Structural and mechanical stability upon annealing of arc-deposited Ti-Zr-N coatings

Ti-Zr-N coatings were formed by the method of vacuum arc deposition using combined Ti and Zr plasma flows in a N₂ atmosphere at different ratios of arc currents of Ti and Zr cathodes. After deposition, obtained samples were annealed in vacuum at the temperature of 850 °C. The element and phase composition, residual stresses and nanohardness were studied by Auger-Electron Spectroscopy, X-ray diffraction (XRD) and nanoindentation, respectively.XRD analysis reveals the formation of ternary Ti-Zr-N nitride coatings with the structure of solid solutions. It is shown that Ti-Zr-N coatings possess high hardness in comparison with TiN and ZrN binary nitrides. An increase in hardness is observed with increasing Zr content. However, it is established that after annealing coatings keep better stability of hardness with decrease of Zr content. The intrinsic stress in the as-deposited coatings is found to be largely compressive (− 4 GPa) and almost independent of Zr content, but much higher than in ZrN and TiN binary nitrides (− 2 GPa). After annealing, a significant stress relaxation is observed in all coatings due to relief of growth-induced point defects. Stress analysis on as-grown and annealed samples enabled us to determine the stress-free lattice parameter a₀. This latter is expanded by ∼ 0.4-0.7% as compared to Vegard's law.The thermal stability of Ti-Zr-N coatings will be discussed in terms of evolution and interdependence between structure, composition and hardness after annealing.     

Effect of thermal annealing on microstructure and mechanical properties of a gradient structured tantalum prepared by plasma activated sintering

Fully dense bulk tantalum compacts of two different nitrogen contents with gradient structure within an individual particle were successfully synthesized by means of plasma activated sintering (PAS). Annealing of the compacts induces disappearing of the gradient structure due to the promoted diffusion of nitrogen in Ta matrix accompanied by enhancement of the strength. For the compact with low nitrogen content of 0.09 wt.%, a drop in ductility was observed. While for the compact with nitrogen content of 0.215 wt.%, improved strength was obtained without sacrificing its ductility.     

Influence of annealing treatment on microstructure and properties of cold sprayed stainless steel coatings

304 stainless steel coatings had been deposited on carbon-steel substrate by cold spray technique, vacuum annealing treatment was applied to the coatings with different temperatures, and the influence of annealing treatment on the microstructure and electrochemical behavior of the coatings in 3.5% NaCl were analyzed. The results indicated that, the cold sprayed coating was constituted by the flattened particles, and the interfaces were clearly observed between the deposited particles. It was also found that...     

Oxidation and hot corrosion behavior of gradient NiCoCrAlYSiB coatings deposited by a combination of arc ion plating and magnetron sputtering techniques

NiCoCrAlYSiB coating was prepared by arc ion plating and Al and Cr gradient NiCoCrAlYSiB coating by a combination of arc ion plating and magnetron sputtering. The results of EPMA show that the Al and Cr are uniformly distributed in the NiCoCrAlYSiB coating but have a graded distribution in the surface layer of the gradient coating. Compared to the bare DSM 11, both the NiCoCrAlYSiB coating and the gradient coating improved the oxidation resistance greatly. After 100 h hot corrosion, the gradient coating showed the best corrosion resistance. The oxidation and hot corrosion mechanisms were discussed.     

激光制备Fe-Ni基非晶复合涂层及退火性能分析

采用15 kW快速轴流型CO2激光器在低碳钢基体上制备了非晶复合涂层Fe31Ni31Si18B18Nb2.利用X射线衍射(XRD)和扫描电镜(SEM)分析了涂层的物相、组织结构与加入元素形态对涂层非晶形成能力的影响.结果表明,Nb元素以铌铁的形式加入更加有利于非晶层的形成,铌铁加入后抑制了Ni2Si和Ni2B相的产生,...     

Composition of electrodeposited Zn–Cr alloy coatings and phase transformations induced by thermal treatment

Zn–Cr alloy coatings were obtained in a flow cell, for modeling the process of high speed electrodeposition on steel strips. Alloy coatings, containing between 6 and 18 at.% Cr were annealed at 260 °C in an inert atmosphere. The phase composition and the crystallographic characteristics of “as prepared” and “annealed” coatings, were studied by XRD. It is shown that non-equilibrium δ- and Γ-(Zn,Cr) phases are major constituents of the “as prepared” coatings. On annealing, equilibrium ζ-CrZn₁₃ phase precipitates from δ- and Γ-supersaturated solid solutions. The lattice parameters and the similarities in phase composition of the annealed coatings, deposited onto two types of substrates – low carbon steel and Cr plated (protected) low carbon steel – show that if Fe from the substrate “contaminates” the precipitated ζ-CrZn₁₃ phases, its relative amount do not exceed few tenths of a percent.The influence of the elemental composition, conditions of electrochemical deposition, and post-deposition thermal treatment on phase composition of the coatings is discussed.     

Thermal stability of nanostructured superhard coatings: A review

It is important to evaluate the thermal stability of hard coating because at high working temperatures the mechanical and tribological properties are deteriorated. The temperature operating on the cutting tool tip during work may reach temperatures as high as 1000 °C. Environmental considerations limiting the use of lubricants and coolant liquids, increase the necessity of finding coatings that can function at such high temperature.Coatings can be differentiated by their hardness, H, into three main categories: hard with H < 40 GPa; superhard with H > 40 GPa; and ultra-hard coatings with H > 80 GPa.There are two main reasons in the high hardness coatings: either high compressive stresses or nano-scale structure. The application of high biaxial compressive stress acts as a driving force for recovery, i.e. the higher the compressive stress, the lower is the thermal activation energy needed to initiate recovery. High biaxial compressive stress increases superhardness, but reduces the coating thermal stability. Dislocations increase the micro-scale compressive stress inside the coating and consequently, enhance recovery. In nano-scale coatings, the small nanometric scale grain size restricted grain growth and boundaries sliding, and therefore the thermal stability is enhanced.This study treats the thermal stability of several types of superhard materials, i.e. nanocomposite coatings and those consisting of a hard transition-metal nitride and a soft metal. It focuses on formation mechanisms, materials and phase composition.     

Structure and phase evolution of Cr-Al-N coatings during annealing

Cr-Al-N coatings are favored for wear protection of tools, dies, molds, as well as for components used in the automotive and aerospace industry due to their excellent mechanical and thermal properties. Cr-Al-N coatings crystallize in the cubic modification for AlN mole fractions below ~ 0.7, whereas higher Al contents favor the hexagonal modification. Here, we use a combination of differential scanning calorimetry and X-ray diffraction to study the structure and phase evolution of Cr-Al-N coatings during annealing up to 1450 °C. The results indicate that cubic Cr-Al-N decomposes during thermal annealing to form AlN precipitates. Hence, the remaining matrix becomes Cr-rich and N-loss at elevated temperatures is promoted. Annealing of hexagonal Cr-Al-N coatings results in the precipitation of CrN. The remaining matrix becomes Al-rich and transforms into AlN. Consequently, CrN is encapsulated in AlN and hence, the N-loss occurs at higher temperatures as compared to cubic Cr-Al-N.The obtained results serve as a basis for further developments of Cr-Al-N films to effectively retard the decomposition process and the N-loss.     

Effects of annealing on the microstructure and the mechanical properties of EB-PVD thermal barrier coatings

The effects of thermal annealing at 1000 °C in air on the microstructure and the mechanical properties (Young's modulus and hardness) of thermal barrier coatings consisting of a 4 mol% Y₂O₃ partially stabilized ZrO₂ top coat and a NiCoCrAlY bond coat, deposited by electron beam physical vapour deposition on nickel-based superalloy IN 625, have been investigated using X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), image analysis and nanoindentation. During annealing, the ceramic top coat undergoes sintering and recrystallization. These processes lead to stress relaxation, an increase of the intra-columnar porosity and the number of large pores as measured by image analysis of SEM micrographs. An increase of the grain size of the γ-phase in the bond coat, accompanied by changes in the morphology of γ-grains with annealing time, is also observed. Correlations between these microstructural changes in the top coat and the bond coat and their mechanical properties are established and discussed.     

Thermal cycling behavior and interfacial stability in thick thermal barrier coatings

The thermal cycling behavior of thermal barrier coatings (TBCs), which were prepared by two different air-plasma spray (APS) guns of 9 MB and TriplexPro™-200, was investigated to understand the effects of the microstructure on the interfacial stability and fracture behavior of TBCs. The porosities of the top coats could be controlled by changing the gun, showing porosity of about 15% using the 9 MB and 19% using the TriplexPro™-200, which decreased slightly with thermal exposure. Defects, such as interlamellar cracks, vertical cracks, and intrasplat cracks, were freshly produced in both TBCs after thermal exposure, showing delamination in the case of 2000 μm TBCs prepared using the TriplexPro™-200. The adhesive strength values of TBCs with 600 and 2000 μm thicknesses were about 8 and 6 MPa, respectively, indicating that the adhesive strength values of TBCs were affected by the coating thickness, independent of the gun. The hardness values increased after thermal exposure, and the TBCs prepared using the TriplexPro™-200 showed higher values than those prepared using the 9 MB for both thicknesses. The toughness values were not dependent on the gun, only showing an effect from coating thickness. The increase in coating thickness enhanced the densification, resulting in higher hardness and toughness values, and the microstructure could be controlled by changing the gun.     

Control of structural and phase processes in detonation spraying of coatings

Issues of obtaining coatings with optinum structure and properties from nickel-clad powdered aluminium oxide are studied. A production method of metal–ceramic composition is offered, the ceramic component gradually increasing from the lower layer to the upper one, ensuring optimal properties of the coating.     

Multi-component nitride coatings derived from Ti-Al-Cr-Si-V target in RF magnetron sputter

The nitride coatings comprised of various constituents Ti, Al, Cr, Si, V were deposited on mild steel by RF magnetron sputtering process. The Ti-Al-Cr-Si-V multi-component target introduced in this study was fabricated by conventional metallurgical method with atomic ratio of each selected element at 1:1:1:1:1. Different coatings were fabricated under various working pressure by adjusting nitrogen flux from 0 to 30 sccm during sputtering. Compositions of the target and the sputtered films were measured by FE-EPMA, and both of them were near equi-molar. According to XRD patterns, amorphous structures were revealed for the metallic and nitride 1 (N = 46.2 at.%) films. The face centered cubic phases were exhibited by nitride 2 and nitride 3 with nitrogen contents around 58 at.%. Two different surface morphologies were investigated by the AFM, and they were consistent with the nanostructure observed in the XRD pattern. In addition, microhardness of the nitride coatings was measured by nanoindentation, and hardness higher than 30 GPa was exhibited in both nitride 2 and nitride 3. The microhardness test provided evidence that the multi-component nitride could be a potential candidate coating for tool steel.     

Multilayered gradient CrN/ZrN coatings synthesized by magnetron sputtering

The multilayer gradient CrN/ZrN coatings were synthesized by a dual cathode DC magnetron sputtering.The influence of different species of reaction gases and partial pressures on structure and mechanical properties was investigated using XRD, AES, XPS, and nanoindentation. The results show that N2-NH3 mixture process gas is of benefit to the synthesis of superhard multilayered gradient CrN/ZrN coatings. The presence of the preferred orientations of CrN(111), (200) and ZrN (111), (220) in the structure is a main reason for superhardness of multilayered gradient coatings.     

立方相对超细晶梯度硬质合金微观组织的影响

以超细WC粉末为原料,采用低压预烧结和梯度烧结两步法制备了超细晶梯度硬质合金。通过添加不同的立方相,研究了立方相对超细晶梯度硬质合金组织和性能的影响。结果表明,仅添加Ti(C,N)可以形成较厚的梯度层,但梯度烧结后WC晶粒尺寸有较大的增长。(W,Ti)C和(Nb,Ta)C的加入不利于较厚梯度层的形成,但在梯度烧结过程中可以抑制WC晶粒的生长。添加(Ti,W)C的合金在梯度烧结后出现了少量尺寸大于1 μm的WC晶粒,(Ta,Nb)C的加入可以很好的抑制合金中芯环结构立方相的形成。     

Microstructure of aluminized stainless steel 310 after annealing

The aluminized coating on type 310 stainless steel prepared by high-activity Al pack cementation method has been annealed at 900 °C for 12 h to transform the brittle δ-Fe₂Al₅ phase into the more ductile β-FeAl phase. The microstructure is studied in detail with transmission electron microscopy. The thick outer layer has β-(Fe, Ni)Al as matrix with cube-like Cr₂Al precipitates. The interfacial layer has a thin layer of metastable FCC phase (layer I) and then mixed β-(Fe, Ni)Al grains and α-(Fe, Cr) grains (layers II and III). The Cr₂Al precipitates are present in the β-(Fe, Ni)Al grains in layer II but not in those in layer III, while β-FeAl precipitates are present in the α-(Fe, Cr) grains in both layers. The orientation relationships between various phases, the formation of the layers, and the precipitation of Cr₂Al in β-(Fe, Ni)Al are discussed.     

真空退火处理对掺Cr类石墨碳膜力学和摩擦学性能的影响

采用闭合场非平衡磁控溅射离子镀技术制备了掺Cr类石墨镀层,研究了真空退火温度对镀层的硬度、结合强度、摩擦系数和比磨损率的影响规律,通过X射线衍射(XRD)分析了镀层结构随退火温度的变化.结果表明:随退火温度的升高,镀层有新相生成,镀层的膜基结合强度降低,镀层硬度随温度的升高先增加后降低,退火温度为500℃时,镀层显微硬度最大;随退火温度的升高镀层摩擦系数呈现出先降低后升高的变化趋势,比磨损率逐渐增大.     

Tool steel and copper coatings by friction surfacing - A thermography study

Infrared thermography was used to record thermal profiles during friction surfacing. Thermal profiles for different sets of consumable rod/substrates (tool steel/steel; copper/steel and copper/copper) were recorded and analyzed. The thermal profiles showed distinct stages of plastic deformation with respect to temperature. The mechanism of bonding or no-bonding was discussed based on thermal profile data. It was found that a metallurgically bonded coating can be obtained if the flow stress of the plasticized material is comparable with the localized stress developed due to axial loading.     

电弧喷涂铁基非晶涂层摩擦磨损性能分析

采用电弧喷涂技术在低碳钢基体上制备Fe-（Cr,Ni）-（C,B）系非晶合金涂层。利用X射线衍射仪、扫描电子显微镜和差热分析仪对涂层的相组成、微观组织和热稳定性进行了分析,用MRH-3型高速环块磨损试验机研究涂层的干摩擦磨损行为.结果表明,涂层中含有一定量的非晶相,呈典型的热喷涂层状组织结构,孔隙率较低;涂层具有良好的热稳定性,在500℃以下使用不会发生晶化转变;涂层具有较高的显微硬度和优异的摩擦磨损性能,平均显微硬度为1 155 HV0.1,相同试验条件下,涂层的相对耐磨性能约为Q235钢的13.3倍,涂层的磨损机制主要以疲劳磨损为主.