Effect of V content on microstructures and properties of TiC cermet fusion welding interface

The effects of vanadium(V)on the microstructures and mechanical properties of the TiC cermet fusion welding interface were studied by adjusting the content of V in the self-developed flux-cored wires using metal inert gas arc(MIG)welding for surfacing on the TiC cermet.The results show that the increase in V content promotes the element diffusion between TiC cermet and weld metal.There are no de-fects observed in the interface,and the diffusion of elements refers to excellent metallurgical bonding.The shear strength of the fusion zone initially decreases and then increases with the increase in V content.The maximum shear strength of the TiC cermet/weld interface,reaching 552 MPa,occurred when the V content reached 0.65%.Meanwhile,the average hardness in the transition zone reached 488.2 HV0.2.

Preparation and properties of flame-sprayed Mo-FeB-Fe cermet coatings

The powders of Mo2FeB2 cermet were prepared with Mo powders, Fe-B alloy powders and Fe powders as raw materials. Mo2FeB2 cermet coatings were prepared on Q235 steel by reactive thermal spraying （RTS） method and heated at 1 000 ℃ in vacuum oven of 1 kPa for 5 h. The properties of coatings were investigated. The results indicate that Fe2B appears after milling for 15 h in the powder at room temperature, a part of ternary borides （Mo2FeB2） are generated in powder sintered at 900 ℃. The coatings are composed of the major phases Mo2FeB2 and a-Fe, a little of Fe203, FeO and some pores. The bonding strength between the substrate and the ceramic coating is 32.73 MPa, the thermal-shock times is about 43 and the wear resistance is enhanced by approximately 5.28 times compared with that of the substrate, respectively. The comprehensive properties of Mo2FeB2 cermet coatings can be imoroved further after vacuum heat-treatment at 1 000 ℃ for 5 h.

Effect of VC/Cr_3C_2 on microstructure and mechanical properties of Ti(C,N)-based cermets

Effects of VC/Cr3C2 on the microstructure and mechanical properties of Ti（C,N）-based cermets were studied. The microstructure was investigated by means of optical microscopy, X-ray diffractometry as well as scanning electron microscopy in combination with energy dispersive spectrometry. Mechanical properties, such as transverse rupture strength, hardness and fracture toughness, were measured. The results show that there are black core-grey rim structure and white core-grey rim structure in the microstructure. The grains become fine due to the VC/Cr3C2, and the grains of cermet added with 0.75VC/0.25Cr3C2 are refined most remarkably. The black core becomes finer with the increase of VC addition and rim phase becomes thicker with the decrease of Cr3C2 addition. The porosity increases with the increase of VC addition in VC/Cr3C2. Compared with the cermet free of VC/Cr3C2, the transverse rupture strength and hardness of cermets with VC/Cr3C2 are both improved, and the maximum values are both found for the cermet with 0.25VC/0.75Cr3C2. The fracture toughness can be effectively promoted by adding VC/Cr3C2 with an appropriate ratio of VC to Cr3C2, and the maximum value is found for the cermet with 0.5VC/0.5Cr3C2.

Effect of additive BaO on corrosion resistance of xCu/(10NiO-NiFe_2O_4) cermet inert anodes for aluminum electrolysis

xCu/（10NiO-NiFe2O4） cermet and 1BaO-xCu/（10NiO-NiFe2O4） cermet（x=5,10,17） inert anodes were prepared as potential inert anodes for aluminum electrolysis and their corrosion resistance to traditional electrolyte was studied with anodic current density of 1.0 A/cm2 in laboratory electrolysis.The substantial corrosion of metal Cu was observed,many pores appeared on the surface of anode and electrolytes infiltrated inside anodes during the electrolysis.The wear rates of 5Cu/（10NiO-NiFe2O4）,10Cu/（10NiO-NiFe2O4）,17Cu/（10NiO-NiFe2O4）,1BaO-5Cu/（10NiO-NiFe2O4）,1BaO-10Cu/（10NiO-NiFe2O4） and 1BaO-17Cu/（10NiO-NiFe2O4） are 2.15,6.50,8.30,4.88,4.70 and 4.48 cm/a,respectively.The addition of BaO to 10Cu/（10NiO-NiFe2O4） cermet and 17Cu/（10NiO-NiFe2O4） cermet is advantageous because BaO can effectively promote densification and thus improve corrosion resistance.But the addition of BaO to 5Cu/（10NiO-NiFe2O4） cermet is unfavorable to corrosion resistance because additive BaO at the grain boundary of anode accelerates possibly the corrosion of cermet.

Effect of sintering atmosphere on corrosion resistance of Ni/(NiFe_2O_4-10NiO) cermet inert anode for aluminum electrolysis

A comparative study on the corrosion resistance of 17Ni/（NiFe2O4-10NiO） cermet inert anode prepared in differentsintering atmospheres was conducted in Na3AlF6-Al2O3 melt. The results indicate that the corrosion rates of NiFe2O4-based cermetanodes prepared in the vacuum and the atmosphere with oxygen content of 2×10^-3 （volume fraction） are 6.46 and 2.71 cm/a,respectively. Though there is a transition layer with lots of holes or pores, a densified layer is formed on the surface of anode due tosome reactions producing aluminates. For the anode prepared in the atmosphere with oxygen content of 2×10^-3, the thickness of thedensification layer （about 50 μm） is thicker than that （about 30 μm） formed on the surface of anode prepared in the vacuum. Thecontents of NiO and Fe（II） in NiFe2xO4-y-z increase with the decrease of oxygen content in sintering atmosphere, which reduces thecorrosion resistance of the material.

Corrosion of NiFe_2O_4-10NiO-based cermet inert anodes for aluminium electrolysis

NiFe2O4-10NiO-based cermet inert anodes for aluminium electrolysis were prepared and their properties were investigated in a lab-scale electrolysis cell. The results show that the inert anodes exhibit good performance during electrolysis in molten salt cryolite at 960 °C, but according to the analyses of phase compositions and microstructures through XRD, SEM/EDX and metallographic analysis, the metal in the anodes is preferentially corroded and many pores are produced on the anode surface after electrolysis. The preferential dissolution of Fe in the NiFe2O4 phase may lead to the non-uniform corrosion of NiFe2O4 grains. Moreover, a dense protective layer of NiFe2O4-NiAl2O4-FeAl2O4 is formed on the anode surface, which originates from the reaction of Al2O3 dissolved in the electrolyte with NiO or FeO, the annexation of NiFe2O4-NiAl2O4-FeAl2O4 to NiO and volume expansion. Thus, the dense NiFe2O4-NiAl2O4-FeAl2O4 layer inhibits the metal loss and ceramic-phase corrosion on the surface of the cermet inert anodes.

Spark Plasma Sintering Properties of Ultrafine Ti(C,N)-based Cermet

Ultrafine Ti(C,N)-based cermet was sintered by SPS from 1050℃ to 1450℃ and its sintering properties,such as porosity,mechanical properties and phase transformation,were investigated by optical microscopy (OM),scanning electron microscopy (SEM),X-ray diffraction (XRD),and differential scanning calorimeter (DSC).It is found that the spark plasma sintering properties of Ti(C,N)-based cermet differ from those of conventional vacuum sintering.The liquid phase appearance is at least lower by 150℃ than that in vacuum sintering.The porosity decreases sharply below 1 200℃ and reaches minimum at 1 200℃,and afterwards it almost keeps invariable and no longer increases.SPS remarkably accelerates the phase transformation of Ti(C,N)-based cermet and it has a powerful ability to remove oxides in Ti(C,N)-based cermets.Above 1 350℃,denitrification occurred.Fresh graphite phase formed above 1 430℃.Both the porosity and graphite are responsible for the poor TRS.

核热推进钨基CERMET燃料模拟件制备工艺研究

核热推进的工作原理是利用核燃料的裂变能将工质加热膨胀然后通过收缩扩张喷管将其加速到超音速,从而产生强大的推动力,来推动火箭或其他飞行器在太空飞行。核热推进反应堆的燃料要求具有高温稳定性、高介质化学相容性、足够的机械强度和良好的瞬时特性等特点。以金属钨为基体,UO_(2)作为弥散燃料的金属陶瓷复合燃料是核热推进反应堆的备选燃料形式之一。本文在对国外钨基CERMET燃料的发展历史、制备工艺、存在问题等方面进行调研分析基础上,结合应用需求和技术现状制定出了符合我国国情的钨基CERMET燃料制备技术路线,并通过模拟实验对该技术路线的可行性进线了验证。

Effects of molybdenum on the microstructure and mechanical properties of Ti(C,N)-based cermets with low Ni

The effects of Mo on the microstructure and mechanical properties of Ti（C,N）-based cermets with low Ni have been studied systematically. Different contents of Mo （4-12 wt.%） were added into Tl（C,N）-based cermets. Specimens were fabricated by conventional powder metallurgy and vacuum sintered at temperatures of 1440, 1450, and 1460℃ individually. The microstructure and fracture morphology were investigated by scanning electron microscope, and the mechanical properties such as transverse strength and hardness were measured. The results show that the microstructure is uniform and the thickness of rim phase is moderate when the content of Mo is 8 wt.%; the mechanical properties of the specimens sintered at 1450℃ are better than those sintered at 1440 and 1460℃. The integrated properties of transverse strength and hardness are the best when the content of Mo is 8 wt.% and the sintering temperature is 1450℃.

EFFECT OF Mo AND Mo_2C ON THE MICROSTRUCTURE AND PROPERTIES OF THE CERMETS BASED ON Ti(C,N)

Effect of Mo and Mo2 C on the microstructure and properties of Ti（C,N）-based cermets was investigated in this article. The results have indicated that the weight percentage of Mo from 5 to 10 can reduce Ti（C,N） grain diameter and thickness of the rim, and Ti（C,N） grain can be wetted by Ni-Cu-Mo liquid so as to get small contiguity of Ti（C,N） grain. In that way, the transverse rupture strength of Ti（C,N）-based cermets has reached 1800-1900 MPa; the fracture toughness has been due to 16-18 MPa.m1/2. But 15 wt pct Mo was not more effective on Ti（C,N）-based cermets, because the thickness of the rim becomes larger. In the circumstance of Mo2 C, 5 wt pct Mo2 C was good for microstructure and properties of Ti（C,N）-based cermets, but 11 wt pct Mo2C has resulted in larger contiguity of Ti（C,N） grain and big Ti（C,N） grain diameter so as to reduce transverse rupture strength and fracture toughness. So that, the effect of Mo on Ti（C,N）-based cermets is better than Mo2C.

Effect of Powder Particle Size on the Properties and Microstructure of Ti(C,N)-Based Cermet

The influence of raw powder particle size on the properties and microstructures of Ti (C, N)-based cermets has been studied. The conclusions are as follows: The microstructures of cermets were composed of two kinds of grains, the one with black cores surrounded by obvious rim structures, and the other whose cores were white with unconspicuous rim structures and adhesive phase. In the cermet made from fine powders, the amount of grains with white cores was much more than that in cermet made from coarse powders. In addition, their properties were also much better.

Microstructure and shear strength of the brazed joint of Ti(C,N)-based cermet to steel

Firm joins were obtained between Ti（C,N）-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thickness on the shear strength of the joints were investigated. The microstructure of welded area and the reaction products of the filler metal were examined by scanning electron microscopy （SEM）, metallographic microscope （OM）, energy-dispersive X-ray analysis （EDS）, and X-ray diffraction （XRD）. The brazing temperature of 870℃, holding time of 15 min, and filler thickness of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of the joints, 176.5 MPa, is achieved. The results of microstructure show that the wettability of the filler metal on Ti（C,N）-based cermet and steel is well. A mutual solution layer and a diffusion layer exist between the welding base materials and the filler metal.

Effect of VC addition on the microstructure and properties of Ti(C,N)-based nano cermets

In this paper, Ti（C,N）-based nano cermets were prepared by nano particles, and the effect of VC addition on the micmstructure and properties of Ti（C,N）-based nano cermets was investigated. The results showed that there existed black-core grayish-rim strucmre as well as gray-core grayish-rim structure in VC-doped Ti（C,N）-based nano cermets. With the increase of VC addition, the number of gray cores in- creased, the lattice parameter of Ti（C,N） phase increased, the grain size decreased, the hardness and fracture toughness of Ti（C,N）-based nano cermets were enhanced, and nearly full densification could be achieved. However, excessive addition of VC to 1 wt% resulted in slight decrease in hardness and fracture toughness. Some deep dimples were found in the fracture surface of cermets with VC addition, which corresponded to ductile fracture.

Effect of Laser Power on Microstructure and Wear Resistance of WC_P/Ni Cermet Coating

Laser cladding nickel-based alloy coating （Ni60） and nickel-based composite coating doped with WC particles by 35 % （WCp/Ni） were produced on the low-carbon steel substrate by CO2 continuous wave laser with power of 5 kW using the injected powder technique. The effect of laser power on microstructure and wear resistance of laser cladding WCp/Ni cermet coating was investigated. The WCp/Ni alloy coating with evenly distributed WC ceramic phases and the better bond with the substrate alloy was obtained at a power of 2.2 kW. Diffusion solution reaction happened between WC particles and the substrate alloy during laser cladding, and led to the formation of block rich-tungsten carbide on the edges of the WC particles, especially at higher power. The WCp/Ni alloy coating consists of the undissolved WC particles, the block or dendritic rich-tungsten carbide, the bar-like rich-chromium carbide, and dendrite solid solution and eutectic structure among the carbides. Microhardness and wear resistance of the WCp/Ni coating at different powers were much higher or better than those of Ni60 alloy coating, and the best results were obtained at power of 2.2 kW.

Influence of Mo on the microstructure and mechanical properties of TiC-based cermets

The microstructures and mechanics properties of TiC-based cermets composed of TiC, WC, Ni, Co, Mo, and Cr3C2 were investigated. The results show that Mo has a great effect on the sintering densification, microstructures, and mechanical properties. The microstructures and distribution of Mo and Ti in the TiC-based cermets were analyzed. It was indicated that a new phase with Ti, Mo, W, and C was formed on the rim of （Ti,W）C grains by means of an addition of Mo into the TiC-based cermets. The new phase with a surrounding structure was of great aid to improve the wettability of the liquid phase on the solid phase surface of TiC, decrease the porosity and refine the grains of the hard phase, which gave rise to the increase in strength and hardness. The properties of the TiC-based cermets could be further improved to some extent by adding WC, Cr2C3, and Co.

EFFECT OF Cu-Ni CONTENT ON THE CORROSION RESISTANCE OF(Cu-Ni)/(10NiO-90NiFe_2O_4)CERMET INERT ANODE FOR ALUMINUM ELECTROLYSIS

（Cu-Ni）/（10NiO-90NiFe204） cermet inert anodes containing metal Cu-Ni0, 5, 10, 15 and 20 wt pct were prepared and their corrosion resistance to Na3AlF6-Al2O3 melts was investigated. The results indicate that the content of metal Cu-Ni has little effect on the steady-state concentration of Ni in the electrolyte and the values could not be used to effectively differentiate their corrosion resistance. The steady-state concentration of Fe decreases from 304×10^-6 to 168×10^-6 and that of Cu increases from 21×10^-6 to 71×10^-6 with the content of metal Cu-Ni increasing from 0 to 20 wt pct. Post-examination shows that metallic phase Cu-Ni is corroded preferentially during electrolysis and many pores are left at the anode surface. Considering the corrosion resistance and electrical conductivity, the cermet containing metal Cu-Ni 5 wt pct should be selected and studied further.

Tribological properties of TiAlN-coated cermets

Ti（C,N）-based cermets were coated with TiAlN using multi-arc ion plating technology. Sliding wear tests were performed on the coated cermets. The microstructure and morphologies of the coated cermets before and after friction and wear tests were characterized. The results show that the TiAlN coating surface was smooth and its root mean square roughness was 16.6 nm. The hardness （HK） of TiAlN coating layers reached approximately 3200 and the critical load （Lc） under which the coating failure occurred was 59 N. The sliding wear test results show that the friction coefficients of the TiAlN-coated cermets were lower than that of the cermets without any coating. Under the same load, the adhesion phenomenon of the counterpart materials on the specimens was improved and the mean friction coefficient increased with increasing sliding velocity. When the sliding velocity was 0.26 m·s^-1, the mass of the coated cermets reduced. At the same sliding velocity, the average friction coefficient of the TiAlN-coated cerrnets was lower under a higher load. The wear mechanisms of the TiAlN-coated cermets were mainly adhesive and abrasive wear.

Phase Evolution during the Sintering of Submicron Ti(C,N)-Based Cermets

The submicron powder mixtures of TiC-TiN-WC-Mo-C-Ni sintered at 1400degreesC or below in vacuum were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The results showed that Mo2C formed at 800degreesC or below. Both WC and Mo2C disappeared at 1200degreesC, and TiN disappeared at 1250degreesC. In addition, the variations of lattice constants of the titanium carbonitride and nickel binder phase with sintering temperature were experimentally obtained, and the reason was analyzed.

Elevated temperature oxidation behavior of HVOF sprayed TiB_2 cermet coating

Oxidation behaviors of Ni(Cr)-TiB2 coating deposited by HVOF technique were studied at 800,900 and 1 000℃in air. The microstructures of as-sprayed and oxidized coatings were characterized by X-ray diffractometry(XRD)and scanning electron microscopy(SEM).After oxidation at 800℃,a thin and adherent oxide layer was formed on the surface of the coating.With increasing exposure temperature,the thickness of the oxide layer increased;and at 1 000℃the oxide layer separated from the coating.Investigation of the kinetics of oxidation by using the thermogravimetric analysis(TGA)technique shows a parabolic oxidation rate.

Microstructure and cutting performance of Ti(C, N)-based cermets heat-treated in nitrogen

Ti（C, N）-based cermets were treated using hot isostatic pressing （HIP） at 1423 K in nitrogen. The microstructures compared with the as-sintered cermets were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and electron microprobe analysis. It was found that high nitrogen activity in the surface zone resulted in the formation of gradient structure. Approximately 20-1am-deep, nitrogen-rich and titanium-rich hard surface zone was introduced by the heat treatment. The nitrogen activity was the driving force that caused the transportation of the atoms through the binder, titanium towards the surface, and tungsten and molybdenum inwards. In the surface zone, the particle size became fine, the inner rim disappeared, and the volume fraction of the outer rim and the binder phase considerably reduced. Small grains of TiN, WC, Mo2C, and nitrogen-rich carbonitlide phases formed in the surface zone during the heat treatment, improving the tlibological property of the heat-treated cermet.