Design of Bulk Stable Nanocrystalline Alloys: A New Approach to Lightweighting

加拿大致力于联合国的可持续发展目标，通过使用可持续结构，最大限度地减少能源消耗和有毒温室气体（GHG）排放，应对全球气候变化。主要贡献者——能源/交通部门——应对气候变化威胁的方法是轻量化，即用较轻的材料（如“较软”的铝合金）取代较重的材料，如“较强”的钢；但这导致了承载能力的丧失。这里的研究不是在轻量化上权衡强度，而是建议使用(i)同样更强的“重”材料，但使用更少的材料，以及（ii）同样更软的“轻”材料，但强度有所提高，两者都提供比市售材料更好的性能。由于材料的强度随着晶粒尺寸的减小而增加，因此通过开发纳米晶（NC）材料来实现提高强度的轻量化概念，纳米晶（NC）材料的晶粒尺寸为~1至100nm（即晶粒尺寸比人类头发厚度小~900倍）。然而，目前使用NC材料存在一个全球性的缺点——(a)纳米颗粒即使在室温下生长，也会导致强度和其他功能特性的损失，(b)即使纳米颗粒在生长过程中很好地稳定下来，它们也仅限于1-100微米厚的薄纳米结构涂层。对于轻量化应用，以最大限度地减少能源和运输部门的能源消耗，需要具有稳定晶界和尺寸/厚度超过当前薄膜尺度的“散装”数控材料。为清楚起见，本提案中的“体积”是指从数百厘米到米尺度的样品尺寸/厚度。粉末加工是一种经济有效且可扩展的合成数控金属的方法，但粉末加工生产批量数控零件的成功取决于固化过程。本课题提出了一种结合两种粉末工艺的新方法——固态机械铣削获得纳米颗粒，冷喷涂增材制造固态逐层沉积稳定粉末，以开发整体稳定的数控元件；通过仔细选择一种倾向于溶剂晶界位置的溶质来稳定纳米颗粒，从而稳定其生长。这项研究的成功将通过降低能源、排放和环境影响的成本，为加拿大节省数十亿美元。该研究方案还将有助于(i)培训高素质人才，（ii） UCalgary推动创新的使命，以及（iii） Alberta的纳米技术和制造方案以及研究优先事项——能源和温室气体减排，以及环境和气候适应目标领域。

Canada is committed to the United Nation's sustainable development goals to combat global climate change via the use of sustainable structures that minimize energy consumption and poisonous greenhouse gas (GHG) emissions. The approach adopted by major contributors-energy/transportation sectors-to tackling the climate change menace is lightweighting i.e., the replacement of heavy materials, say "stronger" steel, with lighter one like "softer" aluminum alloys; but this results in the loss of load-carrying capacity. Rather than trade-off strength upon lightweighting, the research here is proposing the use of the (i) same stronger "heavy" material but using less of it, and (ii) same softer "light" material but with improved strength, both offering even much better properties than what is commercially available. Because strength of materials increases with reduction in grainsize, the proposed lightweighting concept with improved strength is achieved by developing nanocrystalline (NC) materials-materials with ~1 to 100 nm in grain size (i.e., grain size is ~900 times smaller than the thickness of human hair). However, there is currently a global drawback in the use of NC materials-(a) nanograins grow even at room temperature, resulting in loss of strength and other functional properties, and (b) even if the nanograins are well stabilized against growth, they are limited to thin nanostructured coatings of ~1-100 microns thick. For lightweight applications to minimize energy consumption in the energy and transportation sectors, "bulk" NC materials with stabilized grain boundaries and with sizes/thicknesses beyond the current thin-film-scale are required. For clarity, "bulk" in this proposal refers to sample size/thickness from hundreds of centimeter- to meter- scale. A cost-effective and scalable approach to synthesize NC metals is through a powder processing route, but the success of producing bulk NC parts by powder processing rests on the consolidation process. This research program proposes a new approach that involves the union of two powder processes-solid-state mechanical milling to obtain nanograins, and cold spray additive manufacturing process for solid-state layer-by-layer deposition of the stabilized powders to developing bulk stable NC components; the nanograins will be stabilized by carefully selecting a solute that prefers the grain boundary sites of the solvent, thereby stabilizing it against grain growth. The success of this research will save Canada billions of dollars by reducing the cost of energy, emissions, and environmental impacts. The research program will also contribute to the (i) training of highly qualified personnel, (ii) UCalgary's mission to drive innovation, and (iii) Alberta's nanotechnology and manufacturing programs and research priorities-energy and GHG mitigation, and environment and climate adaptation target areas.