Initial material structure, welding parameters as well as subsequentprocessing or loadings can dr... more Initial material structure, welding parameters as well as subsequentprocessing or loadings can drastically influence the durability of welded partsfabricated from austenitic steels or super-alloys. Metallographic analysis performed ona considerable number of TIG welded joints between parts fabricated from austeniticsteels such as AISI 304, AISI 309, AISI 316 or INCOLOY 800 superalloy allowedidentification of different fracture types caused by processing factors: inadequategeometry of the joint, flaws inside the joint or on the heat affected zone (HAZ). Anothercategory of fracture causes is represented by the service conditions such as intercrystallinecorrosion or stress corrosion. The fracture mechanism has been analyzedalso as in connection with the processing by mean of cold deformation that was appliedafter the welding. Some representative examples are presented by mean ofmetallographic analysis on samples that contained cracks or fractures produced duringprocessing or in service...
Ti-based amorphous alloys produced by ultrarapid melt cooling represent an excellent option as bi... more Ti-based amorphous alloys produced by ultrarapid melt cooling represent an excellent option as biomaterials because of their mechanical properties and corrosion resistance. However, complete elimination of toxic elements is affecting the glass-forming ability and amorphous structure could be obtained only for thin ribbons or powders that are subsequently processed by powder metallurgy. Amorphous ribbons of special Ti 42 Zr 40 Ta 3 Si 15 alloy, which is completely free of any toxic element, were produced by melt spinning, and the thermostability of resulting material was investigated in order to estimate its ability for further heat processing. Isochronal differential scanning calorimetry (DSC) was used to determine transformation points such as glass transition temperature T g or crystallization temperature T x. The activation energy for crystallization of amorphous phase was calculated based on Kissinger method, using heating rates ranging between 5 and 20°C min-1. Amorphous structure of resulting ribbon was evidenced by means of X-rays diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). It was determined that amorphous Ti 42 Zr 40 Ta 3 Si 15 alloy has a high activation energy for crystallization, similar to other Ti-based amorphous alloys, which provides good thermal stability for subsequent processing, especially by means of powder metallurgy techniques.
Magneto-rheological suspensions (MRS) are relatively a new class of materials, obtained from ferr... more Magneto-rheological suspensions (MRS) are relatively a new class of materials, obtained from ferromagnetic particles, with a diameter below 1.0 μm, dispersed into a liquid. Under the action of a magnetic field, magneto-rheological suspensions become quite rigid and their ...
The paper is focused on the fracture mechanism of railway axles due to the fatigue of material. T... more The paper is focused on the fracture mechanism of railway axles due to the fatigue of material. The purpose of the present article is to numerically predict the number of cycles (or kilometers) to fracture of tank wagon railway axles in various theoretical conditions. The stresses in the axles were calculated by finite element methods. The number of cycles to fracture was calculated using closed form solution of NASGRO equation for fatigue crack development starting from an initial crack detectable by means of non-destructive testing. In order to demonstrate the deep negative impact of forbidden thermal treatments and operations applied to railway axles, residual stresses of these treatments were calculated and new numerical predictions of number of cycles to fracture have been made.
A new a biocompatible Ti 42 Zr 40 Ta 3 Si 15 (atomic %) porous bulk glassy alloy was produced by ... more A new a biocompatible Ti 42 Zr 40 Ta 3 Si 15 (atomic %) porous bulk glassy alloy was produced by combination of rapid solidification and powder metallurgy techniques. Amorphous alloy ribbons were fabricated by melt spinning, i.e. extremely fast quenching the molten alloy with 10 6 K/s from T = 1973 K down to room temperature. The ribbons were then cryo-milled at liquid nitrogen temperature in order to produce powder , which was subsequently hot pressed. The resulting thick pellets have a porosity of about 14 vol%, a high compression strength of 337 MPa and a Young's modulus of about E = 52 GPa, values very close to those characteristic of cortical bone. Moreover, the morphology of the samples is very similar to that of cortical bone. The biocompatibility, which is due to the absence of any toxic element in the chemical composition, together with the suitable mechanical behavior, make these samples promising for orthopedic and dentistry applications. Statement of Significance Ti-based alloys are nowadays the standard solution for biomedical implants. However, both the conventional crystalline and amorphous alloys have higher rigidity as the human bone, leading to the damage of the bone at the interface, and contains harmful elements like vanadium, aluminum, nickel or beryllium. The hierarchical porous structures based on glassy alloys with biocompatible elements is a much better alternative. This work presents for the first time the manufacturing of such porous bodies starting from Ti-based amorphous alloy ribbons, which contains only non-harmful elements. The morphology and the compressive mechanical properties of these new products are analyzed in regard with those characteristic to the cortical bone.
Titanium-based bulk metallic glasses (BMGs) are considered to have potential for biomedical appli... more Titanium-based bulk metallic glasses (BMGs) are considered to have potential for biomedical applications because they combine favorable mechanical properties and good biocompatibility. Copper represents the most common alloying element, which provides high amorphization capacity, but reports emphasizing cytotoxic effects of this element have risen concerns about possible effects on human health. A new copper-free alloy with atomic composition Ti 42 Zr 10 Pd 14 Ag 26 Sn 8 , in which Cu is completely replaced by Ag, was formulated based on Morinaga's d-electron alloy design theory. Following this theory, the actual amount of alloying elements, which defines the values of covalent bond strength Bo and d-orbital energy Md, situates the newly designed alloy inside the BMG domain. By mean of centrifugal casting, cylindrical rods with diameters between 2 and 5 mm were fabricated from this new alloy. Differential scanning calorimetry (DSC) and X-rays diffraction (XRD), as well as microstructural analyses using optical and scanning electron microscopy (OM/SEM) revealed an interesting structure characterized by liquid phase-separated formation of crystalline Ag, as well as metastable intermetallic phases embedded in residual amorphous phases.
Fully amorphous rods with diameters up to 2 mm diameter were obtained upon 0.5 at.% Cu addition t... more Fully amorphous rods with diameters up to 2 mm diameter were obtained upon 0.5 at.% Cu addition to the Fe 36 Co 36 B 19.2 Si 4.8 Nb 4 bulk metallic glass. The Cu-added glass shows a very good thermal stability but, in comparison with the Cu-free base alloy, the entire crystallization behavior is drastically changed. Upon heating, the glassy (Fe 36 Co 36 B 19.2 Si 4.8 Nb 4) 99.5 Cu 0.5 samples show two glass transitions-like events, separated by an interval of more than 100 K, in between which a bcc-(Fe,Co) solid solution is formed. The soft magnetic properties are preserved upon Cu-addition and the samples show a saturation magnetization of 1.1 T combined with less than 2 A/m coercivity. The relaxation behavior prior to crystallization, as well as the crystallization behavior, were studied by time-resolved X-ray diffraction using synchrotron radiation. It was found that both glassy alloys behave similar at temperatures below the glass transition. Irreversible structural transformations take place when approaching the glass transition and in the supercooled liquid region.
Eric Labbe1,a, Florin Serban1,b, Mircea Nicoara2,c and Alain Lodini1,d ... 1 Laboratoire d&am... more Eric Labbe1,a, Florin Serban1,b, Mircea Nicoara2,c and Alain Lodini1,d ... 1 Laboratoire d'Analyse des Contraintes Mécaniques Université de Reims-Champagne-Ardenne IFTS, 7 bd Jean Delautre 08000 Charleville-Mézières, France ... 2 "Politehnica" University of Timisoara, ...
ABSTRACT Experimental research in both medical sciences and material science rely in many situati... more ABSTRACT Experimental research in both medical sciences and material science rely in many situations on a reduced quantity of available data, due to limited number of patients or high costs of samples. Some statistical data manipulation methods are discussed regarding their applicability, information content, value and limits. A special attention is given to the extreme values eliminated by the GRUBBS test. The necessity of the elimination of the extreme values is demonstrated.
Fabrication of aluminum-based composites reinforced by ceramic particles or intermetallic phases ... more Fabrication of aluminum-based composites reinforced by ceramic particles or intermetallic phases has focused considerable attention in recent decades because significant improvement in mechanical properties and thermal stability. This paper has considered in-situ fabrication by mean of reactive sintering of blended and compacted powders containing an aluminum-copper hardenable alloy and titanium dioxide. An experimental program has been dedicated to optimize the sintering parameters in terms of both treatments temperature, between 650 and 800°C, and duration, in the range of 3 to 6 hours. Microstructural analysis based on Scanning Electron Microscopy (SEM) has been used to determine of distribution of elements involved in sintering reactions, such as aluminum, titanium and oxygen.
ABSTRACT Nickel-titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-s... more ABSTRACT Nickel-titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-selective membrane materials. They can potentially be used in membrane reactors, which can produce high-purity H-2 and CO2 streams from coal-derived syngas at elevated temperatures. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The ingots were induction-melted under a high-purity argon atmosphere in a quartz tube and graphite crucible injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. Thermal stability of the Ni40Ti40Nb20 and Ni32Ti48Nb20 thin tapes has been examined using DTA analysis.
Initial material structure, welding parameters as well as subsequentprocessing or loadings can dr... more Initial material structure, welding parameters as well as subsequentprocessing or loadings can drastically influence the durability of welded partsfabricated from austenitic steels or super-alloys. Metallographic analysis performed ona considerable number of TIG welded joints between parts fabricated from austeniticsteels such as AISI 304, AISI 309, AISI 316 or INCOLOY 800 superalloy allowedidentification of different fracture types caused by processing factors: inadequategeometry of the joint, flaws inside the joint or on the heat affected zone (HAZ). Anothercategory of fracture causes is represented by the service conditions such as intercrystallinecorrosion or stress corrosion. The fracture mechanism has been analyzedalso as in connection with the processing by mean of cold deformation that was appliedafter the welding. Some representative examples are presented by mean ofmetallographic analysis on samples that contained cracks or fractures produced duringprocessing or in service...
Ti-based amorphous alloys produced by ultrarapid melt cooling represent an excellent option as bi... more Ti-based amorphous alloys produced by ultrarapid melt cooling represent an excellent option as biomaterials because of their mechanical properties and corrosion resistance. However, complete elimination of toxic elements is affecting the glass-forming ability and amorphous structure could be obtained only for thin ribbons or powders that are subsequently processed by powder metallurgy. Amorphous ribbons of special Ti 42 Zr 40 Ta 3 Si 15 alloy, which is completely free of any toxic element, were produced by melt spinning, and the thermostability of resulting material was investigated in order to estimate its ability for further heat processing. Isochronal differential scanning calorimetry (DSC) was used to determine transformation points such as glass transition temperature T g or crystallization temperature T x. The activation energy for crystallization of amorphous phase was calculated based on Kissinger method, using heating rates ranging between 5 and 20°C min-1. Amorphous structure of resulting ribbon was evidenced by means of X-rays diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). It was determined that amorphous Ti 42 Zr 40 Ta 3 Si 15 alloy has a high activation energy for crystallization, similar to other Ti-based amorphous alloys, which provides good thermal stability for subsequent processing, especially by means of powder metallurgy techniques.
Magneto-rheological suspensions (MRS) are relatively a new class of materials, obtained from ferr... more Magneto-rheological suspensions (MRS) are relatively a new class of materials, obtained from ferromagnetic particles, with a diameter below 1.0 μm, dispersed into a liquid. Under the action of a magnetic field, magneto-rheological suspensions become quite rigid and their ...
The paper is focused on the fracture mechanism of railway axles due to the fatigue of material. T... more The paper is focused on the fracture mechanism of railway axles due to the fatigue of material. The purpose of the present article is to numerically predict the number of cycles (or kilometers) to fracture of tank wagon railway axles in various theoretical conditions. The stresses in the axles were calculated by finite element methods. The number of cycles to fracture was calculated using closed form solution of NASGRO equation for fatigue crack development starting from an initial crack detectable by means of non-destructive testing. In order to demonstrate the deep negative impact of forbidden thermal treatments and operations applied to railway axles, residual stresses of these treatments were calculated and new numerical predictions of number of cycles to fracture have been made.
A new a biocompatible Ti 42 Zr 40 Ta 3 Si 15 (atomic %) porous bulk glassy alloy was produced by ... more A new a biocompatible Ti 42 Zr 40 Ta 3 Si 15 (atomic %) porous bulk glassy alloy was produced by combination of rapid solidification and powder metallurgy techniques. Amorphous alloy ribbons were fabricated by melt spinning, i.e. extremely fast quenching the molten alloy with 10 6 K/s from T = 1973 K down to room temperature. The ribbons were then cryo-milled at liquid nitrogen temperature in order to produce powder , which was subsequently hot pressed. The resulting thick pellets have a porosity of about 14 vol%, a high compression strength of 337 MPa and a Young's modulus of about E = 52 GPa, values very close to those characteristic of cortical bone. Moreover, the morphology of the samples is very similar to that of cortical bone. The biocompatibility, which is due to the absence of any toxic element in the chemical composition, together with the suitable mechanical behavior, make these samples promising for orthopedic and dentistry applications. Statement of Significance Ti-based alloys are nowadays the standard solution for biomedical implants. However, both the conventional crystalline and amorphous alloys have higher rigidity as the human bone, leading to the damage of the bone at the interface, and contains harmful elements like vanadium, aluminum, nickel or beryllium. The hierarchical porous structures based on glassy alloys with biocompatible elements is a much better alternative. This work presents for the first time the manufacturing of such porous bodies starting from Ti-based amorphous alloy ribbons, which contains only non-harmful elements. The morphology and the compressive mechanical properties of these new products are analyzed in regard with those characteristic to the cortical bone.
Titanium-based bulk metallic glasses (BMGs) are considered to have potential for biomedical appli... more Titanium-based bulk metallic glasses (BMGs) are considered to have potential for biomedical applications because they combine favorable mechanical properties and good biocompatibility. Copper represents the most common alloying element, which provides high amorphization capacity, but reports emphasizing cytotoxic effects of this element have risen concerns about possible effects on human health. A new copper-free alloy with atomic composition Ti 42 Zr 10 Pd 14 Ag 26 Sn 8 , in which Cu is completely replaced by Ag, was formulated based on Morinaga's d-electron alloy design theory. Following this theory, the actual amount of alloying elements, which defines the values of covalent bond strength Bo and d-orbital energy Md, situates the newly designed alloy inside the BMG domain. By mean of centrifugal casting, cylindrical rods with diameters between 2 and 5 mm were fabricated from this new alloy. Differential scanning calorimetry (DSC) and X-rays diffraction (XRD), as well as microstructural analyses using optical and scanning electron microscopy (OM/SEM) revealed an interesting structure characterized by liquid phase-separated formation of crystalline Ag, as well as metastable intermetallic phases embedded in residual amorphous phases.
Fully amorphous rods with diameters up to 2 mm diameter were obtained upon 0.5 at.% Cu addition t... more Fully amorphous rods with diameters up to 2 mm diameter were obtained upon 0.5 at.% Cu addition to the Fe 36 Co 36 B 19.2 Si 4.8 Nb 4 bulk metallic glass. The Cu-added glass shows a very good thermal stability but, in comparison with the Cu-free base alloy, the entire crystallization behavior is drastically changed. Upon heating, the glassy (Fe 36 Co 36 B 19.2 Si 4.8 Nb 4) 99.5 Cu 0.5 samples show two glass transitions-like events, separated by an interval of more than 100 K, in between which a bcc-(Fe,Co) solid solution is formed. The soft magnetic properties are preserved upon Cu-addition and the samples show a saturation magnetization of 1.1 T combined with less than 2 A/m coercivity. The relaxation behavior prior to crystallization, as well as the crystallization behavior, were studied by time-resolved X-ray diffraction using synchrotron radiation. It was found that both glassy alloys behave similar at temperatures below the glass transition. Irreversible structural transformations take place when approaching the glass transition and in the supercooled liquid region.
Eric Labbe1,a, Florin Serban1,b, Mircea Nicoara2,c and Alain Lodini1,d ... 1 Laboratoire d&am... more Eric Labbe1,a, Florin Serban1,b, Mircea Nicoara2,c and Alain Lodini1,d ... 1 Laboratoire d'Analyse des Contraintes Mécaniques Université de Reims-Champagne-Ardenne IFTS, 7 bd Jean Delautre 08000 Charleville-Mézières, France ... 2 "Politehnica" University of Timisoara, ...
ABSTRACT Experimental research in both medical sciences and material science rely in many situati... more ABSTRACT Experimental research in both medical sciences and material science rely in many situations on a reduced quantity of available data, due to limited number of patients or high costs of samples. Some statistical data manipulation methods are discussed regarding their applicability, information content, value and limits. A special attention is given to the extreme values eliminated by the GRUBBS test. The necessity of the elimination of the extreme values is demonstrated.
Fabrication of aluminum-based composites reinforced by ceramic particles or intermetallic phases ... more Fabrication of aluminum-based composites reinforced by ceramic particles or intermetallic phases has focused considerable attention in recent decades because significant improvement in mechanical properties and thermal stability. This paper has considered in-situ fabrication by mean of reactive sintering of blended and compacted powders containing an aluminum-copper hardenable alloy and titanium dioxide. An experimental program has been dedicated to optimize the sintering parameters in terms of both treatments temperature, between 650 and 800°C, and duration, in the range of 3 to 6 hours. Microstructural analysis based on Scanning Electron Microscopy (SEM) has been used to determine of distribution of elements involved in sintering reactions, such as aluminum, titanium and oxygen.
ABSTRACT Nickel-titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-s... more ABSTRACT Nickel-titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-selective membrane materials. They can potentially be used in membrane reactors, which can produce high-purity H-2 and CO2 streams from coal-derived syngas at elevated temperatures. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The ingots were induction-melted under a high-purity argon atmosphere in a quartz tube and graphite crucible injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. Thermal stability of the Ni40Ti40Nb20 and Ni32Ti48Nb20 thin tapes has been examined using DTA analysis.
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