Thermo-reactive Diffusion Process Research Articles

The effect of niobium carbide coating on wear behavior of grey cast iron via thermo-reactive diffusion process

Wear is the limit for grey cast iron (GCI), which is utilized extensively in today’s industries. Coating the surface of a material can enhance its ability to withstand wear. In this study, thermo-reactive diffusion (TRD) process was used to coat the surface of grey cast iron with niobium carbide (NbC). The coatings were applied for 2, 4 and 6 hours at 950ºC and 1050ºC. The coated samples were subjected to metallographic examination to investigate the microstructure of the coating zone. For this purpose, optical microscopy examinations were carried out. Microhardness tests were carried out to assess the mechanical properties of the samples. The coated surfaces were analyzed using energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Wear tests were carried out on the coated surfaces to measure the volumetric wear loss, the wear rate and the changes in the coefficient of friction. Coating thickness rose as furnace waiting time increased, according to optical microstructures of coated surfaces. The hardness of the coated surfaces increased with a longer coating duration. Depending on the duration and temperature of the coating process, the layer thickness ranged from 6 to 52 µm. The lowest microhardness and the highest microhardness values of the coatings were determined at 950ºC for 2 hours and at 950ºC for 6 hours, respectively. Compared to the uncoated samples, the coated samples had a 6-9 times higher hardness value. In the abrasion tests, the loss of wear volume increased with increase in load.

Applying Thermo-Reactive Diffusion Method to Surface Coating of H13 Tool Steel Using Ferrovanadium, Ferrochromium, and Misch Metal

The thermo-reactive diffusion (TRD) process is a method for surface hardening that improves the hardness, corrosion resistance, and wear resistance of the materials. In this study, the effect of composition was investigated, by using 8, 12, 16, 20, and 24 wt% of ferrochrome and ferrovanadium with equal amounts, along with 3 wt% aluminum and borax. The TRD process was carried out at 1000°C for 7 hours on AISI H13 hot work tool steel so that a complex coating of chromium-vanadium carbide was formed on the H13 substrate. Optical and scanning electron microscopes were used to evaluate the thickness and microstructure of the samples, respectively. Moreover, the amount of alloying elements and constituent phases on the surface were analyzed by point analysis and X-ray diffraction. The micro-hardness method was used to evaluate the hardness of the samples. The results of this study showed that by increasing the amount of ferroalloy, the hardness and thickness of the coating increase. The optimal composition with 8% ferrochrome and 8% ferrovanadium was found to yield a coating with a thickness of 7.65 μm and a hardness of 2115 HV.

On the nanoindentation behavior of a TiC layer formed through thermo-reactive diffusion during hot pressing of Ti and cast iron

Hot pressing of pure Ti and cast iron under vacuum formed a ∼15 µm wide TiC-layer through the thermo-reactive diffusion process. Nanoindentation testing of the TiC-layer revealed average hardness and elastic modulus values of ∼35 GPa and ∼400 GPa, respectively. High-resolution indentation mapping indicated hardness change across the boundary with peak values observed within the TiC-layer. Solid state high temperature diffusion holds significant potential for developing uniform hard coatings on pure Ti/Ti-alloys.

Microstructural evolution and wear properties of chromium carbide coating formed by thermo-reactive diffusion (TRD) process on a cold-work tool steel

In the current study, the possibility of forming a chromium carbide layer on the surface of an AISI W1 cold work tool steel was investigated. The coatings were fabricated through a thermo-reactive diffusion (TRD) treatment by the molten salt bath at 800, 900, and 1000 °C for 4, 5, and 6 h using chromium oxide powder. The structural and mechanical properties of the coatings formed at the different conditions (temperature and immersion time) were compared together. For this purpose, the coating layers were characterized by field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectrometer (EDS) as well as X-ray diffraction (XRD) method. Moreover, the hardness and friction coefficient (COF) of the coated samples were examined through micro-indentation and ball-on disk tests, respectively. It was determined that at 800 °C, just chromium carbide nuclei are formed, and the temperature is insufficient to produce a complete chromium carbide layer on the substrate. XRD results of the coating produced at this temperature showed that the main phase is Fe–Cr solid solution. However, compact, adherent, uniform, and crack-free chromium carbide coatings with thickness ranging from 5.14 to 18.06μm were successfully obtained on the substrate at 900 and 1000 °C, mainly consisting of Cr7C3, Cr23C6, and Cr3C2. The XRD results showed that the possibility of forming chromium carbide phases increases with increasing temperature and immersion time. The hardness of the coatings was in the range 771 to 1600 HV, depending on the process condition. The results demonstrated that increasing the temperature and immersion time of the TRD process increases the thickness and hardness of coatings, resulting in low friction coefficient values and improvement in the wear resistance up to 6 times compared to the untreated AISI W1 sample.

The Effect of the Holding Time on the Formation of Niobium-Vanadium Carbide Coating Onto Aisi 420 by Thermo Reactive Diffusion Process

The deep drawing process had been widely used in automobile, aerospace, electronics, and allied industries to produce hollow parts. The quality of the deep drawing is determined by the dies properties especially their wear-resistant and hardness. Austenitic stainless steel AISI 420 is one of the material of choice for making these dies. In order to increase the wear resistance of the dies, surface treatment such as thermo-reactive diffusion (TRD) technique can be applied owing to their simplicity, low cost, and environment friendly process. TRD technique able to deposit hard layers of carbide, nitride, or carbonitride In this research, TRD techniques will be employed to AISI 420 with special attention given to the effect of holding time during TRD process to form niobium-vanadium carbide (NbVC) coating. The TRD process is carried out by the powder-pack method in a sealed steel container containing powder mixture of niobium and vanadium as master alloy, alumina (Al2O3) as an inert filler and ammonium chloride (NH4Cl) as an activator. The samples were covered with powder mixture and then heated in the electric resistance furnace for 2, 4, and 6 hours at 1000˚C. The crosssection analysis of the NbVC coating observed under microscopy shows that coating thickness increased with longer holding time with 6.95 µm measured in 6 hours holding time. The high hardness of 1333.2 HV also found in the longest holding time of 6 hours. This high hardness is expected to contribute in the wear resistance characterisitic of AISI 420 dies.

Characteristics and high temperature wear behavior of chrome vanadium carbide composite coatings produced by thermo-reactive diffusion

In this study, Cr–V–C composite carbide layers were grown on the surface of a GGG-80 ductile iron using thermo-reactive diffusion (TRD). The TRD process was carried out at temperatures of 900, 1000, and 1100 °C for 1 h using nano-sized FeV and FeCr powders. The coatings were characterized by X-ray diffractometry (XRD), 2D profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), microhardness measurements, nanoindentation, and wear tests. The wear tests were performed on untreated and coated samples using a ball-on-disc type wear tester under 10 N load at four different temperatures (25 °C, 250 °C, 500 °C and 750 °C) against a 6-mm WC ball. Metallographic investigations revealed that the graphite nodules near the surface were dissolved as a result of the TRD process. Depending on the TRD process temperature, a coating with a thickness of 12–36 μm, hardness of 24.14–31.38 GPa, and elastic modulus of 198–233 GPa was obtained. An increase in process temperature increased the thickness, hardness, and elastic modulus of the obtained Cr–V–C layers, which resulted in low friction coefficient values and decreased wear rates. Although all coated samples showed improved wear resistance in all wear test conditions, the wear rates were significantly increased at 750 °C due to flaking.

Properties and Corrosion Behavior of Chromium and Vanadium Carbide Composite Coatings Produced on Ductile Cast Iron by Thermoreactive Diffusion Technique

Abstract Ductile iron (DI) owes many of its attractive mechanical properties to the graphite nodules in its structure. However, since galvanic coupling can occur between the graphite nodules and the matrix in aggressive environments, these nodules can, at the same time, reduce its corrosion resistance. In this study, composite carbide coatings were grown on the surface of GGG-80 using the thermoreactive diffusion (TRD) process. The process was carried out at 900, 1000, and 1100 °C for 1 h using nanosized Fe-V and Fe-Cr powders. The coatings were characterized by X-ray diffractometry (XRD), two-dimensional profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and microhardness tests. The corrosion behavior of the coatings were evaluated in three different solutions (3.5 wt% NaCl, 5 wt% H2SO4, and 5 wt% HNO3) using electrochemical open-circuit potential (OCP) and potentiodynamic polarization measurements. Microstructures and hardness tests showed that the nodular graphite in the surface was dissolved at the TRD process temperatures and that a coating of 12–36 µm thickness and 2461–3200 HV0.05 hardness was obtained. The corrosion resistance of the composite coating was up to 10, 33.5, and 75 times higher than the uncoated GGG-80 in NaCl, H2SO4, and HNO3, respectively. The improvement in corrosion resistance was a direct result of the formation of complex carbides and the elimination of graphite nodules in the surface of the alloy.

Effect of duplex coating (VC–VN) on forming mandrel for better wear resistance

ABSTRACT The present work aims at investigating the collective function of thermo-reactive diffusion (TRD) and plasma-nitriding duplex coating (vanadium carbide (VC) and vanadium nitride (VC-VN)) on the wear resistance of AISI M2 axial-forming mandrel. TRD process was carried out in molten salt bath furnace at 1020 ± 25°C for 5–6 h and the samples were subjected to vacuum heat treatment process at 1150°C, followed by plasma-nitriding for 1 h at 550°C. Wear properties were examined by subjecting the VC and VC–VN-coated samples to wear test (pin on disc) at normal and elevated temperature (50° and 150°C) with lubrication. Phase composition, surface morphology and elemental mapping were studied through X-ray diffractometer, SEM and EDS analyses, respectively. Study found that the wear resistance of VC-coated samples was higher than VC–VN-coated samples and wear mechanisms for VC and VC–VN coated specimens were assessed to be abrasive and abrasive-oxidative in nature, respectively.

The Effect of Thermo Reactive Diffusion (TRD) Processing Time with Ferrochromium Powder on Carbide Layer Characteristics on SUJ 2 Tool Steel Substrate

In this study, the formation of chromium carbide layer on SUJ 2 tool steel substrate as a surface treatment by thermo reactive diffusion process with pack cementation method was observed. The powder used are Al2O3, NH4CL, and FeCr as carbide forming elements with the composition of 37%, 3%, 60% for each. TRD process performed in rotating vacuum furnace for 4, 6, and 8 hours on 980°C. The results show time variation effects on the carbide layer. Thickenss carbide layer on SUJ2 after TRD process observed by Optical Microscope. The morphology of carbide layer observed with SEM shows a smooth and dense layer with almost no porosity formed. Cr23C6 and Cr7C3 found on the layer by XRD and hardness value obtained using Vickers microhardness testing for each samples are 1738.62, 1738.72, and 1739.64 HV. The wear rates are inversely proportional with the hardness value where the values are 0.000698, 0.000658, and 0.000627 mm3/m.

Corrosiveness of Palm Biodiesel in Gray Cast Iron Coated by Thermoreactive Diffusion Vanadium Carbide (VC) Coating

Palm biodiesel is a currently used biofuel, principally as an additive or substitute of diesel fuel in vehicular internal combustion engines. In the present work, vanadium carbide (VC) coatings were deposited on gray cast iron (GCI) using the thermoreactive diffusion process (TRD) to evaluate the corrosiveness of palm biodiesel and compare it with gray cast iron corrosion behavior. VC coated and uncoated gray cast iron samples were tested by immersion corrosion tests (291 K and 313 K), cyclic oxidation test (CO), and the electrochemical impedance spectrometry test (EIS). The corrosion test showed the reduction of the corrosion rate for the VC coating when compared to gray cast iron. EIS tests of coated samples showed higher values of polarization resistance when compared with uncoated gray cast iron samples. Results confirmed that while biodiesel was more corrosive than diesel on both coated and uncoated gray cast iron, the VC coating was efficient in protecting the substrate exposed to both fuels.

Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of modified PM Ti surfaces designed for biomedical applications

ABSTRACTThis work focuses on the evaluation of modified surfaces on Ti produced by powder metallurgy. These newly designed surface modifications are achieved by deposition and diffusion of a stable aqueous suspension prepared in one case from micro-sized Nb powder (Ti β-stabilizer element) and in another case from Nb plus the addition of ammonium chloride, NH4Cl, (thermo-reactive diffusion process). Different design parameters such as diffusion element (Nb or Mo), state of the Ti substrate (green or sintered) and the treatment process (diffusion or thermo-reactive diffusion) lead to all the surface-modified materials, GreenTi–Nb, SintTi–Nb and Ti–NbNH4Cl, GreenTi–Mo, SintTi–Mo and Ti–MoNH4Cl. The modified Ti surfaces present a gradient in composition and microstructure (β / α+β / α phases) resulting in an improvement in some of their mechanical properties: (1) higher micro-hardness in all the modified materials and (2) lower elastic modulus (more similar to that of the human bone) in those without NH4Cl.Invited keynote papers from EuroPM2017, Milan.

In-vitro study of the bioactivity and cytotoxicity response of Ti surfaces modified by Nb and Mo diffusion treatments

This work focuses on the bioactivity and biological response of modified Ti surfaces produced by powder metallurgy. They are processed by diffusion of two β-stabilizing elements, Nb and Mo, deposited onto the surface of PM Ti substrates. Moreover, the addition of an activating agent, NH4Cl, to the suspension has been carried out by thermo-reactive diffusion process. The surface modification led to a gradient in composition (Ti-Nb or Ti-Mo) and microstructure (β/α+β/α phases). This work presents the bioactivity results of these Ti-Mo and Ti-Nb surfaces as well as the cell-material response of the Ti-Nb surfaces. The reactivity of the materials was tested through immersion in simulated body fluid considering Ca and P precipitation in order to assess the ability of the materials to induce hydroxyapatite formation. The in-vitro cell response was evaluated by human osteoblast-like cells incubation on the different surfaces for 48h. The investigation led to positive results in terms of surface bioactivity and an improved cell-material interaction of the PM modified Ti-Nb surfaces compared to the reference Ti material.

Galling mechanism in metal forming process with TRD coated die against advanced high strength steel sheet

Abstract Galling behavior in sheet metal forming of advanced high strength steel (AHSS) is of great concern in automobile industry. To examine the galling mechanism in sheet metal forming, Finite element analysis and U-bending test with VC coating die coated by thermo-reactive diffusion process (TRD) against DP780 sheet were carried out. The results show that scratches are firstly observed on the die radius surface, mainly distributed at 0-10°and 30-50°. As the forming number increases, the galling mechanism changes from adhesive wear to abrasive wear, accompanied by adhesive tumors and debris. The Ry increases from 0.481μm to 3.44μm for TRD coated die surface and from 0.718μm to 6.82μm for workpiece, respectively. The wear depth predicted by finite element analysis agrees with the experimental result.

Microstructural behavior of nitriding compound layer for Nb-carbonitride coating grown by thermo-reactive diffusion process

This study aims to understand the microstructural behavior of nitriding compound layer and its effect on Nb-carbonitride growth produced by the thermo-reactive diffusion (TRD) process. Gas nitriding was performed at 550 °C for 3 and 6 h, followed by TRD at 900 °C for 6 h. The nitriding compound layers had thicknesses of 10 and 16 μm for nitriding time of 3 and 6 h, respectively. The corresponding Nb-carbonitride layers produced by TRD were 7.2 and 11.2 μm thick, respectively. Reheating at 900 °C transformed the microstructure of the nitriding compounds to Fe3O4 and FeN0.0939. As reheating proceeded to 30 min, high concentration of nitrogen, initially existing in the nitride layer diffused to 80–90 μm into the substrate. Therefore, the TRD process produced NbN layer at the interfacial area due to intensively dissolved nitrogen from FeN0.0939. As the TRD proceeded, supply of C atoms from the base metal became competitive with the N diffusion. Thus, the TRD coating layer was grown to above the interface. Reheating at 900 °C for the 16-μm-thick nitride layer resulted in a nitrogen content ∼0.4 at% higher than that for the 10-μm-thick nitride layer, thereby producing a thicker Nb-carbonitride layer.

Nb–Cr complex carbide coatings on AISI D2 steel produced by the TRD process

Nb–Cr complex carbide coatings were produced onto AISI D2 steel by the thermo-reactive diffusion process to improve the surface hardness and corrosion resistance of this tool steel. The carbide coating treatment was performed using molten borax added with ferroniobium, ferrochrome and aluminum at temperatures of 1,223, 1,293 and 1,363 K during 2, 3, 4 and 5 h. The coating layers were characterized by optical and Scanning Electron Microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and X-ray fluorescence spectrometry. The coating growth rates were evaluated, and a model of the layer thickness as a function of the treatment time and temperature was established. The hardness of the coating was measured by nanoindentation, and its resistance to corrosion was evaluated with electrochemical tests of potentiodynamic polarization. The produced carbide layers presented a homogeneous thickness as well as an improved hardness and corrosion resistance as compared to the uncoated steel.

The Investigation and Growth Kinetics of TiC Coatings on AISI D3 Steel Produced by Thermo-Reactive Diffusion Technique

Abstract TiC coatings on AISI D3 cold-work tool steel were carried out by pack method thermo-reactive diffusion process (TRD) for 2 and 4 h at 950, 1 000, 1 050 and 1 100 °C, respectively. The carbide layers were evaluated based on microstructure, thickness, hardness, energy dispersive X-ray facility and X-ray diffraction analysis. Titanium carbide layer thickness on the coated specimens ranged from 6 to 23 μm, depending on treatment time and temperature. Growth kinetics of the carbide layers were analyzed measuring the depth of carbide layer as a function of temperature and time. The activation energy was estimated to be 249.42 kJ/mol. The micro-hardness value of the coating layer was obtained to be 2 470 HV in maximum.

Growth Kinetics of CrC Coating Layers on AISI D3 Obtained by Thermo-Reactive Diffusion Technique

Abstract In this study, the characterization and growth kinetics of chromium carbide layer coated on AISI D3 cold-work tool steel by pack method thermo-reactive diffusion process in solid medium were carried out. Coatings were performed by using ferro-chromium powder as Cr source at 950, 1 000, 1 050 and 1 100 °C for 2 and 4 h. The carbide layers were evaluated based on microstructure, thickness, hardness, energy dispersive X-ray facility and X-ray diffraction analysis. Chromium carbide layer thickness on the coated specimens has been in the 4.2–17 μm range depending on treatment time and temperature. Growth kinetics of the carbide layers were analyzed by measuring the depth of carbide layer as a function of temperature and time. The activation energy was estimated to be 180.13 kJ/mol. The microhardness values of the coating layers are range of 1 200–1 600 HV. Ball rotating micro-abrasion technique was used to carry out wear tests on the thin coating layers.

Computer-aided modeling for predicting layer thickness of a duplex treated ceramic coating on tool steels

Five different tool steels (DIN 1.2080, 1.2210, 1.2344, 1.2510 and 1.3343) have been targeted for a duplex surface treatment consisted of nitriding followed by vanadium thermo-reactive diffusion (TRD). TRD process was performed in molten salt bath at 575, 650 and 725°C for 1 to 15h. A duplex ceramic coating of vanadium carbonitride (VCN) with a thickness up to 10.2μm was formed on tool steel substrates. Characterization of the ceramic coating by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) indicated that the diffused compact and dense layers mainly consisted of V(C,N) and V2(C,N) phases. Layer thickness of duplex coating has been modeled by gene expression programming (GEP). Recently, application of GEP as a computer-aided technique has got appreciable attraction especially for modeling and to formulate engineering demands. For GEP approaches, chemical composition of steel substrates along with different bath and processing parameters totally composed of 17 different parameters were considered as inputs to establish mathematical correlations. Finally, the training and testing results in models have shown strong potential for predicting the layer thickness of duplex treated ceramic coating on tool steels.

Effect of Salt Bath Composition on the Chromium Diffusion on Plain Carbon Steels by TRD Process

The thermo-reactive diffusion (TRD) process is used for diffusing an element to the metallic steel substrate. TRD is carried out by using either salt bath or fluidized bed methods. In this research, the molten salt bath method is used. Ferro chromium was dissolved in the molten borax as the source of chromium in the salt. Samples of cylindrical shape of plain carbon steel with 10 mm diameter and 20 mm height were treated at 1000°C for 14 hours in different baths including either low carbon ferro chromium (LCFC) or high carbon ferro chromium (HCFC) powder. The purpose of this research is to investigate the effect of the salt bath composition on the diffusion of chromium and formation of chromium compound layer on plain carbon steel by using the salt bath method. The coating thickness layers were measured by SEM. The different phases formed on the samples, due to different amounts of carbon in treating salt bath, were determined by X-ray diffraction. It was found that in molten borax salt with high carbon content (high carbon ferro chromium) very few amount of chromium diffused into the plain carbon steel. The thickness of the diffused chromium layer in low and high carbon content ferro chromium in molten borax, is around 32±8 µm and 6.8±1.2 µm, respectively. A number of tests were conducted to address this effect.

Vanadium carbide coatings on die steel deposited by the thermo-reactive diffusion technique

Thermal reactive diffusion coating of vanadium carbide on DIN 1.2367 die steel substrate was performed in a powder mixture consisting of ferro-vanadium, ammonium chloride, alumina and naphthalene at 950, 1050 and 1150 °C for 1–5 h. The carbide layers were characterized by means of microstructure, microhardness, X-ray diffraction and chemical analysis. Depending on the coating process time and temperature, the thickness of the vanadium carbide layer formed on the substrate ranged from 2.3 to 23.2 μm. The hardness of vanadium carbide layers was about 2487 HV. Dry wear tests for uncoated and coated DIN 1.2367 die steel were carried out on pin-on-disk configuration and at a sliding speed of 0.13 m/s. The results showed superior wear properties of the coated samples. The kinetics of vanadium carbide coating by the pack method was also studied and the activation energy for the thermo-reactive diffusion process was estimated to be 173.2 kJ/mol.