激光熔覆Ni/TiB2复合涂层的组织与性能研究

在45钢表面利用激光熔覆技术制备了Ni／TiB2金属陶瓷复合涂层，利用光学显微镜、扫描电子显微镜、能谱仪、显微硬度计等，分析了涂层的显微组织特征、元素的分布以及涂层的机理等，并对试样硬度进行了测定。结果表明，在合理的工艺参数下，超细TiB2的加入，细化了激光熔覆涂层的晶粒，熔覆层显微组织主要由细小的等轴晶组成，TiB2陶瓷颗粒分布在枝晶间，而分解后的Ti均布于枝晶内，通过细晶强化、固溶强化及第二相强化等，大大提高了涂层的硬度。     

Al_2O_3-TiB_2 刀具的磨损特性

对ＴｉＢ２颗粒增强Ａｌ２Ｏ３刀具在车削正火态、调质态４５＃钢和球墨铸铁齿轮坯时的刀具磨损性能、磨损机理进行了研究，并与硬质合金刀具的耐磨性能进行了对比。结果表明：Ａｌ２Ｏ３┐ＴｉＢ２陶瓷刀具具有良好的耐磨性能。刀具磨损主要以脆性剥离为主，同时存在着犁耕和塑性流变过程，陶瓷刀具表面形成的粘结层结构疏松，与基体结合力较弱，较易脱落，不易形成粘结磨损。     

Tribological characteristics of composite coatings formed by laser cladding of powders of nickel self-fluxing alloy and bronze

Microstructures, coefficients of friction, and relative wear of composite coatings based on the PG-12N-01 nickel self-fluxing alloy and PG-19M-01 bronze have been considered. It has been found that composite coatings have a complex structure. The bronze coating, which is deposited on the fillets of the nickel alloy, crystallizes in a form of dendrites with axes arranged under an angle of 45°. The nickel alloy has a globular-dendritic structure with the eutectic component crystallizing between its branches. Momentary coefficients of friction in conditions of the concentrated load are independent of the cladding rate, and their values are 0.08–0.12 depending on the load. In this case, the wear rate of coatings depends substantially on the laser cladding. Under conditions of the distributed contact, bilayer coatings have a considerable advantage, and the relative wear is reduced by several tens of times compared with single-layer ones.     

LSM法制备TiB2/Al复合材料

用LSM法制备了TiB2／Al复合材料，用XRD、SEM和图像分析软件考察了净化方式、冷却速度对复合材料相组成、TiB2颗粒分布的影响。结果表明：熔剂法精炼对复合材料中TiB2颗粒的分布无明显影响，精炼后TiB2含量基本保持不变；而浮游法精炼后未检测到TiB2颗粒，即普通铝合金采用的浮游法精炼工艺不适于复合材料的精炼；随着冷却速度加大，复合材料凝固组织细化，TiB2颗粒分布趋于均匀，颗粒团聚减少。     

激光熔覆工艺参数对横向搭接熔覆层结合界面组织的影响

为了提高搭接熔覆层的质量并控制搭接结合界面,研究了工艺参数对横向搭接结合区域组织形态的影响.结果显示,当扫描速度、送粉速率、激光功率分别在100-250 mm/min,6-7.5 g/min,1 500-2 500 W区间变化时,搭接结合区域呈现出不同的界面组织形态,没有出现白亮层.这些界面组织一类表现为具有组织与方向...     

Coarse cemented WC particle ceramic-metal composite coatings produced by laser cladding

Coarse cemented WC particle (600–900 μm) ceramic-metal composite coatings with a thickness of 1.2–1.5 mm were cladded on 20Ni4Mo steel surfaces using a laser of power 2 kW, diameter 5 mm and traverse speed 4–20 mm s⁻¹. The weight fraction of WC particles was 67 wt%. Compared with the behaviour of cemented WC particles of the same size and ratio in atomic hydrogen welded coating (AHWCs), the WC particles in laser-cladded ceramic-metal coating (LCCCs) show a uniform distribution in the molten zone. The microhardness of WC particles in LCCCs is 13.7–16.2 GPa, and their sizes are almost unchanged, which indicates that little heat damage occurs during laser cladding. The abrasive wear results showed that LCCCs have superior wear resistance to AHWCs. The wear mechanisms for LCCCs and AHWCs are analysed and compared.     

合金成分对激光熔覆TiC-TiB_2复合涂层组织性能影响

为增强材料表面硬度和耐磨性,以Ti O2-Al-B4C-C作为粉末体系,利用激光熔覆技术在45#钢基材表面上制备了Ti C-Ti B2增强复合涂层,采用金相显微镜、扫描电镜(SEM)、X射线衍射仪(XRD)、显微硬度计和摩擦磨损试验机研究了不同含量的Ti O2-Al-B4C-C系合金粉末对涂层组织性能的影响。结果表明:复合涂层与基材冶金结合,无裂纹和气孔等缺陷,Ti C、Ti B2弥散分布于涂层中;随着Ti O2-Al-B4C-C系合金粉末含量的增加,涂层组织中Ti C、Ti B2及等轴晶的量逐渐增多;熔覆层的硬度也逐渐增加,当合金粉末含量为70Wt%时,熔覆层硬度最高,为基材的4倍。Ti O2-Al-B4C-C系合金粉末含量为50Wt%时,熔覆层磨损量最小,耐磨性最好     

A method to predict possibility of arcing in EDM of TiB2p reinforced ferrous matrix composite

Electrical Discharge Machining (EDM) is very popular for machining conductive metal matrix composites (MMCs) because the hardness rendered by the ceramic reinforcements to these composites causes very high tool wear and cutting forces in conventional machining processes. EDM requires selection of a number of parameters for desirable results. Inappropriate parameter selection can lead to high overcuts, tool wear, excessive roughness, and arcing during machining and adversely affect machining quality. Arcing leads to short circuit gap conditions resulting in large energy discharges and uncontrolled machining. Arcing is a detrimental phenomenon in EDM which causes spoiling of workpiece and tool electrode and tends to damage the power supply of EDM machine. Parameter combinations that lead to arcing during machining have to be identified and avoided for every tool, work material, and dielectric combination. Proper selection of parameter combinations to avoid arcing is essential in EDM. In the work, experiments were conducted using L27 design of experiment to determine the parameter settings which cause arcing in EDM machining of TiB₂p reinforced ferrous matrix composite. Important EDM process parameters were selected in roughing, intermediate, and finishing range so as to study the occurrence of arcing. Using the experimental data, an artificial neural network (ANN) model was developed as a tool to predict the possibility of arcing for selected parameter combinations. This model can help avoid the parameter combinations which can lead to arcing during actual machining using EDM. The ANN model was validated by conducting validation experiments to ensure that it can work accurately as a predicting tool to know beforehand whether the selected parameters will lead to arcing during actual machining using EDM. Validation results show that the ANN model developed can predict arcing possibility accurately when the depth of machining is included as input variable for the model.     

激光熔覆Fe/(Ti,W)C复合材料的研究

采用CO2激光加工成套设备在45#钢板表面熔覆Fe基涂层和Fe/(Ti,W)C金属陶瓷复合涂层。研究了加入(Ti,W)C对涂层相结构、组织、显微硬度及耐磨性的影响。结果表明,Fe基熔覆层主要组成相为马氏体相,显微组织主要由均匀细小的树枝晶组成;而Fe/(Ti,W)C复合涂层主要由马氏体和(Ti,W)C两种相组成,显微组织主要为花瓣状组织,加入(Ti,W)C颗粒对熔覆层组织有明显影响;熔覆层显微硬度由HV0.2 670提升至HV0.2 900;耐磨性能也有显著提升。     

机械合金化合成TiB2/Fe3Al纳米复合粉体

采用铁、铝、钛、硼四元粉体机械合金化与后续热处理的方法合成纳米TiB_2／Fe_3Al复合粉体,并利用XRD、DSC、SEM和TEM等对粉体进行了表征。结果表明：在球磨过程中,四元粉体形成了Fe(Al,Ti,B)过饱和固溶体,有序度不断降低,逐渐向非晶态转变,同时粉体晶粒尺寸逐渐细化,球磨40h后Fe(Al,Ti,B)的晶粒尺寸为9．6nm;并在热处理过程中Fe(Al,Ti,B)分解生成纳米Fe_3Al和TiB_2复合粉体,同时发生组成相晶粒生长,结构有序度提高等转变。     

激光熔覆Al和微量Al_2O_3对提高AZ91D镁合金表面性能的研究

为了提高AZ91D镁合金表面性能,实验利用5 kW横流CO2激光器在AZ91D镁合金表面熔覆了Al+微量Al2O3涂层(Al2O3的质量分数分别为2%,3%,4%,Al和Al2O3的粒度均为300目),使用激光的功率分别为1.9kW,1.5 kW,1.7 kW,扫描速率为7 mm/s,对不同激光工艺参数下获得的熔覆层组织进行了观察,用扫描电镜(SEM)对熔覆层进行了微观分析,并测试了熔覆层的显微硬度和耐磨性能。实验结果表明:当激光功率为1.7 kW~1.9 kW,扫描速率为7 mm/s时,熔覆层的显微硬度最高达320HV0.2是基体的80HV0.2的4倍,耐磨性比基体明显提高了。     

Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix composite

An aluminium matrix composite with iron aluminide formed in situ as a result of self‐propagated high‐temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle‐like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self‐propagating high‐temperature synthesis consisted only of the Al₃Fe phase.     

Wear properties of Saffil/Al,Saffil/Al2O3/Al and Saffil/SiC/Al hybrid metal matrix composites

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/Al₂O₃/Al and Saffil/SiC/Al hybrid metal matrix composites (MMCs) fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, Al₂O₃ particles and SiC particles on the wear behavior of the composites were elucidated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction (COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffil/Al₂O₃/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.     

Effect of laser beam incidence angle on cladding morphology in laser cladding process

The change of angle θ between laser cladding powder plane and substrate plane will lead to changes in cladding layer's geometric morphology. Therefore, we established a quantitative numerical prediction model for cladding layer geometry. In this model, we consider the variation of θ, the laser energy attenuation rate and the temperature rise of the powder particles. At the same time, the simulation results were verified by experiments. The results show that when θ is in the range of 50°~90°, the initial temperature is 298 K, the scanning speed is 3.75 mm/s, and the laser spot diameter is 4.5 mm, the Fe#1 powder cladding can achieve better forming effect on Q235. In general, with the decrease of θ, the height of the cladding layer decreases and the width of the layer increases. However, when θ is less than 50°, the quality of the formed morphology significantly deteriorated. The experimental results are in good agreement with the simulation results, which verifies the validity and reliability of the model. This work provides a theoretical reference for further understanding the relationship between the laser cladding morphology and the incident angle.     

Al/Fe3Al网状结构复合材料的制备

采用机械合金化及退火工艺制备纳米级Fe3Al金属间化合物粉体;利用有机前驱体烧蚀技术,氩气保护下在真空热处理炉中经过1460℃热处理,制备具有高气孔率、高尺寸稳定性、耐高温的Fe3Al金属间化合物网状结构;采用负压浸渗法制备Al/Fe3Al网状结构复合材料,材料的耐磨性能明显优于基体材料,在100N载荷、400r/min转速的试验条件下,摩擦时间为20min时,Al/Fe3Al复合材料的磨损量较纯Al试样降低66%.     

激光熔覆原位自生Ti-Al-Si复合涂层的微观组织和高温抗氧化性能

为提高钛合金的高温抗氧化性能,采用激光熔覆原位自生技术,在TC4钛合金表面自行设计并制备了原子百分比为Ti∶Al∶Si=41∶41∶18和Ti∶Al∶Si=35∶35∶30的两种涂层。通过XRD、OM、SEM表征了涂层的微观组织和物相组成;借助管式电阻炉测试了涂层和基体试样在800℃×24h×5次循环氧化条件下的高温抗氧化性能;结合氧化增重和氧化动力学曲线分析了涂层的高温抗氧化机理。结果表明,涂层主要由Ti5Si3、Ti7Al5Si12、Ti3Al、TiAl和TiAl3等物相组成。涂层中没有出现一般激光熔覆所产生的外延生长柱状晶组织,全部为细小等轴晶。在800℃×24h×5次循环氧化条件下,TC4基材单位面积的氧化增重约为35.1mg·cm-2,涂层的约为2.8mg·cm-2和3.3mg·cm-2。两种涂层的高温抗氧化性能较钛合金基材分别提高了12.5倍和10.6倍。激光熔覆原位自生Ti-Al-Si复合涂层能明显改善TC4钛合金的高温抗氧化性能。涂层抗氧化性改善的机理,一方面是表面生成了连续致密的TiO2、Al2O3、SiO2氧化层,阻碍了氧扩散;另一方面是提高了氧化层的黏附性,使氧化层不易从涂层表面剥落,对涂层未氧化部分起到了很好的保护作用。     

CR法生成TiB2/Al复合材料制备工艺研究

在实验的基础上 ,分析 CR法生成 Ti B2 / Al复合材料的制备工艺的五个关键问题 ,得出相应的解决方法 ,制备出了颗粒分布均匀、组组致密、性能较理想的 Ti B2 / Al复合材料 ,对复合材料制备工艺的实际应用具有重要意义     

原位复合反应制成TiB对提高管道耐磨性的研究

将自蔓延和离心铸造的方法相结合,制备了原位TiB晶须增强钛基复合材料;采用扫描电子显微镜分析了复合材料的显微组织,结合磨损表面、剖面显微组织.分析探讨了复合材料表面的磨损机制;评价了复合材料的耐磨性能.结果表明：TiB晶须尺寸细小、长径比大、在基体中分布均匀;与基体合金相比,钛基复合材料的耐磨性能显著提高,这是由于TiB晶须具有增强作用和承载作用所致.