Wyniki 1-10 spośród 21 dla zapytania: authorDesc:"Michał Kulka"

Gradient boride layers formed by diffusion processes and by laser modification of diffusion layers

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Boriding is known in literature data as a thermochemical treatment that permits boride layers of good performance properties. The borided layers are characterized by many advantageous properties. The main ones are: a high hardness of iron borides, high abrasive wear resistance, advantageous profile of internal 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]. There isn’t much information referring to the fatigue strength of borided layers. The influence of boronizing on the fatigue strength is ambiguous, because it depends on many factors: the boriding method, boriding parameters, chemical composition of borided steel, heat-treatment after boriding and defects of the layer [8]. An important defect of borided layers is their brittleness [3, 5, 7]. The frequent symptoms of this defect are: microcracks of these layers, chipping and spalling. There are several methods which can lessen the brittleness of boride layers. The three main ones are: the formation of single-phase Fe2B layers [6, 7], the production of multicomponent and complex borided layers (for example: carburized before boronizing, B-C-nitrided or boro-nitrided layers) [9÷18, 26] and laser heat-treatment (LHT) after boriding instead of throughhardening and tempering [19÷26]. The two last specified methods lead to the formation of the gradient boride layers. These la yers are characterized by a changeable microstructure and properties of the diffusion zone. In recent years, laser technology has been widely used in many processes: the heating of materials by laser beam, laser heat-treatment, laser welding, laser overlaying, laser alloying and synthesis of materials by laser beam [8]. In point of laser usage after boronizing, the interesting treatment is surface laser treatment. The examined gradient boride layers were [...]

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 surface re-melting of borided layer

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Influence of laser surface modification with re-melting on structure and properties of borided 41Cr4 steel was investigated. Microhardness and wear resistance of surface layer was tested. Crystallite sizes after laser treatment were estimated from half-width of XRD lines using Scherrer method. Surface layer properties after laser modification have been compared with the results after classic [...]

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[...]

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