Name: processing of bulk nanocrystalline metals at the us army research laboratory
Uploaded: 2018-03-07T14:00:00
Description: Watch this Scientific Journal Video about Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory at JoVE.com

1. 环境条件下纳米晶粉体的小尺度合成
<ol><li>在控制的氩气气氛手套盒中, 放置10克的主要元素 (e. g, 铁在 FeNiZr 合金) 和100克不锈钢/刀具钢铣削球在所需的铣瓶。 注: 需要将粉末装入手套箱内的铣削罐中, 以确保最小吸收氧和/或含水量18,19。</li>
	<li>装货后, 密封罐, 从手套箱中取出。拆卸后, 确保罐完全密封, 并加载到适当的铣床。</li>
	<li>在?...

<ol>
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与其他合成技术相比, 机械合金化是一种非常通用的方法, 用于生产晶粒尺寸 < < 100 纳米的金属和合金粉末。 事实上, 机械合金化是以成本效益高、易于伸缩的方式生产大量纳米材料的为数不多的方法之一。此外, 高能球磨已被证明大大增加了固体溶解度的限制, 在许多金属系统中, 平衡室温溶解度不存在。这就允许用其他平衡加工技术生产出的新型合金。
尽管不一定需要, 但?...

高能机械合金化制备的纳米晶金属与它们的粗粒度相比较显示出优异的机械强度。然而, 根据热力学原理, 纳米晶微结构在高温下会受到晶粒粗化的支配。因此, 这些材料的加工和应用目前由于能够在散装形式下形成稳定的显微组织而受到限制。鉴于这些材料的潜力, 正在努力开发这类系统的两种主要方法。首先, 以动力学方法为基础, 利用多种机制对晶界 (gb) 施加固定力, 以防止晶粒生长。用于引脚的典型机制是次要阶段 (齐纳钉住)1,2,3和/或溶质拖动效果4,5。第二种方法以热力学方法为基础, 通过将溶质原子划分为6、7、8、9、,从而抑制谷物的生长。10,11,12,13,14,15,16。
作为开发具有 nanograined 显微结构的合金的第一步, 建立了在高温下控制晶粒生长和显微组织稳定性的热力学和动力学原理的基本理解。计算材料科学也被用来指导合金的发展。利用这些洞察力, 小规模大量的各种合金粉末生产使用高能铣削和评估广泛的物理和机械性能。对于更有前景的系统, 开发了先进的表征技术, 以充分地将粉末的显微结构与观察到的性能和性能联系起来。
同时, 还获得了从纳米晶粉末中生产大块部件所需的基础设施和设备。一旦这一设备到位, 通过一系列小规模的实验, 开发了从合金粉末中充分整合大块材料所需的加工科学。一旦大量样品可用, 进行了一系列的实验, 以了解这些材料在各种条件下的机械反应 (如疲劳, 蠕变, 高应变率,等)。从这些实验中获得的知识已经被用来开发可能的应用空间, 从而使稳定的大块纳米晶合金商业化。
总的来说, 完成这些任务导致了美国陆军研究实验室 (ARL) 在一个由4家主要实验室组成的纳米金属研究中心的发展。这个实验室综合体代表了2000万美元的总投资, 并且是独一无二的, 因为它跨越了基础、应用和制造科学的各个方面。这些实验室的主要目的是将概念证明观念转变为试点规模和前期制造水平。在这样做的过程中, 预计实验室将能够生产原型零件, 开发必要的专门知识和制造科学进行放大加工, 并允许内部和外部研究机构建立联系, 或工业合作伙伴通过商业化和过渡这一先进的粉末技术。
如前所述, 第一步是确定、生产和快速评估新的合金原型, 以便将合成和制造作为原型零件的可行性。为了做到这一点, 几个独特的, 定制设计的高能振动筛厂已经建设的能力, 处理在广泛的温度范围内的粉末, 从-196 °c 到200摄氏度。顾名思义, 这些磨坊通过剧烈摇晃的动作产生大约10-20 克的细粉, 导致粉末和研磨介质之间的重复撞击, 产生粉末, 其中每个粒子的组成比例与开始元素粉末混合。虽然适合于快速筛选粉末, 这种类型的轧机显然不适合在 (近) 工业规模 (e. g, 公斤) 的粉末生产。
鉴于有必要大量生产粉末, 并在尽可能连续的过程中, 进行了搜索, 以查明可能可行的方法和设备。行星球磨机使用一个支持盘, 从垂直方向的小瓶转向相反的角度, 导致颗粒尺寸减少, 由于磨削和碰撞造成的离心力。大多数行星铣刀的批量大小可达大约2公斤。与传统轧机不同, 机型轧机由一个立式滚筒内的一系列叶轮组成。叶轮的旋转会引起研磨介质的运动, 从而通过粉末、球和叶轮之间的碰撞减少颗粒尺寸。更大的机型工厂能够生产超过200公斤每运行。虽然这两个工厂提供了巨大的增长, 相对于振动筛厂的批量, 他们不能以持续的方式运行, 但必须为每个运行手动加载和卸载。
由于这些缺点, 注意力转向了一系列高能、卧式回转球磨机。这些工厂能够处理多达200公斤的每批, 也可以在惰性的气氛下和真空下运行。最后, 铣削室设计了一个气闸, 允许快速和自动去除粉末一旦铣削过程完成。结合自动喷粉系统, 这意味着球磨机能够以相当连续的方式运行, 从而使其成为一个高度可行的工业环境系统。由于这些特点的组合, ARL 最近购买和安装两个工厂, 现在从事推广内部粉末加工工作。
尽管粉末加工的努力代表着持续努力的一个中心方面, 但最有希望的合金粉末的表征和整合也是重点研究领域。事实上, 如下所述, ARL 在充分评估新粉末的关键特性所需的分析和测试设备方面作出了显著的投资。此外, 成功的样品合并现在允许常规的全面的机械测试和表征 (e. g), 这些材料的张力, 疲劳, 蠕变, 冲击和弹道评估) 通常是不可行的这类材料。本文报告了 ARL 在初始合成、放大、固结和表征块状纳米晶金属和合金方面所使用的协议。
两个主要的粉末合成实验室可以在图 1中看到。图 1A显示了小型粉末加工实验室, 使概念和合金设计得以迅速发展。该实验室包含若干个定制设计的高能磨机, 具有处理温度范围内的粉末的能力 (室温到400°c 和10到-196 摄氏度)。该实验室还包含一个定制的水平管炉, 用于快速评估新金属合金的热和显微结构稳定性 (e. g, 谷物生长研究)。最后, 实验室还安装了几个独特的小型机械测试装置, 包括张力、剪切冲床和印象蠕变测试设备, 以及一种先进的压仪器。经过彻底测试和显示的承诺, 选定的合金被移动到大型加工实验室 (图 1B), 其中工程和制造协议的开发, 以允许大规模 (e. g, 千克) 生产的特定粉末。总体而言, 实验室的投资总额为200万美元, 涵盖了从实验室工作台向试点规模制造水平过渡的新型金属粉末, 从而使原型零件得以生产。
高能球磨/机械合金化是生产纳米晶金属和粉末状合金的通用工艺,17。从粗粒度粉末 (典型的平均晶粒尺寸 ~ 5-10 µm) 开始, 可以获得在铣削后平均晶粒尺寸 < 100 nm 的纳米晶粉末。这种铣削通常在振动/振动筛轧机上进行。该铣瓶充满了所需的粉量以及铣削球, 通常是不锈钢。这个磨房震动小瓶在一项行动包括来回振荡以短的横向运动以速度大约1080个周期极小值-1。每一个复杂的运动, 球相互碰撞, 撞击瓶内和盖子, 并同时减少粉末更细的大小。向粉末中注入的动能等于轴承的平均速度 (19 米 s-1) 的平方乘以一半。铣削功率, e. g。每单位时间交付的能量, 增加以磨房的频率 (15-26 Hz)。在给定的20小时内, 采用典型的球数和最低频率, 撞击的总次数超过1.5 亿。在这些撞击过程中, 粉末经过反复的压裂和冷焊, 直到成分在原子级混合的地步。微观结构的这种混合和细化通过剪切带形式的局部形变和高密度的位错和点缺陷来促进, 从而破坏了显微组织。最终, 当碰撞的热度提高局部温度时, 这些缺陷的重组和湮灭就会与它们的世代保持稳定的状态。缺陷结构最终, 虽然重组, 导致更小和较小的高角等轴晶粒的形成。因此, 球磨是一个过程, 导致严重的塑性变形表现出的存在高密度的缺陷。这一过程允许增加溶质元素的扩散率和二次相的细化和分散以及显微组织的整体 nanostructuring。
高能 cryomilling 是一种类似于高能球铣削的铣削工艺, 但在铣削过程中, 铣瓶在低温温度下保持不变。为了在瓶中达到均匀的温度, 磨机被修改如下。铣瓶首先放在聚四氟乙烯套筒内, 然后用聚四氟乙烯帽密封。套筒连接到含有适当的制冷剂 (液态氮气 (in 2) 或液态氩 ()) 的杜瓦瓶, 通过不锈钢和塑料管材.制冷剂贯穿整个铣削过程中的套筒, 以冷却铣瓶, 并在制冷剂的沸腾温度下保持铣瓶, 如-196 °c 为in 2 和-186 °c 为。低温处理的低温导致更多的韧性金属碎裂, 否则在室温下无法研磨。此外, 低温温度降低了热活化的扩散过程, 如谷物的生长和相分离, 从而允许增加细化的显微组织和溶解度的不溶性元素物种。
高能卧式回转球磨机是一种高能量铣削系统, 由卧式不锈钢铣削罐组成, 具有高速转子, 并在传动轴上固定有多个刀片。将研磨的粉末与铣削球一起转移到罐内。球和粉末的运动是通过在罐子内的轴旋转来实现的。轴在高速旋转, 铣削钢球碰撞, 加速, 并将其动能转移到粉末上。rpm 的范围为 100-1000, 球的平均速度为14米-1。特别是, 磨房被装备到操作在一个范围的铣削温度 (-30 °c 到200°c 高) 并且可以在真空 (mTorr) 或在过压模式 (1500 乇) 下运行 (利用各种类型的覆盖气体)。除底座外, 该轧机还配有载气装置以及连接组件, 允许在惰性气体掩护下进行粉末的装卸。此设备可以在图 2A中看到, 以及典型的 8 L 钢铣削罐 (图 2B)。除了较大的轧机, ARL 已经购买了一个较小的轧机, 已转换为运行在液氮 (图 2C)。本厂可生产每运行周期100-400 克的加工粉。

<table border="0" cellpadding="0" cellspacing="0" width="1063">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Copper powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">42623</td>
			<td style="width:331px;">Spherical, -100+325 mesh, 99.9%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Tantalum powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">10345</td>
			<td>99.97%, -325 mesh</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Iron powder</td>
			<td style="width:243px;">Alfa Aesar&#160;</td>
			<td style="width:141px;">00170</td>
			<td>Spherical, &#60;10 micron, 99.9+%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Nickel powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">43214</td>
			<td>-325 mesh, 99.8%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Zirconium powder</td>
			<td style="width:243px;">American Elements</td>
			<td style="width:141px;">ZR-M-03-P</td>
			<td>99.90%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">SPEX mills (high energy shaker mills)</td>
			<td style="width:243px;">SPEX SamplePrep</td>
			<td style="width:141px;">8000M&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Zoz mills (high energy horizontal rotary ball mill)</td>
			<td style="width:243px;">Zoz GmbH</td>
			<td style="width:141px;">CM01 (small mill) CM08 (large mill)</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Focused Ion Beam</td>
			<td style="width:243px;">FEI&#160;</td>
			<td style="width:141px;">Nova600i Nanolab dual beam FIB/SEM</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Scanning Electron Microscope</td>
			<td style="width:243px;">FEI&#160;</td>
			<td style="width:141px;">Nova600i Nanolab dual beam FIB/SEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Precision Ion Polishing System</td>
			<td style="width:243px;">Gatan&#160;</td>
			<td style="width:141px;">Model 695</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Transmission Electron Microscope</td>
			<td style="width:243px;">JEOL&#160;</td>
			<td style="width:141px;">2100F&#160;</td>
			<td>multipurpose field emission TEM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Atom Probe Tomography</td>
			<td style="width:243px;">CAMECA</td>
			<td style="width:141px;">&#160;LEAP 5000XR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Equal Channel Angular Extrusion</td>
			<td style="width:243px;">ShearForm</td>
			<td style="width:141px;">custom built</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Hot Isostatic Press</td>
			<td style="width:243px;">Matsys</td>
			<td style="width:141px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

processing of bulk nanocrystalline metals at the us army research laboratory

考虑到它们与大粒度的对应物相比, 对性能的显著改善, 许多工作都致力于纳米晶金属的持续发展。尽管作出了这些努力, 这些材料从实验室工作台过渡到实际应用, 但由于无法生产出能保留所需纳米晶微结构的大型零件而受阻。美国陆军研究实验室 (ARL) 在开发了一种经证明能稳定纳米晶粒结构到温度接近特定金属熔点的方法后, 在发展这些材料-即生产适合在一系列相关测试环境中进行测试和评估的大型零件。本报告概述了在 ARL 处理、鉴定和巩固这些材料方面正在进行的努力。特别是, 重点放在用于生产纳米金属粉末的方法, 无论是小规模还是大规模数量, 都是目前研究工作的中心。

大约10克粉末每奔跑生产在高能振动筛磨房。在高能振动筛厂成功合成新型纳米晶金属和合金后, 在高能卧式回转球磨机上进行了放大。
通常, 纳米粉体是利用高能铣削工艺产生的, 其中少量粉末的晶粒尺寸细化, 每批约10克。这在一个小的概念证明范围内是令人满意的。然而, 有需要更大的铣削设备, 可以做相同的, 但生产更大?...

Watch this Scientific Journal Video about Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory at JoVE.com

Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

本文简要概述了陆军研究实验室在处理大块纳米晶金属方面正在进行的工作, 重点介绍了用于生产新型金属粉末的方法。

美国陆军研究实验室散装纳米晶金属的加工

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