颗粒增强钛基复合材料高温氧化性能的研究

针对钛基复合材料高温应用中的关键问题———高温氧化性能,从理论和实验上研究不同成分钛基复合材料的氧化性能。结果表明:钛基复合材料的氧化规律为抛物线规律,以TiC、TiB为增强体的钛基复合材料比只含有TiB增强体的钛基复合材料抗氧化性好,合金元素Al的加入,有助于钛基复合材料抗氧化性能的提高。     

TiC、TiB增强钛基复合材料的高温氧化性能及微观结构

针对钛基复合材料高温应用中的关键问题——高温氧化性能，从理论和实验上研究了不同增强体(TiC、TiB)对钛基复合材料氧化性能和微观结构的影响。结果表明：钛基复合材料的氧化规律为抛物线规律，TiB增强体比TiC增强体更能提高复合材料的高温抗氧化性能，TiB／Ti基复合材料表面氧化膜的状态较TiC／Ti基的致密、均匀，高温氧化后，基体元素Ti和Al会与氧发生反应生成TiO2、Al2O3。     

新型镍基药芯焊丝熔敷金属的高温氧化行为

采用增重法测定了自制新型镍基药芯焊丝熔敷金属在800℃和1000℃空气中的高温氧化行为。采用扫描电镜（SEM）对氧化产物表面和横截面形貌进行了观察,X射线衍射仪（XRD）对氧化膜层的物相进行了分析。结果表明,熔敷金属在800℃氧化时,氧化增重与氧化时间遵从抛物线规律,表面氧化膜无剥落,氧化速率较稳定;在1000℃氧化时,氧化增重与氧化时间近似遵从抛物线规律,表面氧化膜出现少量剥落,且氧化膜增厚,氧化增重是800℃氧化时的4倍左右。氧化过程中,氧化膜主要由Cr2O3组成。     

含二硫化钼镍铬基高温复合材料的高温氧化行为

采用粉末冶金方法制备了添加质量分数为6％二硫化钼的镍铬基复合材料;对其在800,900和950℃的高温氧化行为进行了研究,绘制了氧化动力学曲线;用扫描电镜对其氧化表面形貌和横截面组织进行了观察。结果表明：该镍铬基复合材料在800℃以及900℃氧化100h后,其氧化动力学符合抛物线规律,在材料表面生成了Cr2O3和NiCr2O4氧化膜,具有一定的抗氧化性能;在950℃氧化时,表面氧化膜出现剥落。     

铜、钛元素对镍基耐蚀合金高温氧化行为的影响

采用增重法测出了含铜和钛元素的镍基耐蚀合金在800℃空气中的高温氧化动力学曲线,并用扫描电镜及能谱仪对氧化膜的形貌和成分进行了分析,研究了铜和钛元素对合金高温氧化行为的影响。结果表明:随着铜元素含量的增多,合金的抗高温氧化能力逐渐变弱;在合金中加入一定量的钛元素可以使合金表面的氧化膜更加致密,增强合金的抗高温氧化能力。     

热压烧结碳化硅陶瓷的氧化性能

采用硅作为烧结助剂热压烧结SiC陶瓷,用扫描电镜、X射线衍射仪和热重分析仪研究了不同状态SiC陶瓷的氧化性能.结果表明:未预处理SiC在等温氧化过程中,600～1 100℃区间内,等温氧化动力学曲线服从抛物线规律;而在1 100～1 300℃区间,则偏离了抛物线规律,氧化速率随温度的升高先增大后减小.经过高温预氧化处理之后,SiC试样在等温氧化过程中,氧化动力学曲线为直线,较未预处理试样氧化增重显著减少;连续升温氧化过程中,和未预处理试样相比,剧烈氧化开始温度升高,同时其氧化速率及最终的氧化增重均大幅度降低.说明了高温预氧化处理能够有效提高SiC陶瓷的抗氧化性能.     

机床用新型钴基金属复合材料的制备与性能研究

以少量石墨烯作为增强体,采用分步球磨法,制备了机床用不含稀土的CoWAlSrCrV新型钴基金属复合材料,并进行了显微组织、物相组成、耐磨损性能和抗高温氧化性能的测试与分析。结果表明,该方法制备的新型钴基复合材料具有较佳的耐磨损性能和抗高温氧化性能。与La2CoO4钴基稀土复合材料相比,该新型复合材料的25℃磨损体积减少44.8%、300℃磨损体积减少45.8%、800℃磨损体积减少45.2%,800℃高温氧化100h后的单位面积质量增重减少69.7%。     

合金元素含量对球墨铸铁耐热性能的影响

通过高温氧化性能实验、热疲劳实验得到实验数据,分析材料的抗高温氧化性能和抗高温热疲劳性能,根据Si、Mn、Cr合金元素含量的不同,采用氧化增重法研究材料的高温抗氧化性,探讨合金元素Si、Mn、Cr含量变化对材料氧化增重的影响规律,利用热疲劳实验研究耐热球墨铸铁模具材料的抗热疲劳性,对不同循环次数下疲劳裂纹形貌的观察,分析合金元素Si、Mn、Cr含量变化对热疲劳裂纹的影响。     

电厂锅炉水冷壁管高温抗氧化涂层的制备及性能研究

电厂锅炉水冷壁的高温氧化问题严重地影响了电厂的安全性和经济性，为了解决该问题，文中采用热化学反应法制备了适用于锅炉水冷壁管的陶瓷涂层，以高温抗氧化性为主要指标，对涂层的各项性能进行评价。结果表明：在800℃温度下，涂层单位面积氧化增重为0.83 mg/cm²，涂层结合力为54.6 N，可经受18次循环空冷。制备的陶瓷涂层的氧化增重曲线符合抛物线型，氧化活化能为175.82 k J/mol，抗氧化性能良好，有效地降低了电厂锅炉水冷壁的高温氧化速率，延长了其使用寿命。     

钛基复合材料的焊接

钛合金具有较高的室温和高温比强度、低密度、高弹性模量 ,加入高强度、高刚度的增强相可进一步提高其比弹性模量、比强度和抗蠕变能力 ,因此钛基复合材料 (TMCs)成为超高音速宇航飞行器、先进航空发动机的理想候选材料。钛基复合材料在气体涡轮机发动机风扇叶片、驱动轴、超高速飞行器、飞机起落架、飞机构架结构、导弹结构方面具有良好的工程应用前景。除成本较高之外 ,影响钛基复合材料使用的主要因素是其加工为结构件的能力。就单一的钛合金来说 ,熔化焊是一种广泛使用的效率高、成本效益好的加工方法。但就纤维增强钛基复合材料而言 …     

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。     

SiC长纤维增强Ti基复合材料的制备

Si C长纤维增强 Ti基复合材料在航空领域有广阔的应用前景 ,本文对其制备方法进行了评述。比较了箔 -纤维法、浆料带铸造法、等离子喷涂法及纤维涂层法制备 Ti基复合材料的优缺点及制备成本 ,认为采用纤维涂层法制备 Ti基复合材料航空发动机零部件较好。本文还用纤维涂层法制备了 SCS- 6 Si C/Ti- 10 2 3复合材料试样     

In situ high temperature microscopy study of the surface oxidation and phase transformations in titanium alloys

Two popular commercial titanium alloys, Ti‐6Al‐4V and Ti‐6Al‐2Sn‐4Zr‐2Mo‐0.08Si, were used for in situ high temperature microscopy study. The experiments were performed on an optical microscope equipped with high temperature stage using both normal and florescence lights. Two kinds of experiments were performed, at continuous heating/cooling with different rates and in isothermal conditions at different temperatures. The changes taking place on the sample surface during the experiments were monitored. The morphology of the α?β?α phase transformation was recorded at different heat treatment conditions using the effect of thermal etching. An effect of sample surface oxidation and deoxidation was observed during continuous heating. The appearance and disappearance of ordered titanium oxides Ti₃O and Ti₂O are discussed based on the phase equilibrium diagram. The kinetics of the surface oxidation was monitored in both isothermal and continuous cooling conditions.     

Tribochemistry of a Ti Alloy Under Fretting in Air: Evidence of Titanium Nitride Formation

The present investigation focuses on the tribological transformation occurring on a Ti alloy (Ti17) under fretting in air. Several fretting wear tests were performed on a large scale punch on plane configuration (two types of planes tested: bare Ti6242 and CuNiIn-coated Ti6242) at several temperatures from ambient up to 450 °C. In all the cases, two zones were identified on the scars: a lateral oxidized rim and a highly deformed region at centre. Metallurgical observations revealed similarities with Tribologically Transformed Structure (TTS), previously observed on various Ti alloys. In the framework of this article, careful analyses were conducted (EDX, DRX, XPS, HRTEM and EFTEM) in order to identify the nature and chemistry of this transformed layer. Results demonstrated the formation of a new phase, nanocrystalline, identified as TiO _x N _y . The high content of nitrogen found in the TTS indicated its ability to penetrate inside the contact and react with titanium. At 50 μm under the surface, a FIB preparation enabled the observation in TEM of N-rich lamellae (TiO _x N _y ) in the Ti (α) matrix. Two models were suggested to explain this tribochemical reaction under fretting.     

Mechanical and Tribological Properties of Spark Plasma–Sintered Titanium Composites Filled with Different Al-Cr-Fe Quasicrystal Contents

A new type of Ti composite filled with Al-Cr-Fe quasicrystals (QCs) was developed via a spark plasma sintering process. The mechanical and tribological properties of the Ti/QC composites were systematically investigated. It was found that the hardness of the Ti/QC composites significantly increased with increased QC content due to the higher hardness of incorporated QCs than that of the Ti matrix. The tribological results clearly showed that the wear of the Ti/QC composites apparently decreased with increased QC content to 20 wt% as a result of the increased wear resistance of the composites. An excessive loading of 30 wt% QCs resulted in the decreased wear resistance of the Ti/QC composites. It could be concluded that the incorporation of QCs significantly improved the mechanical and tribological properties of the Ti/QC composites with an optimized QC content of 20 wt%.     

Thick rutile layer on titanium for tribological applications

In the present work, efforts have been made to oxidise the titanium surface, followed by very slow cooling to produce a thick and adherent oxide layer. The response of titanium to oxidation at various temperatures and timings has been investigated, in terms of layer thickness, phase evolution, surface morphology, oxide layer–substrate adhesion, hardness and tribological characteristics. A variety of experimental and analytical techniques, including X-ray diffraction, field-emission scanning electron microscopy, scanning electron microscopy, micro-hardness and tribological testing, have been used to characterise the resultant thermal oxidised surfaces. The results showed that a thick oxide layer with rutile TiO₂ and oxygen diffused Ti structure can be produced, which exhibited excellent adhesion with the titanium substrate, low friction and superior wear resistance during pin-on-disc sliding tests and thus good potential for tribological applications.     

钛合金微弧氧化层的摩擦学性能研究

利用微弧氧化技术在Ti6Al4V合金表面制备了富含钙、磷的多孔氧化陶瓷层,研究了微弧氧化层表面形貌、组成及摩擦学性能。研究结果表明,随着电压的升高,氧化层表面微孔孔径、粗糙度和Ca、P元素含量增大,显微硬度增大。25%小牛血清润滑条件下的微弧氧化层与ZrO2陶瓷球的摩擦学实验表明,微弧氧化层的摩擦因数高于Ti6Al4V钛合金,但磨损率明显降低,表明微弧氧化Ti6Al4V合金具有良好的耐磨性能。     

热处理条件下激光原位合成高铌Ti-Al金属间化合物复合涂层的微结构特征

为了提高钛合金的高温抗氧化性能,推动钛合金在高温和复杂工况环境下的进一步工程应用,利用高能激光束作用下Ti、Al、Nb三种元素混合粉末之间的原位反应在BT3-1钛合金表面制备了高温抗氧化的高铌Ti-Al金属间化合物复合涂层。针对原位反应所制备涂层存在的缺陷,通过自行设计的热处理工艺优化了涂层和界面微观组织。借助光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)分析了热处理前后复合涂层的物相结构及显微形貌。结果表明:热处理前的涂层主要由单质Nb、金属间化合物γ-TiAl、α_2-Ti_3Al、Ti_3Al_2等物相组成;热处理后的复合涂层,单质Nb固溶到γ-TiAl和α_2-Ti_3Al中,同时形成了新相Ti_3AlNb_(0.3),涂层近似为γ-TiAl+α_2-Ti_3Al双相层片状等轴晶组织。此外,涂层中并未观察到减弱抗氧化性的单质Nb颗粒和Ti_3Al_2相,Ti、Al、Nb的宏观偏析得以消除,涂层与基材界面位置的气孔和裂纹均以消失,出现了明显的白亮带冶金结合过渡层,涂层组织也更加均匀致密。热处理对提高钛合金表面Nb的合金化程度和改善Ti-Al金属间化合物的高温抗氧化性能起到了显著的促进作用。     

The abrasive wear resistance of TIC and (Ti,W)C-reinforced Fe–17Mn austenitic steel matrix composites

Pin-on-disc dry sliding wear tests have been carried out to study the wear behaviour of 10 vol% TiC and (Ti,W)C-reinforced Fe–17Mn austenitic steel matrix composites. The composites have been synthesized in situ by means of conventional melting and casting route. It has been observed that the abrasive wear resistance of the composites is higher than that of their unreinforced Fe–17Mn austenitic steel. Compared with the TiC-reinforced composite, the abrasive wear resistance of the (Ti,W)C-reinforced composite is better. The abrasive wear resistance and coefficient of friction of both reinforced and unreinforced materials decrease as the load increases.     

The improvement of wettability,biotribological behavior and corrosion resistance of titanium alloy pretreated by thermal oxidation

The thermal oxidation process was performed on biomedical titanium alloys to improve surface properties for the application in artificial cervical disc. The pretreated Ti6Al4V was characterized with XPS, XRD and SEM. The wettability, biotribological behavior and corrosion resistance were evaluated under distilled water and 25 wt% bovine serum lubricant. Rutile TiO₂ as the main compound was formed with the increase in hardness. The wettability was improved significantly after oxidation. Compared with the untreated, the friction coefficients and wear volumes of treated samples all decreased with about 50% reduction in both dry sliding and lubrication conditions. Corrosion resistance for oxidized samples was also enhanced with a big reduction of corrosion current density and a shift in corrosion potential towards the positive direction.