Diamond-like carbon (DLC) coatings, which improve wear resistance and extend component service life, have gained considerable research attention as an approach for conserving limited resources. The DLC coating is a highly functional film with high hardness and excellent low-friction, wear-resistance, and corrosion-resistance properties; however, it has high residual stress and low adhesion between the substrate and the film. Existing studies have focused on using DLC containing metallic elements (Me-DLC) as an intermediate layer to minimize residual stress, thereby improving adhesion. Si-DLC is deposited using a mixture of hydrocarbon gases, such as methane (CH 4 ) and acetylene (C 2 H 2 ), and silicon gases, such as tetramethylsilane (TMS: Si(CH 3 ) 4 ), H, and Si, to form the DLC coating. The composition, hardness, Young’s modulus, and friction coefficient of the film can be controlled by changing the composition of the gas mixture. This study investigated the effect of the flow rate ratio of source gases (CH 4 and TMS; C 2 H 2 and TMS) on the properties of the DLC film when Si-DLC is deposited as an intermediate layer on austenitic stainless steel SUS304 using plasma-enhanced chemical vapor deposition. The coating time was adjusted to ensure that the thicknesses of the Si-DLC layer and DLC film were 1.0 and 0.2 μm, respectively, under both conditions. The results demonstrated that the durability of the DLC film improved and adhesion decreased with a decrease in the TMS ratio in the Si-DLC intermediate layer. Durability improved and adhesion decreased when C 2 H 2 was used as the source gas, as compared to when CH 4 was used.

In recent years, physical vapor deposition and chemical vapor deposition (CVD) methods have made significant advancements due to the growing demand for surface modification technologies. This study focuses on depositing diamond-like carbon (DLC) as a thin, hard film using plasma-enhanced CVD. DLC possesses properties such as high hardness, low friction, wear resistance, and chemical stability. However, a drawback is low adhesion caused by residual stress and differences in hardness between the film and the substrate material. Therefore, efforts are underway to improve adhesion by introducing a DLC intermediate layer containing metallic elements to reduce residual stress or by applying treatments to harden the substrate material, such as nitriding or carburizing. Active screen plasma nitriding (ASPN) is a nitriding method that eliminates edge effects and electrically insulates the sample during the process. However, during nitriding, deposits can cover the sample and slow down the nitriding rate. To address this, a nitriding method called "direct-current plasma nitriding with screen (S-DCPN)" has been developed. It involves applying a voltage to the sample and screen during ASPN to remove deposits via sputtering action, thereby increasing the nitriding rate. Although the duplex process of ASPN and DLC-coating deposition has been studied, there are limited reports on the duplex process with S-DCPN. This study investigates the effect of intermediate layer composition on mechanical properties by forming a nitrided layer on the surface of SUS304 through S-DCPN treatment, depositing a Si-DLC intermediate layer with varying compositions, and applying a DLC film on the top surface. The results demonstrate that the lower the Si ratio in the Si-DLC intermediate layer, the better the wear resistance. Furthermore, the study reveals that wear resistance and adhesion were improved compared to samples without S-DCPN treatment.

Surface modification involves the chemical or physical impartation of enhanced functionality to the surface of materials, and has become increasingly important in recent years. Nitriding is a surface modification method that hardens the surface of metallic materials by causing nitrogen to permeate and diffuse into the surface to form various nitrides or by supersaturating a solid solution of nitrogen in the metal. This is effective in improving the hardness, corrosion resistance, and wear resistance. Plasma nitriding, a type of nitriding process, has several advantages, such as low energy consumption, short processing time, and low environmental impact. In contrast, the conventional plasma nitriding method forms plasma on the surface of the treated material, which may cause phenomena that lead to defects in the treated material. Therefore, the directcurrent plasma nitriding with screen (S-DCPN) method reduces these problems because plasma is formed not only on the treated material but also on the surface of the screen. Stainless steel has excellent corrosion resistance; however, nitriding treatment above a certain temperature reduces the corrosion resistance owing to chromium nitride precipitation. In this study, the S-DCPN treatment, a type of plasma nitriding method, was applied to form a thick nitrided layer without reducing corrosion resistance. The S-DCPN treatment was performed using ferritic stainless steel SUS430 as the sample and austenitic stainless steel SUS304 as the screen material at treatment temperatures of 633 and 653 K, treatment times of 5 and 15 h, a gas pressure of 200 Pa, and a gas composition of 75% N 2 - 25% H 2 . Consequently, the α N phase with supersaturated nitrogen solid solution was identified under all conditions. Nitrogen diffusion and hardness increased with increasing treatment temperature and time. In the corrosion tests, corrosion resistance improved under all conditions.

Plasma nitriding is the low-nitriding potential process characteristic of its ability to nitride stainless steels and powder metal components without special preparations or unusual controls. This is possible thanks to its specific mechanism and presence of sputtering, the phenomenon which occurs throughout the entirety of the process. Typically, the plasma process produces a nitrided layer with the gamma prime-Fe4N compound zone on top of it. This is very important whenever a good bending fatigue property of the part is needed. The abovementioned materials can also be treated with conventional gas nitriding, but with special cycles requiring very sophisticated control. Mechanical masking, protection from direct contact of the glow discharge with a given surface, prevents hardening of the mechanical components in the areas, which should stay soft, such as the threads, small holes and others. The uniformity of nitriding large/long parts, such as shafts and extruder screws, allows economical treatment in module-type vessels. Easy doping of the plasma with hydrocarbons allows for forming a thicker compound zone of the ε-Fe2NxCy-type. This significantly improves tribological and anticorrosion properties. Enhancement of the wear properties for higher temperature applications is possible when doping plasma with silicon is applied. The plasma process can also be carried out at the temperature range 350-400° C to all types of stainless steels. Formation of expanded austenite at such a low temperature is possible when nitrogen or carbon is diffused. This is applied for stainless steels where their corrosion resistance must be supported or enhanced in their wear resistance applications. Examples of the best applications will be presented.

Carburization is a common method of hardening steel surfaces to be wear-resistant for a wide range of mechanical processes. One critical characteristic of the carburization process is the increase in carbon content that leads to the formation of martensite in the surface layer. Combustion and spark-OES are two common methods for determination of carbon in steels. However, these techniques do not effectively separate carbon from near surface contaminants, carburized layers, and base material composition. Careful consideration of glow discharge spectroscopy as a method of precisely characterizing carbon concentration in surface layers as part of a production process should be evaluated in terms of how the resulting data align with other common analytical and metallurgical measurements. When used together, glow discharge spectroscopy, optical microscopy, and microhardness testing are all useful, complementary techniques for characterizing the elemental composition, visually observable changes in material composition, and changes in surface hardness throughout the hardened case, respectively. Close agreement between related measurements can be used to support the use of each of these techniques as part of a strong quality program for heat treatment facilities.

Controlled nitriding and ferritic nitrocarburizing can significantly improve the corrosion and wear resistance of carbon and low-alloy steels. The framework for maintaining these processes is based on standards, such as AMS 2759/10 and 2759/12A, that specify tolerances for control parameters. This work investigates the impact of admissible deviations in control parameters on the performance of treated alloy samples. The findings of the study demonstrate that although tolerances are allowed, precise control in specific furnace classes is necessary to consistently obtain superior results.

This paper evaluates the influence of niobium additions on the wear behavior of high-silicon steel, representative of the advanced high strength steels used in the automotive industry. It describes the alloy compositions of the test samples used, the heat treatments to which they were subjected, and the tests that were subsequently performed. It also interprets test results and outlines key findings.

The purpose of this work is to incorporate boriding and austempering treatments in a single thermal cycle and assess its effect on two high strength bainitic steels. The combined process, called boro-austempering, is a promising alternative to increase the surface wear resistance of advanced high strength steels as shown in the test results presented.

Gas nitriding is proving to be a viable low temperature case hardening process for stainless steels used in numerous applications. In this study, a comparison between austenitic (grade 304) and martensitic (grade 401) stainless steels shows how pre-oxidation temperature affects the thickness and porosity of the compound layer produced as well as hardness and nitriding diffusion depth. The results indicate that austenitic stainless steel would be the best choice for a part requiring wear resistance and strength, and that a standard rolled martensitic stainless steel would suffice if only a wear resistant surface is needed.

The use of nitriding to improve a component’s resistance to wear, fatigue, and corrosion continues to increase across the industry. However, for nitrided components, no universally accepted definition of “case depth” is available to allow the comparison of different nitriding processes, cycles, and materials. This study documents currently published methods of specifying and determining case depth for nitrided components, and evaluates the reported case depth of multiple materials and cycles in an effort to determine an optimal and robust “universal” method of reporting case depth. After completing this exercise, it appears that the optimal “universal” method of specifying and reporting the case depth for a nitrided component is to report the depth at which a Vickers microhardness traverse crosses a threshold which is 50HV greater than the material hardness below the nitrided case.

The AISI 440B (DIN 1.2210, X90CrMoV18) steel is one of the hardest among martensitic stainless steels. This type of steel is used in a variety of industrial applications where wear and corrosion are determinant, such as molds, parts and tools for the automotive and biomedical industries. Their superior mechanical properties are due to its high carbon (0.75-0.95 % C) and chromium (16-18% Cr) contents. Suitable coatings can increase wear resistance and expand these materials usability range. Boride coatings, with their high hardness and wear resistance are good candidates for this purpose. Boride layers were obtained by boriding treatment in a salt bath (a mixture of sodium borate and aluminum). The layer properties, such as hardness, thickness, layer/substrate interface morphology and phases formed are influenced by steel composition. In this work, the layers produced on AISI 440B steel were harder, thinner, with a smoother interface when compared to plain carbon steels due the larger amount of alloying elements. In order to evaluate mechanical properties of borided layers in samples of stainless steel AISI 440B, Optical Microscopy (OM) microstructural analysis, Vickers microhardness tests and micro-adhesive and micro-abrasive wear resistance tests were performed. The layers produced exhibited a hardness close to 2250 HV and excellent wear resistance far superior to that of substrate.

Transmission-manufacturers constantly need to adapt their products and manufacturing technologies to meet future’s market and legislation requirements such as cost-efficiency, running-smoothness and drivetrain-agility. Components made of powder metal (“PM-components”) are established in today’s transmission industry as a cost efficient alternative even for high strength and high precision powertrain applications. The PM-material and the applied heat treatment processes have made significant improvements in recent years. One major step in the development was to combine the freedom in alloying-concepts of the PM-technology with the advantages of the Low Pressure Carburizing (LPC) heat treatment process. PM-components must be case-hardened to meet design-intent regarding wear resistance and strength. But when case hardening PM-components using a conventional atmospheric carburizing process, this can lead to serious overcarburizing and even massive carbide-formation. Another major challenge when using the conventional process is to clean PM-parts after the traditional oil-quenching process. Therefore, the process of Low Pressure Carburizing (LPC) combined with High Pressure Gas Quenching (HPGQ) was adapted to the special needs of serial production of PM-components. This heat treatment process offers significant benefits, such as: - no overcarburizing and excessive carbide-formation due to precise diffusion of carbon into the components - reproducible microstructures from part to part and from load to load - clean and shiny parts after quenching - superior control of distortion, - no intergranular oxidation, - better fatigue resistance and - the benefits of an environmentally friendly process. Over the past 25 years, Stackpole and ALD worked on powder metal technology and advanced heat treatment processes. Material, process and equipment have seen significant improvements over the last decades to offer true benefits. This presentation will give an insight into benefits and challenges of PM-components heat treated in low pressure with subsequent gas quenching. The paper refers to the industrial series production of components and it refers to R&D - case studies as well.

Gas Nitriding is a common industry process which can improve the hardness, wear resistance, and fatigue strength of steel components. Proper surface activation is reported to be critical in achieving a uniform and repeatable nitriding response, but little data is available to compare various activation techniques for common nitriding alloys. This paper reports the early hour compound layer formation for six activation techniques on both a low alloy steel and a specialized nitriding steel. Both grades of steel showed the best performance when a multi-stage nitride washer was used to prepare the surfaces. Two other processes, namely nitric acid etching and a neutral wash and rinse cycle, were also shown to provide acceptable early hour performance for both alloys under the test conditions in this study.

Thermochemical surface engineering by nitriding/carburizing of stainless steel causes a surface zone of expanded austenite, which improves the wear resistance of the stainless steel while preserving the stainless behavior. As a consequence of the thermochemical surface engineering, huge residual stresses are introduced in the developing case, arising from the volume expansion that accompanies the dissolution of high interstitial contents in expanded austenite. Modelling of the composition and stress profiles developing during low temperature surface engineering from the processing parameters temperature, time and gas composition is a prerequisite for targeted process optimization. A realistic model to simulate the developing case has to take the following influences on composition and stress into account: - a concentration dependent diffusion coefficient - trapping of nitrogen by chromium atoms - the effect of residual stress on diffusive flux - the effect of residual stress on solubility of interstitials - plastic accommodation of residual stress. The effect of all these contributions on composition and stress profiles will be addressed.

Gray cast iron is primarily used for its low cost, high damping capacity, and excellent machinability. These properties are attributed to the presence of free graphite and the high fluidity of the molten metal, which allows for the easy casting of complex parts with thin walls. Applying suitable coatings can enhance wear resistance and broaden the material's range of applications. Niobium carbide, known for its high hardness, is a promising candidate for this purpose. In this study, samples of gray cast iron with the composition 3.47% C, 2.39% Si, 0.55% Mn, 0.15% Ni, 0.65% Cu, and the balance Fe were subjected to a niobizing powder thermo-reactive diffusion treatment. The coating mixture consisted of ferro-niobium, NH 4 Cl, and Al 2 O 3 , and the treatment was conducted at 900 °C for 2 hours. The resulting layers exhibited hardness values of 2000 HV, characteristic of niobium carbides. Micro-adhesive and micro-abrasive wear tests showed a significant increase in wear resistance due to this treatment.

The use of high hardness surface layers can extend the life of components such as molds and dies by increasing their wear resistance. However, corrosion and oxidation resistance are also important to improve the durability of the components, especially for those that work under more demanding environments. In this work, samples of AISI H13 tool steel for hot work were borided by the pack cementation process, producing uniform and high hardness layers (1400-1800 HV). Afterwards the samples were subjected to a quasi-isothermal oxidation testing at 550 °C, the same working temperature of H13 steel in aluminum extrusion dies. Throughout the test, the mass gain of the untreated substrate, used for comparison, was 100%, while the borided sample treated at 900 °C for 2 hours had mass gain of 83% and the sample treated at 1000 °C for 4 hours presented a mass gain of 43%. The oxidation coefficients of the borided samples were similar, indicating similar oxidation kinetics but different from the untreated substrate.

Precipitation-hardening stainless steels are iron-nickel chromium alloys containing precipitation hardening elements such as aluminum, titanium, niobium and copper. In this work, heat treatment of a novel precipitation hardening stainless steel using niobium as a forming element for the hardening precipitates in order to increase its surface hardness and wear resistance was performed. The steel composition was 0.03C - 0.22Si - 17.86Cr - 3.91Ni - 2.19Mo - 1.96Nb (in wt%). The samples were solubilized at 1100 °C for 2 hours. Cooling was done in oil and the samples were subsequently aged at 500, 550 and 600 °C. The solubilized samples exhibited an average hardness of 30 HRc and after the aging treatments, the hardness increased to 46 HRc. The hardness increases during the aging treatments were very fast. A 5 minute treatment achieved hardness levels that were close to the maximum obtained for this alloy. Niobium was an efficient precipitation hardeners forming a Laves phase of the type Fe 2 Nb.

This paper examines the critical role of material selection in the performance of induction-hardened components such as shafts, axles, pins, and gears. The author discusses how material choices impact raw material costs and manufacturing processes, including machining, grinding, and drilling. The paper explores how carbon content fundamentally determines the maximum obtainable hardness in steels, with a detailed analysis of commonly used grades such as 1045, 1050, 1144, and various alloy steels. Key considerations for engineers include applied load characteristics, desired mechanical properties (fatigue strength, wear resistance), and the tradeoffs between carbon content, hardenability, machinability, and susceptibility to quench cracking. The paper provides practical guidance on steel selection based on required hardness profiles, with insights into how alloying elements and prior microstructure affect case depth and hardness distributions in induction-hardened components.

This paper describes the development of a simulation program to model gas nitriding processes for steels and replace traditional trial-and-error methods that are expensive, time-consuming, and often inaccurate. The authors introduce a compound layer growth model that simulates key nitriding outcomes, including phase composition, compound layer thickness, and nitrogen concentration profiles based on process parameters (temperature, time, and nitriding potential or dissociation rate). The model employs computational thermodynamics to construct alloy-specific Lehrer diagrams that describe phase stabilities, uses parabolic law to simulate compound layer growth kinetics, and applies constant effective nitrogen diffusivity in the diffusion zone for specific alloys at given temperatures. Validation testing on AISI 4140 steel under various nitriding conditions demonstrated excellent agreement between simulated and experimental results for both as-washed and pre-oxidized specimens, confirming that the software provides an effective tool for determining optimal nitriding parameters to meet specifications and ensure reliable performance through accurate process control.

Case-hardening is widely used to enhance the durability of transmission gears. Low-pressure carburizing (LPC) and high-pressure gas quenching (HPGQ) offer advantages over other quenching methods, including reduced distortion, higher fatigue strength, and improved wear resistance. Optimizing LPC and HPGQ processes can minimize distortion, making subsequent dimensional corrections more predictable and, in some cases, unnecessary. The geometry and material of the fixture supporting the gears during LPC and HPGQ significantly influence temperature uniformity across the load. This study explores fixture optimization using computational fluid dynamics to achieve uniform temperature distribution during HPGQ.