Carbide stoichiometry in TiCx and Cu–TiCx produced by self-propagating high-temperature synthesis

TiC_x and Cu–TiC_x have been formed by self-propagating high-temperature synthesis (SHS) from elemental powder mixtures with a range of C/Ti ratios. When no copper was present, the carbide stoichiometry closely followed that of the starting powders. In the presence of copper, formation of copper–titanium intermetallics and solid solutions resulted in a different carbide stoichiometry.     

Influence of titanium nitride addition on the microstructure and mechanical properties of TiC-based cermets

In this paper, the TiC-based cermets with addition of TiN were fabricated by a conventional powder metallurgy process. The titanium nitride (TiN) and titanium carbide (TiC) used as starting powders have been synthesized by the self-propagating high temperature synthesis (SHS) method. This exothermic reaction, easy to process, allows to obtain fine and original powders from low-cost raw materials. Cermets obtained by sintering powders of TiC and Mo₂C with nickel binder phase are investigated. The effect of TiN adding on the microstructure and the mechanical properties of these composites are studied. Microstructures have been observed by scanning electron microscopy (SEM). Room temperature mechanical properties such as Young’s modulus, fracture toughness and microhardness have been measured and related to morphology and chemical composition of the samples. Tribological experiments were also performed and the friction coefficient of a cermet containing titanium nitride was compared with that of other hard materials. The SHS starting powders used present some particularities, as it was shown in a previous study [Matériaux à base de carbures et nitrures, pour coupe et usure, obtenus à partir de poudre SHS, PhD Thesis, INSA Lyon, 2004]. The purpose of this work is to show that results concerning the impact of TiN addition on microstructure and mechanical properties obtained on bulk specimens, from these original starting powders, are similar to the ones obtained on alloys from commercial starting powders.     

Bulk titanium nitride material obtained from SHS starting powder: Densification, mechanical characterization and tribological approach

Powders used for this study were synthesized by the self-propagating high temperature synthesis (SHS) process. This method allows producing titanium nitride powders in an economic and easy way. Densification of these original powders is carried out by the hot pressing process. Sintering is achieved, under a 50 MPa pressure, at different temperatures (1400 °C, 1600 °C and 1800 °C). At 1600 °C properties are optimised and bulk specimen density is superior to 98%. In addition, microhardness reaches the average value of 1790 ± 225 H_V and Young modulus measured is 430 ± 10 GPa. A tribological characterization is then carried out with an adapted four balls machine tribometer. Titanium nitride tribological behavior is compared with the one of other hard materials such as 100C6 steel, titanium carbide and two cemented carbides of different compositions. Parameters such as toughness, hardness and wear volume are correlated in order to understand wear mechanisms origins.     

Hard and wear-resistant titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard and wear-resistant titanium nitride coatings were deposited by pulsed high energy density plasma technique on cemented carbide cutting tools at ambient temperature. The coating thickness was measured by an optical profiler and surface Auger microprobe. The elemental and phase compositions and distribution of the coatings were determined by Auger microprobe, x-photon electron spectroscope, and X-ray diffractometer. The microstructures of the coatings were observed by scanning electron microscope and the roughness of the sample surface was measured by an optical profiler. The mechanical properties of the coatings were determined by nanoindentation and nanoscratch tests. The tribological properties were evaluated by the cutting performances of the coated tools applied in turning hardened CrWMn steel under industrial conditions. The structural and mechanical properties of the coatings were found to depend strongly on deposition conditions. Under optimized deposition conditions, the adhesive strength of TiN film to the substrate was satisfactory with the highest critical load up to more than 90 mN. The TiN films possess very high values of nanohardness and Young’s modulus, which are near to 27 GPa and 450 GPa, respectively. The wear resistance and edge life of the cemented carbide tools were improved dramatically because of the deposition of titanium nitride coatings.     

激光熔覆制备Fe-Ti-Mo-C系复合涂层

采用钛铁、钼铁和石墨为激光熔覆粉末,利用激光多道搭接熔覆技术在碳钢基体上制备Fe-Ti-Mo-C复合涂层.利用X射线衍射仪、场发射扫描电镜、电子探针对涂层的相结构和显微组织进行了研究.用显微硬度计和滑动磨损试验机,对涂层的硬度和耐磨性能进行测试.结果表明,涂层中原位生成了(Ti,Mo)C复合碳化物.(Ti,Mo)C呈面心立方结构,晶格常数略小于TiC晶粒.随着原材料中钼铁加入量的增加,涂层显微组织由铁素体、珠光体向马氏体转变,显微硬度和耐磨性增加,但抗裂性能降低.     

Disperse-strengthening by nanoparticles advanced tribological coatings and electrode materials for their deposition

Two types of electrode materials were developed using self-propagating high-temperature synthesis (SHS) and powder metallurgy: 1- composite with nanosized additives; 2- nanostructured cemented carbide WC-Co. Electrospark deposition (ESD) was applied to produce tribological coatings which were disperse-strengthened by incorporation of nanosized particles. Nanostructured electrodes of cemented carbides WC-8% Co provide increasing density, thickness, hardness, Young's modulus, and wear resistance of ESD-coatings. Positive effects of nanostructural state of the electrodes on the deposition process and structure/properties of the coatings are discussed. In that case the tungsten carbide phase becomes predominant in the coatings. A mechanism of the dissolution reaction of WC in Ni at the contact surface of the electrode was proposed. It was shown that formation of the coating structure is initiated on the electrode and accomplished on the substrate.     

大气等离子喷涂TiB2-TiC-Co涂层的组织与性能

利用Co-Ti-B4C自蔓延体系合成TiB2-TiC-Co复合陶瓷粉末，并结合大气等离子喷涂技术在Q235 钢基体表面制备TiB2-TiC-Co陶瓷涂层，研究了自蔓延产物和涂层的相组成、显微组织，以及涂层的结合强度和抗磨损性能。结果表明：Co-Ti-B4C体系自蔓延产物的物相中，除了少量剩余的NaCl添加剂衍射峰外，主要由TiB2和TiC陶瓷相的强衍射峰组成；产物断面中，两相陶瓷颗粒细小。随Co含量增加，TiB2-TiC-Co涂层表面盘状组织增多，表面逐渐平滑，截面涂层厚度均匀，组织致密性逐渐增加；结合强度和耐滑动磨损性能呈先升高后降低的变化趋势。Co含量为10wt.%时，涂层的结合强度和耐滑动磨损性能最好，涂层的滑动磨损机制主要为粘着磨损和层状剥落磨损。     

Tribological properties of TiC-Fe coatings obtained by plasma spraying reactive powders

Titanium carbide-based coatings have been considered for use in sliding wear resistance applications. Carbides embedded in a metal matrix would improve wear properties, providing a noncontinuous ceramic surface. TiC-Fe coatings obtained by plasma spraying of spray-dried TiC-Fe composite powders containing large and angular TiC particles are not expected to be as resistant as those containing TiC particles formed upon spraying. Coatings containing 60 vol% TiC dispersed in a steel matrix deposited by plasma spraying reactive micropellets, sintered reactive micropellets, and spray-dried TiC-Fe composite powders are compared. The sliding wear resistance of these coatings against steel was measured following the test procedure recommended by the Versailles Advanced Materials and Standards (VAMAS) program, and the inherent surface porosity was evaluated by image analysis. Results show that, after a 1-km sliding distance, TiC-Fe coatings obtained after spraying sintered reactive powders exhibit scar ring three times less deep than sprayed coatings using spray-dried TiC-Fe composite powders. For all coatings considered, porosity is detrimental to wear performance, because it generally lowers the coating strength and provides cavities that favor the adhesion of metal. However, porosity can have a beneficial effect by entrapping debris, thus reducing friction. The good wear behavior of TiC-Fe coatings manufactured by plasma spraying of sintered reactive powders is related to their low coefficient of friction against steel. This is due to the microstructure of these coatings, which consists of 0.3 to 1 μm TiC rounded particles embedded in a steel matrix. Presented at the International Conference on Metallurgical Coatings and Thin Films, ICMCTF-92, Apr 6–10, 1992, San Diego.     

Reactive plasma spraying of coatings containing in situ synthesized titanium hard phases

In this investigation, coatings of titanium composites containing in situ synthesized carbides or nitrides were deposited by reactive plasma spraying. Titanium powders were used as starting powder materials. Methane and nitrogen were used as reactive gases. Microstructural analyses revealed that titanium carbides and nitrides were synthesized during spraying. The coatings show high sliding wear resistance and good corrosion performance.     

Formation of the structure of wear-resisting coatings in electron beam deposition of tungsten carbide

The method of out-of-vacuum electron beam deposition of tungsten carbide powder on low-carbon steel is used to produce the coatings whose structure, hardness and wear resistance are determined by the specific surface energy of radiation. It is shown that the highest properties are exhibited by the structure of the carbide inclusions – the austenitic matrix, similar to the structure of the hard alloy whose working principle is based on a compromise between strength and plasticity. Heat treatment of the deposited layers improves the structure and increases hardness and wear resistance. Additional improvement of the properties is achieved by adding a modification agent.     

Effect of Dispersed TiC Content on the Microstructure and Thermal Expansion Behavior of Shrouded-Plasma-Sprayed FeAl/TiC Composite Coatings

FeAl intermetallic matrix composites reinforced by ceramic particles such as titanium carbide have attracted much attention in recent years. In this study, shrouded plasma spraying with nitrogen as a protective gas was employed to deposit FeAl/TiC composite coatings. Fe-35Al powder and Fe-35Al/TiC composite powders containing 35 and 45?vol.% TiC prepared by mechanical alloying were used as feedstock powders. The microstructures of the ball-milled powders and the as-sprayed coatings were characterized by scanning electron microscopy and x-ray diffraction. The mean coefficients of thermal expansion (CTEs) of FeAl and FeAl/TiC were measured. The results showed that dense FeAl and FeAl/TiC coatings with low oxide inclusions were deposited by shrouded plasma spraying. The mean CTEs measured in the present study were reasonably consistent with those calculated based on the formula. As a result, the mean CTE of FeAl-based composite coating can be properly controlled by adjusting TiC content in the composite coating to match with those of different substrate materials.     

Deposition and properties of high-velocity-oxygen-fuel and plasma-sprayed Mo-Mo2C composite coatings

Molybdenum thermal-spray coatings, dispersion strengthened by molybdenum oxides and molybdenum carbides, play an important role in industrial tribological applications. Traditionally, they have been prepared by plasma and wire flame spraying. High porosity and lower cohesion strength limit their application in situations where both galling and abrasion wear is involved. In this study, high-velocity-oxygen-fuel (HVOF) deposition of molybdenum and molybdenum carbide coatings was attempted. Deposition was achieved for all powders used. Composition, microstructure, mechanical, and wear properties of the HVOF synthesized coatings were evaluated and compared with plasma-sprayed counterparts. The HVOF coatings possessed a very good abrasion resistance, whereas plasma deposits performed better in dry sliding tests. Measurements showed a close relationship between the coating surface hardness and its abrasion resistance. Results also suggested correlation between molybdenum carbide distribution in the molybdenum matrix and the sliding friction response of Mo-Mo₂C coatings.     

Study of composite spark-alloyed coatings based on titanium carbide using self-propagating high-temperature synthesis

This work discusses composite coatings obtained by electro-spark alloying and self-propagating high-temperature synthesis. It has been established that the generated composite coatings consist of titanium carbides, which are uniformly distributed in the metal matrix. The titanium carbide grain sizes are in the range of 0.1?C4.0 ??m. The coarse grains of titanium carbide in the coating consist of disperse carbides with sizes of less than 1 ??m. The study of the structure of the composite coatings in friction tracks has demonstrated that the generated coatings possess high wear resistance.     

WC-Co复合粉末的原位合成及于硬质合金涂层制备中的应用

目的为解决超细/纳米WC-Co热喷涂时易于脱碳等瓶颈问题,制备具有高的硬度、断裂韧性、耐磨性和表面质量等优异综合性能的超细及纳米结构硬质合金涂层,并推广其在工业领域中的应用。方法以原位合成技术批量制备的超细/纳米WC-Co复合粉末为原料,利用团聚造粒技术制备得到具有高球形度和致密性,并保持原有超细/纳米结构的喷涂喂料粉末,利用超音速火焰喷涂工艺制备低脱碳、高致密的超细结构WC基涂层。结果降低喂料粉末孔隙度可有效减少涂层中W2C等脱碳相的含量,在优化工艺下制备的超细结构WC基涂层的硬度达到1450HV0.3以上,韧性相对于常规微米结构涂层提高40%以上,在两种载荷和磨料条件下均表现出更高的耐磨性。结论利用原位反应技术批量合成的超细/纳米WC-Co复合粉制备的硬质合金涂层具有优良的综合性能,可应用于对涂层的硬度、耐磨性、强韧性配合和表面质量有较高要求的工况。     

Microstructure and properties of flame sprayed tungsten carbide coatings

This article reports on feasibility experiments carried out with oxy-acetylene spray system with various oxygen to fuel ratios using two different tungsten carbide powders and powder feeding methods, to evaluate the newly developed fused WC, synthesised by transferred arc thermal plasma method. Transferred arc thermal plasma method is more economical and less energy intensive than the conventional arc method and results in a fused carbide powder with higher hardness. The microstructure and phase composition of powders and coatings were analysed by optical and scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Carbon content of the powders and coatings were determined to study the decarburisation of the material during spraying process. Coatings were also characterised by their hardness and abrasive wear. The effects of metallurgical transformation and phase content are related to wear performance. The results demonstrate that the powders exhibit various degree of phase transformation during the spray process depending on the type of powder, powder feeding and spray parameters. The carbon loss during the spray process in excess of 45% resulted in reduced hardness and wear resistance of the coatings. Coatings with high amount of WC and W₂C along with FeW₃C showed higher wear resistance. Thus, coatings of high wear resistance can be produced using fused tungsten carbide powder with WC and W₂C phases, which can be economically synthesised by thermal plasma transferred arc method.     

含碳化物陶瓷粉芯丝材电弧喷涂层的结构和性能

分别将WC、TiC、Cr3C2等碳化物陶瓷粉末与304不锈钢带轧制成3种粉芯丝材,采用电弧喷涂技术在Q235钢基体上制备铁基复合涂层.利用光学显微镜、SEM、XRD对3种涂层的形貌、相组成和磨损表面进行分析,并用湿砂橡胶轮磨损试验机(MLS-225)测试了涂层的抗磨粒磨损性能.结果表明,碳化物陶瓷粉末的加入使涂层的硬度和耐磨性显著提高,涂层的平均显微硬度值高达1100～1200 HV0.1.在本试验条件下,铁基复合涂层的耐磨性比Q235钢高6～18倍.塑性微切削和脆性剥落为涂层的主要磨粒磨损形式.     

Comparison between single and multilayered a-SiC:H coatings prepared by multi-frequency PACVD: Mechanical properties

Due to their low density and good mechanical properties, titanium alloys are commonly used to lighten structures in aeronautical applications. Unfortunately, their friction properties are poor due to titanium oxide layers which naturally occur. To confer to the surface both high mechanical resistance under load and low friction/low wear against other metals, amorphous silicon carbide (a-SiC:H) coatings are deposited on plasma treated substrates, using a multi-frequency plasma CVD device. The present study is devoted to compare scratch properties of single and multilayered a-SiC:H layers including up to 125 asymmetric periods of soft/hard coatings. Standard scratch-testing measurements reveals that the critical load corresponding to the formation of cohesive/adhesive cracks can be significantly increased (by a factor of 2.5) when using multilayered coatings. When optimized coatings are deposited, the substrate is not visible at the bottom of the flaked area until loads higher than 60 N are applied.     

Corrosion characteristics of plasma-sprayed TiN and TiC coatings on steels in salt water

The salt water corrosion characteristics of titanium nitride and titanium carbide coatings on steels, prepared by argon plasma-spraying dry Ti and TiC powders in open air, are described. Both the TiN and TiC coatings are attacked by salt water, the latter being corroded nearly twice as much as the former. The bond-coated and top-sealed (BT) coatings corrode less than the analogous coatings without these (NBNT) in the immersion tests. The BT coatings corrode more than the NBNT coatings in the salt water spray test. CaCO₃ deposits form on the TiC coatings from salt solutions containing Ca ions, but no such calcareous deposit was formed on the TiN coatings.     

激光熔覆Cr_3C_2-Ni复合涂层的减摩性能

以粉末化学镀法制备的Cr_3C_(2-)Ni复合粉末作为预置层,在Q235钢板表面用激光熔覆技术制备了减摩复合涂层.研究了Cr_3C_(2-)-Ni涂层在干摩擦条件下的减摩性能,并对磨损形貌进行了SEM观察,对涂层的硬度进行了测 试.结果表明,该涂层组织均匀致密、硬度较高;涂层的摩擦性能稳定,摩擦系数为0.44;硬质Cr_3C_(2-)粒子与金属粘结相的配合能有效提高熔覆层的承载能力,减小摩擦损失.     

Microstructures and properties of Ni based composite coatings prepared by plasma spray welding with mixed powders

The Ni based composite coatings have been obtained by using the plasma spray welding process and mixed powders (NiCrBSi + NiCr-Cr₃C₂ + WC). Their microstructures and properties were studied. The results showed that the coatings consist mainly of γ-Ni, WC, Cr₂₃C₆, Cr₇C₃, Ni₃Si, Cr₅B₃, CrB and FeNi₃ phases, and the Ni₃Si, Cr₅B₃, CrB and FeNi₃ phases mainly segregated between the carbide grains. The carbide contents in the coatings increased with increasing the mass fractions of NiCr-Cr₃C₂ and WC powders in the mixed powders, which results in enhancing the coating hardness. The abrasive wear resistance of the coatings depends on their hardness. The higher the coating hardness, the stronger the wear resistance is. When the mixed powder (15wt%WC + 30 wt% NiCr-Cr₃C₂ + 55wt%NiCrBSi) was used, the composite coating has higher hardness and more excellent wear resistance, and the coating hardness and weight loss after wear tests are 991 HV and 8.6 mg, respectively.