Materials Science and Technology
　Current research and development in Materials Science and Technology is mainly concerned with materials design and the evaluation of materials which are:
1) durable and reliable, maintaining useful properties in hostile environments, and
2) compatible with natural ecological systems.

　Some current research topics are described in more detail below.

　 Materials Properties
　Work on materials properties is focused on damage mechanics and mechanisms in advanced structural materials such as composites, engineering ceramics, and functionally gradient materials.

　 　Fracture mechanics and electron micro-fractography have been used to investigate fatigue crack growth resistance in alumina matrix composites with SiC whiskers. New ideas about the toughening of ceramics by incorporating a ductile metal phase have been developed and used to improve fracture toughness. These ideas have been successfully applied to both functionally gradient materials and titanium aluminide. [3,4,5,8,14]

　 　The mechanical reliability of structural materials such as austenite stainless steel has been tested at cryogenic temperatures (4.2K) and high magnetic fields (up to 6T).

　 　Non-destructive tests using a SQUID and a Magnetic Force Microscope have also been made to qualitatively evaluate fatigue damage and defects.

　 Fig.1 Improvement of fracture toughness for titanium aluminide by high melting point ductile metallic fibers.

　 　Work has been done on computer simulation techniques to predict materials behavior at the atomic level, together with advanced research on smart structures and information theory in order to ultimately incorporate decision making and learning properties into materials and structural systems.

　 Materials Design
　Research has also been done on the design and Improvement of the microstructure and properties of new metallic materials such as intermetallic compounds, titanium alloys for biomechanical applications, superplastic single-phase stainless steels, nickel-base superalloys, and nanostructured alloys.[7,17,24] For example, work was done on the rheorefining of Al-Sn and Al-Ni alloys, in order to develop methods for efficiently producing high purity metallic materials.[7] In one experiment, an alloy ingot with initial composition Al-50%Sn was reheorefined by pressurizing the ingot for 72ks at a plunger speed of 2.8E-04mm/s, and the result was a material with 98%Al and less than 0.01%Sn. This experiment clearly showed that large amounts of tin could be removed from the ingot, although a small amount of eutectic was formed by a chemical reaction involving the steel filter. Al-Ni ingots with initial composition Al-2%Ni, Al-1%Ni, Al-0.5% Ni, and Al-0.2%Ni were also rheorefined under the same conditions, and it was found that the nickel was effectively removed. Fig. 2 gives results which show that when Al-0.5%Ni ingots are refined under isothermal conditions the amount of exuded filtrate increases and the nickel content decreases with increasing refining temperature.

　 Fig.2 Relation among the rheorefining temperature, the exuded filtrate in mass and the nickel content of the filtrate after the rheorefining of an initial composition Al-0.5%Ni alloy ingot.

　 It was found that slow rheorefining (72ks at a plunger speed of 2.8E-04mm/s) is superior to fast rheorefining (7.2ks at a plunger speed of 2.8E-03mm/s) for removal of impurities from Al-Sn ingots. We also found that if single phase stainless steel (AISI304) was recrystallised, the elongation to failure became greater than 300% and superplasticity was exhibited.[24]

　 Tribology
Tribology research at MEL has concentrated on the study of physico-chemical phenomena at sliding surfaces and the development of tribomaterials which are useful in various different environments.

　 Triboelectromagnetism (which includes tribo-charging, tribo-microplasma formation, and the triboemission of electrons, ions, and photons) has been studied in a tribosystem which simulates the contact area between the head and disk in a computer disk drive. Intense tribomagnetism, which had been predicted at the head/disk interface, was observed in the system.[11,15,25]

　 An EHL film tester and a friction and wear testing chamber have been developed for studying tribology problems associated with the use of environmentally-friendly refrigerants such as HFC134a. The effect of refrigerants on the physical properties of lubricants operating both normally and in the mixed lubrication regime have been investigated.[1,2]

　 Self lubricating composites which can be used over a wide temperature range from room temperature up to 1000
℃ have been developed. It was found that composites including Barium Chromates (BaCrO4, BaCr2O4) and Aluminum Oxide (Al2O3) have better friction and wear properties than general ceramics, particularly at high temperatures.

　 Fig.3 Friction and wear of DLC films sliding against SiC ball in both dry and highly humid airs.

　 The tribology of diamond-like carbon (DLC) films has been investigated. DLC films have both low friction coefficients (about 0.06) and very low wear rates (about 1.0E-08mm3/Nm) in dry air. It was found, however, that the friction and wear rates are strongly dependent on atmosphere.[9,10,18]

　 Laser-assisted plasma spraying and laser assisted gas deposition techniques are under development for synthesising high performance tribo-materials, high temperature multi-functional coatings, and novel allotrope films.[16,22] A novel photon technology for the preparation of well-controlled ultra-fine particles using a high energy-density laser is also under development. Technology is also required to assemble the particles into new micro-scopic structures which have useful optical and electrical properties. An advanced spectroscopic analysis and monitoring technique was studied for measuring the states of the plasma field. [23]

　 　A project to detect the transient electric currents associated with crustal failure (towards prediction of earthquakes) is currently in progress. Geo-currents are detected at multiple sites and several abnormal signals which may be related to recent earthquakes have been detected. In addition to field experiments, laboratory work on the fracturing and friction phenomena associated with rocks under extreme conditions is also under way. [21]

　 Fig.4 Observation sites where candidate seismic precursor signals appeared simultaneously on Sept. 5-6　1996 (solid symbols) by means of a pulse like geelectric current detection system (insert).

---

produced by General Research Counselor