In-Situ Selective Reinforcement of Near-Net-Shape Formed Structures

In order to improve the properties of monolithic metallic materials, alloying additions are made that create secondary phases and/or precipitate structures. These improvements must occur during melt solidification and are governed by the thermodynamics of the process. That is, optimizing the metallic alloy is possible only as much as thermodynamics allow. Developing novel methods to combine metallic compositions/alloys into a fully dense material is of interest to create materials with novel property combinations not available with monolithic alloys.While various approaches for layering two-dimensional materials exist, their capabilities are typically limited and non-isotropic. Further, while three-dimensional composites may be formed with conventional powder metallurgy processes, it is generally very difficult to control the arrangement of the phases, for example due to randomness created by mixing powders. This invention is method for creating a multiple alloy composite structures by forming a three-dimensional arrangement of a first alloy composition, in which the three-dimensional arrangement has a substantially open and continuous porosity. The three-dimensional arrangement of the first alloy composition is infused with at least a second alloy composition. The three-dimensional arrangement is then consolidated into a fully dense solid structure.

The FMLs resulting from the NASA process have similar properties to traditionally produced metal/composite hybrid laminates including, as compared to either the composite or metal only structures, improved load carrying capability, lighter weight, improved stiffness, improved impact resistance and damage tolerance, and improved permeation resistance. The NASA process can be applied to various FML types, including GLARE (glass, aluminum, epoxy), and TIGR (titanium, graphite). Typical manufacturing processes are costly and complex shapes are hard to produce, whereby the NASA process enables use of these kinds of laminates without an autoclave or press, thus increasing the size that can be produced and decreasing the cost. The resin pathways in the foils enable connection between the plies that can improve the interlaminar strength of the final part. Functionally the NASA process creates resin columns in the transverse direction of the plies. NASA is working to optimize the final properties by varying the size and distribution of the pathways.

NASA's plasma-deposition process provides the ability to tailor various properties while designing functional parts by selecting specific materials and processing parameters to meet the end goal. Specifically, the plasma process deposits metal particles that are heated as they travel axially at low velocity through an inert gas plasma. The accelerated powder particles become molten, strike the substrate fabric (uniaxial, biaxial, and multiaxial) and rapidly solidify, imparting very little heat to the substrate while forming a metal-to-fiber bond, as well as a metal-to-metal bond. The resulting metal-coated fabric is porous, so the polymer matrix can pass through the product precursor during the infusion process. The amount of metal deposited can be controlled, as can the number of plies of fabric that are ultimately stacked to produce the preform for the polymer matrix infusion process. A variety of infusion processes can be utilized to prepare the FML, including resin transfer molding (RTM), resin film infusion (RFI), and vacuum-assisted resin transfer molding (VARTM). The tailorable aspect of the process allows for specific product design. By varying the combination of metal particle, fiber, fabric type, metal layer thickness, fabric direction, number of layers, polymer matrix resin, infusion process, and cure conditions, the characteristics of the final part can meet the needs of various applications.

This materials system is comprised of an Al metal matrix with high-performance SMA reinforcements. The combination of the unique matrix composition and SMA elements allow for this material system to self-repair via a two-step crack repair method. When a crack is present in the matrix material, the MMC is heated above the SMA's austenite start (As) temperature. This initiates shape recovery of the SMA, pulling the crack together as the SMA reinforcements return to their initial length. Concurrently, the increased temperature causes softening and liquefaction of the eutectic micro-constituent in the matrix, which enables the recovery of plastic strain in the matrix as well as crack filling. Combined with the crack closure force provided by the SMA reinforcements completely reverting to their original length, the MMC welds itself together and, upon cooling, results in a solidified composite able to realize its pre-cracked, original strength. The research team has demonstrated and tested the new materials. The team induced cracks in prototype materials based on Al-Si matrix with SMA (NiTi) reinforcements and demonstrated the recovery of tensile strength after healing. Data from tensile and fatigue tests of the samples before and after the fatigue crack healing shows a 91.6% healing efficiency on average under tensile conditions.

Shape memory alloys (SMAs) are metals that can return to their original shape following thermal input. They are commonly used as functional materials in sensors, actuators, clamping fixtures and release mechanisms across industries. SMAs can suffer from dimensional/thermal instability, creep, and/or low hardness, resulting in alloys with little to no work output in the long term. To combat these deficiencies, NASA has developed a process of incorporating nanoparticles of refractory materials (i.e., carbide, oxide, and nitride materials with high temperature resistance) into the alloys. Using various processing methods, the nanoparticles can be effectively mixed and dispersed into the metal alloys as shown in the figure below. In these processes the SMA and refractory material powder is mixed and the refractory nanoparticles incorporated through extrusions, melting, or directly used in additive manufacturing to create parts for applications across the aerospace, automotive, marine, or biomedical sectors. The nanoparticle dispersion is a controllable method to strengthen the SMAs, increasing the hardness of the alloys, reducing the impact of creep, and improving the overall dimensional and thermal stability of the alloys. The related patent is now available to license. Please note that NASA does not manufacture products itself for commercial sale.