Wyniki 11-20 spośród 21 dla zapytania: authorDesc:"Michał Kulka"

Gas boriding of Nimonic 80A alloy DOI:10.15199/28.2015.3.6

  Bardzo dobra odporność stopów niklu na korozję i utlenianie pozwala stosować je tam, gdzie występuje agresywne środowisko lub wysoka temperatura. Jednak stosowanie tych stopów w warunkach znacznego zużycia mechanicznego (adhezyjnego lub ściernego) wymaga odpowiedniego zabezpieczenia. Zaproponowano borowanie gazowe w atmosferze N2-H2-BCl3 do wytworzenia warstwy borków na stopie Nimonic 80A. Proces prowadzono w temperaturze 920°C (1193 K) przez 3 godziny. Gaz nośny zawierał 75% N2 i 25% H2. Stosowano gazy o dużej czystości (azot 6.0 i wodór 6.0). Dodatek BCl3 wynosił około 1,3% w odniesieniu do całej stosowanej atmosfery (N2-H2-BCl3). Podczas pierwszego etapu procesu do atmosfery N2-H2 dodawano BCl3. Badano mikrostrukturę i niektóre właściwości warstwy borowanej. Proponowane borowanie gazowe powodowało przyspieszenie dyfuzji boru do powierzchni w porównaniu z innymi metodami dyfuzyjnymi. Otrzymano porównywalną grubość warstwy borków po znacznie krótszym czasie trwania procesu. Mikroanaliza rentgenowska wykazała zwiększone stężenie boru w warstwie. Zaobserwowano znaczne zwiększenie twardości w wyniku gazowego borowania. Słowa kluczowe: borowanie gazowe, Nimonic 80A, mikrostruktura, twardość.1. INTRODUCTION Nickel and Ni-base alloys are widely used in chemical, petrochemical industries, aeronautics, power generations and furnace industries, because of excellent combination of low thermal expansion coefficient, high temperature strength, high resistance to oxidation and corrosion [1÷3]. However, poor wear resistance, as an important disadvantage, causes the limited use of these alloys. Under condition of mechanical wear (abrasive or adhesive), the Ni-base alloys will require suitable protection [1÷4]. The thermochemical processes (nitriding, boriding, carburizing) are promising surface treatments for improving wear resistance [5÷12]. However, the carburizing of nickel is difficult, because nickel has a very low solubility for carbon in the s[...]

Laser boriding of 100CrMnSi6-4 steel using BaF2 self-lubricating addition DOI:10.15199/28.2017.3.6

  1. INTRODUCTION Nowadays, there was a lot of literature data which described various techniques of improving tribological properties of the bearing steel [1÷5]. Some of these methods consisted in a special heat treatment [1, 2]. The surface treatments, such as diffusion nitriding, nitrocarburizing or boronizing as well as CVD and PVD methods, were also applied [3]. Diamond like carbon (DLC) coatings [4] as well as the multicomponent coatings (TiAlN + TiN), produced by PVD methods [5], often increased the tribological properties of bearing steel. The wear resistance of the materials was often improved by increasing the hardness. The surface layers of higher hardness were usually characterized by the better tribological properties. In a considered friction pair, the material with lower hardness usually wore more intensively. However, the wear mechanism also influenced the resistance to friction wear. If the oxidation was confirmed as the main wear mechanism, the oxides ensured the lubrication of the parts, e.g. the V2O5 oxides appeared on the surface of vanadized layers and because of that the lower friction coefficient was measured during wear [6]. The coefficient of friction, characteristic of the mating parts, could be reduced by oils, used as lubricants. But oils proved to be very dangerous in the use as well as during production and utilization. Therefore, the solid lubricants seemed to be more acceptable for lubrication. Many different solid lubricants were applied for improving the wear resistance, e.g.: metals, fluorides, sulfides, sulfur and tungstates. Fluorides, such as CaF2 or BaF2, were wellknown as solid lubricants which could work at elevated temperature (even above 500°C), ensuring reduction of friction coefficient [7, 8]. Barium fluoride was characterized by a low hardness and very good lubrication properties [9÷11]. This lubricant could be added as a component of composite materials, produced by hot-pressing a[...]

Laser-borided layer formed on Inconel 600 alloy

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Nickel and its alloys are known for their excellent resistance to corrosion and oxidation. Therefore, these materials are often used wherever corrosive media or high temperature are to be expected. As a consequence, they are used predominantly in the chemical engineering industry (tanks and apparatus construction), the petroleum industry and in turbine construction. However, the poor wear resistance, as an important disadvantage, causes the limited using of these alloys. Under conditions of appreciable mechanical wear (adhesive or abrasive), these materials have to characterize by suitable wear protection. Processes used for protecting steels, such as nitriding, carburizing or case-hardening, can not be successfully used for Ni-based alloys. The diffusion boronizing could be the thermochemical treatment, which improves tribological properties of nickel and its alloys. It was shown in literature data that they can be borided efficiently using different methods [1÷8] without sacrificing corrosion resistance. This boriding process results in formation of nickel borides at the surface. However, the powder-pack boronizing using commercial Ekabor powder containing SiC [1÷3] is not preferred because of formation of porous silicide layer at the surface. As a consequence, relatively low hardness is usually obtained at the surface (within the range from 750 HV to 980 HV). Fluidized bed technology is not also proper to boronizing of nickel. In spite of using fluidized bed without SiC the obtained layers are characterized by low hardness (about 870 HV) and thickness of 35 μm [4]. The better results were obtained in case of using powders without SiC, e.g. Ekabor Ni powder specially prepared for Ni-based alloys. The powder-pack boronizing of pure nickel using this agent results in formation of thick boride layers (up to 100 μm) of high hardness (1300 HK) [5]. Inconel alloys are also good candidates for boronizing by powder-pack me[...]

Laser alloying of 316L steel with boron

  AISI 316L austenitic stainless steel is known for its most effective balance of carbon, chromium, nickel and molybdenum for corrosion resistance. Therefore, this material is often used for high temperature, aggressively corrosive conditions and nuclear reactor applications. However, the poor wear resistance, as an important disadvantage, causes the limited using of this steel. Under conditions of appreciable mechanical wear (adhesive or abrasive), the materials have to characterize by suitable wear protection. With a low hardness (200 HV) and an austenitic microstructure which cannot be hardened by heat treatment, there is no easy way to improve its wear resistance [1]. Processes used for protecting the constructional or tool steels, such as nitriding, carburizing or boriding, were developed in order to produce the surface layers which could improve the wear behaviour of austenitic steel [2÷11]. Glow discharge assisted lowtemperature nitriding was studied by the papers [2, 3]. The process, carried out at 440°C for 6 h, resulted in formation of a thin layer (4 m) consisting of chromium nitrides (CrN) as well as austenite supersaturated with nitrogen [2]. The layer produced at 550°C (823 K) for 6 h was characterized by the thickness about 20 m [3], and iron nitrides (Fe4N) were additionally observed in microstructure with using the higher process temperature [3, 4]. The chromium nitrides Cr2N also were identified in the nitrided layer [5]. Low temperature plasma carburizing was a thermochemical treatment designed so as to achieve a good combination of wear and corrosion resistance in stainless steels [6÷9]. The process at the temperature below 520°C (793 K) produced the layer consisting only of the austenite supersaturated with carbon, and characterized by an expanded lattice [6÷9], while the chromium carbides, expanded austenite and martensite occurred after carburizing at higher temperature [6]. The layers obta[...]

Low-cycle fatigue strength of borocarburized 15NiCr13 steel DOI:10.15199/28.2015.2.4

  The high fatigue resistance of carburized layers is well known. Simultaneously, there is not much data referring to the fatigue strength of borided layers. Some papers showed the advantageous influence of borocarburizing process on fatigue performance. The resistance of borocarburized layers to the lowcycle fatigue was higher than the one characteristic of typical borided layer formed on medium-carbon steel. In this study, the two-step process: carburizing followed by boriding was used in order to form the borocarburized layer. The investigated material as well as the boriding parameters were adequately selected in order to improve the low-cycle fatigue strength. The borocarburized 15NiCr13 steel was examined. This material was selected because of its advantageous carbon concentration-depth profile beneath iron borides obtained after boriding. The gas boriding in N2-H2-BCl3 atmosphere consisted of two stages: saturation with boron and diffusion annealing, alternately repeated. This treatment was carried out in order to obtain a limited amount of the brittle FeB phase in the boride zone. The low-cycle fatigue strength of through-hardened borocarburized steel was comparable to that obtained in case of throughhardened carburized specimen, which was previously investigated under the same conditions. The advantageous carbon concentration-depth profile as well as limited amount of FeB phase had a positive influence on the low-cycle fatigue strength. Therefore, the fatigue performance of borocarburized layer could approach a limit obtained for carburized layer.1. INTRODUCTION Diffusion boriding being a thermochemical process is widely used for production of boride-type layer. This process results in the formation of FeB and Fe2B needle-like microstructure on the steel’s surface. The occurrence of iron borides increases to a high degree: hardness (up to 2000 HV), wear resistance and corrosion resistance [1÷7]. As for the main disadvantage of[...]

Laser heat treatment of gas-nitrided layer produced on 42CrMo4 steel DOI:10.15199/28.2015.5.21

  Gas nitriding, together with gas carburizing and gas carbonitriding, is the most commonly used thermochemical treatment. This process resulted in many advantageous properties: high hardness, enhanced corrosion resistance, and considerably improved wear resistance and fatigue strength. A wide range of steels, including special nitriding steels (41CrAlMo7, 33CrMoV12-9), low alloy steels, tool steels as well as austenitic steels, can be nitrided. Special attention requires the nitride layer at the surface that is mainly critical to such properties as corrosion resistance or resistance to friction wear. In this study, gas nitriding was carried out on 42CrMo4 steel resulting in ε + γ′ compound layer at the surface. Next, the nitrided layer was laser heat treated (LHT) using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as a single tracks and as multiple tracks with overlapping of about 86%. LHT caused the decomposition of continuous compound layer and an increase in hardness of previously nitrided layer, enlarging the hardened zone. The results showed an advantageous influence of laser heat treatment on the wear resistance. Key words: gas nitriding, laser heat treatment, microstructure, hardness, wear resistance. Laserowa obróbka cieplna warstwy azotowanej wytworzonej na stali 42CrMo4 Azotowanie gazowe, obok gazowych procesów nawęglania i azotonawęglania, jest najpowszechniej stosowaną obróbką cieplno-chemiczną. Proces ten skutkuje wieloma korzystnymi właściwościami: dużą twardością, poprawą odporności korozyjnej oraz znacznie zwiększoną odpornością na zużycie i wytrzymałością zmęczeniową. Proces jest szeroko stosowany w odniesieniu do stali, w tym specjalnych stali do azotowania (41CrAlMo7, 33CrMoV12-9), stali niskostopowych, narzędziowych, jak również stali austenitycznych. Szczególnej uwagi wymaga warstwa azotków przy powierzchni, która ma istotne znaczenie dla takich właściwości jak odporność na korozję czy na zuż[...]

Laser boriding of 100CrMnSi6-4 steel using CaF2 self-lubricating addition DOI:10.15199/28.2015.6.22

  100CrMnSi6-4 steel, being a high carbon chromium steel with increased content of manganese and silicon, is commonly used in the bearing industry as a standard material. This material is predominantly applied to elements of rolling bearings taking into consideration its good wearability as well as good resistance to contact fatigue. The diffusion boronizing was a thermochemical treatment which improved tribological properties of this steel. In this study, instead of diffusion process, the laser boriding was used in order to produce boride layer on this material. The two types of alloying materials were applied. First, the surface of base material was coated by paste including amorphous boron only. The second alloying material consisted of the mixture of amorphous boron and CaF2 as a self-lubricating addition. Next, the surface was remelted by laser beam with using TRUMPF TLF 2600 Turbo CO2 laser. The continuous laser-borided layers were obtained at the surface. They were uniform in respect of the thickness because of the high overlapping used during the laser treatment (86%). The laser-borided layers were significantly thicker than that reported for diffusion boriding. The increased hardness was observed in remelted zone and in heat-affected zone. The significant increase in wear resistance of laser-borided layer was caused by CaF2 self-lubricating addition. Key words: laser boriding, self-lubricating addition, microstructure, hardness, wear resistance. Laserowe borowanie stali 100CrMnSi6-4 z zastosowaniem dodatku samosmarującego CaF2 Stal 100CrMnSi6-4 jako wysokowęglowa stal chromowa ze zwiększoną zawartością manganu i krzemu jest powszechnie stosowana w przemyśle łożyskowym jako standardowy materiał. Stal ta jest przede wszystkim stosowana na elementy łożysk tocznych ze względu na jej dobrą odporność na zużycie, jak również dobrą odporność na zmęczenie kontaktowe. Borowanie dyfuzyjne jest obróbką cieplno-chemiczną, która poprawia właściwości [...]

Laser alloying of 316L steel with boron using CaF2 self-lubricating addition DOI:10.15199/28.2016.1.1

  Good resistance to corrosion and oxidation of austenitic 316L steel is well-known. Therefore, this material is often used wherever corrosive media or high temperature are to be expected. However, under conditions of appreciable mechanical wear (adhesive or abrasive), this steel have to characterize by suitable wear protection. The diffusion boronizing can improve the tribological properties of 316L steel. However, the small thickness of diffusion layer causes the limited applications of such a treatment. In this study, instead of diffusion process, the laser boriding was used. The external cylindrical surface of base material was coated by paste including amorphous boron and CaF2 as a self-lubricating addition. Then the surface was remelted by laser beam. TRUMPF TLF 2600 Turbo CO2 laser was used for laser alloying. The microstructure of remelted zone consisted of hard ceramic phases (iron, chromium and nickel borides) located in soft austenite. The layer was uniform in respect of the thickness because of the high overlapping used during the laser treatment (86%). The obtained composite layer was significantly thicker than that-obtained in case of diffusion boriding. The remelted zone was characterized by higher hardness in comparison with the base material. The significant increase in wear resistance of laser-borided layer was observed in comparison with 316L austenitic steel which was laser-alloyed without CaF2. Key words: laser boriding, self-lubricating addition, microstructure, hardness, wear resistance.1. INTRODUCTION AISI 316L austenitic stainless steel is well-known for its good corrosion resistance as well as good resistance to high temperature. It results from a single-phase austenitic microstructure as well as from an effective balance of carbon, chromium, nickel and molybdenum content. Therefore, this steel is often used wherever a high temperature or aggressive corrosive media occur. However, this material is characterized by l[...]

Effect of laser heat treatment parameters on the microstructure and hardness of gas-nitrided layers DOI:10.15199/28.2016.6.9

  Nitriding is commonly used method of thermochemical treatment in order to produce surface layers of improved hardness and wear resistance. Using a gas nitriding with changeable nitriding potential, a nitrogen concentration at the surface could be controlled, influencing the phase composition and the growth kinetics of the layer. In this study, the hybrid surface treatment was applied. It consisted in gas nitriding and laser heat treatment (LHT) of 42CrMo4 steel. Two nitriding processes were carried out using changeable nitriding potential. Parameters on first process were as follows: temperature 570°C (843 K), time 4 h. The second process was performed at lower temperature 520°C (793 K) and longer duration 10 h. This resulted in various depths of the compound zone at the surface (20 and 8 μm, respectively). Next, the nitrided layers were laser heat-treated using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as the single tracks with various scanning rates (vl = 2.88 m/min and vl = 3.84 m/min). The laser beam power (P) ranged from 0.26 to 0.91 kW. The effects of the depth of compound zone as well as LHT parameters on the microstructure, dimensions and microhardness of laser tracks were analysed. In the majority of the produced laser tracks, remelted (MZ) and heat-affected (HAZ) zones were easily identified. Different microstructure was visible at low laser beam power (0.26 kW). The dimensions of MZ were limited, whereas the HAZ was clearly observed. The compound zone was still visible at the surface. Only the porous ε nitrides were slightly melted. Hardness increased significantly after LHT with complete and partial remelting of compound zone. Laser beam power and scanning rate influenced the depth and width of MZ and HAZ, so the thickness of hardened zone. The greater laser beam power or the smaller scanning rate, the larger hardened zone was observed. Key words: gas nitriding, laser heat treatment, microstructure, hard[...]

Corrosion resistance of laser-borided Inconel 600 alloy DOI:10.15199/28.2017.3.7

  1. INTRODUCTION Nickel and its alloys are important materials in industries, which require excellent corrosion resistant and heat resistance. Most of nickel alloys are characterized by higher resistant to corrosion than the stainless steels, especially in solutions containing reducing acids and in case of stress-corrosion cracking. The groups of nickel alloys resistant to corrosion can be categorized according to their major alloying elements: Ni-Cr, Ni-Cr-Mo, Ni-Cr-Fe, Ni-Cu and Ni-Mo [1]. Inconel series alloys (nickel-chromium-iron) are a standard engineering materials for applications which require resistance to heat and corrosion. These materials are characterized by excellent mechanical properties including combination of high strength and good workability. The high concentration of nickel results in resistance to corrosion by many organic and inorganic compounds and also to chloride-ion stress-corrosion cracking. The role of chromium in the Inconel series alloys is to facilitate the passive film formation. Such a film provides protection in a wide range of oxidizing environments such as nitric (HNO3) and chromic (H2CrO4). A secondary role of chromium is to provide some strengthening of the solid solution [1, 2]. However, an essential drawback of Ni-based alloys is their susceptibility to local types of corrosion (including intergranular corrosion). The intergranular corrosion (IGC) of nickel alloys is caused by segregation of alloying elements at the grain boundaries (for example chromium carbides or nitrides). Upon exposure to a corrosive solution, the chemical and structural segregation at grain boundaries leads to electrochemical heterogeneity and to dissolving metal surface and the development of IGC [3]. The secondary disadvantage of Ni-based alloys are their low resistance to abrasive or adhesive wear, which causes their limited application. The suitable surface treatment could increase the wear resistance of thes[...]

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