Pack Cementation Method Research Articles

Investigation of the Preparation, Corrosion Inhibition, and Wear Resistance of the Chromized Layer on the Surfaces of T9 and SPCC Steels.

To improve the corrosion inhibition and wear resistance of materials, the pack cementation method was used to prepare chromized coatings on the surfaces of high-carbon T9 steel and low-carbon SPCC steel. The results showed the formation of a uniform and dense double-layer structure with a thickness of ~10 μm on the surfaces of two different types of steel. The coating layer for T9 steel was mainly composed of Cr23C6 and Cr7C3, while that for SPCC steel was mainly composed of Cr23C6 and Fe-Cr solid solution. Additionally, both of the steels showed different hardness distributions. The hardness measurements of the outer layers of the T9 steel and SPCC steel were ~1737.72 HV and 1771.91 HV, while the hardness values of the secondary layers were 1378.31 HV and 448.52 HV, respectively. The polarization curves in 3.5 wt.% NaCl solution demonstrated the better corrosion resistance of the chromized coating. Chromizing increased the corrosion potential by ~0.2 V and reduced the corrosion current density by one order of magnitude. Under the presence of an 8 N load, the friction factor before and after the chromizing of T9 steel was about 0.69, and the mass wears were 2 mg and 0.6 mg, respectively. Meanwhile, the friction factor of the SPCC steel before and after chromizing was about 0.73, with respective mass wears of 2 mg and 2.9 mg. The wear resistance of T9 steel after chromizing was superior, but it became worse after chromizing for the SPCC steel.

High temperature oxidation and ablation behaviors of HfB2-SiC/SiC coatings for carbon/carbon composites fabricated by dipping-carbonization assisted pack cementation

To improve the uniformity and the content of HfB2 in HfB2-Si-based ceramic coating and alleviate the damage of substrate, and then enhance the high-temperature (1700 °C) oxidation and cyclic ablation resistances of carbon/carbon composites, a close-knit double layer HfB2-SiC/SiC coatings with a mosaic structure and high content of HfB2 were prepared by a novel dipping-carbonization assisted pack cementation methods (DPCHS/S). In contrast, a HfB2-SiC/SiC coatings were also fabricated by pack cementation (PCHS/S). Results revealed that the oxidation and ablation protective performances of the DPCHS/S coatings were superior to those of PCHS/S coatings. After 30 thermal cycles between 1500 °C and room temperature, the mass gain of the coated sample was 0.78%, and the mass loss was 1.65% after oxidation at 1700 °C for 156 h. Moreover, under an oxyacetylene torch ablation for 180 s (3 cycles), the linear ablation rate of the DPCHS/S coated specimen was 1.62 μm/s, which was much lower than that of PCHS/S coated specimen (3.08 μm/s).

Preparing the SiC coated C/C composites with excellent mechanical and antioxidative properties using a buffer layer

The preparation of SiC coating on C/C composites via a pack cementation method would cause serious mechanical damage to C/C substrate due to the siliconization corrosion by molten silicon during the ultra-high-temperature preparation process (2173–2373 K). In order to prepare SiC coated C/C composites with excellent mechanical and antioxidative properties, we applied a buffer layer on the surface of C/C to inhibit siliconization corrosion and densify coating. Results showed that the siliconized area ratio of the C/C substrate was decreased from 60.9% to 24.8%, and its bending strength was increased from 36.9 MPa to 60.6 MPa. Moreover, the mass loss of the modified SiC coated C/C sample has reduced by ~4.14 times after oxidation for 144 h in air at 1773 K and decreased from 2.44% to − 0.15% after suffering 50 thermal cycles between room temperature and 1773 K.

Wear and oxidation performances of low temperature aluminized IN600

In this study, an aluminide coating was applied to the surface of the Inconel 600 (IN600) superalloy to improve the high-temperature oxidation and wear resistance. The low-temperature aluminizing process was carried out for 3 and 5 h at 650 and 700 °C temperatures without using a protective atmosphere. A continuous and homogeneous coating has been created by providing aluminium diffusion inward in the cross-section of the alloy processed under low temperature and high activity conditions with the pack cementation method. It was observed that there was a super bonding between matrix and coating layers which are smooth, dense and porosity free. Dominant phases of Ni2Al3 and NiAl3 were detected by XRD analysis. The layer thickness was measured from the surface to the matrix and changed from 25 to 75 μm which was increased with increasing process duration and temperature. The aluminizing process positively affected the wear resistance with the durable layers formed on the surfaces. After the isothermal oxidation tests, IN600 and aluminized IN600 show a break-away oxidation trend. The formation of the alumina layer provided better protection for aluminized samples but the formation of pits led to spallation of oxide scale in the oxidation stages.

Studying simultaneous borochromised coatings on low carbon steel

ABSTRACT In this study, a dual B–Cr coating on AISI 1010 plain carbon steel was formed by the simultaneous diffusion of B and Cr using a single-step pack cementation method. This process was performed at 950°C for 4 h using a powder mixture of different portions of boronising and chromising powders. The effect of powder composition on the microstructure, hardness and thickness of the coatings was studied. The coated samples were examined by optical and scanning electron microscopy (SEM), micro hardness measurements and X-ray diffraction analysis. Chemical composition of the coatings was analysed by energy dispersive spectrometer (EDS) and inductively coupled plasma (ICP) tests. The results revealed that Cr7C3, Fe2B and Fe–Cr solid solutions were the main phases existing in the coating. Formation of hard boride phase (Fe2B) in the dual B–Cr coating as the result of simultaneously diffusing B and Cr made this coating harder than the plain chromised coating.

Effect of silicon/graphite ratio and temperature on oxidation protective properties of SiC/ZrB2–SiC coatings prepared by pack cementation

To investigate the silicon/graphite ratio and temperature on preparation and properties of ZrB2–SiC coatings, ZrB2, silicon, and graphite powders were used as pack powders to prepare ZrB2–SiC coatings on SiC coated graphite samples at different temperatures by pack cementation method. The composition, microstructure, thermal shock, and oxidation resistance of these coatings were characterized and assessed. High silicon/graphite ratio (in this case, 2) did not guarantee higher coating density, instead could be harmful to coating formation and led to the lump of pack powders, especially at temperatures of 2100 and 2200 °C. But residual silicon in the coating is beneficial for high density and oxidation protection ability. The SiC/ZrB2–SiC (ZS50-2) coating prepared at 2000 °C showed excellent oxidation protective ability, owing to the residual silicon in the coating and dense coating structure. The weight loss of ZS50-2 after 15 thermal shocks between 1500 °C and room temperature, and oxidation for 19 h at 1500 °C are 6.5% and 2.9%, respectively.

The role of Dy doping on cyclic oxidation behavior of Al-Si coating on new cobalt-based γ/γ′ superalloy

The Al-Si-Dy coating is prepared on the γ′-strengthened cobalt-based superalloys by pack cementation method. Cyclic oxidation resistance of the coating at 1050 ℃ is investigated through experimental and computing methods. The cycle oxidation life of the coating is more than 1.5 times that of Al-Si coating. The oxide scale on Al-Si-Dy coating is denser and has stronger adhesion compared to Al-Si coating. Dy doping improves the cyclic oxidation resistance of Al-Si coated sample. The superior cyclic oxidation resistance of the coating is ascribed to enhanced adhesion energy of oxide scale, which is caused by stronger Dy–O bond.

Kinetic study of boron diffusion in a γ-TiAl intermetallic alloy using the pack-boronising method

ABSTRACT Boronising is a thermochemical treatment which enhances the resistivity of metals used as component in applications dominated by wear and corrosion. In this study, boronising was performed on a gamma-TiAl intermetallic alloy with the pack cementation method. The experiments took place at temperatures 1173–1323 K for 8–14 h and a compact hard boride layer was formed. Its thickness varied between 6 and 25 μm. An 80 μm wide boron diffusion zone with elevated hardness was detected via micro-hardness measurements. The measured thickness values were applied to a mathematical model based on Fick’s second law of diffusion to extract the kinetic parameters of the process. Additionally, the presence of the ΤiΒ2 and the total absence of the TiB phase were confirmed via XRD measurements. The hardness of the coating and the substrate was evaluated using Vickers micro-hardness tester (above 1100 HV at the coating layer).

Isothermal and cyclic oxidation behavior of a sandwiched coating for C/C composites

A ZrC–SiC/TiC–SiC/SiC sandwich-structured coating is prepared on a C/C composite by pack cementation methods. The microstructures of this coating are characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the oxidation resistance is investigated by performing an oxidation test at 1773 K and a cyclic oxidation test. The results show that the mass losses are 7.4% and 3.8% after oxidation for 144 h and 40 cycles, respectively. The sandwich structure relaxes, releases the thermal stress caused by the mismatch in the coefficients of thermal expansion, and absorbs energy to prevent the initiation and propagation of cracks. The ZrC–SiC/TiC–SiC/SiC coating exhibits good isothermal oxidation resistance and excellent cyclic oxidation protection properties.

Improved antioxidative and mechanical properties of SiC coated C/C composites via a SiO2-SiC reticulated layer

To improve the oxidation resistances of SiC coated C/C composites by a pack cementation (PC) method at high temperature and alleviate the siliconization erosion of molten silicon on C/C substrate during the preparation of SiC coating, a SiO2-SiC reticulated layer with SiC nanowires was pre-prepared on C/C composites through combined slurry painting and thermal treatment before the fabrication of SiC coating. The presence of porous SiO2-SiC layer with SiC nanowires was beneficial to fabricate a compact and homogeneous SiC coating resulting from synergistic effect of further reaction between SiO2 and pack powders and the reinforcement of SiC nanowires. Therefore, the results of thermal shock and isothermal oxidation tests showed that the mass loss of modified SiC coating was only 0.02 % after suffering 50-time thermal cycles between room temperature and 1773 K and decreased from 5.95 % to 1.08 % after static oxidation for 49.5 h in air at 1773 K. Moreover, due to the blocking effect of SiO2-SiC reticulated layer on siliconization erosion during PC, the flexural strength of SiC coated C/C composites with SiO2-SiC reticulated layer increased by 64.8 % compared with the untreated specimen.

The Protection, Challenge, and Prospect of Anti-Oxidation Coating on the Surface of Niobium Alloy

Niobium (Nb)-based alloys have been extensively used in the aerospace field owing to their excellent high-temperature mechanical properties. However, the inferior oxidation resistance severely limits the application of Nb-based alloys in a high-temperature, oxygen-enriched environment. Related scholars have extensively studied the oxidation protection of niobium alloy and pointed out that surface coating technology is ideal for solving this problem. Based on the different preparation methods of Nb-based alloys’ surface coatings, this article summarizes the relevant research of domestic and foreign scholars in the past 30 years, including the slurry sintering method (SS), suspension plasma spraying method (SPS), and halide activated pack cementation method (HAPC), etc. The growth mechanism and micromorphology of the coatings access by different preparation methods are evaluated. In addition, the advantages and disadvantages of various coating oxidation characteristics and coating preparation approaches are summarized. Finally, the coating’s oxidation behavior and failure mechanism are summarized and analyzed, aiming to provide valuable research references in related fields.

Microstructural and topographical characterization of the pack cemented aluminide coating applied on Inconel-600

In this research, the pack cementation method was employed to apply a uniform aluminide coating on a substrate of nickel-based superalloy. The obtained intermetallic coating was synthesized using a pack containing 18Al–80Al2O3–2NH4Cl (wt.%) as the main deposition source, an inert filler, and an activator, respectively. The surface morphology and topography, cross-sectional microstructure, the elemental and phase composition, microhardness of the synthesized aluminide coating were studied using atomic force microscopy (AFM), optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), and Vickers microhardness indenter as the characterization techniques. According to the 3D topography results, the average surface roughness of the Inconel-600 substrate was about 2.446 ± 0.239 nm compared to 43.558 ± 3.876 nm measured for the produced aluminide coating. Additionally, the synthesized coating consisted of NiAl and Ni2Al3 as major phases considering the XRD spectrum. It is also observed that the deposited aluminide coating had a three-layer structure including an outer layer, an inner layer, and a diffusion zone. The Vickers microhardness measurements indicated a significant increase in the microhardness of the substrate (from 185.6 ± 15.8 Hv to 1130.4 ± 42.5 Hv) after applying the aluminide coating. Moreover, the microstructural variations across the deposited aluminide coating led to different microhardness values obtained for each layer. The highest microhardness was observed in the coating diffusion zone, whereas the lowest value belonged to the outer layer.

Effect of the Deposition Time and Heating Temperature on the Structure of Chromium Silicides Synthesized by Pack Cementation Process

Transition metal silicides have attracted great interest for their potential use in optoelectronic devices, photovoltaic cells, and thermoelectric conversion elements because of their high melting point, high oxidation resistance, and satisfactory thermoelectric properties. This study focuses on the effect of the deposition time and the heating temperature on the morphology and structure of the chromium silicides synthesized by the pack cementation method. A series of experiments were carried out at various temperatures (1000–1150 °C) with different deposition times (15–120 min). The morphology and the chemical composition of the samples were determined using SEM with an EDS analyzer. The structure determination and phase identification were performed by XRD analysis. The examination of the as-formed materials was completed by performing thermal stability tests. The most suitable conditions for producing CrSi2 sample with satisfactory properties and simultaneously minimizing the cost and production time are listed. It was found that the sample synthesized at 1000 °C for 15 min during the chromizing step, in combination with the siliconizing step at 1000 °C for 60 min, presents the best thermal stability and these selected temperatures offer appropriate, economical, and repeatable results.

Silicon Diffusion in Silicide Coatings Deposition by the Pack Cementation Method on AISI D2 Tool Steel

In the current research, pack cementation method for deposition of silicide on the AISI D2 steel has been investigated. The chemical, phase composition of coatings and microstructure, were evaluated by EDS, SEM, EDS line scan and XRD techniques. Based on the results, FeSi2 phase and Fe2Si, FeSi on the surface of the deeper parts of the coatings and doubled-zone structure were achieved. In order to calculate the diffusion’s coefficient, concentration’s profile was used in the pack cementation method with three types of powder for 2 and 3 h in 950 °C. The nature of calculation method is based on finite difference method that aids different phases for being calculated simultaneously. Afterward, the analysis of diffusion for each phase is done separately.

Cyclic oxidation behavior of Al-Si coating on new γ′-strengthened cobalt-based superalloy: Experimental study and first-principles calculation

The aluminide coatings with and without Si modification were prepared on the new γ′-strengthened cobalt-based superalloy using a pack cementation method. Cyclic oxidation of the coated Co-based superalloy was study at 1050 °C. The weight changes of Al coating and Al-Si coating were -4.28 mg/cm2 after 248 cycles and -3.40 mg/cm2 after 346 cycles, respectively. The cyclic oxidation resistance of the Al coating was effectively improved by Si modification. Based on the experimental study and the first-principles calculation, it is suggested that Si addition facilitated the formation of a protective Al2O3+SiO2 film and reduced oxygen diffusion in the coating.

Comparative study of failure mechanisms of MoSi2 coating on Mo1 wire mesh under isothermal oxidation and hot-fire test using a hydroxylammonium nitrate based monopropellant

A MoSi2 coating was prepared on the Mo1 wire mesh via pack cementation method, and its failure mechanisms under isothermal oxidation and hot-fire test using a hydroxylammonium nitrate based monopropellant were comparatively studied. Under isothermal oxidation at 1300 °C and 1400 °C, degradation of MoSi2 into Mo5Si3 caused failure of the coating, and interdiffusion made a much larger effect relative to oxidation. However, the MoSi2 coating failed because of the synergy of oxidation, ablation, and interdiffusion under hot-fire test. Besides, dissolution of mullite into SiO2 and ablation of high velocity flame contributed to the failure of the coating as well.

Microstructure and oxidation behaviour of MoSi2 coating combined MoB diffusion barrier layer on Mo substrate at 1300 °C

To improve the oxidation resistance of a Mo substrate at high temperatures, MoSi2–MoB double layers were prepared on the surface of the substrate using a two-step pack cementation method. The isothermal oxidation tests indicate that the weight loss of MoSi2–MoB double layers was only 6.3824 mg/cm2 after oxidation at 1300 °C for 15 h, whereas the untreated Mo experienced serious weight loss and the weight loss was 606.775 mg/cm2 after only 90 min. Following oxidation exposure, the oxidized coating became six complex layers due to correlation diffusion among Mo, Si and B. The double layers showed excellent high-temperature oxidation resistance due to the formation of a dense and continuous SiO2 layer with low O2 permeability. Meanwhile, in situ fabrication of a novel Mo5SiB2 layer could prevent inward diffusion of Si.

An effective and low-cost method to prepare Re-doped aluminide coating on a Ni-based single crystal superalloy

In order to prepare Re doped aluminide coating, an effective and low-cost method of electroplating Ni-Re layer and subsequent low temperature high activity pack cementation method was used. Re-doped Ni2Al3 coating was consisted of an outer Ni2Al3 layer with dispersed Re-rich precipitates, a middle Ni2Al3 layer with dispersed W-rich precipitates and a bottom layer of interdiffusion zone (IDZ). Interestingly, Re existed in the outer coating in form of fine Re-rich precipitates because of low solid solubility of Re in Ni2Al3. [Al] was produced and absorbed on the surface of Ni-Re layer, and the activity of Al was far higher than that of Ni during pack cementation at 800 °C. Thus, Re-doped Ni2Al3 coating was mainly formed by virtually singular inward diffusion of [Al] through the Ni2Al3 layer.

Investigation of the high-temperature oxidation behavior of three-dimensional C/C composite and graphite coated by silicon carbide

In this research, SiC coating was applied by pack cementation method at 1600°C to protect graphite and three-dimensional (3D) C/C composite from high temperature oxidation. The powder pack consisted of 50% Si, 40% SiC, and 10% Al2O3. The specimens were heat-treated at 1600°C in Argon atmosphere for 2 hours. Then, the oxidation resistance of coated substrates was studied at 1500°C for 3 hours. The phase microstructure and element distribution of the coating before and after oxidation were investigated by X-Ray diffraction and SEM. The formation of SiC diffusion coating was confirmed, including the compositional gradient of C and Si elements on the substrates. The oxidation results of SiC coated specimens show that the amount of SiO2 phase formed on the graphite is much more than C/C composite. Furthermore, because of the high viscosity of SiO2, it can seal most of the pores on the SiC surface formed on the graphite. Finally, the oxidation test resulted in 40 mg/cm2 and 7.5 mg/cm2 weight loss for C/C composite and graphite specimens, respectively.

Microstructure and hot corrosion behavior of Al-Si-Hf coating on new γ′-strengthened cobalt-based superalloy

An Al-Si-Hf coating was deposited on the new γ′-strengthened cobalt-based superalloy using pack cementation method. The coating was composed of an outer layer consisting of AlCo phase dispersed with Al5Co2 phase and a diffusion zone. The hot corrosion behavior of the Al-Si-Hf coating exposed to 75 wt% Na2SO4 and 25 wt% NaCl at 900 °C for 100 h was studied. The total mass gain was only 0.29 mg/cm2. It is suggested that the addition of Si facilitated the formation of the Al2O3 scale and contributed stable SiO2 against the molten salts. Hf modification reduced the growth rate of the alumina scale by restraining Al ions outward diffusion, and improved the adhesion of the oxide scale by providing pinning effect.