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Nanoindentation experiments were performed using Berkovich and cube-corner indenters to investigate whether nanoindentation-induced phase transformations, such as those observed in silicon, also occur in germanium. Although the indentation load-displacement curves for germanium do not show the unloading pop-out or elbow phenomena observed in silicon, clear evidence for phase transformations was obtained by scanning electron microscopy (SEM) and micro-Raman spectroscopy. SEM showed that there is extruded material around the contact periphery of cube-corner hardness impressions that is metalliclike in its flow characteristics, just as in silicon. Micro-Raman spectroscopy revealed more direct evidence by identifying amorphous and what may be the crystalline BC8 (Ge-IV) phase. The fact that these phenomena are observed primarily and reproducibly only for the cube-corner indenter suggests that the contact geometry significantly affects the transformation behavior. Results are discussed in terms of possible deformation mechanisms and how they may be influenced by the indenter geometry.

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Nanoindentation experiments were performed on single crystals of (100) Si using a series of triangular pyramidal indenters with centerline-to-face angles in the range 35.3° to 85.0°. The influences of the indenter geometry on cracking and phase transformation during indentation were systematically studied. Although reducing the indenter angle reduces the threshold load for cracking and increases the crack lengths, c, at a given indention load, P, the frequently observed relation between P and c3/2 is maintained for all of the indenters over a wide range of load. Features in the nanoindentation load-displacement curves in conjunction with Raman spectroscopy of the crystalline and amorphous phases in and around the contact impression show that the indenter geometry also plays a role in the phase transformation behavior. Results are discussed in relation to prevailing ideas about indentation cracking and phase transformation in silicon.

FOREWARD iv ABSTRACTDuplex stainless steels (DSS) are being specified for chloride containing environments due to their enhanced pitting and stress corrosion cracking resistance. They exhibit improved corrosion performance over the austenitic stainless steels. Duplex stainless steels also offer improved strength properties and are available in various wrought and cast forms. In the study, the corrosion performances of DSS castings were characterized and assessed, including the wrought counterparts for comparison. The evaluation filled the pore of lack of data for cast duplex stainless steels compared to wrought materials. A database of the pitting corrosion and IGC behavior of cast and wrought materials was generated for a greater depth of understanding for the behavior of cast duplex stainless steel. In addition, improved evaluation methods for DSS castings were developed according to ASTM A923, A262, G48 and A494.v The study revealed that when properly heat treated according to the specification, (1) DSS castings have equal or better pitting and intergranular corrosion resistance than their wrought counterparts; (2) Welding reduces the pitting and intergranular corrosion resistance for both the wrought and cast duplex alloys; (3) Castings generally have better toughness than their wrought counterparts in the temperature range of -80°C to +20°C; (4) All shield metal arc (SMA) test welds in DSS castings, with recommended or over matching filler metal, indicate that welding is not a significant factor when considering DSS applications.