Surface strengthening of Ti3SiC2 through magnetron sputtering Cu and subsequent annealing

Magnetron sputtering deposition Cu and subsequent annealing in the temperature range of 900–1100 °C for 30–60 min were conducted with the motivation to modify the surface hardness of Ti₃SiC₂. Owing to the formation of TiC following the reaction Ti₃SiC₂ + 3Cu → 3TiC_0.67 + Cu₃Si, the surface hardness was enhanced from 5.08 GPa to a maximum 9.65 GPa. In addition, the surface hardness was dependent on the relative amount of TiC, which was related to Cu film thickness, heat treatment temperatures and durations of annealing. Furthermore, after annealing at 1000 °C for 30 min the Cu-coated Ti₃SiC₂ has lower wear rate and lower COF at the running-in stage compared with Ti₃SiC₂ substrate. The reaction was triggered by the inward diffusion of Cu along the grain boundaries and defects of Ti₃SiC₂. At low temperature and short annealing time, i.e. 900 or 1000 °C for 30 min, Cu diffused inward Ti₃SiC₂ and accumulated at the trigonal junctions first. At higher temperature of 1100 °C or prolonging the annealing time to 60 min, considerable amount of Cu diffused to Ti₃SiC₂ and filled up the grain boundaries leaving a mesh structure.     

Fabrication of Ti3SiC2 and Ti4SiC3 MAX phase ceramics through reduction of TiO2 with SiC

Ti₃SiC₂ and Ti₄SiC₃ MAX phase ceramics were fabricated through high-temperature vacuum reduction of TiO₂ using SiC as a reductant, followed by hot pressing of the products under 25 MPa of pressure at 1600 °C. It was found that both Ti₃SiC₂ and Ti₄SiC₃ may be obtained in good yields, depending on the annealing time during the reduction step. In addition to MAX phases, the products contained some amounts of TiC. The hot pressing step did not significantly affect the composition of the products, indicating good stability of Ti₃SiC₂ and Ti₄SiC₃ under these conditions. Analysis of the densification behavior of the samples revealed lower ductility in Ti₄SiC₃ compared to Ti₃SiC₂. The samples prepared herein exhibited the flexural strength, fracture toughness and microhardness typical of coarse-grained MAX-phase ceramics.     

Metallization of Al2O3 ceramic by magnetron sputtering Ti/Mo bilayer thin films for robust brazing to Kovar alloy

Ti/Mo bilayer thin films were deposited onto Al₂O₃ ceramic by magnetron sputtering with a subsequent high temperature sintering to ensure the robust brazing of Al₂O₃ ceramic to Kovar (Fe–Ni–Co) alloy. The interface reaction process between Ti film and Al₂O₃ ceramic as well as the joining strength between metallized Al₂O₃ ceramic and Kovar alloy were investigated systematically using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and electronic universal testing machine. The results show that the active Ti film can react with Al₂O₃ ceramic to form Ti₃Al and TiO during high-temperature sintering process, in which the amount, size and morphology of TiO crucially depend on the sintering temperature. As the sintering temperature reaches 1200 °C, a plenty of spherical TiO nanoparticles with ~ 150 nm in diameter and metallic nature can be created across the Ti/Al₂O₃ interfaces, which can effectively act as ‘bridges’ to join Ti film to Al₂O₃ substrate firmly. Hence, the optimal joining strength of 69.6±3.1 MPa between metallized Al₂O₃ ceramic and Kovar alloy can be obtained, much better than those counterparts metallized at 900 °C and 1050 °C almost without the existence of observable TiO.     

Ti3SiC2及其复合材料的研究现状及发展趋势

介绍了Ti3SiC2陶瓷材料的微观结构与性能,认为该材料良好的综合性能有望解决陶瓷材料的脆性问题.并概述了Ti3SiC2及Ti3SiC2基复合材料各种制备方法的特点和研究状况、应用前景和发展趋势.     

Fabrication of Pb(Zr,Ti)O3 thin films utilizing unconventional powder magnetron sputtering (PMS)

Pb(Zr,Ti)O3 (PZT) ferroelectric ceramic films exhibit highly superior ferroelectric, pyroelectric and piezoelectric properties which are promising for a number of applications including non-volatile random access memory devices, non-linear optics, motion and thermal sensors, tunable microwave systems and in energy harvesting (EH) use. In this research, a thin layer of PZT was deposited on two different substrates of Strontium Titanate (STO) and Strontium ruthenate (SRO) by powder magnetron sputtering (PMS) system. The preliminary powders, consisting of PbO, ZrO₂ and TiO_2, were manually mixed and placed into the target holder of the PMS. The deposition was performed at an elevated temperature reaching up to 600 °C via a ceramic heater. This high temperature is required for PZT thin film crystallinity, which is never achieved in conventional physical vapour deposition processes. The phase structure, crystallite size, stress-strain and surface morphology of deposited thin films were characterized using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The composition of the PZT thin films were also analysed by X-ray photoelectron spectroscopy (XPS). The mechanical properties of the thin films were evaluated with micro-scratch adhesive strength and micro hardness equipment. FESEM results showed that the PZT thin films were successfully deposited on both SRO and STO substrates. The surfaces of the coated samples were free from cracks, relatively smooth, uniform and dense. The profile of X-ray diffraction confirmed the formation of single-c-domain/single crystal perovskite phase grown on both substrates. The XPS analysis have shown that the PZT thin film grown by this method and that a target of PZT+10% PbO is a proper target for growing nominal PZT thin films. The adhesion strength and micro hardness results have confirmed the stability and durability of the thin film on the substrates, although higher values have been reported for thin film of PZT deposited on SRO surfaces.     

Improved mechanical properties of reaction-bonded SiC through in-situ formation of Ti3SiC2

Reaction-bonded SiC is a ceramic with excellent thermal properties, good corrosion resistance and the characteristic of near-net-shape manufacturing. However, the poor fracture toughness of free Si limits the applications of reaction-bonded SiC. In this study, TiC was added to reaction-bonded SiC and reacted with free Si to form Ti₃SiC₂. The effects of TiC and carbon black on the mechanical properties of reaction-bonded SiC were investigated. The results demonstrated that the in-situ formation of Ti₃SiC₂ and decrease in the content and size of free Si improved the mechanical properties of reaction-bonded SiC ceramics. The mechanical properties of TiC-added reaction-bonded SiC with 17.5 wt% carbon black were superior to those of TiC-added reaction-bonded SiC with 15 wt% carbon black. Moreover, increasing the TiC content of reaction-bonded SiC with 17.5 wt% carbon black from 0 to 7.5 wt% caused an increase in its bending strength from 183.92 to 424.43 MPa and an increase in fracture toughness from 3.7 to 5.24 MPa m^1/2.     

Fabrication of Ti3SiC2-Ti4SiC3-SiC ceramic composites through carbosilicothermic reduction of TiO2

Dense Ti₃SiC₂-SiC, Ti₄SiC₃-SiC, and Ti₃SiC₂-Ti₄SiC₃-SiC ceramic composites were fabricated through carbosilicothermic reduction of TiO₂ under vacuum, followed by hot pressing of the as-synthesized products under 25 MPa at 1600°C. In the reduction step, SiC either alone or in combination with elemental Si was used as a reductant. A one-third excess of SiC was added in the reaction mixtures in order to ensure the presence of approximately 30 vol.% SiC in the products of synthesis. During the hot pressing step, the samples that contained Ti₃SiC₂ showed better densification compared to those containing Ti₄SiC₃. The obtained composites exhibited the strength properties typical of coarse-grained MAX-phase ceramics. The flexural strength values of 424 and 321 MPa were achieved in Ti₃SiC₂-SiC, and Ti₃SiC₂-Ti₄SiC₃-SiC composites, respectively. The fracture toughness values were 5.7 MPa·m^1/2.     

High temperature interfacial phase stability of a Mo/Ti3SiC2 laminated composite

A Mo/Ti₃SiC₂ laminated composite is prepared by spark plasma sintering at 1300 °C under a pressure of 50 MPa. Al powder is used as sintering aid to assist the formation of Ti₃SiC₂. The fabricated composites were annealed at 800, 1000 and 1150 °C under vacuum for 5, 10, 20 and 40 h to study the composite's interfacial phase stability at high temperature. Three interfacial layers, namely Mo₂C layer, AlMoSi layer and Ti₅Si₃ solid solution layer are formed during sintering. Experimental results show that the Mo/Ti₃SiC₂ layered composite prepared in this study has good interfacial phase stability up to at least 1000 °C and the growth of the interfacial layer does not show strong dependence on annealing time. However, after being exposed to 1150 °C for 10 h, cracks formed at the interface.     

Fabrication of CaLa4(Zr0.05Ti0.95)4O15 thin films by RF magnetron sputtering

Crystalline CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films deposited on n-type Si substrates byRF magnetron sputtering at a fixed RF power of 100 W, an Ar/O₂ ratio of 100/0, an operating pressure of 3 mTorr, and different substrate temperatures were investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction and atomic force microscopy were sensitive to the deposition conditions, such as the substrate temperature. The diffraction pattern showed that the deposited films had a polycrystalline microstructure. As the substrate temperature increased, the quality of the CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films improved, and the kinetic energies of the sputtered atoms increased, resulting in a structural improvement of the deposited CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films. A high dielectric constant of 16.7 (f=1 MHz), a dissipation factor of 0.19 (f=1 MHz), and a low leakage current density of 3.18×10⁻⁷ A/cm² at an electrical field of 50 kV/cm were obtained for the prepared films.     

Fabrication and Properties of Ti3SiC2/SiC Composites

Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effects of hot pressing temperature, the content and particle size of SiC on phase composition, densification, mechanical properties and behavior of stress-strain of the composites were investigated. The results showed that ： （ 1 ） Hot-pressing temperature influenced the phase composition of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. （2） It became more difficult for the composites to densify when the content of SiC in composites increased. It need be sintered at higher temperature to get denser composite. The flexural strength and fracture toughness of composites increased when the content of SiC added in composites increased. However, when the content of SiC reached 50 wt%, the flexural strength and fracture toughness of composites decreased due to high content of pore in composites. （3） When the content of SiC was same, Ti3SiC2/SiC composites were denser while the particle size of SiC added in composites is 12. 8 μm compared with the composites that the particle size of SiC added is 3 μm. The flexural strength and fracture toughness of composites increased with the increase of particle size of SiC added in composites. （4） Ti3SiC2/SiC composites were non-brittle fracture at room temperature.     

Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

Silicon-rich Al₂O₃ films (Si_x(Al₂O₃)_1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface.     

Ti3SiC2陶瓷的制备

Ti3SiC2陶瓷由于具有非常优越的性能而受到广泛关注,但到目前对于反应合成Ti3SiC2的热力学和动力学仍缺乏系统地研究.本文对反应合成Ti3SiC2进行了热力学计算和动力学分析,利用Ti、Si、C混合粉末进行热压,制备了较高纯度的Ti3SiC2陶瓷,并对烧结试样进行XRD和断口SEM分析.热力学计算结果表明:在常用的反应合成Ti3SiC2的材料体系中,Ti-Si-C三元粉末的反应热力学驱动力最大,据此选择Ti、Si、C粉末,按照3:1.2:2的原子比混合作为反应合成Ti3SiC2的原料;动力学分析结果表明:Ti-Si-C三元元素粉末的反应动力学要求必须有较高的升温速度,才能获得Ti3SiC2材料.根据动力学分析结果设计反应合成工艺,利用真空热压获得了纯度达到89%(体积分数,下同)以上的Ti3SiC2材料.     

Synthesis of Ti3SiC2 MAX phase powder through molten salt method

Titanium silicon carbide (Ti₃SiC₂) MAX phase powder was synthesized from elemental reactants using the molten salt synthesis (MSS) method. Optimum experimental parameters were also investigated to determine the purity and synthesis pathway of the Ti₃SiC₂ MAX phase. The results showed that Ti₃SiC₂ was not synthesized using carbon black as the carbon source in the starting materials because of the high quantity of TiC formed along with the TiSi₂ silicide phase. However, Ti₃SiC₂ was successfully synthesized in a relatively high purity (93%) at 1200°C for 2 h using graphite as the source of carbon because of the formation of TiC and Ti₅Si₃ intermediate phases. The Ti₅Si₃ silicide phase was found to play a crucial role in the formation of the Ti₃SiC₂ MAX phase using the MSS method. Moreover, applying a pressure of 150 MPa to the prepared samples and using the eutectic mixture of NaCl–KCl (molar ratio: 1:1) instead of NaCl also resulted in the higher formation of the Ti₃SiC₂ MAX phase. The formation mechanism of Ti₃SiC₂ was determined to be the reaction among Ti₅Si₃, TiC, and residual carbon through the template-growth and dissolution–precipitation mechanisms that occurred at different stages of the synthesis process.     

低温合成Ti3SiC2陶瓷

采用机械合金化和放电等离子烧结技术制备了纯度较高的Ti3SiC2陶瓷,研究了微量Al对Ti3SiC2的机械合金化和放电等离子烧结过程的影响.结果表明:添加适量的Al可以显著提高机械合金化及放电等离子烧结产物中Ti3SiC2的含量,并显著降低高纯度Ti3SiC2的烧结温度.机械合金化10h,成分为3Ti/Si/2C/0.2Al(摩尔比)的混合粉体,经850℃放电等离子烧结可获得质量分数(下同)高达96%的Ti3SiC2块体,烧结温度提高到1 100℃,可获得纯度为99.3%、相对密度高达98.9%的Ti3SiC2致密块体.     

Enhancement of thermoelectric performance of N-type Bi2Te3 based thin films via in situ annealing during magnetron sputtering

In this work, n-type Bi₂Te₃ based thin films were prepared in 300 °C via DC magnetron sputtering, and influences of sputtering power and annealing time on thermoelectric properties of films were investigated. The raise of sputtering power brings about the improvement of deposited rate and enhancement of grain size. Taking the consideration that the large-sized grains are to phonon scattering, we determine the medial power of 30 W as the basic technical parameters for the purpose of further optimizing performance through an in situ annealing process. Subsequently, thin-film treated by in situ annealing process acts out an obvious reduction in electrical conductivity attributed to the decrease in carrier concentration. Especially, the film annealed for 40 min shows an enhancement in the Seebeck coefficient and leads to a maximum power factor 0.82 m W m⁻¹ K⁻² at 543 K.     

Ti3SiC2/SiC复相陶瓷的抗氧化性研究

利用热等静压原位合成技术制备了Ti3SiC2/SiC复相陶瓷,对其高温氧化行为进行了研究.结果表明,Ti3SiC2/SiC复相陶瓷在空气中静态氧化时的氧化增重符合抛物线规律,有比纯Ti3SiC2更好的抗氧化性能,并且在1400℃的长时抗氧化性能优于1200℃.     

Ti3SiC2陶瓷粉末的制备

新型层状陶瓷材料Ti3SiC2集金属和陶瓷的优良性能于一身,如良好的导电导热性、耐氧化、耐热震、高弹性模量、高断裂韧性等,在高温结构陶瓷、电刷和电极材料、可加工陶瓷材料、自润滑材料等领域有着广泛的应用前景。本文综合介绍了Ti3SiC2粉末制备的研究进展。此外,作者以Ti／Si／C／Al元素粉为原料,采用无压烧结的方法制备出纯度较高的Ti3SiC2陶瓷粉末,为Ti3SiC2基复合材料的发展开辟了一条新途径。     

新型层状陶瓷Ti3SiC2的研究进展

新型层状陶瓷Ti3SiC2兼有金属和陶瓷的许多优良性能,具有高的热导率和电导率,易加工,同时具有良好的抗热震性、抗氧化性和高温稳定性.本文从层状陶瓷Ti3SiC2制备方法、结构和性能等方面进行综述,并对其应用前景进行展望.     

Ti3SiC2陶瓷粉末的制备

新型层状陶瓷材料Ti3SiC2集金属和陶瓷的优良性能于一身,如低密度、高熔点、良好的导电导热性、高弹性模量、高断裂韧性、耐氧化、耐热震、易加工且有良好的自润滑性。在高温结构陶瓷、电刷和电极材料、可加工陶瓷材料、自润滑材料等领域有着广泛的应用前景。本文综合介绍了Ti3SiC2粉求制备的研究进展。最近,作者以Ti／Si／C／Al元素粉为原料,采用无压烧结的方法制备出纯度较高的Ti3SiC2陶瓷粉末。为Ti3SiC2基复合材料的发展开辟了一条新途径。