（Oil）和乳化液（Emulsion）共五种冷却润滑条件下的车削实验,分析了冷却润滑方式对刀具边界磨损、刀具破损和后刀面磨损的影响。结果表明:MQL和LN₂有更佳的流体冲刷效果,可以将脱落的SiC颗粒及时带离切削区,减少边界磨损; Oil和Emulsion冲刷效果较差,会加剧边界磨损。LN₂的使用会增加刀具受到的热应力和机械冲击,积屑瘤发生完全脱落,造成切削过程不平稳,当切削距离达到1 100 m时,刀具发生破损; Oil切削时,严重的边界磨损导致刀尖部位尺寸减小,强度降低,当切削距离达到825 m时发生了刀具破损。MQL良好的润滑渗透性和LN₂有效的冷却效果可以减少后刀面磨损。因此,MQL兼具冷却、润滑和流体冲刷效果,更加适合作为切削SiC_P/Al复合材料的冷却润滑方式。      

Study of milling force variation in ultrasonic vibration-assisted end milling

Ultrasonic vibration cutting has been proved to be an effective cutting technology for its excellent cutting performance and has been widely applied in turning and drilling process. However, this kind of technology is rarely tried in milling process. In cutting process, cutting force is an important process parameter, which affects surface finish and tool wear. This paper investigates the milling force variation in ultrasonic vibration-assisted end milling process through a series of slot-milling experiments. The main research contents include two parts, one is the effect of the externally excited vibration on milling force in milling process, and the other is the influence of milling and vibrating parameters matching on milling force value. Experimental results show that ultrasonic vibration can change traditional milling conditions, realize separate-type milling, obtain similar pulse-like profiles of cutting forces, reduce average cutting force value; and the peak value of the feed direction cutting force can also be greatly decreased by adopting reasonable vibration amplitude, an optimal combination of machining parameters is of great benefit to achieving small cutting force. According to the experimental findings, ultrasonic vibration-assisted milling is a prospective technology to achieve precision milling of small part.     

A review on conventional and nonconventional machining of SiC particle-reinforced aluminium matrix composites

Among the various types of metal matrix composites, SiC particle-reinforced aluminum matrix composites (SiC_p/Al) are finding increasing applications in many industrial fields such as aerospace, automotive, and electronics. However, SiC_p/Al composites are considered as difficult-to-cut materials due to the hard ceramic reinforcement, which causes severe machinability degradation by increasing cutting tool wear, cutting force, etc. To improve the machinability of SiC_p/Al composites, many techniques including conventional and nonconventional machining processes have been employed. The purpose of this study is to evaluate the machining performance of SiC p/Al composites using conventional machining, i.e., turning, milling, drilling, and grinding, and using nonconventional machining, namely electrical discharge machining (EDM), powder mixed EDM, wire EDM, electrochemical machining, and newly developed high-efficiency machining technologies, e.g., blasting erosion arc machining. This research not only presents an overview of the machining aspects of SiC_p/Al composites using various processing technologies but also establishes optimization parameters as reference of industry applications.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00313-2     

Experimental Investigation on Rotary Ultrasonic Face Grinding of SiCp/Al Composites

SiCp/Al composites have been widely used in many fields such as aerospace, automobile, advanced weapon system, etc. But this kind of material, especially with high volume fraction, is difficult to machine due to the reinforced particles existing in matrix, which has limited its further application. Rotary ultrasonic machining (RUM) has many excellent features and it has never been used to machine SiCp/Al composites. In order to improve the machinability and application of SiCp/Al composites, the rotary ultrasonic face grinding experiments of SiCp/Al composites reinforced with 45% volume SiC particles were carried out to investigate cutting force, surface quality, tool wear, and abrasive chip shapes. The experimental results indicate that ultrasonic vibration could reduce cutting force, surface roughness, surface defects, and increase plastic removal ratio. The cutting force could be lowered by an average of 13.86% and the surface roughness could be lowered by an average of 11.53%. The examined results of tool wear patterns suggest that tool wear is mainly caused by grain breakage and grain fall-off. Grinding wheel blockage and grinding burn were not observed in machining process.     

TiB_2基陶瓷-42CrMo合金钢层状复合材料界面结构与力学性能

采用自蔓延高温合成离心熔铸工艺可以快速制备出TiB_2基陶瓷-42CrMo合金钢层状复合材料,并在层间界面上形成TiB_2基陶瓷/Fe-Ni合金相三维网络跨尺度连续梯度复合结构,使层状复合材料分为陶瓷基体、中间过渡区与合金钢基底3层结构。通过材料力学性能测试并结合FESEM、HRTEM观察,得出正是由于层间界面上原位生成TiB_2基陶瓷/Fe-Ni合金的三维网络跨尺度连续梯度复合结构,使复合材料不仅具有高的弯曲强度与断裂韧性,而且又使之在三点弯曲测试时呈现出明显的"假塑性"力学行为特征。同时,陶瓷基体附近界面上TiB_2基陶瓷/Fe-Ni基合金复合结构裂纹互锁效应与中间过渡区上TiB_2微纳米/纳米晶沉淀强化机制的协同作用又使TiB_2基陶瓷-42CrMo合金钢层状复合材料具有高的层间界面剪切强度。     

MACHINING OF TiB2 AND ITS COMPOSITES

The mechanism of material removal during electrical discharge machining (EDM) of TiB₂ and its composites was studied by examining surfaces and debris using electron microscopy and X-ray diffraction. In TiB₂, melting occurs due to formation of eutectic liquid with present impurities. In TiB₂-laminates melting and creation of high residual stresses produced cracks and fissures. The surface hardness was comparable to that obtained by polishing. During EDM of BN-TiB₂ composites, TiB₂ forms eutectic liquid at the interface with BN, and residual BN and some TiB₂ spall due to thermal shock. During pause periods parts of the liquid and fragments are flushed out by the dielectric. Composites rich in TiB₂ or with fine TiB₂ grains gave high material removal rates due to their high electrical conductivity. For all BN-TiB₂ composites, the diamond saw yielded much higher material removal rates than EDM but, unlike EDM, the diamond saw gave relatively lower removal rates for compositions rich in TiB₂, and for composites with fine TiB₂ grains due to their high hardness.     

The dispersion mechanism of TiB2 ceramic phase in molten aluminium and its alloys

Titanium diboride (TiB₂) ceramic particulates are dispersed in molten aluminium and its alloys for grain refining and for making cast metal–matrix composites. For producing cast MMC, the dispersion of the ceramic phase via in-situ aluminothermic reduction of K₂TiF₆ and KBF₄ flux mixture with molten aluminium and, via the addition of exogenously formed TiB₂ with the fluoride flux has been studied at 900°C. In this article, the aspects of interfacial energy that govern the dispersion and agglomeration of TiB₂ particulates are examined. The Gibbs-adsorption interface equation is particularly employed to define and to quantify the change in the surface energy as a function of the alloying element concentration and, consequently the effect of interfacial energy on the nucleation rate of TiB₂ formed via metallothermic reduction reaction and the size of the ceramic phase is also explained.     

放电等离子烧结Ni/TiB2-TiC复合材料微观组织及磨损性能

采用放电等离子烧结技术,以Ni、Ti、B₄C混合粉末为原料制备Ni/TiB₂-TiC复合材料,分析了Ni含量对复合材料的物相组成、组织结构、硬度和耐磨性的影响。结果表明：Ni/TiB₂-TiC复合材料主要物相为γ-Ni、TiB₂和TiC,其中TiB₂呈矩形条状和多边形状,TiC则呈现不规则块状;随着原始粉末中Ni含量的增加,TiB₂和TiC陶瓷相尺寸减小,其在Ni粘结相中的分布呈现出均匀化的趋势,复合材料更加致密。Ni含量显著影响Ni/TiB₂-TiC复合材料的耐磨性和磨损机制,Ni含量较低时（20wt%和30wt%）,复合材料摩擦系数（COF）较大且存在明显的波动,出现严重的疲劳磨损;随着Ni量的增加（40wt%）,材料的COF降低且趋于平稳,表现为微切削磨损;当Ni含量持续增加时（50wt%）,由于局部Ni的聚集导致粘着磨损产生,COF有所上升,耐磨性反而下降。     

激光选区熔化成形原位自生TiB2/Al-Si复合材料的微观组织和力学性能

利用激光选区熔化（SLM）技术制备了原位自生TiB₂纳米陶瓷颗粒增强Al-Si基复合材料,并对成形后的TiB₂/Al-Si复合材料进行不同的热处理。通过XRD物相分析、SEM微观组织观察、电子背散射衍射（EBSD）、EDS元素扫描分析和力学拉伸试验等对TiB₂/Al-Si复合材料的微观组织进行观察和力学性能测试。研究表明,在原位自生TiB₂纳米陶瓷颗粒和SLM快速凝固特性的共同作用下,SLM成形的原位自生TiB₂/Al-Si复合材料具有超细晶结构,平均晶粒尺寸为1.1 μm;TiB₂/Al-Si复合材料的力学性能优异,屈服强度为262 MPa,抗拉强度为435 MPa,延伸率为11.88%。对比经不同热处理的TiB₂/Al-Si复合材料,直接时效处理（150℃/12 h）的TiB₂/Al-Si复合材料性能最优,抗拉强度达到488 MPa,提高了53 MPa,延伸率降低至7.2%。     

不同TiB2颗粒粒径的TiB2/Cu复合材料耐电弧侵蚀行为

采用放电等离子烧结法（SPS）制备了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料,研究了3wt% TiB₂/Cu复合材料致密度、导电率、硬度和耐电弧侵蚀性能随TiB₂颗粒粒径的变化规律,重点分析了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料耐电弧侵蚀行为。结果表明:3wt% TiB₂/Cu复合材料致密度和硬度随TiB₂颗粒粒径的增大而略有降低;TiB₂颗粒粒径越小,TiB₂/Cu复合材料的综合性能越好。随着TiB₂颗粒粒径的增大,3wt% TiB₂/Cu复合材料耐蚀稳定性降低,3wt% TiB₂/Cu阴极材料的损耗量明显增加;当TiB₂颗粒粒径为10 μm时,3wt% TiB₂/Cu复合材料的耐电弧侵蚀性能最佳。电弧蚀形貌观察表明:不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料经电弧侵蚀后,3wt% TiB₂/Cu复合材料均由阴极向阳极发生转移;随着TiB₂颗粒粒径的增大,阴极质量损耗逐渐增加,触头表面电弧侵蚀面积增加;而在Cu基体中引入较小的TiB₂颗粒,有利于减弱电接触实验过程中TiB₂/Cu复合材料的喷溅现象。      

原位自生TiB2颗粒增强2024-T4铝基复合材料断裂行为数值模拟

利用SEM结合原位观测技术观察了颗粒体积分数为4.17%的原位自生TiB₂颗粒增强2024-T4铝基复合材料（TiB₂/2024-T4）的损伤断裂行为。试验结果表明,TiB₂颗粒偏聚带中的铝合金基体比颗粒稀疏区域中的铝合金基体率先发生断裂。根据这一试验现象建立了三种含随机颗粒偏聚带的二维体胞有限元模型,并施加拉伸载荷和周期性边界条件,推导了平面应力状态下的径向返回算法,结合Rice-Tracey局部失效准则模拟了颗粒偏聚带中微裂纹的萌生及扩展过程。数值分析结果表明：就单个颗粒来说,颗粒两极附近基体损伤最严重。颗粒偏聚导致损伤在颗粒附近基体中迅速累积,并发展成为基体微裂纹,且随着颗粒偏聚程度加剧,材料断裂应变下降。另外,体胞模型应力-应变曲线的非线性部分低于实测曲线,说明除了本文模型反映的载荷传递强化机制外,还需要进一步考虑颗粒对基体的间接强化机制。     

Comparative investigation towards machinability improvement in hard turning using coated and uncoated carbide inserts: part I experimental investigation

The investigation of low cost uncoated and coated carbide insert in the hard turning of hardened AISI D2 steel (≥55 HRC) will definitely open up a new arena as an economical alternative suitable to industrial machining sectors. Thus, this paper reports the comparative machinability assessment for the hard turning of AISI D2 steel ((55 ±1) HRC) by coated and uncoated carbide insert in a dry environment. Micro hardness and abrasion tests were carried out to assess resistance capability against wear. The above test results confirmed the greater wear resistance ability of Al₂O₃ coated carbide insert over uncoated carbide. Based on the extensive investigation of comparative machinability, the coated carbide insert (TiN-TiCN-Al₂O₃) outperformed the uncoated carbide insert with regard to surface roughness, flank wear, chip-tool interface temperature, and chip morphology. Abrasion and diffusion were observed as the principal tool wear mechanisms in the investigated range. The uncoated carbide failed completely due to the severe chipping and quick dulling of the cutting edge, which led to its unsuitability for machining hardened steel. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0215-z     

多粒径TiB2/Cu复合材料耐电弧侵蚀行为

采用粉末冶金工艺制备了不同配比的多粒径(2 μm+10 μm+50 μm) TiB₂/Cu复合材料。通过JF04C触点材料测试系统对多粒径TiB₂/Cu复合材料进行耐电弧侵蚀性能试验,研究(2 μm+10 μm+50 μm) TiB₂颗粒质量比分别为1∶1∶1、1∶1∶3、1∶3∶1、3∶1∶1时,TiB₂/Cu复合材料的耐电弧侵蚀性能及电弧侵蚀形貌变化规律,探究多粒径配比对TiB₂/Cu复合材料表层耐电弧侵蚀行为的影响。结果表明:当(2 μm+10 μm+50 μm) TiB₂颗粒质量比为1∶1∶1时,TiB₂/Cu复合材料相对密度和导电率最高,分别为99.1%和87.1%IACS。当(2 μm+10 μm+50 μm) TiB₂颗粒质量比为1∶1∶1和1∶3∶1时,TiB₂/Cu复合材料的组织均匀性较好,电弧侵蚀后材料损失相同,材料转移量最少。其中,质量比为1∶3∶1时,TiB₂/Cu复合材料平均燃弧能量最低,且燃弧时间和燃弧能量最稳定。研究表明,这与复合材料的综合物理性能密切相关。在颗粒增强Cu基复合材料设计过程中,引入合适配比的多粒径TiB₂颗粒有助于提高TiB₂/Cu复合材料的密度、导电率等综合物理性能。电弧侵蚀过程中,不同粒径的TiB₂颗粒相互协同作用,有助于提高TiB₂/Cu复合材料的耐电弧侵蚀性能和服役稳定性。      

不同粒径TiB2/Cu复合材料热传导模拟与实验

采用ANSYS对不同粒径TiB₂/Cu复合材料热传导过程进行模拟。采用粉末冶金法制备了不同粒径TiB₂增强的Cu复合材料,采用LINSEIS LFA1600激光导热仪测试了室温至280℃下的TiB₂/Cu复合材料热传导性能变化,并与模拟结果进行对比。结果表明:热导率模拟结果与实验结果吻合较好。在50~200℃之间,复合材料热导率变化不大,在6%~9%范围内波动。200℃之后,模拟值与实验值均呈现出随温度升高而增大的趋势,且吻合度较高。这是由于温度低于200℃时,在模拟过程中未考虑材料界面处两相不同热膨胀系数的影响,导致模拟值与实验值有较大的差异。当温度高于200℃时,模拟值和实验值吻合程度趋于稳定。在200℃时,由于两相热膨胀系数的影响,复合材料内部界面处等效应力大于Cu基体屈服强度,使其发生塑性变形,从而引起热导率发生较大幅度变化。此外,热导率随着TiB₂粒径的增大呈现出先提高后降低的趋势,在10 μm时达到最大。这是由于当颗粒直径小于临界平均直径时,颗粒直径的增大会减少界面数量,从而降低界面热阻。当颗粒直径大于临界平均直径时,平均自由程l的急剧增加导致热导率降低。      

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

铝基碳化硅精密铣削刀具磨损实验研究

针对铝基碳化硅切削加工中刀具易磨损、寿命低、切削难度大和加工成本高等问题,选用不同材料的硬质合金铣刀及金刚石铣刀进行切削加工实验,并利用扫描电镜和工具显微镜对高体积分数铝基碳化硅铣削时刀具磨损形态进行了分析研究.研究表明:硬质合金刀具前刀面和刃口磨损主要形式为粘结磨损和微崩刃,后刀面磨损主要为刻划磨损,而金刚石铣刀加工时刀具磨损很小;YG6X铣刀材料微观组织致密,抗磨损能力较强,宜粗加工时选用;金刚石刀体的硬度远大于SiC颗粒,且金刚石与工件的摩擦系数小,金刚石铣刀寿命远大于硬质合金铣刀,宜精加工时选用.