Advanced materials can provide specialized properties, or combinations of properties, that cannot be obtained in conventional materials. However, advanced materials generally require unusual processing operations in order to achieve their unique microstructures and the resulting greatly improved properties. These materials also tend to be expensive because of the high value added by unusual processing operations that may be labor intensive. Because the relationships among the processing parameters, microstructure, and resulting material properties and performance are not fully understood, and because the microstructure is difficult to control, reproducibility in these materials is often unsatisfactory. A very promising direction toward overcoming these difficulties involves intelligent processing of materials, a computer-based approach to automatically controlling the evolution of microstructure during processing.

In a conventional automated materials processing system, automation involves utilizing sensors to monitor process variables such as temperature and pressure. Data from these sensors are compared with preset values automatically in order to maintain these values with control devices. Nevertheless, the microstructure and properties often experience significant variations. The variations are detected after the fact either by destructive analysis in a quality control laboratory or by nondestructive evaluation (NDE) at the end of the manufacturing process.

In contrast, an intelligent processing system utilizes a new class of NDE sensors to characterize the microstructure of the material in real time. Moreover, the real-time data plus data from conventional process variable sensors are transmitted to a computerized decision maker.

The preservation of U.S. aeronautical leadership is an economic and military necessity, but it is by no means assured. The rise of Airbus, Ariane, and Embraer has been lightning fast; tomorrow could see the development of Japan's FSC or Israel's Lavi. Our competitors are well organized and often enjoy the support of their governments. Our capabilities are no longer unique; thus our future work is clearly defined for us.

The key to continued U.S. preeminence in aerospace is to be found in the further research, development, and application of a group of revolutionary technologies in the areas of propulsion, numerical and symbolic computation, laminar flow modeling, and advanced materials and structures. Exploitation of the emerging technologies in these areas by industry, government, and universities will significantly impact the performance and cost of future aerospace vehicles and systems. Materials science and engineering, particularly the discipline of nondestructive evaluation, will play a major role in making such continued aerospace leadership a reality.

From the use of plastic and glass radomes in the first jet engine demonstrators to the composite parts of today's most advanced aircraft, the need to ensure reliable materials has always been critical. Advanced materials and structural concepts offer the opportunity for significant airframe improvements on all types of aircraft. Indeed tomorrow's aerospace structures, such as the National Aerospace Plane, the Space Station, as well as the ATF and SDI-related items will employ a myriad of exotic materials that must be extremely reliable and highly producible.

Thermal wave physics is playing an ever increasing role in the on-line characterization of semiconductor materials and devices. This is especially true for thermal wave methods that employ laser beams for both the generation and detection of thermal waves. For the modulated reflectance method discussed here, the pump and probe beams are focused on the same spot. They therefore achieve the noncontact advantage of optical methods in addition to the optimum condition for high spatial resolution, a necessary condition for thermal wave measurements on product wafers.

When a material is excited with an intensity-modulated laser beam or pump, a thermal wave is generated in the material and in the air above the sample. The material within this heated region will undergo a thermal expansion which can be detected with a probe beam interferometer or by deflecting the probe beam from the thermoelastic deformation of the surface. Since the complex refractive index of most materials depends on temperature, a modulated temperature will also induce a corresponding modulation in the refractive index and consequently a modulation on a probe beam passing anywhere near the thermal wave. A probe beam directed along the heated surface of the sample, for example, will be deflected as it passes through the heated region above the surface. This mirage effect can also be observed within the sample by directing a transmitting probe through the heated region beneath the surface. Likewise, using a probe beam directed onto the sample surface one can observe a modulation in reflection, transmission, or scattering. A related noncontact method is the photothermal measurement of infrared radiation emitted from the material's heated region. Note that with all these detection methods, thermal wave measurements can be, and most often are, done in air and at room temperature.

The high-temperature structural properties of ceramics make them unique candidates for application in such systems as advanced gas turbines and other heat engines. Of concern, however, is the variability in fast fracture strength of structural ceramics which is due, in part, to the sensitivity of ceramics to very small (e.g., 20–50 μm) critical flaws and the difficulty in detecting and characterizing this type of flaw by nondestructive examination (NDE) techniques.

The flaw sensitivity of ceramics and the typically wide variation in flaw sizes result in the situation illustrated in Figure 1, which is a frequency distribution of fast fracture strengths for a hypothetical structural ceramic with characteristic strength of 350 MPa and Weibull modulus of 5. The strength requirement, 250 MPa, for a particular application is shown. In this illustration, a significant fraction of the population of ceramic parts, 17%, has a strength below the 250 MPa requirement.

The situation illustrated in Figure 1 is typical of structural ceramics today: although in many cases the average properties of a specific ceramic may be suitable for the intended use, a significant fraction of the parts made of that material will be unsuitable. The unacceptable parts are, of course, very difficult to distinguish from the rest of the population.

There are now theories which predict the effect of texture on elastic properties and hence on the velocities of bulk, surface, and guided ultrasonic waves. Furthermore, there is a relation between texture and formability. These relationships can be potentially exploited to make ultrasonic measurements of formability, and partial pole figures can be made with ultrasonic techniques.

This article presents results of various ultrasonic measurements made to characterize the formability of rolled steel and aluminum alloy sheet. A good correlation generally exists between ultrasonic velocity measurements and formability. Furthermore, there is a good possibility of on-line formability measurement using a noncontacting ultrasonic transducer.

The influence of texture on material properties has been long recognized, and several excellent texts have been wholly or partly devoted to the subject. Texture classically has been measured with either x-rays or neutron diffraction. Lately, there has been interest in characterizing texture with ultrasound (high-frequency sound) as well.

Ultrasound has several potential advantages over x-ray and neutron diffraction techniques. Ultrasonic systems are nondestructive, can rapidly scan large volumes of material, require no radiation sources, and can be devised to measure either surface or bulk textures. There is a distinct possibility that ultrasonic texture monitoring can be implemented in real-time in a production environment such as a rolling mill.

As useful as classical x-ray diffraction techniques have been, the ability to obtain x-ray diffraction images with extremely short exposure rimes opens up new opportunities for materials scientists, including real-time materials process control. This article briefly describes state-of-the-art systems for obtaining extremely rapid and real-time x-ray diffraction images and gives several examples of their applications for materials process control.

Two generic electro-optical methods permit real-time viewing and recording of x-ray diffraction images. The first uses a low-intensity conventional x-ray tube source leading to a low-intensity diffraction image, which requires a high-gain electro-optical imaging system. The second uses either a high-intensity rotating anode, synchrotron, or flash x-ray source. Such a high-intensity source produces a high-intensity diffraction image, permitting use of a low-gain high-resolution electro-optical imaging system.

Figure 1 schematically shows two types of image intensifier tubes which have been most often used to view x-ray diffraction images. By cascading three individual first generation image tube stages (Figure 1a), light gains as high as several million can be obtained. The second generation microchannel-plate image intensifier tube (Figure 1b) is similar to a single-stage first generation device except for the extremely important addition of a microchannel plate.

In a number of materials processes, on-line monitoring of surface finish is important to control material quality or process integrity. In rolling some sheet steel into coils, the rollers are intentionally roughened so that a specified roughness range is transferred to the sheet. Then the end product sheet can be optimally spray painted. The rollers, however, eventually wear smooth. Currently, pieces of sheet are sampled by hand and if a piece is too smooth, the coils produced since the last good sample are problematical. In automated machining it is useful to know during the cutting process whether the part will have the required surface finish. More importantly, for a large class of automated machining applications, a dull tool can be defined as one which produces a rougher part surface.

Monitoring the finish of the newly cut surface could allow a decision to be made about changing the tool. For untended machining this could provide a strategy for tool management. The strategy would be much more efficient than the alternative of changing a tool after X hours when it might have lasted 10X hours were it in the upper 10% of the life curve.

To fulfill the need for noncontact surface finish measurement, optical scattering devices have been developed to provide a surface interrogation technique. However, this technique is significantly limited for many applications because the optical beam must interact with a dry surface. This makes its application very difficult in the harsh wet environment encountered in automated machining and in some metal sheet production.