The brittle-to-ductile transition in cold-rolled tungsten sheets: On the loss of room-temperature ductility after annealing and the phenomenon of 45° embrittlement

The high brittle-to-ductile transition (BDT) temperature of conventionally produced tungsten (W), challenges the design of W-based structural components. Recent studies have demonstrated the potential of cold rolling to produce W sheets, which are ductile at room temperature and exhibit a BDT temperature of 208 K. In order to assess the thermal stability of these materials, we conducted isothermal heat treatments (at 1300 K, for annealing durations between 0.1 h and 210 h) combined with studies on the evolution of mechanical properties and microstructure of a severely deformed undoped W sheet. With this work, we demonstrate the need for a stabilized microstructure before utilization of cold-rolled W in high-temperature applications can take place successfully. After annealing at 1300 K for 6 h, the material properties changed remarkably: The BDT temperature increases from 208 K to 473 K and the sharp BDT of the as-rolled condition transforms into a wide transition regime spanning over more than 200 K. This means in fact, an endangered structural integrity at room temperature. We also address the so-called phenomenon of 45° embrittlement of W sheets. Here we show that cleavage fracture in strongly textured W sheets always takes place with an inclination angle of 45° to the rolling direction, independent of the studied material condition, whether as-rolled or annealed. An in-depth study of the microstructure indicates a correlation between an increased BDT temperature caused by annealing and microstructural coarsening presumably by extended recovery. We conclude that 45° embrittlement needs to be comprehended as a combined effect of an increased spacing between grain boundaries along the crack front, leading to an increased BDT, and a high orientation density of the rotated cube component or texture components close to that, which determine the preferred crack propagation of 45° to the rolling direction

ADDITIVE LASER BARCODE PRINTING ON HIGH REFLECTIVE STAINLESS STEEL

In this paper, the process of an additive laser marking on stainless steel parts for barcode printing is presented. It is based on the use of one transition metal oxide chemically-well bonded to the stainless steel substrate, without a usage of any additional materials and cleaning substances. The resulting additive coatings, produced from initial MoO3 powder by irradiation with a laser beam, reveal strong adhesion, high hardness, long durability and high optical contrast, which make the process suitable for barcode printing on materials such as high reflective stainless steel, which was always a challenge for the classical laser marking technologies. The obtained bar patterns are in a compliance with the requirements of the existing standards

Low friction of metallic multilayers by formation of a shear-induced alloy

During sliding of metallic surfaces, the near surfaces undergo significant changes in terms of topography, composition and microstructure. Since friction and wear behavior of the materials are strongly influenced by sub-surface deformations, it is fundamental to investigate these effects. Therefore, the present study aims towards a better understanding of the behavior of friction depending on well-defined initial microstructures. By performing sliding experiments on Au-Ni multilayer samples under ultrahigh vacuum (UHV) conditions, we observe that the individual layer thickness of multilayer systems has a strong influence on friction behavior due to the transition in the dominant deformation mechanism near the surface. The experiments reported here provide a new route for lowering the friction force of metallic material systems in dry contact by providing more stable microstructures and alloy formation. Through ultrafine grains present in the alloy formed by mechanical mixing the number of grain boundaries strongly increases and hence, grain boundary-mediated deformation results in the low friction coefficient

Transition metal oxides as materials for additive laser marking on stainless steel

The product information plays an important role in the improvement of the manufacturing, allowing the tracking of the part through the full life cycle. Laser marking is one of the most versatile techniques for this purpose. In this paper, a modification of the powder bed selective laser melting for additive laser marking of stainless steel parts is presented. This modification is based on the use of only one transition metal oxide chemically bonded to the stainless steel substrate, without using any additional materials and cleaning substances. The resulting additive coatings, produced from initial MoO₃ and WO₃ powders, show strong adhesion, high hardness, long durability and a high optical contrast. For estimation of the chemical and structural properties, the Raman and X-Ray Diffraction (XRD) spectroscopy have been implemented. A computer model of the process of the laser melting and re-solidification has been developed as well. A comparative analysis of the properties of both (MoO₃ and WO₃) additive coatings has been performed. An attempt for a qualitative explanation of the thermo-chemical phenomena during the marking process has been undertaken

Influence of silicon doping type on the adhesion of seedless electrodeposited copper layers

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