We report the development of a method for quantitative, in situ nanoindentation in an electron microscope and its application to study the onset of deformation during the nanoindentation of aluminum films. The load-displacement curve developed during in situ nanoindentation shows the characteristic "staircase" instability at the onset of plastic deformation. The instability corresponds to the first appearance of dislocations in previously defect-free grains, and occurs at a force near that measured in conventional nanoindentation experiments on similarly oriented Al grains. Plastic deformation proceeds through the formation and propagation of prismatic loops punched into the material, and half-loops that emanate from the sample surface. This new experimental technique permits the direct observation of the microstructural mechanisms that operate at the onset of deformation.In nanoindentation a material surface is indented with a small diamond pyramid that has a tip radius in the range 50-400 nm. This method of hardness testing has become an important tool for both scientific research and materials characterization. Since nanoindentation measures the mechanical properties of volumes so small that they can be made defect-free, it probes the fundamental processes that initiate deformation. More practically, it measures the mechanical behavior of small systems, including thin films and microelectromechanical devices (MEMS).The interpretation of nanoindentation data is not always clear. For example, since most metals form native oxides, yielding under the nanoindenter may be governed by fracture of the oxide film rather than the onset of plastic deformation in the material itself. It is difficult to resolve such issues when the microstructure of the material can only be studied after the fact. However, the recent development of a unique in situ stage for transmission electron microscopy (TEM) has made it possible to image nanoindentation in real time. 4The force-displacement relation can be measured simultaneously with a calibrated piezo-ceramic control element. Initial applications of these new tools are described below. Minor, Stach and Morris: Quantitative in situ nano-indentation page 2During in situ nanoindentation, as we practice it, a 3-sided boron-doped diamond indenter approaches the sample in a direction normal to the electron beam (Fig. 1). The sample is a thin film deposited onto a silicon substrate that includes a narrow wedge. The indentation is made in the cap of film on the flat top of the wedge. In order to be transparent to a 200 kV electron beam, the cap width must be less than about 500 nm.The indenter is mounted on a piezo-ceramic actuator, which both controls its position and forces it into the edge of the sample. The piezo-ceramic actuator is also used to measure the force developed as a function of displacement during the test. It must be calibrated in order to do this. The force is determined by the combination of voltage and displacement, and the relation between them must be measured. In the...

Micro/nanomechanical and tribological characterization of SiC has been carried out. For comparison, measurements on SiC, CoCrMo, Ti-6Al-4V, and stainless steel have also been made. Hardness and elastic modulus of these materials were measured by nanoindentation using a nanoindenter. The nanoindentation impressions were imaged using an atomic force microscope (AFM). Scratch, friction, and wear properties were measured using an accelerated microtribometer. Scratch and wear damages were studied using a scanning electron microscope (SEM). It is found that SiC exhibits higher hardness, elastic modulus, scratch resistance as well as lower friction with fewer and smaller debris particles compared to other materials. These results show that SiC possesses superior mechanical and tribological properties that make it an ideal material for use in orthopedic and other biomedical applications.

DISCLAIMERThis document was prepared as an account of work sponsored by the United States Government. Neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any ir_ormation, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, _ademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opi_ons of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California and shall not be used for advertising or produc: endorsement purposes. J 'Lawrence Berkeley Laboratory is an equal opportunity employer. LBL--31203 DE92 002263Grain Growth in AI-2% Cu Thin Films ABSTRACTThe grain size and grain growth kinetics in sputter deposited AI-2% Cu films on silicon substrates were determined by TEM for various film thicknesses and anneal times, temperatures and methods. Grain sizes were found to be typically lognomaally distributed. The as-deposited grain size (do) dependence on film thickness (TIl) was found to be do = C TH1/2, due to competitive grain growth during film formation. Annealed grain size (d) after Rapid Thermal Annealing (RTA) for time (t) at temperature (T) is described by the general equation d -do = C TH 0.7 {t exp (-AEa/kT) }1/8,where ZkEa= 0.85 ev for 0.4 I.tm films and AEa = 1.1 ev for 0.8 I.tm films. Grain growth is largely saturated for these anneals. Grain growth is shown to be more extensive during RTA anneals than furnace annealing and more extensive in 0.4 l.tm films than 0.8 I.tm films for equivalent RTA cycles. The results are discussed in terms of models, simulations and previous results of grain growth in thin metal films.

A unique in situ nanoindentation stage has been built and developed at the National Center for Electron Microscopy in Berkeley, CA. By using piezoceramic actuators to finely position a 3-sided, boron-doped diamond indenter, we are able to image in real time the nanoindentation induced deformation of thin films. Recent work has included the force-calibration of the indenter, using silicon cantilevers to establish a relationship between the voltage applied to the piezoactuators, the displacement of the diamond tip, and the force generated.In this work, we present real time, in situ TEM observations of the plastic deformation of Al thin films grown on top of lithographically-prepared silicon substrates. The in situ nanoindentations require a unique sample geometry (see Figure 1) in which the indenter approaches the specimen normal to the electron beam. in order to meet this requirement, special wedge-shaped silicon samples were designed and microfabricated so that the tip of the wedge is sharp enough to be electron transparent.

SUMMARYThe Al5 layer of a commercial Airco wire containing 2869 Nb filaments was analyzed as a function of heat treatment. Its microstructure is composed of three morphologically distinct concentric shells. The central shell consists of fine equiaxed grains and has a nearly stoichiometric Sn concentration. High resolution electron microscopic analysis suggests that the fine grains are formed through the polygonization of dislocations. The homogeneous composition through the fine-grained layer is a probable consequence of the small grain size. which permits relatively rapid chemical redistributions through grain boundary diffusion. In contrast. the chemical gradient in the large-grained inner and outer shells is steep.The microstructure is established by the reaction heat treatment. and de t e r min est h e c r i tic a I cur r e n t. Th e b est com bin a t ion 0 f g r a ins i z e • composition. and volume of the fine-grained shell is obtained with an intermediate reaction temperature (700 to 730 0 C); this temperature range also yields the best values of J c • Various two-step heat treatments were studied and compared to isothermal aging. The best microstructure and. hence. the best critical current characteristic was obtained by aging the specimen at 700 0 C for 4 days followed by 730 0 C for 2 days.The onset transition temperature and the transition width were measured inductively. The inductive signal is apparently determined by the properties of the smallest volume of superconducting phase that is sufficient to expel the external magnetic flux. The composition gradient within this volume is then reflected in the transition width. The critical temperature first increased (to -18K) and then decreased with increasing reaction time.The J c characteristic of the multifilamentary wire is compared to that found in preliminary tests on an 'internal tin' bronze-processed wire fabricated by Intermagnetics General. The internal tin wire appears to have a much better critical current density at lower field. Possible metallurgical sources of the higher current density are discussed.ACKNOWLEDGMENT