Effects of Mo addition on tribological performance of plasma-sprayed Ti–Si–C coatings

Ti–Si–C–Mo composite coatings were fabricated by plasma spraying using Ti, Si, graphite and Mo powders. The effect of Mo on microstructure and tribological performance of the Ti–Si–C coatings were investigated. The results showed that the Ti–Si–C coating consisted of TiC, Ti₃SiC₂, Ti₅Si₃, and residual graphite. The Ti–Si–C–Mo coatings consisted of TiC, Ti₃SiC₂, Ti₅Si₃, residual graphite, Mo and Mo₅Si₃ phases. With increasing Mo contents, the fractions of Mo and Mo₅Si₃ phases increased, and the fractions of Ti₃SiC₂ and Ti₅Si₃ phases decreased. All the coatings existed a typical lamellar structure. The addition of Mo enhanced the hardness and fracture toughness of Ti–Si–C coating by 16% and 52%, respectively. The coating porosity decreased by 57.6%. The wear resistance of the Ti–Si–C coating was also improved and the mass loss decreased by 83%. The wear mechanism of the Ti–Si–C–Mo coatings was the combination of abrasive wear, adhesive wear, and tribo-oxidation wear.     

原位热压2TiC/Ti/Al合成Ti3AlC2陶瓷

以2TiC/Ti/Al为组分采用原位热压技术制备Ti3AlC2陶瓷。采用XRD和SEM分析不同工艺时合成产物的物相组成和显微结构。结果表明：恰当的加压工艺和升温速率控制,能够合成高纯Ti3AlC2陶瓷。用TiC粉替代C和部分Ti粉有利于Ti3AlC2的原位合成。     

原位热压TiC/Ti/Al合成Ti2AlC的研究

以TiC／Ti／Al为原料，采用热压工艺在1400℃原位合成和烧结了含少量第二相Ti3AlC2的Ti2AlC材料。通过不同温度和不同热压时间下合成试样的：XRD分析探讨了Ti2AlC的合成过程。结果表明，高温下Ti与Al反应生成中间相TiAl金属间化合物，然后TiC与TiAl金属间化合物反应生成Ti2AlC。初期反应非常迅速，大部分Ti2AlC在此阶段生成。反应后期反应物减少，速度变慢，同时生成少量第二相Ti3AlC2。不同温度下合成的Ti2AlC颗粒具有不同的形貌特征。     

原位热压TiC/Ti/Al合成Ti2AlC的研究

本以TiC／Ti／Al为原料，采用热压T艺在1400℃原位合成和烧结含少量第二相Ti3AlC2的Ti2AlC材料。通过不同温度和不同热压时间下合成试样的XRD分析探讨了Ti2AlC的合成过程。结果表明，高温下Ti与Al反应生成中间相TiAl金属间化合物，然后TiC与TiAl金属间化合物反应生成Ti2AlC。不同温度下合成的Ti2AlC颗粒具有不同的形貌特征。     

热压烧结工艺制备Ti2AlC/Ti3AlC2陶瓷材料

以Ti，Al，C为原料，采用热压工艺制备出相组成为Ti2AlC/Ti3AlC2块体材料，合成材料的X—射线衍射和扫描电镜(SEM)分析的结果表明：当烧结温度为1400℃时，材料中的主晶相为Ti2AlC,大小为10μm的板状多晶体；而在1500℃的温度下烧结所得材料的主晶相为Ti3AlC2，其板状多晶体的晶粒尺寸平均约为20μm。     

Ti-Al-C三元系统中Ti3AlC2,Ti2AlC和TiC物相含量的测定

研究了Ti-Al-C三元体系中X射线衍射定量相分析方法,提出了Ti3AlC2,Ti2AlC和TiC这3种物相的特征衍射峰Ti3AlC2的(002)衍射峰,2θ=9.5°;Ti2AlC的(002)衍射峰,2θ=13.0°;TiC的(111)衍射峰,2θ=35.9°.采用混样无标样法推导了一套Ti3AlC2,Ti2AlC和TiC的定量计算公式,根据其特征衍射峰的强度就可计算这3个物相的相对含量.因为该公式推导过程本身就验证了其正确性(即自验证性),所以这个公式可以广泛用于Ti-Al-C三元体系中Ti3AlC2,Ti2AlC和TiC物相的定量测定.因此,这种方法非常简便、易行.     

Bifunctional Ti3C2Tx–CNT/PANI composite with excellent electromagnetic shielding and supercapacitive performance

Ti₃C₂T_x exhibits excellent electromagnetic (EM) shielding and electrochemical properties. However, the inherent re-stacking tendency and easy oxidation of Ti₃C₂T_x limit its further application. In this study, a multi-walled carbon nanotube/polyaniline composite (CNT/PANI, denoted as C–P) was introduced into Ti₃C₂T_x nanosheets to obtain a Ti₃C₂T_x–CNT/PANI composite (T@CP). Owing to the integrated effects of Ti₃C₂T_x and C–P, the contribution of absorption was significantly improved, which finally enhanced the EM shielding performance of T@CP. The highest total EM shielding effectiveness (SE_T) was close to 50 dB (49.8 dB), which was substantially higher than that of pure Ti₃C₂T_x (45.3 dB). Moreover, T@CP demonstrated outstanding supercapacitive performance. The specific capacitance of T@CP (2134.5 mF/cm² at 2 mV/s) was considerably higher than that of pure Ti₃C₂T_x (414.3 mF/cm² at 2 mV/s). These findings provide a new route for the development of high-efficiency Ti₃C₂T_x-based bifunctional EM shielding and electrochemical materials.     

Improving the tribological properties of plasma sprayed NiAl–Bi2O3–Ag–Cr2O3 composite coatings by hot isostatic pressing

In this study, the hot isostatic pressing (HIP) process was adopted to enhance the tribological response of plasma-sprayed NiAl–Bi₂O₃–Ag–Cr₂O₃ coatings under different temperature conditions. The HIP process was performed at a temperature of 800 °C, under a pressure of 100 MPa using argon gas. When compared with as-sprayed NiAl–Bi₂O₃–Ag–Cr₂O₃ composite coatings, the results revealed that the post-HIP process greatly reduced the porosity to a sufficiently low level of 2.7%, and led to a significant transformation from the splat lamellar to composition homogeneity across the entire coating. As highlighted in the hot isostatically pressed (HIPed) coating, more NiBi intermetallic compounds emerged. The mechanical hardness and adhesive strength increased considerably by 15.9% and 22.7%, respectively. The HIPed coating exhibited improved running stability in friction when exposed to different temperatures. In particular, the wear resistance increased significantly by one level of magnitude at the temperature range of room temperature (25 °C) to 400 °C, compared to the as-sprayed composite coating. This was attributed to the presence of the NiBi intermetallic compound and structural restoration after the HIP process. A protective tribo-layer was always present under alternating temperature conditions, and this allowed for continuous inhibition of wear. The mechanical evolution of the tribo-layer was further determined to clarify its effect on the resulting tribological behavior of the HIPed NiAl–Bi₂O₃–Ag–Cr₂O₃ coatings.     

Synthesis and mechanism of ternary carbide Ti3AlC2 by in situ hot pressing process in TiC–Ti–Al system

Abstract

Ti₃AlC₂ is successfully synthesised by in situ hot pressing process from 2TiC/xAl/Ti (x?=?1, 1·2) raw powders. The phases and microstructure of the samples are identified by X-ray diffraction and scanning electron microscopy. It is found that aluminium content influences on the generating content of Ti₃AlC₂ significantly. High purity Ti₃AlC₂ can be obtained from a compacted cylinder composed of TiC–Ti–1·2Al at 1350°C for 2 h, and the purity of Ti₃AlC₂ is nearly 96·9 wt-%. The corresponding density and compressive strength are 3·93 g·cm^?3 and 377·34 MPa respectively. Ti₃AlC₂ grain exhibits typical plate-like structure. When aluminium melts, a mass of Al atoms diffuse to Ti grain rapidly, and Ti–Al intermetallic compounds generate. Then, Ti–Al intermetallic compounds react with TiC to form Ti₃AlC₂ directly. Using TiC powders as the raw materials provides Ti₆C octahedra directly. At elevated temperature, a part of aluminium will evaporate and lose. This will result in that every two layers of Ti₆C octahedra are linked by aluminium planes directly and Ti₃AlC₂ can be formed.     

自蔓延高温合成Ti3AlC2 和Ti2AlC及其反应机理研究

以Ti,Al和C的粉体混合物为原料，在纯氩气气氛，25MPa压力，1600℃保温4h条件下，自蔓延高温合成了Ti3AlC2和Ti2AlCT，利用X射线衍射分析（XRD）和扫描电镜（SEM）等手段对反应产物进行了研究，提出了自蔓延高温合成Ti3AlC2和Ti2AlC应具备的条件，并探讨了Ti，Al和C自蔓延高温合成Ti3AlC2和Ti2AlC的反应机理，结果表明，Ti3AlC2和Ti2AlC能够由Ti,Al和C元素经高温自蔓延合成反应来制备，其制备的必要条件是需要极快的加热速率以防止铝熔化并且改变钛的转移路线，Ti3AlC和Ti2AlC综合了金属材料和陶瓷材料的优点，成功的应用自蔓延高温方法合成Ti2AlC2和TiAlC必将成为该类材料纯块体的合成和制备提供好的原料，从而这类材料的实际应用将起到极大的推动作用。     

Structure and properties of electrodeposited Ni–Co–YZA composite coatings

The aim is to develop an economical composite coating with high thermal stability. Ni–Co alloys are found to possess better thermal, physical and mechanical properties compared to Ni. Also, oxide particles as distributed phase can impart better thermal stability. Hence, particulates of composite Yttria stabilised zirconia, a commonly used high temperature material and alumina (YZA) were reinforced in various Ni–Co alloy matrices through electrodeposition. The influence of YZA on the microhardness, tribology and corrosion behaviour of Ni–Co alloys with Co contents of 0 wt.%, 17 wt.%, 38 wt.% and 85 wt.% was evaluated. Optical and Scanning Electron Microscopy (SEM) confirmed the presence of YZA particles and Energy Dispersive X-ray Analysis (EDX) revealed the composition. Tribology testing showed that composite containing 38 wt.% Co displayed better wear resistance. It was found from the immersion corrosion studies that Ni–17Co–YZA coating displayed improved corrosion resistance. Thermal stability studies showed that Ni–85Co–YZA coating retained its microhardness at temperatures of 600 °C. Thus, these coatings can be tailored for various applications by varying the cobalt content.     

Microstructure and tribological properties of microwave-sintered Ti0.8Ni–0.3Mo/TiB composites

In this study, the Ti–0.8Ni–0.3Mo/XTiB (X = 5, 10, 15, and 20 wt%) composites were prepared using the microwave-sintering assisted powder metallurgy technique, and tribological properties were investigated. X-ray diffraction and scanning electron microscopy (SEM), with the microscope capable of energy dispersive spectroscopy (EDS), were used to characterize the mixed powder. The density and microhardness of the Ti–0.8Ni–0.3Mo/TiB composites were examined. The Ti–0.8Ni–0.3Mo/TiB composites exhibited a hardness of 260 HV, which is a 20% improvement over Ti–0.8Ni–0.3Mo. Tribological properties were studied by conducting experiments using a pin-on-disc wear tester at varying loads, sliding distances, and speeds. The Ti–0.8Ni–0.3Mo/TiB composites exhibited a reduction in wear loss and coefficient of friction values owing to TiB hardness and good bonding with the matrix. The tribological properties of the Ti–0.8Ni–0.3Mo/TiB composites were enhanced by the addition of TiB particles, which resist wear and friction.     

Ti3AlC2陶瓷力学性能强化研究进展

Ti3AlC2具有由边缘共享的Ti6C八面体和二维密排的Al平面交替堆积而成的六方层状特殊结构,既具有陶瓷的熔点高、弹性模量高、耐腐蚀和高温抗氧化能力强等特点,又兼具金属的导电导热性好、剪切模量高和可加工性能优异等优点,被广泛用作高温涂层材料、高温结构材料、化学防腐材料、电极电刷材料、受电弓材料和MXene前驱体材料等...     

新型复合材料Ti3 SiC2/TiC的研究进展

Ti3SiC2/TiC具有陶瓷和金属的共同特性,是一种新型复合材料,它具有室温下优良的导热率、导电率、高弹性模量和抗弯曲能力等。本文重点介绍了Ti3SiC2/TiC复合材料的性能、制备工艺及后续研究方向。     

Single-crystalline δ-Ni2Si nanowires with excellent physical properties

In this article, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) via chemical vapor deposition method using NiCl₂·6H₂O as a single-source precursor. Various morphologies of δ-Ni₂Si NWs were successfully acquired by controlling the growth conditions. The growth mechanism of the δ-Ni₂Si NWs was thoroughly discussed and identified with microscopy studies. Field emission measurements show a low turn-on field (4.12 V/μm), and magnetic property measurements show a classic ferromagnetic characteristic, which demonstrates promising potential applications for field emitters, magnetic storage, and biological cell separation.     

放电等离子制备Ti3AlC2/TiB2复合材料及性能

采用放电等离子烧结(spark plasma sintering,SPS)工艺制备了Ti3AlC2/TiB2复合材料,并研究了复合材料的性能.研究表明:在1 250℃,30MPa烧结8min,可以获得相对密度达98%以上的致密Ti3AlC2/TiB2块体材料;在Ti3AlC2中添加TiB2能大幅度提高材料性能,当TiB2含量为30%(体积分数,下同)时,Ti3AlC2/30%TiB2复合材料的Vickers硬度达到10.39GPa,电导率为3.7×106 S/m;当TiB2含量为10%时,抗弯强度为696MPa,断裂韧性为6.6MPa·m1/2.用电子显微镜对复合材料的显微结构分析表明:Ti3AlC2/TiB2复合材料的晶粒为层状结构.     

The effect of ceramic nanoparticles on tribological properties of alumina sol–gel thin coatings

Thin alumina coatings containing zirconia or alumina nanoparticles having diameter of ～20–30 nm were deposited by the sol–gel dip-coating process on silicon wafers. The mass content of nanoparticles in the alumina coating was fixed at 15% in relation to the theoretical mass of alumina matrix resulted from the amount of the applied precursor. Atomic force microscopy (AFM) was used to image the surface topography of as-made coatings and find out the wear level after frictional tests. Tribological tests were performed with the use of a microtribometer operating in the load range of 30–100 mN. It was found that the presence of α-alumina (corundum) or zirconia nanoparticles enhances the tribological performance of alumina layers annealed at 100 °C by decreasing the average wear rate by 20% and 63% for zirconia and corundum nanoparticles, respectively. No wear was observed for samples containing both types of nanoparticles annealed at 500 °C.     

Novel NaNbO3–Sr0.7Bi0·2TiO3 lead-free dielectric ceramics with excellent energy storage properties

NaNbO₃ (NN) is considered to be one of the most prospective lead-free antiferroelectric energy storage materials due to the merits of low cost, nontoxicity, and low density. Nevertheless, the electric field-induced ferroelectric phase remains dominant after the removal of the electric field, resulting in large residual polarization, which prevents NN ceramics from obtaining superior energy storage performance. In this work, the relaxor ferroelectric Sr_0·7Bi_0·2TiO₃ (SBT) was chosen to partially replace the NN ceramics, and the introduction of the nanodomain of the relaxor ferroelectric hinders the generation of field-induced ferroelectric phases, allowing the material to combine the large polarization strength of the relaxor ferroelectric with the near-zero residual polarization of the antiferroelectric. Large recoverable energy storage density (4.5 J cm^?3) and ultra-high energy storage efficiency (90.3%) were gained in NN-20SBT under an electric field of 288 kV cm^?1. Furthermore, superior temperature (25–120 °C) and frequency (1–500 Hz) stabilities were acquired. These performances demonstrate that NN-20SBT ceramics are potential candidates as dielectric materials for high energy storage density pulsed power capacitors.     

Microstructures and tribological properties of vacuum plasma sprayed B4C–Ni composite coatings

A promising wear resistant coating has been fabricated via vacuum plasma spray (VPS) technique by using electroless plating composite powders comprised of B₄C and different amounts of Ni (10 and 20 vol.%). Tribological evaluation from the ball-on-disk test showed that the wear resistance of the composite coatings was superior to that of the pure B₄C coating, and the composite deposit containing 10 vol.% Ni demonstrated the optimum tribological properties. This mainly attributed to the more uniform microstructures of the composite coatings, and the higher thermal conductivity of the composite coating also contributed to its distinguished wear behaviors. For the coatings investigated, the dominant wear mechanism was determined to be oxidation and the formation of a transfer layer on the worn surface.