康奈尔（Cornell）领导的合作开发了一种3D打印技术，该技术通过以超音速速度将粉末颗粒粉碎在一起，从而创建蜂窝金属材料。
This form of technology, known as “cold spray,” results in mechanically robust, porous structures that are 40% stronger than similar materials made with conventional manufacturing processes. The structures’ small size and porosity make them particularly well-suited for building biomedical components, like replacement joints.
The team’s paper, “Solid-State Additive Manufacturing of Porous Ti-6Al-4V by Supersonic Impact,” published Nov. 9, 2020 in Applied Materials Today.
The paper’s lead author is Atieh Moridi, assistant professor at Cornell's Mechanical and Aerospace Engineering.
“We focused on making cellular structures, which have lots of applications in thermal management, energy absorption and biomedicine,” Moridi said. “Instead of using only heat as the input or the driving force for bonding, we are now using plastic deformation to bond these powder particles together.”
Moridi的研究小组专门通过增材制造工艺创建高性能金属材料。但是，增材制造并非没有自己的挑战。其中最重要的是：金属材料需要在高温超过其熔点的高温下加热，这可能会导致残留的应力积累，失真和不需要的相变。
To eliminate these issues, Moridi and collaborators developed a method using a nozzle of compressed gas to fire titanium alloy particles at a substrate.
莫里迪说：“这就像绘画一样，但事情在3D中的发展得多。”
颗粒的直径在45至106微米之间（微米为一百万米），以每秒600米的速度行驶，比声速快。为了透视这一点，另一个主流添加剂过程，直接的能量沉积，以每秒10米的速度以10米的速度通过喷嘴提供粉末，使Moridi的方法速度快60倍。
The particles aren’t just hurled as quickly as possible. The researchers had to carefully calibrate titanium alloy’s ideal speed. Typically in cold spray printing, a particle would accelerate in the sweet spot between its critical velocity – the speed at which it can form a dense solid – and its erosion velocity, when it crumbles too much to bond to anything.
取而代之的是，Moridi的团队使用计算流体动力学来确定钛合金颗粒的临界速度下的速度。当以稍慢的速度发射时，颗粒会产生更多孔的结构，这是生物医学应用的理想选择，例如膝盖或髋关节的人造关节，以及颅/面部植入物。
莫里迪说：“如果我们用这种多孔结构制作植入物，并且将它们插入体内，则骨骼可以在这些毛孔内生长并产生生物固定。”“这有助于减少植入物松动的可能性。这很重要。患者必须进行许多修订手术，以清除植入物，只是因为它松动并且会引起很多痛苦。”
尽管该过程在技术上称为冷喷雾剂，但确实涉及一些热处理。一旦颗粒碰撞并粘合在一起，研究人员就会加热金属，使组件将相互扩散并像均匀的材料一样沉降。
“我们只集中在钛合金和生物医学applications, but the applicability of this process could be beyond that,” Moridi said. “Essentially, any metallic material that can endure plastic deformation could benefit from this process. And it opens up a lot of opportunities for larger-scale industrial applications, like construction, transportation and energy.”
Co-authors include doctoral student Akane Wakai and researchers from MIT, Polytechnic University of Milan, Worcester Polytechnic Institute, Brunel University London and Helmut Schmidt University.
资料来源：康奈尔编年史
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