The presence of γ precipitates in β phase in Cu-Zn-Al single crystals makes the martensitic trans... more The presence of γ precipitates in β phase in Cu-Zn-Al single crystals makes the martensitic transformation temperatures of thermal origin rise, and bring about a decrease in heat and entropy values associated with the transformation. For mechanical origin martensitic transformation, the presence of precipitates causes the critical stress to decrease. As mechanical cycling is carried out this stress increases for the direct β→martensite transformation, but decreases for reverse martensite→transformation
Description de la conception, la construction et l'optimisation du dispositif de production d... more Description de la conception, la construction et l'optimisation du dispositif de production des monocristaux base sur la methode de Bridgman. Production des alliages a memoire de forme de differentes orientations cristallographiques
Proceedings, annual meeting, Electron Microscopy Society of America, 1990
The copper-based alloys studied belong to the group of those materials showing Shape Memory Effec... more The copper-based alloys studied belong to the group of those materials showing Shape Memory Effect (SME). Diffusion Bonding (DB) procedure is an alternative joining method of welding copper-based Shape Memory Alloys, traditionally welded by techniques like electron bean welding (EBW). However EBW provides embrittlement to the joint. This situation has been corrected by DB as confirm the SEM-EDS study presented here.A material shows SME when once has been thermomechanically deformed, it is able to recover its original (as fabricated) shape by means of a simple heat-up. This pheno menom is possible only for those materials which have β phase prone to undergo martensitic transformation. DB technique estimulates diffusion processes betwen materials by the combination of pressure, temperature, time, surface materials roughness and atmosphere condition in the experimental unit with the aid, sometimes, of a third material, in foil or plated form, which is known by the name of interlayer. T...
Stainless steel 316L AISI were coated with hydroxyapatite b y Air Plasma Spraying (APS). Differen... more Stainless steel 316L AISI were coated with hydroxyapatite b y Air Plasma Spraying (APS). Different coatings were obtained by changing the stand -off istance spraying. The coatings were subjected to bond test and ball-on-disc test. It was found that low er spraying stand-off distances show slightly better adhesion at the interface substra te/HAp and the main wear mechanism is the brittle cracking of the coating.
Thermal spraying offers a wide range of coatings with very different composition and properties. ... more Thermal spraying offers a wide range of coatings with very different composition and properties. NiCrBSi is a Ni-base superalloy widely used to obtain high wear resistant coatings. This coating is usually heat treated after thermal spraying to improve their tribological properties. In this work a tribological comparison between NiCrBSi coatings obtained by spray&fuse and as-sprayed coatings obtained by Atmospheric Plasma
Abstract By using a calorimetric technique, the entropy values of the martensitic transformation ... more Abstract By using a calorimetric technique, the entropy values of the martensitic transformation of thermal origin have been determined and compared with those obtained by mechanical compression tests for the stress-induced martensitic transformation.
... 2., which can be expressed by equations 0 250 (7(MPo) Fig. 2. Gibbs free energies of the stre... more ... 2., which can be expressed by equations 0 250 (7(MPo) Fig. 2. Gibbs free energies of the stress-induced martensite versus the applied stress for ^-Cu-Zn-Al single crystals. ... ACKNOWLEDGEMENT The present research was supported by CICYT project MAT 89-0407-...
Abstract The particular temperatures of the martensitic transformation, the heat exchanged during... more Abstract The particular temperatures of the martensitic transformation, the heat exchanged during transformation, the entropy variation, the chemical origin enthalpy, the contribution of the elastic energy and the friction work for Cu-Zn-Al-Mn shape-memory alloys have all been determined using flow calorimetry.
ABSTRACT With most surface engineering procedures it is necessary to create good initial surface ... more ABSTRACT With most surface engineering procedures it is necessary to create good initial surface conditions. In the case of thermal spraying processes it is recommended that a rough surface is created to enhance adhesion of the coating, especially when the coating contains ceramics. For optimum mechanical properties, in particular fatigue behaviour, the surface must remain in a compressive stress state. When high velocity oxyfuel spraying is used a compressive residual stress condition is strongly advised in view of the pressure and velocity with which the powder particles reach the substrate. The method of surface preparation employed can strongly affect the resultant compressive stresses. The effects of grit blasting conditions on the resultant residual stress state have been studied. Compressive residual stress in the surface layer increases with grit blasting time. Time, gun-specimen distance, and impingement angle have also been evaluated and show complementary behaviour.
ABSTRACT Interesting properties that intermetallics possess have made them to be promising materi... more ABSTRACT Interesting properties that intermetallics possess have made them to be promising materials to be used either as bulk materials or as coatings, both at medium or elevated temperature environments. This group of materials possesses a long-range order, which can be kept by some intermetallics until their melting point, which is the main reason why they possess a good stability at high temperatures. Some other properties can be summarized as follows: high thermal conductivity; low density; great strength, particularly at high temperatures; good oxidation resistance at high temperatures (because of the formation of oxide films); low ductility, brittle fracture at room temperature.FeAl coatings from powder of nominal composition Fe–40Al–0.05 Zr (at.%) with 50 ppm B and 1 wt.% Y2O3 have been prepared using high velocity oxy-fuel (HVOF) technique. Several standard spraying conditions have been assessed; some parameter variations from those standards intend to find optimal spraying conditions. The characterization has been carried out by DRX, EDS and Scanning Electron Microscopy. The results conclude that a major intermetallic FeAl phase has been obtained.Microhardness and wear properties have been evaluated for those coatings obtained with optimal conditions. Compared to room temperature sliding wear behaviour, the friction coefficient is reduced when the test is performed at 400 °C.
The presence of γ precipitates in β phase in Cu-Zn-Al single crystals makes the martensitic trans... more The presence of γ precipitates in β phase in Cu-Zn-Al single crystals makes the martensitic transformation temperatures of thermal origin rise, and bring about a decrease in heat and entropy values associated with the transformation. For mechanical origin martensitic transformation, the presence of precipitates causes the critical stress to decrease. As mechanical cycling is carried out this stress increases for the direct β→martensite transformation, but decreases for reverse martensite→transformation
Description de la conception, la construction et l'optimisation du dispositif de production d... more Description de la conception, la construction et l'optimisation du dispositif de production des monocristaux base sur la methode de Bridgman. Production des alliages a memoire de forme de differentes orientations cristallographiques
Proceedings, annual meeting, Electron Microscopy Society of America, 1990
The copper-based alloys studied belong to the group of those materials showing Shape Memory Effec... more The copper-based alloys studied belong to the group of those materials showing Shape Memory Effect (SME). Diffusion Bonding (DB) procedure is an alternative joining method of welding copper-based Shape Memory Alloys, traditionally welded by techniques like electron bean welding (EBW). However EBW provides embrittlement to the joint. This situation has been corrected by DB as confirm the SEM-EDS study presented here.A material shows SME when once has been thermomechanically deformed, it is able to recover its original (as fabricated) shape by means of a simple heat-up. This pheno menom is possible only for those materials which have β phase prone to undergo martensitic transformation. DB technique estimulates diffusion processes betwen materials by the combination of pressure, temperature, time, surface materials roughness and atmosphere condition in the experimental unit with the aid, sometimes, of a third material, in foil or plated form, which is known by the name of interlayer. T...
Stainless steel 316L AISI were coated with hydroxyapatite b y Air Plasma Spraying (APS). Differen... more Stainless steel 316L AISI were coated with hydroxyapatite b y Air Plasma Spraying (APS). Different coatings were obtained by changing the stand -off istance spraying. The coatings were subjected to bond test and ball-on-disc test. It was found that low er spraying stand-off distances show slightly better adhesion at the interface substra te/HAp and the main wear mechanism is the brittle cracking of the coating.
Thermal spraying offers a wide range of coatings with very different composition and properties. ... more Thermal spraying offers a wide range of coatings with very different composition and properties. NiCrBSi is a Ni-base superalloy widely used to obtain high wear resistant coatings. This coating is usually heat treated after thermal spraying to improve their tribological properties. In this work a tribological comparison between NiCrBSi coatings obtained by spray&fuse and as-sprayed coatings obtained by Atmospheric Plasma
Abstract By using a calorimetric technique, the entropy values of the martensitic transformation ... more Abstract By using a calorimetric technique, the entropy values of the martensitic transformation of thermal origin have been determined and compared with those obtained by mechanical compression tests for the stress-induced martensitic transformation.
... 2., which can be expressed by equations 0 250 (7(MPo) Fig. 2. Gibbs free energies of the stre... more ... 2., which can be expressed by equations 0 250 (7(MPo) Fig. 2. Gibbs free energies of the stress-induced martensite versus the applied stress for ^-Cu-Zn-Al single crystals. ... ACKNOWLEDGEMENT The present research was supported by CICYT project MAT 89-0407-...
Abstract The particular temperatures of the martensitic transformation, the heat exchanged during... more Abstract The particular temperatures of the martensitic transformation, the heat exchanged during transformation, the entropy variation, the chemical origin enthalpy, the contribution of the elastic energy and the friction work for Cu-Zn-Al-Mn shape-memory alloys have all been determined using flow calorimetry.
ABSTRACT With most surface engineering procedures it is necessary to create good initial surface ... more ABSTRACT With most surface engineering procedures it is necessary to create good initial surface conditions. In the case of thermal spraying processes it is recommended that a rough surface is created to enhance adhesion of the coating, especially when the coating contains ceramics. For optimum mechanical properties, in particular fatigue behaviour, the surface must remain in a compressive stress state. When high velocity oxyfuel spraying is used a compressive residual stress condition is strongly advised in view of the pressure and velocity with which the powder particles reach the substrate. The method of surface preparation employed can strongly affect the resultant compressive stresses. The effects of grit blasting conditions on the resultant residual stress state have been studied. Compressive residual stress in the surface layer increases with grit blasting time. Time, gun-specimen distance, and impingement angle have also been evaluated and show complementary behaviour.
ABSTRACT Interesting properties that intermetallics possess have made them to be promising materi... more ABSTRACT Interesting properties that intermetallics possess have made them to be promising materials to be used either as bulk materials or as coatings, both at medium or elevated temperature environments. This group of materials possesses a long-range order, which can be kept by some intermetallics until their melting point, which is the main reason why they possess a good stability at high temperatures. Some other properties can be summarized as follows: high thermal conductivity; low density; great strength, particularly at high temperatures; good oxidation resistance at high temperatures (because of the formation of oxide films); low ductility, brittle fracture at room temperature.FeAl coatings from powder of nominal composition Fe–40Al–0.05 Zr (at.%) with 50 ppm B and 1 wt.% Y2O3 have been prepared using high velocity oxy-fuel (HVOF) technique. Several standard spraying conditions have been assessed; some parameter variations from those standards intend to find optimal spraying conditions. The characterization has been carried out by DRX, EDS and Scanning Electron Microscopy. The results conclude that a major intermetallic FeAl phase has been obtained.Microhardness and wear properties have been evaluated for those coatings obtained with optimal conditions. Compared to room temperature sliding wear behaviour, the friction coefficient is reduced when the test is performed at 400 °C.
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