Zeolite synthesis in the system pyrrolidine-Na2OAl2O3SiO2H2O

Crystallization of zeolites from the system pyrrolidine-Na₂OAl₂O₃SiO₂H₂O was investigated. Five zeolites, ZSM—5, ZSM—35, ZSM—39, ZSM—48 and KZ—1, were synthesized as single phases, whose crystallinity was very high. In this work zeolite ZSM—48 was prepared from the pyrrolidine system for the first time. It was suggested that pyrrolidine might stabilize certain aluminosilicate polyanions which have building units of oxygen five-membered rings. It was also presumed that all zeolites, except ZSM—39, have a pore opening of oxygen ten-membered rings.     

Effect of thermomechanical processing on superplasticity in Ti–Al–Mo–Zr alloy

Abstract

Superplasticity in terms of total tensile elongation was studied in a titanium alloy of nominal composition Ti–6·5Al–3·3Mo–1·6Zr (wt-%) for three strain rates (1·04 × 10^?3, 2·1 × 10^?3, and 4·2 × 10^?3s^?1) and in the temperature range 1123–1223 K for microstructures obtained by different processing schedules. Fine equiaxed microstructure with a low aspect ratio of 1·15 was accomplished in this alloy by combining two types of deformation. While the first step consists of heavy deformations for refining and intermixing the phases, a second step, consisting of light homogeneous reductions in several stages, was necessary to remove the banding that developed during the first step. The resulting microstructure underwent enormous tensile elongation (1700–1725%), even under relatively high strain rates (1·04 × 10^?3 and 2·1 × 10^?3s^?1), making this alloy most suitable for commercial superplastic forming. The present investigation also revealed that the usual sheet rolling practice of heavy reductions to refine the microstructure leads to localised banding which could not be removed by annealing; therefore, the tensile elongation was limited to 770% only. The reason for this may be attributed to the resistance in grain boundary sliding and rotation encountered in microstructures with shear bands and grains with high aspect ratio. Strain enhanced grain growth was also greater in these microstructures.

MST/555     

Micromechanics of fracture in a NiCrMo alloy

In a NiCrMo steel, quenched and tempered at various temperatures, the critical stress and strain at fracture have been computed in the SEN bending fracture toughness specimens and the effect of triaxiality factor on the fracture ductility has been studied. The experimental investigation included the tensile and fracture toughness (K_Ic, COD, J_Ic) tests, quantitative microscopy for statistical size distribution analysis of inclusions, and the quantitative fractography. An attempt has been made to identify the effective inclusion size to characterize the microfracture process under uniaxial and triaxial loading situations and the mechanics of void expansion has been investigated. A quantitative relationship between the process zone size and material microstructure as well as fractographic features has been presented for the cleavage and the microvoid coalescence mode of fracture.