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

加拿大致力于实现联合国的可持续发展目标，通过使用最大限度减少能源消耗和有毒温室气体排放的可持续结构来应对全球气候变化。主要贡献者--能源/运输部门--为应对气候变化威胁所采取的办法是轻量化，即用较轻的材料，如“较软”的铝合金取代较重的材料，例如“较强”的钢；但这会导致丧失承载能力。这里的研究不是在强度和轻量化之间进行权衡，而是建议使用(I)相同的更坚固的“重”材料但使用更少的材料，以及(Ii)相同的更软的“轻”材料但强度更高，这两种材料都提供了比商业上可用的更好的性能。由于材料的强度随着颗粒尺寸的减小而增加，因此提出的轻量化概念是通过开发纳米晶(NC)材料来实现的，纳米晶(NC)材料是指颗粒尺寸约为1到100 nm(即，颗粒尺寸小于人类头发厚度的~900倍)的材料。然而，目前使用纳米材料存在一个全球性的缺陷--(A)纳米颗粒即使在室温下也会生长，导致强度和其他功能特性的损失，以及(B)即使纳米颗粒在生长过程中得到很好的稳定，它们也仅限于厚度约1-100微米的薄纳米结构涂层。为了使能源和交通部门的能源消耗降至最低，需要具有稳定晶界且尺寸/厚度超过当前薄膜尺度的“大块”NC材料。为清楚起见，本提案中的“散装”是指从数百厘米到米的样品尺寸/厚度。合成NC金属的一种经济有效且可扩展的方法是通过粉末加工路线，但通过粉末加工生产大宗NC零件的成功取决于固结过程。这项研究计划提出了一种新的方法，涉及两种粉末工艺的结合-固态机械球磨获得纳米颗粒，以及冷喷涂添加剂制造工艺用于固态逐层沉积稳定的粉末以开发块状稳定的NC组件；通过仔细选择偏爱溶剂晶界位置的溶质来稳定纳米颗粒，从而稳定其防止颗粒长大。这项研究的成功将通过减少能源成本、排放和环境影响为加拿大节省数十亿美元。该研究计划还将有助于(I)高素质人才的培训，(Ii)加州大学卡尔加里分校推动创新的使命，以及(Iii)艾伯塔省的纳米技术和制造计划以及研究重点--能源和温室气体缓解，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.