Papers by Author: Thomas Buslaps

Abstract: Welding using low transformation temperature (LTT) filler materials is an innovative approach to mitigate detrimental welding residual stresses without cost-intensive post weld-treatments [1, 2]. Due to the local generation of compressive residual stresses in the weld line by means of a delayed martensite transformation a significant enhancement of the cold cracking resistance of highly stressed welded components can be expected. For the effective usage of these materials a deeper understanding of the microstructural evolution inside the weld material is necessary to determine the complex processes that cause the residual stress formation during welding. Solid-state phase transformation kinetics and the evolution of strain in LTT weld filler materials are monitored in-situ at the instrument ID15A@ESRF in Grenoble. The transferability to real components is implemented by using a realistic MAG welding process under consideration of structural restraint. During welding of multilayer joints, the phase transformation and phase specific strain evolution of each individual layer is investigated in transmission geometry by means of energy-dispersive X-ray diffraction EDXRD using high energy synchrotron radiation with a counting rate of 2.5 Hz. The measurement results of a 10% Cr / 10% Ni LTT weld filler are compared to data monitored for the conventional weld filler material G89. The in-situ data clearly indicate a strong effect on the local strain evolution and the formation of compressive strain. This results from the restraint volume expansion during the postponed austenite to martensite transformation of the LTT weld filler, which counteracts the thermal shrinkage. In contrast, for the conventional weld filler material the thermal contraction strains lead to tensile residual strain during welding. Furthermore, the results of in-situ observation during welding show that the transformation kinetic is dependent on the welding sequence.

Abstract: In the present work, the mechanical behavior of phases in duplex steel during tensile test was studied. Special interest was taken in the analysis of damage process just before failure. In this aim two diffraction methods: in-situ time of flight neutron diffraction and X-ray synchrotron diffraction were applied. Using diffraction data, the slip mechanism on crystallographic planes during plastic deformation was investigated. In the case of aged UR45N steel, it was found that significant softening caused by damage process was initiated in the ferritic phase. The lattice strains measured in situ by two above mentioned diffraction methods were compared with prediction of the self-consistent model.

Abstract: Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale, i.e. phase and grain scale. In situ synchrotron diffraction (transmission mode) during tensile tests and modified self-consistent elastoplastic model were used to study elastic and plastic phenomena occurring in polycrystalline specimens during deformation. The evolution of stress for grains which belong to different phases of duplex stainless steel and pearlitic steel was analyzed.

Abstract: The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the residuals stresses and texture of the new bone crystals reconstituted at the interface using synchrotron radiation on ID15 at ESRF in Grenoble, France.

Abstract: Synchrotron X-ray diffraction is reliable to measure residual stresses and characterize existing phases close to substrate/coating interface. In the present study, we focus on the cobalt-alloys coating deposited on stainless steel forging tools via Plasma Transfer Arc (PTA) process. Forging tools always work in high temperature conditions. Since fatigue crack is often detected near to the interface, we used synchrotron radiation to characterize residual stress profiles both in the substrate and coating sides. Also, we defined phases inside diluted substrate layers and in the stellite coating using a Rietveld refinement.

Abstract: The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca₁₀ (PO₄)₆ (OH)₂, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the texture of the reconstituted bone crystals at the interface applying non destructive x-ray diffraction. The required high spatial resolution was achieved utilizing high-energy synchrotron radiation on ID15 at ESRF in Grenoble, France.

Abstract: Residual stresses in welds are of major concern for the structure integrity assessment in industrial components. The stresses in the final weld can be determined relatively simple using well established destructive or non-destructive techniques. However, such measurements reflect only the final condition and it remains unclear how stresses built up during the welding process. In order to optimise the final residual stresses in the weld, it is important to monitor the formation of residual strain and stress during the welding process and as such to gain insight into the mechanisms of stress development. In this work non-destructive high energy dispersive synchrotron X-ray diffraction at a high count rate is applied in order to dissolve the welding process in-situ in time and temperature. However, the achievable time resolution at commonly used instruments is restricted by either a limited photon flux or the read out electronics of the detector system resulting in counting times usually much longer than 1sec. We present an energy dispersive detector and read-out-electronics setup realized at the high flux and energy beam line ID15A at the ESRF. The setup allowed for monitoring the strain evolution in two perpendicular directions simultaneously at a sampling rate of 5Hz, resulting in sufficient time and temperature resolution. The change in detector dead time is accounted for by a correction function, which was specifically determined for the detector setup as used for this in-situ experiment.

Abstract: The use of the implants has become current since 1930. With the improvement of technology, titanium alloy coated with nano-hydroxyapatite has been used in the medical field. As a long-term establishment is a meter of the therapeutic success, it is necessary to use biocompatible implants in order to have good mechanical and fracture resistance at the interface bone-implant. In orthopaedic surgery Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca₁₀ (PO₄)₆ (OH)₂, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface the new bone reconstituted after implantation must have the same mechanicals properties as the natural bone in order to accept the implant. Therefore we studied the residuals stresses of the new bone crystals reconstituted at the interface applying non destructive x-ray diffraction and using finite element analysis in order to compare the results.

Abstract: Technology developments of implant composition and manufacture have been used in the medical field. Several different implants have been developed with varying degrees of commercial success. As a long-term establishment is a measure of the therapeutic success, it is necessary to use biocompatible implants in order to have good mechanical and fracture resistance of new bone reconstructed at the interface with the implant. Titanium (Ti-Al-4V) implants coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2 are widely used in orthopedic applications in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface the new bone reconstituted after implantation must have the same orientation as the natural bone in order to accept the implant. Therefore we studied the texture and the crystallinity of the new bone crystals reconstituted at the interface applying by high-energy synchrotron radiation on beamline ID15 at ESRF in Grenoble, France.

Abstract: The present study is dedicated to high energy x-ray diffraction measurements of residual stress at bone-implant interfaces. Bone regeneration is different from soft tissue repair as scar formation never occurs and as de novo bone tissue is produced with proliferation and differentiation of mesenchymal cells. To start the bone remodelling, the stress – the most important mechanical factor – should stimulate the osteocytes. Osseointegration is also observed with non-functional implants, in particular with dental implants. This means that a stress similar to a residual stress must exist.