Bulk fabrication of tungsten-based composite materials with excellent low-temperature strength and ductility through powder innovation

Tungsten (W), a body-centered cubic (BCC) metal, is recognized for its outstanding high-temperature mechanical properties, leading to its widespread use in various high-temperature environments [[1], [2], [3], [4]]. Nonetheless, its significant brittleness at room temperature and high ductile-to-brittle transition temperature (DBTT) [5] restrict its use in many engineering applications. To address this issue, scientists have explored methods to improve the room-temperature ductility of tungsten materials. Consequently, tungsten-based composites have become a popular research topic. These materials, which are formed by combining tungsten with other elements or compounds, can synergistically enhance the strength and ductility at low temperatures [[6], [7], [8]]. However, the fabrication of such composites often faces many challenges, such as complex molding processes, demanding equipment requirements, and difficulties in achieving industrial-scale production. It has become fairly common to improve the performance of metals and alloys through deformation techniques. For tungsten-based composites, various severe plastic deformation techniques have been employed to enhance their low-temperature properties; these techniques include rolling [[9], [10], [11], [12]], swaging [[13], [14], [15], [16]], equal-channel angular pressing [17,18], high-pressure torsion [19], and high-energy rate forging (HERF) [[20], [21], [22], [23]]. Nonetheless, owing to the insufficient sintering activity of the powders, sintered tungsten bulk bodies often fail to meet the prerequisites for severe plastic deformation. Cracking frequently occurs during plastic deformation owing to inadequate density or excessively low deformation temperatures, leading to scrapping of the entire sample. To avoid this phenomenon, very high temperatures are often required for sintering and plastic deformation; for example, sintering of rolled tungsten needs to be conducted at temperatures above 2200 °C and hot rolling must be performed above 1400 °C [24], which can easily lead to rapid coarsening of the global microstructure (normal grain growth) or local microstructure (abnormal grain growth) [25]. This significantly affects the performance of tungsten-based composite materials. It seems that existing molding techniques have reached a bottleneck in their ability to enhance the performance of tungsten-based composites, with the main issues focusing on powder innovation.

For tungsten-based powders, achieving high-density materials through the sintering of precursor powders at low temperatures has consistently presented a significant challenge. Generally, the complete densification of micron-sized tungsten powder necessitates ultra-high temperatures above 2700 °C [26]. For example, sintering a tungsten compact with a grain size of 1.8 μm at 1650 °C results in a relative density of merely 76 %. However, increasing the temperature to 2500 °C allows a tungsten powder compact with a grain size of 3 μm to attain a relative density of 95 % [27]. In recent years, nano-powder sintering has gained attention because of the smaller grain size, larger specific surface area, and greater capillary sintering driving force of nano-powders, which lead to a lower onset temperature for sintering. Several studies have reported their excellent sintering performance. Malewar et al. reported a significant reduction in the sintering temperature of nano-W powders prepared by high-energy mechanical ball milling to 1700 °C [26]. Wang et al. investigated the sintering of nano tungsten powders and found that sintering 20 nm nano-tungsten powder at 1100 °C in a hydrogen atmosphere could achieve a density of ρ = 98 % [28]. Therefore, synthesis of high-quality nano-powders is a prerequisite for manufacturing high-performance tungsten-based composite materials. However, the preparation of nano tungsten powder presents certain difficulties, such as mechanical alloying, which is limited by powder contamination and low productivity [29], making its application in actual industrial production difficult. Therefore, low-cost and efficient production technologies for nano powders, along with forming processes, are essential for tungsten-based composite materials.

In this study, we add vanadium (V) and yttrium (Y) sources using a wet chemical method to prepare ultrafine tungsten-based nano-powders, which achieve a density of 95.2 % upon sintering at 1400 °C. The dispersed second-phase particles within the grains and grain boundaries suppress rapid grain boundary migration and inhibit the formation of intragranular pores. Subsequently, large-sized S-WVY tungsten-based composite materials with excellent low-temperature performance are fabricated at low temperatures through swaging, owing to the innovative end of the powder. The S-WVY retains a fine grain size while ensuring a high proportion of low-angle grain boundaries (LAGBs), thus significantly synergizing the strength and ductility at low temperatures, while achieving room-temperature ductility. We employ simple element addition to synergistically enhance cost-effectiveness, simplify the preparation process, and achieve large-scale production, thus significantly advancing the industrial application prospects of refractory metals and alloys.