RESUMEN
Ultra-long metal nanowires and their facile fabrication have been long sought after as they promise to offer substantial improvements of performance in numerous applications. However, ultra-long metal ultrafine/nanowires are beyond the capability of current manufacturing techniques, which impose limitations on their size and aspect ratio. Here we show that the limitations imposed by fluid instabilities with thermally drawn nanowires can be alleviated by adding tungsten carbide nanoparticles to the metal core to arrive at wire lengths more than 30 cm with diameters as low as 170 nm. The nanoparticles support thermal drawing in two ways, by increasing the viscosity of the metal and lowering the interfacial energy between the boron silicate and zinc phase. This mechanism of suppressing fluid instability by nanoparticles not only enables a scalable production of ultralong metal nanowires, but also serves for widespread applications in other fluid-related fields.
RESUMEN
While laser-printed metals do not tend to match the mechanical properties and thermal stability of conventionally-processed metals, incorporating and dispersing nanoparticles in them should enhance their performance. However, this remains difficult to do during laser additive manufacturing. Here, we show that aluminum reinforced by nanoparticles can be deposited layer-by-layer via laser melting of nanocomposite powders, which enhance the laser absorption by almost one order of magnitude compared to pure aluminum powders. The laser printed nanocomposite delivers a yield strength of up to 1000 MPa, plasticity over 10%, and Young's modulus of approximately 200 GPa, offering one of the highest specific Young's modulus and specific yield strengths among structural metals, as well as an improved specific strength and thermal stability up to 400 °C compared to other aluminum-based materials. The improved performance is attributed to a high density of well-dispersed nanoparticles, strong interfacial bonding between nanoparticles and Al matrix, and ultrafine grain sizes.
RESUMEN
Cooling, nucleation, and phase growth are ubiquitous processes in nature. Effective control of nucleation and phase growth is of significance to yield refined microstructures with enhanced performance for materials. Recent studies reveal that ultrafine grained (UFG)/nanocrystalline metals exhibit extraordinary properties. However, conventional microstructure refinement methods, such as fast cooling and inoculation, have reached certain fundamental limits. It has been considered impossible to fabricate bulk UFG/nanocrystalline metals via slow cooling. Here, we report a new discovery that nanoparticles can refine metal grains to ultrafine/nanoscale by instilling a continuous nucleation and growth control mechanism during slow cooling. The bulk UFG/nanocrystalline metal with nanoparticles also reveals an unprecedented thermal stability. This method overcomes the grain refinement limits and may be extended to any other processes that involve cooling, nucleation, and phase growth for widespread applications.
RESUMEN
Nano-treating is a novel concept wherein a low percentage of nanoparticles is used for microstructural control and property tuning in metals and alloys. The nano-treating of AA7075 was investigated to control its microstructure and improve its structural stability for high performance. After treatment with TiC nanoparticles, the grains were significantly refined from coarse dendrites of hundreds of micrometers to fine equiaxial ones smaller than 20 µm. After T6 heat treatment, the grains, with an average size of 18.5 µm, remained almost unchanged, demonstrating an excellent thermal stability. It was found that besides of growth restriction factor by pinning behavior on grain boundries, TiC nanoparticles served as both an effective nucleation agent for primary grains and an effective secondary phase modifier in AA7075. Furthermore, the mechanical properties of nano-treated AA7075 were improved over those of the pure alloy. Thus, nano-treating provides a new method to enhance the performance of aluminum alloys for numerous applications.
RESUMEN
Glassy materials can be broadly defined as any amorphous solid, which are important in nature and have significant societal value for their applications in daily life and industry. Although many methods have been applied, the fracture toughness of traditional glasses is still very low due to intrinsic brittleness, significantly limiting their use for structural applications. While nanoelements may be added into glasses and ceramics to form nanocomposites with enhanced properties, it is extremely difficult to distribute and disperse them inside the liquid glass/ceramic matrix with traditional processing methods. It is shown that a strong and tough glass can be fabricated through a direct-solidification process using a nanoparticle self-dispersion mechanism in a glass melt (2MgO·2Al2 O3 ·5SiO2 ) with the assistance of B2 O3 , delivering a 6.1% strain limit and strength up to E/14 (E is elastic modulus), which is close to the theoretical limit of E/10 and one of the highest among all materials reported so far. The fracture toughness of the glass with 30 vol% SiC nanoparticles is significantly higher than any other inorganic glass tested under similar conditions. This new method opens up remarkable opportunities for glass and ceramic research, manufacturing, and applications.
RESUMEN
Lightweight materials are of paramount importance to reduce energy consumption and emissions in today's society. For materials to qualify for widespread use in lightweight structural assembly, they must be weldable or joinable, which has been a long-standing issue for high strength aluminum alloys, such as 7075 (AA7075) due to their hot crack susceptibility during fusion welding. Here, we show that AA7075 can be safely arc welded without hot cracks by introducing nanoparticle-enabled phase control during welding. Joints welded with an AA7075 filler rod containing TiC nanoparticles not only exhibit fine globular grains and a modified secondary phase, both which intrinsically eliminate the materials hot crack susceptibility, but moreover show exceptional tensile strength in both as-welded and post-weld heat-treated conditions. This rather simple twist to the filler material of a fusion weld could be generally applied to a wide range of hot crack susceptible materials.
RESUMEN
There is a longstanding challenge to disperse metal nanoparticles uniformly in bulk polymers for widespread applications. Conventional scale-down techniques often are only able to shrink larger elements (such as microparticles and microfibers) into micro/nano-elements (i.e. nanoparticles and nanofibers) without much altering their relative spatial and size distributions. Here we show an unusual phenomenon that tin (Sn) microparticles with both poor size distribution and spatial dispersion were stretched into uniformly dispersed and sized Sn nanoparticles in polyethersulfone (PES) through a stack and draw technique in thermal drawing. It is believed that the capillary instability plays a crucial role during thermal drawing. This novel, inexpensive, and scalable method overcomes the longstanding challenge to produce bulk polymer-metal nanocomposites (PMNCs) with a uniform dispersion of metallic nano-elements.
RESUMEN
Effective control of melting and solidification behaviours of materials is significant for numerous applications. It has been a long-standing challenge to increase the melted zone (MZ) depth while shrinking the heat-affected zone (HAZ) size during local melting and solidification of materials. In this paper, nanoparticle-induced unusual melting and solidification behaviours of metals are reported that effectively solve this long-time dilemma. By introduction of Al2O3 nanoparticles, the MZ depth of Ni is increased by 68%, while the corresponding HAZ size is decreased by 67% in laser melting at a pulse energy of 0.18 mJ. The addition of SiC nanoparticles shows similar results. The discovery of the unusual melting and solidification of materials that contain nanoparticles will not only have impacts on existing melting and solidification manufacturing processes, such as laser welding and additive manufacturing, but also on other applications such as pharmaceutical processing and energy storage.
