Master curve in upper region of ductile brittle transition: a modification based on local damage approach

AbstractThe fracture behaviour of ferritic/ferritic martensitic steels in Ductile to Brittle Transition (DBT) region is well captured by Master Curve approach, except in the upper region of transition due to ductile tearing prior to cleavage. The fracture toughness behavior in the upper region of DBT is generally censored by Master Curve. In this work the Master Curve approach is modified to extend its applicability to the upper region of transition. The ductile tearing in the upper region of transition, increased sampled volume and constraint increment are addressed in this work using constraint parameter Tstress and numerical analyses using GTN damage

Effect of NdB6 addition on densification and properties of ZrB2

This paper reports on the effect of NdB₆ addition on densification and properties of ZrB₂. NdB₆ powder (2.5,5 and 10wt.%) was added to ZrB₂ powder and consolidated by hot pressing. It was found that NdB₆ addition assisted in densification of ZrB₂ at lower hot pressing temperature of 1750°C. Formation of solid solution was observed at the interface of ZrB₂ and NdB₆ phases. Hardness was found to be slightly increased by 2.5wt.% NdB₆ addition but decreased by 5 and 10% NdB₆ addition. Fracture toughness of composite is found to be higher than the monolithic ceramic. It was found that composite samples have excellent oxidation resistance at 900°C in air

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 A degrees C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 A degrees C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of gamma aEuro(3) phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 A degrees C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the delta-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases

STRESS INDUCED MARTENSITIC TRANSFORMATION IN Ti-20V

The deformation induced product in Ti-2C%V is characterized and the influence of this "transformation" on the deformation behaviour of this alloy is studied. Flate shaped stress assisted products are shown to consist of the orthorhombic α'' phase and the ω phase in the matrix of a β-orientation which is twin related to the parent grain. The tensile ductility of the alloy shows improvement due to the stress assisted "transformation"