陶瓷相（Ti,W）C的价电子结构与力学性能的关系

计算了陶瓷相（Ｔｉ，Ｗ）Ｃ的价电子结构，比较了陶瓷相（Ｔｉ，Ｗ）Ｃ，ＴｉＣ，ＴｉＮ，ＴｉＯ之间的价电子结构与力学性能之间的关系，指出陶瓷相价电子结构中的最强键ｎＡ的大小在晶体结构相同时可作为硬度高低的比较标准，陶瓷相的强度可由η＝ｎｃ／ｎＴ来衡量。     

（Nb，Ti）C－35Ni金属陶瓷的高温抗弯强度

对热等静压方法制备的（Ｎｂ，Ｔｉ）Ｃ－３５Ｎｉ金属陶瓷的高温抗弯强度进行了研究。采用ＸＲＤ，ＳＥＭ及ＴＥＭ等方法对该金属陶瓷的显微结构作了分析。结果表明，在氧化气氛中，温度为７００℃时该金属陶瓷的抗弯强度就明显下降，温度为１０００℃时其抗弯强度约只有室温时的２０％。     

Ti(C,N)基金属陶瓷显微组织的研究

用粉末冶金方法制备了Ｔｉ（Ｃ,Ｎ）基金属陶瓷,其硬度、抗弯强度和断裂韧性分别可达ＨＲｎ９１．２,１２５０ＭＰａ和１３．４ＭＰａ·ｍ＾１／２同样ＴＥＭ研究表明,陶瓷相／金属相、陶瓷相／陶瓷相界面分别存在一定的取向关系,揭示了液相在烧结后的凝固过程。     

（Nb,Ti）C—35Ni金属陶瓷的高温抗弯强度

对热等静压方法制备的（Ｎｂ，Ｔｉ）Ｃ－３５Ｎｉ金属陶瓷的高温抗弯强度进行了研究。采用ＸＲＤ，ＳＥＭ及ＴＥＭ等方法对该金属陶瓷的显微结构的作了分析，结果表明，在氧化气氛中，温度为７００℃时该金属瓷的抗弯强度就明显下降，温度为１０００℃时其抗弯强度约只有室温时的２０％。     

（Ng,Ti）C—Ni金属陶瓷中包裹结构的形成机理及其化学键研究

利用ＳＥＭ，ＥＰＭＡ，ＴＥＭ／ＥＤＡＸ等测手段对（Ｎｂ，Ｔｉ）Ｃ－Ｎｉ金属陶瓷中的包裹结构形成机理作了研究。结果表明：它是由于该金属陶瓷在烧结时，细小的（Ｎｂ，Ｔｉ）Ｃ颗粒溶解在熔融态的Ｎｉ中，当Ｔｉ，Ｎｂ及Ｃ的浓度达到大颗粒的饱和浓度时，在大颗粒表面沉淀，继面Ｎｉ同其扩散而形成的，用离散变分－Ｘａ方法计算表明：包裹层的金属键程度要比包裹结构中心的高。     

（Nb，Ti）C－Ni金属陶瓷中包裹结构的形成机理及其化学键研究

利用ＳＥＭ，ＥＰＭＡ，ＴＥＭ／ＥＤＡＸ等测试手段对（Ｎｂ，Ｔｉ）Ｃ－Ｎｉ金属陶瓷中的包裹结构形成机理作了研究。结果表明：它是由于该金属陶瓷在烧结时，细小的（Ｎ５，Ｔｉ）Ｃ粒溶解在熔融态的Ｎｉ中，当Ｔｉ，Ｎｂ及Ｃ的浓度达到大颗粒的饱和浓度时，在大颗粒表面沉淀，继而Ｎｉ向其扩散而形成的。用离散变分──Ｘ＿α方法计算表明：包裹层的金属键程度要比包裹结构中心的高。     

金刚石表面金属气相传递涂层形成时的物理—化学相互作用及其结构组成

本文研究形成于金刚石颗粒表面的Ｃｒ、Ｔｉ、Ｍｏ、Ｖ、Ｗ涂层的相组成及其厚度。所用涂覆物为在真空中退火处理过的铬粉或Ｔｉ、Ｍｏ、Ｖ和Ｗ氧化粉末混合物。涂层由金属和碳化物相组成。涂层厚度增长过程中，随着涂覆度的上升、时间的延续，碳的扩散作用为铬、钛和钒的碳化提供了条件（它引起涂覆物中金属相成分减少，而碳化物相相应增加），高价碳化物（Ｃｒ３Ｃ２、ＶＣ、ＷＣ）依赖于低价碳化物（Ｃｒ７Ｃ３、Ｖ２Ｃ、Ｗ２Ｃ）     

Ti(C,N)基金属陶瓷中陶瓷相芯/壳组织的观察与分析

用ＸＲＤ，ＳＥＭ，ＴＥＭ和ＨＲＥＭ观察、分析和方法研究了Ｔｉ（Ｃ，Ｎ）基金属陶瓷中陶瓷相的芯、壳组织。结果表明，在ＳＥＭ，ＴＦＭ观察中，芯、壳之间存在相界面，而ＨＲＥＭ观察显示陶瓷相的芯／壳组织具有连续相同的点阵结构。     

MoSi2和WSi2相结构和性能的电子理论研究

根据固体与分子经验电子理论,对ＭｏＳｉ２和ＷＳｉ２相进行价电子结构分析,通过键距差方法,计算了ＭｏＳｉ２和ＷＳｉ２晶体中各键上的共价电子数。结果表明：ＭｏＳｉ２和ＷＳｉ２相是靠键距为     

PZN－PFN－PFW系陶瓷的介电性质和钙钛矿相的稳定作用

研究了Ｐｈ（Ｚｎ１／３Ｎｂ２／３）ｘ（Ｆｅ１／２Ｎｂ１／２）０．６４－ｘ（Ｆｅ２／３Ｗ１／３）０．３６Ｏ３（ＰＺＮ－ＰＦＮ－ＰＦＷ）系陶瓷中ＰＺＮ含量与焦录石相形成间的关系，以及少量添加剂对钙钛矿相的稳定和介电性能的影响。在该系中仅添加０．１５ｗｔ％ＭｎＣＯ３就可制备１００％钙钛矿型结构的陶瓷。文中报导了该系组成的相关系和介电性质。钙钛矿结构的陶瓷介电常数高，电容温度系数较低。     

(Ti,Mo,W,Ta,V,Nb)(C,N)多元陶瓷相的价电子结构

运用固体与分子经验电子理论(EET理论)计算了(Ti,Mo,W,Ta,V,Nb)(C,N)多元陶瓷相的价电子结构.结果表明,价电子结构参数(nA)随碳化物添加量的增加而增加.不同碳化物对价电子结构参数的影响不同,其中VC的影响最为显著.价电子结构参数(nA)可以用来评价金属陶瓷的力学性能,提出了相关的判据关系式.     

碳化钛粒径对碳氮化钛基金属陶瓷微观结构和力学性能的影响

用粉末冶金真空烧结法制备了超细晶粒碳氮化钛[Ti(C,N)]基金属陶瓷.研究了原始粉末粒径对Ti(C,N)基金属陶瓷微观结构和力学性能的影响.结果表明:在化学成分相同的条件下,晶粒细化使材料的Vickers硬度和抗弯强度上升,但断裂韧性有所下降.在超细晶粒Ti(C,N)基金属陶瓷微观组织中出现了一种新型的白芯/灰壳结构和一种特殊化合物(Ni2Mo2.5W1.3)Cx.初步研究表明:由于原始粉末粒径微小,促进了扩散反应因而生成了这种芯/壳结构.芯/壳结构有利于提高材料的抗弯强度和断裂韧性.(Ni2Mo2.5W1.3)Cx有利于提高材料的Vickers硬度,但是降低了Ti(C,N)基金属陶瓷的抗弯强度和断裂韧性.     

Influence of molybdenum addition on the microstructure and mechanical properties of TiC-based cermets with nano-TiN modification

Effect of Mo addition on the microstructure and mechanical properties of TiC–TiN(nm)–WC–Co–Ni–C system cermets was studied in the work. Specimens were fabricated by conventional powder metallurgy techniques. The microstructure was investigated using transmission electron microscope (TEM) and the scanning electron microscope (SEM). Chemical compositions of different phases such as ceramic phase with core/rim structure [the core being TiC and rim being (Ti,W,Mo)(C,N)] and metallic phase were analyzed quantitatively by EDX. Mechanical properties such as flexural strength, fracture toughness and hardness were also measured. Results show that flexural strength and fracture toughness have a trend to decline with increasing Mo addition, but the change of hardness is not apparent with the increase of Mo addition. Results also reveal that finer microstructure and thicker rim phase will be obtained with the increase of Mo addition. The optimal addition of Mo can be estimated to be 4 wt.% with respect to TiC–10TiN(nm)–15WC–5Co–Mo–5Ni–1C system cermets. Fracture micrographs show that main failure mode of the cermets is a mixed one, i.e., trans-granular and inter-granular fractures both exist.     

Preparation of Ni–Mo–C/Ti(C,N) coated powders and its influence on the microstructure and mechanical properties of Ti(C,N)-based cermets

Ni–Mo–C/Ti(C,N) coated powders, namely Ni–Mo alloy and Mo₂C coated Ti(C,N) composite powders, were synthesized by using a heterogeneous precipitation and thermal reduction method, then pressed and vacuum sintered to fabricate cermets. The chemical composition, microstructure and phases of the composite powders and the microstructure and properties of sintered cermets were experimentally investigated. The results show that a fine and uniform microstructure of (Ti,Mo)(C,N)-Ni cermets without the conventional core-rim structure is obtained. The phases formed during the preparation of the coated powders as well as the cermets were analyzed by means of a X-ray diffraction (XRD) technique. The XRD result confirms the formation of the Ni₃Ti phase in the cermets. Due to the formation of the non-magnetic Ni₃Ti and the dissolution of Mo in Ni binder phase, the magnetic properties are strongly retarded. The fracture of the cermets is mainly characterized by inter-granular and dimple fractures. Better mechanical properties can be obtained in comparison with conventionally fabricated ones.     

Effect of carbon and tungsten content on the phase equilibria,microstructure, and mechanical properties of (Nb,W)C–Ni cermets

With the assistance of thermodynamic simulation, the NbC–Ni based cermets with different W and C additions were designed and sintered in liquid state at 1390°C for 90 min in vacuum. By controlling the carbon and tungsten content, (Nb,W)C–Ni based cermets were prepared with varied phase constitution, microstructure, and mechanical properties. The microstructure, composition of phases, grain size, and equilibrium phases were investigated using scanning electron microscopy, electron probe microanalysis, EBSD, and X-ray diffraction. The simulation reasonably predicted the experimentally observed phase constitutions. Depending on the additions, detailed analysis indicated that the cermets were composed of either a combination of cubic (Nb,W)C solid solution and Ni alloy binder or with an additional carbon-deficient phase. Furthermore, mechanical analysis showed a strong dependence of its mechanical properties (Vickers hardness, indentation toughness, and flexural strength) on the phases and NbC grain size.     

Effects of (Ti,Ta,Nb,W)(C,N) on the microstructure,mechanical properties and corrosion behaviors of WC-Co cemented carbides

Homogeneous solid-solution (Ti, Ta, Nb,W)(C,N) powders were synthesized through carbothermal reduction-nitridation method. The effects of (Ti, Ta, Nb,W)(C,N) powders on the microstructure, mechanical properties and corrosion resistance of WC-10Co cemented carbides were investigated using XRD, SEM, electrochemical test and mechanical properties tests. The results showed that cemented carbides with pre-alloyed powder addition had a similar microstructure appearance: weak core/rim structure consisting of solid-solution phase embedded in the WC-Co system. The black core and gray rim, both of which contained similar elements, were identified as (Ti, Ta, Nb,W)(C,N), but the latter contained higher amount of heavy elements.With the addition of (Ti, Ta, Nb,W)(C,N) powders, the density, transverse rupture strength and fracture toughness of samples decreased monotonously. However, the hardness rose sharply at first, reached a peak at 15 wt% solid-solution addition, then slightly decreased, and finally increased again. Results also revealed that increasing (Ti, Ta, Nb,W)(C,N) made the open circuit potential (OCP) in 1 M sulphuric acid solution more negative than that of WC-Co, and all specimens exhibited pseudo-passivation phenomenon in the test solution. In addition, increasing pre-alloyed powders led to decreasing corrosion current density, which implies that (Ti, Ta, Nb,W)(C,N) could remarkably improve the corrosion resistance of WC-Co cemented carbides.     

Influence of ZrC addition on the microstructure,mechanical properties and oxidation resistance of Ti(C,N)-based cermets

In this study, Ti(C,N)-WC-NbC-ZrC-Co-Ni cermets were prepared by sintering-hip at 1450?°C. The effect of ZrC addition on the microstructure, mechanical properties, oxidation resistance and wear resistance of Ti(C,N)-WC-NbC-Co-Ni cermets were explored in detail. The results show that ZrC addition plays the role of inhibitor in the dissolution–reprecipitation process, which can increase the wear-resistant carbide phases and inhibit the precipitation of brittle (Ti,W,Nb)(C,N) rim phase. Therefore, the core-rim structures are refined and the Nb content in binder increases, which enhance mechanical properties and oxidation resistance of cermets. With the increasing ZrC content, the oxidation resistance of cermets can be improved constantly, while the transverse rupture strength, fracture toughness and wear resistance of these cermets increase first and then decrease. The cermet with 1?wt% ZrC exhibits the transverse rupture strength of 2549?MPa and highest fracture toughness of 13.0?MPa?m^1/2. The oxidation weight gain of cermets containing 5?wt% ZrC after holding 100?h at 750?°C in air is 2.8?×?10^?6 g?mm^?2, which is only 22% of that in the cermets without ZrC addition.     

Stability and mechanical properties of single-phase quinary high-entropy metal carbides: First-principles theory and thermodynamics

We have employed thermodynamics and first-principles density-functional calculations to investigate the structural stability and mechanical properties of fifty-six quinary high-entropy metal carbides composed of carbon and Groups IVB, VB, and VIB refractory transition metals, Ti, Zr, Hf, V, Nb, Ta, Mo, and W, thirty-eight of which have not yet been synthesized. To determine the stability of the quinary high-entropy metal carbides, we have constructed a three-dimensional phase diagram in terms of the average melting point, mixing enthalpy, mixing entropy, and lattice size difference, from which we predict that it is feasible to synthesize 38 new high-entropy metal carbides. We have further found that all the 56 metal carbides would have unique mechanical properties of high hardness and high fracture toughness. In addition, our study suggests that the brittleness of high-entropy metal carbides steadily decreases with the increase of the valence electron concentration.     

Synthesis of rare earth containing single-phase multicomponent metal carbides via liquid polymer precursor route

Novel high-entropy carbide ceramics (HEC) containing rare earth metals, namely (Ti, Zr, Hf, Ta, La, Y)C, (Ti, Zr, Hf, Ta, Nb, La, Y)C, and (Ti, Zr, Hf, Ta, Nb, Mo, W, La)C were prepared with single-phase structure by polymer precursor method. Controlled co-hydrolysis and polycondensation of equiatomic metal-containing monomers were conducted successively, followed by blending allyl-functional novolac resin as carbon source, and the polymer precursors were obtained as clear viscous liquid solutions. The single-phase formation possibility was theoretically analyzed from the aspects of size-effect parameter δ of the designed compositions. All as-obtained ceramics possessed single face-centered-cubic structure of metal carbides and high-compositional uniformity from nanoscale to microscale. The (Ti, Zr, Hf, Ta, Nb, Mo, W, La)C ceramic powder pyrolyzed at 1800°C exhibited low-oxygen impurity content of 1.2 wt%. Thus, multicomponent high-entropy carbide nanoceramics with over five metal elements containing even rare earth element were firstly synthesized and characterized.     

Evolution of microstructure and interfacial characteristics of complete solid-solution Ti(C,N)-based cermets fabricated by mechanical activation and subsequent in situ carbothermal reduction

Complete solid-solution Ti(C,N)-based cermet, with no typical core-rim structure, was synthesized through mechanical activation and subsequent in situ carbothermal reduction method. XRD, SEM, TEM, and C/N analysis were used to investigate the microstructure, phase transformation, and the interfacial characteristics of the present cermets. During solid-state sintering, the (Ti,Mo)C/(Ti,Mo)(C,N) phases formed through the transformation of Mo-based solid solution which generated by mechanical activation. Then, the formed (Ti,Mo)C/(Ti,Mo)(C,N) continuously dissolved into the nickel-based binder above 1100 °C. It was found that in the subsequent stage of liquid sintering, the mechanical activation and also the presence of extremely fine TiC/Ti(C,N) particles accelerated the Mo diffusion into the hard phase, resulting in a large quantity of (Ti,Mo)(C,N) solid solutions formed in the nickel-based binder. Finally, complete (Ti,Mo)(C,N) solid-solution phase was obtained via dissolution and re-precipitation. The higher toughness and transverse rupture strength (TRS) of the synthesized new cermet, as compared with traditional cermets, were mainly caused by the increased crack deflection and transgranular fracture of the novel cermets. Moreover, the interface among the Ni-based binder phase and complete solid solution hard phase exhibited a semi-coherency state with high-density dislocations, which also significantly improved the TRS and toughness of the synthesized cermets.