Investigation of In situ Cu-TiB2 Composite on the Copper Using Laser Melting Synthesis

A surface composite layer reinforced with TiB₂ particles was produced on copper by use of the laser remelting in situ synthesis. The microstructure, electrical conductivity, and sliding wear behavior of the in situ Cu-TiB₂ composite were investigated. The experimental results show that the size of reinforcing TiB₂ particles is about 800 nm and the microhardness of composite layer reaches HV 210. Although the electrical conductivity of the composite layer is reduced with increasing TiB₂ volume fraction, the decrease of the integrated conductivity of the samples containing composite layer and copper substrate is insignificant. The wear resistance of composite layer is 10 times better than that of the copper sample.     

The Oxidation of TiB2 Ceramics Containing Cr and Fe

The oxidation behavior of TiB₂, TiB₂–0.5 wt.% Cr–0.5 wt.% Fe and TiB₂–1 wt.% Cr–1 wt.% Fe was studied at 800, 900, and 1000°C in static air. These ceramics oxidized rather rapidly and formed thick oxide scales. The oxidation rates of TiB₂-base ceramics were comparable to TiO₂ formation on pure titanium. The scale formed on TiB₂ consisted of TiO₂ and B₂O₃. For TiB–Cr–Fe ceramics, a small amount of Cr- and Fe-oxides was additionally formed. B₂O₃ formed during oxidation tended to evaporate because of its high vapor pressure, making oxide scales porous and fragile. The oxidation of the TiB₂-base ceramics appeared to be governed by the inward transport of oxygen via the highly porous oxide scale. The oxidation resistance of TiB₂–Cr–Fe ceramics was similar to or better than that of TiB₂.     

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.     

The Oxidation of TiB2 Particle-Reinforced TiAl Intermetallic Composites

The oxidation kinetics of TiAl alloys with and without (3, 5, 10 wt.%) TiB₂ dispersoids were studied between 1073 and 1273 K in atmospheric air. The inert TiB₂ dispersoids effectively increased the oxidation resistance of TiAl alloys. The higher the TiB₂ dispersoids content, the more pronounced the effect. The oxide scale formed on TiAl–TiB₂ composites was triple-layered, consisting mainly of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner (TiO₂+Al₂O₃) mixed layer. No B₂O₃ was observed within the oxide scale because of its high vapor pressure. A thin Ti₃Al sublayer and discrete TiN particles were found at the oxide–substrate interface. During the oxidation of TiAl alloys with and without TiB₂ dispersoids, titanium ions diffused outwardly to form the outer TiO₂ layer, while oxygen ions transported inwardly to form the inner (TiO₂+Al₂O₃) mixed layer. The increased oxidation resistance by the addition of TiB₂ was attributed to the enhanced alumina-forming tendency and thin and dense scale formation.     

粉末冶金法与电弧熔炼法制备TiB2/Cu复合材料

以Cu、Ti、B_4C合金粉末为原料,分别用粉末冶金法和电弧炉熔炼法制备TiB_2/Cu复合材料,研究了制备工艺、配料比等因素对Cu基中生成相的影响。结果表明:随TiB_2理论生成量增加,粉末冶金法烧结后得到含多种不同的硼化物的铜基复合材料;电弧炉熔炼法则可得到单一的TiB_2增强Cu基复合材料,且致密度、硬度和电导率均高于粉末冶金法制得的试样。     

燃烧合成TiB2-Al2O3陶瓷复合粉体及其表征

采用TiB2-Al2O3-Al还原体系，通过燃烧还原技术制备了TiB2-Al2O3陶瓷复合粉体。利用XRD，XPS和SEM技术对合成粉体的相组成、化学组成及宏观组织结构进行了分析。复合粉的显微结构由TEM和HREM进行表征。结果表明，用燃烧合成法在420℃～700℃之间可制得TiB2-Al2O3陶瓷复合粉体。该粉体仅由TiB2和Al2O3两相组成，颗粒分布较均匀。由于TiB2与Al2O3间形成了结合良好的界面，颗粒间彼此能有效地抑制晶粒长大，从而使TlB2-Al2O3陶瓷复合粉的粒径减小，颗粒平均粒度在3μm～5μm之间。     

Effect of SiC, Si3N4 and TiB2 additions on the oxidation resistance of TiAl alloys

The oxidation behavior of TiAl alloys containing dispersed particles of (5, 10, 15 wt.%) SiC, (3,5 wt.%) Si₃N₄ or (3, 5, 10 wt.%) TiB₂ was studied between 800 and 1200°C in atmospheric air. The TiAl−(SiC, Si₃N₄) alloys oxidized to TiO₂, Al₂O₃, and SiO₂. The TiAl−TiB₂ alloys oxidized to TiO₂, Al₂O₃, and B₂O₃ which evaporated during oxidation. Improvement in oxidation resistance accompanied by thin, dense scale formation due to the addition of dispersoids originated primarily from the enhanced alumina-forming tendency, improved scale adhesion by oxide grain refinement owing to the beneficial effect of dispersoids, and the incorporation of SiO₂ within the oxide scale in the case of TiAl−(SiC, Si₃N₄) alloys.     

Comparison of vacuum and pressure-assisted sintering of TiB2-Ni

A relatively new generation of cermet materials, based on TiB₂-Ni, has been investigated. These borides currently are being examined for industrial applications with the aim of exploiting their excellent wear resistance. Optimization of the liquid-phase sintering process for a TilB₂-Ni composition was studied. The mechanical properties of cermet materials prepared using vacuum and pressure sintering techniques were determined. Criteria for optimal sintering conditions were established according to hardness, strength, and fracture toughness properties.     

Cyclic oxidation behavior of TiAl composites incorporated with TiB2 dispersoids

TiAl alloys incorporated in (0,3,5,10) wt.% TiB₂ dispersoids were manufactured via mechanical alloyingspark plasma sintering (MA-SPS), and their cyclic oxidation characteristics were studied at 800, 900 and 1000°C in air. The cyclic oxidation resistance of the prepared TiAl-TiB₂ composites effectively increased with increases in TiB₂ content. The oxide scale formed consisted of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner (Al₂O₃+TiO₂) mixed layer. The scale adherence was relatively good, and much thinner oxide scales, when compared to TiB₂-free TiAl alloys, were formed on the prepared composites. The incorporated TiB₂ dispersoids oxidized to TiO₂ and B₂O₃ which evaporated during oxidation.     

机械合金化制备TiB2-Ni(Al)复合粉末组织结构研究

目的通过原位合成技术获得TiB_2-Ni(Al)复合粉末。方法采用机械合金化方法在不同球磨时间的条件下,制备不同体积含量的TiB_2陶瓷相增强Ni(Al)基复合粉末,其中Ni粉和Al粉的摩尔比为1:1。采用扫描电子显微镜(SEM)以及X-射线衍射仪(XRD)分析球磨后粉末的显微组织结构及物相,研究不同球磨时间对制备TiB_2-Ni(Al)复合粉末物相演变、组织结构及粒子间界面结合状态的影响。结果在球磨过程中,球磨时间越长,Ni/Al间的塑变有利于原子之间的扩散,TiB_2陶瓷相颗粒逐渐变小。当球磨时间增长到一定程度时,延展性好的Al粉颗粒发生扁平化且其表面积不断增大,使得碎化后的Ni粉颗粒不断嵌入Al粉颗粒中,最终形成Ni(Al)固溶体。同时根据XRD分析发现,随着球磨时间的延长,TiB_2-Ni(Al)复合粉末中的Al峰逐渐减小,说明Al不断固溶到Ni中,形成了一定量的Ni(Al)固溶体。结论通过机械球磨技术在球磨一定时间后可原位合成Ni(Al)固溶体,这说明随着Ni与Al之间的相互扩散有利于形成Ni(Al)固溶体。     

Effects of trace TiB2 on microstructure in cast titanium alloys

Abstract

Effects of trace TiB₂ on solidification microstructure of Ti–6Al–4V alloy were investigated. The result shows that the microstructure of the ingot was refined by the added TiB₂. The grain size and α lath size were reduced gradually with the increase in TiB₂. The grain size is reduced by about an order of magnitude with an addition of 0·96 wt-%TiB₂, and the dendrite appears in the ingot. Such a tendency is similar to the change of the microstructure with boron addition. Ti–6Al–4V–B phase diagram and growth restriction factor Q are applied to analyse the influence mechanism of trace TiB₂ on the microstructure.     

碳化硼基双复合装甲板制备与靶试

B4C基复合材料有一定韧性且硬度能与B4C匹配,依靠该复合材料约束B4C板,降低B4C板韧性低的不利影响,可充分发挥B4C板硬度高的优势。为获得硬度高、密度低且抗连续打击的陶瓷基复合靶板,设计了由B4C板与B4C基复合材料构成的靶板。靶板中复合材料自身是三维微观结构复合,与B4C板间的结合则是二维宏观复合。通过理论分析和试验确定靶板的制备方法和工艺。靶试显示Ф82mm×15mm靶板可抗2发7.62mm穿甲燃烧弹,防护面密度为38kg/m2。     

超细WC-Co复合粉制备及快速烧结技术研究进展

超细WC-Co复合粉是制备高性能超细/纳米晶硬质合金的重要原料之一,近年来发展了多种复合粉的制备技术。本文综述了其中的喷雾转换工艺法、化学沉淀法、原位还原碳化法、化学气相反应合成法和机械合金化法的研究和应用状况。同时简要介绍了一些新型的快速烧结技术的原理,以及这些新型的快速烧结技术制备的超细/纳米晶硬质合金上的研究进展,并对快速烧结技术在硬质合金领域发展前景进行了分析。     

磨损条件对等离子熔覆TiB2-TiC/Ni复合涂层磨损性能的影响

利用等离子熔覆技术以Q235低碳钢为基体制备了TiB_2-TiC强化Ni基复合材料涂层,涂层中的主要物相为TiB_2、TiC和γ-Ni,硬度达1 050 HV0.5,涂层与基体呈冶金结合状态。分别采用Al2O3陶瓷球和不锈钢球为对摩副,在30、60和120 N磨损载荷下进行往复干滑动摩擦磨损试验。结果表明:Al2O3陶瓷球为对摩副时,低载荷下(30 N)表现为微切削磨损形式;60 N载荷时,出现压实层的结构,降低了摩擦因数,磨损机理转变为粘着磨损的形式;当载荷增加到120 N时,磨损机理为氧化磨损和剥层磨损。而采用不锈钢磨球时,涂层硬度大于对摩不锈钢球硬度,磨球发生剪切破坏,部分转移到涂层表面,相对于Al2O3陶瓷磨副时具有更大的粘着效应,且随着载荷的增大转移量增加,粘着磨损加剧,所以摩擦因数呈现出随着载荷加大一直上升的趋势。     

25vol%B4Cp/2009Al复合材料热变形本构模型

对25vol% B₄Cp2009/Al复合材料进行等温压缩实验,采用的温度范围为300℃—500℃,应变速率范围为0.001s_-1—1s_-1。结果表明,B₄Cp2009/Al复合材料的高温流变曲线随着变形温度的升高和应变速率的降低而下降。对流变曲线进行了摩擦修正,修正后的流变应力值低于实验结果。摩擦力的影响随着温度的降低和应变速率的增大而更明显。随后构建了基于Arrhenius形式的本构方程,求解了不同应变量下的材料常数(α,n,Q和A)。与实验结果进行对比,利用构建的本构方程计算得到的流变应力值具有很高的计算精度,相关系数达到0.992。研究发现,较高的温度和较低的应变速率有助于B₄Cp2009/Al复合材料的高温热变形。     

Si3N4／SiC复合陶瓷粉末的研制

研究了添加晶种的碳热还原ＳｉＯ２法制取Ｓｉ３Ｎ４／ＳｉＣ复合粉末的工艺。发现反应温度的升高、反应时间的延长、原料ＳｉＯ２粉比表面的增大、添加Ｓｉ３Ｎ４晶种以及提高Ｎ２流速，均有利于Ｓｉ３Ｎ４、ＳｉＣ相含量的增加。当ＳｉＯ２：Ｃ为１：２，加入１０Ｗｔ％Ｓｉ３Ｎ４品种时，在１３５０℃下于Ｎ２流速为０．４ｍ３·ｈ－１气氛下反应４ｈ，可得到平均粒度为０．４６ｍ，含Ｎ２３．９ｗｔ％、Ｃ６．２５Ｗｔ％、Ｏ２．９０ｗｔ％的Ｓｉ３Ｎ４／ＳｉＣ超细复合粉末。     

粉末液相模锻法制备BN增强Al-Cu基复合材料

采用粉末液相模锻技术制备出近全致密Al-5.3%Cu-3.0%h-BN(质量分数,下同)复合材料,研究了该技术制备的复合材料的致密化及界面结合状况。采用SEM、XRD、TEM等分析手段对球磨前后粉末形貌、复合材料显微结构及物相组成进行表征,利用布氏硬度计对复合材料硬度进行测试。结果表明:在大量液相存在的情况下,施加外力可有效促进复合材料的致密化。粗铝粉(35μm)制备的复合材料晶粒呈细条状,具有方向性,T6热处理后发生原位再结晶;细铝粉(2μm)制备的复合材料晶粒细小,晶粒形貌不明显。复合材料界面由Al/Al2O3/BN组成,清晰可见,结合紧密。复合材料与基体合金相比,硬度提高近15%,细铝粉制备的复合材料硬度比粗铝粉略高。     

Synthesis, microstructure and mechanical properties of reaction-infiltrated TiB2-SiC-Si composites

TiB₂-C preforms formed with different compositions and processing parameters were reactively infiltrated by Si melts at 1450 °C to fabricate TiB₂-SiC-Si composites. Phase constituent and microstructure of these composites were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The resulting composites are generally composed of TiB₂ and reaction-formed β-SiC major phases, together with a quantity of residual Si. Unreacted carbon is detected in the samples with a starting composition of 2TiB₂ + 1C formed at higher pressure and in all of the ones at the composition of 1TiB₂ + 1C. The distribution of these phases is fairly homogeneous in microstructure. TiB₂-SiC-Si composites show good mechanical properties, with representative values of 19.9 GPa in hardness, 395 GPa in elastic modulus, 3.5 MPa m^1/2 in fracture toughness and 604 MPa in bending strength. The primary toughening and strengthening mechanism is attributed to the crack deflection of TiB₂ particles.     

碳化硼-硼化钛复合陶瓷的制备

研究了TiB2、TiC、Ti三种添加剂对超细B4C粉末的无压烧结(2 200℃×1 h)密度的影响.结果表明,加入Ti粉末对B4C的烧结没有产生明显的影响,最高密度不超过86%理论密度;而TiB2对B4C的烧结致密化有明显的促进作用,当TiB2含量达到50%时,复合陶瓷的烧结密度达到92%理论密度;TiC对B4C的烧结致密化影响比较复杂,过少或过多时均不能获得最高的烧结密度,当TiC含量为30%时,密度达到最高值(94.5%理论密度).B4C-TiC反应烧结陶瓷由B4C、TiB2、C三相组成.     

Synchrotron Characterisation of Ultra-Fine Grain TiB2/Al-Cu Composite Fabricated by Laser Powder Bed Fusion

Isotropy in microstructure and mechanical properties remains a challenge for laser powder bed fusion (LPBF) processed materials due to the epitaxial growth and rapid cooling in LPBF. In this study, a high-strength TiB₂/Al-Cu composite with random texture was successfully fabricated by laser powder bed fusion (LPBF) using pre-doped TiB₂/Al-Cu composite powder. A series of advanced characterisation techniques, including synchrotron X-ray tomography, correlative focussed ion beam-scanning electron microscopy (FIB-SEM), scanning transmission electron microscopy (STEM), and synchrotron in situ X-ray diffraction, were applied to investigate the defects and microstructure of the as-fabricated TiB₂/Al-Cu composite across multiple length scales. The study showed ultra-fine grains with an average grain size of about 0.86 μm, and a random texture was formed in the as-fabricated condition due to rapid solidification and the TiB₂ particles promoting heterogeneous nucleation. The yield strength and total elongation of the as-fabricated composite were 317 MPa and 10%, respectively. The contributions of fine grains, solid solutions, dislocations, particles, and Guinier-Preston (GP) zones were calculated. Failure was found to be initiated from the largest lack-of-fusion pore, as revealed by in situ synchrotron tomography during tensile loading. In situ synchrotron diffraction was used to characterise the lattice strain evolution during tensile loading, providing important data for the development of crystal-plasticity models.