Multi-step Heat Research Articles

Improvements in the optical quality of AgGaSe 2 crystals

As-grown AgGaSe 2 crystals contain a high density of precipitates which cause optical scattering. These can be removed by a postgrowth heat-treatment process in the presence of Ag 2Se. Often the optical quality after heat-treatment varies from one crystal to another. A video technique for imaging near-IR light scattering in heat-treated AgGaSe 2 crystals has made it possible to assess the density of optical defects persisting after the usual single step heat-treatment process. Identification of the chemical composition of the precipitates, and having an accurate assessment of the density remaining after a single heat-treatment step, has led to the development of a more effective multi-step heat treatment process. With this improvement, optical scattering losses have been reduced by at least a factor of four. The known condensed phase equilibria in the AgGaSe system accounts for this behavior, predicting the direction in which chemical reactions occur during growth and heat-treatment, but it does not account for the subtle effects encountered in this system.

Oxygen Precipitation in Oxygen-Ion Implanted Silicon

Heat treatment of oxygen-ion implanted CZ-silicon may be expected to induce precipitation of oxygen-rich precipitates when the peak total oxygen concentration is above the oxygen solubility limit, but not far enough above to result in a “buried” SiOx layer. We report here first results of an investigation of oxygen-rich precipitates formed in oxygenimplanted CZ-silicon given a multistep post-irradiation heat treatment with maximum temperatures of 1050°C. The implantation energy and dose were 400kV and 3xl015cm-2 respectively, yielding a peak oxygen concentration of 6.8x1019 cm-3 at a projected range of 1μm, based on LSS statistics. This concentration is about one order of magnitude above the oxygen solubility limit and three orders of magnitude below the stoicheometric oxide concentration.

Microstructural sources of toughness in QLT-Treated 5.5Ni cryogenic steel

In commercial practice 5.5Ni steel is toughened for cryogenic service by a three-step heat treatment designated the “QLT” treatment. To determine why this treatment is necessary and successful, a series of two-step heat treatments was applied to 5.5Ni steel and the resulting microstructural states were characterized and compared with that obtained through the QLT treatment. It was concluded from this analysis that the QLT treatment lowers the ductile-brittle transition temperature by precipitating a dense distribution of thermally stable austenite along the boundaries of martensite laths, which interrupts the crystallographic alignment of laths within martensite packets and prevents cooperative trans-packet cleavage. Essentially, it reduces the mean free fracture path for cleavage. The multistep heat treatment is necessary because of the low nickel content; a single step heat treatment leads to an austenite precipitate which is either too lean in solute to be retained or too coarse in its distribution to be effective. The problem is avoided in the QLT treatment since the intercritical anneal (L) serves to create regions of high solute content along the prior martensite lath boundaries. The intercritical temper (T) then precipitates a dense distribution of high solute, stable austenite within these enriched regions.

Oxygen Precipitation Effects in Degenerately – Doped Silicon

ABSTRACTIn this paper we report preliminary observations of oxygen precipitation in degenerately-doped silicon using etching, optical microscopy and transmission electron microscopy. It was found that n+ material was resistant to precipitation, but p+ material precipitated readily. A multistep heat treatment starting with a low temperature step to achieve a high supersaturation ratio was sucessfully used to induce precipitation in n+ material.