Wyniki 1-10 spośród 13 dla zapytania: authorDesc:"Natalia Makuch"

Laser-modified boride layer formed on 100CrMnSi6-4 steel

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Boriding being a thermochemical process was widely used for boride-type coating. This process generally resulted in the formation of FeB and Fe2B needle-like microstructure at the surface. The presence of iron borides, formed on the steel’s surface, increased to a high degree: hardness (up to 2000 HV), wear resistance and corrosion resistance [1÷7]. As for the main disadvantage of boriding the brittleness of borided layers, especially of FeB boride [3, 5, 7], needs to be mentioned. There are several factors that cause the brittleness of borided layers: first, the FeB and Fe2B have high hardness, second, a large hardness gradient exists between the borided layer and the substrate. There are many methods, which can lessen the brittleness of the boride layers. The top three methods are: obtaining a single-phase Fe2B layer [6, 7], the production of multicomponent and complex borided layers [8÷19] and laser-heat treatment (LHT) after boriding [20÷29]. In recent years, laser technology was widely used in many processes: the heating of materials by the laser beam, laser-heat treatment (LHT), laser welding, laser overlaying, laser alloying and synthesis of materials by the laser beam [30, 31]. The laser boriding process was also widely developed [32÷36]. In this paper, the laser surface modification was used in order to the formation of gradient boride layer on 100CrMnSi6-4 steel. The laser-heat treatment, instead of conventional hardening, was carried out, after diffusion boriding. The microstructure, the microhardness profiles, and the abrasive wear resistance were investigated and compared to the properties obtained for typical diffusion-borided layer. EXPERIMENTAL PROCEDURE 100CrMnSi6-4 steel was used for investigation. Its chemical composition was presented in Table 1. The ring-shaped specimens (external diameter ca. 20 mm, internal diameter 12 mm and height 12 mm) were used. Gas boriding was carried out in H2-BCl3 atmosp[...]

Laser boriding of carburized steel

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Boriding being a thermochemical process is widely used for boridetype coating. This process generally results in the formation of FeB and Fe2B needle-like microstructure at the surface. The presence of iron borides formed on the steels surfaces increases largely their hardness (up to 2000 HV), wear resistance and corrosion resistance [1÷7]. The main disadvantage of boriding is the brittleness of borided layers, especially of FeB boride [3, 5, 7]. There are several factors that cause the brittleness of borided layers: first, the FeB and Fe2B have high hardness; second, a large hardness gradient exists between the borided layer and the substrate. Many methods can decrease the brittleness of the boride layers. Three main are: obtaining a single-phase Fe2B layer [6, 7]; the production of multicomponent and complex borided layers [8÷17] and laser heat treatment (LHT) after boriding [18÷26]. The borocarburizing process [12÷16, 27] leads to the formation of multicomponent layers (B-C) by tandem diffusion processes: precarburizing and boriding. These layers are characterized by improved properties, especially increased abrasive wear resistance and increased low-cycle fatigue strength in comparison with typical borided layers. In recent years, laser technology has been widely used in many processes: the heating of materials by laser beam, laser heat-treatment (LHT), laser welding, laser overlaying, laser alloying and synthesis of materials by laser beam [28, 29]. The laser boriding process has been widely developed [30÷33], too. In this paper the laser alloying by boron was used in order to formation of gradient boride layers. The laser boriding, instead of diffusion process, was carried out after diffusion carburizing. The microstructure, microhardness profiles and abrasive wear resistance were investigated and compared with these properties obtained in the case of typical borided or borocarburized layers. EXPERIM ENTAL PROC EDUR E [...]

Two-stage gas boriding of carburized steel in N2–H2–BCl3 atmosphere

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Boronizing is a thermochemical surface treatment in which boron atoms diffuse into the surface of a workpiece to form borides with the base material. When applied to the adequate materials, boronizing provides high hardness, wear and abrasion resistance, heat resistance or corrosion resistance [1÷7]. This process generally results in the formation of FeB and Fe2B needle-like microstructure at the surface of steel. The main disadvantage of boriding is the brittleness of borided layers, especially of FeB boride [3, 5, 7]. There are several factors that cause the brittleness of borided layers: first, the FeB and Fe2B have high hardness; second, a large hardness gradient exists between the borided layer and the substrate. Many methods can lessen the brittleness of the boride layers. Three main are: obtaining a single-phase Fe2B layer [6, 7]; the production of multicomponent and complex borided layers [8÷18] and laser heat treatment (LHT) after boriding [19÷27]. The borocarburizing process [12÷16, 18] leads to the formation of multicomponent layers (B-C) by tandem diffusion processes: precarburizing and boriding. These layers are characterized by improved properties, especially increased abrasive wear resistance [12÷15] and increased low-cycle fatigue strength [18] in comparison with typical borided layers. In this paper new method of gas boronizing was used to the formation of gradient borocarburized layers. First, instead of H2- BCl3 atmosphere [12÷18], more safe gas mixture consisting of N2-H2-BCl3 was used [28]. Second, the two-stage boriding was applied in order to acceleration of boron diffusion and to minimize of FeB phase presence. This process consists in two stages: saturation by boron and diffusion annealing. During first step BCl3 was added to N2-H2 atmosphere. BCl3 to hydrogen ratio was higher than that previously added [12÷18]. Second step consisted in diffusion annealing while an addition of BCl3 was switched off. Th[...]

Cohesion and fracture toughness of gradient boride layers formed by borocarburizing

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Boriding being a thermochemical process is widely used for boridetype coating. This process generally results in the formation of FeB and Fe2B needle-like microstructure at the surface. The presence of iron borides formed on the steels surfaces increases largely their hardness (up to 2000 HV), wear resistance, corrosion resistance and heat resistance [1÷3]. The main disadvantage of boriding is the brittleness of borides, especially of FeB phase. There are several factors that cause the brittleness of borided layers: first, the FeB and Fe2B have high hardness; second, a large hardness gradient exists between the borided layer and the substrate. The frequent symptoms of this defect are: microcracks of these layers, chipping and spalling. The literature data [4, 5] show, that the following factors influence the brittleness of borides: case depth of the layer, hardness, phase composition, internal stresses and chemical composition of borided steel. Many methods can lessen the brittleness of the boride layers. Three main are: obtaining a single-phase Fe2B layer [1÷3], the production of multicomponent and complex borided layers [6÷9] and laser heat treatment (LHT) after boriding [10÷12]. The one of these methods is boriding of previously carburized steel [7÷9]. This process called borocarburizing aims at forming a transition layer between the borided layer and the substrate. The transition area has a relatively higher carbon concentration and higher hardness, what reduces the hardness gradient of the iron borides to the substrate. Hence the brittleness of borided layer is lessened. The borocarburized layers are characterized by improved abrasive wear resistance and increased low-cycle fatigue strength in comparison with typical borided layers formed on medium-carbon steel [7, 9]. Although the fracture toughness of typical borided layers is well known, there is not information referring this property in case of borocarburized layers.[...]

Wear resistance improvement of pure titanium by laser boriding

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Titanium and its alloys are known for their excellent mechanical and chemical properties. Some exceptional properties are characteristic of titanium alloys: very high strength-to-weight ratio (even at high temperature), high stiffness, toughness, low elastic modulus and, finally, excellent biocompatibility. They possess also excellent corrosion resistance because of the formation of a continuous and stable oxide film on their surface. However, the poor wear resistance, as an important disadvantage limits the potential use of these alloys [1÷3]. Therefore, these materials have to be protected against friction and wear. Among its numerous applications, titanium is widely applied for biomedical implants: bone screws, hip and knee joints, heart pumps or dental posts. However, its poor tribological properties in comparison with other biomedical materials such as Co-Cr alloys [4] and Al2O3 ceramics are a limiting factor when employed as a bearing material in articulating joint implants [5]. The diffusion boronizing could be the thermochemical treatment, which improves tribological properties of titanium and its alloys. It was shown in literature data [2, 3, 6÷10] that titanium and its alloys can be borided efficiently, but the use of conventional methods is limited owing to relatively long processing time, and only a thin layer is produced. Titanium can be boronized without sacrificing corrosion resistance. The boriding process results in formation of two types titanium borides (TiB and TiB2) at the surface. TiB2 borides grow as solid monolithic layer at the surface while the TiB borides occur below and predominantly grow as pristine whiskers, generally perpendicular to the surface [2, 3, 6÷10]. In work [2] a 10 μm thick continuous boride layer, composed of TiB2 and TiB phases, was formed on the surface of a Ti-6Al-4V alloy using a pack boriding technique in commercial Ekabor II powder at 1100°C for 2.5 h. The hardness of the bo[...]

Gas boriding of Inconel 600 alloy

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Boronizing is a thermochemical surface treatment in which boron atoms diffuse into the surface of a workpiece to form borides with the base material. When applied to the adequate materials, boronizing provides wear and abrasion resistance comparable to sintered carbides. Borided layers can be often characterized by more than double increase in the wear resistance of metal parts that were previously carburized, nitrided, nitrocarburized, or hard chrome plated in numerous applications. The selection of material is very important. The possibilities of borides formation with different materials are generally known. Boriding can be applied to a wide range of steel alloys, including carbon steel, low alloy steel, tool steel and stainless steel. Low alloy steels that have been carburized can be subsequently boronized and then rehardened. Boriding of steels generally results in the formation of FeB and Fe2B needle-like microstructure at the surface. The boride layers are characterized by many advantageous properties: high hardness of iron borides (up to 2000 HV), high abrasive wear resistance, the advantageous profile of residual stresses, high heat resistance, high corrosion resistance in acid and alkaline solutions, high resistance to influence of liquid metals and alloys and high hardness at increased temperatures [1÷7]. The main disadvantage of these layers is their brittleness, especially of FeB boride [3, 5, 7]. There are several factors that cause this brittleness: first, the FeB and Fe2B have a high hardness, second, a large hardness gradient exists between the boride layer and the substrate. There are many methods, which can lessen the brittleness of the boride layers. The top three methods are: obtaining a single-phase Fe2B layer [6, 7], the production of multicomponent and complex boride layers [8÷15] and laser heat treatment (LHT) after boriding [16÷20]. The borocarburizing process [11÷15] leads to the formation of hybrid l[...]

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-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[...]

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