Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, Oct 13, 2011
The mechanical properties of Ti-6Al-4V parts fabricated by shaped metal deposition, an additive l... more The mechanical properties of Ti-6Al-4V parts fabricated by shaped metal deposition, an additive layer manufacturing technique applying wire-based tungsten inert gas welding, have been measured, with the emphasis of comparing the effect of two different deposition rates. Similar part geometries were obtained for two parts fabricated with deposition rates of 0.1 and 0.3 m/min by adjusting the energy input and the wire feed rate accordingly. This affected the thermal history of the parts, and consequently the morphology, microstructure and mechanical performance. The ultimate tensile strength was between 880 and 1000 MPa, where the strength and hardness were lower for the slower deposition rate. The strain at failure was significantly better for tensile testing perpendicular rather than parallel to the base plate, and considerably larger for the part fabricated with the lower deposition rate. The Young’s modulus was comparable for both deposition rates, and independent of the orientation.
A novel near net-shape layer-by-layer welding technique-Shaped Metal Deposition (SMD)-using Tungs... more A novel near net-shape layer-by-layer welding technique-Shaped Metal Deposition (SMD)-using Tungsten Inert Gas (TIG) welding was employed to produce components from a 308 stainless steel wire. This technique is meant to fabricate metal components for rapid prototyping or for reparation of components when no additional tooling is available. The mechanical properties of components prepared by this novel route have to be known before application, since they do not necessarily coincide with the properties of components derived from conventional fabrication methods. The component exhibits a microstructure composed of austenite and vermicular d ferrite with the predominance of austenite. Neither the structure nor the mechanical properties are dependent on the height of the component. The mechanical properties are comparable to those of components prepared by conventional techniques.
Development of thermoelectric materials based on iron-sulfide minerals is reviewed with focusing ... more Development of thermoelectric materials based on iron-sulfide minerals is reviewed with focusing on n-type doped CuFeS 2. It is found that the thermoelectric properties of Zn-doped CuFeS 2 strongly depend on the synthesis method, especially on the cooling rate and heat treatment conditions after spark-plasma sintering (SPS). A high power factor exceeding 1 mW/K 2 m is achieved around room temperature for samples annealed and slowly cooled after SPS. With aiming at reducing thermal conductivity, several methods are applied including the high-pressure torsion technique and nano-structuring by ball milling. These experiments successfully yield reduced thermal conductivity, though experimental conditions needs to be optimized to reduce electrical resistivity simultaneously.
ZrO2 stabilized with Y2O3 varies very much in appearance, crystallography, microstructure as well... more ZrO2 stabilized with Y2O3 varies very much in appearance, crystallography, microstructure as well as mechanical properties depending on the yttria concentration and on the thermal pre-history. As shown by the phase diagram1 of the ZrO2-Y2O3 system, the high-temperature cubic and tetragonal phases can be stabilized down to room temperature. At yttria concentrations above about 8 mol% the material is cubic. In the concentration range between about 3 and 7 mol% precipitates of the tetragonal phase are contained in a cubic or tetragonal matrix. The material is then called partially stabilized ZrO2 (PSZ).2, 3, 4, 5 The size and concentration of the precipitates most sensitively depend on the particular heat treatment. Domains of tetragonal structure with different orientations of the c-axis may form large colonies. A specific tetragonal phase, the so-called t’-ZrO2, formed by a displacive composition-invariant transformation of the cubic phase during rapid cooling6, 7, 8 has a microstructure similar to the two-phase material.
ABSTRACT Ceramic thermal barrier coatings (TBC) can exhibit premature in-service failure due to s... more ABSTRACT Ceramic thermal barrier coatings (TBC) can exhibit premature in-service failure due to spallation as a consequence of exposure to elevated temperatures, aggressive environments, and cyclic thermal and mechanical loading. In this study, the influence of cyclic mechanical loading and thermal gradients on the damage mechanisms in TBC systems is investigated. Performed tests were thermal fatigue with superimposed mechanical fatigue load and thermal gradient over the cross section as well as isothermal mechanical fatigue at high temperature. The stress states generated by mechanical loading and thermal gradients in the course of the respective test cycle were analyzed by Finite Element calculations. The calculated stress distributions were used to discuss specific damage patterns observed for the different test types. In the case of thermal gradient mechanical fatigue tests, which generate stresses most closely to in-service conditions of rotating gas turbine blades, the observed evolution of cracks parallel to the coating surface can explain accelerated TBC spallation.
In a companion paper, the correlation between the temperature field and the microstructure has be... more In a companion paper, the correlation between the temperature field and the microstructure has been studied in a series of specimens made by Shaped Metal Deposition (SMD). The aim of the present paper is to improve the microstructure evolution model by taking into account not only the temperature and its rate but also the kinetics of the different solid phase transformations occurring in the Ti-6Al-4V alloy along the multiple heating and cooling cycles. At high temperature (above the beta-transus ~1000°C), Ti-6Al-4V is in the beta phase field. During cooling, the beta phase may transform to martensitic or massive alpha, Widmanstätten alpha or grain-boundary or colony alpha, depending on the cooling rate. Transformation to martensitic/massive alpha takes place under rapid cooling and is assumed to be diffusionless or instantaneous. At lower cooling rates, Widmanstätten and grain boundary/colony alpha growth is diffusion-controlled. Further, the diffusive transformation of martensitic/massive alpha into Widmanstätten alpha is considered during cooling based on observations. In addition, during heating, diffusion-controlled transformation of martensitic/massive alpha into Widmanstätten alpha and instantaneous growth of the beta phase fraction at the expenses of the fractions of martensitic/massive alpha, Widmanstätten alpha, and grain-boundary/colony alpha is assumed. For diffusive transformation, the temperature history of a point (computed as described in the companion paper) is approximated as a series of isothermal steps where the transformation is governed by the Johnson-Mehl-Avrami law. Massive/martensitic transformation is described using the Koistinen-Marburger law, while transformation of martensitic/massive alpha, Widmanstätten alpha, and grain-boundary/colony alpha into beta during heating is assumed to follow the beta equilibrium curve. Numerical results are compared to the experimentally observed microstructure, which helps to understand the complex transformation modes taking place during the repeated heating and cooling sequences of a SMD run.
Copper presents a number of challenges for additive manufacturing. These include high thermal con... more Copper presents a number of challenges for additive manufacturing. These include high thermal conductivity, significant light reflectivity, and sever oxide formation. The electron beam as an energy source can overcome these difficulties in the production of copper AM components due to the high power available, the high process energy efficiency and the fact that the process takes place in vacuum. Non-porous copper components can be produced at high deposition rates of up to 2.5 kg/h using wire electron beam additive manufacturing. This technique can also create multi-material components in both copper and steel, and copper features on copper components. It should be emphasised that an average power of 3.0 kW was sufficient to produce copper features on copper components at the high deposition rate mentioned above. The power and energy distribution of the electron beam can be adjusted at any time. This allows grain growth and the associated microstructure to be influenced. It has been found that using a copper base plate instead of a steel base plate requires significantly different process parameters. Successfully producing geometries on copper base plates is challenging due to the high thermal conductivity of copper and requires a large beam power in the early layers. Pure copper components made by wire electron beam additive manufacturing have an electrical conductivity of 100% of the international standard for annealed copper. By optimising the energy input and distribution, the ultimate tensile strength of 206 MPa with a strain at failure of 31% can be achieved.
The additive manufacturing of copper faces following challenges:-high thermal conductivity-signif... more The additive manufacturing of copper faces following challenges:-high thermal conductivity-significant light reflectivity-sever oxide formation. The electron beam is predestined to meet these challenges due to the high power available, the high efficiency of the process energy and the operation in vacuum. Directed energy deposition with the electron beam (DED-EB) allows the production of large-scale copper components at high deposition rates with high quality. Commonly, the semi-finished product is built on a base plate which must be removed afterwards. However, it is also possible to add copper features to a base component which is part of the final product. This base product may be out of copper or another metal if no metallurgical restrictions apply. The aim of this paper is to report on microstructure and material properties and to present case studies of copper components.
Les aubes de turbine a gaz dans des propulseurs ou pour la production d'electricite sont soum... more Les aubes de turbine a gaz dans des propulseurs ou pour la production d'electricite sont soumises a de fortes sollicitations thermiques qui surviennent de maniere cyclique et rendent la surface metallique rugueuse. Selon la presente invention, la surface metallique est pourvue d'un revetement mince en ceramique d'une epaisseur inferieure a 50 µm, ce qui permet d'eviter que ladite surface ne devienne rugueuse.
Shaped Metal Deposition (SMD) is a novel technology to build near-net shaped parts by successive ... more Shaped Metal Deposition (SMD) is a novel technology to build near-net shaped parts by successive weld deposition. The SMD rig consists of a robot with a Tungsten Inert Gas (TIG) welding torch and a manipulator, which are housed inside a sealed chamber. The heat transfer problem is modeled in a series of walls made by SMD of Ti-6Al-4V alloy. The studied specimens have different dimensions and were obtained using a wide range of process parameters (number of layers, layer height, wire feed rate, travel speed, heat input, etc.). The aim is to correlate the temperature field predicted using the finite element model developed by Centro Internacional de Métodos Computacionales en Ingeniería (Santa Fe, Argentina) to macro-, meso-and micrographical observations done at the Department of Metallurgy and Materials Engineering (Katholieke Universiteit Leuven, Belgium), as a way of validating the model of such a complex process. SMD subjects the build part repeatedly to a specific temperature field which results in a unique morphology and in microstructures usually not achievable by conventional fabrication techniques. The appearance of distinct microstructures in the top of the walls, in the substrate and in the intermediate region is explained on the basis of temperature and temperature rate results. Modelling of microstructure evolution in terms of phase kinetics based on phase transformation diagrams is dealt with in a companion paper.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2011
A component prepared by shaped metal deposition (SMD) using 300M steel wire is studied to reveal ... more A component prepared by shaped metal deposition (SMD) using 300M steel wire is studied to reveal structure and material properties. The component exhibits a bainitic microstructure changing from distinct sheaves to homogenous from top to bottom. This change in microstructure is reflected by a step-like increase of the volume fraction of austenite towards the bottom of the component, and a step-like decrease of the microhardness. A certain deviation of the general change in the morphology of bainite from top to bottom appears at the very bottom of the component, caused by the influence of the base plate. Tensile tests show a very high ultimate tensile strength of about 1500 MPa and an elastic modulus of 200 GPa, which is comparable to that of material in cast condition.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, Oct 13, 2011
The mechanical properties of Ti-6Al-4V parts fabricated by shaped metal deposition, an additive l... more The mechanical properties of Ti-6Al-4V parts fabricated by shaped metal deposition, an additive layer manufacturing technique applying wire-based tungsten inert gas welding, have been measured, with the emphasis of comparing the effect of two different deposition rates. Similar part geometries were obtained for two parts fabricated with deposition rates of 0.1 and 0.3 m/min by adjusting the energy input and the wire feed rate accordingly. This affected the thermal history of the parts, and consequently the morphology, microstructure and mechanical performance. The ultimate tensile strength was between 880 and 1000 MPa, where the strength and hardness were lower for the slower deposition rate. The strain at failure was significantly better for tensile testing perpendicular rather than parallel to the base plate, and considerably larger for the part fabricated with the lower deposition rate. The Young’s modulus was comparable for both deposition rates, and independent of the orientation.
A novel near net-shape layer-by-layer welding technique-Shaped Metal Deposition (SMD)-using Tungs... more A novel near net-shape layer-by-layer welding technique-Shaped Metal Deposition (SMD)-using Tungsten Inert Gas (TIG) welding was employed to produce components from a 308 stainless steel wire. This technique is meant to fabricate metal components for rapid prototyping or for reparation of components when no additional tooling is available. The mechanical properties of components prepared by this novel route have to be known before application, since they do not necessarily coincide with the properties of components derived from conventional fabrication methods. The component exhibits a microstructure composed of austenite and vermicular d ferrite with the predominance of austenite. Neither the structure nor the mechanical properties are dependent on the height of the component. The mechanical properties are comparable to those of components prepared by conventional techniques.
Development of thermoelectric materials based on iron-sulfide minerals is reviewed with focusing ... more Development of thermoelectric materials based on iron-sulfide minerals is reviewed with focusing on n-type doped CuFeS 2. It is found that the thermoelectric properties of Zn-doped CuFeS 2 strongly depend on the synthesis method, especially on the cooling rate and heat treatment conditions after spark-plasma sintering (SPS). A high power factor exceeding 1 mW/K 2 m is achieved around room temperature for samples annealed and slowly cooled after SPS. With aiming at reducing thermal conductivity, several methods are applied including the high-pressure torsion technique and nano-structuring by ball milling. These experiments successfully yield reduced thermal conductivity, though experimental conditions needs to be optimized to reduce electrical resistivity simultaneously.
ZrO2 stabilized with Y2O3 varies very much in appearance, crystallography, microstructure as well... more ZrO2 stabilized with Y2O3 varies very much in appearance, crystallography, microstructure as well as mechanical properties depending on the yttria concentration and on the thermal pre-history. As shown by the phase diagram1 of the ZrO2-Y2O3 system, the high-temperature cubic and tetragonal phases can be stabilized down to room temperature. At yttria concentrations above about 8 mol% the material is cubic. In the concentration range between about 3 and 7 mol% precipitates of the tetragonal phase are contained in a cubic or tetragonal matrix. The material is then called partially stabilized ZrO2 (PSZ).2, 3, 4, 5 The size and concentration of the precipitates most sensitively depend on the particular heat treatment. Domains of tetragonal structure with different orientations of the c-axis may form large colonies. A specific tetragonal phase, the so-called t’-ZrO2, formed by a displacive composition-invariant transformation of the cubic phase during rapid cooling6, 7, 8 has a microstructure similar to the two-phase material.
ABSTRACT Ceramic thermal barrier coatings (TBC) can exhibit premature in-service failure due to s... more ABSTRACT Ceramic thermal barrier coatings (TBC) can exhibit premature in-service failure due to spallation as a consequence of exposure to elevated temperatures, aggressive environments, and cyclic thermal and mechanical loading. In this study, the influence of cyclic mechanical loading and thermal gradients on the damage mechanisms in TBC systems is investigated. Performed tests were thermal fatigue with superimposed mechanical fatigue load and thermal gradient over the cross section as well as isothermal mechanical fatigue at high temperature. The stress states generated by mechanical loading and thermal gradients in the course of the respective test cycle were analyzed by Finite Element calculations. The calculated stress distributions were used to discuss specific damage patterns observed for the different test types. In the case of thermal gradient mechanical fatigue tests, which generate stresses most closely to in-service conditions of rotating gas turbine blades, the observed evolution of cracks parallel to the coating surface can explain accelerated TBC spallation.
In a companion paper, the correlation between the temperature field and the microstructure has be... more In a companion paper, the correlation between the temperature field and the microstructure has been studied in a series of specimens made by Shaped Metal Deposition (SMD). The aim of the present paper is to improve the microstructure evolution model by taking into account not only the temperature and its rate but also the kinetics of the different solid phase transformations occurring in the Ti-6Al-4V alloy along the multiple heating and cooling cycles. At high temperature (above the beta-transus ~1000°C), Ti-6Al-4V is in the beta phase field. During cooling, the beta phase may transform to martensitic or massive alpha, Widmanstätten alpha or grain-boundary or colony alpha, depending on the cooling rate. Transformation to martensitic/massive alpha takes place under rapid cooling and is assumed to be diffusionless or instantaneous. At lower cooling rates, Widmanstätten and grain boundary/colony alpha growth is diffusion-controlled. Further, the diffusive transformation of martensitic/massive alpha into Widmanstätten alpha is considered during cooling based on observations. In addition, during heating, diffusion-controlled transformation of martensitic/massive alpha into Widmanstätten alpha and instantaneous growth of the beta phase fraction at the expenses of the fractions of martensitic/massive alpha, Widmanstätten alpha, and grain-boundary/colony alpha is assumed. For diffusive transformation, the temperature history of a point (computed as described in the companion paper) is approximated as a series of isothermal steps where the transformation is governed by the Johnson-Mehl-Avrami law. Massive/martensitic transformation is described using the Koistinen-Marburger law, while transformation of martensitic/massive alpha, Widmanstätten alpha, and grain-boundary/colony alpha into beta during heating is assumed to follow the beta equilibrium curve. Numerical results are compared to the experimentally observed microstructure, which helps to understand the complex transformation modes taking place during the repeated heating and cooling sequences of a SMD run.
Copper presents a number of challenges for additive manufacturing. These include high thermal con... more Copper presents a number of challenges for additive manufacturing. These include high thermal conductivity, significant light reflectivity, and sever oxide formation. The electron beam as an energy source can overcome these difficulties in the production of copper AM components due to the high power available, the high process energy efficiency and the fact that the process takes place in vacuum. Non-porous copper components can be produced at high deposition rates of up to 2.5 kg/h using wire electron beam additive manufacturing. This technique can also create multi-material components in both copper and steel, and copper features on copper components. It should be emphasised that an average power of 3.0 kW was sufficient to produce copper features on copper components at the high deposition rate mentioned above. The power and energy distribution of the electron beam can be adjusted at any time. This allows grain growth and the associated microstructure to be influenced. It has been found that using a copper base plate instead of a steel base plate requires significantly different process parameters. Successfully producing geometries on copper base plates is challenging due to the high thermal conductivity of copper and requires a large beam power in the early layers. Pure copper components made by wire electron beam additive manufacturing have an electrical conductivity of 100% of the international standard for annealed copper. By optimising the energy input and distribution, the ultimate tensile strength of 206 MPa with a strain at failure of 31% can be achieved.
The additive manufacturing of copper faces following challenges:-high thermal conductivity-signif... more The additive manufacturing of copper faces following challenges:-high thermal conductivity-significant light reflectivity-sever oxide formation. The electron beam is predestined to meet these challenges due to the high power available, the high efficiency of the process energy and the operation in vacuum. Directed energy deposition with the electron beam (DED-EB) allows the production of large-scale copper components at high deposition rates with high quality. Commonly, the semi-finished product is built on a base plate which must be removed afterwards. However, it is also possible to add copper features to a base component which is part of the final product. This base product may be out of copper or another metal if no metallurgical restrictions apply. The aim of this paper is to report on microstructure and material properties and to present case studies of copper components.
Les aubes de turbine a gaz dans des propulseurs ou pour la production d'electricite sont soum... more Les aubes de turbine a gaz dans des propulseurs ou pour la production d'electricite sont soumises a de fortes sollicitations thermiques qui surviennent de maniere cyclique et rendent la surface metallique rugueuse. Selon la presente invention, la surface metallique est pourvue d'un revetement mince en ceramique d'une epaisseur inferieure a 50 µm, ce qui permet d'eviter que ladite surface ne devienne rugueuse.
Shaped Metal Deposition (SMD) is a novel technology to build near-net shaped parts by successive ... more Shaped Metal Deposition (SMD) is a novel technology to build near-net shaped parts by successive weld deposition. The SMD rig consists of a robot with a Tungsten Inert Gas (TIG) welding torch and a manipulator, which are housed inside a sealed chamber. The heat transfer problem is modeled in a series of walls made by SMD of Ti-6Al-4V alloy. The studied specimens have different dimensions and were obtained using a wide range of process parameters (number of layers, layer height, wire feed rate, travel speed, heat input, etc.). The aim is to correlate the temperature field predicted using the finite element model developed by Centro Internacional de Métodos Computacionales en Ingeniería (Santa Fe, Argentina) to macro-, meso-and micrographical observations done at the Department of Metallurgy and Materials Engineering (Katholieke Universiteit Leuven, Belgium), as a way of validating the model of such a complex process. SMD subjects the build part repeatedly to a specific temperature field which results in a unique morphology and in microstructures usually not achievable by conventional fabrication techniques. The appearance of distinct microstructures in the top of the walls, in the substrate and in the intermediate region is explained on the basis of temperature and temperature rate results. Modelling of microstructure evolution in terms of phase kinetics based on phase transformation diagrams is dealt with in a companion paper.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2011
A component prepared by shaped metal deposition (SMD) using 300M steel wire is studied to reveal ... more A component prepared by shaped metal deposition (SMD) using 300M steel wire is studied to reveal structure and material properties. The component exhibits a bainitic microstructure changing from distinct sheaves to homogenous from top to bottom. This change in microstructure is reflected by a step-like increase of the volume fraction of austenite towards the bottom of the component, and a step-like decrease of the microhardness. A certain deviation of the general change in the morphology of bainite from top to bottom appears at the very bottom of the component, caused by the influence of the base plate. Tensile tests show a very high ultimate tensile strength of about 1500 MPa and an elastic modulus of 200 GPa, which is comparable to that of material in cast condition.
The Nuclear AMRC was set up to help industry partners to win work in the civil nuclear sector – i... more The Nuclear AMRC was set up to help industry partners to win work in the civil nuclear sector – in new build, operations and decommissioning with the aim to reduce cost, lead time, cycle time, and risk in manufacturing and to improve quality. Large manufacturing facilities have been set up for working on production-scale technology demonstrators using an array of state-of-the-art manufacturing equipment. While Electron Beam Welding (EBW) is a widely used manufacturing technology in many sectors, so far this technology has not penetrated the nuclear industry. Acknowledging the great potential of EBW the Nuclear AMRC aims to change that by utilising its two EBW facilities. Many nuclear components are of large scale. Therefore an EBW facility with a vacuum chamber volume of 208 m 3 has been installed. This is currently the largest EBW facility in the UK. The mobile 30kW, 60kV gun is attached to an x-y-z gantry along with two rotary axes. These axes together with turn and tilt tables are all CNC controlled allowing a very flexible approach for welding of parts up to 100 tons with sizes up to 6 x 4 x 3 metres. This paper aims to introduce the EBW capabilities at the Nuclear AMRC and to present some of the achievements to date.
Wire Electron Beam Additive Manufacturing (WEBAM) facilitates great opportunities to provide semi... more Wire Electron Beam Additive Manufacturing (WEBAM) facilitates great opportunities to provide semi-finished products of certain materials, where other additive manufacturing technologies experience great challenges. The advantages of WEBAM are related to the specific properties and capabilities of the electron beam, and to the operation in a high vacuum. An overview of the WEBAM activities at pro-beam with different geometries and a variety of materials such as titanium, stainless steel, Inconel and copper is shown.
• Comparison of LASER cladding with that of arc and resistance cladding for large-scale corrosion... more • Comparison of LASER cladding with that of arc and resistance cladding for large-scale corrosion protection in nuclear manufacturing • Novel powder jet 45 mm wide nozzle for LASER cladding presented • Deposition rates of 10.8 kg/h and 8.1 kg/h for IN82 and 308L powders respectively, with a coverage rate of 1 m2/h • LASER cladding achieves high quality clads with competitive coverage rates and reduced heat input
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Papers by Bernd Baufeld
• Novel powder jet 45 mm wide nozzle for LASER cladding presented
• Deposition rates of 10.8 kg/h and 8.1 kg/h for IN82 and 308L powders respectively, with a coverage rate of 1 m2/h
• LASER cladding achieves high quality clads with competitive coverage rates and reduced heat input