David J. Harach

Bio: David J. Harach is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Intermetallic & Crack growth resistance curve. The author has an hindex of 2, co-authored 2 publications receiving 347 citations.

Microstructure evolution in metal-intermetallic laminate (MIL) composites synthesized by reactive foil sintering in air

Abstract: Metal-intermetallic (aluminide) laminate (MIL) composites have been fabricated in air using dissimilar metal foils. Foils of varying Al thickness were reacted with foils of Ti-3Al-2.5V resulting in microstructures of well-bonded metal-intermetallic layered composites with either Ti or Al residual metal layers alternating with the Al3Ti intermetallic layers. The MIL composites exhibit a very high degree of microstructural design and control. Microstructure characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractometry (XRD) has been performed, and basic physical properties of the Ti-Al composites have been determined. The Ti-Al reaction has been studied by interrupting the reaction processing, in steps, to observe the microstructural changes. An oxide layer between the Ti and Al foils initially controls the reaction kinetics. After breakdown of the oxide layer, a two-phase Al+Al3Ti layer (∼10 µm thickness) is formed. After formation of the two-phase layer, liquid phases are continuously present, and Al3Ti spherules (∼10 µm diameter) are formed through interfacial tension, solidify (in times of 2 to 4 µs), and are expelled into the liquid. This mechanism allows for a continuous reaction interface and higher reaction rates. Both reaction regimes, diffusion through the oxide, and, subsequently, the intermetallic phase reaction mechanism result in linear kinetics.

Growth of intermetallic layer in multi-laminated Ti/Al diffusion couples

Abstract: Solid-state reactive diffusion between Ti and Al was investigated in the temperature range of 520-650 degrees C by employing multi-laminated Ti/Al diffusion couples. In samples annealed up to 150 h intermetallic TiAl3 is the only phase observed in the diffusion zone and the preferential formation of this compound in Ti/Al diffusion couples was predicted using an effective heat of formation model. The present work indicated that both Ti and Al diffused into each other and the growth of the TiAl3 layers occurred mainly towards the Al side. The TiAl3 growth changes from parabolic to linear kinetics between 575 and 600 degrees C, characterized by activation energy of 33.2 and 295.8 kJ mol(-1), respectively. It is suggested that the low-temperature kinetics is dominated by the diffusion of Ti atoms along the grain boundaries of the TiAl3 layers, while the reaction at the TiAl3/Al interfaces in the high-temperature regime is limited by the diffusion of Ti atoms in the Al foils as a result of increased solubility of Ti in Al with increasing temperature. (c) 2006 Elsevier B.V. All rights reserved.

A novel biomimetic approach to the design of high-performance ceramic-metal composites.

Abstract: The prospect of extending natural biological design to develop new synthetic ceramic–metal composite materials is examined. Using ice-templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine-scale laminated ceramic–metal (bulk) composites that are inexpensive, lightweight and display exceptional damage-tolerance properties. Specifically, Al2O3/Al–Si laminates with ceramic contents up to approximately 40 vol% and with lamellae thicknesses down to 10 µm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa√m at a tensile strength of approximately 300 MPa. Salient toughening mechanisms are described together with further toughening strategies.