胶水或墨水可以改善柔软的金属切割

Focus: Glue or Ink Improves Soft Metal Cuts

Coating a soft metal with any compound that adheres leads to smoother cuts because the coating makes the surface more brittle.涂上一层柔软的金属，任何一种粘在一起的化合物都会使伤口更平滑，因为涂层会使表面变得更加脆弱。

A. Udupa/Purdue Univ.

Fixing the chips. A microscope image (about 400 micrometers wide) shows that the free side of the chip shaved off of a bare copper block by a cutting blade has a folded, “sinuous” texture (left). But if the block’s surface is coated with ink, the chi… 修复芯片。一个显微镜图像（大约400微米宽）显示，一个切割刀片削掉的铜块的自由面有一个折叠的、“弯曲的”纹理（左图）。但是如果块表面涂上了墨水，那么气……

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A. Udupa et al., Phys. Rev. Applied (2018)

Close-up of the chip being shaved off of a copper block by a cutting blade positioned vertically along the right edge of the frame (the camera moves with the blade). At first the copper is bare, and the chip has a sinuous form. But at about 0:08, the blade reaches a glue-coated section, and the shape of the chip changes abruptly to a series of slabs, as it fractures in a brittle manner. At the same time, the force needed for cutting falls dramatically.在框架的右边缘垂直放置一个切割刀片的切割刀片的特写镜头（相机与刀片一起移动）。一开始，铜是光秃秃的，而芯片有一种弯曲的形式。但在大约0:08的时候，刀片到达了一个胶着的部分，芯片的形状突然变成了一系列的厚板，因为它以一种易碎的方式断裂。与此同时，切割所需的力急剧下降。

Gummy metals are used in components for robotic welders, medical implants, and many other products, but turning, milling, and drilling these materials can be costly and time-consuming, thanks to the difficulty of making clean cuts. In 2015 a team at Purdue University in Indiana, led by Srinivasan Chandrasekar, explained that the gumminess of these metals can be understood by observing the thin layer of material shaved off by a cutting blade. 胶质金属被用于机器人焊接、医用植入物和许多其他产品的部件中，但由于难以进行清洁切割，这些材料的旋转、研磨和钻孔都是昂贵且耗时的。2015年，印第安纳州普渡大学的一个研究小组，由Srinivasan Chandrasekar领导，解释说，通过观察切割刀片削掉的薄层材料，可以理解这些金属的黏性。In a gummy metal, this “chip” forms a series of folds—what the researchers call a “sinuous” shape—as it peels away from the surface [1]. The folding may cause the chip to pull off other parts of the surface as the blade advances, leaving it pitted and rough. This behavior, paradoxically, means that a relatively large force is required to make cuts, despite the metal’s softness.在一种胶状金属中，这种“芯片”形成了一系列的褶皱——研究人员称之为“弯曲”的形状——当它从表面剥离出来的时候。当刀片向前推进时，折叠可能会导致芯片拉出表面的其他部分，使其变得坑坑洼洼和粗糙。矛盾的是，这种行为意味着需要一个相对较大的力量来进行切割，尽管金属是柔软的。

The researchers found in 2015 that the cut was smoother and required less force if they coated the metal with Dykem ink, which is commonly used to mark metals and which consists of pigments dissolved in alcohol [1]. It appeared that the ink provided these benefits by suppressing the sinuous folding. “We were as puzzled as anyone else” about why no one had noticed this trick before, says Purdue team member Anirudh Udupa.研究人员在2015年发现，如果他们用Dykem墨水涂上金属，那么这种切割就会更平滑，而且需要更少的力。这种墨水通常被用来标记金属，其中包括溶解在酒精中的颜料。墨水似乎通过抑制弯曲的折叠来提供这些好处。普渡大学的团队成员Anirudh Udupa说：“我们和其他人一样困惑，为什么没有人注意到这个把戏。”

To learn which coating properties matter most, Chandrasekar and colleagues have now systematically investigated the cutting of iron, aluminum, and copper coated with other materials, such as Sharpie permanent marker ink, glues, Scotch tape, and soap. They have also examined the cutting process under a microscope to understand why coating the metal improves the cutting process at all.为了了解哪种涂层性能最重要，Chandrasekar和他的同事们现在已经系统地研究了切割其他材料的铁、铝和铜的切割，如Sharpie永久标记墨水、胶水、透明胶带和肥皂。他们还在显微镜下观察切割过程，以了解为什么涂层金属可以改善切割过程。

The coatings fall into three classes, they find. The first, including glues and inks, adhere strongly to the metals through physical adsorption (the presence of attractive van der Waals interactions, not chemical bonds). All such substances improve the cutting performance, producing a smoother surface and allowing cuts with less force.他们发现，这种涂层可以分为三类。第一个，包括胶水和墨水，通过物理吸附（有吸引力的范德瓦尔斯相互作用，而不是化学键）牢牢地附着在金属上。所有这些物质都能提高切割性能，使表面更光滑，并能减少使用力。 The second group, pure alcohols, work only for aluminum, with which they form chemical bonds. The third group, including acetone, paraffin wax, and water, has no real propensity to adsorb to the metal surface and exerts no influence on cutting.第二组，纯醇，只适用于铝，它们形成化学键。第三组，包括丙酮、石蜡和水，没有吸附到金属表面的真正倾向，对切割没有影响。

In the presence of a strongly interacting coating, the shape of the chip is quite different from that for the bare metal. Instead of a sinuous, folded surface, the chip fragments repeatedly into slab-like segments 0.1-0.2 mm thick. In other words, the metal deforms in a brittle, rather than ductile, fashion.在一种强相互作用的涂层面前，芯片的形状与裸金属的形状是完全不同的。它不是一个弯曲的、折叠的表面，而是不断地重复成片状的片段，比如0。1-0。2毫米厚。换句话说，金属的变形是脆弱的，而不是延展性的。

The team applied a simple model of metal deformation to learn what causes this ductile-to-brittle transition. Brittle materials can crack, while in a ductile material cracks can be suppressed. Instead of advancing, a crack can dissipate its energy by radiating dislocations—shifts of one layer of the crystal with respect to the next that can propagate through a crystal. By lowering the metal’s surface energy, a coating makes it harder for dislocations to form and spread and thus undermine cracks, so the metal fractures in a brittle way.研究小组应用了一种简单的金属变形模型来了解是什么导致了这种延展性的转变。脆性材料可以破裂，而在韧性材料的裂缝中可以被抑制。一个裂缝可以通过辐射错位来驱散它的能量——一层晶体的转移，而另一层则可以通过晶体传播。通过降低金属表面的能量，涂层使分离变得更加难以形成和扩散，从而破坏裂缝，所以金属的破裂是脆弱的。

“Our initial hypothesis was that there was a particular chemical in all of these media that was inducing the transition,” says Udupa. “But we soon realized that the effect was due simply to the fact that the media stick to the surface.”Udupa说：“我们最初的假设是，在所有这些媒体中，有一种特殊的化学物质正在诱导这种转变。”“但我们很快意识到，这种影响仅仅是由于媒体坚持了表面。”

The researchers say that the “mechanochemical” effect they identify could improve the quality and lower the cost of machining and surface finishing of these metals. For example, the right coating could improve engineers’ ability to machine gummy, nickel-based alloys, which are used for corrosion-resistant equipment in oil and gas prospecting.研究人员说，他们所识别的“机械化学”效应可以提高这些金属的加工和表面加工的质量，降低成本。例如，正确的涂层可以提高工程师的能力，使其能够在石油和天然气勘探中使用耐腐蚀设备。

This research is published in Physical Review Applied.

–Philip Ball

Philip Ball is a freelance science writer in London; his latest book is Beyond Weird, a survey of interpretations of quantum mechanics.

这项研究发表在物理评论上。 菲利普球 Philip Ball是伦敦的一名自由科学作家;他的最新著作超越了怪异，这是对量子力学解释的一项调查。