A family of inexpensive, Al2O3-forming, high–creep strength austenitic stainless steels has been developed. The alloys are based on Fe-20Ni-14Cr-2.5Al weight percent, with strengthening achieved through nanodispersions of NbC. These alloys offer the potential to substantially increase the operating temperatures of structural components and can be used under the aggressive oxidizing conditions encountered in energy-conversion systems. Protective Al2O3 scale formation was achieved with smaller amounts of aluminum in austenitic alloys than previously used, provided that the titanium and vanadium alloying additions frequently used for strengthening were eliminated. The smaller amounts of aluminum permitted stabilization of the austenitic matrix structure and made it possible to obtain excellent creep resistance. Creep-rupture lifetime exceeding 2000 hours at 750°C and 100 megapascals in air, and resistance to oxidation in air with 10% water vapor at 650° and 800°C, were demonstrated.

A conceptual approach to evaluate glass-forming ability for various glass-forming systems has been proposed from a physical metallurgy point of view. It was found that the glass-forming ability for noncrystalline materials was related mainly to two factors, i.e., 1/(Tg + Tl) and Tx (wherein Tx is the onset crystallization temperature, T g the glass transition temperature, and Tl the liquidus temperature), and could be predicated by a unified parameter γ defined as Tx/(Tg +Tl). This approach was confirmed and validated by experimental data in various glass-forming systems including oxide glasses, cryoprotectants, and metallic glasses.

Six La-based La-Al-Ni-Cu-(Co) alloys were subjected to a systematical study of glass formation by Bridgman unidirectional solidification at growth velocities between 0.1 and 4.82 mm/s at a temperature gradient of 15 K/mm. With increased Cu content the critical growth velocity for glass formation in La55Al25Cu20-xNix (x=0-20) alloys shows a steep minimum at 10 at.% Cu, indicating the largest glass forming ability for the La55Al25Ni10Cu10 alloy. However, replacement of Ni by Co leads to a further decrease in the critical cooling rate for the La55Al25Ni5Cu10Co5 alloy. Critical cooling rates for glass formation in the present alloys were also obtained through a study of their melting and solidification behaviors by thermal analytical measurement. The e.ect of alloying addition and the significance of reduced glass transition temperature for the glass forming ability of these alloys is discussed. c1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.

A new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid. The interrelationship between this new parameter and the critical cooling rate or critical section thickness is elaborated and discussed in comparison with two other representatives, i.e. reduced glass transition temperature Trg ( =Tg /Tl, where Tg and Tl are the glass transition temperature and liquidus temperature, respectively) and supercooled liquid range △Txg ( =Tx-Tg, where Tx is the onset crystallization temperature and Tg the glass transition temperature). Our results have shown that △Txg alone cannot infer relative GFA for BMGs while the new parameter g, defined as Tx/ (Tg +Tl), has a much better interrelationship with GFA than Trg. An approximation of the critical cooling rate and critical section thickness for glass formation in bulk metallic glasses is also formulated and evaluated. 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.

A new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid. The interrelationship between this new parameter and the critical cooling rate or critical section thickness is elaborated and discussed in comparison with two other representatives, i.e. reduced glass transition temperature Trg ( =Tg /Tl, where Tg and Tl are the glass transition temperature and liquidus temperature, respectively) and supercooled liquid range △Txg ( =Tx-Tg, where Tx is the onset crystallization temperature and Tg the glass transition temperature). Our results have shown that △Txg alone cannot infer relative GFA for BMGs while the new parameter g, defined as Tx/ (Tg +Tl), has a much better interrelationship with GFA than Trg. An approximation of the critical cooling rate and critical section thickness for glass formation in bulk metallic glasses is also formulated and evaluated. 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.