TiB2含量和烧结温度对B4C/Al2O3基复合陶瓷的影响

利用原位反应热压工艺制备了B4C/Al2O3基复合陶瓷,研究了TiB2含量和烧结温度对B4C/Al2O3基复合陶瓷力学性能和微观结构的影响.结果表明,当TiB2含量低于8.7％时,随原位反应生成的TiB2含量的增加,有效的促进了B4C/Al2O3/TiB2复合陶瓷的烧结,提高相对密度,改善了力学性能.当烧结温度低于1900℃时,其力学性能随烧结温度增加而提高;当超过1900℃时,其力学性能随烧结温度的提高而降低.在1900℃,60 min时,B4C/Al2O3/TiB2复合陶瓷获得最佳综合力学性能,其硬度、断裂韧性和抗弯强度分别为24.8 GPa、4.82 MPa·m1/2和445.2 MPa.     

TC4钛合金表面氧化锆催渗渗硼工艺的优化

以渗层厚度和表面硬度为评定依据,采用正交试验对TC4钛合金表面氧化锆催渗渗硼工艺进行了优化,其中渗硼温度影响最大,其次为渗硼时间和ZrO2含量,B4C含量影响最小,最优工艺为:渗硼温度1 050℃,渗硼时间25h,渗硼剂配比(质量分数):B4C 20%,ZrO24%,SiC 76%。利用X射线衍射仪和光学显微镜对渗层的物相组成和厚度进行分析,结果表明:渗层表面主要由TiB2、TiB、TiB12、TiC、TiN组成,渗层厚度为46.67μm。与基础渗硼剂所得渗层相比,渗硼层厚度、渗层硬度、界面结合力和耐磨性都有所提高。     

钛金属表面熔盐电解法制备TiB2/TiB表面层

运用渗硼技术改进金属钛及其合金的表面特性。以无水硼砂为主渗硼剂,无水碳酸钠为助熔剂和高温络合剂的渗剂体系,在电流密度为7.3 A/dm2,保温温度为900℃,通电时间为30 min的电解渗硼工艺下制备出复合硼化物表面层。通过热重与差热图谱确定几种硼砂-碳酸钠配比体系的初晶温度。对4种不同配比的渗硼剂试验得到的样品做XRD测试,分析了相结构。并对硼化物生长机理与结构进行了研究与分析。结果显示:质量比为8∶2的渗硼剂组成最优。纯硼砂电解的样品表面物相组成与二渗硼钛标准粉末的XRD完全吻合。钛金属表面主要生成TiB2与TiB;扫描电镜图像可知渗硼表面致密,TiB2与TiB分层较为明显;TiB厚度可达35μm,TiB2厚度为43μm。     

TiB2合成反应机理的优势区相图分析

随着碳热还原反应的进行,B2O3被C还原生成B2O2,B2O2进一步被碳还原生成B4C.碳热还原TiO2和B2O3合成TiB2的反应机理如下在1200～1300℃温度下,TiO2被C还原成中间产物Ti3O5;在1250～1300℃温度范围,B2O3被C还原生成中间气相产物B2O2;当还原反应温度达到1300℃以上时,中间产物Ti3O5与B2O2一起被C还原生成TiB2.     

TiB2含量对B4C-TiB2-Al复合材料组织与力学性能的影响

通过在B4C-TiB2预烧体中真空熔渗Al制备了B4C-TiB2-Al复合材料,研究了TiB2含量对复合材料显微组织和力学性能的影响.结果表明: B4C-TiB2-Al复合材料主要由B4C,TiB2,Al和Al3BC等相组成;随着TiB2含量的增加,复合材料的HRA硬度逐渐降低,抗弯强度逐渐增大,断裂韧性先增大后稍微降低,当TiB2含量为40%(质量分数)时,复合材料的气孔率、硬度HRA、抗弯强度和断裂韧性分别为1.32%,80.3,559.4 MPa和7.83 MPa·m1/2;延性Al的加入,裂纹的偏转和分叉、B4C和TiB2晶粒的细化以及B4C基体和TiB2晶粒热膨胀的不匹配,是造成材料断裂韧性提高的主要原因;随着Al渗入量的增加,复合材料断口中金属撕裂棱及韧窝的比例增加.     

Ti-6Al-4V钛合金固体渗硼法表面改性

对TC4钛合金(Ti-6Al-4V)进行表面渗硼使其表面硬度显著提高.渗硼温度为1000℃到1050℃,渗硼时间为5 h到20h.文内测量和比较了渗硼后钛合金表面的微结构、形貌、相组成等性质,研究了渗硼过程中Ti,Al,V,B等元素的扩散行为.在低温短时间渗硼时,渗硼层厚度仅0.8μm,而在高温长时间渗硼时,渗硼层厚度可达15 μm.实验证明,渗硼层由TiB和TiB2两相组成,并且它们的含量随渗硼温度提高而增加.渗硼层表面主要含TiB2,其显微硬度可达2200 HV0.01,渗硼层内表层主要含TiB,其显微硬度为1100 HV0.01.渗硼层的硬度远高于TC4钛合金的硬度.     

温度对B4C涂层氧化防护性能和防护机制的影响

目的 研究温度对B4C涂层氧化防护性能和防护机制的影响,得出B4C涂层最佳氧化防护温度范围,以及B4C涂层在不同温度的氧化防护机制演变。方法 以石墨为基体,采用放电等离子烧结法在石墨表面制备B4C涂层,通过不同恒温氧化试验(800、1 000、1 200、1 400 ℃)和室温至1400 ℃宽温域动态氧化试验来测试其氧化防护性能,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)和能谱仪(EDS)对B4C涂层石墨试样氧化前后的物相组成、微观形貌、氧扩散等进行分析。结果 B4C涂层氧化后可生成B2O3玻璃膜,在800、1 000、1 200、1 400 ℃恒温氧化的防护效率分别为98.43%、98.61%、94.4%和92.8%,在室温至1 400 ℃宽温域动态氧化的防护效率为93.1%。B4C涂层在800 ℃以下主要依赖结构阻氧,800至900 ℃由结构阻氧向惰化阻氧转变,900 ℃以上主要依赖惰化阻氧。1 100 ℃以上,随温度升高B2O3玻璃膜的挥发加剧,B4C涂层惰化阻氧能力减弱。结论 B4C涂层的氧化防护效率随温度上升先增大后减小,结构阻氧机制逐渐降低,惰化阻氧机制先升高后降低。B4C涂层在800至1 100 ℃具有良好的氧化防护性能。     

渗硼用Na2B4O7-Na2CO3熔盐热分析

对渗硼用Na2B4O7-Na2CO3熔盐体系进行DTA和TG热分析。DTA分析表明,在Na2B4O7中添加Na2CO3并没有大幅降低Na2B4O7的初晶温度。TG分析表明,Na2B4O7中添加Na2CO3能促进Na2B4O7的分解,平均每添加10%Na2CO3体系质量损失4%。Na2B4O7-Na2CO3体系的温度升高过程分别对应固体Na2B4O7的分解、渗剂熔化以及B2O2的氧化过程。硼砂熔盐渗硼最佳温度为905℃。     

TC4钛合金表面氧化镧催渗渗硼工艺优化

以渗层厚度和表面硬度为评定依据,采用正交试验对TC4钛合金表面氧化镧催渗渗硼工艺进行优化。结果表明,渗硼温度对渗硼层影响最大,其次为渗硼时间、B₄C含量和La₂O₃含量。最优的催渗渗硼工艺为：渗硼温度1050 ℃,渗硼时间20 h,渗硼剂配比20wt%B₄C+4wt%La₂O₃+76wt%SiC。渗层表面由TiB、Ti₂B₅、TiC和Ti组成;与未添加氧化镧渗硼层相比,添加氧化镧渗硼层厚度与表面硬度明显提高,耐磨性也得到显著改善。     

TiB_2含量对原位反应合成TiB_2/B_4C复合材料的组织结构和力学性能的影响(英文)

以B4C,TiO2和石墨粉为原料,采用原位反应热压烧结工艺(2050℃,35MPa,1h)制备了致密的TiB2含量为10%～40%(体积分数)的TiB2/B4C复合材料,并对复合材料的组织结构和力学性能进行了研究。扫描电子显微镜和透射电子显微镜分析结果表明:在B4C晶内及晶界处均匀分布着纳米或亚微米级的TiB2颗粒,随着TiB2含量的增加,弹性模量和断裂韧性明显增大,而弹性模量和抗弯强度却随之减小。40%(体积分数)TiB2/B4C复合材料具有高的断裂韧性,高达8.2MPam1/2,主要增韧机制由微裂纹增韧和裂纹偏转增韧。     

TC4合金表面激光熔覆B4C及B4C＋Ti粉末涂层的微观组织

利用XRD，SEM和EDS分析手段对B4C和B4C＋10％Ti（质量分数，下同）激光熔覆层的微观组织进行了分析。结果表明，TC4合金表面B4C与B4C＋10％Ti激光熔覆层的组成相基本相同，均由TiC1-x，TiB，TiB2和Ti相组成，说明在TC4合金表面熔覆过程中有一部分Ti进入熔覆层并与B4C发生化学反应原位生成了TiB，TiB2和TiC1-x相。TiC1-x相以树枝状相形式存在，TiB2相以粗大须状相形式存在，TiB相以细小须状相形式存在。熔覆层与基底结合良好，没有发现裂纹与孔洞。基底热影响区呈淬火组织形貌，为典型的针状马氏体组织特征。与B4C激光熔覆层相比，B4C＋10％Ti激光熔覆层的组织细小，TiB相含量增多，TiB2相含量减少。     

Oxidation behavior of atomized Fe40Al intermetallics doped with boron and reinforced with alumina fibers

Isothermal oxidation resistance of Fe40 (at.%) Al-based atomized and deposited intermetallic alloys has been evaluated. The alloys included Fe40Al, Fe40Al + 0.1B, and Fe40Al + 0.1B + 10Al₂O₃ at 800, 900, 1000, and 1100 °C. The tests lasted approximately 100 h, although in most cases there was scale spalling. At 800 and 900 °C, the Fe40Al + 0.1B alloy had the lowest weight gain, whereas the Fe40Al alloy had the highest weight gain at 800 °C (0.10 mg/cm²) and the Fe40Al + 0.1B + 10Al₂O₃ alloy was the least oxidation resistant at 900 °C with 0.20 mg/cm². At 1000 °C, the Fe40Al + 0.1B alloy showed the highest weight gain with 0.12 mg/cm² and the Fe40Al alloy the lowest. At 1100 °C, again, as at 900 °C, the Fe40Al alloy was the least resistant, whereas the Fe40Al + 0.1B alloy performed the best, but the three alloys exhibited a paralinear bahavior on the weight-gain curves, indicating the spalling, breaking down, and rehealing of the oxides. This spalling was related to voids formed at the metal-oxide interface.     

Effects of electrochemical boriding process parameters on the formation of titanium borides

In this study, the boriding of titanium via molten salt electrolysis was investigated in borax based electrolyte at various current densities (50–700 mA/cm²), temperatures (900–1200°C) and process durations (1 min-4 h). Thin film XRD results revealed that two main titanium boride phases TiB₂ and TiB was formed even after 1 minute of process time. Scanning electron microscopy (SEM) images conducted on the cross-sections demonstrated a bilayer boride structure composed of a continuous uniform TiB₂ phase and TiB whiskers that grew below the TiB₂ layer toward the substrate. Dependence of boride layer thickness and morphology on the process parameters was evaluated. The results of the study showed that temperature of boriding was the most critical parameter both on boriding rate and morphology of the boride layer. It was possible to grow 8 μm thick TiB₂ layer on titanium in 30 minutes of boriding at 1200°C.     

Densification and compressive strength ofin-situ processed Ti/TiB composites by powder metallurgy

In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB₂, B₄C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB₂ or B₄C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100, 1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB₂ compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of the composite made from TiB₂ reactant powder was higher than that of the composite made from B₄C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between matrix and reinforcement made from TiB₂ reactant powder was better than that made from B₄C.     

Processing and microstructure control of (α2+B2+O) alloy sheet in Ti–Al–Nb system

Rolling processing and microstructure evolution during rolling and heat treatment for two typical α₂+B2+O alloys, Ti–24Al–14Nb–3V and Ti–23Al–17Nb (at%), were investigated. The experimental results showed that the alloys have good workability for rolling at temperatures both in the α₂+B2 and in α₂+B2+O fields. The thickness reduction up to 99% was obtained for the sheets rolled above 900°C in a quasi-isothermal condition without cracking. A typical duplex microstructure of the α₂+B2+O phases formed when the sheets were rolled and then solution treated at temperatures in the α₂+B2 phase field plus aging in the O+B2 field. Such duplex microstructure was proved to have good mechanical properties both in room and elevated temperatures. A microstructure of fine equiaxed α₂ and O phases distributed in B2 matrix was obtained for the sheets rolled and then solution treated at the temperatures in the α₂+B2+O phase field, which possess excellent room temperature ductility and superplasticity in temperatures of 900∼1000°C. An advanced cold rolling processing plus a proper vacuum heat-treatment used for the production of high-quality foils of Ti–24Al–14Nb–3V (at%) alloy are also reported.     

TC4钛合金表面B-Al复合渗层的组织和性能

采用固体粉末包埋渗两步法,在TC4钛合金表面先1050 ℃渗硼 4~6 h再950~1050 ℃渗铝 4 h制备出B-Al复合耐磨渗层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、波谱仪(WDS)和能谱仪(EDS)、显微硬度仪和摩擦磨损试验机对复合渗层的物相组成、显微组织、微区成分、表面硬度和摩擦因数进行测试和分析。结果表明:B-Al复合渗层厚为37~115 μm,主要由TiB₂相和TiAl₃相组成,外层是弥散分布TiB₂的TiAl₃层,向内依次形成厚度较小的TiAl₂、TiAl及Ti₃Al等Ti-Al金属间化合物层。B-Al复合渗层表面硬度为1041.7~1429.4 HV0.1,约为TC4钛合金硬度的3.03~4.16倍;经1050 ℃×6 h渗B后1050 ℃×4 h渗Al,其摩擦因数约为0.3,较TC4钛合金基体下降约25%。     

Ti含量对镍基高温合金抗热腐蚀性能的影响

采用涂盐方法研究了不同Ti含量的镍基高温合金的热腐蚀过程。研究发现,在900℃涂盐条件下,Ni基高温合金中加入质量分数为0.55%的Ti就可以显著提高合金自身的热腐蚀抗力,并且随着Ti含量增加,合金的热腐蚀抗力进一步增强。研究认为,合金中加入Ti后,能促使合金表层形成致密、连续的Cr2O3层,并且随着Ti含量增加,Cr2O3层厚度增加,Al2O3层逐渐向外腐蚀层迁移,从而提高了合金的热腐蚀抗力。     

Oxidation behavior of FeAl+Hf,Zr, B

The oxidation behavior of Fe-40Al-1Hf, Fe-40Al-1Hf-0.4B, and Fe-40Al-0.1Zr-0.4B (at.%) alloys was characterized after 900°, 1000°, and 1100°C exposures. Isothermal tests revealed parabolic kinetics after a period of transitional -alumina scale growth. The parabolic growth rates for the subsequent -alumina scales were about five times higher than those for NiAl+O.1Zr alloys. The isothermally grown scales showed a propensity toward massive scale spallation due to both extensive rumpling from growth stresses and to an inner layer of HfO₂. Cyclic oxidation for 200 1-hr cycles produced little degradation at 900 or 1000°C, but caused significant spaliation at 1100°C in the form of small segments of the outer scale. The major difference in the cyclic oxidation of the three FeAl alloys was increased initial spallation for FeAl+Zr, B. Although these FeAl alloys showed many similarities to NiAl alloys, they were generally less oxidation-resistant. It is believed that this resulted from nonoptimal levels of dopants and larger thermal-expansion mismatch stresses.     

Relation Between the Microstructure and Properties of Commercial Titanium Alloys and the Parameters of Gas Nitriding

Titanium alloys are unique materials with an excellent combination of properties. However, their applications are limited due to low surface hardness. In the present work gas nitriding is performed with the aim of improving the surface properties of commercial titanium alloys. Four widely used titanium alloys, namely, Ti – 6% Al – 4% V, Ti – 6% Al – 2% Sn – 4% Zr – 2% Mo, Ti – 8% Al – 1% Mo – 1% V, and Ti – 10% V – 3% Fe – 3% Al, are studied. The process is performed in a nitrogen atmosphere at 950 and 1050°C for 1, 3, and 5 h. The resulting surface hardness exceeds the normal value for titanium alloys by a factor of 3 – 5 due to the change in the phase composition of the surface layer, yielding a solid solution of nitrogen in an α-Ti phase, a TiN nitride, and TiO₂ dioxide. The influence of the parameters of the treatment process and the chemical composition of the alloys on the phase composition, microstructure, microhardness, and thickness of the surface layer is analyzed. It is shown that nitriding of alloys with α- and (α + β)-structures at 1050°C yields surface layers with inhomogeneous composition and irregular thickness, whereas after nitriding at 950°C the surface layers are homogeneous and have high properties. Practical recommendations are given for choosing nitriding parameters for different alloys and variants of application are discussed.