Hot Deformation Behavior and Simulation of Hot-Rolled Damage Process for Fine-Grained Pure Tungsten at Elevated Temperatures.

Fine-grained pure tungsten fabricated by a sol drying reduction low-temperature sintering method and hot isothermal compression tests were performed by using the Gleeble 3800 thermo mechanical simulator at deformation temperatures from 1273 K to 1473 K and strain rates from 0.001 s-1 to 1 s-1. In addition, the constitutive equation was established by least square method combined with the Zerilli-Armstrong model, and the hot deformation behavior was discussed. Moreover, based on constitutive equation, the influence of the rolling process and its parameters on temperature, strain, density and rolling force in the hot rolling process was investigated at elevated temperature by the finite element model (FEM). Furthermore, the form of rolling damage and its formation mechanism were analyzed. Results showed the grains of pure tungsten are dense, irregular polyhedral spherical and very fine, and the average grain size is about 5.22 µm. At a high strain rate, the flow stress increases rapidly with the increase in strain, while the stress-strain curve shows a flattening trend in the tested strain rate range with increasing temperature, and no flow stress peak exists, showing obvious dynamic recovery characteristics. Furthermore, the FEM simulation showed that compared with the rolling temperature, the reduction has a greater influence on the temperature, stress-strain field and its distribution. There are three kinds of damage in the hot rolling process: transverse cracks, longitudinal cracks and side cracks, which are attributed to the competition between additional stress caused by uneven deformation and material strength. Moreover, the control method of hot rolling defects had been preliminarily proposed. These results should be of relevance for the optimum design of the hot rolling process of pure tungsten.

Effect of Microstructure Refinement on Surface Morphology and Dynamic Mechanical Properties of W-Cu Alloys.

Two ultrafine-grained W-Cu alloys and two coarse-grained W-Cu alloys were prepared to study the effect of tungsten grain refinement on the interface characteristics between coating and W-Cu alloys. The experimental results show that in the coarse-grained W-Cu alloys, the tungsten phase near the surface is easy to form pits and cracks during impact loading, while the fine-grained tungsten alloy is not prone to this phenomenon. Simulations show that refining tungsten grains can not only reduce the impact absorption energy, but also increase the contact area of tungsten and copper phases, thereby reducing the fracture probability of tungsten phases and improving the dynamic mechanical properties of the W-Cu alloys under impact loading. The tested results show that the shear strength of gold studs on the coating is increased by about 33%, after grain refinement for the W-Cu alloys.

Size-Dependent Alloying Ability of Immiscible W-Cu Bimetallic Nanoparticles: A Theoretical and Experimental Study.

The preparation of alloyed bimetallic nanoparticles (BNPs) between immiscible elements is always a huge challenge due to the lack of thermodynamic driving forces. W-Cu is a typical immiscible binary system, and it is difficult to alloy them under conventional circumstances. Here, we used the bond energy model (BEM) to calculate the effect of size on the alloying ability of W-Cu systems. The prediction results show that reducing the synthesis size (the original size of W and Cu) to less than 10 nm can obtain alloyed W-Cu BNPs. Moreover, we prepared alloyed W50Cu50 BNPs with a face-centered-cubic (FCC) crystalline structure via the nano in situ composite method. Energy-dispersive X-ray spectroscopy (EDS) coupled with scan transmission electron microscopy (STEM) confirmed that W and Cu are well mixed in a single-phase particle, instead of a phase segregation into a core-shell or other heterostructures. The present results suggest that the nanoscale size effect can overcome the immiscibility in immiscible binary systems. In the meantime, this work provided a high-yield and universal method for preparing alloyed BNPs between immiscible elements.

Corrigendum: Strain-stress relationship and dislocation evolution of W-Cu bilayers from a constructed n-body W-Cu potential (2019 J. Phys.: Condens. Matter 31 305002).

An n-body W-Cu potential is constructed under the framework of the embedded-atom method by means of a proposed function of the cross potential. This W-Cu potential is realistic to reproduce mechanical property and structural stability of WCu solid solutions within the entire composition range, and has better performances than the three W-Cu potentials already published in the literature. Based on this W-Cu potential, molecular dynamics simulation is conducted to reveal the mechanical property and dislocation evolution of the bilayer structure between pure W and W0.7Cu0.3 solid solution. It is found that the formation of the interface improves the strength of the W0.7Cu0.3 solid solutions along tensile loading perpendicular to the interface, as the interface impedes the evolution of the dislocation lines from the W0.7Cu0.3 solid solutions to the W part. Simulation also reveals that the interface has an important effect to significantly reduce the tensile strength and critical strain of W along the tensile loading parallel to the interface, which is intrinsically due to the slip of the edge or screw dislocations at low strains as a result of the lattice mismatch.