This Small Business Innovation Research Phase I project relates to the use of nano-structured chemicals in the processing of light-weight magnesium (Mg) alloys for high performance applications. It is postulated that reactive nano-structured chemicals such as polyhedral oligomeric silsesquioxane (POSS) with multiple silanol functionalities will be added to Mg alloys by solid phase mixing and in-situ reaction to achieve microstructure stability at higher temperatures leading to a significant performance enhancement for Mg alloys. This in-situ processing route is achieved through creating an environment where surface metal ions, with oxides removed and positively charged by acid or flux, bond to Si-OH groups in POSS. The end reaction results in chemical attachment of high concentrations of nanoscale Si-O cage compounds that are chemically and thermally stable near the grain boundary. These nanoscale cage compounds provide obstacles to prevent overgrowth of intermetallic compounds (IMC) and retard the motions between grains at high temperatures for microstructure stability of Mg alloys. The in-situ process overcomes the common problem of dispersing nanoparticles in a metal matrix where agglomeration and clustering of nanoparticles can occur. The resulting Mg alloys will be demonstrated to have improved service and mechanical properties at both ambient and elevated temperatures.
The broader impact/commercial potential of this project will be to significantly improve performance of structural Mg components enabling widespread application in the automotive and aerospace industries. The automotive and aerospace industries are under ever-increasing pressure to reduce both fuel consumption and harmful emissions. Reducing the overall weight of vehicles and aircraft is key to achieving these goals and magnesium alloys, with their low density, can often be a viable proposition. However, the widespread use of magnesium is limited by its relatively poor mechanical and high-temperature creep properties. The project goal is to produce high-strength, creep-resistant magnesium material suitable for structural applications by POSS processing. Material with high concentrations of nanoscale Si-O cage compounds will be used as a master alloy in casting operations to produce large net shaped components. The manufacturing technology developed will provide a cost advantage over foreign competition for manufacturers of structural automotive and aerospace parts.
Under NSF funding, Vinci Technology has developed a new process which incorporates nano-structured polyhedral oligomeric silsesquioxane (POSS) with multiple silanol functionalities into aluminum (Al) alloys to form silanol-embedded Al alloys which exhibit excellent mechanical properties. It is Vinci’s intention to set up a commercial US-based business to further develop the process to manufacturing readiness, produce the alloy either in house or by a contract manufacturer in US, and extend it to a wider family of Al alloys. Thus, the ultimate purpose of the NSF SBIR program will be fulfilled. The in-situ process overcomes the common problem of dispersing nanoparticles in a metal matrix where agglomeration and clustering of nanoparticles can occur. It is based on the chemical reaction between the Si-OH groups in POSS and the surfaces of metal powder particles in an environment where surface metal ions, with oxides removed and positively charged by acid or flux, bond to Si-OH groups in POSS to form silanol-metallic nanocompound. This structural silanol compound is chemically and thermally stable, and is dispersed uniformly in the Al matrix. Incorporation of structural silanol-metallic compounds in bulk metal was first used in Sn-based solder alloys to significantly improve isothermal mechanical properties, reduce grain size, and improve thermal-mechanical fatigue property. Vinci’s goal in this SBIR Phase I project was to apply the same principle but to higher temperature Al alloys. Consequently, great challenges arose on the issues of: the selection of suitable acids or fluxes to clean and activate Al surface; developing a process which satisfies the temperature range of the thermal stability of POSS; ensuring that the reaction between POSS and Al occurs efficiently; and demonstrating enhanced mechanical properties. Cost for the materials, processes, and final products would have to be considered in every step of the project for the commercialization plan in the Phase II. Study on the pure Al powder treated with POSS confirmed the success of reaction, and reveals Si particles to be uniformly dispersed in an Al matrix. POSS-treated A4047, A319, and A359 show dramatic improvement in ductility (elongation to failure), from 23% to 250% increase, over the same alloys without POSS added. More surprisingly, there is no decrease in the yield strength (YS) and ultimate tensile strength (UTS) with the increase of the ductility, which are opposite to common practice in alloy development. Metallography showed refined spheroidic Si cuboids in the Si-Al eutectic phase and refined a-Al phase, which explains the improvement in ductility. The refinement effect from structural silanol matches that from other grain refiner elements, e.g. strontium (Sr), sodium (Na), titanium (Ti), boron (B), beryllium (Be), etc. Funding for a Phase IB was received to develop a low-temperature process for Sn-based solder for the possible near-term revenue in the Phase II. In previous studies of implementing POSS to Sn solder, a "one step" process was used with POSS mixed with proprietary commercial paste which contains Sn solder powder, fluxes, and carriers. The reaction with POSS and the Sn-based powder particles and the casting process occurred in a single step around the melting temperature of the Sn alloy. Vinci has developed a "two step" process for both Sn and Al, with first step of the POSS treatment with metal powder or chips at ambient or low temperature, and the second step of melting POSS-treated powder to form an ingot. The newly developed two-step process ensures the treatment reaction occurred below the maximum allowed temperature for POSS, and it permits better management of the cost and availability of feedstock materials, and control of intellectual property.
