金属的未来.docxVIP

The Future of Metals K. Lu 金属的未来 卢珂 On 15 December 2009, the worlds most fuel-efficient commercial jetliner—the Boeing 787 Dreamliner—completed its first flight. The airliner is mostly made from carbon fiber–reinforced polymeric composites (50% by weight, up from 12% in the Boeing 777) (1). Traditional metals are substantially replaced by composites with higher strength/weight ratios; aluminum usage has dropped to 20% (versus 50% in the 777). Ever since the 1950s, when “engineering materials” mainly meant metals (2), the share of metals in engineering materials has been diminishing. What are the reasons behind this trend, and which applications are likely to stay in the domain of metals? 2009年12月15日，世界上最省油的商业喷气客机-波音787梦想飞机，完成了首次飞行。客机主要由碳纤维强化高分子复合材料（占50％的重量，在波音777的12％）（1）。传统的金属基本上是由复合材料取代，具有较高的强度/重量比，铝的使用已下降至20％（相对于50％的777）。自从20世纪50年代，“工程材料”，主要的意思金属（2），金属在工程材料比重不断下降。这种趋势背后的原因是什么，以及哪些应用很可能会留在金属领域的呢？ The main property limitation of metals as structural materials is their low specific strength (the strength/weight ratio). Most engineering designs call for structural materials that have high strength, fracture toughness (a measure of the energy required for propagating cracks), and stiffness while minimizing weight. Most metals have high strength and stiffness, but because they are dense (steels are several times as dense as ceramics and polymers), their strength/weight and stiffness/weight ratios are low relative to competing materials (see the figure). This is a key reason for replacing metals in aircraft and sporting goods, where weight is a primary concern. Some metals such as aluminum and magnesium are light, but they are too soft for many applications and have low toughness and stiffness. Titanium alloys partly overcome these problems: They are about half as dense as steels, have higher strength, and are very tough. Titanium was first used in airliners in the 1960s in the Boeing 707 and its use has increased to 15% in the Boeing 787 (1). 作为结构材料的金属的主要属性的限制是其低的比强度（强度