Since man discovered how to harden steel, the modification of the molecular structure of materials has had an impact on military effectiveness. Today, the nature of materials affects the lethality of weapons, the survivability of troops, the performance of aircraft, the costs of production of new systems and every aspect of every component of defence equipment. The scandal of the aircraft coffee-maker which was designed to withstand much greater 'g' forces than the aircraft which carried it is an indication of the pervasiveness of materials technology in every aspect of military hardware.

In the search for ever greater effectiveness from weapons, the designer can look for new materials which offer benefits over the old in capability, ease of manufacture, or lower cost. New materials may offer weapon designs that were previously impossible. The use of carbon-fibre in aircraft to provide greater strength for less weight than conventional materials is now widely used. However, there are penalties. The increased strength-to-weight ratio is bought at the price of greater manufacturing difficulties, and thus increased costs. The trade-off in capability against cost is relatively easy to make in the case of aircraft and missiles, where extra mass requires extra power and restricts manoeuvre. In slower surface vehicles, the pay-off may not be so clear. In this field, the more productive area for research may be in making manufacturing processes easier and cheaper, and in using materials which are more readily repairable under combat conditions. In this chapter, we examine those aspects of materials science which may help military effectiveness.

Materials are everywhere. Without them, armies would fight naked with bare knuckles. In the past, trial and error sorted out the militarily useful materials from those of less merit. Some processes, such as the refining of metals, hardening, the making of alloys and the manufacturing developments of the industrial revolution brought great improvements to weapons. Indeed the mechanisation of the battlefield was a product of the new material processes of the nineteenth century. However, it is only in this century that the nature of matter has become understood in sufficient detail to tailor materials to specific requirements. Glass and ceramics, once synonymous with fragility, can today be stronger than steel. Strength, weight, electrical properties, melting points, and all other characteristics are now designed, and this technological facility has great implications for future military equipment.

Every company depends on a range of materials for its economic and security well-being. The oil crisis of 1973 was seen at the time as showing the dependence of the industrialised nations on oil supplies. The resolve shown in countering the Iraq invasion of Kuwait suggests that States continue to take a keen interest in the availability of their oil supplies. There are other less obvious key substances: chromium, manganese, cobalt and platinum. In some areas fresh water takes on the characteristics of a strategic material. While other commodities may be vital, sources of supply are either so numerous or so secure that they do not worry governments. A time may come when quite common materials become scarce either through natural exhaustion of supplies or political changes in supplier countries. In any event, population increases and growth in economies will lead to greater demand for key minerals. For the crucial commodities, nations may form strategic stockpiles to help them weather particular difficulties. After the 1973 oil embargo, the United States established a strategic petroleum reserve of some 590 million barrels. The reserve costs $200 million per year to maintain.(1)

A safer solution to the dependence on others for strategic commodities is to develop alternative materials. The impetus for such research is economic and commercial as much as a security issue. Civil manufacturers do not wish their products to depend on unreliable sources of raw materials, especially if finite resources lead to increasing costs. In some cases, it is possible to develop processes which use smaller quantities of the key material per unit of production. Indeed the total material required may also be reduced. The weight of the modern motor car has been reduced significantly by the production of high-strength low-alloy steels. Certain parts are now formed from polymer materials which have high strength: plastic bumpers for example. The commercial factors at work will be a financial assessment of performance, material costs and manufacturing costs. The relative importance of these factors may be different for the military. Nevertheless, commercial interests will lead the development of new materials which can have military uses.

A good example of the application of materials science is in the manufacture of combat aircraft. A modern high performance aircraft is subject to extreme stresses. Airframe temperatures may vary from -55C at altitude to supersonic skin temperatures of 500C. Engine components will operate at temperatures over 1000C. Ambient pressures vary from atmospheric to near vacuum, while hydraulic pipes and engine casings will operate at much higher pressures. Manoeuvring may increase component weight by a factor of 10, and such 'g' forces may be applied in very short periods. Engine components also suffer from extreme mechanical loadings, corrosive hot gases and high vibration levels. Modern and future combat aircraft design is crucially dependent on new materials. (2)

While research must produce materials which can operate under such extreme conditions, the most crucial consideration for aircraft is the question of weight. For a commercial airliner, a reduction in weight reduces operating costs and increase carrying capacity for a given distance. For military aircraft, a reduction in weight also brings great benefits. For a given design, a lighter aircraft can carry more weapons, go further and carry more fuel. With the same engine performance and payload, a lighter aircraft can accelerate faster, climb to operating altitude more quickly, and be better at evading or pursuing. Lighter materials may allow a different design to give a smaller aircraft for a given capability. This can reduce the radar cross-section and improve survivability. It could use surplus carrying capability for self protection systems; it could be more manoeuvrable. All these options improve survivability.

The aerospace industry has been at the forefront of the new materials research and development. Advances have been made in the synthesising of new materials and also in the development of composite materials. The products can be designed not just to have great strength but also to grow stronger a temperature increases. (3) Nickel-based superalloys are strongest at about 850C, and retain strength to around 1000C. This means that they can be used in jet engine turbine blade manufacture. Cobalt-based alloys have higher temperature characteristics, but lower overall strength. Where weight is the most critical factor, titanium alloys offer an answer.

Strength can be provided not only by the composition of these alloys, but also by adjusting the crystalline structure of the substance to tailor strength to the role of the particular component. A turbine blade can be given greater strength along its axis of greatest strain through the process of directional solidification. In this process, the crystals in the alloy are grown in columns by selective heating and cooling. The metal is constructed with unique characteristics for the component. Another advance has been in the process of rapid-solidification technology. Just as the blacksmith would temper his red hot metal by plunging it into cold water, today's materials engineer adjusts an alloy's characteristics by rapid cooling. At cooling rates in excess of one million degrees per second, it is possible to produce predictable microstructure in alloys. Such techniques are able to produce aluminium alloys with strength/weight ratios better than titanium. One of the rapid cooling processes uses high powered lasers passing over the metal's surface. Using pre-alloyed powder, this laser-glazing process can construct complex shapes with great strength and temperature resistance.

While advanced metals are produced by adjusting alloy mixes and tailoring processing to obtain the required characteristics, composite materials are artificial constructions designed to produce materials with the desired qualities. An early composite was fibreglass-reinforced plastic. This now familiar car body repair material uses the very high tensile strength of spun glass fibres reinforced in a matrix of plastic bonding substance. The composite material has properties of strength and flexibility unknown in its components. The strength and stiffness of the composite is determined by the reinforcing material. Single fibres or whiskers of substances such as glass, silicon carbide and aluminium oxide show greater strength than large pieces because, at the size of single crystals, they have fewer flaws. By bundling the fibres together, like bamboo canes, they add their strength together. If one strand breaks, the others take the load. The matrix material holds the bundles of fibres in the desired configuration. While fibreglass consisted of short fibres embedded in polyester, the advanced composites are arranged in a rigid polymer structure which gives much greater strength. Resins which can survive temperatures in excess of 300C have now been developed. At the highest temperatures, ceramic matrix materials offer great promise. Borosilicate glass reinforced with silicon carbide fibres retains its strength at 1000C, with more exotic mixes operating up to 1700C.(4) Manufacture is difficult because the ceramic materials are themselves heat resistant. For even higher temperatures, the use of carbon-carbon composite material is possible. Here graphite crystals form the fibres, with amorphous carbon as the matrix. The advanced composites allow considerable reduction in weight, better stiffness, improved fatigue characteristics, greater fracture resistance and good thermal shock tolerance.

These new materials have applications in many fields outside of aerospace. However the demands of the aircraft and space system manufacturers will drive the research. New materials are not just offering better replacements of traditional substances. In some areas the new materials offer the prospect of new capabilities. The transmission and processing of information has depended on electrical transmission through conductors such as copper. New materials are changing this dependence on the electrical conductivity of copper. Superconducting materials allow electrical transmission without loss. Information may be transmitted by photons rather than electrons using fibre optics.

Superconductivity is the absence of all electrical resistance in a substance. Over 80 years ago, it was demonstrated to occur in mercury when it was cooled to temperatures close to absolute zero. As such, it was an interesting laboratory phenomenon. The energy required to cool the material exceeded any energy savings gained from lossless transmission. Gradually researchers have developed materials which exhibit superconductivity at ever higher temperatures. In 1987, researchers at the University of Houston developed a compound of yttrium, barium and copper oxide (YBCO) that superconducts at 90C above absolute zero. This is a temperature that can be achieved at very low cost, as liquid nitrogen is industrially produced and boils at 77 C above absolute zero. There were two problems with YBCO: it was a difficult material to work with as it was ceramic rather metallic; and it was unable to cope with external magnetic fields. Moving from wires to thin films has overcome these problems. Thin films of YBCO can conduct five million amperes of current per square centimetre at the temperature of liquid nitrogen. High-power permanent electro-magnets, new forms of computer memory, lossless power transmission and low level magnetic detection all become possible. The research into relatively high temperature superconductivity will continue because of the potential commercial benefits, but there are also possible military applications. Superconducting computer components will offer increases in speed and power. Superconducting electric motors may offer both transport and weapon projectile applications. Sensors for magnetic anomalies and for electromagnetic radiation can be orders of magnitude more sensitive, with implications for reconnaissance systems. Devices using superconducting materials are now arriving in the military signal processing field. A new sonar device covering a previously inaccessible frequency range was developed in 1993 using superconducting coils. Research continues on higher temperature superconducting materials in the hope that a room temperature material will prove possible. At the time of writing, the record is held by a mercury, barium, calcium, copper oxide substance which superconducts at a temperature of -109C, which is a temperature obtainable with current air conditioning technology.

For the processing of information, the advent of glass fibre has made the use of photons feasible. Lasers can produce discrete pulses of light which are conducted in an analogous manner to electrical signals. The very high frequencies associated with light make the information-carrying capacity of a fibre optic system between ten and one hundred times greater than that of copper wire. From a military aspect, fibre optic not only offers greater data bandwidth but also greater security from jamming and interception. The widespread replacement of copper wire based communication lines in the developed world by fibre optic cable is only the first stage of the upgrading of world communications. Above a transmission speed of about 50 gigabits per second, problems arise from the interface between the optical and the electronic parts of any network. Research is now focused on replacing the electronic amplifiers with optronic methods. Optronic amplifiers with optical multiplexing systems offer the prospect of 25 terabit per second per fibre bandwidth. Commercial pressures will ensure that development work in this important area continues, and bandwidth in communication should not be a problem in the future.

In the field of electronics, considered in more detail in chapter 12, materials technology also has much to offer. Semiconductors have led from the transistor to the integrated circuit with ever higher component density. Today. chips containing tens of millions of transistors are manufactured. Using silicon, the limit of component density is fast being reached. To achieve faster processing, it will be necessary to move to new materials, such as gallium arsenide, and new material structures of a three-dimensional arrangement. At this stage the work on optronic systems may come together with the integrated circuit development to produce photonic integrated circuits, which use photonic switches instead of transistor elements. Prototypes are already available. The increasing use of glass fibre based networks will ensure that research in this area has a commercial incentive. It is likely that the development of photonic switches controlled by photonic signals will lead to the development of very high speed, high capacity information-processing systems.

All the materials considered so far have been produced by processes which have been evolutionary from the blacksmith tempering the steel for a sword. Manufacturing processes have been discovered which can reliably reproduce desired material characteristics in large scale production. We are now on the verge of a revolutionary change in our approach to materials. It was suggested by the physicist Richard Feynman in 1959 that there were no laws of physics which precluded the moving of material atom by atom. The idea that materials can be assembled atom by atom offers a virtually infinite prospect of novel substances. The term Nanotechnology has been used to cover the technologies associated with manufacturing processes at the sub-micron level. However, the revolutionary materials will be produced from nanotechnology at the molecular level. The positioning of individual Xenon atoms in a single crystal nickel surface, using a Scanning Tunnelling Microscope (STM),has already been demonstrated.. The STM is a needle shaped probe which has a tip of a single atom. A current tunnels from the tip to a conductive surface to move small groups of atoms. Research is directed in a number of areas. Smaller and smaller machines are being designed. Just as the integrated circuit has led to a doubling of transistor density each 18 months, there is a parallel trend in microelectromechanical systems (MEMS). These MEMS are produced by similar photolithographic processes to integrated circuits. In 1995, it was reported that this technology had been used to produce four micromotors to move an STM. These tiny engines can push or pull the atomic tip of the STM at speeds as high as a million times per second. (7). If such a system, with an array of STMs, were used as a form of data storage, then the contents of 500 Encyclopaedia Britannica's would fit on a one square centimetre chip.

If it proves possible to produce materials which contain microscopic machines, which can manipulate the structure at the molecular level, the world will become a very different place. Self assembling machines become possible; materials will repair themselves; they will adapt their properties intelligently to the requirements of their environment; they could be self replicating. Since the properties of the material could be designed in at the research stage, and the manufacturing cost would be much reduced, and the product would not wear out in the normal sense; these new materials would revolutionise the economy. It is likely therefore that commercial interest will continue to sponsor research in the field of nanotechnology. There will also be very significant military implications for the use of such materials, and it is an area of study which may repay investment in the medium term.

Looking to the military implications of the many new areas for materials technology, it is clear that developments will profoundly affect operational capabilities. In the construction of weapon platforms, new materials will allow aircraft to fly further and faster, tanks to survive better, warships to stay at sea longer and submarines to range further while hidden. Reducing size for a given performance will reduce detectability, and materials which absorb rather than reflect radar can be built into the design. Jet engines will be able to operate at higher internal temperatures for greater efficiency. Communications will be more assured, and information density greater. Greater computing power will be available in smaller weapons. New sensors will make detection of the enemy easier by day and by night.

At the same time, some of these materials are more difficult to manufacture, and may require individual design for each component> This can make them difficult to repair and expensive to replace. In any new design , it will be necessary to consider the costs as well as the benefits. Battle damage repair may be much simpler in traditional materials. Indeed, new materials are designed for the forecasts stresses; but unpredictable battle conditions may test beyond specification. The tale is told of the corrosion proof fibreglass car which turns to powder on crash impact. Weapons must be robust as well as efficient.

In space, the new materials will assume yet greater importance, given the need to reduce weight wherever possible. The reductions in weight, increase in strength and increase in engine performance may begin to blur the distinction between operations in air and in space.

Notes to Chapter 10

1. For a discussion on the merits of a strategic oil reserve see 'Buy High, Sell Low' in Scientific American December 1995 p18.

2. 'Materials in Aerospace' by M.A.Steinberg in Scientific American October 1986 pp59-64.

3.For a detailed explanation of processing techniques see 'Advanced metals' by B.H.Kear in Scientific American, October 1986 pp 137-45.

4. 'Composites' by T-W Chou, R.L.MCCullough & R.B.Pipes, in Scientific American October 1986 p 170.

5. 'High-Temperature Superconductors' by P.C.W.Chu in Scientific American September 1995 pp 128-131.

6. "All-Optical Networks' by V.W.S.Chan in Scientific American September 1995 pp 56-59

7. 'Engineering Microscopic Machines' by K.J.Gabriel in Scientific American September 1995 pp 118-121.

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