https://aziz.seas.harvard.edu/files/mja026.pdf

Continuous growth model for interface motion during alloy solidification

The paper presents a review of original investigations on the surface modification of metallic materials with low energy (up to 40 keV), high current (up to 40 J/cm 2 ) electron beams of microsecond duration. Based on material research and on simulations of temperature and stress fields, the regularities and mechanisms for the changes in the defect structure and in the strain–stress state of pure metals (Fe) on pulsed heating are considered. The peculiarities of the formation of non-equilibrium structure-phase states and graded structures on pulsed melting of film–substrate (Fe–Ta, Al–Si, and Al–C) systems have been studied. For a broad spectrum of structural and tool materials (steels, aluminum and titanium alloys, hard alloys) it has been shown that the most pronounced changes in the structure-phase state occur in the near-surface layer quenched from the liquid state, where the velocity of the crystallization front reaches its maximum. In this layer, the second phases are partially or completely dissolved, and oversaturated solid solutions and nanosized second-phase segregates are formed. This substantially improves the electrochemical and strength properties of the surface layer. It has been established that the action of dynamic stresses has the result that the modified layer with enhanced strength properties is substantially thicker than the heat-affected zone.

Physical foundations for surface treatment of materials with low energy, high current electron beams

A study is presented of the relation between microstructure and 1.54 μm photoluminescence (PL) in high‐energy ion‐implantated Er in Si as a function of implant dose, energy, and temperature and subsequent anneal. Transmission electron microscopy (TEM) of material implanted at 500 keV and ≳100 °C and annealed at 900 °C to activate the Er PL suggests the solubility of Er in Si to be ≊1.3±0.4× 1018 cm−3 at 900 °C. Precipitates take the form of platelets (probably ErSi2) ≊100–300 A in diameter and ≊10 A thick. The 1.54 μm PL saturates at ≊5× 1017 cm−3, before the apparent solubility limit. Layers in which the Si is fully amorphized and subsequently regrown by solid phase epitaxy during an anneal show increased Er incorporation in the crystalline Si but segregation at the amorphous‐crystalline interface. In buried amorphous layers regrown from top and bottom, segregation leads to a line of high Er concentration near the center of the layer: Regrowth from a single interface leads to a segregation pileup of Er a...

Microstructure of erbium-implanted si

Mechanisms of nanostructure and metastable phase formations in the surface melted layers of a HCPEB-treated D2 steel

With rapid solidification following pulsed laser melting, we have measured the dependence on interface orientation of the amount of solute trapping of several group III, IV, and V elements (As, Ga, Ge, In, Sb, Sn) in Si. The aperiodic stepwise growth model of Goldman and Aziz accurately fits both the velocity and orientation dependence of solute trapping of all of these solutes except Ge. The success of the model implies a ledge structure for the crystal/melt interface and a step‐flow mechanism for growth from the melt. In addition, we have observed an empirical inverse correlation between the two free parameters (‘‘diffusive speeds’’) in this model and the equilibrium solute partition coefficient of a system. This correlation may be used to estimate values of these free parameters for other systems in which solute trapping has not or cannot be measured. The possible microscopic origin of such a correlation is discussed.

/pdf/solute-trapping-of-group-iii-iv-and-v-elements-in-silicon-by-4k2wbghgv8.pdf

Alloying

Papers

Surface Modification and Alloying: by Laser, Ion, and Electron Beams