the scanning proton microprobe, which has been developed and is being marketed by this laboratory. It is essentially a charged particle accelerator capable of detecting all elements, with low background and high sensitivity. It records all events in time sequence and is capable of real time monitoring and data analysis. It performs total quantitative scanning analysis (TQSA), a concept promoted by the center. In a later model the system has the capabilities of auto-monitoring, and channeling contrast microscopy. The resolution is in the range of 1 to 2μm with up to 8 MeV protons or 2 MeV He*. At this university I also had the opportunity to meet Professor Williams, who is engaged in research in the area of process metallurgy, which included the study of the kinetics of metallurgical processes and slag chemistry.

Swinburne Institute of Technology is another teaching organization of note. In addition to preparing students for the degree courses in engineering and computer science, this institute has a

CONCLUSIONS

1. The Asia-Pacific Workshop on

Center for Computer Integrated Manufacture. There are almost 2,300 PCs in the institute, and every student is provided one so that each student is computer literate. The objective of the center is to develop a flexible manufacturing system (FMS) that can operate at multiple levels of control and to develop dynamic simulation software that is networked to the cell and is capable of extrapolating system state as well as simulating FMS control algo- 2. rithms. Another objective of the center is to develop expert systems that would improve the quality of machined components through selection of tooling and cutting parameters and would link to a machining cell and track component accuracy, providing advice on possible causes of out-of-tolerance errors. The institute also has research programs involving robotic assembly of lock mechanisms, robotic polishing of door furniture, thin film coatings of cold/warm/hot forging dies, just-in-time (JIT) forward scheduling in a network manufacturing resource planning (MRP) system, etc.

Intelligent Materials Systems and Structures was very successful and productive. It is expected to generate not only new research opportunities in Australia but also close interactions between Australian scientists and U.S. DOD laboratories.

The quality of materials science research in the laboratories visited is very good, particularly in the areas of thin film technology and fine ceramics. Australian researchers are eager to work closely with U.S. scientists.

Iqbal Ahmad is the director of the Army Research Office (ARO) Far East. He has a Ph.D. degree in physical chemistry from Imperial College, London, and is a Fellow of the Royal Society of Chemistry, London. Prior to his present position, Dr. Ahmad was a program manager in the area of materials science at ARO, Research Triangle Park, North Carolina.

• Functionally Gradient Materials

• Composite Materials

The Ti-Al System

Intermetallic compounds within the Ti-Al system, namely TiAl, Ti,Al, and

In the following sections of this paper these topics will be discussed to identify some of the important research and the investigators in these areas.

INTERMETALLIC COMPOUNDS

An excellent overview of high temperature intermetallics in Japan has recently been prepared by Yamaguchi (Ref 1). There is a very substantial research effort on intermetallics in Japan. Since 1981, the Ministry of International Trade and Industry (MITI) has had a research program on "Basic Technologies for Future Industries." This program is focussed on the following four broad areas: New Materials, Biotechnology, New Electronic Devices, and Superconductivity. There are nine projects in the New Materials area. One of these projects is "High Performance Materials for Severe Environments." The objective of this project is to develop new structural materials for use in severe environments, such as those encountered in various aerospace vehicles, and in different energy generating operations. This effort is to continue for at least 5 more years. Intermetallic compounds are being investigated under the High Performance Materials for Severe Environments project. Research programs are in progress at some national laboratories, universities, and industrial laboratories. Currently, fundamental data are being generated for alloy design, and various fabrication processes are being examined, including melting and casting, rolling and forging, as well as powder metallurgical methods.

number of investigators. The overview paper by Yamaguchi (Ref 1) is an excellent source for summaries on relevant research as well as for identifying the important researchers in Japan. In addition to Yamaguchi at Kyoto University, Umakoshi at Osaka University, Hirano at NRIM Tsukuba Laboratory, and Tsujimoto at NRIM Tokyo Laboratory are performing very impressive research on TiAl intermetallic compounds. Some of the projects in Tsujimoto's group at NRIM include:

Environmental Effects on Mechanical Properties of TiAl Base Alloys

• Effect of Impurities Such as Oxygen on the Microstructure of TiAl Base Alloys

• Effect of Alloying Elements on Mechanical Properties of TiAl Base Alloys

• High Temperature Oxidation of TiAl Base Alloys

• The Relationship Between Microstructure and Ductility of TiAl Binary Alloys

• Coatings for Protecting TiAl

As discussed by Yamaguchi (Ref1), much of the work on TiAl is focussed on compositions on the titanium rich side of stoichiometry. Cast alloys of such compositions usually contain randomly oriented grains having a lamellar structure composed of TiAl and Ti,Al. When cast ingots are remelted and unidirectionally solidified by using the floating zone technique, a single lamellar grain can be formed. The

The TiAl phase contains a large number of twins parallel to the lamellar boundaries. A number of investigators are studying such polysynthetic twinned structures (Ref 2 and 3). The yield stress of this material is dependent on the orientation between the lamellae and the loading axis since two deformation mechanisms are operative. There is easy shear deformation parallel to the lamellae boundaries and hard shear deformation across such boundaries (Ref 2). Umakoshi (Ref 4) has shown that the spacing of the lamellae can be changed by controlling the crystal growth rate and by controlling the aluminum content. A linear relationship exists between the yield stress and the reciprocal of the square root of the lamellar spacing. When the tensile axis is at 90° to the lamellar boundaries, room temperature yield strengths of about 1,400 MPa with approximately 12% elongation are observed. Work is now being directed at improving the ductility more. By utilizing the easy mode of deformation, polysynthetically twinned TiAl crystals have been rolled to 50% reduction at room temperature (Ref 5). This work also includes examining the effects of alloying using elements such as Mn and Cr (Ref 6 and 7).

Aluminum rich TiAl is also being studied, but ductility cannot be improved by attempting to control microstructure (Ref 1), and there has been little improvement in its poor ductility. The compound TiAl, is being studied by Yamaguchi (Ref 1,3,8), by Umakoshi (Ref 8), and others (Ref 9). This com

temperatures. Attempts to improve ductility consist of the use of alloying elements to enhance the two major deformation modes (Ref 3) and to attempt to change the tetragonal DO2 structure into a more symmetric cubic Ll structure (Ref 9).

pound has very limited solubility, and polycrystalline specimens usually contain a small amount of a dispersed second phase, often aluminum, which decreases the yield stress and increases the ductility. Single crystals, prepared by the floating zone method, have been used to study the mechanical properties of TiAl,. The stress-strain behavior of TiAl, Ni,Al and the yield stress depend upon crystal orientation. In Figure 1 some examples of stress-strain curves for single crystals of TiAl, generated by compression loading at temperatures in the range of 25 to 900 °C are presented (Ref 8). Such results are consistent with the fact that the major mode of deformation in TiAl, is ordered twinning, which is augmented by slip at high 500

22

As indicated by Yamaguchi (Ref 1), research activity on Ni,Al is declining. Review

papers are available that describe recent progress on the anomalous strengthening and high temperature deformation of Ni,Al (Ref 10 and 11). Some valuable results have been recently obtained by Hirano of NRIM Tsukuba Laboratory using

[001] R.T.

200

[011] 895°C

Figure 1. Compression stress-strain curves for single crystals of TiAl..
Reprinted with permission, Figure 6 from an article titled
"Deformation Behavior of Single and Polycrystalline Al Ti and
Al Ti with Ternary Alloying Additions," by M. Yamaguchi,
Y. Shirai, and Y. Umakoshi, published in Dispersion
Strengthened Aluminum Alloys, edited by Y.W. Kim and
W.M. Griffith, The Metalllurgical Society, 420 Commonwealth
Drive, Warrendale, PA, 1988, pp 721-740.

unidirectionally solidified specimens prepared by the floating zone method (Ref 12-14). Since the floating zone method is used to prepare specimens of a wide variety of intermetallic compounds, a sketch of this apparatus is presented in Figure 2 (Ref 15). The raw material rod is usually prepared by arc melting and drop casting into a copper mold. Use of the floating zone method permits the growth rate to be controlled. Seed crystals are used to grow single crystals and typical growth rates are 2 to 24 mm/h. Hirano has shown that stoichiometric Ni,Al, with no alloying elements, when grown unidirectionally has high ductilities. Typical results obtained at room temperature are presented in Table 1 (Ref 14). Since specimens exhibited ductility even when the tensile axis was normal to the grain boundaries, he proposes that the grain boundaries are intrinsically resistant to cracking. The floating zone-unidirectionally solidified technique appears to be an attractive method for improving the ductility of Ni,Al without using alloying additions.

MoSi

Umakoshi and Hirano are studying the mechanical properties of MoSi2 crystals prepared by the floating zone technique (Ref 16-21). Crystals of MoSi are brittle at low temperatures but can be deformed above about 900 °C (Ref 18 and 21). At approximately 900 °C, slip occurred on both (110) and (103) planes, but in the case of slip on (103) planes it was limited to orientations near the <001> direction. Some results are presented in Figure 3, where it is evident that the yield stress is dependent upon temperature and slip system. The yield stress decreases and ductility increases above 1,200 °C. The addition of chromium to MoSi, was observed not to significantly affect the yield stress for (110) slip; however, a substantial increase was observed for (103) slip (Figure 3). This latter effect was