References of "Paydas, Hakan"
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See detailLaser cladding as repair technology for Ti6Al4V alloy: Influence of building strategy on microstructure and hardness
Paydas, Hakan ULg; Mertens, Anne ULg; Carrus, Raoul et al

in Materials & Design (in press)

Laser cladding is a metal deposition technique used to fabricate or repair components made from high value metallic alloys. In the present work Ti-6Al-4V deposits with variable thickness are made to ... [more ▼]

Laser cladding is a metal deposition technique used to fabricate or repair components made from high value metallic alloys. In the present work Ti-6Al-4V deposits with variable thickness are made to assess the use of laser cladding as a repair technology. Both the effect of the building strategy (BS) and the incident energy (IE) on the metallurgical characteristics of the deposits in relation to their complex thermal history have been studying. It is shown that for the configuration consisting in a decreasing track length (DTL) under high IE, a gradient of cooling rate exists that leads to the presence of different phases within the microstructure. Conversely homogeneous microstructures are present either for the configuration with a constant track length (CTL) under high IE, and for the strategy obtained from a DTL under low IE. Depending on the possible heat accumulation the nature of the phases are determined together with hardness maps within the deposits. Some qualification criteria are set prior to tensile tests to selected the adequate candidate-deposit that does not weaken the cladded material when it is stressed. A thermo-metallurgical scheme is proposed that helps understanding the effect of both the BS and the IE on the microstructure. [less ▲]

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See detailOn the Laser Cladding of Ti Alloy Ti-6Al-4V with Low Laser Power
Mertens, Anne ULg; Paydas, Hakan ULg; Tchuindjang, Jérôme Tchoufack ULg et al

in Pilchak, Adam (Ed.) Proc. of Ti 2015: 13th World Conference on Titanium, Vol. 6: Additive and Near Net Shape Manufacturing (in press)

Laser cladding is an economic layer-by-layer near-net-shape process for the production and the repair of metallic parts. In this process, a metallic powder is projected onto a substrate while being molten ... [more ▼]

Laser cladding is an economic layer-by-layer near-net-shape process for the production and the repair of metallic parts. In this process, a metallic powder is projected onto a substrate while being molten by a laser beam. Laser sources with fairly high power – i.e. typically 2kW − are often used to ensure short building times and high productivity. However, this approach has limitations. Indeed, it is very difficult to produce thin walls at high laser power. Moreover, an increase of the incident energy may give rise to a relatively coarser microstructure, and this will in turn affect the mechanical properties of the component. In order to address these issues, this paper aims at assessing the potential of a laser source with a lower maximum power of 300W to enhance the flexibility of the process. Two types of samples – i.e. thin walls or bulk deposits − were produced at low laser power from alloy Ti-6Al-4V. Their geometry, microstructures and local hardness are characterised and correlated with the thermal history experienced during fabrication. [less ▲]

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See detailCarbides and grain size quantification methods in high speed steel alloys
Tchuindjang, Jérôme Tchoufack ULg; Paydas, Hakan ULg; Hashemi, Seyedeh Neda ULg et al

Conference (2015, July)

High speed steel (HSS) grades are widely used as in highly stressed applications where carbides content promote enhanced mechanical properties together with oxidation and wear resistances. Such a ... [more ▼]

High speed steel (HSS) grades are widely used as in highly stressed applications where carbides content promote enhanced mechanical properties together with oxidation and wear resistances. Such a tribological behaviour is mainly due to the presence of primary carbides. It is thus important to quantify the carbide volume fraction in HSS to correlate this result with the mechanical and tribological properties of the materials. Depending of the steel composition several types of carbides are precipitated in HSS: MC (Nb and V-rich), M2C (Mo and W-rich), Cr-rich M7C3 and some others, depending of the chemical composition. Two groups of HSS were analyzed in this study: cast HSS manufactured by centrifugal casting and cladded HSS manufactured by laser cladding. Depending on the chemical composition and the manufacturing process of the studied material, several methods have been used to quantify the carbide volume fraction and the grain size. [less ▲]

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See detailDevelopment of quantification methods applied to HSS alloys for carbides volume fraction and grain size assessments
Tchuindjang, Jérôme Tchoufack ULg; Paydas, Hakan ULg; Hashemi, Seyedeh Neda ULg et al

Poster (2015, July)

High speed steels (HSS) are used in applications where enhanced mechanical properties together with hot oxidation and wear resistances are required. Such an improved physico-chemical behaviour is mainly ... [more ▼]

High speed steels (HSS) are used in applications where enhanced mechanical properties together with hot oxidation and wear resistances are required. Such an improved physico-chemical behaviour is mainly due to the presence of primary carbides within the microstructure. Depending of the initial chemical composition several types of carbides can precipitate in HSS such as MC (Nb and V-rich), M2C (Mo and W-rich), Cr-rich M7C3, etc. Two groups of HSS were analysed in this study, which are the so-called cast HSS grades that are manufactured by a centrifugal casting process and the cladded HSS manufactured by laser cladding. Purpose: Quantify the carbide volume fractions and the grain size within HSS grades in order to set correlations between the microstructure and both the mechanical and the tribological properties of the materials. Findings: The metallurgical features such as carbides nature and shape have been determined that are related to the manufacturing process of the studied material, and several methods have been used to quantify the carbide volume fractions and to assess the grain size. [less ▲]

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See detailProcessing of alloy Ti-6Al-4V and of stainless steel 316L by Laser Beam Melting
Mertens, Anne ULg; Paydas, Hakan ULg; Reginster, Sylvie ULg et al

Conference (2014, May)

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic ... [more ▼]

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials such as Ti alloys and stainless steels. Practically, in SLM, a metallic powder is deposited layer-by-layer in a powder bed and then molten locally according to the desired shape. An important feature of this process is that the structure undergoes an ultra-fast cooling once the beam leaves the working zone, thus giving rise to strongly out-of-equilibrium microstructures. In the case of Ti alloy Ti-6Al-4V, in particular, the microstructural anisotropy resulting from the epitaxial growth of the newly deposited layer on the material previously solidified has been shown to exert a very strong influence on the mechanical properties [1] In the present work, the thermophysical behaviour of Ti-alloy Ti-6Al-4V and of stainless steel 316L has been characterised in details, in order to reach a better understanding of the phenomena controlling the microstructures and mechanical properties of parts. In particular, the thermal conductivity of Ti-alloy Ti-6Al-4V and of stainless steel 316L at high temperature has been determined by combining dilatometry, Differential Scanning Calorimetry (DSC) and laser flash diffusivimetry based on Laplace’s equation. Since Ti-alloy Ti-6Al-4V and stainless steel 316L exhibit quite different physical behaviours, their careful comparison is shown to shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformations and/or internal stresses in the additive manufacturing of metallic materials. [less ▲]

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See detailMechanical properties of alloy Ti-6Al-4V and of stainless steel 316L processed by Selective Laser Melting: Influence of out-of-equilibrium microstructures
Mertens, Anne ULg; Reginster, Sylvie ULg; Paydas, Hakan ULg et al

in Powder Metallurgy (2014), 57(3), 184-189

Ti-6Al-4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the ... [more ▼]

Ti-6Al-4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the investigated conditions, Ti-6Al-4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti-6Al-4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of “lack of melting” defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was shown to increase strongly with increasing temperature and the thermophysical properties appeared to be influenced by variations in the initial metallurgical state. [less ▲]

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See detailMeasuring the thermophysical properties of materials at high temperature - Application to the additive manufacturing of alloy Ti-6Al-4V and of stainless steel 316L
Mertens, Anne ULg; Paydas, Hakan ULg; Reginster, Sylvie ULg et al

Conference (2013, November 07)

In view of optimising the microstructures of metallic materials and obtaining the desired properties, the accurate characterisation of the thermophysical behaviour of these materials has long been ... [more ▼]

In view of optimising the microstructures of metallic materials and obtaining the desired properties, the accurate characterisation of the thermophysical behaviour of these materials has long been considered of paramount importance e.g. by allowing for the in-situ study of phase transformations, by providing data for numerical simulations and, essentially, by contributing to a better understanding of the fundamental mechanisms at play during processing. In the present work, the thermophysical behaviour of Ti-alloy Ti-6Al-4V and of stainless steel 316L has been characterised in details, in order to reach a better understanding of the phenomena controlling the microstructures and mechanical properties of parts made by additive manufacturing techniques that appear nowadays very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials. In particular, the thermal conductivity of Ti-alloy Ti-6Al-4V and of stainless steel 316L at high temperature has been determined by combining dilatometry, Differential Scanning Calorimetry (DSC) and laser flash diffusivimetry based on Laplace’s equation : k(T)=α(T)ρ(T)Cp(T) where k(T) is the thermal conductivity (W/m*K) α(T) is the thermal diffusivity (mm2/s) ρ(T) is the specific mass (g/cm3) Cp(T) is the specific heat capacity (J/g*K). Since Ti-alloy Ti-6Al-4V and stainless steel 316L exhibit quite different physical behaviours, their careful comparison is shown to shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformations and/or internal stresses in the additive manufacturing of metallic materials. [less ▲]

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See detailOn the Role of Out-of-Equilibrium Microstructures in Ti-6Al-4V and in Stainless Steel 316L Processed by Selective Laser Melting in Determining their Mechanical Properties
Mertens, Anne ULg; Reginster, Sylvie ULg; Paydas, Hakan ULg et al

Conference (2013, September 12)

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic ... [more ▼]

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials such as Ti alloys and stainless steels. Practically, in SLM, a metallic powder is deposited layer-by-layer in a powder bed and then molten locally according to the desired shape. An important feature of this process is that the structure undergoes an ultra-fast cooling once the beam leaves the working zone, thus giving rise to strongly out-of-equilibrium microstructures. In the case of Ti alloy Ti-6Al-4V, in particular, the microstructural anisotropy resulting from the epitaxial growth of the newly deposited layer on the material previously solidified has been shown to exert a very strong influence on the mechanical properties [1]. In the present work, the microstructures and mechanical properties of Ti-6Al-4V and of stainless steel 316L processed by SLM have been characterised in details. Since these two materials exhibit quite different physical behaviours, their careful comparison might shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformation and/or internal stresses in determining the mechanical properties of metallic parts processed by SLM. [less ▲]

Detailed reference viewed: 88 (11 ULg)