Materials Science Forum Vol. 1016

Abstract: In additive manufacturing, technologies based on the fusion of a metallic wire using an electric arc represent an interesting alternative to current manufacturing processes, particularly for large metal parts, thanks to higher deposition rates and lower process costs than powder or wire-laser technologies. A versatile 3D printing device using a DED-W Arc (Direct Energy Deposition by wire-arc) station to melt a metallic filler wire is developed to build titanium parts by optimizing the process parameters and control the geometrical, metallurgical and the mechanical properties of produced parts. In this study, the impact of two different CMT synergic lines on the energetic and geometric behavior of Ti-6Al-4V single deposits is highlighted. These are related to first order parameters: wire feed speed (WFS) and travel speed (TS). The results show difference on energy, geometric of deposits and different deposition regime between these two law with identical process parameters. The second part of this study focuses on the transition from single deposits to walls and blocks. By first choosing the best set of process parameters to make the construction of thin walls (composed of stacked layers), and then the research the optimal horizontal step of deposition (overlapping) for thicker constructions, results obtained made it possible to validate transition from single deposits (1D) to thick walls (3D) without any weld pool collapse or lack of fusion.

Abstract: Thermomechanical (TM) rolling schedules have been developed using mathematical modelling, physical simulation and industrial trials to produce C-Mn steel plate with yield strengths of 400MPa and good impact toughness without the need of expensive micro-alloying additions or accelerated cooling. The process relies on careful selection of delay times to accumulate sufficient retained strain during austenite conditioning for enhanced nucleation of ferrite. An integrated heat transfer-austenite processing model was used to predict the final microstructure and mechanical properties. The extent of strain accumulation and progress of recrystallisation during rolling were confirmed by laboratory simulation. Based on these results, carefully controlled industrial TM rolling trials were performed on C-Mn steels. Adequate grain refinement and properties are achieved through suppression of recrystallisation and strain accumulation in the low austenite temperature region after a sufficient delay period prior to finishing.

Abstract: This paper deals with activities carried out in the frame of GEMMA project on welded samples of 15/15 Ti stainless steel. The focus of GEMMA project has been on the investigation of material properties and associated welded joints for GEN IV nuclear plants. The RCC-MRx code uses the standard Base Metal Grade nomenclature (EN/ISO), but provides also additional specifications. Titanium stabilized “15-15Ti” stainless steel has been the primary choice for fuel cladding of current fast spectrum research reactor projects. The choice of cladding material is based on past experiences and the availability of material databases from similar steel grades proven in past sodium-cooled fast reactors programs [1-4]. On the basis of ENEA past experience, a strict specification has been written to realize a new heat treatment of this special stainless steel (SS). One of the main problems faced with this material is the high tendency to crack after the welding process. Several preliminary welding tests permitted to select TIG and laser welding processes for the 15/15 Ti SS. This fact because the main applications involve small thicknesses without filler material. The welding of the 15/15 Ti was performed using a fully automated TIG work station at ENEA CR-Casaccia. The base materials to evaluate the welding parameters were 15/15 Ti plates 100 X 170 X 3 mm welded under different shielding gas atmospheres and process parameters arrangements that permitted to obtain good quality joints avoiding catastrophic hot-cracking. The welded samples underwent a mechanical and metallographic characterization and the main results are here presented.

Abstract: Transient liquid phase (TLP) bonds using Cu-Sn system have been suggested as high strength and temperature resistant joints for power electronics applications. While the physical and mechanical properties of these joints has been investigated to some extent, studies on fatigue properties and long term reliability of TLP joints are scarce. In this work TLP bonding was performed to produce thin Cu-Sn intermetallic joints by using Cu and 97Sn3Cu solder alloy as interlayer. Different processing conditions resulted in three types of thin joints consisting of three phases (Cu₃Sn/Cu₆Sn₅/solder remnants), two phases (Cu₃Sn/Cu₆Sn₅) and a single phase (Cu₃Sn) with an overall thickness of ≤ 20 μm. The shear strength of the TLP joint containing one or two high melting point IMC layers showed a significant temperature resistance up to 200°C. Fatigue studies of TLP joints were conducted by using a 3-point-cyclic bending test system operating at 20 kHz. The highest fatigue resistance was obtained for the single-phase Cu₃Sn joints with superior shear and flexural resistance. The two phase joints (Cu₃Sn/Cu₆Sn₅) showed a slightly lower lifetime than the three phase system containing IMCs and residual solder. Fracture surfaces analysis in correlation with static and cyclic mechanical properties, provided insight into the failure mechanism of the Cu-Sn TLP joints.

Abstract: The thermal and magnetic properties of the ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys have been investigated. It has been discovered that the ternary Fe-B-C amorphous alloys with compositions close to Fe_79.3B_14.3C_6.4 exhibit a glass transition prior to crystallization on heating. The alloys also have high mass magnetization of 176–178 A m²/kg at room temperature. In addition, the glass-forming ability (GFA) of the alloys is significantly enhanced by the addition of 4 at% Si while maintaining high magnetization of approximately 170 A m²/kg at room temperature. In was found that the Fe₂₃(B, C)₆ phase (Cr₂₃C₆-type) is formed during crystallization of the quaternary Fe-B-C-Si alloys with the large GFA. It was also confirmed that the amorphous powders of Fe-Cr-B-C-Si alloys could be produced by a conventional water atomization method and exhibit the low core losses of 305–362 kW/m³ at 100 kHz and 100 mT. The quaternary Fe-B-C-Si amorphous alloys with high GFA, high magnetization and low core losses are suitable for a core material of various magnetic components.

Abstract: Over the course of the last decade 3D printing has become a more established technology in terms of prototype development (rapid prototyping). The current effort is focused on transferring this knowhow into a product driven approach in order to manufacture even small batch sizes more economic. In terms of this work, this idea is adapted for the development of injection molds (rapid manufacturing). Hereby, a hardened polymer is used to create a forming cavity instead of tool-steel. In order to fulfil the mechanical process requirements of micro injection molding such as form stability under temperature and pressure this cavity is nevertheless integrated into a metal housing. A first set of experiments has been carried out using this develop mold to verify the capabilities of the developed prototype as well as molding process. Based on these first results, an optimization is carried out to improve the next iteration of this molding tool.

Abstract: This study develops a fast and simple way to produce high purity magnetite (Fe₃O₄) microparticles from mill scale by using hydrogen reduction with the addition of vapour as a retarding agent. By optimising the reduction temperature and gas flow rate, the characterisations by X-ray diffractometry technique shown that the Fe₃O₄ fraction of over 93 wt.-% is shown at the reduction temperature of 550 – 650 oC with the flow rate of the 4.5-5.5 mol%H₂ + Ar gas + H₂O gas mixture from 100 – 200 ml/min. The highest Fe₃O₄ fraction of over 99 wt.-% can be achieved from the reduction with the mixed gas at 650 oC and the flow rate of 200 ml/min for 4 hour.

Abstract: An Al-4.57Mg-0.35Mn-0.2Sc-0.09Zr (wt. %) alloy was studied in the fine-grained state obtaining after equal channel angular pressing. The mechanical behavior of alloy at the temperatures 173 K, 298 K and 348 K and at strain rate 1×10^–3 s^–1 is studied. Increase of the temperature testing from 173 K to 348 K decreases the yield stress by 80 MPa, the ultimate tensile strength by 60 MPa while elongation-to failure increases by a factor of 1.4. It was found that at temperatures of 298 and 173 K, the studied alloy mainly demonstrates the mode of ductile fracture, and at a temperature of 348 K the mechanism can be described as mixed ductile-brittle fracture. It was also established that of the studied alloy is the temperature dependence of the size of the dimples on the fracture surface. The formation of smaller dimples in the samples deformed at 298 K was observed.

Abstract: Laser cladding of a Ni based powder on Cu-Ni-Al or cast iron was performed with a 4kW continuous Nd: YAG laser. The Cu-Ni-Al and cast-iron substrates are used for their thermal properties in glass mold industry. But the issue of these materials is their lack of resistance on corrosion and abrasion. The role of the Ni based alloy is to protect the mold without affecting its thermal properties (Heat Affected Zone (HAZ)). The purpose of this research is to produce a well bonded Ni based melted powder without pores or cracks on a non-planar surface (curvilinear section). An investigation of the impact of the processing parameters, power (1500-3200 W), scanning speed (2.5-10 mm/s) and powder feeding rate (24.5-32.5 g/min) on the bonding quality, the porosity propagation and HAZ appearance is performed. The used methods are neutronography, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Electron BackScatter Diffraction (EBSD). These multi-scale techniques are obviously complementary. Neutronography is a well-adapted non-destructive method to observe the porosity in the volume thanks to the contrast between materials. EBSD analysis allows us to analyze the microstructural evolution of the coating notably by observing the dendrites growth. This same method also permits to observe the HAZ nature according to the laser cladding parameters. Those methods allowed to optimize the processing parameters in a way to obtain perfect bonding, to avoid porosity propagation and to limit the HAZ emergence.

Abstract: The problems for fixing rib fractures are usually challenged with different rib fixators whose design strongly depends of the material selected for construction. Main issues refer to rib surgery implantation and tissue acceptance for a duration longer than the osteosynthesis. In this paper we discuss how a material selection can strongly suggest different design solutions both in shape of a rib fixator and even constraining or directing the surgical application with an invasive or noninvasive implantation. In particular, in discussing the general issues and specific experiences of the authors the paper illustrates examples of two different solutions under patent request that are dictated by the material whose selection give the design solutions with innovative aspects.