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.     

Processing optimization,surface properties and wear behavior of HVOF spraying WC–CrC–Ni coating

In this work, the optimal coating process (OCP) designed by Taguchi program for high velocity oxy-fuel (HVOF) thermal spraying WC–CrC–Ni powder on Inconel 718 substrate (IN 718) is obtained by optimizing hardness (38 FMR oxygen flow rate, 53 FMR hydrogen flow rate, 25 g/min powder feed rate and 7 in. spray distance). Oxygen flow rate affects hardness mostly. The surface properties such as microstructure, crystalline phase, hardness, and porosity of WC–CrC–Ni coating have been investigated. The phase of coating has been changed during the OCP spraying because a portion of carbides, such as WC, Cr₇C₃, Ni₃C decomposes to W₂C, Cr, Ni and free carbon. Hardness (1150 ± 50 Hv) and porosity (1.2 ± 0.2%) of the OCP coating have been improved by optimization. The friction and wear behaviors of the WC–CrC–Ni coating, electrolytic hard chrome (EHC) plating and IN 718 have been studied comparatively. The lubrication due to free carbon and metal oxide debris results in a decrease of friction coefficients of the WC–CrC–Ni, compared to EHC and IN 718 at both 25 and 450 °C. It is concluded that HVOF WC–CrC–Ni coating performs more excellent anti-wear than others at both temperatures.     

Reactive oxide-dispersed Ni3Al intermetallic coatings by sediment co-deposition

Ni–Al-reactive oxide (REO) ternary composite coatings were successfully deposited from a Watt's nickel bath containing Al particles and REO particles via the sediment co-deposition (SCD) technique. Three different composite systems, Ni–Al-nano CeO₂, Ni–Al-5 μm CeO₂, and Ni–Al–Y₂O₃ (<1 μm), were studied. The volume fraction of the Al particles in the composite coatings was significantly decreased with an increase of the REO bath loading, while the REO particle content positively increased. The REO particles in the plating bath evidently interfered with the deposition of Al particles. The development of intermetallic phases in the annealed Ni–Al-REO composite coatings mainly depended on the Al content in the coatings. REO-dispersed Ni₃Al intermetallic coatings could be formed as long as the REO particle loading in the bath was controlled below a critical level. Transformation of CeO₂ phase to CeAlO₃ was found in the Ni–Al-nano CeO₂ composite coatings during the annealing treatment at 800 °C.     

Annealing effects on the intermetallic compound formation of cold sprayed Ni,Al coatings

The annealing of Ni and Al coatings under various conditions on substrates fabricated by a cold gas dynamic spray process (CDSP) were investigated. The powder particles were accelerated through a standard De Laval-type nozzle with air used as the main carrying gas. The coatings were annealed at 450–550 °C in either argon or air atmospheres for 4 h. In the case of Ni coatings during annealing both in argon and air atmospheres, intermetallic compound layers such as Al₃Ni and Al₃Ni₂ were observed at the interfaces between the Ni coating and Al substrate. Also, the intermetallic layer formation of Al₃Ni and Al₃Ni₂ at the interfaces depended on the solid-state diffusion and the annealing temperature. The intermetallic compound AlNi was obtained at the interface of Al coating on a Ni substrate by low-temperature annealing under the melting temperature.     

Effect of Ni content on the compression properties and abrasive wear behavior of the (TiB2–TiCxNy)/Ni composites

The (TiB₂–TiC_xN_y)/Ni composites were fabricated by the method of combustion synthesis and hot press consolidation in a Ni–Ti–B₄C–BN system. The effect of Ni content on the microstructure, hardness, compression properties and abrasive wear behavior of the composites has been investigated. The results indicate that with the increase in Ni content from 30 wt.% to 60 wt.%, the average size of the ceramic particles TiB₂ and TiC_xN_y decreases from 5 μm to ≤ 1 μm, while the hardness and the abrasive wear resistance of the composites decrease. The composite with the Ni content of 30 wt.% Ni possesses the highest hardness (1560.8 Hv) and the best abrasive wear resistance. On another hand, with the increase in the Ni content, the compression strength increases firstly, and then decreases. The composite with 50 wt.% Ni possesses the highest compression strength (3.3 GPa). The hardness and fracture strain of the composite with 50 wt.% Ni are 1251.2 Hv and 3.9%, respectively.     

A comparative study of laser cladding high temperature wear-resistant composite coating with the addition of self-lubricating WS2 and WS2/(Ni–P) encapsulation

In order to inhibit its decomposition and improve its compatibility with the metal matrix during laser cladding, WS₂ powder was encapsulated with a layer of micro Ni–P by electroless plating. The microstructure and tribological properties of the NiCr–Cr₃C₂/30%WS₂ and NiCr–Cr₃C₂/30%WS₂(Ni–P) high temperature self-lubricating wear-resistant composite coatings at RT (room temperature), 300 °C and 600 °C were investigated, respectively. It was found that the NiCr–Cr₃C₂/30%WS₂(Ni–P) coating had a microstructure consisting of primary Cr₇C₃ dendrite, γ-(Fe,Ni)/Cr₇C₃ eutectic and solid lubricant particles WS₂ and CrS, Ni–P electroless plating had decreased the decomposition of WS₂ to some extent, the WS₂ solid lubricant particles dispersed in the ductile γ-(Fe,Ni)/Cr₇C₃ matrix. Friction and wear experiments indicated that the tribological properties of the NiCr–Cr₃C₂/30%WS₂(Ni–P) coating was better than that of NiCr–Cr₃C₂/30%WS₂ coating, the NiCr–Cr₃C₂/30%WS₂(Ni–P) coating presents lower friction coefficient at RT and 300 °C and lower wear rate from RT to the elevated temperature of 600 °C.     

The constitution of the ternary system Fe–Ni–Si

The ternary system Fe–Ni–Si was investigated using X-ray diffraction (XRD), metallography (SEM), energy dispersive spectroscopy (SEM/EDS), magnetic susceptibility measurements, and differential thermal analysis (DTA). The existence of the ternary phase τ is corroborated and its crystal structure is confirmed to be isostructural to Cr₃Ni₅Si₂. At 700 °C the homogeneity of this phase extends from 43 to 55 at.% iron at constant 20 at.% Si. Furthermore, for the binary phases NiSi₂, Ni₂Si and Ni₃₁Si₁₂ extensive solubilities for iron are found, while the solubility of Fe in NiSi, Ni₃Si₂ or Ni₃Si does not exceed 5 at.%. On the other side of the system, the phases FeSi and Fe₃Si have large solubilities for Ni, while this is rather limited in FeSi₂. The (binary high temperature) phase Fe₅Si₃ is stabilized by Ni at least down to 700 °C. Tie lines exist between τ and solid solutions based on Fe₃Si, Ni₃₁Si₁₂ as well as γ (Ni). DTA measurements for the vertical section Fe₂Si–Ni₂Si strongly indicate that Fe₂Si and θNi₂Si form a complete series of solid solutions θ(Fe, Ni)₂Si and are thus isostructural. A critical evaluation of the available crystal structure data for Fe₂Si supports this assumption. Iron rich θ(Fe, Ni)₂Si is a weak ferromagnet. The magnetic moment of ～1 μB per Fe-atom in θ(Fe, Ni)₂Si is only half of the magnetic moment per Fe-atom measured for τ Fe₅Ni₃Si₂. A reaction scheme accounting for all DTA data of the entire system is established and in combination with observations on the first crystallizing phase(s) the liquidus surface of Fe–Ni–Si is revised.     

TC4钛合金表面激光熔覆WC增强镍基复合涂层的组织及耐磨性

为提高TC4钛合金的耐磨性,利用激光熔覆技术(laser cladding,LC)在TC4钛合金表面制备Ni60+50%WC(体积分数)和deloro22(d22)粉末打底+(Ni60+50%WC)2种耐磨复合涂层。采用扫描电子显微镜(SEM)、能谱仪(EDS)以及X射线衍射仪(XRD)来表征涂层的微观结构和物相组成;使用HV-1000显微维氏硬度计、HRS-2M型高速往复摩擦磨损试验机和WDW-100D电子万能试验机来分析涂层的性能。结果表明:2种涂层均由W₂C、TiC、Ni₁₇W₃、Ni₃Ti和Ti_xW_1-x相组成,2种涂层不仅与基体呈现出优异的冶金结合,而且组织均匀致密,没有裂纹瑕疵;由于涂层中存在着原位合成的硬质相和细晶强化共同作用使得涂层硬度显著提高,约为TC4基体的2.82倍;2种涂层的摩擦系数(COF)和磨损量都远低于TC4钛合金基体;Ni60+50%WC复合涂层和d22粉末打底+(Ni60+50%WC)复合涂层的抗剪切结合强度分别为188....     

High hydrogen permeability in the Nb-rich Nb–Ti–Ni alloy

The microstructure and the hydrogen permeability of the Nb-rich Nb–Ti–Ni alloy, i.e., the Nb₅₆Ti₂₃Ni₂₁ alloy were investigated and compared with those of the Nb₄₀Ti₃₀Ni₃₀ alloy. The Nb₅₆Ti₂₃Ni₂₁ alloy consisted of a combination of the primary phase bcc- (Nb, Ti) solid solution with the eutectic phase {bcc- (Nb, Ti) + B2-TiNi}. The volume fraction of the former and the latter phases were 62 and 38 vol.%, respectively. The Nb₅₆Ti₂₃Ni₂₁ alloy showed the higher Φ value of 3.47 × 10⁻⁸ (mol H₂ m⁻¹ s⁻¹ Pa^−0.5) at 673 K, which is 1.8 times higher than that of the Nb₄₀Ti₃₀Ni₃₀ alloy, which has been reported to be highest in the Nb–Ti–Ni system. The present work demonstrated that the Nb-rich Nb–Ti–Ni alloys consisting of only the primary phase bcc- (Nb, Ti) and the eutectic phase {bcc- (Nb, Ti) + B2-TiNi} are promising for the hydrogen permeation membrane.     

Microstructure and cavitation erosion behavior of WC–Co–Cr coating on 1Cr18Ni9Ti stainless steel by HVOF thermal spraying

A WC–Co–Cr coating was deposited by a high velocity oxy-fuel thermal spray (HVOF) onto a 1Cr18Ni9Ti stainless steel substrate to increase its cavitation erosion resistance. After the HVOF process, it was revealed that the amorphous phase, nanocrystalline grains (Co–Cr) and several kinds of carbides, including Co₃W₃C, Co₆W₆C, WC, Cr₂₃C₆, and Cr₃C₂ were present in the coating. The hardness of the coating was improved to be 11.3 GPa, about 6 times higher than that of the stainless steel substrate, 1.8 GPa. Due to the presence of those new phases in the as-sprayed coating and its higher hardness, the cavitation erosion mass loss eroded for 30 h was only 64% that of the stainless steel substrate. The microstructural analysis of the coating after the cavitation erosion tests indicated that most of the corruptions took place at the interface between the un-melted or half-melted particles and the matrix (Co–Cr), the edge of the pores in the coating, and the boundary of the twin and the grain in the stainless steel 1Cr18Ni9Ti.     

Grain-boundary diffusion of nickel in Cr-, Fe-, and Zr-modified Ni3Al intermetallic

Tracer grain-boundary diffusion of ⁶³Ni in slightly hypostoichiometric (x_Al < 25 at.%) Ni₃Al alloys containing several percents of Cr, Fe and Zr was studied using both serial sectioning and residual activity methods. Measurements of grain-boundary diffusivity P were carried out in the temperature interval 873–1273 K. It was found that the additions of Cr, Fe and Zr decrease the P and increase the activation enthalpy of ⁶³Ni grain-boundary diffusion.     

Effects of Ti addition on microstructure homogenization and wear resistance of wide-band laser clad Ni60/WC composite coatings

Ni60/WC composite coatings were fabricated by wide-band laser cladding. The effects of Ti addition on microstructure homogenization and coating properties were investigated. Coating microstructure, phase constitution, microhardness and wear resistance were studied and grading analysis of in-situ synthesized ceramic particles was carried out. Results indicated that ceramics particles of Cr₅B₃ and M₂₃C₆ (M represents for Cr and W) carbides were in-situ synthesized in original Ni60-20WC coatings. With Ti addition, dissolution of original WC was facilitated and lots of TiC particles were synthesized instead of M₂₃C₆ carbides. Furthermore, the block Cr₅B₃ particles were greatly homogenized due to the net structure formed by dispersive TiC particles. With Ti addition, D50 of particle size decreased from 8.94 μm to 4.45 μm and particle morphologies were transformed from star-like shapes to uniform square blocks. Microhardness distribution became more uniform with average value decreased from 799 ± 89 HV_0.2 to 744 ± 77 HV_0.2. Due to the homogenized ceramic particles, wear resistance of coatings with Ti addition was enhanced to 2.6 times that of the original coatings.     

Splitting phenomenon in the precipitation evolution in an Fe–Ni–Al–Ti–Cr stainless steel

The evolution of precipitation and mechanical properties of an Fe–Ni–Al–Ti–Cr stainless steel was studied during ageing at 525 °C. Atom probe tomography and transmission electron microscopy were applied to follow the microstructural evolution. An initial hardening reaction, which is remarkable in terms of extent, is reported to be caused by the formation of complex multi-component clusters. They are composed mainly of Ni, Al and Ti. After ageing to peak hardness (3 h), splitting of these clusters into spherical and elongated particles was observed. Based on the chemical composition, the spherical precipitates were identified to be of type NiAl B2, and the elongated particles were associated with the η-phase (Ni₃(Ti, Al)). Βoth types of precipitates contribute to the strength of the material.     

Microstructure and hydrogen permeation of cold rolled and annealed Nb40Ti30Ni30 alloy

The ultimate rolling reduction rate (r_u) of the as-cast Nb–TiNi alloys was evaluated by measuring the thickness changes in cold rolled samples. Furthermore, the effects of cold rolling and subsequent anneal on hardness, microstructure, hydrogen permeability (Φ) and hydrogen flux J of the as-cast Nb₄₀Ti₃₀Ni₃₀ alloy (mol%) were examined by a Vickers hardness tester, a scanning electron microscope (SEM), and a mass flow meter, respectively. The value of Φ for the Nb₄₀Ti₃₀Ni₃₀ alloy was reduced with increasing rolling reduction rate and attained to one third of the original one by 50% rolling reduction, but recovered to the original one by anneal at 1373 K for 605 ks. Hydrogen flux J varied inversely proportional to the membrane thickness at 673 K. J of 12 ccH₂/cm²/min was attained for the sample with the thickness of 120 μm. The present work has demonstrated that rolling and the subsequent anneal are effective and useful for the preparation of the hydrogen permeation Nb–TiNi alloy membrane.     

Amorphous and nanocrystalline Al82Ni10Y8 alloy powder prepared by gas atomization

An Al–10Ni–8Y (at.%) alloy was atomized by Ar gas and the morphology, microstructure, thermal stability, phase composition and microhardness of the as-atomized powder were investigated. Most of the powders are spherical in shape, but the surface morphology was different for powder of different size. The cross-section microstructure of powder with size below 15 μm in diameter showed no detailed feature, indicating existence of amorphous phase or nanocrystalline structure. The as-atomized powder showed four distinct exothermic peaks when heated at 296, 340, 366 and 456 °C. The glass transition temperature T_g, crystallization temperature T_x, and the temperature interval of the supercooled liquid region ΔT_x (=T_x−T_g) were detected to be about 266, 288 and 22 °C. The Al₈₂Ni₁₀Y₈ alloy powder exhibits a high Vickers hardness of 230.6, and shows great potential for structural application.     

The scaling behavior of sputtered Ni3Al coatings with and without Pt modification

A Ni₃Al nanocrystalline film was deposited on the Ni₃Al-based superalloy IC6 by magnetron sputtering. Pt-modified coatings were obtained by electroplating 1.5 μm platinum onto the sputtered Ni₃Al film with and without annealing. Duplex scale developed on the sputtered Ni₃Al film after 20 h isothermal exposure at 1050 °C. Uphill diffusion of Al occurred in the Pt-modified coating system, which implied that inward diffusion of Al from coating to substrate was prevented. Platinum promoted selective oxidation of Al, although 5 at.% Pt was insufficient for the development of exclusive alumina scale on the Pt-modified sputtered γ′-Ni₃Al coating.     

Microstructural characterization and hardness evaluation of HVOF sprayed Ni–5Al coatings on Ni- and Fe-based superalloys

HVOF sprayed Ni–5Al coatings on Ni- and Fe-based superalloy substrates were characterized to assess the microstructural features and strength in the as deposition condition for their applications in high-temperature corrosive environment of gas turbine. X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), and X-ray mapping analysis are used to characterize the Ni–5Al coatings. The dense coatings with less porosity and inclusions were produced using HVOF process. The deposited Ni–5Al coatings exhibited splat like layered morphologies due to deposition and resolidification of successive molten and semi molten powder particles. The hardness of coatings on three different superalloy substrates was measured and it was in the range of 210–272 Hv. The average bond strength and surface roughness of the as-sprayed coatings were 42.62 MPa and 9.22–9.45 μm, respectively. Diffusion of alloying elements from the substrate into the coating has occurred in all the three superalloy substrates as observed from the X-ray mapping analysis.     

The structure and mechanical and tribological properties of TiBCN nanocomposite coatings

TiBCN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system using pulsed magnetron sputtering of a TiBC compound target with various Ar/N₂ mixtures. TiBCN coatings were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, Rockwell C indentation and ball-on-disk wear tests. The coatings with a nitrogen content of less than 8 at.% exhibited superhardness values in the range of 44–49 GPa, but also showed poor adhesion and low wear resistance. Improvements in the coating adhesion, H/E ratio and wear resistance were achieved together with a decrease in the coating hardness to 35–45 GPa as the N content in the coatings was increased from 8 to 15 at.%. The microstructure of the coatings changed from a nano-columnar to a nanocomposite structure in which 5–8 nm nanocrystalline Ti(B,C) and Ti(N,C) compounds were embedded in an amorphous matrix consisting of BN, free carbon and CN phases. With a further increase in the N content in the coatings to levels greater than 20 at.%, the inter-particle spacing of the nanocrystalline compounds increased significantly due to the formation of a large amount of the amorphous BN phase, which also led to low hardness and poor wear resistance of the TiBCN coatings.     

Microstructure and mechanical properties of TiB2–SiC ceramic composites by Reactive Hot Pressing

TiB₂–SiC ceramic composites with different contents of Ni as additive were prepared by the Reactive Hot Pressing (RHP) process at 1700 °C under a pressure of 32 MPa for 30 min. For comparison, a monolithic TiB₂ ceramic and TiB₂–SiC ceramic composite were also fabricated under the identical temperature, pressure and holding time by the Hot Pressing (HP) process. The effects of the fabrication process and Ni on the microstructure and mechanical properties of the composites were investigated. About 8 vol.% of elongated TiB₂ grains with an aspect ratio of 3–6 and a diameter of 0.5–1 μm were produced in the composite prepared by the RHP process. The improvement of the fracture toughness was attributed to the toughening and strengthening effects of SiC particles and the elongated TiB₂ grains such as crack deflection. The TiB₂–SiC–5 wt.% Ni ceramic composite had the optimum mechanical properties with a flexural strength of 858 ± 87 MPa, fracture toughness of 8.6 ± 0.54 MPa·m^1/2 and hardness of 20.2 ± 0.94GPa. The good mechanical properties were ascribed to the relatively fine and homogeneous microstructure and the strengthening effect of Ni. Ni inhibited the anisotropic growth of TiB₂.     

Phase equilibria between the B2, L12, and fcc phases in the Ir–Ni–Al system

The isotherms of the Ir–Ni–Al in the composition range up to 50 at% Al are presented at 1573 K. The phase constitution and microstructure of the Ir–Ni–Al alloys were examined using X-ray diffractometry (XRD), scanning electron microscopy (SEM) with an electron probe microanalyzer (EPMA), and transmission electron microscopy (TEM) after heat treatment at 1573 K for 168 h. The B2-NiAl and B2-IrAl phases connected with each other at 1573 K. The highest solubility limit of Ir into Ni₃Al was about 3.5 at% in the tested alloys. Then, a wide fcc + B2 and a narrow fcc + L1₂ and B2 + L1₂ two-phase region appeared in the isothermal section. In part of the B2 phase, a martensitic transformation from the B2 to the L1₀ phase was observed.