Improvement of crystal quality and surface morphology of Ge/Gd2O3/Si(111) epitaxial layers by cyclic annealing and regrowth

The role of post-growth cyclic annealing (PGCA) and subsequent regrowth, on the improvement of crystal quality and surface morphology of (111)-oriented Ge epitaxial layers, grown by low temperature (300 C) molecular beam epitaxy (MBE) on epi-Gd2O3/Si(111) substrates, is reported. We demonstrate that PGCA is efficient in suppressing rotational twins, reflection microtwins and stacking faults, the predominant planar defect types in Ge(111) epilayers. Continuing Ge growth after PGCA, both at low (300 C) and high (500 C) temperatures, does not degrade the crystal quality any further. By promoting adatom downclimb, PGCA is observed to also heal the surface morphology, which is further improved on Ge re-growth. These results are promising for development of high-quality Ge(111) epitaxial layers for photonic and electronic applications.

Cyclic annealing versus continuous annealing of 20 wt.% chromium white cast iron

To destabilize as-cast microstructure of 20 wt.% chromium white iron, cyclic annealing involving repeated austenitization for short duration of 0.6 h at 900, 950, 1000, 1050 and 1100 °C followed by forced air cooling is conducted as an alternative to continuous annealing requiring austenitization for longer period of 4–6 h at the said temperatures followed by furnace cooling. Continuous austenitization destabilizes the austenite matrix through precipitation of secondary carbides and transforms the alloy depleted austenite to pearlite on furnace cooling, thereby reducing the as-cast hardness from HV 669 to HV466. In contrast, repeated austenitization not only destabilizes the austenite matrix through precipitation of secondary carbides followed by its transformation to martensite on forced air cooling, but also causes disintegration of longer eutectic carbides to shorter segments with subsequent increase in hardness to as high as HV 890. Notched impact toughness after both continuous and cyclic annealing remains uniformly at 12.0 J as compared to as-cast value of 6.0 J. Besides, an unexpected rise in abrasive wear resistance after cyclic annealing treatment makes the alloy superior than that obtained by continuous annealing treatment as practiced in industries.

Optimized Corrosion Performance of AISI 1345 Steel in Hydrochloric Acid Through Thermo–Mechanical Cyclic Annealing Processes

The thermo–mechanical treatments and cyclic annealing processes have the potential of optimizing the corrosion performance of carbon steels in corrosive environments. Herein, an attempt has been made to optimize the corrosion performance of AISI 1345 steel in hydrochloric acid by thermo–mechanical cyclic annealing treatments. AISI 1345 steel was produced and cast in the laboratory and subjected to three types of thermo–mechanical cyclic annealing treatments (TMCA). The first TMCA treatment comprised hot rolling at 1050 °C followed by oil quenching and single austenitizing at 900 °C followed by furnace cooling (TMSA). The second and the third TMCA treatments involved similar hot rolling processes with double austenitizing and furnace cooling (TMDA) and triple austenitizing and furnace cooling (TMTA) processes. Microstructure analysis showed that dual-phase (retained austenite + pearlite) microstructure was achieved after all TMCA treatments with an exception of secondary phase particles precipitation after TMSA treatment. Maximum fractions of retained austenite and minimum fractions of pearlite were achieved after TMTA treatment. Highly refined microstructure of size 26.7 µm was achieved after TMDA treatment whereas; TMSA treatment offered coarse grained microstructure of size 254 µm. Electrochemical analysis was performed in 5 vol% HCl solution using Tafel scan technique. Results revealed that both TMDA and TMTA treatments caused three-fold reduction in corrosion rates (3.025, 2.771 mpy) compared to non-treated steel sample. After 168 h of immersion corrosion analysis in 5 vol% HCl solution, the surface of TMTA treated sample was observed to be partially covered with a very thin, crack-free oxide layer exhibiting minimum oxygen (8.16%) percentage. These features indicated that the TMTA treated sample underwent a very low-intensity minor corrosion attack of HCl solution and exhibited the best immersion corrosion performance among all samples. Electrochemical and immersion corrosion analysis results were in good agreement.