Pack Cementation Method Research Articles

High heat flux ablation behaviors of Ir-Hf coatings in wind tunnel tests up to 6.6 MW/m²

The Ir-Hf coatings have good resistance to oxidative ablation, in order to investigate the ablation resistance limit and ablation failure mechanism of the Ir-Hf coatings, graphite/Re/Ir/Ir-Hf samples were prepared by an optimized pack cementation method. The Ir-Hf coating samples were tested for anti-ablation properties under stepwise and constant working conditions in a high-frequency plasma wind tunnel, respectively. The results showed that the Ir-Hf coating passed the high-frequency plasma wind tunnel test at a heat flux of 5.7 MW/m2 for 650 s without defects. And the heat flux limit of the Ir-Hf coating was about 6.6 MW/m2 in the plasma wind tunnel with a lifetime no less than 400 s and a surface temperature of about 2200℃, exceeding most of the reported heat flux limits for non-ablative materials, such as SiC, ZrB2 and HfC. The failure mechanism of the Ir-Hf coating is as follows: when the surface temperature reaches a certain level, the interface temperature between Ir and the oxide layer will exceed its low eutectic point and a liquid phase will appear, triggering failure. The Ir-Hf coatings have the advantages of high heat flux resistance, zero ablation, low thermal response and good protection of the graphite substrate, which makes them promising as the thermal protection coatings in ultra-high temperature (over 2000 °C) aerospace applications.

Microstructure and properties of multicomponent silicide ceramic coatings on Ta substrate prepared by slurry sintering method

High entropy silicide (Mo0.2Cr0.2Ta0.2Nb0.2W0.2)Si2 (named as MeSi2) coating was successfully prepared on Ta substrate by slurry sintering method. Firstly, precursor powders were initially obtained through mechanical alloying of silicide powders. Then powder slurry was coated on Ta substrate, and then the samples were sintered. For comparison, TaSi2 coating prepared by halide-activated pack cementation method was synthesized. Subsequently, the static oxidation resistance of both MeSi2 coating and TaSi2 coating was examined at 1200 °C, results revealing that the MeSi2 coating demonstrates an effective protection time of more than 60 h. The protective effect and duration of the MeSi2 coating on Ta substrate are significantly greater than that of TaSi2, indicating an improvement oxidation resistance due to the high entropy effect of the silicide coating. After oxidation, the coating evolved an outer SiO2 layer, followed by MeSi2, Me5Si3, TaSi2, and Ta5Si3 layers. As the oxidation progressed, MeSi2 gradually transformed into Me5Si3, leading to a loss of the coating's antioxidant capacity.

Deposition of a low-activity type cobalt-modified aluminide coating by slurry aluminizing of a pre-Co-electroplated Ni-based superalloy (IN738LC)

Incorporating the Co element into the β-NiAl phase as a third element enhances the hot corrosion and oxidation properties of aluminide coatings. The deposition of Co-modified aluminide coatings is limited to co-deposition by the pack cementation method or a two-step pack cementation process of Co and Al, so far. This study investigates the possibility of depositing a low-activity type of Co-modified aluminide coating by combining the electroplating process with the slurry aluminizing method. To accomplish this objective, different thicknesses of Co-electroplated layers, deposited by a Watts bath, ranging from 5 to 20 μm are slurry aluminized using a slurry consisting of Al particles as the Al source and a PVA aqueous solution as the binder at 1100 °C for 2 h. Formation mechanisms are discussed through slurry aluminizing of 5, 10, and 20 μm thick Co-electroplated layers at the temperature range of 700–1100 °C with 100 °C intervals at zero time. FE-SEM surface morphology, BSE-SEM cross-sectional observation, surface XRD characterization, and EDS elemental analysis are utilized to characterize the coatings. Results show a critical thickness of the Co layer is required to deposit a defect-free low-activity type of Co-modified aluminide coating, which is determined to be ∼10 μm in this study. The final aluminide coating thickness decreases from ∼140 to ∼65 μm by increasing the Co-electroplated layer thickness from 5 to 20 μm. The identified phases on the surface differ from β-NiAl to β-CoAl by increasing the Co-electroplated layer thickness up to critical value. The Void formation occurs by the Kirkendall effect in coatings with more Co-electroplated layer thickness than the critical value, segregating the coatings within the β-CoAl phase.

Thermal analyses and weight gain modeling study on Ti–Al – based intermetallic coated Ti6Al4V alloy

Abstract Ti6Al4V alloy is a commonly used α + β alloy among titanium alloys. In this study, in order to improve the oxidation resistance of the Ti6Al4V alloy, Ti–Al – based aluminum coating was deposited to the surface by the pack cementation method. The aluminizing process was carried out in an open atmosphere oven at 700 °C for 4 and 6 h. It has been observed that the coating layer thickness varies between 13 and 17 µm depending on the duration of cementation process. From XRD analysis, it has been detected the TiAl3, TiAl2, and TiAl phases on the coating layer. Aluminum coated and untreated Ti6Al4V alloys were subjected to oxidation tests at 800, 850, and 900 °C for 4, 20, and 40 h. The obtained nonlinear weight gain characteristic has been modeled to determine the coating status of the samples. It was determined that the highest weight gain was in the untreated sample. Using the provided model, samples were classified in terms of coating condition by systematic approach based on weight gain profile versus time. Oxidation tests also supported with DTA and TG analyses.

The Structure of Boride Diffusion Coatings Produced on Selected Grades of Structural Steels

In the article the microstructure and phase composition of boride coatings deposited on selected structural steels were investigated. The boride coatings were produced using pack cementation method using commercial EKABOR-2 mixture containing of 50 wt. % of new and 50 wt. % of used powder. Boride coatings were deposited on alloyed structural steels grades (PN/EN 10084 standard): 16MnCr5, 18CrNiMo7-6, 41CrAlMo7 42CrMo4. Cylindrical samples with a diameter of 30 mm and a height of 30 mm were boronized in powder at 1000°C for 2, 4 and 6 hours in an argon atmosphere. The process was carried out in an industrial CVD Bernex BPX 325S device. The microstructure was analyzed using scanning electron microscope Phenom XL equipped with EDS spectrometer. The XRD phase analysis was conducted using XTRa diffractometer (ARL). The thickness as well as phase composition was analyzed on coatings formed on each grades of steels. The most of obtained boride coatings were characterized by single-phase structure (Fe2B). The formation of brittle FeB phase was detected only on 16MnCr5 steel grades steels.

Improvement of wear and hot melt loss resistance of metal carbide layers on H13 steel

Abstract In this paper, H13 steel was pre-carburized. Then niobizing and vanadizing layers were prepared by pack cementation method. The high temperature friction and wear properties and hot melt loss properties of different layers and substrates were studied by microhardness tester, metallographic microscope, scanning electron microscope, energy dispersive spectrometer, high temperature friction and wear tester, optical profilometer and Raman spectrometer. The results show that the thickness of the vanadizing layer is 12.7 μm, and the microhardness of the niobizing layer and the vanadizing layer is close, which is about 5 times that of the matrix. The lowest wear rate at 500 °C of the vanadizing layer is 1.03 , which is about 1/6 of the matrix. The vanadizing layer and niobiumizing layer can effectively reduce the friction coefficient, greatly improve the surface hardness and wear resistance of H13 steel, and prolong its service life. The comprehensive performance of vanadizing layer is the best. The vanadizing and niobiumizing treatment can significantly improve hot melt loss resistance of H13 steel and it can be used to prolong the serving life of hot die casting mold for Al.

Ir–Zr coating through a pack cementation method for ultra-high temperature applications

An Ir–Zr intermetallic coating was prepared onto Re/Ir coated graphite through a pack cementation method. The microstructure, nanoindentation and ablation behaviors of the coating system were investigated. The Ir–Zr coating was about 20 μm thick and consisted of 4 intermetallic phases which showed a quasi-gradient transition in composition. Nanoindentation measurements indicated that most of the intermetallic phases had higher hardness but lower Young's modulus compared to pure iridium. By ablation test in a high-frequency plasma wind tunnel, the heat flux limit of the Ir–Zr coating was measured to be about 6.1 MW/m2, and the endurance time was about 100 s under this condition. The coating failed at ∼2240 °C during the ablation test when the iridium melted, but the unfused parts remained complete and in good adhesion with the iridium beneath. The average normal emissivity between 2 and 5 μm of the sample was measured to be ∼0.82 at around 2092 °C before failure, which was higher than pure iridium and bulk ZrO2.

LOW TEMPERATURE ALUMINIZATION EFFECT ON MONEL 400 ALLOY PRODUCED BY PACK CEMENTATION METHOD

In this study, aluminum coating process was performed on Monel 400 alloy at a temperature of 600°C using the low-temperature pack cementation method for durations of 2, 4, and 6 hours. The mixture for the coating consisted of metallic Al powder as the aluminum source, Al2O3 as the inert filler, and Ammonium Chloride (NH4Cl) as the activator. The formed coatings were characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses to examine their microstructures, and phase analyses were conducted using and X-Ray Difraction Analyses (XRD). SEM analysis revealed that the coating layers were homogeneous, compact, and pore-free, demonstrating a strong bond between the coating and the matrix. The thickness of the coating layer was measured from the surface to the matrix, and it was observed to vary between 4 µm and 10 µm. It was determined that 600°C was sufficient for the accumulation of an aluminide layer and a successful coating layer was obtained. The hardness values of the alumina layer formed on the surface were measured, and an increase in hardness values was observed with increasing process duration and temperature.

Effect of Si, Al2O3 additives on the ablation behavior of ZrB2-SiC coating with Al2O3-modified SiC bond coat for C/C composites

This work firstly evaluated the effect of temperature on the preparation of SiC coating using Al2O3 as catalyst by pack cementation (PC) method. SiC/ZrB2-SiC-Si (ZSS) and SiC/ZrB2-SiC-Al2O3 (ZSA) coating were prepared on the surface of C/C composites by PC combined with atmospheric plasma spraying (APS). The objective of this work is to study the influence of Si and Al2O3 additives for ablation performances of ZrB2-SiC coating. The coated samples were subjected to ablation test, and the phase composition and microstructure evolution were investigated. The results indicated that SiC/ZSA coating had better ablation resistance because phase transformation and growth of ZrO2 grain was restrained by Al2O3.

Refractory high-entropy aluminized coating with excellent oxidation resistance and lubricating property prepared by pack cementation method

Refractory high-entropy alloys (RHEAs) exhibit superior mechanical properties at high temperatures compared to that of conventional high-temperature alloys. However, some refractory metallic elements are highly susceptible to oxygen absorption at room temperature and the resulting oxide films are not protective, resulting in catastrophic oxidation before they can exhibit excellent mechanical properties. Therefore, it is essential for them to improve the high-temperature oxidation properties of RHEAs. The pack cementation method can be used to prepare the aluminized coatings on the surface of RHEAs to improve their high-temperature oxidation resistance. In the present work, the aluminized high-entropy coatings were prepared on the surface of as-cast Ta25Nb25W25V25 RHEAs. The diffusion activation energy required for aluminization was experimentally calculated to be 137.667 kJ/mol, thus the growth kinetics of the coating was constructed. Aluminized coatings with the thickness of ∼75 μm and Vickers hardness of ∼680 HV0.01 obtained by holding at 1100 °C for 9 h were selected for the study. The oxidation activation energy of the aluminized coating at 800–1000 °C was 96.981 kJ/mol, while that of as-cast RHEAs was only 48.816 kJ/mol, so the oxidation resistance of the specimen was greatly improved. At 20–600 °C, the aluminized coatings also exhibited excellent wear resistance and lubrication properties. In particular, the average coefficients of friction were reduced by 0.13–0.24 compared to that of as-cast RHEAs, which can be attributed to the AlW intermetallic compound particles formed within the aluminized coating acting as self-lubricating particles.

Microstructure and high-temperature oxidation behaviour of MoSi2 protective coatings on Mo-based combustion chamber in rocket engines

This paper presents a detailed characterization of the microstructure and high-temperature oxidation behaviour of MoSi2 coatings obtained by pack cementation methods on a Mo-based substrate. The author focused on the challenges of applying Mo-based combustion chambers in rocket engines. Due to these assumptions, the high-temperature oxidation resistance of MoSi2 coatings was analyzed in the temperature range of 1200–1700 °C. A particular area of interest was the surface condition of MoSi2 coatings after oxidation tests, characterized by their roughness. The presented studies showed very beneficial behaviour of oxidized MoSi2 coatings from the point of view of both protective coating's morphology and durability under these conditions and the surface roughness responsible for the gas flow stability in actual working conditions. The identified microstructural phenomena related to MoSi2-based coating formation, its thermal stability and oxidation interaction were described from the thermodynamic point of view. Those analyses revealed that thermodynamically the most stable silicide compound during the first stage of coating formation is Mo5Si3, not MoSi2. It suggests that the interaction between the Si-rich gas atmosphere and the Mo5Si3 layer determines the growth progress of silicide coating. The necessary condition for further growth is an excess of active silicon sources in the reactive atmosphere in the pack cementation process.

Modeling of Surface Modification of Stainless Steel by Halide Activated Pack Cementation Method

In high-temperature applications, ferrous-based materials are important due to their excellent combination of desirable mechanical properties, ease of production, corrosion resistance at room temperature and cost-effectiveness. However, mechanical properties must be optimized against environmental effects. Depending on the industrial applications, various corrosion types may also occur. An approach to preserve the mechanical properties of the structural alloy being protected against corrosion is the application of protective coatings to the surfaces. Diffusion coatings are an effective method to obtain corrosion, oxidation and abrasion resistance against detrimental conditions of high temperature. According to the literature, the halide activated pack cementation method has been widely used for ferrous-based materials for a long time. However, most studies concerned with developing coating applications are based on experimental investigations that include microscopic, chemical, and mechanical analyses. Limited studies have been conducted based on computational alloy approaches. In this study, Cr coating of the AISI 316L steel by halide activated pack cementation method was considered as a diffusional problem and the kinetics of the coating deposition process were examined. The effect of process variables such as temperature, time and the compositions of coating layers formed on the surfaces were investigated thermodynamically with Thermo-Calc software and kinetically with DICTRA module. This approach provides insight into the dependence of solid-state diffusions on the processing parameters, and a better understanding of the phases that form along the coating and substrate material.

Enhanced high temperature oxidation resistance of discontinuous distributed TiBw reinforced TA15 titanium alloy by simple pack cementation method

Discontinuous distributed TiB whiskers reinforced TA15 titanium alloy (TiBw/TA15) is a potential high-temperature structural material but has poor oxidation resistance. In this paper, an aluminide coating was prepared by pack cementation to enhance the oxidation resistance of TiBw/TA15 at 800 °C. The influences of TiBw on the formation mechanism of the aluminide coating were revealed by density functional theory. The oxidation resistance mechanism of the aluminide coating was investigated by experimental and theoretical methods at both macroscopic and atomic levels. The good oxidation resistance was mainly attributed to the dense and continuous Al2O3 layer formed by the TiAl3 phase, which effectively prevented the diffusion of oxygen to the substrate.

Tribological behavior of boronized Fe40Mn20Cr20Ni20 high-entropy alloys in high temperature

Boronization can improve the wear resistance of high-entropy alloys (HEAs). However, the tribological tests on boronized HEAs were generally carried out at room temperature. In fact, materials are often applied in high temperature. Therefore, it is essential to investigate the effect of boronization on the tribological properties and mechanism of HEAs in high temperature. In present work, the hot-rolled Fe40Mn20Cr20Ni20 HEAs were boronized by the pack cementation method at 900 °C for 6 h. The tribological tests of the alloys before and after boronization were conducted in 20–600 °C. The results showed that the boronized alloys showed higher wear resistance at 20–600 °C, whose average coefficients of friction and wear rate were lower than those of hot-rolled alloys. At 20–200 °C, the main wear mechanisms of the hot-rolled alloys were abrasive and adhesive wears; while the main wear mechanism of the boronized alloys was polishing effect. At 300–600 °C, the main wear mechanisms of the alloys before and after boronization were oxidation and abrasive wear. The wear rate was reduced by the B2O3 produced on the surface of the boronized layer during wear and the good thermal stability of the boronized layer, which indicated that boronization improved the wear resistance of HEAs in high temperature.

Comparative study on high-temperature oxidation behavior of MoSi2 and MoSi2/SiC-Mo2C composite coatings on Mo substrates at 1300 °C

In this study, MoSi2/SiC-Mo2C composite coatings and single-layer MoSi2 coatings are prepared on pure molybdenum substrates using the pack cementation method. The oxidation behavior of the coatings at 1300 °C is investigated. The calculated thermal stress of the MoSi2/SiC-Mo2C composite coatings is 366.76 MPa, whereas that of the single-layer MoSi2 coating is 1775.98 MPa. After oxidation for 30 h, the masses of the MoSi2/SiC-Mo2C composite coatings and MoSi2 single-layer coating increased by 0.61 and 0.38 mg/cm2, respectively. The average service life of the MoSi2/SiC-Mo2C composite coatings is 56.67 h, whereas that of the MoSi2 single-layer coating is only 46.67 h. The excellent performance of the MoSi2/SiC-Mo2C composite coatings can be attributed to the formation of a SiC-depleted zone, which reduces the generation of cracks within the coating. In addition, the Mo2C transition layers can effectively delay the mutual diffusion between the MoSi2 coating and substrate.

The preparation and properties of Mn–Co–O spinel coating for SOFC metallic interconnect

To meet the performance requirements of solid oxide fuel cell (SOFC) metallic interconnect, the Mn–Co–O spinel coating is prepared on the surface of AISI430 by pack cementation method to reduce the growth kinetics of oxides and inhibit the outward diffusion of Cr. The microstructural characterization shows that a dense, uniform, defect-free spinel coating is successfully fabricated on the surface of AISI430. Under the simulated SOFC cathode environment, the weight gain of coated steel (0.608 mg cm−2) after oxidation at 800 °C for 800 h is significantly lower than that of uncoated (1.586 mg cm−2). In addition, the area specific resistance (ASR) of the coated steel oxidized for 500 h is 17.69 mΩ cm2, much smaller than that of the bare steel, indicating that the oxidation resistance and electrical conductivity of AISI430 are significantly improved by Mn–Co–O spinel coating. Cross-sectional observations of the Mn–Co–O spinel coating are conducted to assess the compatibility of substrate with the adjacent coating and its effectiveness in reducing the growth of the Cr2O3 layer.

Improved wear and hot melting loss resistance of a vanadium carbide layer prepared on H13 steel

To improve surface properties of H13 steel and provide guidance for extending service life. Method: tantalizing, niobizing and vanadizing layers were prepared on H13 steel using pack cementation method under 940 °C, 7 h condition. The wear and hot melting loss resistance of the layers was evaluated. Conclusion Compared with normal treated H13 steel, the wear resistance is increased by nearly 6 times, and hot melt loss resistance is improved many times. The vanadizing layer can effectively improve the wear and hot melt resistance of H13 steel, which is perspective to prolong the service life.

Oxidation behaviour of a MoSiBTiC alloy coated by a (Si+B) co-deposition pack cementation method

A MoSiB based coating was applied to the 1st-generation MoSiBTiC alloy using pack cementation process. After conditioning at 1300 °C for 10 h in air, the coating developed into four layers: an oxide layer, a MoSi2 layer with Mo5Si3 and MoB precipitates, a Mo5Si3 layer, and a MoB+Mo5SiB2 (T2) layer. However, visible holes often formed in the coating due to defects, and the oxidation proceeded to the substrate during subsequent cyclic oxidation. In a controlled test on a MoSiBTiC alloy with lower TiC volume fraction, an intact coating formed after the conditioning at 1300 °C and provided an effective oxidation resistance.

The formation of Al-Si aluminide coatings by pack cementation method on TNM-B1 intermetallic alloy

The TiAl intermetallics are the promising material for aerospace application. According to its insufficient oxidation resistance above 900oC the using of protective coatings is necessary. The diffusion aluminide coatings based on TiAl2 or TiAl3 phases permits to formation of alumina scale on the surface of TiAl alloys. The pack cementation with Si doping is one of the most popular method of this type of coatings production. In present article the influence of Si content in the pack, process time and temperature during pack cementation process were investigated. The thickness of obtained coating was in range 20-50 μm. When Si content was higher the formation of titanium silicides was observed using almost all analysed values of process parameters. The results showed that using of 24 wt. % Si containing pack and process parameters: 4h/950oC enables to obtain the coating characterized by optimal thickness and structure. The porosity and cracks in coatings according to TiAl phases brittleness was observed.

Improvement of High-Temperature Oxidation Resistance of Iron-Base Heat Storage Materials by Aluminizing Using Pack Cementation Method

Improvement of High-Temperature Oxidation Resistance of Iron-Base Heat Storage Materials by Aluminizing Using Pack Cementation Method